Catalyst for carboxylate production and method for producing carboxylate

Abstract

A catalyst for carboxylate production, comprising catalyst particles containing at least one element selected from the group consisting of nickel, cobalt, palladium, lead, platinum, ruthenium, gold, silver, and copper, and a carrier on which the catalyst particles are supported, wherein a half-value width Wa of a pore size distribution of the catalyst for carboxylate production, calculated from an adsorption isotherm obtained by a nitrogen adsorption method using a BJH method, is 10 nm or less.

Description

Technical Field

[0001] This invention relates to catalysts for the manufacture of carboxylic acid esters and methods for manufacturing carboxylic acid esters. Background Technology

[0002] Nickel or nickel compounds are widely used as catalysts in chemical synthesis for oxidation, reduction, and hydrogenation reactions. In recent years, through various modifications and improvements to nickel-based catalysts, the oxygen-catalyzed oxidation of alcohols has been achieved. Of course, in the chemical industry, nickel and nickel compounds are known to be applicable not only to the oxidation of alcohols, but also to various other oxidation, reduction, and hydrogenation reactions, as well as to catalysts for purifying automobile exhaust and photocatalysts.

[0003] For example, as a method for manufacturing carboxylic acid esters, Patent Document 1 proposes using a composite particle support as a catalyst. The composite particle support comprises composite particles and a support on which the composite particles are supported. The composite particles are composed of nickel in an oxidized state and X (X represents at least one element selected from the group consisting of nickel, palladium, platinum, ruthenium, gold, silver, and copper). The composite particle support has a supported layer in which the composite particles are locally present. It is claimed that according to this catalyst, high reactivity can be maintained for a long period. Furthermore, as a support applicable to this catalyst, it is claimed that in Patent Document 1, the pore structure can be adjusted by performing a prescribed aging process. Similarly, it is claimed that in Patent Document 2, a support with a uniform pore structure, in which most pore diameters are in a narrow range of 3 to 5 nm, can be obtained by performing a prescribed hydrothermal treatment.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 4803767

[0007] Patent Document 2: Japanese Patent No. 5794993 Summary of the Invention

[0008] The problem the invention aims to solve

[0009] When using the catalysts described in Patent Documents 1 and 2 to manufacture carboxylic acid esters, methacrylic acid is generated as a byproduct, causing the pH to decrease during the reaction. Consequently, there is a tendency for the catalyst activity to decrease. Considering this tendency, it has been considered to control the pH of the reaction system within a specified range, for example, by adding an alkaline substance. However, it has also been considered that the addition of such an alkaline substance may cause a local increase in pH within the reaction system. Considering the long-term use of such reaction systems over several years, it is necessary to improve the catalyst's resistance to pH fluctuations (hereinafter also referred to as "pH fluctuations"), i.e., its acid and alkali resistance (hereinafter also referred to as "pH fluctuation tolerance").

[0010] In addition, the production of carboxylic esters can be carried out at lower temperatures, but considering long-term use in the form of years, the activity and selectivity of the catalyst are sometimes reduced due to exposure to higher temperature conditions, thus requiring temperature tolerance.

[0011] As mentioned above, when envisioning long-term use of catalysts in units of several years, it is desirable to improve the durability (hereinafter referred to as "durability"), taking into account both pH fluctuation tolerance and / or temperature tolerance. However, the technologies described in Patent Documents 1-2 still have room for improvement in terms of this durability.

[0012] The present invention was made in view of the problems of the prior art described above, and its object is to provide a catalyst for the manufacture of carboxylic esters with excellent durability for long-term use.

[0013] Solution for solving the problem

[0014] The inventors discovered through their research that by ensuring the half-width of the pore diameter distribution of the catalyst for manufacturing carboxylic esters, measured using a prescribed method, is within a specified range, and by suppressing deviations in the pore diameter within the pores of the support, the durability during long-term use is expected to be improved, thus completing the present invention.

[0015] That is, the present invention includes the following methods.

[0016] [1] A catalyst for the manufacture of carboxylic acid esters, comprising catalyst particles and a support on which the catalyst particles are supported, wherein the catalyst particles contain at least one element selected from the group consisting of nickel, cobalt, palladium, lead, platinum, ruthenium, gold, silver and copper.

[0017] The half-value width Wa of the pore size distribution of the aforementioned catalyst for carboxylic ester production, calculated using the BJH method based on the adsorption isotherm obtained by nitrogen adsorption, is less than 10 nm.

[0018] [2] The catalyst for manufacturing carboxylic acid esters according to [1], wherein the half-width Wd of the pore size distribution of the aforementioned catalyst for manufacturing carboxylic acid esters, obtained by the desorption isotherm obtained by nitrogen adsorption and calculated by the BJH method, is less than 5 nm.

[0019] [3] The catalyst for manufacturing carboxylic acid esters according to [1] or [2], wherein the mode particle size Da of the pores of the aforementioned catalyst for manufacturing carboxylic acid esters, obtained by the adsorption isotherm obtained by the nitrogen adsorption method and calculated by the BJH method, is 2 nm or more and 20 nm or less.

[0020] [4] The catalyst for manufacturing carboxylic acid esters according to any one of [1] to [3], wherein the modal particle size Da of the pores obtained by the adsorption isotherm obtained by the nitrogen adsorption method and calculated by the BJH method and the half-value width Wa of the aforementioned catalyst for manufacturing carboxylic acid esters satisfy the following relationship (1).

[0021] 1 / 2Wa<Da (1)

[0022] [5] The catalyst for manufacturing carboxylic acid esters according to any one of [1] to [4], wherein the modal particle size Dd of the pores of the aforementioned catalyst for manufacturing carboxylic acid esters, obtained by the desorption isotherm obtained by nitrogen adsorption and calculated by the BJH method, is 2 nm or more and 15 nm or less.

[0023] [6] The catalyst for manufacturing carboxylic acid esters according to any one of [1] to [5], wherein the mode particle size Dd of the desorption isotherm obtained by nitrogen adsorption and calculated by BJH method according to the catalyst for manufacturing carboxylic acid esters satisfies the following relationship (2) with the half-value width Wd of the pore size distribution obtained by nitrogen adsorption and calculated by BJH method according to the catalyst for manufacturing carboxylic acid esters.

[0024] 1 / 2Wd<Dd (2)

[0025] [7] A catalyst for the manufacture of carboxylic acid esters according to any one of [1] to [6], wherein the aforementioned half-width Wa is 0.1 nm or more.

[0026] [8] A catalyst for the manufacture of carboxylic acid esters according to any one of [1] to [7], wherein the catalyst particles contain at least one element selected from the group consisting of nickel, cobalt, palladium, lead and gold.

[0027] [9] A catalyst for the manufacture of carboxylic acid esters according to any one of [1] to [8], wherein the catalyst particles are composite particles containing nickel and / or cobalt in an oxidized state and containing X (X represents at least one element selected from the group consisting of nickel, palladium, platinum, ruthenium, gold, silver and copper).

[0028]

[10] The catalyst for the manufacture of carboxylic acid esters according to [9], wherein the composition ratio of nickel or cobalt to X in the aforementioned composite particles is 0.1 or more and 10 or less, calculated as the Ni / X atomic ratio or the Co / X atomic ratio.

[0029]

[11] The catalyst for the manufacture of carboxylic esters according to [9], wherein the aforementioned composite particles contain gold and nickel in an oxidized state.

[0030]

[12] The catalyst for manufacturing carboxylic acid esters according to

[10] , wherein the composition ratio of nickel to gold in the aforementioned composite particles is 1.1 or more and 10 or less in terms of Ni / Au atomic ratio.

[0031]

[13] The catalyst for manufacturing carboxylic acid esters according to any one of [1] to

[12] , wherein the average particle size of the catalyst particles is 2 nm or more and 10 nm or less.

[0032]

[14] A catalyst for the manufacture of carboxylic acid esters according to any one of [1] to

[13] , wherein the aforementioned support is a support comprising an aluminum-containing silica-based composition, the aluminum-containing silica-based composition comprising silica and aluminum oxide.

[0033]

[15] A catalyst for the manufacture of carboxylic acid esters according to any one of [1] to

[14] , wherein the aforementioned support is a silica-based material, comprising, with the total molar amounts of at least one fourth-period element selected from the group consisting of silicon, aluminum, at least one basic element selected from the group consisting of iron, cobalt, nickel, and zinc, and at least one basic element selected from the group consisting of alkali metals, alkaline earth metals, and rare earth elements, respectively, ranging from 42 mol% to 90 mol%, 3 mol% to 38 mol%, 0.5 mol% to 20 mol%, and 2 mol% to 38 mol%, respectively:

[0034] The aforementioned silicon;

[0035] The aforementioned aluminum;

[0036] The aforementioned fourth-period elements; and

[0037] The aforementioned alkaline elements.

[0038]

[16] The catalyst for manufacturing carboxylic acid esters according to any one of [1] to

[15] , wherein a supported layer of the aforementioned catalyst particles is present in a region from the surface of the aforementioned catalyst for manufacturing carboxylic acid esters to 40% of the equivalent diameter of the aforementioned catalyst for manufacturing carboxylic acid esters.

[0039]

[17] The catalyst for manufacturing carboxylic acid esters according to any one of [1] to

[16] , wherein the equivalent diameter of the catalyst for manufacturing carboxylic acid esters is 200 μm or less, and a supported layer of the catalyst particles is present in a region from the surface of the catalyst for manufacturing carboxylic acid esters to 30% of the equivalent diameter of the catalyst for manufacturing carboxylic acid esters.

[0040]

[18] The catalyst for manufacturing carboxylic acid esters according to any one of [1] to

[17] , wherein an outer layer substantially free of catalyst particles is formed on the outside of the supported layer in which the aforementioned catalyst particles are locally present, and the outer layer is formed with a thickness of 0.01 μm or more and 15 μm or less.

[0041]

[19] A catalyst for the manufacture of carboxylic acid esters according to any one of [9] to

[18] , wherein the catalyst particles have a core containing X, the core being coated with nickel and / or cobalt in an oxidized state.

[0042]

[20] A method for manufacturing a carboxylic acid ester, comprising the following reaction steps: in the presence of a catalyst for manufacturing a carboxylic acid ester as described in any one of [1] to

[19] and oxygen, (a) reacting an aldehyde with an alcohol or (b) reacting one or more alcohols.

[0043]

[21] The method for manufacturing carboxylic acid esters according to

[20] , wherein the aforementioned aldehyde is acrolein and / or methacrolein.

[0044]

[22] The method for manufacturing carboxylic acid esters according to

[20] or

[21] , wherein the aforementioned aldehyde is acrolein and / or methacrolein, and the aforementioned alcohol is methanol.

[0045]

[23] The method for manufacturing a carboxylic acid ester according to any one of

[20] to

[22] , wherein the aforementioned reaction steps are carried out in the liquid phase.

[0046]

[24] The method for manufacturing a carboxylic acid ester according to any one of

[20] to

[23] , wherein the aforementioned reaction step is carried out while adding an alkaline substance to make the pH of the reaction system 6 or higher and 8 or lower.

[0047] The effects of the invention

[0048] According to the present invention, a catalyst for the manufacture of carboxylic esters with excellent durability for long-term use can be provided. Attached Figure Description

[0049] Figure 1 A cross-sectional schematic diagram illustrating a typical example of the pore structure of a catalyst for the manufacture of carboxylic esters according to one embodiment of the present invention.

[0050] Figure 2A cross-sectional schematic diagram illustrating a typical example of the pore structure of a conventional catalyst.

[0051] Figure 3 A conceptual diagram illustrating the method for determining the half-value width. Detailed Implementation

[0052] The embodiments of the present invention (hereinafter also referred to as "this embodiment") will be described in detail below. It should be noted that the present invention is not limited to the following embodiments, and can be implemented in various modifications within its scope.

[0053] Catalysts for the manufacture of carboxylic esters

[0054] The catalyst for producing carboxylic esters according to this embodiment comprises catalyst particles and a support on which the catalyst particles are loaded. The catalyst particles contain at least one element selected from the group consisting of nickel, cobalt, palladium, lead, platinum, ruthenium, gold, silver, and copper. The half-width Wa of the pore size distribution of the catalyst for producing carboxylic esters, calculated using the BJH method based on the adsorption isotherm obtained by nitrogen adsorption, is less than 10 nm. Because it is constructed in this way, the catalyst for producing carboxylic esters according to this embodiment is designed to have excellent durability for long-term use. More specifically, the catalyst for producing carboxylic esters according to this embodiment exhibits excellent tolerance to, for example, pH fluctuations and / or temperature variations.

[0055] The pore structure of the catalyst for producing carboxylic esters in this embodiment can be said to originate from the pores of the support. In this embodiment, the pore structure is determined by the half-width of the pore size distribution (hereinafter also referred to as "half-width Wa"), which is calculated based on the adsorption isotherm obtained by nitrogen adsorption using the BJH (Barrett, Joyner and Halenda) method. It should be noted that, as the pore size distribution based on the BJH method, two methods can be considered: a method of obtaining the adsorption isotherm and calculating the pore size distribution (pore size distribution on the adsorption side); and a method of obtaining the desorption isotherm and calculating the pore size distribution (pore size distribution on the desorption side). The latter method can obtain an evaluation result that appropriately reflects the pore diameter near the pore inlet, but this evaluation result cannot accurately reflect the deviation of the pore diameter inside the pore. In contrast, the former method can obtain an evaluation result (true distribution) reflecting the deviation from the pore inlet to the interior. Therefore, it can be considered a suitable evaluation index for obtaining a relatively uniform support from the pore inlet to the interior. In this embodiment, the former method is used to determine the pore structure and adjust the half-width Wa of its pore size distribution to less than 10 nm, thus forming a catalyst for the manufacture of carboxylic acid esters with a uniform structure from the pore inlet to the interior (e.g., in...). Figure 1In the cross-sectional diagram shown, the diameters L1, L2, and L3 inside the pores are all uniform values.

[0056] On the other hand, when the half-width Wa exceeds 10 nm, even if the pore diameter is uniform near the pore inlet, the pore diameter inside the pore will deviate (e.g., in...). Figure 2 In the cross-sectional schematic diagram shown, the diameters L4, L5, and L6 inside the pores are values ​​with deviations. Due to long-term use, the changes in the pore structure become obvious, making it difficult to maintain catalytic performance for a sufficiently long time.

[0057] Based on the above viewpoint, the half-width Wa is 10 nm or less, preferably 8 nm or less, more preferably 7 nm or less, and even more preferably 5 nm or less.

[0058] The lower limit of the half-width Wa is not specifically limited; for example, it can be above 0.1nm, above 1nm, or above 3nm.

[0059] The value of the half-value width Wa is determined by the method described in the embodiments described later.

[0060] There are no particular limitations on the method for adjusting the half-value width Wa. For example, by employing the preferred manufacturing method described later, the half-value width Wa of the catalyst for carboxylate production can be made sufficiently small. More specifically, it can be considered that by using preferred conditions in the manufacturing method described later to prepare the slurry, it is easy to keep the size of the silica chains consistent. That is, it can be considered that the uniformity of the pore diameter of silica depends on the size of the silica chains in the carrier slurry. If the size of the silica chains is uniform, the size of the pore diameter is easily kept consistent. As a result, because the size of the silica chains is uniform, the inner walls constituting the pores are easily made denser, and even in the event of pH fluctuations, the increase in the pore diameter of silica is suppressed, and the pH fluctuation tolerance is improved. However, it can be considered that the above is only one of the reasons why the catalyst for carboxylate production of this embodiment can obtain the above structure, and the mechanism of action of this embodiment is not limited to this.

[0061] In this embodiment, when the pore diameter near the inlet of the pores in the support also becomes uniform, the durability of the catalyst during long-term use can be further improved compared to the case where only the internal pores are uniform. As a result, there is a tendency for the conversion rate to be further improved. From the above point of view, the half-value width (hereinafter also referred to as "half-value width Wd") of the pore size distribution of the catalyst for the manufacture of carboxylic esters, calculated by the desorption isotherm obtained by the nitrogen adsorption method and using the BJH method, is preferably 5 nm or less, more preferably 4 nm or less, and even more preferably 3 nm or less.

