Process for the preparation of a catalyst for the oxidation of isobutene to methacrolein and use thereof

Abstract

This invention provides a method for preparing a catalyst for the oxidation of isobutylene to methacrolein and its application. The preparation method includes the following steps: Step 1: Mixing a molybdenum-containing precursor solution I, a bismuth-containing precursor solution II, and a cobalt- and iron-containing precursor solution III to obtain solution V; Step 2: Adding a hydroxylated polycarboxylic acid to solution V and performing a crystallization reaction to obtain a catalyst precursor; Step 3: Calcining the catalyst precursor to obtain a catalyst for the oxidation of isobutylene to methacrolein; wherein the hydroxylated polycarboxylic acid is selected from one or more combinations of glycolic acid, lactic acid, citric acid, malic acid, and tartaric acid. This invention, through pretreatment with hydroxylated polycarboxylic acids, can block dispersed oxide lattice clusters, inhibit the formation of large particle structures, and fully expose the active defect sites of the catalyst, thereby improving catalytic activity.

Description

Technical Field

[0001] This invention relates to a method for preparing a catalyst for the oxidation of isobutylene to prepare methacrolein and its application, belonging to the field of olefin oxidation catalyst technology. Background Technology

[0002] C4 fraction is one of the main byproducts of catalytic cracking and catalytic pyrolysis units in refineries, accounting for about 8% of the feedstock. With the rapid development of refining capacity, the production of C4 resources has also increased significantly. The main uses of C4 resources can be divided into two categories: petroleum products and chemicals. Petroleum product utilization involves converting C4 components into gasoline blending components through processes such as aromatization, isomerization, or alkylation. Chemical utilization involves separating or cracking the components and using them as raw materials to produce high-value-added chemical products.

[0003] Isobutylene, as the most utilized component of C4, produces methyl methacrylate (MMA), a crucial organic chemical intermediate used in the production of polymethyl methacrylate (PMMA), polyethyl methacrylate (PMEA), and polymethyl methacrylate-styrene copolymer (MS resin). These materials are widely used in optical components, plastic glass, and transparent sheets, offering broad market prospects and significant economic benefits.

[0004] Currently, there are three main processes for producing methacrylic acid: the acetone cyanohydrin method, the acetylene method, and the isobutylene oxidation method. Among these, the isobutylene oxidation method uses isobutylene as a raw material, catalytically oxidizing it in air to produce methacrolein, which is then further oxidized to produce methacrylic acid. Compared to the other two methods, this method has advantages such as abundant raw material sources, high atom utilization and yield, good product quality, and less environmental impact. Therefore, its application rate is increasing globally, making it the main method for manufacturing MMA both domestically and internationally.

[0005] The oxidation of isobutylene to methacrolein (MAL) is the first and most crucial step in the three-step oxidation process for MMA. This oxidation reaction requires the supply of oxygen species, such as oxygen gas or air, to the reaction sites. The oxygen in the reaction products does not originate directly from the gas phase but is provided by the catalyst; the oxygen in the gas phase is only used to replenish the portion consumed by the catalyst during the reaction. Only through efficient coordination between oxygen activation sites and reaction sites can the catalyst activity be significantly improved. This can be achieved through the migration of active oxygen species caused by bulk diffusion. Furthermore, the elemental composition of the catalyst needs to be maintained in a suitable ratio to effectively activate and regenerate the active sites. Simultaneously, excessive adsorption and activation of the reactant isobutylene on the catalyst can easily lead to over-oxidation, resulting in a large amount of carbon oxide byproducts.

[0006] In the early 1960s, with the application of Mo-Bi catalysts in the propylene-to-acrylonitrile industry, companies such as Asahi Kasei, Shokubai, and Standard Oil in Japan successively applied Mo and Bi-based multi-component composite oxide catalysts to the selective oxidation of isobutylene to prepare methacrolein. The oxidation mechanism of isobutylene is similar to that of propylene, mainly consisting of the following steps: ① Isobutylene is adsorbed on the empty d orbitals of Mo; ② The oxygen on the Bi bonded to the active Mo site removes the hydrogen from the methyl group of isobutylene; ③ A dehydration reaction is carried out to generate MAL and water molecules; ④ MAL is desorbed from the catalyst surface; ⑤ The catalyst is re-oxidized and its activity is restored.

