Preparation method of catalyst for preparing methyl glycolate through dimethyl oxalate hydrogenation

Abstract

The invention discloses a preparation method of a catalyst for preparing methyl glycolate through dimethyl oxalate hydrogenation, and relates to a preparation method of a catalyst. According to the catalyst, a silver-based metal-organic framework (Ag-MOF) is used for re-dispersing and anchoring silver on modified mesoporous silica (SiO2-m), VIII and IB family transition metal nitrate of a periodic table of elements is introduced as a cocatalyst, and the catalyst is used in a reaction for generating methyl glycolate through hydrogenation of dimethyl oxalate. The catalyst combines the high catalytic activity of an Ag nanoparticle active center derived from a silver-based metal-organic framework (Ag-MOF) and the stability provided by a mesoporous silica carrier. The catalyst disclosed by the invention is simple in preparation method and good in synthesis repeatability, and when the catalyst is applied to a reaction for preparing methyl glycolate through dimethyl oxalate hydrogenation, the catalyst is good in activity and relatively high in stability, and the selectivity of the methyl glycolate is high.

Description

Technical Field

[0001] The present invention relates to a method for preparing a catalyst, and more particularly to a method for preparing a catalyst for the hydrogenation of dimethyl oxalate to methyl glycolate. Background Art

[0002] Methyl glycolate (MG) is an important chemical raw material and intermediate, which is widely used in the synthesis of fine chemicals such as pharmaceuticals and fragrances. With the rapid development of China's economy, the demand for methyl glycolate is gradually increasing. At present, most of the production of methyl glycolate relies on petrochemical routes, but this method has problems such as strong corrosion and serious pollution. At the same time, affected by the oil crisis, the price fluctuations of oil resources also affect the production cost. Therefore, developing a process for synthesizing methyl glycolate by hydrogenating dimethyl oxalate (DMO) with syngas as the raw material has become a more economical and environmentally friendly production route. DMO hydrogenation is a continuous reaction. According to the degree of hydrogenation, MG (DMO→MG) and ethylene glycol (EG, MG→EG) are generated. Converting dimethyl oxalate (DMO) into methyl glycolate through selective hydrogenation reaction not only opens up a new extension direction for the ethylene glycol industrial chain, but also provides an effective solution to alleviate the problem of overcapacity of ethylene glycol.

[0003] Cu-based catalysts have been widely used in DMO hydrogenation due to their excellent performance in the hydrogenation of C=O bonds. However, Cu-based catalysts face significant challenges in achieving a balance between DMO conversion and MG selectivity. Existing studies have shown that the kinetic constant of MG hydrogenation on a conventional Cu / SiO 2 catalyst is 15 times higher than that of DMO hydrogenation, resulting in a low MG yield (<80%). Therefore, it is necessary to develop a DMO hydrogenation catalyst that meets industrial requirements and has high selectivity for MG. Compared with other catalysts, silver (Ag)-based catalysts perform better because their hydrogenolysis activity for DMO is relatively weak, which is beneficial for selective hydrogenation to MG rather than complete hydrogenation to ethylene glycol (EG). Some studies have shown that the dispersion or particle size of Ag has a significant impact on the catalytic performance.

[0004] Japanese Patent JP06135895 reported earlier the hydrogenation of dimethyl oxalate to methyl glycolate, and used the copper ammonia steaming ammonia method to prepare Cu-Ag / SiO 2The catalyst has a methyl glycolate yield of less than 70%, and at high yields, DMO is not completely converted, which causes difficulties in the subsequent product separation. Tianjin University in China (CN101138730A) also carried out research on this reaction earlier. It used a modified silica-impregnated supported copper-silver catalyst, and the methyl glycolate yield could reach over 68%. However, these catalysts have disadvantages such as low atomic utilization rate, low selectivity, and poor stability, which hinder their further industrial applications. Therefore, it is necessary to develop a new method to prepare stable and small-sized metal alloy nanoparticles.