[0062] There is no particular limitation on the lower limit of the half-width Wd. For example, it can be greater than 0.1nm, greater than 1nm, or greater than 2nm.

[0063] The value of the half-value width Wd is determined by the method described in the embodiments described later.

[0064] There are no particular limitations on the method for adjusting the half-value width Wd. For example, by adopting the preferred manufacturing method described later, the half-value width Wd of the catalyst for the manufacture of carboxylic esters can be adjusted to the above range.

[0065] In this embodiment, the modal particle size Da of the pores in the catalyst for carboxylic ester production, calculated using the BJH method based on the adsorption isotherm obtained by nitrogen adsorption, is derived from the pore structure of the support. From the viewpoint of promoting the growth of composite particles within the pores, it is preferably 2 nm or more. On the other hand, from the viewpoint of preventing catalyst breakage, the modal particle size Da of this pore is preferably 20 nm or less. Therefore, the internal pore diameter Da of the catalyst for carboxylic ester production is preferably 2 nm or more and 20 nm or less, more preferably 2 nm or more and 15 nm or less, and even more preferably 3 nm or more and 10 nm or less.

[0066] The value of the mode particle size Da of the pores was determined by the method described in the examples described later.

[0067] There are no particular limitations on the method for adjusting the mode particle size Da of the pores. For example, by adopting the preferred manufacturing method described later, the mode particle size Da of the pores can be adjusted to the above range.

[0068] It should be noted that the half-value width Wa and the mode particle size Da of the pores preferably satisfy the following relationship (1).

[0069] 1 / 2Wa<Da(1)

[0070] In this embodiment, from the viewpoint of maintaining high reactivity without excessively increasing the diffusion resistance within the pores so as not to restrict the diffusion rate of the reactant substrate, the modal particle size Dd of the pores in the catalyst for carboxylic ester production is preferably 2 nm or more, based on the desorption isotherm obtained by nitrogen adsorption and calculated using the BJH method. On the other hand, from the viewpoint of preventing catalyst breakage, the modal particle size Dd of the pores is preferably 15 nm or less. Therefore, the pore inlet diameter Dd of the catalyst for carboxylic ester production is preferably 2 nm or more and 15 nm or less, more preferably 2 nm or more and 7 nm or less, and even more preferably 3 nm or more and 7 nm or less.

[0071] The value of the mode particle size Dd of the pores was determined by the method described in the examples described later.

[0072] There are no particular limitations on the method for adjusting the mode particle size Dd of the pores. For example, by adopting the preferred manufacturing method described later, the mode particle size Dd of the pores can be adjusted to the above range.

[0073] It should be noted that the preferred half-value width Wd and the mode particle size Dd of the pores satisfy the following relationship (2).

[0074] 1 / 2Wd<Dd(2)

[0075] In this embodiment, the catalyst particles contain at least one element selected from the group consisting of nickel, cobalt, palladium, lead, platinum, ruthenium, gold, silver, and copper. The catalyst particles have the function of catalyzing the reaction for the production of carboxylic acid esters. Preferably, the catalyst particles in this embodiment contain at least one element selected from the group consisting of nickel, cobalt, palladium, lead, and gold; more preferably, they are composite particles containing nickel and / or cobalt in an oxidized state and containing X (X represents at least one element selected from the group consisting of nickel, palladium, platinum, ruthenium, gold, silver, and copper).

[0076] In this embodiment, the catalyst for carboxylic ester production preferably has a supported layer in which composite particles are locally present. The term "supported layer in which composite particles are locally present" refers to a region within the support where composite particles are concentrated. In the catalyst for carboxylic ester production of this embodiment, the composite particles are preferably selectively supported in a fixed region, rather than randomly supported in the support; this region is referred to as the "supported layer in which composite particles are locally present." In the catalyst for carboxylic ester production, if the composite particles are concentrated in a fixed region compared to other areas, this region is a "supported layer in which composite particles are locally present." Therefore, which region is the "supported layer in which composite particles are locally present" can be determined using X-ray microprobe analysis or secondary electron reflectance images from a high-resolution scanning electron microscope, as described later. The supported layer in which composite particles are locally present is preferably located in the region extending from the surface of the catalyst for carboxylic ester production to 40% of the equivalent diameter of the catalyst. If the supported layer in which composite particles are locally present exists in the above-mentioned region, the influence of the diffusion rate of reactants within the support is reduced, and the reactivity tends to increase.

[0077] The catalyst for producing carboxylic esters according to this embodiment can have various sizes and shapes with a substantial thickness or particle size on the order of μm to cm. Specific examples of the shape of the catalyst for producing carboxylic esters are not limited to the following examples, and can include various shapes such as spherical, elliptical, cylindrical, tablet-like, hollow cylindrical, plate-like, rod-like, sheet-like, and honeycomb-like. The shape can be appropriately changed according to the reaction mode, and is not limited to the following shapes; for example, in fixed-bed reactions, hollow cylindrical or honeycomb shapes with low pressure loss are selected, while in liquid-phase slurry suspension conditions, spherical shapes are generally selected.

[0078] The term "equivalent diameter" as used herein refers to the diameter of a spherical particle, or, in the case of irregularly shaped particles, the diameter of a sphere with the same volume as the particle or a sphere having the same surface area as the particle. Methods for determining the equivalent diameter include using a laser diffraction / scattering particle size distribution measuring device to determine the average particle size (volume basis) and using it as the equivalent diameter; or using the number-average particle size measured using a scanning electron microscope (SEM) as the equivalent diameter.

[0079] The thickness of the supported layer containing composite particles is selected within an optimal range based on the thickness and particle size of the support, the type of reaction, and the reaction mode. It should be noted that the "equivalent diameter of the catalyst for carboxylic ester production" is usually the same as the "equivalent diameter of the support," therefore, the "equivalent diameter of the catalyst for carboxylic ester production" can be determined based on the equivalent diameter of the support.

[0080] For example, when using a large support with an equivalent diameter exceeding 200 μm (e.g., several mm or more) for a catalyst used in the production of carboxylate esters, it is generally used in slow-moving liquid-phase or gas-phase reactions. Therefore, by loading composite particles, which are the active component, onto a region extending from the surface of the catalyst to 40% of its equivalent diameter and from the outer surface to 80 μm, and by providing a layer without the composite particles inside the catalyst, there is a tendency to obtain a catalyst for the production of carboxylate esters that is less affected by the diffusion rate of the reactants. As a result, the composite particles can be utilized effectively.

[0081] On the other hand, when the equivalent diameter of the catalyst for carboxylic ester production is 200 μm or less, it is preferable to load the composite particles in a region from the surface of the catalyst to 30% of its equivalent diameter. Especially in liquid-phase reactions, the reaction rate and the diffusion rate of the reactants within the pores of the support can be affected; therefore, conventionally, the particle size of the support has been designed to be relatively small depending on the reaction. In this embodiment, by thinning the supported layer where the composite particles are locally present, a highly active catalyst for carboxylic ester production can be obtained without reducing the support particle size. This also has the advantage that the catalyst can be easily separated by sedimentation, allowing for separation using a small-capacity separator. On the other hand, if the volume of the portion of the catalyst for carboxylic ester production without the composite particles becomes too large, there is an unnecessary increase in volume for each reactor, resulting in waste. Therefore, it is preferable to set the support particle size and the necessary thickness of the supported layer where the composite particles are locally present and the thickness of the layer without the composite particles, based on the reaction morphology.

[0082] The catalyst for the production of carboxylic esters can have an outer layer that is substantially free of composite particles, located outside the supported layer where composite particles are locally present. The outer layer is preferably formed with a thickness of 0.01 to 15 μm from the outer surface of the support. By providing an outer layer within this range, it can be used as a catalyst that is highly resistant to catalyst poisoning and inhibits the shedding of composite particles due to abrasion in reactions using reactors such as flow layers, bubble columns, and stirred reactors where friction between catalyst particles is a concern, and in reactions where poisoning substances accumulate. Furthermore, since the outer layer can be controlled to be extremely thin, a significant decrease in activity can be suppressed.

[0083] The thickness of the outer layer, which is essentially free of composite particles, is selected within an optimal range based on reaction characteristics, carrier properties, and the loading of composite particles. Preferably, it is 0.01–15 μm, more preferably 0.1–10 μm, and even more preferably 0.2–5 μm. If the thickness of the outer layer (the layer without loaded composite particles) exceeds 15 μm, the effect of improving catalyst lifetime remains unchanged when the composite particles are used as a catalyst, but it may sometimes lead to a decrease in catalytic activity. If the thickness of the outer layer is less than 0.01 μm, there is a tendency for composite particles to detach due to wear.

[0084] In this embodiment, the term "substantially free of composite particles" means that in the secondary electron reflectance images of X-ray microprobe analysis and high-resolution scanning electron microscopy described later, there are substantially no peaks with a relative intensity of more than 10% showing the distribution of nickel and / or cobalt and X (X represents at least one element selected from the group consisting of nickel, palladium, platinum, ruthenium, gold, silver and copper) in an oxidized state.

[0085] The composite particles of this embodiment preferably contain nickel and / or cobalt in an oxidized state, as described above.

[0086] Nickel in its oxidized state is preferably a nickel oxide (e.g., Ni2O, NiO, NiO2, Ni3O4, Ni2O3) formed by nickel bonding with oxygen, or a nickel oxide compound or solid solution or mixture thereof formed by nickel bonding with X and / or one or more other metal elements with oxygen.

[0087] In addition, cobalt in the oxidized state is preferably a cobalt oxide (e.g., CoO, Co2O3, Co3O4) formed by cobalt bonding with oxygen, or a cobalt oxide compound or solid solution or a mixture thereof formed by cobalt bonding with X and / or one or more other metal elements with oxygen.

[0088] The term "nickel oxide" as used herein refers to compounds containing nickel and oxygen. Nickel oxides include: Ni2O, NiO, NiO2, Ni3O4, Ni2O3 or their hydrates as exemplified above; hydroperoxides of nickel containing an OOH group or peroxides of nickel containing an O2 group or mixtures thereof, etc.

[0089] Furthermore, the term "complex oxide" mentioned here refers to oxides containing two or more metals. "Complex oxide" refers to oxides obtained by the formation of compounds from two or more metal oxides, including dual oxides that do not have oxyacid anions as structural units (such as perovskite oxides and spinel oxides of nickel). It is a broader concept than dual oxides, encompassing oxides entirely composed of two or more metals. Oxides obtained by the formation of solid solutions from two or more metal oxides also fall under the category of complex oxides.

[0090] In the catalyst for the manufacture of carboxylic esters according to this embodiment, when nickel oxide and / or cobalt oxide are complexed with X as described above, there is a tendency to exhibit significantly higher catalytic performance than catalysts formed from various single components, thereby triggering the original catalytic activity of nickel oxide and / or cobalt oxide with oxidative esterification activity. This can be considered a unique effect exhibited by complexing nickel oxide and / or cobalt oxide with X, because a novel catalytic effect completely different from that of various single components is derived through the binary functional effect between the two metal components or the generation of new active species. Furthermore, when oxidized nickel and / or oxidized cobalt and X are loaded onto a support in a highly dispersed state, there is a particular tendency to achieve revolutionary catalytic performance that cannot be obtained using conventional catalysts.

[0091] For example, if gold is chosen as X, and nickel oxide and gold are highly dispersed on the support, there is a tendency to exhibit significantly higher catalytic performance. Compared to catalysts obtained by supporting nickel oxide or gold separately as monomers on the support, this catalyst for carboxylate production exhibits higher selectivity for carboxylate esters and a tendency to significantly increase activity when the Ni / Au composition ratio is within a specific range. Regarding the catalytic activity of each metal atom, it shows high activity compared to particulate supports formed from various single components, and the expression of catalytic function achieved through its composite composition strongly depends on the supporting composition of nickel and gold. This can be presumed to be because there exists an optimal ratio for forming the oxidation state of nickel most suitable for the reaction. In this way, since both nickel oxide and gold are dispersedly supported on the support, there is a tendency to exhibit significant composite effects that cannot be predicted by the simple addition of various single components.

[0092] In the aforementioned catalysts for the manufacture of carboxylic acid esters, where gold is chosen as X as described above, oxidized nickel and gold are highly dispersed on the support, exhibiting a tendency for the two components to be composited at the nanoscale. When this catalyst for the manufacture of carboxylic acid esters is observed using transmission electron microscopy / scanning transmission electron microscopy (TEM / STEM), a structure typically observed is formed by roughly spherical nanoparticles of 2–3 nm uniformly dispersed and supported on the support.

[0093] In addition, when performing elemental analysis on nanoparticles based on energy dispersive X-ray spectroscopy (EDS), it was typically observed that nickel and gold coexisted in any particle, with nickel morphology covering the surface of gold nanoparticles. Furthermore, in addition to nanoparticles containing nickel and gold, nickel was also observed to be loaded onto a support in the form of monomers.

[0094] Furthermore, by employing X-ray photoelectron spectroscopy (XPS) and powder X-ray diffraction (powder XRD), the state of the metal can be confirmed. Typically, gold is observed to exist as a crystalline metal, while nickel exists as an amorphous oxide with a divalent valence.

[0095] Furthermore, if ultraviolet-visible spectrophotometry (UV-Vis) is used to observe changes in electronic excited states, the surface plasmon resonance absorption peak (approximately 530 nm) observed in gold nanoparticles of a single metal species typically disappears due to the recombination of nickel oxide and gold. This disappearance of the surface plasmon resonance absorption peak is not observed in catalysts composed of combinations of gold and other metal oxides (such as chromium oxide, manganese oxide, iron oxide, cobalt oxide, copper oxide, and zinc oxide) that do not have an effect observed in the reaction. It can be assumed that the disappearance of the surface plasmon resonance absorption peak is due to the mixing of electronic states at the interface between oxidized nickel and gold, resulting in, in other words, recombination of the two metal species.

[0096] It should be noted that the conversion to highly oxidized nickel oxide can be confirmed using the color change of the catalyst and ultraviolet-visible spectrophotometry (UV-Vis). By adding gold to nickel oxide, the oxide changes from grayish-green to brownish-red, with absorption appearing almost entirely in the visible region of the UV spectrum. The shape of this UV spectrum and the color of the catalyst are similar to those of highly oxidized nickel peroxide (NiO2) measured as a reference sample. Thus, it can be inferred that nickel oxide is converted to a highly oxidized nickel oxide state by adding gold.

[0097] Based on the above results, it can be concluded that the structure of the composite particle when gold is chosen as X is a form in which gold particles serve as the core and their surface is covered by nickel oxide in a highly oxidized state. There are no gold atoms on the surface of the composite particle.

[0098] The composite particles are preferably loaded onto the carrier in a highly dispersed state. More preferably, the composite particles are dispersed and loaded in the form of microparticles or thin films, with an average particle size of preferably 2-10 nm, more preferably 2-8 nm, and even more preferably 2-6 nm.

[0099] If the average particle size of the composite particles is within the above range, there is a tendency to form a specific active species structure containing nickel and / or cobalt and containing X, resulting in increased reactivity. Here, the average particle size in this embodiment refers to the number-average particle size measured using a transmission electron microscope (TEM). Specifically, in an image observed using a transmission electron microscope, the black contrast portion represents the composite particles, and the diameter of each particle can be measured, and its number-average particle size can be calculated.

[0100] The composition of nickel or cobalt and X in the composite particles is preferably in the range of 0.1 to 10, more preferably 0.2 to 8.0, and even more preferably 0.3 to 6.0, based on the Ni / X atomic ratio or Co / X atomic ratio. If the Ni / X atomic ratio or Co / X atomic ratio is within the above range, a specific active species structure composed of nickel and / or cobalt and X is formed, as well as the oxidation state of nickel and / or cobalt most suitable for the reaction. As a result, there is a tendency for increased activity and selectivity compared to cases deviating from the above range.