[0007] The Mo-Bi catalyst system possesses a unique structure with diverse and complex components. The different combinations of elements result in varying interactions between oxides. Elemental ratios and co-precipitation reaction conditions significantly influence the catalyst structure and surface properties. Fully leveraging the interactions of the active phases is crucial for improving the conversion rate of isobutylene and the selectivity of methacrolein. However, in actual preparation processes, the composite metal oxide precursor tends to form multilayered, large-particle structures, with internal defects easily embedded within, preventing full exposure and leading to reduced catalytic activity.

[0008] Therefore, developing a suitable catalyst to improve the isobutylene conversion activity and the yield of methacrolein has very important industrial application value. Summary of the Invention

[0009] To address the aforementioned technical problems, the present invention aims to provide a method for preparing a catalyst for the oxidation of isobutylene to methacrolein and its application, thereby improving the isobutylene conversion rate and the selectivity and yield of methacrolein.

[0010] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing a catalyst for the oxidation of isobutylene to methacrolein, the method comprising the following steps:

[0011] Step 1: Mix the molybdenum-containing precursor solution I, the bismuth-containing precursor solution II, and the cobalt and iron-containing precursor solution III to obtain solution V;

[0012] Step 2: Add the hydroxylated polycarboxylic acid to the solution V and carry out a crystallization reaction to obtain the catalyst precursor;

[0013] Step 3: Calcining the precursor of the catalyst to obtain a catalyst for the oxidation of isobutylene to prepare methacrolein;

[0014] The hydroxylated polycarboxylic acid is selected from one or more of glycolic acid, lactic acid, citric acid, malic acid, and tartaric acid.

[0015] According to a specific embodiment of the present invention, preferably, the atomic ratio of molybdenum, bismuth, cobalt and iron is (10-16):(0.6-10):(0.1-6):(0.5-5).

[0016] According to a specific embodiment of the present invention, preferably, step one further includes the operation of adding a precursor solution IV containing elements ABC, specifically including: mixing a molybdenum-containing precursor solution I, a bismuth-containing precursor solution II, a cobalt and iron-containing precursor solution III, and a precursor solution IV containing elements ABC to obtain solution V; here, elements ABC refer to elements A, B, and C that can be selected and combined, and do not necessarily contain elements A, B, and C simultaneously;

[0017] The catalyst for the oxidation of isobutylene to prepare methacrolein is shown in formula (1):

[0018] Mo a Bi b Co c Fe d A e B f C g O x (1)

[0019] A is selected from one or more of the following: nickel, magnesium, copper, lead, manganese, cerium, tellurium, antimony, tin, zinc, and tungsten.

[0020] B is selected from one or more of zirconium, silicon, aluminum, phosphorus, sulfur, and boron;

[0021] C is selected from one or more of potassium, sodium, cesium, calcium, barium, and thallium;

[0022] x represents the total number of oxygen atoms required to satisfy the requirements of each oxide;

[0023] a: b: c: d: e: f: g = (10-16): (0.6-10): (0.1-6): (0.5-5): (0-6): (0-15): (0-3).

[0024] According to a specific embodiment of the present invention, preferably, the molybdenum-containing precursor solution I is obtained by dissolving a molybdenum-containing metal salt in a solvent; more preferably, the molybdenum-containing metal salt is ammonium molybdate, and the solvent is water;

[0025] Bismuth-containing precursor solution II is obtained by dissolving a bismuth-containing metal salt in a solvent; more preferably, the bismuth-containing metal salt is bismuth nitrate, and the solvent is nitric acid;

[0026] Mixture III of the precursor solution containing cobalt and iron is obtained by dissolving a cobalt-containing metal salt and an iron-containing metal salt in a solvent; more preferably, the cobalt-containing metal salt is cobalt nitrate, the iron-containing metal salt is ferric nitrate, and the solvent is water;

[0027] The precursor mixed solution IV containing elements ABC specifically refers to one or more combinations of the above-mentioned elements A, B, and C required for the catalyst, excluding Mo, Bi, Co, and Fe; it is obtained by dissolving metal salts containing A and / or metal salts containing B and / or metal salts containing C in a solvent; more preferably, it can be a metal nitrate or a metal sulfate, and the solvent is water.

[0028] According to a specific embodiment of the present invention, preferably, the hydroxylated polycarboxylic acid is selected from one or more combinations of lactic acid, citric acid, and tartaric acid; more preferably, it is citric acid and lactic acid, the combination of their large and small molecules allows the hydroxylated polycarboxylic acid to be more fully bound on the surface of the catalyst precursor, resulting in better catalyst performance.

