CN109569600B

CN109569600B - Catalyst for synthesizing methyl methacrylate and preparation method thereof

Info

Publication number: CN109569600B
Application number: CN201811446358.1A
Authority: CN
Inventors: 黄家辉; 吕强
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Weifang Sanli Benno Chemical Industry Co ltd; Dalian Institute of Chemical Physics of CAS
Priority date: 2018-11-29
Filing date: 2018-11-29
Publication date: 2020-09-15
Anticipated expiration: 2038-11-29
Also published as: CN109569600A

Abstract

The invention discloses a preparation method of a catalyst for synthesizing methyl methacrylate, which is prepared by a macromolecule protection method and comprises an active center and a carrier, wherein the active center comprises gold and two lanthanide metals, the carrier comprises silicon dioxide, aluminum oxide and one of alkali metal or alkaline earth metal, and the alkali metal or the alkaline earth metal exists in the catalyst in the form of oxide. The catalyst has the advantages of low Au loading capacity, simple preparation process, convenient operation, excellent activity, good stability, low catalyst price, high methacrolein conversion rate and MMA selectivity, and suitability for industrial production.

Description

Catalyst for synthesizing methyl methacrylate and preparation method thereof

Technical Field

The invention belongs to the technical field of catalyst preparation, and particularly relates to a catalyst for synthesizing methyl methacrylate, and a preparation method and application thereof.

Background

Methyl Methacrylate (MMA) is an important organic polymer monomer, and polymethyl methacrylate (PMMA) prepared by using the MMA as a raw material is widely applied to the fields of national defense and military industry, buildings, traffic transportation, advertisement decoration, cultural and educational sanitation, instruments and meters, daily necessities and the like; in addition, the coating composition has many applications in the fields of water-soluble coatings, emulsion paints and the like.

Currently, the production processes for producing MMA in the world mainly include the acetonitrilic alcohol process (ACH process), the isobutylene process and the ethylene process. In global MMA production capacity, the acetone cyanohydrin method accounts for 83%, the isobutylene method accounts for 16%, and the ethylene method accounts for 1%. The ACH method has the characteristics of simple process and high maturity, but hydrocyanic acid used as a raw material in the method is extremely toxic, hydrocyanic acid and sulfuric acid have strong corrosivity, the requirement on reaction equipment is high, the discharge amount of waste acid is large, and the method possibly causes great harm to the environment.

The methacrylic acid-methanol oxidation esterification method was first industrialized by Mitsubishi rayon in Japan over 20 years of research and development. The process is that isobutene and oxygen are oxidized in two steps under the action of molybdenum-based catalyst, i.e. isobutene is firstly oxidized into methacrolein, methacrolein is then oxidized into methacrylic acid, and methacrylic acid is finally esterified with methanol to produce MMA. The method is relatively simple, only three steps of reaction are needed, but methacrylic acid has strong corrosivity and higher requirement on equipment, and the production cost is increased.

The method directly uses air or oxygen as an oxidant, and directly oxidizes methacrolein and methanol into a target product MMA in one step is undoubtedly a simple and green process route with economic competitiveness, because no methacrylic acid is generated in the middle and no subsequent esterification process of methacrylic acid and methanol is generated, the production cost can be greatly saved, and meanwhile, the byproduct in the process is water, so that the method is green and environment-friendly. However, the difficulty of this process is in the preparation of the catalyst, and therefore, many attempts have been made to solve this problem. For example, Japanese Asahi chemical development has developed the oxidation of isobutylene to methacrolein, which is then subjected to oxidative esterification with methanol under the action of a Pd-Pb catalyst to prepare MMA. The process does not relate to methacrylic acid with strong corrosivity and has low requirements on reaction equipment. In addition, the process is very simple and requires only two reactions. The byproduct is only water, so the method is green and environment-friendly. Compared with the original MMA preparation process, the process has the advantages of lower raw material cost, high product purity, compact equipment and obviously reduced construction cost, but has high requirements on the design and preparation of the catalyst. The first generation of Pd-Pb catalysts has a low selectivity for MMA, about 84%, which increases the cost of subsequent separation and affects the quality of the product.