[0101] Regarding the morphology of the composite particles, there are no particular limitations. A preferred morphology is one in which both nickel and / or cobalt and X coexist within the particles and possess a phase structure. This phase structure can be, for example, a solid solution structure where chemical species randomly occupy crystal sites, a core-shell structure where each chemical species separates in a concentric spherical pattern, an anisotropic phase-separated structure where phase separation occurs anisotropically, or a heterophilic structure where two chemical species are adjacent on the particle surface. A more preferred morphology is one containing a core of X, the surface of which is covered by oxidized nickel and / or cobalt. Regarding the shape of the composite particles, there are no particular limitations as long as both components are present; any shape, such as spherical or hemispherical, is acceptable.

[0102] As an analytical method for observing the morphology of composite particles, transmission electron microscopy / scanning transmission electron microscopy (TEM / STEM) is effective, for example, as described above. By irradiating the nanoparticle image observed using TEM / STEM with electron beams, elemental analysis of the particles and mapping of elemental distribution can be achieved. As shown in the embodiments described later, the composite particles of this embodiment contain nickel and / or cobalt and X in all particles, with the surface of X covered by nickel and / or cobalt. In this morphology, the atomic ratio of nickel and / or cobalt to X varies depending on the location of the composition analysis point in the particle, with more nickel and / or cobalt detected at the particle edges compared to the central part of the particle. Therefore, in each particle, the atomic ratio of nickel or cobalt to X varies depending on the location of the analysis point, and its range is within the range of the aforementioned Ni / X atomic ratio or Co / X atomic ratio.

[0103] When gold, silver, or copper is selected as X, ultraviolet-visible spectroscopy (UV-Vis) is an effective means of determining its structure. In gold / silver / copper nanoparticle monomers, the photoelectric field in the visible to near-infrared region couples with the surface free electrons of the metal, exhibiting surface plasmon resonance absorption. For example, when a catalyst loaded with gold particles is irradiated with visible light, an absorption spectrum based on plasmon resonance originating from the gold particles is observed at a wavelength of approximately 530 nm. However, in the catalyst for manufacturing carboxylic acid esters loaded with nickel oxide and gold in this embodiment, since this surface plasmon resonance absorption disappears, it can be considered that gold is not present on the surface of the composite particles in this embodiment.

[0104] As for the solid form of nickel, there are no particular limitations as long as the specified activity can be obtained; the preferred form is an amorphous state in which no diffraction peaks are observed in X-ray diffraction. It can be inferred that by preparing it into this form, the interaction with oxygen is increased when it is used as a catalyst for oxidation reactions, and thus the interface between oxidized nickel and X increases, therefore, there is a tendency to obtain better activity.

[0105] In this embodiment, X is at least one element selected from the group consisting of nickel, palladium, platinum, ruthenium, gold, silver and copper. X is preferably selected from at least one element selected from nickel, palladium, ruthenium, gold and silver, more preferably selected from at least one element selected from palladium and gold, and even more preferably gold.

[0106] The chemical state of X can be a metal, an oxide, a hydroxide; a complex compound containing X and containing nickel, cobalt, or one or more other metallic elements; or a mixture thereof. The preferred chemical state is a metal or an oxide, more preferably a metal. Furthermore, the solid form of X is not particularly limited as long as the specified activity can be obtained, and it can be any form of crystalline or amorphous material.

[0107] The term "other metallic elements" as used here refers to: third constituent elements or metallic components such as alkali metals, alkaline earth metals and rare earth metals contained in catalysts for the manufacture of carboxylic acid esters, other than the constituent elements of the support, nickel and / or cobalt in their oxidized state, and X, as described below.

[0108] In this embodiment, from the viewpoint of further improving pH fluctuation tolerance, the composite particles preferably contain gold and nickel in an oxidized state. Furthermore, the nickel to gold composition ratio in the composite particles, in terms of the Ni / Au atomic ratio, is preferably 1.1 or more and 10 or less, more preferably 2 or more and 9 or less, and even more preferably 3 or more and 8 or less.

[0109] The catalyst for carboxylate production in this embodiment exhibits excellent performance by loading X and oxidized nickel and / or cobalt onto a support as described above, forming composite particles composed of X and oxidized nickel and / or cobalt. It should be noted that the term "composite particle" mentioned in this embodiment refers to a particle containing different binary metal species within a single particle. Examples of different binary metal species include binary metal particles where both nickel and / or cobalt and X are metals, and metal particles forming alloys or intermetallic compounds of nickel and / or cobalt and X. When these are used as catalysts for chemical synthesis, compared to the catalyst for carboxylate production in this embodiment, there is a tendency for lower selectivity and catalytic activity towards the target product.

[0110] Regarding the catalyst for carboxylic ester production in this embodiment, unlike composite particles composed of nickel and / or cobalt in their oxidized state and X, it is preferable to contain nickel and / or cobalt in their oxidized state alone on a support. By including nickel and / or cobalt in their oxidized state that are not composited with X, the structural stability of the catalyst for carboxylic ester production is further improved, and the increase in pore diameter caused by long-term reactions and the accompanying particle growth of composite particles are suppressed. As will be described later, this effect tends to become more pronounced when using an aluminum-containing silica-based composition containing silica and alumina as a support.

[0111] The following explains the effect of nickel and / or cobalt in an oxidized state on a support on improving the structural stability of catalysts for the manufacture of carboxylic acid esters, and suppressing the increase in pore diameter and the accompanying particle growth of composite particles caused by long-term reactions.

[0112] As will be described later, in the synthesis reaction of carboxylic esters, by adding alkali metal or alkaline earth metal compounds to the reaction system, the pH of the reaction system is maintained at 6 to 9, more preferably at neutral conditions (e.g., pH 6.5 to 7.5), that is, as close to pH 7 as possible, thereby tending to suppress byproducts inherent in the carboxylic ester manufacturing reaction, such as acetals caused by acidic substances represented by methacrylic acid or acrylic acid.

[0113] According to the researchers of the present invention, when using gold particle-supported materials obtained by loading single-component gold particles onto a support formed of an aluminum-containing silica-based composition comprising silica and alumina, and conducting a long-term reaction using the aforementioned reaction operation, although the reaction is slow, there is a tendency for structural changes to occur in the gold particle-supported materials. This phenomenon can be attributed to the fact that, through the aforementioned reaction operation, the supported particles are repeatedly and locally exposed to acids and alkalis, causing some of the Al in the support to dissolve and precipitate, resulting in a rearrangement of the silica-alumina cross-linked structure, thereby increasing the pore diameter of the supported particles. Furthermore, with the change in pore diameter, sintering of the gold particles occurs, reducing the surface area, and thus, there is a tendency for a decrease in catalytic activity.

[0114] On the other hand, by having composite particles and individually oxidized nickel and / or cobalt present on the support, there is a tendency for the structural stability of the supported particles based on the above-described reaction operation to be improved, while the expansion of pore diameter and the growth of composite particles are suppressed. The main reason for this, as mentioned above, is that the oxidized nickel and / or cobalt react with the constituent elements of the support to generate nickel and / or cobalt oxide compounds or solid solutions, etc., containing nickel and / or cobalt composite oxides. It can be considered that the stabilization effect of this nickel compound on the silica-alumina crosslinked structure results in a significant improvement in the structural changes of the supported particles. The inventors speculate that this structural stabilization effect of the supported material originates from the presence of oxidized nickel and / or cobalt in the support. Therefore, it can be considered that when the oxidized nickel and / or cobalt contained in the composite particles are in contact with the support, this effect is naturally obtained; and when the oxidized nickel and / or cobalt are present alone on the support, a greater stabilization effect can be obtained.

[0115] As the support for the catalyst used in the production of carboxylic esters in this embodiment, there are no particular limitations as long as the catalyst particles in this embodiment can be supported, and a catalyst support conventionally used for chemical synthesis can be used.

[0116] Examples of suitable carriers include activated carbon, silica, alumina, silica-alumina, titanium dioxide, silica-titanium dioxide, zirconium oxide, magnesium oxide, silica-magnesium oxide, silica-alumina-magnesium oxide, calcium carbonate, zinc oxide, zeolite, and crystalline metal silicates. Activated carbon, silica, alumina, silica-alumina, silica-magnesium oxide, silica-alumina-magnesium oxide, titanium dioxide, silica-titanium dioxide, and zirconium oxide are preferred, with silica-alumina and silica-alumina-magnesium oxide being more preferred.

[0117] In addition, the support may contain one or more metal components selected from alkali metals (Li, Na, K, Rb, Cs), alkaline earth metals (Be, Mg, Ca, Sr, Ba), and rare earth metals (La, Ce, Pr). Preferably, the supported metal component is one that has formed an oxide, for example, through calcination of nitrates, acetates, etc.

[0118] As a support, a support formed from an aluminum-containing silica-based composition comprising silica and aluminum is preferred. That is, the support preferably comprises silica and alumina. This support exhibits higher water resistance compared to silica and higher acid resistance compared to alumina. Furthermore, it is harder and has higher mechanical strength than activated carbon, possessing superior physical properties compared to conventionally used supports, and can stably support oxidized nickel and / or cobalt, as well as X, as active ingredients. As a result, the catalyst for carboxylic ester production tends to maintain high reactivity for a longer period.

[0119] When used as a catalyst for chemical synthesis, a catalyst for the manufacture of carboxylic acid esters with nickel and / or cobalt in an oxidized state having a specific atomic ratio with X and using an aluminum-containing silica-based composition as a support tends to have the following characteristics: a high surface area suitable for use as a catalyst support, high mechanical strength, physical stability, and corrosion resistance to the inherent liquidity of the reaction.

[0120] The following describes the characteristics of the support formed from an alumina-containing silica-based composition comprising silica and alumina, according to this embodiment, which significantly improves catalyst lifetime. The reasons for the significant improvement in the mechanical strength and chemical stability of the support can be inferred as follows.

[0121] It can be assumed that the carrier formed by the aluminum-containing silica-based composition, by adding aluminum (Al) to the uncrosslinked silica (Si-O) chains of the silica gel, novel Si-O-Al-O-Si bonds are formed without losing the stability of the original acidic Si-O chains, thus forming an Al crosslinked structure. This strengthens the Si-O bonds and significantly improves hydrolytic stability (hereinafter referred to as "water resistance"). Furthermore, it can be assumed that if a Si-O-Al-O-Si crosslinked structure is formed, compared to the case of silica gel alone, the number of uncrosslinked Si-O chains is reduced, and the mechanical strength is increased. That is, it can be inferred that the amount of Si-O-Al-O-Si structure formed is related to the improvement in the mechanical strength and water resistance of the resulting silica gel.

[0122] One reason why X, as well as nickel and / or cobalt in their oxidized state, can be stably loaded onto the support over a long period is that, as mentioned above, the mechanical strength and chemical stability of the support are significantly improved, exhibiting superior physical properties compared to conventionally used supports. Consequently, it can be considered that nickel and / or cobalt, as active components, are not easily desorbed from X, and can be stably loaded over a long period.

[0123] Commonly used supports, such as silica or silica-titanium dioxide, tend to leach nickel and / or cobalt components slowly during long-term reactions. Conversely, the use of these supports tends to suppress the dissolution of nickel and / or cobalt components over a long period. In particular, results from X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM / EDX), and high-resolution X-ray fluorescence (HRXRF) confirm that when using silica or silica-titanium dioxide supports, the dissolved nickel and / or cobalt components are nickel oxide or cobalt oxide present solely on the support. It can be inferred that since nickel oxide or cobalt oxide are acid-soluble compounds, when used as a catalyst for carboxylic acid ester synthesis, dissolution occurs due to acidic substances represented by the inherent byproducts of the reaction, namely methacrylic acid or acrylic acid.

[0124] Based on the analysis of the chemical state of nickel and / or cobalt using bicrystalline high-resolution fluorescence X-ray spectroscopy (HRXRF), it can be inferred that the nickel and / or cobalt in the catalyst for the production of carboxylic esters in this embodiment are not only nickel oxide and / or cobalt oxide as single compounds, but also complex oxides containing nickel and / or cobalt, such as nickel oxide and / or cobalt oxide compounds or solid solutions or mixtures thereof, formed by the bonding of nickel oxide and / or cobalt oxide with the constituent elements of the support.

[0125] High-resolution X-ray fluorescence (HRXRF) with dual-crystal structure offers extremely high energy resolution, allowing analysis of chemical states based on the energy positions (chemical shifts) and shapes of the resulting spectra. In particular, the Kα spectra of 3d transition metals exhibit changes in chemical shifts and shapes due to variations in valence and electronic states, enabling detailed analysis of the chemical states. In the catalyst for the manufacture of carboxylic esters according to this embodiment, typically as shown in the examples described later, the NiKα spectrum changes, confirming a chemical state of nickel different from that of nickel oxide, which is a single compound.

[0126] For example, nickel aluminate, formed from nickel oxide and aluminum oxide, is an acid-insoluble compound. It can be inferred that the formation of this nickel compound on a support would significantly improve the dissolution of nickel.

[0127] In this embodiment, the carrier is preferably a silicon dioxide-based material, which contains silicon, aluminum, the aforementioned fourth-period element, and the aforementioned basic element in the range of 42 mol% or more and 90 mol% or less, 3 mol% or more and 38 mol% or less, 0.5 mol% or more and 20 mol% or less, and 2 mol% or more and 38 mol% or less, respectively, relative to the total molar amount of silicon, aluminum, at least one fourth-period element selected from the group consisting of iron, cobalt, nickel, and zinc, and at least one basic element selected from the group consisting of alkali metal elements, alkaline earth metal elements, and rare earth elements.

[0128] When a silica-based material containing silicon, aluminum, the aforementioned fourth-period elements, and the aforementioned basic elements contains silicon in the range of 42-90 mol%, aluminum in the range of 3-38 mol%, the fourth-period elements in the range of 0.5-20 mol%, and the basic elements in the range of 2-38 mol%, the silicon, aluminum, fourth-period elements, basic elements, and oxygen atoms form a specific and stable bond structure, and this bond structure is easily formed in a uniformly dispersed state within the silica-based material. From the above viewpoint, in this embodiment, it is more preferable to contain 70-90 mol% silicon, 5-30 mol% aluminum, 0.75-15 mol% fourth-period elements, and 2-30 mol% basic elements; even more preferably, it contains 75-90 mol% silicon, 5-15 mol% aluminum, 1-10 mol% fourth-period elements, and 2-15 mol% basic elements. In particular, when the composition ratio of fourth-period elements is set to 0.75 mol% or more, resulting in a state where each component is uniformly dispersed throughout the material, there is a tendency for the structure to contain fewer portions of fourth-period elements, thus yielding silica-based materials that exhibit resistance (high acid and alkali resistance) even when repeatedly exposed to acids and / or alkalis. From the viewpoint of obtaining silica-based materials with high mechanical strength and large specific surface area, it is preferable that the fourth-period elements are 10 mol% or less and the basic elements are 30 mol% or less.

[0129] The silicon to aluminum ratio is set within a range preferred from the viewpoint of the acid and alkali resistance and water resistance of silica-based materials. The silicon to aluminum ratio is preferably (silicon / aluminum) = 2 to 4. When the (silicon / aluminum) ratio is less than the above range, there is a tendency for decreased acid and alkali resistance. When the (silicon / aluminum) ratio is greater than the above range, there is a tendency for decreased water resistance.

[0130] Alkali metals, which are components of alkaline metals, include Li, Na, K, Rb, and Cs; alkaline earth metals include Be, Mg, Ca, Sr, and Ba; and rare earth metals include La, Ce, and Pr.

[0131] For example, in a silica-based material formed from a composite oxide containing silicon-aluminum-nickel-magnesium, with nickel selected as a fourth-period element and magnesium selected as a basic element, when the chemical state of nickel is analyzed using bicrystalline high-resolution fluorescence X-ray diffraction (HRXRF), the nickel in the silica-based material of this embodiment does not exist as nickel oxide, a single compound. Instead, the nickel exists as a nickel-containing composite oxide, such as a nickel oxide compound or solid solution, or a mixture thereof, formed by the bonding of nickel oxide with aluminum oxide and / or magnesium oxide.

