Manganese-based catalysts for the oxidation esterification of unsaturated aldehydes to carboxylic acid esters, methods of making and methods of producing carboxylic acid esters

Abstract

The present application provides a kind of manganese-based support, the support contains the composite nanoparticles of manganese in oxidation state and X (X represents at least one element selected from the group consisting of cerium, praseodymium, samarium, erbium) and the carrier of the composite nanoparticles before loading, the composite nanoparticle support is " eggshell " structure, wherein the surface of shell layer contains little active component, and active component is mainly distributed in the local area below the outer surface of nanoparticle support.The catalyst is used for catalyzing the reaction of unsaturated fatty aldehyde oxidation esterification to synthesize unsaturated carboxylic acid ester.The catalyst of the present application does not contain noble metal relative to existing catalyst, has good water resistance, good acid and alkali resistance, can still maintain higher mechanical strength and chemical stability during long time reaction process, and has the advantages such as simple preparation method and low cost.

Description

Technical Field

[0001] The present invention relates to an "eggshell" type composite particle support on which composite particles composed of manganese in an oxidized state and X (X represents at least one element selected from the group consisting of iron, cerium, praseodymium, neodymium, samarium and europium) are loaded on a support, and a method for manufacturing the composite particle support as a catalyst for the production of unsaturated carboxylic acid esters. Background Technology

[0002] Methyl methacrylate (MMA) is an important polymeric monomer that can be polymerized to produce multi-component copolymers or polymethyl methacrylate. It is mainly used in plexiglass, and is also used in the manufacture of other resins, plastics, coatings, adhesives, lubricants, impregnating agents for wood and cork, paper varnishes, etc., with a wide range of applications.

[0003] Currently, the main industrial processes for producing methyl methacrylate include the traditional acetone cyanohydrin process and the isobutylene oxidation process. Compared with the acetone cyanohydrin process, the isobutylene oxidation process uses abundant C4 resources from oil refineries as raw material, with water as a byproduct, making it more environmentally friendly and attracting increasing attention.

[0004] Currently, the main developed processes for isobutylene oxidation include direct oxidation (three-step method) and direct methyl esterification (two-step method). Among these, the catalysts reported for the one-step oxidation and esterification of unsaturated aldehydes to unsaturated carboxylic acid esters in the direct methyl ester method are mostly palladium-lead catalysts, such as: US5969178, US6107515, EP0890569, EP0972759, JP58154534, JP8332383, JP10263399, JP20032241345, JP2003305366, etc. However, the catalysts in these patents have a high content of palladium, the main active component, which leads to problems such as low conversion rate, numerous byproducts, and poor selectivity in the reaction. To improve efficiency, Asahi Kasei Corporation developed a series of Au-supported catalysts for one-step oxidative esterification to prepare methyl methacrylate (MMA) using patents CN 101815579A, CN101835532A, and CN103097296, achieving conversion rates of 40-76% and selectivity of approximately 97%. To further enhance reaction performance, CN101835532 controlled the distribution of nickel-gold composite particles within the support to form a NiOAu / SiO2-Al2O3-MgO catalyst with a specific range of supported layers. When used in the reaction, the MAL conversion was 75.4% and the MMA selectivity was 97.2% after 500 hours of reaction, and 75.1% and 97.1% after 2000 hours, demonstrating high efficiency and minimal change in reactivity over long periods, effectively addressing the aforementioned issues. Meanwhile, Evonik's patent CN107107034A reported solving the catalyst water resistance problem by using a specific combination of gold, silicon oxides, and aluminum oxides as catalyst components. However, it is still not free from the restrictions of precious metals, and in addition, due to technological monopoly, it cannot meet the market demand in my country. Summary of the Invention

[0005] Our research group provides a manganese-based composite particle catalyst for the oxidative esterification of unsaturated aldehydes to prepare carboxylic acid esters. Compared to existing catalysts, this catalyst is free of precious metals, exhibits good water resistance and acid / alkali resistance, maintains high mechanical strength and chemical stability during prolonged reactions, and boasts advantages such as simple preparation method and low cost. When used in the catalytic synthesis of methyl methacrylate, it achieves a maximum conversion rate of over 98% for methacrolein and a maximum selectivity of 97% for methyl methacrylate, reducing the post-processing costs of other byproducts such as acetals and carboxylic acids.

[0006] The multi-component water-resistant catalyst provided in this patent has a "core-shell" structure, in which the shell layer contains very few MnmXn particles. These particles are mostly distributed in a localized area below the outer surface of the support. This structure has advantages such as simple preparation method, low cost, and good long-term reaction stability. The MnmXn particles are not uniformly loaded into the interior of the support, which reduces the diffusion resistance of the support to the reactants and products. The shell surface contains very few active components, which reduces the problems of active sites being covered and deactivated due to the adsorption of by-products and the accumulation of poisoning substances. At the same time, the "shell" of this catalyst can reduce the loss of active components caused by mechanical wear.

[0007] When this composite particle-supported material is used in the preparation reaction of unsaturated carboxylic acid esters, the conversion rate of methacrolein is the highest at over 98%, and the selectivity of methyl methacrylate is the highest at 97%. After 1000 hours of reaction, the activity of the catalyst remains basically unchanged, and only trace amounts of manganese are stripped and dissolved before and after the reaction, thus effectively solving the above-mentioned problems.

[0008] The implementation method of the present invention is as follows: A manganese-based catalyst for the oxidative esterification of unsaturated aldehydes to prepare carboxylic acid esters, wherein the catalyst contains manganese in its oxidized state and X supported on a support in an Mn / X atomic ratio ranging from 0.01 to 0.99 (preferably 0.3 to 0.8, more preferably 0.5 to 0.8). Among them, the valence state of manganese is a mixture of hexavalent and tetravalent, or a mixture of tetravalent and trivalent, or a mixture of trivalent and divalent, and X represents at least one element or two or more elements composed of cerium, praseodymium, samarium, and erbium.