[0005] Metal-organic frameworks (MOFs) have been widely used in the preparation of a series of nanostructured materials such as porous metals / carbons, metal oxides, and metal-free heteroatom-doped carbons due to their unique structural characteristics. The metals or cluster sites in MOFs can not only directly participate in catalytic reactions, but also these materials can be modified after synthesis to introduce other single-site metals. However, MOF materials have poor thermal stability under high-temperature conditions and are prone to decomposition. Therefore, to solve this problem, we propose a strategy of combining MOFs with stable support materials such as mesoporous silica. Mesoporous silica materials have a high specific surface area and good thermal stability. Modified mesoporous silica can well support the catalytic oxidation metal cluster sites generated by the decomposition of MOFs and enhance their catalytic performance. Summary of the Invention

[0006] The present invention aims to provide a preparation method of a catalyst for the hydrogenation of dimethyl oxalate to prepare methyl glycolate. The present invention successfully synthesizes an Ag-MOF-M / SiO 2 -m catalyst by a two-step hydrothermal method and uses it in the reaction of catalytically preparing methyl glycolate from dimethyl oxalate to improve the disadvantages of traditional catalysts such as low atomic utilization rate, low selectivity, and poor stability, and obtain higher conversion rates and selectivities.

[0007] The object of the present invention is achieved by the following technical solutions: A preparation method of a catalyst for the hydrogenation of dimethyl oxalate to prepare methyl glycolate, wherein the catalyst uses mesoporous silica (SiO 2 -m) as a carrier. The carrier is prepared by combining the modified Stöber method and the hydrothermal method and is surface-modified. The main active component is Ag, and the promoter is M (Fe, Co, Ni, Cu). The particle size distribution of the active component is regulated by the metal-organic framework (MOF) technology. The mass fraction of the active component Ag in this catalyst is 1% - 30%, and the promoters Co, Ni, and Cu are 0.005 - 5%, and the rest is the carrier silica.

[0008] The method includes the following preparation steps: Step 1: Weigh an appropriate amount of cetyltrimethylammonium bromide (CTAB) and an appropriate amount of triethanolamine (TEA), and dissolve them in deionized water (H 2 2O). Stir magnetically at 60 °C for 30 - 90 min until completely dissolved and dispersed to obtain a transparent solution; Step 2: Weigh an appropriate amount of tetraethyl orthosilicate (TEOS) and an appropriate amount of absolute ethanol (EtOH), and drop them into the obtained transparent solution. Stir at 60 °C for 12 - 24 h; Step 3: Add a small amount of (3-aminopropyl)triethoxysilane to the obtained mixed solution, then transfer it to a 200 mL stainless steel autoclave with a Teflon liner, and place it in an oven to react at 100 °C for 12 - 24 h, and then naturally cool to room temperature; Step 4: Centrifuge the reacted solution to obtain the reaction product, and then wash it alternately and repeatedly with deionized water and absolute ethanol; Step 5: Put the washed reaction product into a drying oven at a constant temperature, and conduct drying treatment at 120 °C overnight. After drying, cool it to obtain surface-modified mesoporous silica (SiO 2 2-m); Step 6: Weigh an appropriate amount of surface-modified mesoporous silica (SiO 2 2-m), disperse it in a mixed solution of an appropriate amount of deionized water and absolute ethanol, and stir magnetically at room temperature for 30 - 90 min until completely dispersed, denoted as solution A; Step 7: Weigh an appropriate amount of 2-methylimidazole, an appropriate amount of silver nitrate (AgNO 3 3), and nitrates of an appropriate amount of auxiliary agent M (Fe, Co, Ni, Cu), dissolve them in an appropriate amount of absolute ethanol solution, and stir magnetically at room temperature for 30 - 90 min until completely dissolved and dispersed, denoted as solution B; Step 8: Mix solution A and solution B, and stir magnetically at room temperature for 30 - 90 min until completely mixed; Step 9: Transfer the obtained solution to a 200 mL stainless steel autoclave with a Teflon liner, and place it in an oven to react at 120 °C for 12 - 24 h, and then naturally cool to room temperature; Step 10: Centrifuge the reacted solution to obtain the reaction product, and then wash it alternately and repeatedly with deionized water and absolute ethanol; Step 11: Put the washed reaction product into a drying oven at a constant temperature, conduct drying treatment at 80 °C overnight, and put the dried product into a muffle furnace to calcine at 450 °C for 4 - 9 h and then cool to obtain the Ag-MOF-M / SiO 2 2-m catalyst.

[0009] In Steps 1 and 2, by mass ratio, cetyltrimethylammonium bromide (CTAB): triethanolamine (TEA): deionized water (H 2 O): tetraethyl orthosilicate (TEOS): absolute ethanol (EtOH) is preferably 1:(8 - 12):(0.3 - 0.6):(1 - 4):(1 - 5).