[0132] It can be inferred that in the aforementioned silica-based materials, nickel exists, for example, as a spinel compound of nickel oxide and aluminum oxide, namely nickel aluminate (NiAl2O4), or as a solid solution of nickel oxide and magnesium oxide (NiO·MgO). It can be assumed that the aforementioned fourth-period elements, other than nickel, similarly contribute to stabilizing the silica-alumina crosslinked structure by forming spinel compounds with aluminum oxide or solid solutions with alkali metal oxides, thereby increasing chemical stability.

[0133] From the viewpoints of acid and alkali resistance, mechanical strength, and water resistance, when the fourth-period element is nickel and the basic element is magnesium, the silica-based material formed from a composite oxide containing silicon, aluminum, nickel, and magnesium preferably contains silicon in the range of 42–90 mol%, aluminum in the range of 3–38 mol%, nickel in the range of 0.5–20 mol%, and magnesium in the range of 2–38 mol%. More preferably, it contains silicon in the range of 70–90 mol%, aluminum in the range of 5–30 mol%, nickel in the range of 0.75–15 mol%, and magnesium in the range of 2–30 mol%. Even more preferably, it contains silicon in the range of 75–90 mol%, aluminum in the range of 5–15 mol%, nickel in the range of 1–10 mol%, and magnesium in the range of 2–15 mol%. If the elemental composition of silicon, aluminum, nickel, and magnesium is within the above ranges, silicon, aluminum, nickel, and magnesium readily form a specific and stable bond structure. In particular, for a more preferred composition ratio, even if the aforementioned stable bonded structure is expected to be uniformly dispersed in the silica-based material, it is anticipated that it will be formed at a sufficient density to contribute to the overall stabilization of the silica-based material. As a result, silica-based materials tend to exhibit good acid and alkali resistance and mechanical strength capable of withstanding repeated use.

[0134] [Determination of the constituent element content of silica-based materials and noble metal supports]

[0135] The concentrations of Si, Al, fourth-period elements, and basic elements in the aforementioned silica-based materials were quantified using a Thermo Fisher Scientific ICP-AES MS device, model "IRIS Intrepid II XDL" (trade name). The sample was prepared as follows.

[0136] First, a silica-based material was weighed into a Teflon (registered trademark) decomposition container, and nitric acid and hydrogen fluoride were added. The resulting solution was then heated and decomposed using a microwave decomposition apparatus, "ETHOS·TC type" (trade name), manufactured by Milestone General KK, and evaporated to dryness on a heater. Next, nitric acid and hydrochloric acid were added to the precipitated residue, and the mixture was decomposed under pressure using the aforementioned microwave decomposition apparatus. The resulting decomposition solution was then diluted to a specific volume with pure water and used as a sample.

[0137] Using the above-mentioned ICP-AES and the internal standard method to quantify the sample, the contents of Si, Al, fourth-period elements and basic elements in the silica-based material and the contents of metal elements in the noble metal loading were determined by subtracting the operation blank value performed at the same time. The composition ratio (molar basis) and loading amount were then calculated.

[0138] Next, a preferred method for preparing a carrier having the aforementioned structure and / or composition will be described.

[0139] The method for preparing a carrier formed from an aluminum-containing silica-based composition containing silica and aluminum oxide is not particularly limited. For example, hydrothermal synthesis can be carried out under the conditions described later, followed by drying and calcination, thereby preparing an aluminum-containing silica composition that allows silica sol to react with an aluminum compound solution.

[0140] The following section provides a detailed explanation of the preparation method for the carrier.

[0141] As the silica source, silica sol or silica gel can be used, for example. As for the silica gel, any material with uncrosslinked Si sites that react with Al is acceptable; the length of the Si-O chains is not particularly limited. Preferred aluminum compounds are water-soluble compounds such as sodium aluminate, aluminum chloride hexahydrate, aluminum perchlorate hexahydrate, aluminum sulfate, aluminum nitrate nonahydrate, and aluminum diacetate. Even water-insoluble compounds such as aluminum hydroxide and aluminum oxide can be used, as long as they react with the uncrosslinked Si in the silica sol or silica gel.

[0142] A silica sol is mixed with an aluminum compound to obtain a sol mixture containing both silica sol and aluminum compound. This mixture undergoes a multi-stage hydrothermal reaction at 20–100°C for 1–48 hours. The mixture is then dried to obtain a gel. Calcination is then performed under the temperature / time / atmosphere conditions described later. Alternatively, an alkaline aqueous solution is added to the sol mixture to cause co-precipitation of silica and the aluminum compound. Hydrothermal synthesis is then performed under the conditions described later, followed by drying and calcination. Furthermore, by directly micronizing the sol mixture using a spray dryer, or by drying the sol mixture and granulating the gel, a carrier formed from an aluminum-containing silica-based composition with a desired particle size can also be prepared.

[0143] The method for preparing a support comprising silica, alumina, and an oxide of at least one alkali metal selected from alkali metals, alkaline earth metals, and rare earth metals can be carried out by drying a slurry obtained by mixing an alkali metal compound, an alkaline earth metal compound, and / or a rare earth metal compound into the silica and aluminum components, and then calcining it under the conditions described below, according to the method for preparing a support formed from an aluminum-containing silica-based composition comprising silica and alumina.

[0144] As a raw material for alkali metals, alkaline earth metals, and rare earth metals, commercially available compounds can be used in the same way as aluminum raw materials. Water-soluble compounds are preferred, and hydroxides, carbonates, nitrates, and acetates are more preferred.

[0145] Other preparation methods include adsorbing alkali metal components selected from alkali metals, alkaline earth metals, and rare earth metals onto a support formed from an aluminum-containing silica-based composition. For example, methods such as impregnation (adding the support to a liquid containing a dissolved alkali metal compound and then drying it) or infiltration (immersing the pore-capacity portion of the alkali compound into the support and then drying it) can be used. In these methods, the subsequent adsorption of the alkali metal component requires careful dispersion of the alkali metal component in the support, followed by liquid drying under mild conditions.

[0146] In addition, in order to control the properties of the slurry, fine-tune the pore structure of the product and the physical properties of the resulting carrier, inorganic and organic substances can be added to the mixed slurry of the above-mentioned raw materials.

[0147] Specific examples of the inorganic substances used include inorganic acids such as nitric acid, hydrochloric acid, and sulfuric acid; metal salts of alkali metals such as Li, Na, K, Rb, and Cs; alkaline earth metals such as Mg, Ca, Sr, and Ba; and water-soluble compounds such as ammonia and ammonium nitrate. Clay minerals that disperse in water to form suspensions can also be listed. Specific examples of organic substances include polymers such as polyethylene glycol, methylcellulose, polyvinyl alcohol, polyacrylic acid, and polyacrylamide.

[0148] The effects of adding inorganic and organic substances are varied, primarily affecting the formation of spherical carriers and the control of pore diameter and volume. Specifically, a crucial factor in obtaining spherical carriers is the consistency of the mixed slurry. By utilizing inorganic or organic substances to adjust viscosity and solids concentration, the slurry consistency can be modified to facilitate the formation of spherical carriers. Furthermore, the control of pore diameter and volume can be achieved through a multi-stage hydrothermal synthesis process of the mixed slurry, as described later. Additionally, it is preferable to appropriately select and use optimal organic compounds that remain internally during the carrier formation stage and can be removed through post-formation calcination and washing operations.

[0149] In the hydrothermal synthesis process of this embodiment, the mixing of the slurry is carried out while adjusting the heating and stirring conditions.

[0150] The heating conditions are preferably as follows: In the first stage, the temperature is raised to a specified temperature and held for a specified time; in the second stage, the temperature is lowered to a specified temperature and held for a specified time; and then, in the third stage, the temperature is raised to a specified temperature and held for a specified time. Specifically, regarding the temperature T1 in the first stage, it is preferably adjusted to 70–90°C and held for 1–10 hours; regarding the temperature T2 in the second stage, it is preferably adjusted to 20–40°C and held for 0.5–10 hours; and regarding the temperature T3 in the third stage, it is preferably adjusted to 40–60°C and held for 1–20 hours. By adopting such conditions, the formation of secondary particles in the mixed slurry can be easily controlled, and there is a tendency to obtain a uniform pore structure from near the pore inlet to the interior of the pore. From the same viewpoint, the value of T1–T2 is preferably 30–70°C, more preferably 40–60°C, and the value of T3–T2 is preferably 5–40°C, more preferably 15–30°C.

[0151] Next, as a stirring condition, it is preferable to adjust the tip speed of the stirring blades (hereinafter also referred to as "stirring blade tip speed"). The stirring blade tip speed V can be defined by the following formula.

[0152] V = N / 60 × πD (N: rotational speed in rpm, D: diameter of the stirring blade)

[0153] The speed V of the stirring impeller tip is not particularly limited, but is preferably 5.0 to 20 m / s.

[0154] The diameter of the stirring blade is not particularly limited and can be set to 0.3 to 5 m, preferably 0.5 to 3 m, and more preferably 0.5 to 2 m.

[0155] The shape of the mixing blades is not particularly limited, and examples include anchor-type mixing blades, paddle-type mixing blades, and turbine-type mixing blades. From the viewpoint of shear performance, paddle-type mixing blades and turbine-type mixing blades are preferred, and turbine-type mixing blades are more preferred. Examples of turbine-type mixing blades include radial turbine blades, axial turbine blades, and blade turbine blades.

[0156] In the hydrothermal synthesis process of this embodiment, it is preferable to use one of the above-mentioned heating conditions and stirring conditions, and more preferably both.

[0157] The carrier can be manufactured by spray drying a mixture of the aforementioned raw materials and additives. As a method for forming the mixture into droplets, known spraying devices such as rotating disk spraying, two-fluid nozzle spraying, and pressurized nozzle spraying can be used.

[0158] The liquid to be sprayed must be used in a fully mixed state. Poor mixing can lead to reduced durability and affect the performance of the carrier due to imbalances in composition. In particular, during the preparation of raw materials, the viscosity of the slurry may increase and localized gelation (colloidal condensation) may occur, raising concerns about the formation of uneven particles. Therefore, in addition to slow mixing of raw materials under stirring, it is sometimes preferable to control the mixture to a metastable region of silica sol, such as around pH 2, by adding acids or bases.

[0159] The liquid to be sprayed needs to have a certain viscosity and solids concentration. If the viscosity and solids concentration are too low, the porous body obtained by spray drying will not form perfect spheres, but rather more concave spheres. Conversely, if the viscosity and solids concentration are too high, in addition to sometimes adversely affecting the dispersion of the porous bodies, droplet formation may be unstable depending on the properties. Therefore, the viscosity is preferably in the range of 5 to 10000 cp, provided that spraying is possible. From a shape perspective, a sprayable high viscosity is preferred, and from a balance with operability, a range of 10 to 1000 cp is more preferable. Furthermore, from the perspective of shape and particle size, a solids concentration in the range of 10 to 50% by mass is preferred. It should be noted that, as standard spray drying conditions, the hot air temperature at the inlet of the spray dryer tower is preferably in the range of 200 to 280°C, and the outlet temperature of the drying tower is preferably in the range of 110 to 140°C.

[0160] The calcination temperature of the carrier is typically selected from the range of 200–800°C. Calcination at temperatures exceeding 800°C tends to significantly reduce the specific surface area, and is therefore not preferred. Furthermore, the calcination atmosphere is not particularly limited and is usually carried out in air or nitrogen. The calcination time is determined based on the specific surface area after calcination, and is typically 1–48 hours. Since the carrier's physical properties, such as porosity, change, appropriate temperature and heating conditions must be selected for the calcination process. If the calcination temperature is too low, it tends to be difficult to maintain durability as a composite oxide; if it is too high, it may lead to a decrease in pore volume. Additionally, a slow heating process, such as programmed heating, is preferred. Rapid calcination at high temperatures intensifies the gasification and combustion of inorganic and organic materials, exposing them to excessively high temperatures, which can cause pulverization, and is therefore not preferred.

[0161] From the perspectives of ease of loading composite particles, reactivity when used as a catalyst, difficulty of removal, and reactivity, the specific surface area of ​​the support is preferably 10 m² in the BET nitrogen adsorption method for determination. 2 / g or more, more preferably 20m 2 / g or more, further preferably 50m 2 / g or more. Furthermore, from the viewpoint of activity, there are no particular limitations; however, from the viewpoint of mechanical strength and water resistance, 700m is preferred. 2 / g or less, more preferably 350m 2 / g or less, more preferably 300m 2 / g or less.

[0162] If the pore diameter of the support is less than 3 nm, there is a tendency for the exfoliation properties of the loaded metal to become better. However, when used as a catalyst in liquid-phase reactions, etc., from the viewpoint of maintaining high reaction activity by avoiding excessive diffusion resistance within the pores so as not to control the diffusion rate of the reaction matrix, a pore diameter of 3 nm or more is preferred. On the other hand, from the viewpoint of the difficulty of fragmentation of the supported material and the difficulty of exfoliation of the loaded metal, a pore diameter of 50 nm or less is preferred. Therefore, the pore diameter of the support is preferably 3 nm to 50 nm, more preferably 3 nm to 30 nm. Pore volume is necessary for the existence of pores supporting composite nanoparticles. However, if the pore volume increases, a tendency for a sharp decrease in strength is observed. Therefore, from the viewpoint of strength and loading characteristics, the pore volume is preferably in the range of 0.1 to 1.0 mL / g, more preferably in the range of 0.1 to 0.5 mL / g. The support of this embodiment preferably has both the pore diameter and pore volume satisfying the above ranges.

[0163] Regarding the shape of the support, depending on the reaction mode, hollow cylindrical or honeycomb morphologies with low pressure loss are selected in fixed beds. Spherical shapes are typically chosen under liquid slurry suspension conditions. The optimal particle size is selected based on reactivity and separation methods. For example, in processes where catalysts are typically separated using simple sedimentation separation, a particle size of 10–200 μm is preferred, more preferably 20–150 μm, and even more preferably 30–150 μm, is preferred from the perspective of balancing reaction characteristics. In cross-filter systems, small particles of 0.1–20 μm or smaller are preferred due to higher reactivity. The type and form can be changed according to the intended use, and the catalyst can be used for chemical synthesis.

[0164] The loading amount of oxidized nickel or cobalt on the support is not particularly limited, but is typically 0.01 to 20% by mass, preferably 0.1 to 10% by mass, more preferably 0.2 to 5% by mass, and even more preferably 0.5 to 2% by mass, relative to the mass of the support. The loading amount of X on the support is typically 0.01 to 10% by mass, preferably 0.1 to 5% by mass, more preferably 0.2 to 2% by mass, even more preferably 0.3 to 1.5% by mass, and particularly preferably 0.5 to 1.0% by mass, relative to the mass of the support.

[0165] Furthermore, in this embodiment, the atomic ratio of nickel and / or cobalt to the constituent elements of the aforementioned support is within a suitable range. When using the support formed from an aluminum-containing silica-based composition comprising silica and alumina as described in this embodiment, the compositional ratio of nickel or cobalt to alumina in the catalyst, in terms of Ni / Al atomic ratio or Co / Al atomic ratio, is preferably 0.01 to 1.0, more preferably 0.02 to 0.8, and even more preferably 0.04 to 0.6. Furthermore, when using a support comprising silica, alumina, and an oxide of at least one alkali metal selected from alkali metals, alkaline earth metals, and rare earth metals, the composition ratio of nickel or cobalt to alumina in the support is preferably 0.01 to 1.0, more preferably 0.02 to 0.8, and even more preferably 0.04 to 0.6, in terms of Ni / Al atomic ratio or Co / Al atomic ratio. Additionally, the composition ratio of nickel or cobalt to the alkali metal component is preferably 0.01 to 1.2, more preferably 0.02 to 1.0, and even more preferably 0.04 to 0.6, in terms of Ni / (alkali metal + alkaline earth metal + rare earth metal) atomic ratio or Co / (alkali metal + alkaline earth metal + rare earth metal) atomic ratio.