[0009] The catalyst consists of composite nanoparticles of oxidized manganese and oxides of cerium (X), with particle sizes ranging from 2 to 100 nm. Transmission electron microscopy (TEM) observations revealed that nearly spherical nanoparticles of 2-3 nm in size were uniformly dispersed and loaded onto a support. Elemental analysis of the nanoparticles using energy-dispersive X-ray spectroscopy (EDS) showed that each particle contained both manganese and cerium, with cerium coating the surface of the manganese nanoparticles. In addition to the observed manganese and cerium-containing nanoparticles, separate manganese components were also observed loaded onto the support.

[0010] The carrier surface contains very few active components, which are mainly distributed in a localized area below the outer surface of the composite particle load. A comparison of Examples 7 and 8 suggests that manganese and X work together to load the carrier, possibly forming an alloy-like structure that alters their electron cloud state. EDX images of Example 8 show extremely low manganese content on the carrier surface. Furthermore, after titration of the remaining filtrate from the homogeneous precipitation method in Example 8, only 0.1 mmol of manganese and 0.4 mmol of cerium remained (i.e., 95% of the manganese and 90% of the cerium were immobilized on the carrier). This suggests that the active component composite particles are mainly distributed below the surface of the load.

[0011] The carrier is a composite oxide containing silicon dioxide, aluminum oxide, and other metal element oxides, wherein the molar proportion of the other elements other than oxygen is: 40-90 mol% silicon, 5.5-38 mol% aluminum, and 2-40 mol% other metal elements besides silicon and aluminum. Other elements are selected from one or more of the five elements: magnesium, iron, erbium, lanthanum, and cerium; (for example: silicon dioxide-aluminum oxide-magnesium oxide, silicon dioxide-aluminum oxide-magnesium oxide-iron oxide, silicon dioxide-aluminum oxide-lanthanum oxide, silicon dioxide-aluminum oxide-lanthanum oxide-erbium oxide, or silicon dioxide-aluminum oxide-magnesium oxide-cerium dioxide, etc.).

[0012] The specific surface area of ​​the carrier is 20-360m² 2 / g, pore size 3-80nm, pore capacity 0.1-1.0mL / g, particle size 10-510 µm.

[0013] The composition ratio of manganese to silicon oxide, expressed as Mn / Si atomic ratio, is 0.01-1.2.

[0014] The catalyst is prepared by first preparing a support, and then loading oxidized manganese and oxidized X onto the support; Preparation of composite oxide supports: A precursor of Al2O3, precursors of one or more oxides selected from MgO, Fe2O3, La2O3, Er2O3, and CeO2, and an aqueous solution of SiO2 precursor are mixed uniformly with concentrated nitric acid of 60%-85% by mass at 0-100℃ (preferably 30-50℃). The mixture is stirred and matured at 50-80℃ for 10-48 hours, then evaporated by rotary evaporation to remove water and dried to obtain a white solid powder. After calcination at 200-900℃, a composite oxide carrier is obtained. The material is roasted in a tube furnace under one or more atmospheres such as oxygen, air, nitrogen or argon, preferably under a nitrogen atmosphere; the roasting temperature is 200–900℃, preferably 400–600℃, and the roasting time is 2–20 h, preferably 2–8 h. The SiO2 precursor is selected from one or more of the following: 20-60 wt% silica sol, 60-400 mesh (preferably 200-300 mesh) column chromatography silica gel, and thin-layer chromatography silica gel; the amount of concentrated nitric acid used is 0.1-1.5 times the weight of silica sol and / or 1-4 times the weight of silica gel. The precursor of MgO is selected from one or more magnesium salts such as magnesium oxalate, magnesium acetate, magnesium nitrate, magnesium chloride, magnesium hydroxide, magnesium carbonate, or magnesium oxide. The precursor of Al2O3 is selected from one or more aluminum salts such as aluminum hydroxide, ammonium aluminum carbonate, ammonium aluminum sulfate, aluminum bicarbonate, aluminum nitrate, or aluminum trichloride. The precursor of Fe2O3 is selected from one or more iron salts such as ferric nitrate, ferric acetate, ferric oxalate, and ferric chloride. The precursor of La2O3 is selected from one or more lanthanum salts such as lanthanum nitrate and lanthanum acetate; The precursor of Er2O3 is selected from one or more erbium salts such as erbium nitrate, erbium acetate, and erbium oxalate; The precursor of CeO2 is selected from one or both of cerium nitrate and cerium ammonium nitrate.

[0015] Loading manganese in its oxidized state and X in its oxidized state onto a support comprises the following steps: Step 1: Prepare an aqueous solution containing soluble metal salts of manganese and X, add a precipitant and a composite oxide carrier, react at 50-100 °C for 0.5-3 h, cool the mixture to room temperature and filter to obtain the solid. The concentration of manganese in aqueous solution is 0.01-0.1 mol / L; The precipitant is selected from one or two of urea and hexamethyltetramine, and its concentration in aqueous solution is 0.05-1 mol / L; The soluble metal salts of manganese are one or more of manganese nitrate, manganese acetate, and manganese dichloride; The soluble metal salt of X is one or more of the following: cerium nitrate hexahydrate, cerium ammonium nitrate, praseodymium nitrate hexahydrate, praseodymium acetate, samarium nitrate, samarium acetate, erbium nitrate pentahydrate, and erbium acetate. The second step involves vacuum drying the obtained catalyst solid at 30-100℃, followed by high-temperature calcination to oxidize the manganese, and then cooling it down to obtain the catalyst. The calcination is carried out in a muffle furnace; the calcination temperature is 300–900℃, preferably 400–600℃, and the calcination time is 2–20h, preferably 2–8h.

[0016] In the presence of the aforementioned manganese-based catalyst and oxygen and / or air, unsaturated aldehydes are oxidatively esterified with methanol in one step to generate carboxylic acid esters. The reaction conditions are as follows: 2.5 g of the manganese-based catalyst is added to a fixed-bed reactor; a methanol solution with an unsaturated aldehyde mass fraction of 10-50% is continuously added at a rate of 5-30 mL / h; oxygen and / or air are bubbled in at a rate of 10-50 mL / h; the pressure is 1-5 kg / cm3; and the reaction is carried out continuously at 40℃-45℃ to produce carboxylic acid esters.

