Preparation and application of gold-based catalyst for preparing carboxylic acid ester by direct oxidation esterification of aldehyde

Abstract

The invention provides a supported gold-based catalyst. The structure of the supported gold-based catalyst can be divided into five layers from the inside to the outside in terms of elemental composition. By means of the catalyst, methyl methacrolein and methanol can be converted into methyl methacrylate in the presence of oxygen. The catalyst of the invention is particularly distinguished by high mechanical, high conversion and selectivity, chemical stability and water resistance over time.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to the preparation and application of a gold-based catalyst for the direct oxidative esterification of aldehydes to prepare carboxylic acid esters. Background Technology

[0002] Oxidation and esterification reactions are among the most widely used organic synthetic routes, and the resulting esters are an important class of organic compounds in fine and bulk chemicals. In recent years, extensive research and large-scale production have been conducted on the direct oxidative esterification of alcohols and aldehydes due to their considerable economic and environmental benefits. The aerobic oxidative coupling reaction of methacrolein (MAL) with methanol to produce methyl methacrylate (MMA) is a typical example.

[0003] Methyl methacrylate (MMA) is a high-value-added, widely used organic chemical raw material, primarily used as a monomer in the production of polymethyl methacrylate (PMMA). In addition, it is widely used in the production of coatings, emulsion resins, adhesives, textile sizing materials, and medical functional materials. In recent years, with the gradual maturation of related production processes, my country's MMA production capacity has increased significantly. As domestic MMA output steadily increases, import dependence will gradually decrease.

[0004] Currently, C2, C3, and C4 routes are the main synthetic routes for MMA. The largest and highest-capacity process globally is the acetone cyanohydrin (ACH) process within the C3 method. However, this process suffers from several problems: the use of toxic hydrogen cyanide (HCN) as a raw material, high costs associated with treating the byproduct ammonium bisulfate, and environmental pollution from both reactants and byproducts. These problems are detrimental to human development and do not meet the requirements of green chemistry. Therefore, developing a new green process to replace the ACH method holds great promise. In recent years, the two-step isobutylene process within the C4 method has attracted widespread attention. The steps of the two-step process are as follows:

[0005] The first step involves the direct oxidation of isobutylene (IB) / tert-butanol (TBA) as the starting material to prepare MAL;

[0006] In the second step, MAL, MeOH, and O2 undergo a gas-liquid-solid three-phase reaction in a stirred tank or fixed bed under the action of a catalyst to obtain the product MMA.

[0007] The two-step isobutylene process for aerobic oxidative coupling of methacrolein (MAL) and methanol is simple, economical, and the raw material methanol can be recycled, making it a clean and efficient production method and currently the most competitive.

[0008] In recent years, researchers have shown great interest in supported gold-based catalysts due to their unique selective catalytic behavior in different types of chemical reactions, especially in the direct oxidative esterification of aldehydes to prepare carboxylic acid esters. For example, various metal oxides or mixed oxides, such as MgO-Al2O3, SiO2-Al2O3, and porous ceramic spheres embedded with alkaline earth metals, have been used as supports to support gold nanoparticles for one-step oxidative esterification reactions.

[0009] While existing technologies offer a variety of supported gold-based catalyst systems, the activity and stability of these systems need improvement. Furthermore, the use of liquid-based additives increases costs and is environmentally unfriendly. Therefore, developing high-performance and stable high-efficiency gold catalysts in alkali-free catalytic systems is of great significance for the industrial application of direct oxidative esterification of aldehydes to prepare carboxylic acid esters. Summary of the Invention

[0010] This invention provides a method for preparing a supported gold nanoparticle-based catalyst and its application in the direct oxidative esterification of aldehydes to prepare carboxylic acid esters. The catalyst of this invention exhibits high conversion and selectivity, chemical stability, and maintains good catalytic performance even after four cycles.

[0011] On one hand, the present invention provides a supported gold-based catalyst, the structure of which can be divided into five layers from the inside out according to elemental composition:

[0012] The first layer of elements consists of magnesium, aluminum, oxygen, and sodium.

[0013] The second layer of elements consists of magnesium, aluminum, oxygen, nickel, and sodium.

[0014] The third layer of elements consists of magnesium, aluminum, oxygen, nickel, carbon, and sodium.

[0015] The fourth layer of elements consists of magnesium, aluminum, oxygen, nickel, carbon, gold, sodium, and chlorine.

[0016] The fifth layer of elements consists of gold, carbon, and chlorine.