[0166] If the atomic ratio of nickel and / or cobalt to aluminum and alkali metal oxides, which are the supporting elements, is within the above-mentioned range, there is a tendency for a greater improvement in the dissolution of nickel and / or cobalt and the structural changes of the supported particles. This can be attributed to the fact that within the above-mentioned range, nickel and / or cobalt, aluminum, and alkali metal oxides form specific composite oxides, resulting in a stable bonded structure.

[0167] In the catalyst for producing carboxylic acid esters according to this embodiment, in addition to nickel and / or cobalt in their oxidized states as active components and X, a third component element may also be included. This third component element may include, for example, titanium, vanadium, chromium, manganese, iron, zinc, gallium, zirconium, niobium, molybdenum, rhodium, cadmium, indium, tin, antimony, tellurium, hafnium, tantalum, tungsten, rhenium, osmium, iridium, mercury, thallium, lead, bismuth, aluminum, boron, silicon, and phosphorus. The content of these third component elements in the supported material is preferably 0.01 to 20% by mass, more preferably 0.05 to 10% by mass. Furthermore, the catalyst for producing carboxylic acid esters may also contain at least one metal component selected from alkali metals, alkaline earth metals, and rare earth metals. The content of alkali metals, alkaline earth metals, and rare earth metals in the supported material is preferably selected from a range of 15% by mass or less.

[0168] It should be noted that these third component elements, or alkali metals, alkaline earth metals, and rare earth metals, can be contained in the supported material during the manufacture and reaction of catalysts for carboxylic acid ester production, or they can be pre-contained in the support.

[0169] From the viewpoint of reactivity and the difficulty of removing active components, the specific surface area of ​​the catalyst for carboxylic ester production in this embodiment is preferably 20 to 350 m², as determined by the BET nitrogen adsorption method.2 / g, more preferably 50-300m 2 / g, further preferably 100-250m 2 The range of / g.

[0170] The pore diameter of the catalyst for carboxylic ester production is derived from the pore structure of the support. If it is less than 3 nm, there is a tendency for the stripping properties of the supported metal component to become better. When used as a catalyst in liquid-phase reactions, etc., from the viewpoint of maintaining high reaction activity without causing excessive diffusion resistance within the pores so as not to control the diffusion rate of the reaction matrix, a pore diameter of 3 nm or more is preferred. On the other hand, from the viewpoint of the difficulty of fragmentation of the supported material and the difficulty of stripping the supported composite particles, it is preferred to be 50 nm or less. Therefore, the pore diameter of the catalyst for carboxylic ester production is preferably 3 nm to 50 nm, more preferably 3 nm to 30 nm, and even more preferably 3 nm to 10 nm. From the viewpoint of loading characteristics and reaction characteristics, the pore volume is preferably in the range of 0.1 to 1.0 mL / g, more preferably 0.1 to 0.5 mL / g, and even more preferably in the range of 0.1 to 0.3 mL / g. The catalyst for carboxylic ester production in this embodiment preferably has both the pore diameter and pore volume satisfying the above ranges.

[0171] [Method for manufacturing catalysts for carboxylic ester production]

[0172] The method for manufacturing the catalyst for producing carboxylic esters according to this embodiment is not particularly limited and may include the following preferred steps. Each step will be described below.

[0173] As a first step, an aqueous slurry containing a support is mixed with an acidic aqueous solution containing a soluble metal salt selected from the group consisting of nickel, cobalt, palladium, lead, platinum, ruthenium, gold, silver, and copper. The temperature is adjusted such that the temperature of the mixture of the two liquids is 60°C or higher. A precursor for a carboxylic acid ester manufacturing catalyst is generated in the mixture, with catalyst particles precipitated on the support.

[0174] Next, as a second step, the precursor obtained in the first step is washed with water, dried, and then heated to obtain a catalyst for the manufacture of carboxylic acid esters.

[0175] According to this method, a catalyst for the manufacture of carboxylic acid esters can be obtained, which has a supported layer in which composite particles are locally present, but does not contain composite particles in the region including the center of the support.

[0176] In this embodiment, it is preferable to perform a water dispersion step, which involves dispersing and maturing the carrier in water, before the first step. By pre-dispersing the carrier in water, a more concentrated distribution layer of composite particles can be obtained. Based on pore size distribution measurements using a nitrogen adsorption method, it can be inferred that the effect achieved by water dispersion of the carrier is due to the rearrangement of the carrier's pore structure, resulting in a more uniform and concentrated pore structure. The water dispersion temperature can be room temperature, but since the change in pore structure is slow, it is preferable to select a temperature higher than room temperature, i.e., in the range of 60–150°C. When carried out under normal pressure, the temperature range of 60–100°C is preferred. Furthermore, the carrier immersion time in water is not particularly limited and can be set to 0.5–10 minutes. From the viewpoint of further reducing the half-value width Wd, it is preferably 0.5–8 minutes, and more preferably 0.5–6 minutes. Moreover, the water dispersion treatment time varies depending on the temperature conditions; for example, at 90°C, it is preferably 1 minute to 5 hours, more preferably 1–60 minutes, and even more preferably 1–30 minutes. As a first step, the carrier can be temporarily dried and calcined after being dispersed in water before use. However, it is preferable to contact the slurry in which the carrier is dispersed in water with an acidic aqueous solution containing a soluble metal salt selected from the group consisting of nickel, cobalt, palladium, lead, platinum, ruthenium, gold, silver and copper, so that the catalyst particles are immobilized on the carrier insolublely.

[0177] Examples of soluble metal salts containing nickel include nickel nitrate, nickel acetate, and nickel chloride. Additionally, examples of soluble metal salts containing X include, for instance, palladium chloride and palladium acetate when palladium is chosen as X; ruthenium chloride and ruthenium nitrate when ruthenium is chosen as X; chloroauric acid, sodium gold chloride, potassium dicyandiamide, diethylamine trichloride, and gold cyanide when gold is chosen as X; and silver chloride and silver nitrate when silver is chosen as X.

[0178] The concentrations of the aqueous solutions containing nickel and / or cobalt and containing X are typically in the range of 0.0001–1.0 mol / L, preferably 0.001–0.5 mol / L, and more preferably 0.005–0.2 mol / L. The ratio of nickel or cobalt to X in the aqueous solution, expressed as Ni / X atomic ratio or Co / X atomic ratio, is preferably in the range of 0.1–10, more preferably 0.2–5.0, and even more preferably 0.5–3.0.

[0179] The temperature at which the support contacts the aforementioned acidic aqueous solution is one of the important factors controlling the distribution of catalyst particles. Although it varies depending on the amount of catalyst particles pre-loaded on the support, there is a tendency for the reaction to slow down and the distribution of catalyst particles to expand when the temperature is too low. In the manufacturing method of this embodiment, from the viewpoint of obtaining a supported layer with a more concentrated local distribution of catalyst particles, the temperature at which the support contacts the aforementioned acidic aqueous solution is a temperature that can obtain a high reaction rate, preferably 60°C or higher, more preferably 70°C or higher, further preferably 80°C or higher, and particularly preferably 90°C or higher. As long as the temperature of the liquid obtained by mixing the acidic aqueous solution and the water slurry is 60°C or higher, it is sufficient to mix them. Therefore, the water slurry can be preheated to a level where the mixture exceeds 60°C even after adding the acidic aqueous solution, or conversely, only the acidic aqueous solution can be preheated. It is also possible to preheat both the acidic aqueous solution and the water slurry to 60°C or higher.

[0180] The reaction can also be carried out under pressure at a temperature above the boiling point of the solution; however, for ease of operation, it is generally preferred to carry it out at a temperature below the boiling point. The time for immobilizing nickel and / or cobalt with component X is not particularly limited, and varies depending on the type of support, the loading amount of nickel and / or cobalt with X, the ratio, etc., and is generally in the range of 1 minute to 5 hours, preferably 5 minutes to 3 hours, and more preferably 5 minutes to 1 hour.

[0181] The method for manufacturing the catalyst for carboxylic ester production according to this embodiment can be implemented, for example, based on the principle of immobilizing nickel and / or cobalt and component X by chemically reacting an oxide of at least one alkali metal selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals pre-loaded on a support with a soluble metal salt containing nickel and / or cobalt and containing component X. To further enhance the composite composition of nickel and / or cobalt and component X, it is preferable to simultaneously immobilize the two components in a mixed aqueous solution.

[0182] In addition, in the manufacturing method of this embodiment, the water slurry containing the carrier preferably contains at least one alkaline metal salt selected from the group consisting of alkali metals, alkaline earth metals and rare earth metals, and the carrier is loaded with an oxide of at least one alkaline metal selected from the group consisting of alkali metals, alkaline earth metals and rare earth metals.

[0183] Therefore, the formation of metallic black in X can be suppressed, the complexation of nickel and / or cobalt with X can be promoted, and the distribution of the complex particles can be more precisely controlled. It can be inferred that this effect is due to the addition of at least one metal salt selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals to the aqueous solution, thereby controlling the rate of chemical reaction between the pre-loaded alkaline metal oxide on the support and the soluble metal salt containing nickel and / or cobalt and containing X.

[0184] As at least one alkaline metal salt selected from the group consisting of alkali metals, alkaline earth metals and rare earth metals, one or more water-soluble salts selected from these metals, such as organic acid salts, nitrates, chlorides and other inorganic salts, may be used.

[0185] The amount of at least one alkaline metal salt selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals varies depending on the amount and ratio of nickel and / or cobalt to component X, and is also determined by the amount of alkaline metal oxide preloaded onto the support. Typically, it is 0.001 to 2 moles, preferably 0.005 to 1 mole, relative to the amount of nickel and / or cobalt and component X in the aqueous solution.

[0186] Furthermore, the aqueous slurry containing the carrier preferably contains a soluble aluminum salt, wherein the carrier is loaded with an oxide of at least one alkali metal selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals. Aluminum chloride and aluminum nitrate can be used as soluble aluminum salts.

[0187] By adding soluble aluminum salts to the aqueous slurry, an outer layer that is substantially free of composite particles can be formed on the outside of the load layer where composite particles are locally present. This is also based on the aforementioned insoluble immobilization principle. As soluble aluminum salts, soluble salts such as aluminum chloride and aluminum nitrate can be used. Through chemical reaction with the alkaline metal oxides pre-loaded on the support, aluminum reacts on the outer surface of the support, consuming the reaction sites of nickel and / or cobalt with X. Subsequently, immobilization is achieved through the reaction of the aforementioned alkaline metal oxides inside with the nickel and / or cobalt with X components.

[0188] The amount of aluminum varies depending on the thickness of the layer without nickel and / or cobalt and without the X component, which is set to a few μm, and is also determined by the amount of alkaline metal oxide pre-loaded on the support. Typically, it is 0.001 to 2 moles, preferably 0.005 to 1 mole, relative to the amount of alkaline metal oxide loaded on the support.

[0189] There are still many unclear details regarding the mechanism by which the distribution of nickel and / or cobalt and component X is achieved, but it can be inferred that this is because, under the conditions of this embodiment, the diffusion rate of the soluble component containing nickel and / or cobalt and containing X within the carrier is perfectly balanced with the rate at which the component becomes insoluble due to chemical reaction, thus enabling the composite particles to be fixed in an extremely narrow area near the surface of the carrier.

[0190] It can also be inferred that when forming an outer layer that is substantially free of composite particles on the outer surface of the carrier, if aluminum reacts with the alkaline metal components near the outer surface of the carrier to consume the alkaline metal components near the outer surface of the carrier that can react with nickel and / or cobalt and X, and then nickel and / or cobalt and X are loaded, then since the reactive alkaline metal components near the outer surface of the carrier have been consumed, they are immobilized by reacting with the alkaline metal oxides inside the carrier through nickel and / or cobalt and X.

[0191] Next, the second process will be explained.

[0192] Before the heat treatment in the second step, the first precursor is washed with water and dried as needed. The heating temperature of the first precursor is typically 40–900°C, preferably 80–800°C, more preferably 200–700°C, and even more preferably 300–600°C.

[0193] The heat treatment can be carried out in air (or atmospheric atmosphere), an oxidizing atmosphere (oxygen, ozone, nitrogen oxides, carbon dioxide, hydrogen peroxide, hypochlorous acid, inorganic / organic peroxides, etc.), or an inert gas atmosphere (helium, argon, nitrogen, etc.). The heating time can be appropriately selected based on the heating temperature and the amount of the first precursor. Furthermore, the heat treatment can be carried out under normal pressure, pressurized pressure, or reduced pressure.

[0194] Following step 2 above, a reduction treatment can also be performed in a reducing atmosphere (hydrogen, hydrazine, formaldehyde, formic acid, etc.) if necessary. In this case, a treatment method is chosen where the oxidized nickel and / or cobalt are not completely reduced to their metallic state. The temperature and time of the reduction treatment can be appropriately selected based on the type of reducing agent, the type of X, and the amount of catalyst.

[0195] Furthermore, after the aforementioned heat treatment or reduction treatment, oxidation treatment can also be carried out in air (or atmosphere) or an oxidizing atmosphere (oxygen, ozone, nitrogen oxides, carbon dioxide, hydrogen peroxide, hypochlorous acid, inorganic / organic peroxides, etc.) as needed. The temperature and time at this time are appropriately selected based on the type of oxidant, the type of X, and the amount of catalyst.

[0196] Third constituent elements, besides nickel and / or cobalt and X, can be added during the preparation of the supported material or under reaction conditions. Alkali metals, alkaline earth metals, and rare earth metals can also be added during catalyst preparation or added to the reaction system. Furthermore, the raw materials for the third constituent elements, alkali metals, alkaline earth metals, and rare earth metals are selected from organic acid salts, inorganic acid salts, hydroxides, etc.

[0197] [Methods for manufacturing carboxylic esters]

[0198] The catalyst for producing carboxylic esters according to this embodiment can be widely used as a catalyst for chemical synthesis. For example, it can be used for the formation of carboxylic esters between aldehydes and alcohols, or for the formation of carboxylic esters from alcohols. That is, the method for producing carboxylic esters according to this embodiment may include a reaction step in the presence of the catalyst for producing carboxylic esters according to this embodiment and oxygen, (a) reacting an aldehyde with an alcohol or (b) reacting one or more alcohols.

[0199] The catalyst for carboxylic acid ester production described in this embodiment exhibits excellent performance, particularly when used as a catalyst for oxidation reactions. In addition to the aldehydes and alcohols used in the carboxylic acid ester formation reactions shown in the examples, various other reaction substrates can be used as reaction substrates in this embodiment, such as alkanes, alkenes, alcohols, ketones, aldehydes, ethers, aromatic compounds, phenols, sulfur compounds, phosphorus compounds, oxygen-nitrogen compounds, amines, carbon monoxide, and water. These reaction substrates can be used alone or in mixtures containing two or more. Various industrially useful oxidation products, such as oxygen-containing compounds, oxidative adducts, and oxidative dehydrogenates, can be obtained from these reaction substrates.

[0200] As a reaction substrate, specifically as alkanes, examples include aliphatic alkanes such as methane, ethane, propane, n-butane, isobutane, n-pentane, n-hexane, 2-methylpentane, and 3-methylpentane; and alicyclic alkanes such as cyclopentane, cyclohexane, cycloheptane, and cyclooctane.

[0201] Examples of alkenes include aliphatic alkenes such as ethylene, propylene, butene, pentene, hexene, heptene, octene, decene, 3-methyl-1-butene, 2,3-dimethyl-1-butene, and allyl chloride; alicyclic alkenes such as cyclopentene, cyclohexene, cycloheptene, cyclooctene, and cyclodecene; and aromatic substituted alkenes such as styrene and α-methylstyrene.

[0202] Examples of alcohols include saturated and unsaturated aliphatic alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, n-pentanol, n-hexanol, n-heptanol, allyl alcohol, and crotonol; saturated and unsaturated alicyclic alcohols such as cyclopentanol, cyclohexanol, cycloheptanol, methylcyclohexanol, and cyclohexen-1-ol; aliphatic and alicyclic polyols such as ethylene glycol, propylene glycol, trimethylenediol, 1,3-butanediol, 1,2-cyclohexanediol, and 1,4-cyclohexanediol; and aromatic alcohols such as benzyl alcohol, salicylol, and diphenylmethanol.