Subsequently, in subsequent researches, the japanese asahi chemical synthesis finds that the nano gold catalyst (Au @ NiOx) with the core-shell structure can efficiently catalyze the co-oxidation of methacrolein and methanol to prepare MMA, the process is simple, and the catalyst shows excellent stability. However, the catalyst has high preparation technical requirements, and when the conversion rate of methacrolein is 65%, the selectivity of MMA is about 95%, and in the practical application process, high activity (usually in terms of high conversion rate) is required to be ensured, and high selectivity of a target product can be maintained; in addition, the catalyst is also high in cost, and the cost is about 600 ten thousand per ton, so that the industrial application of the catalyst is limited to a certain extent.

Chinese patent publication No. CN107107034A discloses a gold-based catalyst for the oxidative esterification of aldehydes to obtain carboxylic esters, having gold as an active component and silicon, aluminum and other elements in the oxidized state as carriers, the other elements being selected from alkali metals, alkaline earth metals, rare earth metals, Ti, Zr, Cu, Mn, Pb, Sn or Bi, forming a catalyst in particle form, which catalyst can be used for the oxidative esterification of aldehydes to carboxylic esters over a long period of time, especially in a mixture containing water and a carboxylic acid. However, in the reaction of catalyzing the conversion of methacrolein into MMA, the catalyst has harsh catalytic conditions and single active center, so that the conversion rate of methacrolein and the selectivity of MMA are not ideal enough, and especially, the selectivity of MMA in an industrial scale-up test is not high, thereby affecting the product quality.

Disclosure of Invention

In order to make up the defects of the prior art, the invention provides the preparation method of the catalyst for synthesizing the methyl methacrylate and the synthesis method of the methyl methacrylate, the preparation process of the catalyst is simple, the operation is convenient, the catalyst has excellent activity and good stability, the conversion rate of the methacrolein and the selectivity of MMA are high, and the catalyst is suitable for industrial production.

The invention is realized by the following technical scheme:

the invention provides a catalyst for synthesizing methyl methacrylate, which is prepared by a macromolecule protection method; the catalyst comprises an active center and a carrier; the active center comprises gold and two lanthanide metals; the support comprises silica, alumina and one of an alkali metal or an alkaline earth metal; the alkali metal or alkaline earth metal is present in the catalyst in the form of an oxide; the gold and lanthanide metals are present in elemental form; in the catalyst, the mass ratio of the active center to the carrier is 0.51-3.96: 99.49-96.04.

Based on the technical scheme, preferably, the two lanthanide metals are any two of La, Ce, Pr and Nd

Based on the technical scheme, it is further preferable that the mass fraction of the lanthanide metal in the active center is 50-96%, and the preferable range is 55-95%. The lanthanide metal is added as an active center, so that the selectivity of methyl methacrylate can be greatly improved, and the two lanthanide metals are added as the active centers, so that the conversion rate of methacrolein can be effectively improved while the selectivity of methyl methacrylate is changed, and the stability of the catalyst is also influenced to a certain extent; the lanthanide metals comprise elements with atomic numbers of 57-71, but not all lanthanide metals can effectively improve the selectivity of methyl methacrylate, and the combination of any two lanthanide metals of La, Ce, Pr and Nd in the application can be synergistically catalyzed with Au active centers, so that the selectivity of methyl methacrylate is improved to the maximum extent, and the catalyst has positive effects of improving the conversion rate of methacrolein and the stability of the catalyst.

Based on the above technical scheme, preferably, in the carrier, SiO₂The mass fraction of (A) is in the range of 55-95%, preferably in the range of 60-85%; a1₂O₃The mass fraction is in the range of 4-44%, preferably in the range of 15-30%; the mass fraction of the alkali metal and the alkaline earth metal ranges from 1 to 25 percent.