[0017] From the first to the fourth floor:

[0018] The content of magnesium, aluminum, and nickel increases further outwards;

[0019] In the fourth layer structure, gold and nickel are evenly distributed; that is, the active components gold content is consistent at different depths in the fourth layer structure, and the nickel content is consistent in the fourth layer structure.

[0020] In some embodiments, the size of the gold particles in the supported gold-based catalyst is 0.1–7.9 nm, preferably 1.8–4.8 nm, more preferably 2.0–4.5 nm, and even more preferably 2.2–3.2 nm.

[0021] In some embodiments, the carbon element in the supported gold-based catalyst exists in the form of carbon nanotubes, which are supported on a nickel-modified composite oxide support in the form of single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

[0022] In some embodiments, based on the total weight of the catalyst:

[0023] The mass fraction of gold element is 0.2–20 wt.%, preferably 0.5–3.0 wt%, preferably 0.8–2.5 wt%, preferably 0.9–2.0 wt%, and more preferably 1.0–1.5 wt%.

[0024] The mass fraction of nickel is 0.1–10 wt.%, preferably 0.5–7.0 wt%, preferably 1.0–6.5 wt%, preferably 1.2–5.0 wt%, and more preferably 1.5–4.5 wt%.

[0025] The carbon element mass fraction is 0.01–0.20 wt.%, preferably 0.02–0.16 wt%, preferably 0.06–0.14 wt%, preferably 0.07–0.12 wt%, and more preferably 0.08–0.11 wt%.

[0026] In some embodiments, the molar ratio of magnesium to aluminum in the carrier is 0.2 to 4.0.

[0027] On the other hand, the present invention also provides a method for preparing a supported gold-based catalyst according to the present invention, comprising the steps of:

[0028] 1) The aqueous solution of the first precipitant is added dropwise to the aqueous solution of magnesium compound and aluminum compound, mixed and aged at 20-70℃ for 6-12 hours, and the filter residue is calcined in a muffle furnace at 450-650℃ for 180-300 minutes to obtain the first layer of carrier.

[0029] 2) Add the nickel compound to the aqueous solution of the dispersant, then add the first layer of carrier obtained in step 1), and then add the aqueous solution of the second precipitant dropwise. After stirring the mixture, heat it at 90-100°C for 1-2 hours. After filtering, washing and drying the filter residue, calcine it in a muffle furnace at 400-600°C for 120-240 minutes in air or nitrogen to obtain the first / second layer of carrier.

[0030] 3) Calcine the first / second layer support at 400-600℃ in a hydrogen atmosphere for 90-120 minutes, maintain the hydrogen atmosphere at 600-800℃, switch to a methane atmosphere, keep the temperature constant at the methane atmosphere for 50-90 minutes, then stop the gas intake and cool down to obtain the first / second / third layer support.

[0031] 4) Stir the protective agent aqueous solution to create foam, add chloroauric acid aqueous solution and stir, then add the reducing agent, then add the first / second / third layer support and stir to ensure that the gold is completely loaded onto the support, wash and dry to form the first / second / third / fourth layer support;

[0032] 5) The first / second / third / fourth layer support is calcined in air or nitrogen in a muffle furnace at 300-500℃ for 120-240 min to obtain a supported gold-based catalyst with a first / second / third / fourth / fifth layer structure.

[0033] In some embodiments, the molar ratio of magnesium compound, aluminum compound, nickel compound and chloroauric acid is (1-50):(80-150):(5-15):(60-90); preferably, the molar ratio of magnesium compound, aluminum compound, nickel compound and chloroauric acid is 30:130:9:78.

[0034] In some embodiments,

[0035] The magnesium compound is selected from one or more of magnesium nitrate, magnesium sulfate, and magnesium chloride;

[0036] The aluminum compound is selected from one or more of aluminum nitrate, aluminum sulfate, and aluminum chloride;

[0037] The nickel compound is selected from one or more of nickel nitrate, nickel sulfate, and nickel chloride;

[0038] The dispersant is selected from one or more of PVP-k30, CMC, and PEG200;

[0039] The reducing agent is selected from one or more of NaBH4, sodium citrate, formaldehyde, and hydrazine hydrate;

[0040] The first precipitant is selected from one or more of sodium hydroxide, sodium carbonate, and urea;

[0041] The second precipitate is selected from one or more of urea, sodium hydroxide, and sodium carbonate;

[0042] The protective agent is selected from one or more of PVP, CTAB and PVA;

[0043] On the other hand, the present invention also provides a method for producing methyl methacrylate, using methacrolein and methanol as raw materials, introducing oxygen, and using the supported gold-based catalyst described in the present invention or the supported gold-based catalyst prepared by the preparation method described in the present invention to carry out a catalytic reaction.