[0203] Examples of aldehydes include aliphatic saturated aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, isobutyraldehyde, and glyoxal; aliphatic α,β-unsaturated aldehydes such as acrolein, methacrolein, and crotonaldehyde; aromatic aldehydes such as benzaldehyde, tolylaldehyde, benzaldehyde, and benzoxaldehyde, and their derivatives.

[0204] Examples of ketones include aliphatic ketones such as acetone, methyl ethyl ketone, diethyl ketone, dipropyl ketone, and methyl propyl ketone; alicyclic ketones such as cyclopentanone, cyclohexanone, cyclooctanone, 2-methylcyclohexanone, and 2-ethylcyclohexanone; and aromatic ketones such as acetophenone, phenylacetone, and benzophenone.

[0205] Examples of aromatic compounds include benzene, toluene, xylene, naphthalene, anthracene, or their derivatives that have been substituted with alkyl, aryl, halogen, sulfone, etc.

[0206] Examples of phenols include phenol, cresol, xylenol, naphthol, anthraquinone (hydroxyanthracene), and their derivatives (substances in which the hydrogen atoms of the aromatic ring are replaced by alkyl, aryl, halogen, sulfonic acid, etc.).

[0207] Examples of sulfur compounds include methyl mercaptan, ethyl mercaptan, propyl mercaptan, benzyl mercaptan, thiophenol, and other thiols.

[0208] Examples of amines include aliphatic amines such as methylamine, ethylamine, propylamine, isopropylamine, butylamine, dimethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, allylamine, diallylamine, etc.; alicyclic amines such as cyclopentylamine, cyclohexylamine, cycloheptylamine, cyclooctylamine, etc.; and aromatic amines such as aniline, benzylamine, toluidine, etc.

[0209] These reaction matrices can be used alone or in mixtures of two or more. Furthermore, purification is not always necessary; they can be mixtures with other organic compounds.

[0210] The following description will use the catalyst for producing carboxylic acid esters according to this embodiment as an example to illustrate a method for producing carboxylic acid esters from aldehydes and alcohols through an oxidative esterification reaction in the presence of oxygen.

[0211] Aldehydes used as raw materials include, for example, formaldehyde, acetaldehyde, propionaldehyde, isobutyraldehyde, glyoxal, etc. (C1-C) 10 Aliphatic saturated aldehydes; acrolein, methacrolein, crotonaldehyde, etc. (C3-C) 10 Aliphatic α·β-unsaturated aldehydes; benzaldehyde, methylbenzaldehyde, benzaldehyde, phthalaldehyde, etc. (C6-C) 20 Aromatic aldehydes; and derivatives of these aldehydes. These aldehydes can be used alone or in mixtures of any two or more. In this embodiment, the aldehyde is preferably selected from acrolein, methacrolein, or mixtures thereof.

[0212] Examples of alcohols include methanol, ethanol, isopropanol, butanol, 2-ethylhexanol, octanol, etc. (C1-C) 10Aliphatic saturated alcohols; C5-C alcohols such as cyclopentanol and cyclohexanol 10 Alicyclic alcohols; ethylene glycol, propylene glycol, butylene glycol, etc. (C2-C) 10 Diols; allyl alcohol, methyl allyl alcohol, etc. (C3-C) 10 Aliphatic unsaturated alcohols; benzyl alcohol, etc. (C6-C) 20 Aromatic alcohols; hydroxyoxetanes such as 3-alkyl-3-hydroxymethyloxetane. These alcohols can be used alone or in mixtures of any two or more. In this embodiment, the aldehyde is preferably acrolein and / or methacrolein, and the alcohol is preferably methanol.

[0213] In this embodiment, from the viewpoint of further improving the reaction performance, it is preferable to set the water content in the alcohol to 10% by mass or less, more preferably to 0.01% by mass or more and 10% by mass or less, even more preferably to 7% by mass or less, even more preferably to 5% by mass or less, and even more preferably to 1% by mass or less.

[0214] It should be noted that the water content in the above-mentioned alcohol is preferably low; therefore, the lower limit value is not particularly limited. For example, the water content can be 0.01% by mass, or it can be a value smaller than that.

[0215] There is no particular limitation on the molar ratio of aldehyde to alcohol. For example, it can be implemented in a wide range of 10 to 1 / 1000 in terms of the molar ratio of aldehyde to alcohol, and usually in the range of 1 / 2 to 1 / 50 in terms of the molar ratio.

[0216] The amount of catalyst used can be varied greatly depending on the type of reactants, the composition of the catalyst, the preparation method, the reaction conditions, the reaction form, etc., and there is no particular limitation. When the catalyst reacts in a slurry state, the concentration of solid components in the slurry is preferably in the range of 1 to 50% by mass / capacity, more preferably in the range of 3 to 30% by mass / capacity, and even more preferably in the range of 10 to 25% by mass / capacity.

[0217] In the manufacture of carboxylic acid esters, any method, such as gas-phase reaction, liquid-phase reaction, or trickle reaction, can be used in any manner, either batch or continuous. The above reaction process is preferably carried out in the liquid phase.

[0218] The reaction can also be carried out under solvent-free conditions, using solvents that are inactive to the reactants, such as hexane, decane, benzene, dioxane, etc.

[0219] The reaction can also be based on existing known forms such as fixed-bed, fluidized-bed, and stirred-tank reactors. For example, when implemented in the liquid phase, it can be based on any reactor form such as a bubble column reactor, a flow tube reactor, or a stirred-tank reactor.

[0220] The oxygen used in the manufacture of carboxylic esters can be in the form of molecular oxygen, that is, oxygen itself or a mixture of oxygen obtained by diluting it with a diluent that is inactive for the reaction, such as nitrogen or carbon dioxide. From the point of view of operability and economy, air is preferred as the oxygen raw material.

[0221] The partial pressure of oxygen varies depending on the type of aldehyde, alcohol, and other reactants, reaction conditions, or reactor type. However, in practical applications, the partial pressure of oxygen at the reactor outlet is a concentration below the lower limit of the explosive range, preferably managed to be between 20 and 80 kPa. The reaction pressure can be implemented over any wide pressure range from depressurization to pressurization, typically between 0.05 and 2 MPa. Furthermore, from a safety perspective, it is preferable to set the total pressure such that the oxygen concentration of the gas exiting the reactor does not exceed the explosive limit (e.g., an oxygen concentration of 8%).

[0222] In this embodiment, it is preferable to carry out the reaction process while adding an alkaline substance to make the pH of the reaction system between 6 and 8. Examples of alkaline substances include alkali metal compounds or alkaline earth metal compounds (e.g., oxides, hydroxides, carbonates, carboxylates). These alkali metal compounds or alkaline earth metal compounds can be used alone or in combination of two or more.

[0223] The reaction temperature for producing carboxylic acid esters can also be carried out at high temperatures above 200°C, preferably 30–200°C, more preferably 40–150°C, and even more preferably 60–120°C. The reaction time is not particularly limited and varies depending on the conditions, therefore it cannot be generalized, but is typically 1–20 hours.

[0224] Example

[0225] The following examples illustrate this implementation in more detail, but this implementation is not limited to these examples.

[0226] In the following examples and comparative examples, the determination of the distribution of nickel and X in the composite particle load, the observation of the shape of the support and the composite particle load, the determination of the average particle size, the determination of the loading amount of Ni and X and the Ni / (Ni+X) atomic ratio, the determination of the content of the supporting element (Si, Al, alkali metal), the analysis of the crystal structure of the composite particles, the analysis of the chemical state of the metal components of the composite particles, the analysis of the chemical state of nickel, the observation of the morphology and elemental analysis of the composite particles, the determination of the ultraviolet-visible spectrophotometer of the composite particles, and the determination of the physical properties (specific surface area, pore diameter, pore volume) of the support and the composite particle load were carried out by the following methods.

[0227] [Determination of the distribution of nickel and X in composite particle-supported materials]

[0228] Using a Shimadzu 1600 X-ray electron probe microanalysis (EPMA) manufactured by Shimadzu Corporation, the sample obtained by embedding the composite particle load in resin and grinding was measured at an accelerating voltage of 15 kV. Ni and X(Au) were analyzed from the outer surface to their depth direction using reflected electron imaging and X-ray analysis (Ni: wavelength 14.5829 nm, RAP spectrophotometer; X(Au): wavelength 5.8419 nm, PET spectrophotometer).

[0229] [Shape observation of carriers and composite particle-loaded materials]

[0230] The carrier and composite particle loadings were observed using an X-650 scanning electron microscope (SEM) manufactured by Hitachi.

[0231] [Determination of the average particle size of the carrier and composite particle-loaded material]

[0232] The average particle size (volume standard) was determined using a Beckman Coulter LS230 laser diffraction / scattering particle size distribution measuring device.

[0233] [Determination of Ni and X loading and Ni / X atomic ratio]

[0234] The concentrations of nickel and X in the composite particle loading were quantified using an IRIS Intrepid II XDL ICP-AES (MS) system manufactured by Thermo Fisher Scientific.

[0235] Regarding sample preparation, the loaded material was weighed into a Teflon decomposition container, nitric acid and hydrogen fluoride were added, and the sample was decomposed by heating using an ETHOS TC type microwave decomposition device manufactured by Milestone General KK. The sample was then evaporated and dried on a heater. Nitric acid and hydrochloric acid were added to the precipitated residue, and the sample was decomposed under pressure using a microwave decomposition device. The resulting decomposition solution was diluted to a certain volume with pure water and used as the test solution.

[0236] Regarding the quantitative method, ICP-AES was used for quantification, and the internal standard method was employed. The nickel and X contents in the catalyst were determined by subtracting the blank values ​​of the simultaneously implemented operation, and the loading and atomic ratio were calculated.

[0237] [Determination of the content of carrier components (Si, Al, alkali metals)]

[0238] Samples were prepared by dissolving the carrier in aqua regia and by melting the carrier with an alkaline molten salt. Using a JY-38P2 type ICP-AES instrument manufactured by Seiko Electronics Co., Ltd., the contents of alkali metals and / or Mg in the sample dissolved in aqua regia were determined, and the contents of Al and Si in the sample melted with the alkaline molten salt were determined. The atomic ratios were calculated from the obtained metal contents.

[0239] [Analysis of the crystal structure of composite particles]

[0240] The X-ray diffraction (XRD) was performed using a Rint2500 powder X-ray diffractometer manufactured by Rigaku Corporation, under the following conditions: X-ray source Cu tube bulb (40 kV, 200 mA), measurement range 5–65 deg (0.02 deg / step), measurement speed 0.2 deg / min, and slit width (scattering, divergence, and reception) 1 deg, 1 deg, and 0.15 mm.

[0241] Regarding the samples, they were uniformly distributed on a non-reflective sample plate and fixed with neoprene rubber.

[0242] [Analysis of the chemical state of the metallic components in the composite particles]

[0243] The analysis was performed using an ESCALAB250 X-ray photoelectron spectroscopy (XPS) system manufactured by THERMO ELECTRON Co., Ltd., under the following conditions: an excitation source of AlKα 15kV × 10mA, an analysis area of ​​approximately 1mm (elliptical shape), a readout region of 0–1100eV for full-spectrum scanning, and a narrow-area scanning of Ni2p.

[0244] For the test samples, the composite particle loading material was crushed using an agate mortar and pestle, collected using a powder-specific sample stage, and used for XPS analysis.

[0245] [Chemical state analysis of nickel]

[0246] The NiKα spectrum was measured using a Technos XFRA190 dual-crystal high-resolution fluorescence X-ray spectroscopy (HRXRF) instrument. The obtained parameters were compared with the corresponding parameters of standard substances (nickel metal and nickel oxide) to infer the chemical state of nickel in the supported material, such as its valence.

[0247] The test samples were provided in their original state for measurement. The Kα spectrum of Ni was measured using a partial spectral mode. A Ge(220) spectrophotometer was used, with a slit having a longitudinal divergence angle of 1°. The excitation voltage and current were set to 35 kV and 80 mA, respectively. Using filter paper as the absorber for the standard sample, and with the loaded sample, a counting time was selected for each sample to ensure that the peak intensity of the Kα spectrum was below 3000 cps and above 10000 counts. Each sample was measured five times, with measurements of the metal sample taken before and after each repetition. After smoothing the measured spectra (SG method, 7 points - 5 times), the peak position, half-width at half-maximum (FWHM), and asymmetry coefficient (AI) were calculated. The peak position was processed as a shift relative to the measured values ​​of the metal sample before and after the sample measurement, and a chemical shift (ΔE).

[0248] [Morphological observation and elemental analysis of composite particles]

[0249] Using a JEOL 3100FEF transmission electron microscope / scanning transmission electron microscope (TEM / STEM) [accelerating voltage 300kV, with energy dispersive X-ray detector (EDX)], we measured TEM bright field images, STEM dark field images, and performed STEM-EDS composition analysis (point analysis, mapping, and line analysis).

[0250] Regarding data analysis software, for TEM and STEM image analysis (length measurement, Fourier transform analysis): Digital Micrograph is used. TM Ver. 1.70.16, Gatan and EDS data analysis (mapping image processing, quantitative composition calculation): using NORAN System SIX ver. 2.0, Thermo Fisher Scientific.

[0251] Regarding the test sample, the composite particle load was crushed in a mortar and dispersed in ethanol. After ultrasonic washing for about 1 minute, it was dropped onto a Mo microgrid and air-dried to serve as a sample for TEM / STEM observation.

[0252] [Determination of UV-Vis spectroscopic spectroscopy of composite particles]

[0253] The measurements were performed using a V-550 UV-Vis spectrophotometer (with integrating sphere unit and sample holder for powder samples) manufactured by Nippon Spectroscopy Corporation, under the conditions of a measurement range of 800-200 nm and a scanning speed of 400 nm / min.

[0254] For the test sample, the composite particle load is ground into powder using an agate mortar and placed in a sample holder for powder test, for UV-Vis measurement.

[0255] [The half-width Wa and mode particle size Da of the catalyst's pore size distribution, and the half-width Wd and mode particle size Dd]

[0256] Using Quantachrome's Quadrasorb evo, nitrogen was used as the adsorbed gas to determine the pore diameter (nitrogen adsorption method). The "He measure" mode was used, employing the reference cell included with the Quadrasorb evo and a 9 mm Largebulb as the sample cell, with pure helium used for free-space determination.

[0257] It should be noted that the drying process for removing moisture from the sample was carried out under reduced pressure at 200℃ for 18 hours. The sample amount was set to 0.1g. Under adsorption, the measurement point was set at a relative pressure (P / P0) of 0.025–0.9875, and under desorption, the measurement point was set at a relative pressure of 0.975–0.025.

[0258] It should be noted that the BJH method was used to calculate the pore size distribution for adsorption and desorption, respectively. Adsorption and desorption were plotted using the pore diameter (D) and the value obtained by differentiating the cumulative pore volume (V) with respect to the common logarithm of the pore diameter (D) (dV / d(logD)), respectively. Figure 3 For example, the pore diameter at peak A is taken as the mode particle size Da and Dd. A vertical line is drawn from the peak and intersects the baseline to obtain line segment AC. A horizontal line is drawn at point B, which divides line segment AC into two equal parts. The lengths of the intersection points D and E of the line segment AC and the pore size distribution are taken as the half-value widths Wa and Wd.