[0010] In Step 3, by mass ratio, (3-aminopropyl)triethoxysilane: the mixed solution is preferably 1:(30 - 300), and (3-aminopropyl)triethoxysilane is added. (3-aminopropyl)triethoxysilane is used as a surface modifier.

[0011] In Step 6, by volume ratio, deionized water: absolute ethanol is preferably 1:(0.5 - 3).

[0012] The application method of the Ag-MOF-M / SiO 2 -m catalyst of the present invention in the reaction of hydrogenating dimethyl oxalate to methyl glycolate includes the following steps: Step 1: Load the catalyst into a fixed-bed continuous reactor for reduction. After completion, cool it to the reaction temperature of 100 - 300 °C, and then introduce hydrogen and dimethyl oxalate with a molar ratio of 20:1 - 100:1 for reaction to obtain methyl glycolate. Among them, the liquid hourly space velocity of dimethyl oxalate is 0.1 - 5.0 h -1 ; the hydrogen pressure is 0.5 - 5.0 MPa; among them, the catalyst needs to be reduced with hydrogen before use, and the reduction conditions are a hydrogen pressure of 0.5 - 5.0 MPa, a hydrogen space velocity of 100 - 150 h -1 , a reduction temperature of 150 - 400 °C, and a reduction time of 2 - 16 h; Step 2: After the reduction is completed, cool it to the reaction temperature of 100 - 300 °C, and then add the reaction raw materials for hydrogenation reaction. Control the reaction pressure to be 0.5 MPa - 5.0 MPa, the reaction temperature to be 100 °C - 300 °C, and the liquid hourly space velocity of dimethyl oxalate to be 0.1 - 5.0 h -1 , dimethyl oxalate is dissolved in methanol, and the mass ratio of methanol to dimethyl oxalate is 5 - 15, and the molar ratio of hydrogen to dimethyl oxalate is 20 - 100.

[0013] Advantages and beneficial effects of the present invention: (1) The present invention combines the improved Stöber method with hydrothermal synthesis and surface modification, and then performs washing and drying treatments to successfully prepare a modified mesoporous silica support (SiO2-m). The modified mesoporous silica support (SiO 2 -m) prepared by this method can effectively load and disperse the active metal, and at the same time is conducive to the regulation of the active metal.

[0014] (2) The prepared Ag-MOF-M / SiO 2 -m catalyst has a large specific surface area and a complex pore structure, which are derived from the characteristics of its original modified mesoporous silica. These structural features can provide more active sites, effectively promote the adsorption of dimethyl oxalate, and thus enhance the catalytic activity. This catalyst exhibits a high conversion rate of dimethyl oxalate and excellent selectivity for methyl glycolate.

[0015] (3) The Ag-MOF-M / SiO 2 -m catalyst prepared by the present invention with the active center regulated by MOF has a smaller particle size of Ag, which can significantly improve the activity of the catalytic reaction. The addition of additives can obtain higher selectivity for the corresponding products. It can stably and efficiently catalyze the hydrogenation of dimethyl oxalate to prepare methyl glycolate and is suitable for industrial mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is the XRD spectra of the products prepared in Examples 1, 2, and 3; Figure 2 (a) is the scanning electron microscope image of the product prepared in Example 1; Figure 2 (b) is the scanning electron microscope image of the product prepared in Example 2; Figure 2 (c) is the scanning electron microscope image of the product prepared in Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0017] The technical solution of the present invention will be further described in detail below with reference to the specific embodiments shown in the drawings, but these embodiments do not limit the protection scope of the present invention.