[0044] In some embodiments, the molar ratio of methacrolein to methanol is 1:(20-50);

[0045] And / or, the oxygen flow rate is 15–25 mL / min;

[0046] And / or, a polymerization inhibitor is added during the reaction; preferably, the polymerization inhibitor is hydroquinone;

[0047] And / or, the reaction temperature is 50–80℃, the reaction pressure is 0.15–0.35MPa, and the reaction time is 1.5–3.5h.

[0048] The dispersant is used to dilute and disperse the carrier to a certain concentration, so that the carrier can come into uniform contact with other reactants, thereby enabling a complete reaction. Generally, the amount of dispersant used is conventional in the art. In this invention, the mass ratio of dispersant to carrier is approximately 0.07:1, that is, the mass ratio of dispersant to carrier can be (0.05~0.15):1; it can also be (0.05~0.1):1; or it can be 0.07:1. For example, if 3g of carrier is added, approximately 0.21g of dispersant is added.

[0049] The amount of precipitant used should be sufficient to adjust the pH of the solution to facilitate co-precipitation of the solute, and its residue should not affect the final performance of the catalyst.

[0050] The amount of protective agent used is generally within the conventional range in the art; in this invention, the ratio of the amount of protective agent to the amount of carrier is approximately (0.01 to 0.05):1.

[0051] Beneficial effects

[0052] 1. The catalyst prepared by this invention has a five-layer structure, which has the following advantages: (1) The carbon nanotubes in the third to fifth layers are hydrophobic and are one of the "protective layers" of gold nanoparticles. In a mixture containing water and carboxylic acid esters, the selectivity of the catalyst can be maintained for a certain period of time; (2) The nickel element in the second to fourth layers is another "protective layer" of gold. The nickel element exists in various forms such as elemental nickel and / or nickel oxide and / or nickel hydroxy oxide. This inhibits the loss and aggregation of gold during the use of the gold catalyst and further enhances the activity and stability of the catalyst; (3) The sodium element present in each layer not only enhances the basicity of the catalyst but also protects the basic sites of the catalyst; (4) Each layer of the catalyst contains a small amount of Cl. - This makes it easier for gold species to be uniformly loaded onto the inner and outer surfaces of the carrier. Meanwhile, low Cl... -The content can also effectively reduce the aggregation of gold particles during the roasting process; (5) The multi-layer structure of the catalyst can also reduce the wear of the component gold under high mechanical stress stirring and further extend its service life;

[0053] 2. In preparing magnesium-aluminum hydrotalcite composite oxide supports and nickel loading using co-precipitation and deposition-precipitation methods, the present invention achieves high raw material utilization and good dispersibility and uniformity; while in loading gold using the sol-gel method, the agglomeration and growth of gold particles are well avoided, ensuring the uniformity of gold particle size; the method of first loading nickel, then growing carbon nanotubes, and finally loading gold ensures the uniqueness of the catalyst structure.

[0054] 3. The catalyst support prepared by this invention possesses a high specific surface area, abundant pore structure, and a large number of acidic and basic sites. Acidic sites affect the oxidation capacity of the catalyst, while basic sites affect its activity. When the support contains a certain number of basic sites, the catalyst possesses the prerequisite for high activity. Simultaneously, the sodium contained in the support precipitates during the reaction, enhancing the alkalinity of the reaction solution. Therefore, no additional liquid alkali needs to be added during the reaction, saving costs and demonstrating high economic efficiency. It should also be noted that the sodium and chlorine elements contained in the catalyst may form sodium chloride crystals.

[0055] Terminology Explanation

[0056] Certain embodiments of the present invention will now be described in detail. The present invention is intended to cover all alternatives, modifications, and equivalents, all of which are included within the scope of the invention as defined in the claims. Those skilled in the art will recognize that many similar or equivalent methods and materials described herein can be used to practice the present invention. The present invention is by no means limited to the methods and materials described herein. In the event that one or more of the incorporated documents, patents, and similar materials differ from or contradict this application (including, but not limited to, defined terminology, application of terminology, described techniques, etc.), this application shall prevail.

[0057] It should be further appreciated that certain features of the invention, for clarity, have been described in multiple independent embodiments, but may also be provided in combination in a single embodiment. Conversely, various features of the invention, for brevity, have been described in a single embodiment, but may also be provided individually or in any suitable sub-combination.