[0259] [Example 1]

[0260] An aqueous solution, prepared by dissolving 18.75 parts by mass of aluminum nitrate nonahydrate, 12.8 parts by mass of magnesium nitrate, and 2.7 parts by mass of 60% nitric acid in 25 parts by mass of pure water, was slowly added dropwise to 100 parts by mass of a silica sol solution (SiO2 content 30% by mass) with a colloidal particle size of 10-20 nm, maintained at 15°C and stirred, to obtain a mixed slurry of silica sol, aluminum nitrate, and magnesium nitrate. The slurry was then held at 80°C for 5 hours, cooled to 30°C and stirred for 5 hours, and then heated to 50°C and held for 10 hours, continuously stirred with a paddle-type stirring blade with a blade diameter of 0.5 m at a tip speed of 6.5 m / s. After cooling to room temperature, the mixture was spray-dried using a spray drying apparatus with an outlet temperature set to 130°C to obtain a solid.

[0261] Next, the obtained solid material was filled into an open stainless steel container, with a filling thickness of approximately 1 cm. The container was then heated in an electric furnace from room temperature to 300°C over 2 hours and held for 3 hours. The temperature was further increased to 600°C over 2 hours and held for 3 hours, followed by slow cooling to obtain the support. The obtained support contained 83.3 mol% silicon, 8.3 mol% aluminum, and 8.3 mol% magnesium, respectively, relative to the total molar amount of silicon, aluminum, and magnesium. The specific surface area based on the nitrogen adsorption method was 149 m². 2 The particle size distribution is 0.27 mL / g, with a pore volume of 0.27 mL / g and an average pore diameter of 7 nm. Based on particle size distribution measurements using laser scattering, the average particle size of the carrier is 60 μm. Furthermore, observations using scanning electron microscopy (SEM) indicate that the carrier is approximately spherical in shape.

[0262] Add 300g of the carrier obtained above to 1.0L of water heated to 90°C for 1 minute to disperse it, and stir at 90°C for 15 minutes. Next, prepare an aqueous solution containing 16.35g of nickel nitrate hexahydrate and 12mL of chloroauric acid aqueous solution at 1.3mol / L, heat it to 90°C and add it to the above carrier slurry, and continue stirring at 90°C for 30 minutes to immobilize the nickel and gold components on the carrier insolublely.

[0263] Next, the mixture was allowed to stand and the supernatant was removed. After washing several times with distilled water, it was filtered. The mixture was then dried in a dryer at 105°C for 10 hours, followed by calcination in a muffle furnace at 450°C for 5 hours in air, thus obtaining a catalyst for the manufacture of carboxylic acid esters (a composite particle supported on NiOAu / SiO2-Al2O3-MgO) containing 1.05% by mass of nickel and 0.91% by mass of gold. The Ni / Au atomic ratio in the composite particles of the obtained catalyst for the manufacture of carboxylic acid esters was 4.0.

[0264] (Physical property evaluation of catalysts for the manufacture of carboxylic esters)

[0265] The specific surface area of ​​the catalyst used in the production of carboxylic acid esters was calculated to be 141 m². 2 / g. Additionally, regarding the pore size distribution results, the half-width at half-maximum (WWHM) of the adsorbed pore size distribution is 5 nm, and the half-width at half-maximum (WWHM) of the desorbed pore size distribution is 2 nm.

[0266] Next, the sample obtained by embedding the catalyst for the production of the carboxylic ester in resin and grinding it was subjected to line analysis of the particle cross-section using X-ray electron probe microanalysis (EPMA). It was confirmed that there was a substantially nickel- and gold-free outer layer in the region at a depth of 0.5 μm from the outermost surface of the support, and nickel and gold were loaded in the region at a depth of 10 μm from the surface. There were no composite particles inside the support.

[0267] The morphology of the catalyst for the production of the carboxylic ester was then observed using transmission electron microscopy (TEM / STEM). The results confirmed the presence of spherical nanoparticles with a large distribution (number average particle size: 3.0 nm) at a particle size of 2–3 nm on the support. Further magnification revealed lattice fringes corresponding to the facet spacing of Au(111) on the nanoparticles. STEM-EDS-based compositional point analysis of each nanoparticle showed the detection of nickel and gold in each particle. The average nickel / gold atomic ratio of the nanoparticle (calculated in 50 samples) was 1.05. Further nanoregion analysis of the observed particles showed a Ni / Au atomic ratio of 0.90 in the central region and 2.56 at the edges. Only trace amounts of nickel were detected outside the particles. The same measurements were performed on 50 points, revealing a significant amount of nickel around the edges of each particle. EDS elemental mapping showed that the distribution of nickel and gold was generally consistent. Furthermore, based on the line profile, the distribution of nickel is larger than that of gold in each scanning direction.

[0268] According to the results of powder X-ray diffraction (XRD), no diffraction pattern was observed from nickel, confirming its existence in an amorphous state. On the other hand, although the peaks were not clearly defined, they were broad, comparable to those of gold crystals. Although the peaks were close to the detection limit of powder X-ray diffraction (2 nm), the average crystallite diameter calculated using the Scherer formula was approximately 3 nm. Regarding the chemical state of nickel, X-ray photoelectron spectroscopy (XPS) confirmed that nickel is divalent.

[0269] Based on the results of high-resolution X-ray fluorescence (HRXRF) analysis of a twin-crystal structure, it is inferred that the nickel is in a high-spin-2 valence state. The difference in the NiKα spectrum indicates that it is a different chemical state from nickel oxide as a single compound. The half-width at half-maximum (FWHM) of the catalyst's NiKα spectrum obtained from the measured spectra is 3.470, and the chemical shift (ΔE) is 0.335. The half-width at half-maximum (FWHM) of the NiKα spectrum of nickel oxide, measured as a standard, is 3.249, and the chemical shift (ΔE) is 0.344.

[0270] Furthermore, the results of investigating the changes in the electronic excitation state of the catalyst for the production of the carboxylic acid ester by ultraviolet-visible spectroscopy (UV-Vis) showed that no surface plasmon absorption peak from gold nanoparticles appeared near 530 nm, while a broad absorption originating from NiO2 appeared in the wavelength region of 200–800 nm.

[0271] Based on the above results, it can be inferred that the microstructure of the composite particles has the following morphology: gold nanoparticles as the core, and their surface is covered with nickel in an oxidized state.

[0272] (Manufacturing of carboxylic acid esters)

[0273] 240 g of the obtained catalyst for carboxylic acid ester production was added to a stirred stainless steel reactor equipped with a catalyst separator and a liquid phase section of 1.2 L. The contents were stirred at a speed of 4 m / s at the tip of the stirrer blades while the reaction of aldehyde and alcohol to produce carboxylic acid esters was carried out. A 36.7 wt% methacrolein / methanol solution (using a methanol solution with a water content of 0.50 wt%) was continuously supplied to the reactor at a rate of 0.6 L / hr, and a 1–4 wt% NaOH / methanol solution was continuously supplied to the reactor at a rate of 0.06 L / hr. Air was blown in at an outlet oxygen concentration of 4.0 vol% (equivalent to an oxygen partial pressure of 0.02 MPa) at a reaction temperature of 80 °C and a reaction pressure of 0.5 MPa. The concentration of NaOH supplied to the reactor was controlled to maintain the pH of the reaction system at 7. The reaction products were continuously collected from the reactor outlet via overflow and analyzed by gas chromatography to investigate reactivity.

[0274] The conversion rate of methacrolein was 75.2% and the selectivity of methyl methacrylate was 98.1% after 500 hours from the start of the reaction.

[0275] (Durability test)

[0276] Then, to evaluate the acid resistance, alkali resistance, and temperature tolerance of the catalyst for carboxylate production, a durability test was conducted using the following method. 10 g of the unused catalyst obtained as described above was added to 100 mL of pH 4 buffer solution in a glass container. After stirring continuously at 90°C for 10 minutes, the mixture was allowed to stand, the supernatant was removed, and the product was washed with water and decanted. The resulting solid was then added to 100 mL of pH 10 buffer solution in a glass container. After stirring continuously at 90°C for 10 minutes, the mixture was allowed to stand, the supernatant was removed, and the product was washed with water and decanted. This process was repeated as one cycle, for a total of 100 cycles. For the catalyst after the durability test, the half-maximum width of the pore size distribution was calculated as described above. Furthermore, for all the catalyst after the durability test, a 500-hour carboxylate production process was performed as described above, and the conversion rate of methacrolein and the selectivity of methyl methacrylate were calculated. The results are shown in Table 1.

[0277] [Comparative Example 1]

[0278] The stirring conditions for the mixed slurry before spray drying using a spray drying device were changed to: stirring was performed using an anchor-type stirring blade with a blade diameter of 0.2 m at a stirring tip speed of 1.3 m / s (100 rpm). The hydrothermal synthesis conditions for preparing the support were changed to those shown in the table. Otherwise, the catalyst for the production of carboxylic acid esters was obtained in the same manner as in Example 1. The aforementioned durability test was performed on the catalyst for the production of carboxylic acid esters, and the half-maximum width of the pore size distribution, the conversion rate of methacrolein, and the selectivity of methyl methacrylate before and after the test were determined in the same manner as in Example 1. The results are shown in Table 1.

[0279] [Example 2]

[0280] (Manufacturing of catalysts for the production of carboxylic esters)

[0281] 300g of the carrier obtained in Example 1 was added to 1.0L of water heated to 90°C and dispersed within 1 minute, and stirred at 90°C for 15 minutes. Next, an aqueous solution containing 16.36g of cobalt nitrate hexahydrate and 12mL of chloroauric acid aqueous solution (1.3mol / L) was prepared, heated to 90°C, and added to the above carrier slurry. The mixture was then stirred at 90°C for another 30 minutes to immobilize the cobalt and gold components on the carrier.

[0282] Next, the mixture was allowed to stand and the supernatant was removed. After washing several times with distilled water, it was filtered. The mixture was then dried in a dryer at 105°C for 10 hours, followed by calcination in a muffle furnace at 450°C for 5 hours in air, thereby obtaining a catalyst (CoOAu / SiO2-Al2O3-MgO composite particle supported on 1.05% by mass of cobalt and 0.91% by mass of gold) for the manufacture of carboxylic acid esters. The Co / Au atomic ratio of the obtained catalyst for the manufacture of carboxylic acid esters was 4.0.

[0283] (Physical property evaluation of catalysts for the manufacture of carboxylic esters)

[0284] The specific surface area of ​​the catalyst used for the production of carboxylic acid esters was calculated to be 139 m². 2 / g. Additionally, regarding the pore size distribution results, the half-width at half-maximum (WW) of the adsorbed pore size distribution is 5 nm, and the half-width at half-maximum (WD) of the desorbed pore size distribution is 3 nm.

[0285] (Manufacturing of carboxylic acid esters)

[0286] 240 g of the obtained catalyst for carboxylic acid ester production was added to a stirred stainless steel reactor equipped with a catalyst separator and a liquid phase section of 1.2 L. The contents were stirred at a speed of 4 m / s at the tip of the stirrer blades while the reaction of aldehyde and alcohol to produce carboxylic acid esters was carried out. A 36.7 wt% methacrolein / methanol solution (using a methanol solution with a water content of 0.50 wt%) was continuously supplied to the reactor at a rate of 0.6 L / hr, and a 1–4 wt% NaOH / methanol solution was continuously supplied to the reactor at a rate of 0.06 L / hr. Air was blown in at an outlet oxygen concentration of 4.0 vol% (equivalent to an oxygen partial pressure of 0.02 MPa) at a reaction temperature of 80 °C and a reaction pressure of 0.5 MPa. The concentration of NaOH supplied to the reactor was controlled to maintain the pH of the reaction system at 7. The reaction products were continuously collected from the reactor outlet via overflow and analyzed by gas chromatography to investigate reactivity.

[0287] The conversion rate of methacrolein was 74.5% and the selectivity of methyl methacrylate was 97.8% after 500 hours from the start of the reaction.

[0288] Then, a durability test was conducted using the method described in Example 1. The results are shown in Table 1.

[0289] [Example 3]

[0290] The mixing conditions of the mixed slurry before spray drying were changed to: stirring was performed using a turbine-type stirring blade with a blade diameter of 0.5 m at a blade tip speed of 6.5 m / s. Otherwise, the support was obtained using the same method as in Example 1. Then, 300 g of the support was added to 1.0 L of water heated to 90 °C for 1 minute to disperse it, and stirred at 90 °C for 30 minutes. Otherwise, the catalyst for carboxylic acid ester production was obtained using the same method as in Example 1. The aforementioned durability test was performed on the catalyst for carboxylic acid ester production, and the pore size distribution half-width, methacrolein conversion, and methyl methacrylate selectivity before and after the test were determined in the same manner as in Example 1. The results are shown in Table 1.

[0291] [Example 4]

[0292] 300 g of the support obtained in Example 1 was added to 1.0 L of water heated to 90 °C and dispersed within 1 minute. The mixture was stirred at 90 °C for 10 minutes, and the catalyst for the production of carboxylic esters was obtained in the same manner as in Example 1. The aforementioned durability test was performed on the catalyst for the production of carboxylic esters, and the half-maximum width of the pore size distribution, the conversion rate of methacrolein, and the selectivity of methyl methacrylate before and after the test were determined in the same manner as in Example 1. The results are shown in Table 1.

[0293] [Comparative Example 2]

[0294] After obtaining the support in the same manner as in Comparative Example 1, a catalyst for the manufacture of carboxylic esters was further obtained in the same manner as in Example 2. The aforementioned durability test was performed on the catalyst for the manufacture of carboxylic esters, and the half-maximum width of the pore size distribution, the conversion rate of methacrolein, and the selectivity of methyl methacrylate before and after the test were determined in the same manner as in Example 1. The results are shown in Table 1.

[0295] [Comparative Example 3]

[0296] 300 g of the support obtained in Comparative Example 1 was added to 1.0 L of water heated to 90 °C and dispersed over 1 minute. The mixture was stirred at 90 °C for 30 minutes, and the catalyst for the production of carboxylic esters was obtained in the same manner as in Example 3. The aforementioned durability test was performed on the catalyst for the production of carboxylic esters, and the half-maximum width of the pore size distribution, the conversion of methacrolein, and the selectivity of methyl methacrylate before and after the test were determined in the same manner as in Example 1. The results are shown in Table 1.

[0297] [Example 5]

[0298] Aluminum nitrate, magnesium nitrate, and 2.7 parts by mass of 60% nitric acid were dissolved in 25 parts by mass of pure water, with the total molar amounts of aluminum and magnesium relative to silicon being 36.6 mol% and 17.2 mol%, respectively. The resulting aqueous solution was slowly added dropwise to 100 parts by mass of a silica sol solution (SiO2 content 30% by mass) with a colloidal particle size of 10–20 nm, maintained at 15°C and stirred, to obtain a mixed slurry of silica sol, aluminum nitrate, and magnesium nitrate. The slurry was then maintained at 80°C for 5 hours, cooled to 30°C and stirred for 5 hours, then heated to 50°C and maintained for 10 hours. During this period, it was continuously stirred using a paddle-type stirring blade with a blade diameter of 0.5 m at a tip speed of 6.5 m / s. After cooling to room temperature, it was spray-dried using a spray drying apparatus with an outlet temperature set to 130°C to obtain a solid product.

[0299] Next, the obtained solid material was filled into an open-top stainless steel container to a thickness of approximately 1 cm. The container was then heated in an electric furnace from room temperature to 300°C over 2 hours and held for 3 hours. The temperature was further increased to 800°C over 2 hours and held for 3 hours, followed by slow cooling to obtain the support. Based on particle size distribution measurements using laser scattering, the average particle size of the support was 64 μm. Furthermore, observations using scanning electron microscopy (SEM) showed that the support was approximately spherical in shape.

[0300] Add 300g of the carrier obtained above to 1.0L of water heated to 85°C over 3 minutes and disperse it. Stir at 85°C for 10 minutes.

[0301] Next, an aqueous solution containing 16.35 g of nickel nitrate hexahydrate and 13 mL of chloroauric acid aqueous solution of 1.3 mol / L was prepared. After being heated to 85°C, the solution was added to the above slurry. The mixture was then stirred at 85°C for another 30 minutes to allow nickel and gold to be separated onto the carrier.