[0018] Ag-MOF-M / SiO 2 -m catalyst preparation method, including the following steps: Step 1: Weigh an appropriate amount of cetyltrimethylammonium bromide (CTAB) and an appropriate amount of triethanolamine (TEA), dissolve them in deionized water, and magnetically stir at 60 °C for 30 - 90 min to completely dissolve and disperse them to obtain a transparent solution; Step 2: Weigh an appropriate amount of tetraethyl orthosilicate (TEOS) and an appropriate amount of absolute ethanol (EtOH), drop them into the obtained transparent solution, and stir at 60 °C for 12 - 24 h; Step 3: Add a small amount of (3-aminopropyl)triethoxysilane to the obtained mixed solution, transfer it to a 200 mL stainless steel autoclave with a polytetrafluoroethylene lining, place it in an oven at 100 °C for reaction for 12 - 24 h, and then naturally cool to room temperature; Step 4: Centrifuge the reacted solution to obtain the reaction product, and then wash it repeatedly with deionized water and absolute ethanol alternately; Step 5: Put the washed reaction product into a drying oven at a constant temperature and conduct drying treatment overnight at 120 °C. After drying, cool it to obtain surface-modified mesoporous silica (SiO 2 ); Step 6: Weigh an appropriate amount of surface-modified mesoporous silica (SiO 2 ) and disperse it in a mixed solution of deionized water and absolute ethanol. Stir magnetically at room temperature for 30 - 90 min to make it completely dispersed, and record it as solution A; Step 7: Weigh an appropriate amount of 2-methylimidazole, an appropriate amount of silver nitrate (AgNO 3 ) and an appropriate amount of nitrate of auxiliary agent M (Fe, Co, Ni, Cu), dissolve them in an absolute ethanol solution, and stir magnetically at room temperature for 30 - 90 min to make them completely dissolved and dispersed, and record it as solution B; Step 8: Mix solution A and solution B, and stir magnetically at room temperature for 30 - 90 min to make them completely mixed; Step 9: Transfer the obtained solution into a 200 mL stainless steel autoclave with a polytetrafluoroethylene liner, and place it in an oven to react at 120 °C for 12 - 24 h, then cool it naturally to room temperature; Step 10: Centrifuge the reacted solution to obtain the reaction product, and then wash it repeatedly with deionized water and absolute ethanol alternately; Step 11: Put the washed reaction product into a drying oven at a constant temperature and conduct drying treatment overnight at 80 °C. Put the dried product into a muffle furnace and calcine it at 450 °C for 4 - 9 h and then cool it to obtain the Ag-MOF-M / SiO 2 catalyst.

[0019] In Steps 1 and 2, by mass ratio, cetyltrimethylammonium bromide (CTAB): triethanolamine (TEA): deionized water (H 2 O): tetraethyl orthosilicate (TEOS): absolute ethanol (EtOH) is preferably 1:(8 - 12):(0.3 - 0.6):(1 - 4):(1 - 5).

[0020] In Step 3, by mass ratio, (3-aminopropyl)triethoxysilane: mixed solution is preferably 1:(30 - 300). Add (3-aminopropyl)triethoxysilane. Use (3-aminopropyl)triethoxysilane as the surface modifier.

[0021] In Step 6, by volume ratio, deionized water: absolute ethanol is preferably 1:(0.5 - 3).

[0022] Application steps of the Ag-MOF-M / SiO 2 -m catalyst in the hydrogenation of dimethyl oxalate to methyl glycolate reaction: Step 1: Load the catalyst into a fixed-bed continuous reactor for reduction. After completion, cool it to the reaction temperature of 100~300 °C, and then introduce hydrogen and dimethyl oxalate with a molar ratio of 20:1~100:1 for reaction to obtain methyl glycolate. Among them, the liquid hourly space velocity of dimethyl oxalate is 0.1~5.0 h -1 ; the hydrogen pressure is 0.5~5.0 MPa; among them, the catalyst needs to be reduced with hydrogen before use, and the reduction conditions are hydrogen pressure of 0.5~5.0 MPa, hydrogen space velocity of 100~150 h -1 , reduction temperature of 150~400 °C, and reduction time of 2~16 h; Step 2: After the reduction is completed, cool it to the reaction temperature of 100~300 °C, and then add the reaction raw materials for hydrogenation reaction. Control the reaction pressure to be 0.5 MPa~5.0 MPa, the reaction temperature to be 100 °C~300 °C, and the liquid hourly space velocity of dimethyl oxalate to be 0.1~5.0 h -1 , dimethyl oxalate is dissolved in methanol, and the mass ratio of methanol to dimethyl oxalate is 5~15, and the molar ratio of hydrogen to dimethyl oxalate is 20~100. Example 1