Based on the technical scheme, preferably, the alkali metal or the alkaline earth metal is one of Rb, Cs, Mg and Sr; the alkali metal or alkaline earth metal as a carrier can increase the activity of the catalyst, improve the stability of the catalyst and protect Au particles from agglomeration.

In another aspect, the present invention provides a preparation method of the above catalyst for synthesizing methyl methacrylate, comprising the following steps:

(1) preparation of oxide carrier:

under the condition of stirring, uniformly mixing an alkali metal or alkaline earth metal precursor, a silicon dioxide precursor and an alumina precursor aqueous solution at the temperature of 10-90 ℃ (preferably 40-80 ℃), adding a certain amount of acid to adjust the pH value to 0.5-5.5 (preferably 1.5-4.0), continuously stirring for 1-24h to obtain a mixture, carrying out spray drying and forming on the mixture to obtain spherical particles with the particle size of 50-100 mu m, and roasting the spherical particles in an air atmosphere to obtain an oxide carrier;

(2) preparing a catalyst by a macromolecule protection method:

under the condition of stirring, fully mixing a gold precursor, a reducing agent and deionized water to obtain stable and uniform gold sol with a high dispersion state, sequentially adding two lanthanide series metal precursors and the oxide carrier prepared in the step (1) into the gold sol in the presence of a high-molecular protective agent, continuously stirring for 1-24h, slowly heating to 60-80 ℃, cooling to room temperature after stirring, standing, filtering, washing with deionized water until no chloride ion is detected, drying, and roasting in the air to obtain the catalyst.

Preferably, the acid in step (1) is one of nitric acid, sulfuric acid, hydrochloric acid and phosphoric acid, and nitric acid may be more preferred.

As a preferred scheme, in the step (1), the precursor of the alkali metal or the alkaline earth metal is a simple substance, an oxide, a hydroxide, other compounds or a compound of the corresponding metal, the precursor of the silicon dioxide is one of silica sol, solid silica gel and white carbon black, and the silica sol is preferred; the alumina precursor is one of aluminum nitrate, aluminum sulfate, aluminum phosphate, aluminum acetate or alumina powder, preferably aluminum nitrate, and can be selected according to actual conditions in industrial production.

Preferably, in the catalyst prepared in step (2), the precursor of Au is selected from, but not limited to, gold cyanide (Au (CN))₃) Potassium aurous cyanide, aurous chloride (AuC1), gold chloride (AuC1)₃) One or more than two of chloroauric acid, chloroauric acid salt, sodium gold sulfite or ranigold.

Preferably, in the catalyst obtained in step (2), the precursor of the lanthanide metal is selected from, but not limited to, the sulfate, nitrate, phosphate, carbonate, acetate of the corresponding metal.

Preferably, in the catalyst prepared in step (2), the reducing agent is selected from but not limited to sodium citrate, tetrakis (hydroxymethyl) phosphonium chloride (THPC), oxalic acid (H)₂C₂O₄) And sodium borohydride.

Preferably, in the catalyst prepared in step (2), the polymeric protectant is selected from, but not limited to, polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), tetrakis (hydroxymethyl) phosphonium chloride (THPC), poly (dimethyl-ammonium chloride) (PDDA), sodium citrate, and thiol.

Preferably, in the catalyst obtained in step (2), the lanthanide metal: gold element: reducing agent: high-molecular protective agent: carrier: the mass ratio of the water is 1 (0.02-0.98), (0.2-0.5), (50-200), (200-400).

The invention also provides application of the catalyst for synthesizing the methyl methacrylate, and relates to a method for synthesizing the methyl methacrylate.

Based on the above technical scheme, preferably, the synthesis method of methyl methacrylate comprises the following steps: adding the reaction raw materials into a reactor, fully mixing, and adding the catalyst for synthesizing the methyl methacrylate into the reactor; sealing the reactor, starting stirring, introducing air and inert gas at the bottom of the reactor at the speed of 0.8-1.3L/min and 2.5-3.2L/min respectively, adding reaction raw materials into the reactor at the speed of 8-12ml/min by adopting a liquid constant flow pump, and storing a product after reaction in a storage tank at the same speed as the adding speed of the reaction raw materials; the mass concentration of methanol in the reaction mixture is 50-70%, and the reaction raw material and the catalyst form a reaction system; the mass concentration of the catalyst in a reaction system is 15-20%.