[0029] According to a specific embodiment of the present invention, preferably, in step two, the rate at which the hydroxylated polycarboxylic acid is added to solution V is 5-20 mL / min, more preferably 10-15 mL / min. If the rate of addition of the hydroxylated polycarboxylic acid is too low, the operation time will be too long, the dropping rate will be too fast, the reaction will be uneven, and the anchoring effect of the hydroxylated polycarboxylic acid on the catalyst surface will be affected.

[0030] According to a specific embodiment of the present invention, preferably, the total molar ratio of the hydroxylated polycarboxylic acid to the catalyst metal element is (0.2-2):1. If the ratio is lower than the range of the present invention, the addition of the hydroxylated polycarboxylic acid does not significantly improve the performance; if the ratio is higher than the range of the present invention, excessive hydroxylated polycarboxylic acid will accumulate on the surface, resulting in a decrease in the performance of the catalyst.

[0031] According to a specific embodiment of the present invention, preferably, in step two, the temperature of the crystallization reaction is 150-250°C, more preferably 205-250°C; and the time of the crystallization reaction is 18-36 hours, more preferably 30 hours.

[0032] According to a specific embodiment of the present invention, preferably, the calcination temperature is 400-600℃, more preferably 450-480℃; if the calcination temperature is too high, it will affect the performance of the catalyst; the calcination time is 2-6h, more preferably 6h.

[0033] According to a specific embodiment of the present invention, preferably, step one further includes a heating reaction process on the mixed solution V, wherein the heating reaction temperature is 70-85°C, more preferably 85°C; the heating reaction time is 0.5-3h, more preferably 3h; and the pH of solution V during the reaction is controlled to be 4.5-6.5, more preferably 5.5-6, to prevent the solution from becoming alkalized and causing some metal ions to precipitate prematurely.

[0034] According to a specific embodiment of the present invention, preferably, step one includes the following specific process: the molybdenum-containing precursor solution I is first stirred at a rate of 100-300 rpm / min; then heated to 50-70°C, more preferably 60-70°C; then the bismuth-containing precursor solution II, the mixture of the cobalt and iron-containing precursor solutions III, and the precursor mixture IV containing elements ABC are added to obtain solution V.

[0035] Secondly, the present invention also provides a catalyst for the oxidation of isobutylene to prepare methacrolein, which is prepared by the above-described preparation method.

[0036] The catalyst of the present invention contains molybdenum, bismuth, cobalt, and iron in a molar ratio of (10-16):(0.6-10):(0.1-6):(0.5-5). Preferably, in addition to molybdenum, bismuth, cobalt, and iron, the catalyst also contains one or more combinations of elements A, B, and C. Specifically, it may include a combination of elements A and C, or a combination of elements A, B, and C. Furthermore, in the above combinations, elements A, B, and C may each be one or more combinations of optional metal elements, such as a combination of a single element A and a single element C, a combination of two elements A and a single element C, a combination of a single element A and two elements C, or a combination of a single element A, a single element B, and a single element C. These are just examples, and the actual technical solution is not limited thereto.

[0037] According to a specific embodiment of the present invention, preferably, a:b:c:d:e:f:g = (10-16):(0.6-10):(0.1-6):(0.5-5):(0-6):(0-15):(0-3); more preferably, a:b:c:d:e:f:g = (10-16):(0.6-10):(0.1-6):(0.5-5):(1-6):(0-15) (0.01-3); More preferably, (10-16): (0.6-10): (0.1-6): (0.5-5): (1-6): (6-15): (0.01-3); Even more preferably, a:b:c:d:e:f:g = (10-16): (1-10): (1-6): (1-5): (1-3): (8-10): (0.05-1.3).

[0038] According to a specific embodiment of the present invention, preferably, A is selected from one or more combinations of nickel, magnesium, copper, cerium, and antimony;

[0039] B is selected from one or more of silicon, zirconium, aluminum, and boron;

[0040] C is selected from potassium and / or cesium.

[0041] Thirdly, the present invention provides the application of a catalyst prepared by the above-described method for preparing a catalyst for the oxidation of isobutylene to methacrolein in the oxidation of isobutylene to methacrolein.

[0042] According to a specific embodiment of the present invention, preferably, the application includes the following steps: placing the catalyst in a fixed-bed reactor, mixing isobutylene, oxygen and water after preheating, and undergoing an oxidation reaction under the action of the catalyst to obtain methacrolein.

[0043] According to a specific embodiment of the present invention, preferably, the conditions for the oxidation reaction are: a reaction temperature of 300-380°C.

[0044] According to a specific embodiment of the present invention, preferably, the composition of the feed gas is 9%-15% isobutylene by volume, 20%-65% oxygen by volume, and the remainder is water vapor; the feed gas space velocity (GSHV) is 900-1500 mL / (g·h).