[0023] Preparation of Ag / SiO 2 -m catalyst Step 1: Weigh 15 g of cetyltrimethylammonium bromide (CTAB) and 0.5 g of triethanolamine (TEA) and dissolve them in 60 g of deionized water. Stir magnetically at 60 °C for 30 min to completely dissolve and disperse them to obtain a transparent solution; Step 2: Weigh 20 g of tetraethyl orthosilicate (TEOS) and 28 g of absolute ethanol (EtOH) and drop them into the obtained transparent solution, and stir at 60 °C for 12 h; Step 3: Add 0.1 g of (3-aminopropyl)triethoxysilane to the obtained mixed solution, transfer it to a 200 mL stainless steel autoclave with a polytetrafluoroethylene lining, and place it in an oven at 100 °C for reaction for 12 h, and then naturally cool to room temperature; Step 4: Centrifuge the reaction solution to obtain the reaction product, and then wash it alternately with deionized water and absolute ethanol repeatedly; Step 5: Put the washed reaction product into a constant temperature drying oven and dry it overnight at 120 °C. After drying is completed, cool it to obtain unmodified mesoporous silica (SiO 2 ); Step 6: Weigh 4 g of surface-modified mesoporous silica (SiO2 ) was dispersed in a 50 ml mixed solution of deionized water and absolute ethanol with a volume ratio of 1:1, and magnetically stirred at room temperature for 30 min to make it completely dispersed, denoted as solution A; Step Seven: Weigh 1 g of silver nitrate (AgNO 3 ), dissolve it in 30 ml of absolute ethanol solution, and magnetically stir at room temperature for 30 min to make it completely dissolved and dispersed, denoted as solution B; Step Eight: Mix solution A and solution B, and magnetically stir at room temperature for 30 min to make them completely mixed; Step Nine: The obtained solution was transferred into a 200 mL stainless steel autoclave with a polytetrafluoroethylene liner and placed in an oven at 120 °C for 12 h, and then naturally cooled to room temperature; Step Ten: The reaction solution after the reaction was centrifuged to obtain the reaction product, and then washed alternately with deionized water and absolute ethanol repeatedly; Step Eleven: The washed reaction product was placed in a constant temperature drying oven and dried at 80 °C overnight. After drying, the product was calcined in a muffle furnace at 450 °C for 4 h and cooled to obtain the Ag / SiO 2 -m catalyst.

[0024] Ag / SiO 2 -m Catalyst Structure Characterization The crystal structure of the product was characterized by an XRD powder diffractometer (XRD, Shimadzu XRD-600). Figure 1 is the XRD pattern of the product. The diffraction peaks of the Ag / SiO 2 sample are consistent with the standard cards of Ag and SiO 2 Ag PDF # 04-00-6437 and SiO 2 PDF # 97-081-9401. There are four obvious peaks at 2θ = 38.1◦, 44.3◦, 64.4◦ and 77.4◦, which belong to the (111), (200), (220) and (311) crystal planes of metallic Ag respectively, and no other impurity peaks appear, indicating its high purity and proving that Ag exists in the form of a single substance.

[0025] The morphology of the product was characterized by a scanning electron microscope (FESEM, ZEISS Ultra Plus). As Figure 2 (a) shows, the Ag / SiO in the product 2 sample is formed by the accumulation of a large number of particles, and the diameter of a single particle is about 30 nm. Example 2

[0026] (1) Preparation of Ag / SiO with different structures 2-m catalyst Step 1: Weigh 16 g of cetyltrimethylammonium bromide (CTAB) and 0.8 g of triethanolamine (TEA), dissolve them in 60 g of deionized water, and magnetically stir for 30 min at 60 °C to completely dissolve and disperse them, obtaining a transparent solution; Step 2: Weigh 20 g of tetraethyl orthosilicate (TEOS) and 30 g of absolute ethanol (EtOH), and drop them into the obtained transparent solution, then stir at 60 °C for 12 h Step 3: Add 0.1 g of (3-aminopropyl)triethoxysilane to the obtained mixed solution, then transfer it to a 200 mL stainless steel autoclave with a polytetrafluoroethylene liner, and place it in an oven to react at 100 °C for 12 h, then naturally cool to room temperature; Steps 3, 4, 5, 6, 7, 8, 9, and 10 are the same as in Example 1; Step 11: Put the washed reaction product into a drying oven at a constant temperature, conduct drying treatment overnight at 80 °C, and put the dried product into a muffle furnace to calcine at 450 °C for 4 h and then cool down to obtain Ag / SiO with different structures 2 -m catalyst.