Based on the technical scheme, preferably, the materials in the reactor start to react at 80 ℃, products in the storage tank can be taken out at certain intervals for gas chromatographic analysis, and the conversion rate of the methacrolein and the selectivity of the target product methyl methacrylate are calculated. The reaction indexes obtained after the reaction for 150-200h are as follows: the conversion rate of methacrolein is more than or equal to 97%, the selectivity of methyl methacrylate is more than or equal to 98%, and after the continuous reaction for 4000 hours, the active center on the catalyst is not lost.

Advantageous effects

The invention has the beneficial effects that: the invention adopts a macromolecule protection method to prepare the catalyst with multiple metal active centers. The preparation of the supported catalyst by the macromolecule protection method has low requirements on the carrier, wide optional range, high activity of the obtained active center and stable performance. The gold active center and the two lanthanide metal active centers are cooperatively catalyzed, so that the activity of the catalyst is improved, the conversion rate of the methacrolein is improved, the selectivity of the methyl methacrylate is improved, and the catalytic effect of the catalyst is superior to that of all gold-based catalysts on the market. And the active center Au and lanthanide metal still stably exist on the catalyst after the continuous reaction for 4000h without loss. The active center Au prepared by the macromolecule protection method has small and uniform granularity, high activity, simple preparation process of the catalyst, convenient operation, low production cost, good stability, long service life and low load capacity, so that the catalyst has low price and is suitable for large-scale industrial production.

Drawings

FIG. 1 is an electron micrograph of the catalyst prepared in example 6.

Detailed Description

The present invention will be described in further detail with reference to specific embodiments thereof to assist those skilled in the art in providing a more complete, accurate and thorough understanding of the inventive concept and aspects thereof, and the scope of the present invention includes, but is not limited to, the following examples, and any modifications in the details and form of the technical aspects thereof that fall within the spirit and scope of the present application are intended to be included therein.

Example 1

Weighing 50kg of silica sol (30 wt%) under the condition of stirring, adding 9kg of aluminum nitrate during stirring, adding 7kg of magnesium nitrate after dissolution, uniformly mixing at 50 ℃, adding 250ml of concentrated nitric acid to adjust the pH value, continuously stirring for 24 hours at 50 ℃, cooling to room temperature, and then carrying out spray drying, wherein the spray conditions are as follows: 10ml/min, inlet temperature 200-₂-Al₂O₃MgO powder, then roasting the powder for 6h at 700 ℃ in an air atmosphere, and cooling to room temperature for later use.

Under the condition of stirring, 250g of chloroauric acid, 275g of sodium citrate and 60L of deionized water are fully mixed to obtain stable and uniform gold sol with a high dispersion state, 280g of polyvinylpyrrolidone (PVP, molecular weight 8000,10000) is added under the condition of stirring, then 940g of lanthanum nitrate and 935g of cerium nitrate are sequentially added to be completely dissolvedAfter decomposition, 30kg of the SiO prepared above was added₂-Al₂O₃MgO powder, continuously stirring and slowly heating to 75 ℃, continuously stirring at the temperature for 14h, then cooling to room temperature, standing, pouring out an upper layer liquid, washing a lower layer precipitate by deionized water until no chloride ion is detected in the solution, drying at 100 ℃ for 24h, and then roasting in 300 ℃ air for 24h to obtain the catalyst La-Ce-Au/SiO₂-Al₂O₃-MgO. Wherein the mass percentage of La, Ce and Au in the catalyst is respectively 1%, 1% and 0.48%.