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] In this invention, after synthesizing the composite metal oxide precursor by co-precipitation, a hydroxyl-linked polycarboxylic acid is pretreated. The introduced hydroxyl-linked polycarboxylic acid groups are anchored at defect sites. Due to their large molecular structure and abundant groups, they can block the formation of dispersed oxide lattice clusters, inhibit the formation of large particle structures, and "fine-crystalize" the molybdenum-based composite metal oxide, thereby improving catalytic activity. At the same time, the hydroxyl-linked polycarboxylic acid bound to the defect sites can provide a supporting localization environment. After subsequent preparation and calcination, the hydroxyl-linked polycarboxylic acid is burned off while the catalyst retains its defect structure. This fully exposes the defect structure of the active sites of the molybdenum-based composite metal oxide, which is beneficial for the rapid adsorption, desorption, and migration of oxygen in the reaction, thereby improving the selectivity and yield of methacrolein. Attached Figure Description

[0047] Figure 1 This is a SEM image of the catalyst prepared in Comparative Example 1 of the present invention.

[0048] Figure 2 This is a SEM image of the catalyst prepared in Example 1 of the present invention. Detailed Implementation

[0049] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0050] Example 1

[0051] This embodiment provides a method for preparing a catalyst for the oxidation of isobutylene to methacrolein, comprising the following steps:

[0052] Step 1: Weigh 163.7g of ammonium molybdate into a beaker and add it to 500mL of deionized water. Stir until completely dissolved to obtain molybdenum-containing precursor solution I. In another beaker, weigh 45g of bismuth nitrate pentahydrate and dissolve it in 20wt.% nitric acid. Stir until completely dissolved to obtain bismuth-containing precursor solution II. Weigh 33.7g of cobalt nitrate hexahydrate and 78.4g of ferric nitrate nonahydrate and dissolve them in deionized water. Stir until completely dissolved to obtain a mixture of cobalt and iron-containing precursor solutions III.

[0053] Molybdenum-containing precursor solution I was slowly heated to 70°C with stirring, and the stirring rate was adjusted to 120 r / min. Then, bismuth-containing precursor solution II and a mixture of cobalt and iron-containing precursor solutions III were slowly added to obtain solution V. Solution V was then heated to 85°C, the pH of the solution was adjusted to 6, and stirring was continued for 1 h.

[0054] Step 2: Weigh 166.5g of citric acid and dissolve it in deionized water. After complete dissolution, add it to solution V at a rate of 15mL / min. Transfer the solution to a hydrothermal synthesis reactor and crystallize it at 190℃ for 30h. After crystallization, dry the solution to obtain the catalyst precursor.

[0055] Step 3: The precursor of the catalyst was calcined in air at 450°C for 6 hours and then cooled to room temperature to obtain the catalyst Cat-MAL-2 for the oxidation of isobutylene to methacrolein.

[0056] The SEM image of the catalyst prepared in Example 1 is shown below. Figure 2 As shown, with Figure 1 Compared with the catalyst in Comparative Example 1, the catalyst particle size of the present invention after the addition of hydroxyl polycarboxylic acid is significantly reduced.

[0057] Example 2

[0058] This embodiment provides a method for preparing a catalyst for the oxidation of isobutylene to methacrolein, comprising the following steps:

[0059] Step 1: Weigh 163.7g of ammonium molybdate into a beaker and add it to 500mL of deionized water. Stir until completely dissolved to obtain molybdenum-containing precursor solution I. In another beaker, weigh 45g of bismuth nitrate pentahydrate and dissolve it in 20wt.% nitric acid. Stir until completely dissolved to obtain bismuth-containing precursor solution II. Weigh 33.7g of cobalt nitrate hexahydrate and 78.4g of ferric nitrate nonahydrate and dissolve them in deionized water. Stir until completely dissolved to obtain a mixed solution of cobalt and iron precursor solutions III. Weigh 32.5g of nickel nitrate hexahydrate, 23.1g of cerium nitrate hexahydrate, and 1.53g of cesium nitrate and dissolve them in deionized water. After complete dissolution, obtain a mixed precursor solution IV containing nickel, cerium, and cesium.

[0060] Molybdenum-containing precursor solution I was slowly heated to 70°C with stirring, and the stirring rate was adjusted to 120 r / min. Then, bismuth-containing precursor solution II, a mixture of cobalt and iron precursor solutions III, and a mixture of nickel, cerium, and cesium precursor solutions IV were slowly added to obtain solution V. Solution V was then heated to 85°C, the pH of the solution was adjusted to 6, and stirring was continued for 1 h.