[0058] Unless otherwise stated, all technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. All patents and publications related to this invention are incorporated herein by reference in their entirety.

[0059] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0060] In the following content, all figures disclosed herein, whether or not they use words such as "approximately" or "about," are approximate values. The value of each figure may vary by 1%, 2%, 5%, 7%, 8%, 10%, 15%, or 20%, etc. Whenever a figure with a value of N is disclosed, any figure with a value of N+ / -1%, N+ / -2%, N+ / -3%, N+ / -5%, N+ / -7%, N+ / -8%, N+ / -10%, N+ / -15%, or N+ / -20% will be explicitly disclosed, where "+ / -" indicates addition or subtraction. Attached Figure Description

[0061] Figure 1 The XRD patterns are those of the supported gold-based catalysts prepared in Examples 1-3 of this invention.

[0062] Figure 2 The image shows the SEM pattern of the supported gold-based catalyst prepared in Comparative Example 3 of this invention.

[0063] Figure 3 The HS-LEISS map of each layer structure in Embodiment 2 of the present invention is shown.

[0064] Figure 4 HS-LEISS pattern of the fourth layer structure in Embodiment 2 of the present invention.

[0065] Figure 5 These are the Raman spectra of Embodiments 1 and 2 of the present invention.

[0066] Figure 6 The cycling stability test results of the supported gold-based catalysts prepared in Examples 2 and 4-6 of this invention show the conversion rate of methacrolein.

[0067] Figure 7 The results of the cyclic stability test of the supported gold-based catalysts prepared in Examples 2 and 4-6 of this invention show the selectivity of methyl methacrylate. Detailed Implementation

[0068] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention in any way. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of this disclosure. Such structures and techniques have also been described in many publications.

[0069] All reagents used in this invention can be purchased commercially or prepared by the methods described in this invention.

[0070] Catalyst preparation:

[0071] Preparation method of supported gold-based catalysts:

[0072] 1) Add aqueous solutions of sodium hydroxide and sodium carbonate dropwise to aqueous solutions of magnesium nitrate hexahydrate and aluminum nitrate nonahydrate, mix and age at 70°C for 6-12 hours, filter the residue and calcine at 450-650°C for 300 minutes in a muffle furnace to obtain the first layer of carrier.

[0073] 2) Add nickel nitrate hexahydrate to the aqueous solution of PVP-30, then add the first layer of carrier obtained in step 1), and then add the aqueous solution of urea dropwise. After stirring the mixture, heat it at 90-100℃ for 2 hours. After filtering, washing and drying the filter residue, calcine it in a muffle furnace at 400-600℃ for 240 minutes to obtain the first / second layer of carrier.

[0074] 3) The first / second layer support is calcined in a hydrogen atmosphere at 400-600℃ for 120 min, and the hydrogen atmosphere is maintained at 600-800℃. Then, the atmosphere is switched to methane and kept at a constant temperature in the methane atmosphere for 90 min. Then, the gas inlet is stopped and the temperature is lowered to obtain the first / second / third layer support.

[0075] 4) Stir the PVA aqueous solution to create foam, add chloroauric acid aqueous solution and stir, then add NaBH4 solution to reduce, then add the first / second / third layer support and stir to fully load the gold onto the support, wash and dry to form the first / second / third / fourth layer support.

[0076] 5) The first / second / third / fourth layer support is calcined in air or nitrogen in a muffle furnace at 300-500℃ for 240 min to obtain a supported gold-based catalyst with a first / second / third / fourth / fifth layer structure.

[0077] The catalyst of this invention comprises a support and an active component and a co-active component supported on the support. The magnesium-aluminum hydrotalcite composite support comprises Mg5Al3(OH). 19(H2O)4, γ-Al2O3, MgO; the active components are gold and nickel, and the co-active component is carbon nanotubes. In this invention, gold exists in the form of nanoparticles, and nickel, in the form of elemental nickel and / or nickel oxide and / or nickel hydroxyoxide, forms a solid solution with the composite oxide support; the co-active carbon nanotubes are supported on the nickel-modified composite oxide support in the form of single-walled carbon nanotubes and / or multi-walled carbon nanotubes; the gold nanoparticles supported on the support may exist inside or outside the carbon nanotubes; the supported gold-based catalyst provided by this invention can be divided into five layers from the inside to the outside according to the elemental composition:

[0078] The first layer of elements consists of magnesium, aluminum, oxygen, and sodium.