Example 2

The support was shaped under the same conditions as in example 1, in which magnesium nitrate was replaced with rubidium nitrate under the same mass fraction of metal to obtain spherical SiO having a particle size of about 70 μm₂-Al₂O₃And (4) baking the RbO powder at 700 ℃ in an air atmosphere for 6 hours, and cooling to room temperature for later use.

The catalyst preparation conditions were the same as in example 1 to obtain the catalyst La-Ce-Au/SiO₂-Al₂O₃-RbO, wherein the mass percentages of La, Ce and Au in the catalyst are respectively 1%, 1% and 0.48%.

Example 3

The support was shaped under the same conditions as in example 1, in which magnesium nitrate was replaced with cesium nitrate under the same metal mass fraction to give a spherical SiO having a particle size of about 70 μm₂-Al₂O₃-CsO powder, then roasting the powder for 6h at 700 ℃ in an air atmosphere, and cooling to room temperature for later use.

The catalyst preparation conditions were the same as in example 1 to obtain the catalyst La-Ce-Au/SiO₂-Al₂O₃-CsO, wherein the mass percentages of La, Ce and Au in the catalyst are respectively 1%, 1% and 0.48%.

Example 4

The support was shaped under the same conditions as in example 1, in which magnesium nitrate was replaced with strontium nitrate under the same metal mass fraction to give a spherical SiO having a particle size of about 70 μm₂-Al₂O₃SrO powder, and then the powder is roasted for 6 hours at 700 ℃ in an air atmosphere and cooled to room temperature for later use.

The catalyst preparation conditions were the same as in example 1 to obtain the catalyst La-Ce-Au/SiO₂-Al₂O₃SrO, wherein the mass percentages of La, Ce and Au in the catalyst are respectively 1%, 1% and 0.48%.

Example 5

The support was shaped under the same conditions as in example 2 to give a spherical SiO particle size of about 70 μm₂-Al₂O₃And (4) baking the RbO powder at 700 ℃ in an air atmosphere for 6 hours, and cooling to room temperature for later use.

The catalyst preparation conditions were the same as in example 2, in which lanthanum nitrate was replaced with praseodymium nitrate under the same metal mass fraction conditions to obtain the catalyst Pr-Ce-Au/SiO₂-Al₂O₃-RbO, wherein the mass percentages of Pr, Ce and Au in the catalyst are respectively 1%, 1% and 0.48%.

Example 6

The catalyst preparation conditions were the same as example 2, in which lanthanum nitrate was replaced with neodymium nitrate under the same metal mass fraction conditions to obtain the catalyst Nd-Ce-Au/SiO₂-Al₂O₃and-RbO, wherein the mass percentages of Nd, Ce and Au in the catalyst are respectively 1%, 1% and 0.48%, and as can be seen from an electron microscope image of figure 1, the obtained catalyst has very good sphericity and a very smooth surface.

Example 7

The catalyst preparation conditions were the same as in example 2, in which cerium nitrate was replaced with praseodymium nitrate under the same metal mass fraction conditions to obtain the catalyst La-Pr-Au/SiO₂-Al₂O₃-RbO, wherein La,Pr and Au account for 1 percent, 1 percent and 0.48 percent respectively by mass in the catalyst.

Example 8

The catalyst preparation conditions were the same as in example 2, in which cerium nitrate was replaced with neodymium nitrate under the same metal mass fraction conditions to obtain the catalyst La-Nd-Au/SiO₂-Al₂O₃-RbO, wherein the mass percentages of La, Nd and Au in the catalyst are respectively 1%, 1% and 0.48%.

Example 9

The catalyst preparation conditions were the same as in example 2, in which lanthanum nitrate was replaced with praseodymium nitrate and cerium nitrate was replaced with neodymium nitrate under the same metal mass fraction conditions, to obtain the catalyst Pr-Nd-Au/SiO₂-Al₂O₃-RbO, wherein the mass percentages of Pr, Nd and Au in the catalyst are respectively 1%, 1% and 0.48%.