[0061] Step 2: Weigh 166.5g of citric acid and dissolve it in deionized water. After complete dissolution, add it to solution V at a rate of 15mL / min. Transfer the solution to a hydrothermal synthesis reactor and crystallize it at 190℃ for 30h. After crystallization, dry the solution to obtain the catalyst precursor.

[0062] Step 3: The precursor of the catalyst was calcined in air at 450°C for 6 hours and then cooled to room temperature to obtain the catalyst Cat-MAL-4 for the oxidation of isobutylene to methacrolein.

[0063] Example 3

[0064] This embodiment provides a method for preparing a catalyst for the oxidation of isobutylene to methacrolein, which differs from Example 2 only in that:

[0065] In step two, 145.1g of lactic acid was weighed and dissolved in deionized water to finally obtain the catalyst Cat-MAL-5.

[0066] Example 4

[0067] This embodiment provides a method for preparing a catalyst for the oxidation of isobutylene to methacrolein, which differs from Example 2 only in that:

[0068] In step two, 226.3g of tartaric acid was weighed and dissolved in deionized water to finally obtain the catalyst Cat-MAL-6.

[0069] Example 5

[0070] This embodiment provides a method for preparing a catalyst for the oxidation of isobutylene to methacrolein, which differs from Example 2 only in that:

[0071] In step two, 193.2g of glycolic acid was weighed and dissolved in deionized water to finally obtain the catalyst Cat-MAL-7.

[0072] Example 6

[0073] This embodiment provides a method for preparing a catalyst for the oxidation of isobutylene to methacrolein, which differs from Example 2 only in that:

[0074] In step two, 92.5g of citric acid was weighed and dissolved in deionized water to finally obtain the catalyst Cat-MAL-8.

[0075] Example 7

[0076] This embodiment provides a method for preparing a catalyst for the oxidation of isobutylene to methacrolein, which differs from Example 2 only in that:

[0077] In step two, 323.8g of citric acid was weighed and dissolved in deionized water to finally obtain the catalyst Cat-MAL-9.

[0078] Example 8

[0079] This embodiment provides a method for preparing a catalyst for the oxidation of isobutylene to methacrolein, comprising the following steps:

[0080] Step 1: Weigh 163.7g of ammonium molybdate into a beaker and add it to 500mL of deionized water. Stir until completely dissolved to obtain molybdenum-containing precursor solution I. In another beaker, weigh 45g of bismuth nitrate pentahydrate and dissolve it in 20wt.% nitric acid. Stir until completely dissolved to obtain bismuth-containing precursor solution II. Weigh 33.7g of cobalt nitrate hexahydrate and 78.4g of ferric nitrate nonahydrate and dissolve them in deionized water. Stir until completely dissolved to obtain a mixed solution of cobalt and iron precursor solutions III. Weigh 32.5g of nickel nitrate hexahydrate, 23.1g of cerium nitrate hexahydrate, and 1.53g of cesium nitrate and dissolve them in deionized water. After complete dissolution, obtain a mixed precursor solution IV containing nickel, cerium, and cesium.

[0081] Molybdenum-containing precursor solution I was slowly heated to 70°C with stirring, and the stirring rate was adjusted to 120 r / min. Then, bismuth-containing precursor solution II, a mixture of cobalt and iron precursor solutions III, and a mixture of nickel, cerium, and cesium precursor solutions IV were slowly added to obtain solution V. Solution V was then heated to 80°C, the pH of the solution was adjusted to 6, and stirring was continued for 1 h.

[0082] Step 2: Weigh 111.2g of citric acid and 72.5g of lactic acid and dissolve them in deionized water. After complete dissolution, add the solution to solution V at a rate of 15mL / min. Transfer the solution to a hydrothermal synthesis reactor and crystallize it at 190℃ for 30h. After crystallization, dry the solution to obtain the catalyst precursor.

[0083] Step 3: The precursor of the catalyst was calcined in air at 450°C for 6 hours and then cooled to room temperature to obtain the catalyst Cat-MAL-10 for the oxidation of isobutylene to methacrolein.

[0084] Example 9

[0085] This embodiment provides a method for preparing a catalyst for the oxidation of isobutylene to methacrolein, which differs from Example 2 only in that:

[0086] In step two, 111.2g of citric acid and 96.5g of tartaric acid were weighed and dissolved in deionized water to finally obtain the catalyst Cat-MAL-11.