[0079] The second layer of elements consists of magnesium, aluminum, oxygen, nickel, and sodium.

[0080] The third layer of elements consists of magnesium, aluminum, oxygen, nickel, carbon, and sodium.

[0081] The fourth layer of elements consists of magnesium, aluminum, oxygen, nickel, carbon, gold, sodium, and chlorine.

[0082] The fifth layer of elements consists of gold, carbon, and chlorine.

[0083] From the first to the fourth floor:

[0084] The content of magnesium, aluminum, and nickel increases further outwards;

[0085] In addition, gold and nickel are evenly distributed in the fourth layer structure; that is, the gold content of the active components is consistent at different depths in the fourth layer structure, and the nickel content is consistent in the fourth layer structure.

[0086] Example 1 Au1Ni 2.4 Preparation of -CNT-HT-0.2

[0087] 7.693 g of magnesium nitrate hexahydrate (Mg(NO3)2·6H2O, relative atomic mass 256.41 g / mol, 30 mmol) and 48.77 g of aluminum nitrate nonahydrate (Al(NO3)3·9H2O, relative atomic mass 375.13 g / mol, 130 mmol) were weighed and dissolved in 160 mL of water; this is solution A. 12.80 g of sodium hydroxide (NaOH, relative atomic mass 40 g / mol, 320 mmol) and 6.784 g of sodium carbonate (Na2CO3, relative atomic mass 106 g / mol, 64 mmol) were weighed and dissolved in 160 mL of deionized water; this is solution B. Solution B was slowly added dropwise to solution A, and the mixture was aged in a water bath at 70 °C for 10 h. After filtration, washing, and vacuum drying, the mixture was calcined in a muffle furnace at 500 °C for 300 min. The resulting support is denoted as HT-0.2.

[0088] Weigh 0.21 g of PVP-k30 and dissolve it in 45 mL of water. Then add 0.3568 g of nickel nitrate hexahydrate (Ni(NO3)2·6H2O, relative molecular mass 290.79 g / mol, 1.23 mmol). After the nickel salt dissolves, add 3.000 g of HT-0.2 and stir for 30 minutes. This solution is labeled C. Weigh 3.868 g of urea (relative molecular mass 60.06, 64.4 mmol) and dissolve it in 45 mL of water. This solution is labeled D. Slowly add solution D dropwise to solution C and continue stirring for 30 minutes. Transfer the mixed solution to an oil bath at 90 °C and incubate for 2 hours. After the oil bath, wash the solid in the solution with water, dry it, and calcine it in air at 400 °C for 240 minutes in a muffle furnace to obtain a nickel oxide-modified support, labeled Ni. 2.4 -HT-0.2-DP+Air, approximately 3g.

[0089] Ni 2.4 The -HT-0.2-DP+Air support was calcined at 500℃ in a hydrogen atmosphere for 120 min, then maintained at the hydrogen atmosphere until 800℃, followed by switching to a methane atmosphere and holding at that temperature for 90 min. The gas inlet was then stopped, and the temperature was allowed to drop. This support is denoted as Ni. 2.4 -CNT-HT-0.2.

[0090] Finally, the gold-loading step was performed. 0.01 g of PVA was weighed and dissolved in 100 mL of water, and stirred at high speed until foaming occurred. Then, 1.1 mL of chloroauric acid aqueous solution (50 g / mL) was added, and the mixture was stirred for a period of time. Next, 0.5 mL of NaBH4 aqueous solution (0.03–0.05 mol / L) was added to reduce the chloroauric acid; the solution quickly turned wine-red. After stirring for 20 min, 1 g of Ni was added. 2.4-CNT-HT-0.2 support. This solid-liquid mixture requires thorough stirring for 15 hours to ensure complete gold loading onto the support. After washing and drying, it is calcined in a muffle furnace at 400℃ for 240 minutes to remove PVA. The prepared catalyst is designated Au1Ni. 2.4 -CNT-HT-0.2, approximately 1g.

[0091] Example 2

[0092] The preparation method is basically the same as in Example 1, except that the masses of magnesium nitrate hexahydrate and aluminum nitrate nonahydrate are changed to 12.82 g and 41.26 g, respectively. The prepared catalyst is designated as Au1Ni. 2.4 -CNT-HT-0.5.

[0093] Example 3

[0094] The preparation method is basically the same as in Example 1, except that the masses of magnesium nitrate hexahydrate and aluminum nitrate nonahydrate are changed to 17.95 g and 33.76 g, respectively. The prepared catalyst is designated Au1Ni. 2.4 -CNT-HT-0.8.