[0027] (2) Ag / SiO 2 Structure characterization of the -m catalyst The crystal structure of the product was characterized using an XRD powder diffractometer (XRD, Shimadzu XRD-6100). As can be seen from the XRD pattern of Ag / SiO 2 -m, there are four obvious peaks at 2θ = 38.1◦, 44.3◦, 64.4◦, and 77.4◦, which belong to the (111), (200), (220), and (311) crystal planes of metallic Ag respectively. For Ag / SiO 2 -m with the regulated support structure, the diffraction peak intensity is greater, indicating that the synthesized sample has better purity and crystallinity.

[0028] The morphology of the product was characterized using a scanning electron microscope (FESEM, ZEISS Ultra Plus). As shown in Figure 2 (b), the structure with a large number of particle accumulations in the product hardly changes significantly. However, compared with the Ag / SiO 2 -m sample without the regulated support structure, the nanoparticles in the sample with the regulated support structure gradually become distinct. This may be because the adjustment of the SiO 2 -m structure of the support increases the porosity and reduces the degree of nanoparticle aggregation. Example 3

[0029] (1) Preparation of Ag-MOF / SiO 2 -m catalyst Steps 1, 2, 3, 4, 5, and 6 are the same as in Example 2; Step 7: Weigh 1.5 g of 2-methylimidazole and 1 g of silver nitrate (AgNO 3 ), dissolve them in 30 ml of anhydrous ethanol solution, and magnetically stir for 30 min at room temperature until they are completely dissolved and dispersed, denoted as Solution B; Steps 8, 9, and 10 are the same as in Example 2; Step 11: Put the washed reaction product into a drying oven at a constant temperature and dry it overnight at 80 °C. After drying, put the product into a muffle furnace and calcine it at 450 °C for 4 h and then cool it to obtain the Ag-MOF / SiO 2 -m catalyst.

[0030] (2) Structure characterization of the Ag-MOF / SiO 2 -m catalyst Use an XRD powder diffractometer (XRD, Shimadzu XRD-6100) to characterize the crystal structure of the product. Figure 1 As shown in the XRD pattern of the product, there are four obvious peaks at 2θ = 38.1°, 44.3°, 64.4°, and 77.4°, which belong to the (111), (200), (220), and (311) crystal planes of metallic Ag respectively. The diffraction peak intensity of Ag-MOF / SiO 2 -m is greater, indicating that the synthesized sample has the best purity and crystallinity.

[0031] Use a scanning electron microscope (FESEM, ZEISS Ultra Plus) to characterize the morphology of the product. As Figure 2 shown in (c), the nanoparticles of the product sample become clearer, the packing is looser, and there are more pore structures. Example 4

[0032] (1) Preparation of the Ag-MOF-Co / SiO 2 -m catalyst Steps 1, 2, 3, 4, 5, and 6 are the same as in Example 2; Step 7: Weigh 1.5 g of 2-methylimidazole, 1 g of silver nitrate (AgNO 3 ) and 0.3 g of cobalt nitrate (Co(NO 3 ) 2 ), dissolve them in 30 ml of anhydrous ethanol solution, and magnetically stir for 30 min at room temperature until they are completely dissolved and dispersed, denoted as Solution B; Steps 8, 9, and 10 are the same as in Example 2; Step Eleven: Put the washed reaction product into a drying oven at a constant temperature and conduct drying treatment overnight at 80 °C. After drying, put the product into a muffle furnace and calcine it at 450 °C for 4 h and then cool it to obtain the Ag-MOF-Co / SiO 2 -m catalyst. Example 5

[0033] (1) Preparation of Ag-MOF-Ni / SiO 2 -m catalyst Steps One, Two, Three, Four, Five, and Six are the same as those in Example 2; Step Seven: Weigh 1.5 g of 2-methylimidazole, 1 g of silver nitrate (AgNO 3 ), and 0.3 g of nickel nitrate (Ni(NO 3 ), 2 ) and dissolve them in 30 ml of anhydrous ethanol solution. Stir magnetically at room temperature for 30 min to completely dissolve and disperse them, and record it as Solution B; Steps Eight, Nine, and Ten are the same as those in Example 2; Step Eleven: Put the washed reaction product into a drying oven at a constant temperature and conduct drying treatment overnight at 80 °C. After drying, put the product into a muffle furnace and calcine it at 450 °C for 4 h and then cool it to obtain the Ag-MOF / SiO 2 -m catalyst. Example 6