[0017] The unsaturated aldehyde is one or more of acrolein or methacrolein; The water content in the unsaturated aldehyde-methanol solution is less than 0.5%.

[0018] Catalyst evaluation: A certain amount of catalyst was weighed and added to a fixed-bed reactor, and unsaturated aldehydes and alcohols were continuously introduced. At the reaction temperature, air (a mixture containing oxygen or pure oxygen) was introduced, and stirring was started. After a certain reaction time, the reaction was stopped and samples were taken for analysis.

[0019] This catalyst is used to catalyze the oxidative esterification of unsaturated aliphatic aldehydes to synthesize unsaturated carboxylic acid esters. Compared with existing catalysts, the catalyst of this invention does not contain precious metals, has good water resistance and acid and alkali resistance, and can maintain high mechanical strength and chemical stability during long-term reactions. It also has the advantages of simple preparation method and low cost. Attached Figure Description

[0020] Figure 1 This is a transmission electron microscope (TEM) image of the catalyst for the production of carboxylic acid esters in Example 8.

[0021] Figure 2 This is a scanning electron microscope (SEM) image of the catalyst for the production of carboxylic acid esters in Example 8.

[0022] Figure 3 This is a scanning electron microscope (EDX) image of the surface of the catalyst for the production of carboxylic acid esters in Example 8. Detailed Implementation

[0023] The present invention is not limited to the following embodiments, and can be implemented in various ways within the scope of its spirit.

[0024] Carrier preparation examples Example 1 30% silica sol (pH=4.5) (20g, 10mmol), aluminum nitrate nonahydrate (3g, 8mmol), magnesium hydroxide (0.116g, 2mmol), 6g of 65% concentrated nitric acid, and 120mL of deionized water were mixed uniformly at 25℃. The mixture was then stirred and matured at 50℃ for 24h to obtain a homogeneous solid solution suspension. Water was removed by rotary evaporation, and the mixture was vacuum dried at 80℃ to obtain a white powder. This solid was placed in a tube furnace and calcined under nitrogen using a programmed temperature rise method: starting at 30℃, the temperature was increased to 300℃ at a rate of 2.25℃ / min, held at 300℃ for 4h, then starting at 300℃ again, the temperature was increased to 600℃ at a rate of 2.5℃ / min, and held at 600℃ for 4h. After natural cooling, a SiO2-Al2O3-MgO metal composite oxide support was obtained. The molar ratio of silicon, aluminum, and magnesium in this support was 50:40:10. The carrier has a specific surface area of ​​320m². 2 / g, pore size 8-20nm, pore capacity 0.7mL / g, particle size 10-50µm.

[0025] Example 2 30% silica sol (pH=4.5) (20g, 10mmol), aluminum nitrate nonahydrate (2.25g, 6mmol), magnesium hydroxide (0.058g, 1mmol), ferric nitrate nonahydrate (0.4g, 1mmol), 4g of 80% concentrated nitric acid, and 120mL of deionized water were mixed uniformly at 25℃. The mixture was then stirred and matured at 50℃ for 24h to obtain a homogeneous solid solution suspension. Water was removed by rotary evaporation, and the solution was vacuum dried at 80℃ to obtain a white powder. The solid was placed in a tube furnace and calcined under nitrogen atmosphere with a programmed temperature increase: 30-300℃ for 3h (heating rate 1.5℃ / min), held at 300℃ for 4h, then 300-600℃ for 3h (heating rate 1.7℃ / min), held at 600℃ for 4h. After natural cooling, a SiO2-Al2O3-MgO-Fe2O3 metal composite oxide support was obtained. The molar ratio of silicon, aluminum, magnesium, and iron in this carrier is 55.6:33.3:5.6:5.6. The specific surface area of ​​this carrier is 280 m². 2 / g, pore size 6-18nm, pore capacity 0.9mL / g, particle size 20-45µm.

[0026] Example 3 A mixture of 20 g (10 mmol) of 30% silica sol (pH=4.5), 2.25 g (6 mmol) of aluminum nitrate nonahydrate, 0.433 g (1 mmol) of lanthanum nitrate hexahydrate, 6 g of 60% concentrated nitric acid, and 120 mL of deionized water was stirred and matured at 50 °C for 24 h to obtain a homogeneous solid solution suspension. The suspension was removed by rotary evaporation and dried under vacuum at 80 °C to obtain a white powder. The solid was placed in a tube furnace and calcined under nitrogen atmosphere with a programmed temperature increase: 30-300 °C for 3 h (heating rate 1.5 °C / min), held at 300 °C for 4 h; 300-600 °C for 3 h (heating rate 1.7 °C / min), held at 600 °C for 4 h. After natural cooling, a SiO2-Al2O3-La2O3 metal composite oxide support was obtained. The molar ratio of silicon, aluminum, and lanthanum in this support was 58.8:35.3:5.9. The carrier has a specific surface area of ​​268m². 2 / g, pore size 10-22nm, pore capacity 0.8mL / g, particle size 23-50µm.

[0027] Example 4 30% silica sol (pH=4.5) (20 g, 10 mmol), aluminum nitrate nonahydrate (1.13 g, 3 mmol), lanthanum nitrate hexahydrate (0.433 g, 1 mmol), and erbium nitrate pentahydrate (0.443 g, 1 mmol), along with 6 g of 75% concentrated nitric acid and 120 mL of deionized water, were mixed thoroughly at 25 °C. The mixture was then stirred and matured at 50 °C for 24 h to obtain a homogeneous solid solution suspension. Water was removed by rotary evaporation, and the solution was vacuum dried at 80 °C to obtain a white powder. The solid was placed in a tube furnace and calcined under nitrogen atmosphere with a programmed temperature increase: 30-300 °C for 3 h (heating rate 1.5 °C / min), held at 300 °C for 4 h; 300-600 °C for 3 h (heating rate 1.7 °C / min), held at 600 °C for 4 h. After natural cooling, a SiO2-Al2O3-La2O3–Er2O3 metal composite oxide support was obtained. The molar ratio of silicon, aluminum, lanthanum, and erbium in this support was 66.7:20:6.7:6.6. The specific surface area of ​​this support was 278 m². 2 / g, pore size 8-20nm, pore capacity 0.9mL / g, particle size 13-43µm.