Example 10

The support was shaped under the same conditions as in example 6 to give a spherical SiO particle size of about 70 μm₂-Al₂O₃And (4) baking the RbO powder at 700 ℃ in an air atmosphere for 6 hours, and cooling to room temperature for later use.

The catalyst was prepared under the same conditions as in example 6, except that the precursor of the Au component was changed to Au (CN)₃The reducing agent is replaced by Tetrakis Hydroxymethyl Phosphonium Chloride (THPC), the macromolecular protective agent is replaced by poly dimethyl diallyl ammonium chloride (PDDA), and the catalyst Nd-Ce-Au/SiO is obtained₂-Al₂O₃-RbO, wherein the mass percentages of Nd, Ce and Au in the catalyst are respectively 1%, 1% and 0.48%.

Example 11

The catalyst was prepared under the same conditions as in example 6, except that the precursor of the Au component was replaced with gold potassium cyanide and the reducing agent was replaced with oxalic acid (H)₂C₂O₄) The macromolecular protective agent is changed into polyvinyl alcohol (PVA) to obtain the catalyst Nd-Ce-Au/SiO₂-Al₂O₃-RbO, wherein the mass percentages of Nd, Ce and Au in the catalyst are respectively 1%, 1% and 0.48%.

Example 12

The preparation conditions of the catalyst were the same as in example 6, in which the precursor of the Au component was replaced with sodium gold sulfite, the reducing agent was replaced with sodium borohydride, and the polymeric protective agent was replaced with Tetrakis Hydroxymethyl Phosphonium Chloride (THPC), thereby obtaining the catalyst Nd-Ce-Au/SiO₂-Al₂O₃-RbO, wherein the mass percentages of Nd, Ce and Au in the catalyst are respectively 1%, 1% and 0.48%.

Comparative example 1

The catalyst Au/SiO was prepared by the method and preparation procedure of example 20 in CN107107034A₂-Al₂O₃-MgO. Wherein the mass percentage of Au in the catalyst is 0.48 percent respectively, and the performance of the catalyst is shown in the table.

Comparative example 2

The catalyst preparation conditions were the same as in example 6, except that neodymium nitrate was not added to obtain the catalyst Ce-Au/SiO₂-Al₂O₃RbO, wherein Ce, Au are in the catalystThe mass percentage of the components is 1 percent and 0.48 percent respectively.

Comparative example 3

The catalyst preparation conditions were the same as in example 6, in which cerium nitrate was not added to obtain a catalyst Nd-Au/SiO₂-Al₂O₃-RbO, wherein the mass percentages of Nd and Au in the catalyst are respectively 1% and 0.48%.

Comparative example 4

The catalyst preparation conditions were the same as in example 6, wherein cerium nitrate and neodymium nitrate were not added to obtain the catalyst Au/SiO₂-Al₂O₃-RbO, wherein the mass percentage of Au in the catalyst is 0.48 percent respectively.

Comparative example 5

Under the condition of stirring, fully mixing 750g of chloroauric acid, 775g of sodium citrate and 60L of deionized water to obtain stable and uniform gold sol with a high dispersion state, adding 780g of polyvinylpyrrolidone (PVP, molecular weight 8000-10000) under the condition of stirring, then sequentially adding 940g of lanthanum nitrate and 935g of cerium nitrate, after complete dissolution, adding 30kg of the prepared SiO₂-Al₂O₃MgO powder, continuously stirring and slowly heating to 75 ℃, continuously stirring at the temperature for 14h, then cooling to room temperature, standing, pouring out an upper layer liquid, washing a lower layer precipitate by deionized water until no chloride ion is detected in the solution, drying at 100 ℃ for 24h, and then roasting in 300 ℃ air for 24h to obtain the catalyst La-Ce-Au/SiO₂-Al₂O₃-MgO. Wherein the mass percentage of La, Ce and Au in the catalyst is respectively 1%, 1% and 1.4%.