[0087] Example 10

[0088] This embodiment provides a method for preparing a catalyst for the oxidation of isobutylene to methacrolein, which differs from Example 2 only in that:

[0089] In step two, 111.2g of citric acid and 71.3g of glycolic acid were weighed and dissolved in deionized water to finally obtain the catalyst Cat-MAL-12.

[0090] Example 11

[0091] This embodiment provides a method for preparing a catalyst for the oxidation of isobutylene to methacrolein, which differs from Example 2 only in that:

[0092] In step one, the mixed solution IV consisted of 28.66 g magnesium sulfate, 27.00 g copper nitrate trihydrate and 1.53 g cesium nitrate, and finally the catalyst Cat-MAL-13 was prepared.

[0093] Example 12

[0094] This embodiment provides a method for preparing a catalyst for the oxidation of isobutylene to methacrolein, which differs from Example 2 only in that:

[0095] In step one, the mixed solution IV consists of 32.5g nickel nitrate hexahydrate, 1.53g cesium nitrate and 0.61g potassium nitrate, and finally the catalyst Cat-MAL-14 is prepared.

[0096] Example 13

[0097] This embodiment provides a method for preparing a catalyst for the oxidation of isobutylene to methacrolein, which differs from Example 2 only in that:

[0098] In step one, the mixed solution IV consisted of 32.5 g nickel nitrate hexahydrate, 4.79 g zirconium nitrate and 1.53 g cesium nitrate, and finally the catalyst Cat-MAL-15 was prepared.

[0099] Example 14

[0100] This embodiment provides a method for preparing a catalyst for the oxidation of isobutylene to methacrolein, which differs from Example 2 only in that:

[0101] In step one, the mixed solution IV consists of 32.5g of nickel nitrate hexahydrate and 0.61g of potassium nitrate. After obtaining solution V, silica sol solution is added to finally obtain the catalyst Cat-MAL-16.

[0102] Comparative Example 1

[0103] This comparative example provides a method for preparing a catalyst for the oxidation of isobutylene to methacrolein, comprising the following steps:

[0104] Step 1: Weigh 163.7g of ammonium molybdate into a beaker and add it to 500mL of deionized water. Stir until completely dissolved to obtain molybdenum-containing precursor solution I. In another beaker, weigh 45g of bismuth nitrate pentahydrate and dissolve it in 20wt.% nitric acid. Stir until completely dissolved to obtain bismuth-containing precursor solution II. Weigh 33.7g of cobalt nitrate hexahydrate and 78.4g of ferric nitrate nonahydrate and dissolve them in deionized water. Stir until completely dissolved to obtain a mixture of cobalt and iron-containing precursor solutions III.

[0105] Molybdenum-containing precursor solution I was slowly heated to 70°C with stirring, and the stirring rate was adjusted to 120 r / min. Then, bismuth-containing precursor solution II and a mixture of cobalt and iron-containing precursor solutions III were slowly added to obtain solution V. Solution V was then heated to 85°C, the pH of the solution was adjusted to 6, and stirring was continued for 1 h.

[0106] Step 2: Transfer the above solution to a hydrothermal synthesis reactor and crystallize it at 190℃ for 30 hours. After crystallization, dry it to obtain the catalyst precursor.

[0107] Step 3: The precursor of the catalyst was calcined in air at 450°C for 6 hours and then cooled to room temperature to obtain the catalyst Cat-MAL-1 for the oxidation of isobutylene to methacrolein.

[0108] The SEM image of the catalyst prepared in Comparative Example 1 is shown below. Figure 1 As shown.

[0109] Comparative Example 2

[0110] This comparative example provides a method for preparing a catalyst for the oxidation of isobutylene to methacrolein, comprising the following steps:

[0111] Step 1: Weigh 163.7g of ammonium molybdate into a beaker and add it to 500mL of deionized water. Stir until completely dissolved to obtain molybdenum-containing precursor solution I. In another beaker, weigh 45g of bismuth nitrate pentahydrate and dissolve it in 20wt.% nitric acid. Stir until completely dissolved to obtain bismuth-containing precursor solution II. Weigh 33.7g of cobalt nitrate hexahydrate and 78.4g of ferric nitrate nonahydrate and dissolve them in deionized water. Stir until completely dissolved to obtain a mixed solution of cobalt and iron precursor solutions III. Weigh 32.5g of nickel nitrate hexahydrate, 23.1g of cerium nitrate hexahydrate, and 1.53g of cesium nitrate and dissolve them in deionized water. After complete dissolution, obtain a mixed precursor solution IV containing nickel, cerium, and cesium.