[0028] Example 5 30% silica sol (pH=4.5) (20 g, 10 mmol), aluminum nitrate nonahydrate (1.13 g, 3 mmol), magnesium hydroxide (0.058 g, 1 mmol), and cerium nitrate (0.434 g, 1 mmol), along with 6 g of 75% concentrated nitric acid and 180 mL of deionized water, were mixed uniformly at 25 °C. The mixture was then stirred and matured at 50 °C for 24 h to obtain a homogeneous solid solution suspension. Water was removed by rotary evaporation, and the solution was vacuum dried at 80 °C to obtain a white powder. The solid was placed in a tube furnace and calcined under nitrogen using a programmed temperature rise method: heating from 30-300 °C for 3 h (heating rate 1.5 °C / min), holding at 300 °C for 4 h, then heating from 300-600 °C for 3 h (heating rate 1.7 °C / min), holding at 600 °C for 4 h. After natural cooling, a SiO2-Al2O3-MgO-CeO2 metal composite oxide support was obtained. The molar ratio of silicon, aluminum, magnesium, and cerium in this carrier is 66.7:20:6.7:6.6. The specific surface area of ​​this carrier is 270 m². 2 / g, pore size 7-29nm, pore capacity 0.7mL / g, particle size 8-39µm.

[0029] Example 6 6 g of 200-300 mesh silica gel, 1.13 g (3 mmol) of aluminum nitrate nonahydrate, 0.058 g (1 mmol) of magnesium hydroxide, 3 g of 65% concentrated nitric acid, and 60 mL of deionized water were mixed uniformly at 25 °C. The mixture was then stirred and matured at 50 °C for 24 h to obtain a homogeneous solid solution suspension. The suspension was removed by rotary evaporation and dried under vacuum at 80 °C to obtain a white powder. This solid was placed in a tube furnace and calcined under nitrogen atmosphere with a programmed temperature increase: starting at 30 °C, the temperature was increased to 300 °C at a rate of 2.25 °C / min, held at 300 °C for 4 h, then increased to 600 °C starting at 300 °C at a rate of 2.5 °C / min, and held at 600 °C for 4 h. After natural cooling, a SiO2-Al2O3-MgO metal composite oxide support was obtained. The molar ratio of silicon, aluminum, and magnesium in this support was 71.4:21.4:7.2. The specific surface area of ​​this carrier is 293m². 2 / g, pore size 9-21nm, pore capacity 0.8mL / g, particle size 8-35µm.

[0030]

[0031] Catalyst Preparation Examples Example 7 In a reactor, 6 g of SiO2-Al2O3-MgO support A, 1.5 g of urea, 0.358 g of manganese nitrate (2 mmol), and 60 mL of deionized water were added sequentially and mixed thoroughly. The mixture was reacted at 80 °C for 0.5 h. After cooling to room temperature, the mixture was filtered (the remaining filtrate, after titration, showed a manganese content of 0.09 mmol). The resulting solid was vacuum dried at 80 °C for 1 h and then calcined in a muffle furnace at 500 °C for 3 h. After cooling, catalyst A1 was obtained. ICP analysis showed a manganese content of 1.7% with a valence state of +3.9 (a mixed valence state of tetravalent and trivalent manganese), and a Mn / Si atomic ratio of 0.0345. EDX electron imaging showed that the manganese content on the support surface was 0. SEM analysis determined the particle size of the active manganese to be 1-2 nm.

[0032] Example 8 In a reactor, 6 g of SiO2-Al2O3-MgO support A, 1.5 g of urea, 0.358 g of manganese nitrate (2 mmol), 1.74 g of cerium nitrate hexahydrate (4 mmol), and 100 mL of deionized water were added sequentially and mixed thoroughly. The mixture was reacted at 80 °C for 0.5 h. After cooling to room temperature, the mixture was filtered (the remaining filtrate, after titration, contained 0.10 mmol of manganese and 0.40 mmol of cerium). The resulting solid was vacuum dried at 80 °C for 1 h and then calcined in a muffle furnace at 500 °C for 3 h. After cooling, catalyst A2 was obtained. ICP analysis showed that the cerium content was 7.4% (mass content, the same below), the manganese content was 1.54% (mass content, the same below), the valence state was +4.1 (the valence state of manganese was a mixture of hexavalent and tetravalent valence states), the Mn / Ce atomic ratio was 0.530, and the Mn / Si atomic ratio was 0.0343. EDX electron imaging shows that the manganese content on the carrier surface is 0.001 of all elements (i.e., the carrier surface contains very few active components, which are mainly distributed in a local area below the outer surface of the composite particle load). SEM measurements of the active manganese-cerium composite particles show a particle size of 2-3 nm.

[0033] Example 9 In a reactor, 6 g of SiO2-Al2O3-MgO support A, 1.5 g of urea, 0.358 g of manganese nitrate (2 mmol), 1.33 g of erbium nitrate pentahydrate (3 mmol), and 60 mL of deionized water were added sequentially and mixed thoroughly. The mixture was reacted at 80 °C for 0.5 h. After cooling to room temperature, the mixture was filtered (the remaining filtrate, after titration, contained 0.11 mmol of manganese and 0.42 mmol of erbium). The resulting solid was vacuum dried at 80 °C for 1 h and then calcined in a muffle furnace at 500 °C for 3 h. After cooling, catalyst A3 was obtained. ICP analysis showed that the erbium content was 6.7%, the manganese content was 1.56%, the valence state was +4.1 (the manganese valence state was a mixture of hexavalent and tetravalent valences), the Mn / Er atomic ratio was 0.709, and the Mn / Si atomic ratio was 0.0341. EDX electron imaging shows that the manganese content on the carrier surface is 0.001 of all elements (i.e., the carrier surface contains very few active components, which are mainly distributed in a local area below the outer surface of the composite particle load). SEM measurements of the active manganese-erbium composite particles show a particle size of 2-3 nm.