Example 13

The catalysts described in examples 1 to 12 and comparative examples 1 to 5 were applied to the synthesis of methyl methacrylate under the same conditions, respectively:

the method comprises the steps of fully mixing 2000mL of mixed material of methacrolein and methanol in a 3L stainless steel high-pressure reaction kettle, adding 280g of catalyst, fully mixing, wherein the concentration of methacrolein is 30 wt%, sealing the reaction kettle, starting stirring, starting reaction when the temperature of a system is raised to 80 ℃, introducing air and nitrogen at the bottom of the reaction kettle at the speed of 1L/min and 3L/min respectively, adding reaction raw materials into the reaction kettle at the speed of 10mL/min by adopting a liquid constant-flow feeding pump, continuously discharging generated products to a storage tank, taking out feed liquid at regular intervals, analyzing the discharged liquid by using a gas chromatograph, calculating the conversion rate of methacrolein and the selectivity of methyl methacrylate by using n-decane as an internal standard substance, and reacting for 200 hours.

Example 14

The method comprises the following steps of fully mixing 2000mL of mixed material of methacrolein and methanol in a 3L stainless steel high-pressure reaction kettle, adding 280g of the catalyst in the embodiment 1, fully mixing, wherein the concentration of methacrolein is 30 wt%, sealing the reaction kettle, starting stirring, starting the reaction when the temperature of the system is raised to 80 ℃, introducing air and nitrogen at the bottom of the reaction kettle at the rates of 1L/min and 3L/min respectively, adding reaction raw materials into the reaction kettle at the rate of 10mL/min by using a liquid constant-flow feeding pump, continuously discharging generated products to a storage tank, taking out feed liquid at regular intervals, analyzing the discharged liquid by using a gas chromatograph, calculating the conversion rate of methacrolein and the selectivity of methyl methacrylate by using n-decane as an internal standard substance, and reacting for 4000 hours. The results are shown in the following table, and it can be seen from the table that the catalyst prepared by the present invention has better conversion rate of methacrolein and selectivity of methyl methacrylate, and it can be seen that the addition of the lanthanide metal improves the activity of the catalyst, so that the conversion rate and selectivity are improved. The catalyst in the comparative example was lower in performance than the catalyst prepared in the present invention, and the performance of the catalyst was reduced after increasing the loading amount of Au. The catalytic performance of the catalyst is lower when only one lanthanide metal is added than when two metals are added.

Claims

1. A catalyst for synthesizing methyl methacrylate, which is characterized in that: the catalyst comprises an active center and an oxide carrier; the active center comprises gold and two lanthanide metals; the oxide support comprises silica, alumina and one of an alkali metal or an alkaline earth metal; the alkali metal or alkaline earth metal is present in the catalyst in the form of an oxide; in the catalyst, the mass ratio of the active center to the carrier is 0.51-3.96: 99.49-96.04;

the gold and lanthanide metals are present in elemental form;

the two lanthanide metals are any two of La, Ce, Pr and Nd.

2. The catalyst for the synthesis of methyl methacrylate according to claim 1, characterized in that: in the carrier, SiO₂The mass fraction of A1 is 55-95%₂O₃The mass fraction of the components is 4-44%; the mass fraction of alkali metal and alkaline earth metal is 1-25%.

3. The catalyst for the synthesis of methyl methacrylate as claimed in claim 1, wherein: the alkali metal or alkaline earth metal is one of Rb, Cs, Mg and Sr.

4. The catalyst for the synthesis of methyl methacrylate according to claim 2, characterized in that: in the active center, the mass fraction of lanthanide metal is 55-95%.