[0095] Example 4

[0096] The method is basically the same as in Example 2, except that the mass of nickel nitrate hexahydrate is changed to 0.1742 g. The prepared catalyst is denoted as Au1Ni. 1.2 -CNT-HT-0.5.

[0097] Example 5

[0098] The method is basically the same as in Example 2, except that the mass of nickel nitrate hexahydrate is changed to 0.2676 g. The prepared catalyst is denoted as Au1Ni. 1.8 -CNT-HT-0.5.

[0099] Example 6

[0100] The method is basically the same as in Example 2, except that the mass of nickel nitrate hexahydrate is changed to 0.4460 g. The prepared catalyst is denoted as Au1Ni. 3.0 -CNT-HT-0.5.

[0101] Figure 1 The XRD patterns are those of the supported gold-based catalysts prepared in Examples 1-3 of this invention. Figure 2 The image shows the SEM pattern of the supported gold-based catalyst prepared in Comparative Example 3 of this invention. Figure 3 The HS-LEISS map of each layer structure in Embodiment 2 of the present invention is shown. Figure 4 HS-LEISS pattern of the fourth layer structure in Embodiment 2 of the present invention. Figure 5 These are the Raman spectra from Embodiments 1 and 2 of the present invention. From... Figure 3 , Figure 4 The elemental distribution in each layer of the catalyst can be analyzed; Figure 5 Raman spectroscopy results indicate the formation of multi-walled carbon nanotubes.

[0102] Comparative Example 1

[0103] The preparation method is basically the same as that in Example 1, except that: after preparing Ni 2.4 After -HT-0.2-DP+Air, only hydrogen treatment is required. That is, Ni 2.4 The -HT-0.2-DP+Air support was calcined in air and then calcined with hydrogen at 500°C for 120 min. This support is designated as Ni. 2.4 -HT-0.2-DP+Air+H2. This support is then used when loading gold. The prepared catalyst is designated Au1Ni. 2.4 -HT-0.2-DP+Air+H2.

[0104] Comparative Example 2

[0105] The preparation method is basically the same as that in Example 2, except that: after preparing Ni 2.4 After -HT-0.5-DP+Air, only hydrogen treatment is required. That is, Ni 2.4 The -HT-0.5-DP+Air support was calcined in air and then calcined with hydrogen at 500°C for 120 min. This support is designated as Ni. 2.4 -HT-0.5-DP+Air+H2. This support is then used when loading gold. The prepared catalyst is designated Au1Ni. 2.4 -HT-0.5-DP+Air+H2.

[0106] Comparative Example 3

[0107] The preparation method is basically the same as that in Example 3, except that: after preparing Ni 2.4 After -HT-0.8-DP+Air, only hydrogen treatment is required. That is, Ni 2.4 The -HT-0.8-DP+Air support was calcined in air and then calcined with hydrogen at 500°C for 120 min. This support is designated as Ni. 2.4 -HT-0.8-DP+Air+H2. This support is then used when loading gold. The prepared catalyst is designated Au1Ni. 2.4 -HT-0.8-DP+Air+H2.

[0108] Applications of catalysts:

[0109] Methanol and methacrolein were used as reactants, and the catalysts prepared in Examples 1-6 and Comparative Examples 1-3 were used for catalytic reactions.

[0110] First, 0.002 g of hydroquinone polymerization inhibitor was added, followed by 20 mL of methanol and 1 mL of methacrolein. The molar ratio of alcohol to aldehyde in the raw materials was 40, and the catalyst dosage was 0.5 g. The reaction temperature was 60℃, and oxygen was continuously introduced at a flow rate of 20 mL / min under a pressure of 0.2 MPa, maintaining the reaction at 60℃ for 2 hours. After the reaction was complete, the reaction solution was filtered, and the filtrate was analyzed by gas chromatography. The main product of the reaction was methyl methacrylate, and the byproducts included isobutylene dimethyl acetal, methyl isobutyrate, and carbon dioxide. The results are shown in Table 1 below.

[0111] Table 1:

[0112]

[0113]

[0114] *Reaction performance of catalyst recycling for the 4th time

[0115] As can be seen from the data in Table 1, the catalysts prepared in this invention all exhibit high initial activity, with methacrolein conversion and methyl methacrylate selectivity both exceeding 85%. Preferred Example: Au1Ni 2.4 -CNT-HT-0.5 achieves a 100.0% conversion rate of methacrolein in its first application, with a methyl methacrylate selectivity of up to 95.84%. Furthermore, supported carbon nanotubes can improve the overall conversion rate and selectivity of the catalyst.