[0034] Example 10 In a reactor, 6 g of SiO2-Al2O3-MgO support A, 1.5 g of urea, 0.358 g of manganese nitrate (2 mmol), 1 g of samarium nitrate (3 mmol), and 60 mL of deionized water were added sequentially and mixed thoroughly. The mixture was reacted at 80 °C for 0.5 h. After cooling to room temperature, the mixture was filtered (the remaining filtrate, after titration, contained 0.12 mmol of manganese and 0.41 mmol of samarium). The resulting solid was vacuum dried at 80 °C for 1 h and then calcined in a muffle furnace at 500 °C for 3 h. After cooling, catalyst A4 was obtained. ICP analysis showed that the samarium content was 6.1%, the manganese content was 1.57%, the valence state was +4.2 (the manganese valence state was a mixture of hexavalent and tetravalent), the Mn / Sm atomic ratio was 0.704, and the Mn / Si atomic ratio was 0.0344. EDX electron imaging showed that the manganese content on the carrier surface was 0 (i.e., the carrier surface contained very few active components, which were mainly distributed in a local area below the outer surface of the composite particle load). SEM measurements of the active manganese samarium composite particles showed a particle size of 2-3 nm.

[0035] Example 11 In a reactor, 6 g of SiO2-Al2O3-MgO support A, 1.5 g of urea, 0.358 g of manganese nitrate (2 mmol), 1.3 g of praseodymium nitrate hexahydrate (3 mmol), and 60 mL of deionized water were added sequentially and mixed thoroughly. The mixture was reacted at 80 °C for 0.5 h. After cooling to room temperature, the mixture was filtered (the remaining filtrate, after titration, contained 0.11 mmol of manganese and 0.42 mmol of praseodymium). The resulting solid was vacuum dried at 80 °C for 1 h and then calcined in a muffle furnace at 500 °C for 3 h. After cooling, catalyst A5 was obtained. ICP analysis showed that the praseodymium content was 5.7%, the manganese content was 1.58%, the valence state was +4.1 (the manganese valence state was a mixture of hexavalent and tetravalent valences), the Mn / Pr atomic ratio was 0.711, and the Mn / Si atomic ratio was 0.0341. EDX electron imaging shows that the manganese content on the carrier surface is 0.001 of all elements (i.e., the carrier surface contains very few active components, which are mainly distributed in a local area below the outer surface of the composite particle load). SEM measurements of the active manganese-praseodymium composite particles show a particle size of 2-3 nm.

[0036] Example 12 In a reactor, 6 g of SiO2-Al2O3-MgO-Fe2O3 support B, 0.8 g of hexamethyltetramine, 0.358 g of manganese nitrate (2 mmol), 1.33 g of erbium nitrate pentahydrate (3 mmol), and 60 mL of deionized water were added sequentially and mixed thoroughly. The mixture was reacted at 80 °C for 0.5 h. After cooling to room temperature, the mixture was filtered (the remaining filtrate, after titration, contained 0.10 mmol of manganese and 0.40 mmol of erbium). The resulting solid was vacuum dried at 80 °C for 1 h and then calcined in a muffle furnace at 500 °C for 3 h. After natural cooling, catalyst B was obtained. ICP analysis showed that the erbium content was 6.74%, the manganese content was 1.56%, the valence state was +4.2 (the manganese valence state was a mixture of hexavalent and tetravalent valences), the Mn / Er atomic ratio was 0.705, and the Mn / Si atomic ratio was 0.0325. EDX electron imaging showed that the manganese content on the carrier surface was 0 (i.e., the carrier surface contained very little active component, and the active component was mainly distributed in a local area below the outer surface of the composite particle load). SEM measurements of the active manganese-erbium composite particles showed a particle size of 2-3 nm.

[0037] Example 11 In a reactor, 6 g of SiO2-Al2O3-La2O3 support C, 0.8 g of hexamethyltetramine, 0.358 g (2 mmol) of manganese nitrate, and 60 mL of deionized water were added sequentially and mixed thoroughly. The mixture was reacted at 80 °C for 0.5 h. After cooling to room temperature, the mixture was filtered (the remaining filtrate, after titration, showed a manganese content of 0.09 mmol). The resulting solid was vacuum dried at 80 °C for 1 h and then calcined in a muffle furnace at 500 °C for 3 h. After natural cooling, catalyst C1 was obtained. ICP analysis showed a manganese content of 1.69% and a valence state of +3.9 (manganese in a mixed valence state of trivalent and tetravalent), with a Mn / Si atomic ratio of 0.0338. EDX electron imaging showed that the manganese content on the support surface was 0 (i.e., the support surface contained very little active component, and the active component was mainly distributed in a local area below the outer surface of the composite particle support). SEM analysis showed that the particle size of the active manganese particles was 1-2 nm.

[0038] Example 12 In a reactor, 6 g of SiO2-Al2O3-La2O3 support C, 0.8 g of hexamethyltetramine, 0.358 g of manganese nitrate (2 mmol), 1.30 g of cerium nitrate hexahydrate (3 mmol), and 60 mL of deionized water were added sequentially and mixed thoroughly. The mixture was reacted at 80 °C for 0.5 h. After cooling to room temperature, the mixture was filtered (the remaining filtrate, after titration, contained 0.09 mmol of manganese and 0.39 mmol of cerium). The resulting solid was vacuum dried at 80 °C for 1 h and then calcined in a muffle furnace at 500 °C for 3 h. After natural cooling, catalyst C2 was obtained. ICP analysis showed that the cerium content was 5.69%, the manganese content was 1.58%, the valence state was +4.1 (the valence state of manganese was a mixture of hexavalent and tetravalent valences), the Mn / Ce atomic ratio was 0.708, and the Mn / Si atomic ratio was 0.0335. EDX electron imaging shows that the manganese content on the carrier surface is 0.001 of all elements (i.e., the carrier surface contains very few active components, which are mainly distributed in a local area below the outer surface of the composite particle load). SEM measurements of the active manganese-cerium composite particles show a particle size of 2-3 nm.