[0112] Molybdenum-containing precursor solution I was slowly heated to 70°C with stirring, and the stirring rate was adjusted to 120 r / min. Then, bismuth-containing precursor solution II, a mixture of cobalt and iron precursor solutions III, and a mixture of nickel, cerium, and cesium precursor solutions IV were slowly added to obtain solution V. Solution V was then heated to 85°C, the pH of the solution was adjusted to 6, and stirring was continued for 1 h.

[0113] Step 2: Transfer the above solution to a hydrothermal synthesis reactor and crystallize it at 190℃ for 30 hours. After crystallization, dry it to obtain the catalyst precursor.

[0114] Step 3: The catalyst precursor was calcined in air at 450°C for 6 hours and then cooled to room temperature to obtain the catalyst Cat-MAL-3 for the oxidation of isobutylene to methacrolein.

[0115] The catalyst samples prepared in the above examples were evaluated for their activity in a fixed-bed single-tube reactor heated by a salt bath. The reactants, isobutylene, oxygen, and water vapor, were preheated before entering the single-tube reactor. The catalyst loading was 15 mL, the salt bath temperature was 300-380 °C, and the gas hourly space velocity (GSHV) was 900-1500 mL / (g·h). The gas composition consisted of 9%-15% isobutylene, 20%-65% oxygen, and the remainder water vapor. The gas was pumped from a gas cylinder through a pressure reducing valve and a preheater into a mixer for mixing. Water was injected into a vaporizer via a micro-flow pump, vaporized at 200 °C, and then mixed with isobutylene and oxygen before entering the reactor. Specific catalytic activities are shown in Table 1.

[0116] Table 1

[0117]

[0118]

[0119] According to the results in Table 1:

[0120] The catalyst in Example 1 contains Mo, Bi, Co, and Fe, while the catalyst in Example 2 contains Mo, Bi, Co, Fe, Ni, Ce, and Cs. The doping of Ni, Ce, and Cs mainly regulates the active valence state and acidity / basicity of the catalyst, while the addition of hydroxyl polycarboxylic acid promotes and amplifies the performance of the catalyst and the other doped elements (Ni, Ce, and Cs).

[0121] The catalyst in Example 1 incorporates a hydroxylated polycarboxylic acid, whose elements include Mo, Bi, Co, and Fe. The catalyst in Comparative Example 1 was prepared without the introduction of a hydroxylated polycarboxylic acid. The catalyst in Example 1 showed improved isobutylene conversion and selectivity and yield of methacrolein compared to Comparative Example 1. The catalyst in Example 2 incorporates a hydroxylated polycarboxylic acid, whose elements include Mo, Bi, Co, Fe, Ni, Ce, and Cs. The catalyst in Comparative Example 2 was prepared without the introduction of a hydroxylated polycarboxylic acid. The performance of Example 2 was significantly improved compared to the Comparative Example. This is mainly because the purpose of introducing the polycarboxylic acid is to block the dispersed oxide lattice clusters, inhibit the formation of large particle structures, and fully expose the active defect sites of the catalyst. Therefore, the more fully the effective active components in the catalyst are exposed on the surface through the hydroxylated polycarboxylic acid, the greater the catalytic activity can be improved.

[0122] Example 2 used citric acid, achieving an isobutylene conversion of 96.7%, a methacrolein selectivity of 85.6%, and a methacrylic acid yield of 82.8%. Examples 3-5, using lactic acid, tartaric acid, and glycolic acid respectively, all showed lower performance than Example 4. This indicates that the type of hydroxylated polycarboxylic acid selected during pretreatment significantly impacts catalyst performance. Citric acid, with its large molecular weight and abundant carboxyl and hydroxyl groups, possesses a strong ability to anchor active sites, facilitating the full exposure of these sites. Therefore, catalysts prepared with citric acid exhibit better performance.

[0123] Example 2 used citric acid, achieving an isobutylene conversion of 96.7%, a methacrolein selectivity of 85.6%, and a methacrylic acid yield of 82.8%. Example 8, on the other hand, used two hydroxylated polycarboxylic acids, citric acid and lactic acid, achieving an isobutylene conversion of 98.3%, a methacrolein selectivity of 86.8%, and a methacrylic acid yield of 85.3%. This indicates that the catalyst obtained by treating with a mixture of multiple hydroxylated polycarboxylic acids exhibits superior performance compared to treatment with a single hydroxylated polycarboxylic acid. In particular, the combination of citric acid and lactic acid, with their varying molecular sizes, allows for more complete bonding of the hydroxylated polycarboxylic acids to the catalyst precursor surface, resulting in a better catalyst performance.