[0302] Next, the mixture was allowed to stand and the supernatant was removed. After washing several times with distilled water, it was filtered. After drying at 105°C for 16 hours, it was calcined in air at 500°C for 3 hours, thus obtaining a catalyst (NiOAu / SiO2-Al2O3-MgO) supported on 1.0% by mass of nickel and 0.90% by mass of gold for the manufacture of carboxylate esters. The Ni / Au atomic ratio in the composite particles of the obtained catalyst was 3.7. According to particle size distribution determination based on laser scattering, the average particle size of the catalyst was 65 μm. Observation based on scanning electron microscopy (SEM) showed that the catalyst was approximately spherical.

[0303] Wa is 6 nm and Wd is 7 nm. In addition, the morphology of the active species of the catalyst was observed using transmission electron microscopy (TEM / STEM). The results showed that nanoparticles with a large distribution in the particle size of 2-3 nm (number average particle size: 3.3 nm) were loaded on the support.

[0304] The aforementioned durability test was performed on the catalyst for the manufacture of the carboxylic ester, and the half-maximum width of the pore size distribution, the conversion rate of methacrolein, and the selectivity of methyl methacrylate before and after the test were determined in the same manner as in Example 1. The results are shown in Table 1.

[0305] [Example 6]

[0306] 300 g of the support obtained in Example 1 was added to 1.0 L of water heated to 90 °C and dispersed within 1 minute, and stirred at 90 °C for 15 minutes. Then, the temperature was lowered to 60 °C, and while stirring, a dilute hydrochloric acid solution of palladium chloride and an aqueous solution of lead nitrate, respectively, in amounts equivalent to 2.5% by mass of Pd and Pb, were rapidly added dropwise. The mixture was then maintained at 60 °C for 1 hour, and 1.2 times the stoichiometric amount of hydrazine was added for reduction. Next, the mixture was allowed to stand, the supernatant was removed, and the mixture was washed several times with distilled water and filtered. Finally, it was vacuum dried at 60 °C to obtain a catalyst for the manufacture of carboxylic acid esters (a composite particle supported on PdPb / SiO2-Al2O3-MgO) loaded with 2.5% by mass of Pd and Pb, respectively.

[0307] Based on the powder X-ray diffraction (XRD) results of the above-mentioned noble metal supported materials, diffraction peaks (2θ = 38.6°, 44.8°, 65.4°, 78.6°) of intermetallic compounds belonging to Pd3Pb1 were observed.

[0308] The aforementioned durability test was performed on the catalyst for the manufacture of the carboxylic ester, and the half-maximum width of the pore size distribution, the conversion rate of methacrolein, and the selectivity of methyl methacrylate before and after the test were determined in the same manner as in Example 1. The results are shown in Table 1.

[0309] [Comparative Example 4]

[0310] The stirring conditions for the mixed slurry before spray drying using the spray drying device were changed to: stirring was performed using anchor-type stirring blades with a diameter of 0.2 m at a stirring tip speed of 1.3 m / s. The hydrothermal synthesis conditions for preparing the carrier were changed to those shown in the table. Otherwise, the catalyst for the production of carboxylic acid esters was obtained in the same manner as in Example 6. The aforementioned durability test was performed on the catalyst for the production of carboxylic acid esters, and the half-maximum width of the pore size distribution, the conversion rate of methacrolein, and the selectivity of methyl methacrylate before and after the test were determined in the same manner as in Example 1. The results are shown in Table 1.

[0311] [Example 7]

[0312] 300 g of the support obtained in Example 1 was added to 1.0 L of water heated to 90 °C and dispersed over 3 minutes. The mixture was stirred at 85 °C for 10 minutes, then cooled to 60 °C. The catalyst for carboxylic acid ester production was obtained in the same manner as in Example 6. The aforementioned durability test was performed on the catalyst for carboxylic acid ester production, and the half-maximum width of the pore size distribution, the conversion rate of methacrolein, and the selectivity of methyl methacrylate before and after the test were determined in the same manner as in Example 1. The results are shown in Table 1.

[0313] [Example 8]

[0314] The hydrothermal synthesis conditions for preparing the support were changed to those shown in the table, and the catalyst for carboxylic ester production was obtained in the same manner as in Example 1. The aforementioned durability test was performed on the catalyst for carboxylic ester production, and the half-maximum width of the pore size distribution, the conversion of methacrolein, and the selectivity of methyl methacrylate before and after the test were determined in the same manner as in Example 1. The results are shown in Table 1.

[0315] [Example 9]

[0316] The stirring conditions of the mixed slurry before spray drying using a spray drying apparatus were changed to a stirring blade tip speed of 10.2 m / s. Otherwise, the catalyst for carboxylic acid ester production was obtained in the same manner as in Example 8. The aforementioned durability test was performed on the catalyst for carboxylic acid ester production, and the pore size distribution half-width, methacrolein conversion rate, and methyl methacrylate selectivity before and after the test were determined in the same manner as in Example 1. The results are shown in Table 1.

[0317] [Example 10]

[0318] The mixing conditions of the mixed slurry before spray drying were changed to: stirring was performed using a turbine-type stirring blade with a blade diameter of 0.5 m at a blade tip speed of 6.5 m / s. Otherwise, the catalyst for carboxylic acid ester production was obtained in the same manner as in Example 8. The aforementioned durability test was performed on the catalyst for carboxylic acid ester production, and the pore size distribution half-width, methacrolein conversion rate, and methyl methacrylate selectivity before and after the test were determined in the same manner as in Example 1. The results are shown in Table 1.

[0319] [Example 11]

[0320] Prepare an aqueous solution by dissolving 1.5 parts by mass of aluminum nitrate nonahydrate, 0.24 parts by mass of nickel nitrate hexahydrate, 0.98 parts by mass of magnesium nitrate hexahydrate, and 0.27 parts by mass of 60% nitric acid in 3.0 parts by mass of pure water.

[0321] The aqueous solution was slowly added dropwise to 100 parts by mass of a silica sol solution (SiO2 content of 30% by mass) with a colloidal particle size of 10-20 nm, which was kept at 15°C and stirred, to obtain a mixed slurry of silica sol, aluminum nitrate, nickel nitrate and magnesium nitrate. Otherwise, a carrier containing silica was obtained in the same manner as in Example 1.

[0322] The resulting silica-containing carrier contains 85.3 mol% silicon, 6.8 mol% aluminum, 1.4 mol% nickel, and 6.5 mol% magnesium, relative to the total molar amount of silicon, aluminum, nickel, and magnesium.

[0323] Using the silica-containing support described above, a catalyst for the manufacture of carboxylic acid esters (a composite particle supported on NiOAu / SiO2-Al2O3-NiO-MgO) was obtained in the same manner as in Example 1. The Ni / Au atomic ratio in the composite particles contained in the obtained catalyst for the manufacture of carboxylic acid esters was 4.0.

[0324] The aforementioned durability test was performed on the catalyst for the manufacture of the carboxylic ester, and the half-maximum width of the pore size distribution, the conversion rate of methacrolein, and the selectivity of methyl methacrylate before and after the test were determined in the same manner as in Example 1. The results are shown in Table 1.

[0325] [Example 12]

[0326] 300 g of the support obtained in Example 1 was added to 1.0 L of water heated to 95°C and dispersed over 3 minutes. The mixture was stirred at 95°C for 15 minutes, otherwise the same procedure as in Example 1 was followed to obtain the catalyst for carboxylic ester production. The aforementioned durability test was performed on the catalyst, and the half-maximum width of the pore size distribution, the conversion rate of methacrolein, and the selectivity of methyl methacrylate before and after the test were determined in the same manner as in Example 1. The results are shown in Table 1.

[0327] [Table 1-1]

[0328] Table 1 (1 / 3)

[0329]

[0330] Macr: Methacrolein MMA: Methyl methacrylate

[0331] [Table 1-2]

[0332] Table 1 (2 / 3)

[0333]

[0334] Macr: Methacrolein MMA: Methyl methacrylate

[0335] [Table 1-3]

[0336] Table 1 (3 / 3)

[0337]

[0338] Macr: Methacrolein MMA: Methyl methacrylate

Claims

1. A catalyst for the manufacture of carboxylic acid esters, comprising catalyst particles and a support on which the catalyst particles are supported, wherein the catalyst particles are composite particles containing nickel and / or cobalt in an oxidized state and containing X, wherein X represents at least one element selected from the group consisting of nickel, palladium, platinum, ruthenium, gold, silver, and copper. The half-value width Wa of the pore size distribution of the catalyst for the production of the carboxylic ester, calculated using the BJH method based on the adsorption isotherm obtained by nitrogen adsorption, is less than 10 nm.

2. The catalyst for producing carboxylic esters according to claim 1, wherein, The half-width Wa is less than 8 nm.

3. The catalyst for the manufacture of carboxylic esters according to claim 1, wherein, The half-width Wa is less than 7 nm.

4. The catalyst for the manufacture of carboxylic esters according to claim 1, wherein, The half-width Wa is less than 5 nm.

5. The catalyst for the manufacture of carboxylic esters according to claim 1, wherein, The catalyst for the manufacture of the carboxylic ester has a half-width Wd of less than 5 nm, which is obtained from the desorption isotherm by nitrogen adsorption and calculated using the BJH method.

6. The catalyst for producing carboxylic esters according to claim 5, wherein, The half-width Wd is greater than or equal to 0.1 nm.

7. The catalyst for the manufacture of carboxylic acid esters according to any one of claims 1 to 6, wherein, The catalyst for the manufacture of carboxylic esters is based on an adsorption isotherm obtained by nitrogen adsorption and the mode particle size Da of the pores calculated by the BJH method is 2 nm or more and 20 nm or less.

8. The catalyst for the manufacture of carboxylic esters according to claim 7, wherein, The mode particle size Da of the pores is greater than 2 nm and less than 15 nm.

9. The catalyst for the manufacture of carboxylic acid esters according to claim 7, wherein, The mode particle size Da of the pores is greater than 3 nm and less than 10 nm.

10. The catalyst for the manufacture of carboxylic esters according to claim 1, wherein, The catalyst for the manufacture of the carboxylic ester is based on the adsorption isotherm obtained by nitrogen adsorption and the mode particle size Da of the pores calculated by the BJH method, and the half-value width Wa satisfies the following relationship (1). 1 / 2Wa < Da (1).

11. The catalyst for the manufacture of carboxylic esters according to claim 1, wherein, The catalyst for the manufacture of the carboxylic ester is based on the desorption isotherm obtained by nitrogen adsorption and the modal particle size Dd of the pores calculated by the BJH method is greater than 2 nm and less than 15 nm.

12. The catalyst for the manufacture of carboxylic esters according to claim 11, wherein, The mode particle size Dd of the pores is greater than 3 nm and less than 7 nm.

13. The catalyst for the manufacture of carboxylic esters according to claim 1, wherein, The modal particle size Dd of the pores obtained by nitrogen adsorption isotherm and calculated by BJH method for the catalyst for carboxylic ester production satisfies the following relationship with the half-value width Wd of the pore size distribution obtained by nitrogen adsorption isotherm and calculated by BJH method for the catalyst for carboxylic ester production, as shown in equation (2). 1 / 2Wd < Dd (2).

14. The catalyst for the manufacture of carboxylic acid esters according to claim 1, wherein, The half-width Wa is greater than 0.1 nm.

15. The catalyst for the manufacture of carboxylic acid esters according to claim 14, wherein, The half-width Wa is greater than 1 nm.

16. The catalyst for the manufacture of carboxylic acid esters according to claim 14, wherein, The half-width Wa is 3 nm or more.

17. The catalyst for the manufacture of carboxylic esters according to claim 1, wherein, The composition ratio of nickel or cobalt to X in the composite particles is 0.1 or more and less than 10, calculated as the Ni / X atomic ratio or the Co / X atomic ratio.

18. The catalyst for the manufacture of carboxylic acid esters according to claim 17, wherein, The composition ratio of nickel or cobalt to X in the composite particles is 0.2 or more and 8.0 or less, calculated as the Ni / X atomic ratio or the Co / X atomic ratio.

19. The catalyst for the manufacture of carboxylic acid esters according to claim 17, wherein, The composition ratio of nickel or cobalt to X in the composite particles is 0.3 or more and 6.0 or less, calculated as the Ni / X atomic ratio or the Co / X atomic ratio.

20. The catalyst for the manufacture of carboxylic esters according to claim 1, wherein, The composite particles contain gold and nickel in an oxidized state.

21. The catalyst for the manufacture of carboxylic acid esters according to any one of claims 17 to 20, wherein, The nickel to gold composition ratio in the composite particles is 1.1 or higher and 10 or lower, calculated as a Ni / Au atomic ratio.

22. The catalyst for the manufacture of carboxylic acid esters according to claim 21, wherein, The nickel to gold composition ratio in the composite particles is greater than 2 and less than 9 in terms of Ni / Au atomic ratio.

23. The catalyst for the manufacture of carboxylic acid esters according to claim 21, wherein, The nickel to gold composition ratio in the composite particles is 3 or more and 8 or less, calculated as a Ni / Au atomic ratio.

24. The catalyst for the manufacture of carboxylic acid esters according to claim 1, wherein, The average particle size of the catalyst particles is greater than 2 nm and less than 10 nm.

25. The catalyst for the manufacture of carboxylic acid esters according to claim 1, wherein, The carrier is a carrier comprising an aluminum-containing silica-based composition, wherein the aluminum-containing silica-based composition contains silica and aluminum oxide.

26. The catalyst for the manufacture of carboxylic acid esters according to claim 1, wherein, The carrier is a silica-based material, wherein the total molar amount of the silica-based material relative to silicon, aluminum, at least one fourth-period element selected from the group consisting of iron, cobalt, nickel, and zinc, and at least one basic element selected from the group consisting of alkali metals, alkaline earth metals, and rare earth elements is 42 mol% or more and 90 mol% or less, 3 mol% or more and 38 mol% or less, 0.5 mol% or more and 20 mol% or less, and 2 mol% or more and 38 mol% or less, respectively. The silicon; The aluminum; The fourth periodic element; and The alkaline element.

27. The catalyst for the manufacture of carboxylic acid esters according to claim 1, wherein, The supported layer of the catalyst particles is present in a region extending from the surface of the catalyst for producing carboxylic acid esters to 40% of the equivalent diameter of the catalyst.

28. The catalyst for the manufacture of carboxylic esters according to claim 1, wherein, The equivalent diameter of the catalyst for producing carboxylic acid esters is less than 200 μm, and a supported layer of the catalyst particles is locally present in the region from the surface of the catalyst to 30% of the equivalent diameter of the catalyst.

29. The catalyst for the manufacture of carboxylic acid esters according to claim 1, wherein, The outer layer, which contains catalyst particles in a localized area, has an outer layer that is substantially free of catalyst particles, and the outer layer is formed with a thickness of 0.01 μm or more and 15 μm or less.

30. The catalyst for the manufacture of carboxylic acid esters according to claim 29, wherein, The outer layer is formed with a thickness of 0.1 μm or more and 10 μm or less.

31. The catalyst for the manufacture of carboxylic acid esters according to claim 29, wherein, The outer layer is formed with a thickness of 0.2 μm or more and 5 μm or less.

32. The catalyst for the manufacture of carboxylic acid esters according to claim 1, wherein, The catalyst particles have a core containing X, which is coated with nickel and / or cobalt in an oxidized state.

33. A method for producing a carboxylic acid ester, comprising the following reaction steps: In the presence of a catalyst for the manufacture of carboxylic acid esters as described in any one of claims 1 to 32 and oxygen, (a) an aldehyde is reacted with an alcohol or (b) one or more alcohols are reacted.

34. The method for producing a carboxylic acid ester according to claim 33, wherein, The aldehyde is acrolein and / or methacrolein.

35. The method for producing a carboxylic acid ester according to claim 33 or 34, wherein, The aldehyde is acrolein and / or methacrolein, and the alcohol is methanol.

36. The method for producing a carboxylic acid ester according to claim 33, wherein, The reaction process is carried out in the liquid phase.

37. The method for producing a carboxylic acid ester according to claim 33, wherein, The reaction process is carried out while adding an alkaline substance to make the pH of the reaction system above 6 and below 8.

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