[0039] Example 13 In a reactor, 6 g of SiO2-Al2O3-La2O3–Er2O3 support D, 1.5 g of urea, 0.358 g of manganese nitrate (2 mmol), and 60 mL of deionized water were added sequentially and mixed thoroughly. The mixture was reacted at 80 °C for 0.5 h. After cooling to room temperature, the mixture was filtered (the remaining filtrate, after titration, showed a manganese content of 0.10 mmol). The resulting solid was vacuum dried at 80 °C for 1 h and then calcined in a muffle furnace at 500 °C for 3 h. After cooling, catalyst D1 was obtained. ICP analysis showed a manganese content of 1.69% with a valence state of +4.0 and a Mn / Si atomic ratio of 0.0351. Electron microscopy (EM) images showed that the manganese content on the support surface was 0.001 of all elements (i.e., the support surface contained very few active components, which were mainly distributed in a localized area below the outer surface of the composite particle support). SEM analysis determined the particle size of the active manganese to be 1-2 nm.

[0040] Example 14 In a reactor, 6 g of SiO2-Al2O3-La2O3–Er2O3 support D, 1.5 g of urea, 0.358 g (2 mmol) of manganese nitrate, 1.33 g (3 mmol) of erbium nitrate pentahydrate, and 60 mL of deionized water were added sequentially and mixed thoroughly. The mixture was reacted at 80 °C for 0.5 h. After cooling to room temperature, the mixture was filtered (the remaining filtrate, after titration, contained 0.11 mmol of manganese and 0.42 mmol of erbium). The resulting solid was vacuum dried at 80 °C for 1 h and then calcined in a muffle furnace at 500 °C for 3 h. After cooling, catalyst D2 was obtained. ICP analysis showed that the erbium content was 13.47%, the manganese content was 1.564%, the valence state was +4.2 (the manganese valence state was a mixture of hexavalent and tetravalent valences), the Mn / Er atomic ratio was 0.353, and the Mn / Si atomic ratio was 0.0353. EDX electron imaging showed that the manganese content on the carrier surface was 0.002 of all elements (i.e., the carrier surface contained very few active components, which were mainly distributed in a localized area below the outer surface of the composite particle load). SEM measurements of the active manganese-erbium composite particles showed a particle size of 2-3 nm.

[0041] Example 15 In a reactor, 6 g of SiO2-Al2O3-MgO-CeO2 support E, 0.8 g of hexamethyltetramine, 0.358 g of manganese nitrate (2 mmol), and 60 mL of deionized water were added sequentially and mixed thoroughly. The mixture was reacted at 80 °C for 0.5 h. After cooling to room temperature, the mixture was filtered (the remaining filtrate, after titration, showed a manganese content of 0.09 mmol). The resulting solid was vacuum dried at 80 °C for 1 h and then calcined in a muffle furnace at 500 °C for 3 h. After cooling, catalyst E1 was obtained. ICP analysis showed a manganese content of 1.69% and a valence state of +3.9 (manganese in a mixed valence state of trivalent and tetravalent), with a Mn / Si atomic ratio of 0.0306. EDX electron imaging showed that the manganese content on the support surface was 0 (i.e., the support surface contained very little active component, and the active component was mainly distributed in a local area below the outer surface of the composite particle support). SEM analysis showed that the particle size of the active manganese particles was 1-2 nm.

[0042] Example 16 In a reactor, 6 g of SiO2-Al2O3-MgO-CeO2 support E, 0.8 g of hexamethyltetramine, 0.358 g of manganese nitrate (2 mmol), 1.33 g of erbium nitrate pentahydrate (3 mmol), and 60 mL of deionized water were added sequentially and mixed thoroughly. The mixture was reacted at 80 °C for 0.5 h. After cooling to room temperature, the mixture was filtered (the remaining filtrate, after titration, contained 0.09 mmol of manganese and 0.39 mmol of erbium). The resulting solid was vacuum dried at 80 °C for 1 h and then calcined in a muffle furnace at 500 °C for 3 h. After cooling, catalyst E2 was obtained. ICP analysis showed that the erbium content was 6.73%, the manganese content was 1.56%, the valence state was +4.1 (the manganese valence state was a mixture of hexavalent and tetravalent valences), the Mn / Er atomic ratio was 0.706, and the Mn / Si atomic ratio was 0.0304. EDX electron imaging showed that the manganese content on the carrier surface was 0 (i.e., the carrier surface contained very little active component, and the active component was mainly distributed in a local area below the outer surface of the composite particle load). SEM measurements of the active manganese-erbium composite particles showed a particle size of 2-3 nm.

[0043] Example 17 In a reactor, 6 g of SiO2-Al2O3-MgO-CeO2 support E, 0.8 g of hexamethyltetramine, 0.358 g of manganese nitrate (2 mmol), 1.30 g of cerium nitrate hexahydrate (3 mmol), and 60 mL of deionized water were added sequentially and mixed thoroughly. The mixture was reacted at 80 °C for 0.5 h. After cooling to room temperature, the mixture was filtered (the remaining filtrate, after titration, contained 0.09 mmol of manganese and 0.39 mmol of erbium). The resulting solid was vacuum dried at 80 °C for 1 h and then calcined in a muffle furnace at 500 °C for 3 h. After cooling, catalyst E3 was obtained. ICP analysis showed that the cerium content was 7.81%, the manganese content was 1.58%, the valence state was +4.2 (the manganese valence state was a mixture of hexavalent and tetravalent valences), the Mn / Ce atomic ratio was 0.516, and the Mn / Si atomic ratio was 0.0305. EDX electron imaging shows that the manganese content on the carrier surface is 0.001 of all elements (i.e., the carrier surface contains very few active components, which are mainly distributed in a local area below the outer surface of the composite particle load). SEM measurements of the active manganese-cerium composite particles show a particle size of 2-3 nm.