5. A method for preparing the catalyst for synthesizing methyl methacrylate according to any one of claims 1 to 4, characterized in that: the catalyst is prepared by adopting a macromolecule protection method, and specifically comprises the following steps:

(1) preparation of oxide support

Under the condition of stirring, uniformly mixing an alkali metal or alkaline earth metal precursor, a silicon dioxide precursor, an alumina precursor and water at the temperature of 10-90 ℃, adding a certain amount of acid to adjust the pH value to 0.5-5.5, continuously stirring for 1-24h to obtain a mixture, carrying out spray drying and forming on the mixture to obtain spherical particles with the particle size of 50-100 mu m, and roasting the spherical particles in an air atmosphere to obtain the oxide carrier;

(2) preparation of the catalyst

Under the condition of stirring, adding a gold precursor and a reducing agent into deionized water, mixing to obtain a gold sol, sequentially adding two lanthanide series metal precursors and the carrier prepared in the step (1) into the gold sol in the presence of a high-molecular protective agent, and heating to 60-80 DEG^oAnd C, continuously stirring for 1-24h, cooling to room temperature after stirring, standing, filtering, washing with deionized water until no chloride ion is detected, drying, and roasting in the air to obtain the catalyst.

6. The method for preparing a catalyst for the synthesis of methyl methacrylate according to claim 5, wherein: in the step (1), the acid is one of nitric acid, sulfuric acid, hydrochloric acid and phosphoric acid.

7. The method for preparing a catalyst for the synthesis of methyl methacrylate according to claim 5, wherein: in the step (1), the precursor of the alkali metal or the alkaline earth metal is a simple substance, an oxide, a hydroxide or a compound of the corresponding metal.

8. The method for preparing a catalyst for the synthesis of methyl methacrylate according to claim 5, wherein: in the step (2), the Au precursor is gold cyanide (Au (CN)₃) Potassium aurous cyanide, aurous chloride (AuC1), gold chloride (AuC1)₃) Chloroauric acid, chloroauric acid salt, sulfurous acidOne or more than two of sodium gold sulfate or gold.

9. The method for preparing a catalyst for the synthesis of methyl methacrylate according to claim 5, wherein: in the step (2), the precursor of the lanthanide metal is sulfate, nitrate, phosphate, carbonate or acetate of the corresponding metal.

10. The method for preparing a catalyst for the synthesis of methyl methacrylate according to claim 5, wherein: in the step (2), the reducing agent is selected from sodium citrate, tetrakis (hydroxymethyl) phosphonium chloride, oxalic acid and sodium borohydride; the polymer protective agent is polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), tetrakis (hydroxymethyl) phosphonium chloride (THPC), poly (dimethyl-ammonium chloride) (PDDA), sodium citrate, and thiol.

11. The method for preparing a catalyst for the synthesis of methyl methacrylate according to claim 5, wherein: the mass ratio of the lanthanide metal, gold, the reducing agent, the polymer protective agent, the carrier and water is 1: 0.02-0.98: 0.2-0.5: 50-200: 200-400.

12. The method for preparing a catalyst for the synthesis of methyl methacrylate according to claim 5, wherein: the precursor of the silicon dioxide is one of silica sol, solid silica gel and white carbon black.

13. The method for preparing a catalyst for the synthesis of methyl methacrylate according to claim 5, wherein: the precursor of the aluminum oxide is one of aluminum nitrate, aluminum sulfate, aluminum phosphate, aluminum acetate or aluminum oxide powder.

14. A method for synthesizing methyl methacrylate is characterized in that: the catalyst for synthesizing methyl methacrylate according to any one of claims 1 to 4 is used for catalytically synthesizing methyl methacrylate by a one-step oxidation method by using methacrolein and methanol as reaction raw materials.

15. The method for synthesizing methyl methacrylate according to claim 14, wherein: the method comprises the following steps: adding reaction raw materials into a reactor for full mixing, then adding the catalyst for synthesizing the methyl methacrylate into the reactor, sealing the reactor, and starting stirring; introducing air and inert gas at the bottom of the reactor at the speed of 0.8-1.3L/min and 2.5-3.2L/min respectively, adding reaction raw materials at the speed of 8-12ml/min by adopting a liquid constant flow pump, and storing the reacted product at the same speed as the reaction raw materials; the mass concentration of methanol in the reaction mixture is 50-70%, and the reaction raw material and the catalyst form a reaction system; the mass concentration of the catalyst in a reaction system is 15-20%.