[0116] The catalyst prepared in this invention exhibits a certain degree of decrease in conversion rate and selectivity after four applications without in-situ growth of carbon nanotubes. After in-situ growth of carbon nanotubes, the catalyst performance stabilizes. For example, Au1Ni... 2.4 -CNT-HT-0.2 and Au1Ni 2.4 The conversion rate and selectivity of -CNT-HT-0.5 remained stable at around 98% and 95%, respectively, after four cycles, while Au1Ni 2.4 The conversion rate and selectivity of -CNT-HT-0.8 remained stable at around 95% and 92%, respectively. The effect of different amounts of carbon nanotubes on the conversion rate and selectivity first increased and then decreased. Figure 6 and Figure 7 The results are the cycle stability test results of the supported gold-based catalysts prepared in Examples 2 and 4-6 of this invention. Figure 6 The conversion results of methacrolein in these four examples are shown. Figure 7 The methyl methacrylate selectivity results for these four examples are shown.

[0117] The method of this invention has been described through preferred embodiments. Those skilled in the art will readily be able to modify or appropriately alter and combine the methods and applications described herein within the scope, spirit, and context of this invention to implement and apply the technology of this invention. Those skilled in the art can refer to the content herein to appropriately improve process parameters. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included within the scope of this invention.

Claims

1. A supported gold-based catalyst, characterized in that, The supported gold-based catalyst structure can be divided into five layers from the inside out according to its elemental composition: The first layer of elements consists of magnesium, aluminum, oxygen, and sodium. The second layer of elements consists of magnesium, aluminum, oxygen, nickel, and sodium. The third layer of elements consists of magnesium, aluminum, oxygen, nickel, carbon, and sodium. The fourth layer of elements consists of magnesium, aluminum, oxygen, nickel, carbon, gold, sodium, and chlorine. The fifth layer of elements consists of gold, carbon, and chlorine. From the first to the fourth floor: The content of magnesium, aluminum, and nickel increases further outwards; In the fourth layer, gold and nickel are evenly distributed; In the supported gold-based catalyst, carbon elements are supported on a nickel-modified composite oxide support in the form of carbon nanotubes. Based on the total weight of the supported gold-based catalyst: the mass fraction of gold is 0.2~20 wt%; the mass fraction of nickel is 0.1~10 wt%; and the mass fraction of carbon is 0.01~0.20 wt%.

2. The supported gold-based catalyst according to claim 1, characterized in that, The supported gold-based catalyst has gold particles with a size of 0.1~7.9 nm.

3. The supported gold-based catalyst of claim 2, wherein, The supported gold-based catalyst has gold particles with a size of 1.8~4.8 nm.

4. The supported gold-based catalyst of claim 2, wherein, The supported gold-based catalyst has gold particles with a size of 2.0~4.5 nm.

5. The supported gold-based catalyst according to claim 2, characterized in that, The supported gold-based catalyst has gold particles with a size of 2.2~3.2 nm.

6. The supported gold-based catalyst according to claim 1, characterized in that, Single-walled carbon nanotubes and / or multi-walled carbon nanotubes are loaded onto nickel-modified composite oxide supports.

7. The supported gold-based catalyst according to claim 1, characterized in that, The gold content, based on the total weight of the catalyst, is 0.5–3.0 wt%.

8. The supported gold-based catalyst according to claim 1, characterized in that, The gold content, based on the total weight of the catalyst, is 0.8–2.5 wt%.

9. The supported gold-based catalyst according to claim 1, characterized in that, The gold content, based on the total weight of the catalyst, is 0.9–2.0 wt%.

10. The supported gold-based catalyst according to claim 1, characterized in that, The gold content is 1.0–1.5 wt% based on the total weight of the catalyst.

11. The supported gold-based catalyst according to claim 1, characterized in that, The mass fraction of nickel, based on the total weight of the catalyst, is 0.5–7.0 wt%.

12. The supported gold-based catalyst according to claim 1, characterized in that, The mass fraction of nickel, based on the total weight of the catalyst, is 1.0–6.5 wt%.

13. The supported gold-based catalyst according to claim 1, characterized in that, The mass fraction of nickel, based on the total weight of the catalyst, is 1.2–5.0 wt%.