[0044] Example 18 6g of SiO2-Al2O3-MgO support F, 1.5g of urea, 0.358g of manganese nitrate (2mmol), and 60mL of deionized water were added sequentially to a reactor and mixed thoroughly. The mixture was reacted at 80℃ for 0.5h. After cooling to room temperature, the mixture was filtered (the remaining filtrate, after titration, showed a manganese content of 0.09mmol). The resulting solid was vacuum dried at 80℃ for 1h and then calcined in a muffle furnace at 500℃ for 3h. After cooling, catalyst F1 was obtained. ICP analysis showed a manganese content of 1.6% with a valence state of +3.9 (manganese in a mixed valence state of trivalent and tetravalent), and a Mn / Si atomic ratio of 0.0251. EDX electron imaging showed that the manganese content on the support surface was 0.001 of all elements (i.e., the support surface contained very few active components, which were mainly distributed in a localized area below the outer surface of the composite particle support). SEM analysis showed that the particle size of the active manganese particles was 1-2nm.

[0045] Example 19 6 g of SiO2-Al2O3-MgO support F, 1.5 g of urea, 0.358 g of manganese nitrate (2 mmol), 1 g of samarium nitrate (3 mmol), and 60 mL of deionized water were added sequentially to a reactor and mixed thoroughly. The mixture was reacted at 80 °C for 0.5 h. After cooling to room temperature, the mixture was filtered (the remaining filtrate, after titration, contained 0.09 mmol of manganese and 0.39 mmol of samarium). The resulting solid was vacuum dried at 80 °C for 1 h and then calcined in a muffle furnace at 500 °C for 3 h. After cooling, catalyst F1 was obtained. ICP analysis showed that the samarium content was 6.0%, the manganese content was 1.55%, the valence state was +4.2 (the manganese valence state was a mixture of hexavalent and tetravalent), the Mn / Sm atomic ratio was 0.707, and the Mn / Si atomic ratio was 0.0249. EDX electron imaging shows that the manganese content on the carrier surface is 0.001 of all elements (i.e., the carrier surface contains very few active components, which are mainly distributed in a local area below the outer surface of the composite particle load). SEM measurements of the active manganese samarium composite particles show a particle size of 2-3 nm.

[0046] Experimental results of catalysts for the preparation of methyl methacrylate (1): 2.5 g of catalyst was added to a fixed-bed reactor, and a 35% (w / w) methacrolein-methanol solution was continuously added at a rate of 12 mL / h, wherein the water content of the methacrolein-methanol solution was less than 0.5%. Air was bubbled in at a rate of 20 mL / h and a pressure of 3 kg / cm3. The reaction was carried out continuously at 40℃-45℃ to produce methyl methacrylate. The experimental results for 1 h and 1000 h of reaction are shown in Table 1.

[0047] Table 1

Claims

1. A method for preparing a manganese-based catalyst for the oxidative esterification of unsaturated aldehydes to prepare carboxylic acid esters, characterized in that, The catalyst contains oxidized manganese and titanium oxide X, which are loaded on a support in the range of 0.01-0.99 in Mn / X atomic ratio. Among them, the valence state of manganese is a mixture of hexavalent and tetravalent, or a mixture of tetravalent and trivalent, or a mixture of trivalent and divalent, and X represents at least one element or more elements selected from cerium, praseodymium, samarium, and erbium; The active component of the catalyst is composed of nanoparticles of oxidized manganese and oxides of X, with a particle size of 2-100 nm. The catalyst is prepared by first preparing a support, and then loading oxidized manganese and oxidized X onto the support; Preparation of composite oxide supports: The precursors of Al2O3, MgO, Fe2O3, La2O3, Er2O3, and CeO2, and the aqueous solution of SiO2 precursor are mixed evenly at 0-100℃ with concentrated nitric acid of 60%-85% by mass concentration. The mixture is stirred and matured at 50-80℃ for 10-48 hours, then evaporated by rotary evaporation to remove water and dried to obtain a white solid powder. After calcination at 200-900℃, a composite oxide carrier is obtained. Loading manganese in its oxidized state and X in its oxidized state onto a support comprises the following steps: In the first step, prepare an aqueous solution containing soluble metal salts of manganese and X, add a precipitant and a composite oxide carrier, react at 50-100 °C for 0.5-3 h, cool the mixture to room temperature and filter to obtain a solid. The concentration of manganese in aqueous solution is 0.01-0.1 mol / L; The precipitant is selected from one or two of urea and hexamethyltetramine, and its concentration in aqueous solution is 0.05-1 mol / L; The second step involves vacuum drying the obtained catalyst solid at 30-100℃, followed by high-temperature calcination to oxidize the manganese, and then cooling it down to obtain the catalyst. The roasting was carried out in a muffle furnace; the roasting temperature was 300–900℃ and the roasting time was 2–20 h.

2. The method for preparing the manganese-based catalyst for the oxidative esterification of unsaturated aldehydes to carboxylic acid esters according to claim 1, characterized in that, The calcination in the preparation of the composite oxide carrier is carried out in a tube furnace, under one or more atmospheres of oxygen, air, nitrogen or argon; the calcination temperature is 200–900℃, and the calcination time is 2–20 h. The SiO2 precursor is selected from one or more of the following: 20-60 wt% silica sol, 60-400 mesh column chromatography silica gel, and thin-layer chromatography silica gel; the amount of concentrated nitric acid used is 0.1-1.5 times the weight of the silica sol and / or 1-4 times the weight of the silica gel. The precursor of MgO is selected from one or more of magnesium oxalate, magnesium acetate, magnesium nitrate, magnesium chloride, magnesium hydroxide, magnesium carbonate, or magnesium oxide. The precursor of Al2O3 is selected from one or more of aluminum hydroxide, ammonium aluminum carbonate, ammonium aluminum sulfate, aluminum bicarbonate, aluminum nitrate or aluminum trichloride; The precursor of Fe2O3 is selected from one or more of ferric nitrate, ferric acetate, ferric oxalate, and ferric chloride. The precursor of La2O3 is selected from one or more of lanthanum nitrate and lanthanum acetate; The precursor of Er2O3 is selected from one or more of erbium nitrate, erbium acetate, and erbium oxalate; The precursor of CeO2 is selected from one or both of cerium nitrate and cerium ammonium nitrate; In the first step, the soluble metal salt of manganese is one or more of manganese nitrate, manganese acetate, and manganese dichloride. The soluble metal salt of X is one or more of the following: cerium nitrate hexahydrate, cerium ammonium nitrate, praseodymium nitrate hexahydrate, praseodymium acetate, samarium nitrate, samarium acetate, erbium nitrate pentahydrate, and erbium acetate.