Claims

1. A method for preparing a catalyst for the oxidation of isobutylene to methacrolein, wherein, The preparation method includes the following steps: Step 1: Mix the molybdenum-containing precursor solution I, the bismuth-containing precursor solution II, and the cobalt and iron-containing precursor solution III to obtain solution V; Step 2: Add the hydroxylated polycarboxylic acid to the solution V and carry out a crystallization reaction to obtain the catalyst precursor; Step 3: Calcining the precursor of the catalyst to obtain a catalyst for the oxidation of isobutylene to prepare methacrolein; The hydroxylated polycarboxylic acid is selected from one or more of glycolic acid, lactic acid, citric acid, malic acid, and tartaric acid.

2. The preparation method according to claim 1, wherein, The atomic ratio of molybdenum, bismuth, cobalt, and iron is (10-16):(0.6-10):(0.1-6):(0.5-5).

3. The preparation method according to claim 1, wherein, Step one also includes adding a precursor solution IV containing elements ABC, specifically including: mixing a molybdenum-containing precursor solution I, a bismuth-containing precursor solution II, a cobalt and iron-containing precursor solution III, and an ABC-containing precursor solution IV to obtain solution V; The catalyst for the oxidation of isobutylene to prepare methacrolein is shown in formula (1): Mo a Bi b Co c Feb d A e B f C g O x (1) A is selected from one or more of the following: nickel, magnesium, copper, lead, manganese, cerium, tellurium, antimony, tin, zinc, and tungsten. B is selected from one or more of zirconium, silicon, aluminum, phosphorus, sulfur, and boron; C is selected from one or more of potassium, sodium, cesium, calcium, barium, and thallium; x represents the total number of oxygen atoms required to satisfy the requirements of each oxide; a: b: c: d: e: f: g = (10-16): (0.6-10): (0.1-6): (0.5-5): (0-6): (0-15): (0-3).

4. The preparation method according to claim 1 or 3, wherein, In step two, the rate at which the hydroxyl polycarboxylic acid is added to solution V is 5-20 mL / min; And / or, the total molar ratio of the hydroxylated polycarboxylic acid to the metal element of the catalyst is (0.2-2):1; And / or, the crystallization reaction is carried out at a temperature of 150-250°C for a time of 18-36 hours.

5. The preparation method according to claim 1 or 3, wherein, In step three, the roasting temperature is 400-600℃ and the time is 2-6 hours.

6. The preparation method according to claim 1 or 3, wherein, Step one also includes heating the resulting solution V to react at a temperature of 70-85°C for 0.5-3 hours. And / or, during the heating process, the pH of solution V in the reaction is controlled to be 4.5-6.

5.

7. A catalyst for the oxidation of isobutylene to prepare methacrolein, which is prepared by the preparation method according to any one of claims 1-6.

8. The catalyst for the oxidation of isobutylene to methacrolein according to claim 7, wherein, It is prepared by the preparation method according to any one of claims 3-6; In equation (1), a:b:c:d:e:f:g=(10-16):(0.6-10):(0.1-6):(0.5-5):(1-6):(0-15):(0.01-3).

9. The catalyst for the oxidation of isobutylene to prepare methacrolein according to claim 8, wherein, In equation (1), a:b:c:d:e:f:g = (10-16):(0.6-10):(0.1-6):(0.5-5):(1-6):(6-15):(0.01-3).

10. The catalyst for the oxidation of isobutylene to methacrolein according to any one of claims 7-9, wherein, A is selected from one or more of nickel, magnesium, copper, cerium, and antimony; B is selected from one or more of silicon, zirconium, aluminum, and boron; C is selected from potassium and / or cesium.

11. The application of a catalyst prepared by the method for preparing a catalyst for the oxidation of isobutylene to methacrolein as described in any one of claims 7-10 in the oxidation of isobutylene to methacrolein.

12. The application according to claim 11, wherein, The application includes the following steps: placing the catalyst in a fixed-bed reactor, mixing isobutylene, oxygen and water vapor, and then subjecting the mixture to an oxidation reaction under the action of the catalyst to produce methacrolein.

13. The application according to claim 12, wherein, The conditions for the oxidation reaction are: a reaction temperature of 300-380℃.

14. The application according to claim 12, wherein, The feed gas consists of 9%-15% isobutylene by volume, 20%-65% oxygen by volume, and the remainder is water vapor; the feed gas space velocity (GSHV) is 900-1500 mL / (g·h).

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