14. The supported gold-based catalyst according to claim 1, characterized in that, The mass fraction of nickel, based on the total weight of the catalyst, is 1.5–4.5 wt%.

15. The supported gold-based catalyst according to claim 1, characterized in that, The carbon content, based on the total weight of the catalyst, is 0.02–0.16 wt%.

16. The supported gold-based catalyst according to claim 1, characterized in that, The carbon content, based on the total weight of the catalyst, is 0.06–0.14 wt%.

17. The supported gold-based catalyst according to claim 1, characterized in that, The carbon content, based on the total weight of the catalyst, is 0.07–0.12 wt%.

18. The supported gold-based catalyst according to claim 1, characterized in that, The carbon content, based on the total weight of the catalyst, is 0.08–0.11 wt%.

19. The supported gold-based catalyst according to any one of claims 1-18, characterized in that, The molar ratio of magnesium to aluminum in the composite oxide carrier is 0.2 to 4.

0.

20. A method for preparing the supported gold-based catalyst according to any one of claims 1-19, characterized in that, Including the following steps: 1) The aqueous solution of the first precipitant is added dropwise to the aqueous solution of magnesium compound and aluminum compound, mixed and aged at 20~70 ℃ for 6~12 hours, and the filter residue is calcined in a muffle furnace at 450~650 ℃ for 180~300 min to obtain the first layer of carrier; 2) Add the nickel compound to the aqueous solution of the dispersant, then add the first layer of carrier obtained in step 1), and then add the aqueous solution of the second precipitant dropwise. After stirring the mixture, heat it at 90~100 ℃ for 1~2 h. After filtering, washing and drying the filter residue, calcine it in a muffle furnace at 400~600 ℃ for 120~240 min in air or nitrogen to obtain the first / second layer of carrier. 3) Calcine the first / second layer support at 400~600 ℃ in a hydrogen atmosphere for 90~120 min, maintain the hydrogen atmosphere at 600~800 ℃, switch to a methane atmosphere, keep the temperature constant at the methane atmosphere for 50~90 min, then stop the gas intake and cool down to obtain the first / second / third layer support. 4) Stir the protective agent aqueous solution to create foam, add chloroauric acid aqueous solution and stir, then add the reducing agent, then add the first / second / third layer support and stir to ensure that the gold is completely loaded onto the support, wash and dry to form the first / second / third / fourth layer support; 5) The first / second / third / fourth layer support is calcined in air or nitrogen in a muffle furnace at 300~500 ℃ for 120~240 min to obtain a supported gold-based catalyst with a first / second / third / fourth / fifth layer structure.

21. The preparation method according to claim 20, characterized in that, The molar ratio of magnesium compound, aluminum compound, nickel compound and chloroauric acid is (1~50):(80~150):(5~15):(60~90).

22. The preparation method according to claim 21, characterized in that, The molar ratio of magnesium compound, aluminum compound, nickel compound and chloroauric acid is 30:130:9:

78.

23. The preparation method according to claim 20, characterized in that, The magnesium compound is selected from one or more of magnesium nitrate, magnesium sulfate, and magnesium chloride; The aluminum compound is selected from one or more of aluminum nitrate, aluminum sulfate, and aluminum chloride; The nickel compound is selected from one or more of nickel nitrate, nickel sulfate, and nickel chloride; The dispersant is selected from one or more of PVP-k30, CMC, and PEG200; The reducing agent is selected from one or more of NaBH4, sodium citrate, formaldehyde, and hydrazine hydrate; The first precipitant is selected from one or more of sodium hydroxide, sodium carbonate, and urea; The second precipitate is selected from one or more of urea, sodium hydroxide, and sodium carbonate; The protective agent is selected from one or more of PVP, CTAB and PVA.

24. A method for producing methyl methacrylate, characterized in that, Using methacrolein and methanol as raw materials, oxygen is introduced, and a catalytic reaction is carried out using the supported gold-based catalyst according to any one of claims 1-19 or the supported gold-based catalyst prepared by the preparation method according to any one of claims 20-23.

25. The method according to claim 24, characterized in that, The molar ratio of methacrolein to methanol is 1:(20-50). And / or, the oxygen flow rate is 15~25 mL / min; And / or, a polymerization inhibitor is added during the reaction; And / or, the reaction temperature is 50~80 ℃, the reaction pressure is 0.15~0.35 MPa, and the reaction time is 1.5~3.5 h.

26. The method according to claim 25, characterized in that, The polymerization inhibitor is hydroquinone.

Images