3. The method for preparing the manganese-based catalyst for the oxidative esterification of unsaturated aldehydes to carboxylic acid esters according to claim 2, characterized in that, The composite oxide support is prepared by mixing an aqueous solution of Al2O3 precursor, precursors of one or more oxides selected from MgO, Fe2O3, La2O3, Er2O3, and CeO2, and SiO2 precursor at 30-50℃ with concentrated nitric acid of 60%-85% by mass concentration, stirring and aging at 50-80℃ for 10-48 hours, removing water by rotary evaporation, drying to obtain a white solid powder, and calcining at 200-900℃ to obtain the composite oxide support. The material is roasted in a tube furnace under one or more atmospheres of oxygen, air, nitrogen, or argon; the roasting temperature is 400-600℃ and the roasting time is 2-8 h. The SiO2 precursor is selected from one or more of the following: 20-60 wt% silica sol, 200-300 mesh column chromatography silica gel, and thin layer chromatography silica gel. The catalyst contains oxidized manganese and titanium dioxide X, with an Mn / X atomic ratio ranging from 0.3 to 0.8, supported on a carrier.

4. The method for preparing the manganese-based catalyst for the oxidative esterification of unsaturated aldehydes to carboxylic acid esters according to claim 2, characterized in that, The active component of the catalyst is composed of nanoparticles of oxidized manganese and X oxides, with a particle size of 2-10 nm.

5. The method for preparing the manganese-based catalyst for the oxidative esterification of unsaturated aldehydes to carboxylic acid esters according to claim 4, characterized in that, The catalyst contains oxidized manganese and titanium dioxide X, with an Mn / X atomic ratio ranging from 0.5 to 0.8, supported on a support. The active component of the catalyst is composed of nanoparticles of oxidized manganese and oxides of X, with a particle size of 2-5 nm.

6. The method for preparing the manganese-based catalyst for the oxidative esterification of unsaturated aldehydes to carboxylic acid esters according to claim 1, characterized in that, In the first step, the concentration of manganese in the aqueous solution is 0.01-0.05 mol / L; The precipitant is selected from one or both of urea and hexamethyltetramine, and its concentration in aqueous solution is 0.1-0.6 mol / L; In the second step, the roasting temperature is 400-600℃ and the roasting time is 2-8 h.

7. The method for preparing the manganese-based catalyst for the oxidative esterification of unsaturated aldehydes to carboxylic acid esters according to claim 6, characterized in that, In the first step, the concentration of manganese in the aqueous solution is 0.01-0.04 mol / L.

8. The method for preparing the manganese-based catalyst for the oxidative esterification of unsaturated aldehydes to carboxylic acid esters according to claim 1, characterized in that, The carrier is a composite oxide containing silicon dioxide, aluminum oxide, and other metal element oxides, wherein the molar proportion of the other elements other than oxygen is: 40-90 mol% silicon, 5.5-38 mol% aluminum, and 2-40 mol% other metal elements besides silicon and aluminum. Other elements are selected from one or more of the five elements: magnesium, iron, erbium, lanthanum, and cerium.

9. The method for preparing the manganese-based catalyst for the oxidative esterification of unsaturated aldehydes to carboxylic acid esters according to claim 1, characterized in that, The composite oxides are specifically silicon dioxide-alumina-magnesium oxide, silicon dioxide-alumina-magnesium oxide-iron oxide, silicon dioxide-alumina-lanthanum oxide, silicon dioxide-alumina-lanthanum oxide-erbium oxide, or silicon dioxide-alumina-magnesium oxide-cerium dioxide.

10. The method for preparing the manganese-based catalyst for the oxidative esterification of unsaturated aldehydes to carboxylic acid esters according to claim 8, characterized in that, The specific surface area of ​​the carrier is 20-360m² 2 / g, pore size 3-80nm, pore capacity 0.1-1.0mL / g, particle size 10-510 µm.

11. The catalyst for the oxidative esterification of unsaturated aldehydes to prepare manganese-based carboxylic acid esters prepared by the preparation method according to any one of claims 1-10, characterized in that, The composition ratio of manganese to silicon oxide, expressed as Mn / Si atomic ratio, is 0.01-1.

2.

12. The manganese-based catalyst according to claim 11, characterized in that, The composition ratio of manganese to silicon oxide, expressed as Mn / Si atomic ratio, is 0.01-0.

2.

13. The manganese-based catalyst according to claim 12, characterized in that, The composition ratio of manganese to silicon oxide, expressed as Mn / Si atomic ratio, is 0.01-0.

1.

14. A method for preparing a carboxylic acid ester, characterized in that: In the presence of the manganese-based catalyst as described in claim 11 and oxygen and / or air, an unsaturated aldehyde is oxidized and esterified with methanol in one step to generate a carboxylic acid ester. The reaction conditions are as follows: 2.5 g of the manganese-based catalyst according to claim 11 is added to a fixed-bed reactor; a methanol solution with an unsaturated aldehyde mass fraction of 10-50% is continuously added at a rate of 5-30 mL / h; oxygen and / or air are bubbled in at a rate of 10-50 mL / h; and the pressure is 1-5 kg / cm². 3 Carboxylic acid esters are produced by continuous reaction at 40℃-45℃.

15. The preparation method according to claim 14, characterized in that: The unsaturated aldehyde is one or more of acrolein or methacrolein; The water content in the unsaturated aldehyde-methanol solution is less than 0.5%.

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