[0034] (1) Preparation of Ag-MOF-Cu / SiO 2 -m catalyst Steps One, Two, Three, Four, Five, and Six are the same as those in Example 2; Step Seven: Take 1.5 g of 2-methylimidazole, 1 g of silver nitrate (AgNO 3 ), and 0.3 g of copper nitrate (Cu(NO 3 ), 2 ) and dissolve them in 30 ml of anhydrous ethanol solution. Stir magnetically at room temperature for 30 min to completely dissolve and disperse them, and record it as Solution B; Steps Eight, Nine, and Ten are the same as those in Example 2; Step Eleven: Put the washed reaction product into a drying oven at a constant temperature and conduct drying treatment overnight at 80 °C. After drying, put the product into a muffle furnace and calcine it at 450 °C for 4 h and then cool it to obtain the Ag-MOF-Cu / SiO 2 -m catalyst.

[0035] Load the prepared catalyst into a fixed-bed continuous reactor for reduction. After the reduction is completed, conduct relevant performance tests on its catalytic hydrogenation of dimethyl oxalate to methyl glycolate: As can be seen from Table 1, the DMO conversion rate of all catalysts is relatively low at lower temperatures. As the temperature increases, the DMO conversion rate begins to rise. The DMO conversion rates of Example 3 and Example 2 are close to 100% at 220 °C. As the temperature continues to rise, the DMO conversion rate remains almost unchanged. However, the DMO conversion rate of Example 1 reaches its maximum at 240 °C. Compared with Example 3 and Example 2, the DMO conversion rate of Example 1 is lower and the catalytic activity of the catalyst is lower, which proves that the structural adjustment of the silica support is beneficial to improving the catalytic activity of Ag on the surface.

[0036] The selectivity of MG decreases as the temperature increases. This is because at higher temperatures, MG is more likely to be further hydrogenated to form EG. Compared with Example 3, in Example 2, MG is more likely to be further hydrogenated to form EG, resulting in a lower selectivity of MG. In Example 1, because the hydrogenation ability of the catalyst is relatively low, MG is not easily further hydrogenated, so there is a relatively high selectivity of MG. This shows that the selectivity of MG of the catalyst is improved by the regulation of MOF.

[0037] As can be seen from Table 2, the selectivities of the catalysts with different promoters are different. The catalyst with nickel as the promoter has the highest selectivity for MG, and other promoters are likely to cause MG to be further hydrogenated to form EG.

[0038] The catalyst of the present invention can stably and efficiently hydrogenate dimethyl oxalate to methyl glycolate, with a conversion rate as high as 99% and a selectivity of methyl glycolate of more than 95%.

[0039] Table 1 Comparison of Catalyst Performance at Different Temperatures

[0040] Table 2 Comparison of Different Catalyst Performances Conversion rate of dimethyl oxalate / % Selectivity of methyl glycolate / % Example 1 79.3 94.9 Example 2 98 84.8 Example 3 99 93.1 Example 4 99 80.5 Example 5 99 95.7 Example 6 99 79.2

Claims

1. A method for preparing a catalyst for preparing methyl glycolate by hydrogenating dimethyl oxalate, characterized in that: The catalyst uses mesoporous silica (SiO2-m) as a carrier, which is prepared by combining a modified Stöber method with a hydrothermal method and is surface-modified; the active component is Ag, the auxiliary agent is M (Fe, Co, Ni, Cu), and the particle size distribution of the active component is regulated by metal organic framework (MOF) technology; the mass fraction of the active component Ag in the catalyst is 1% to 30%, the auxiliary agents Co, Ni, and Cu are 0.005-5%, and the rest is carrier silica; The specific preparation steps are as follows: (1) Weigh cetyltrimethylammonium bromide (CTAB) and triethanolamine (TEA) and dissolve them in deionized water (H2O). Stir them magnetically at 60°C for 30-90 min to completely dissolve and disperse them to obtain a transparent solution. (2) Weigh tetraethyl orthosilicate (TEOS) and anhydrous ethanol (EtOH) and drop them into the resulting transparent solution, and stir at 60°C for 12-24 hours; (3) The obtained mixed solution was added with (3-aminopropyl)triethoxysilane and then transferred into a 200 mL polytetrafluoroethylene-lined stainless steel autoclave, and placed in an oven at 100 °C for 12-24 h, and then naturally cooled to room temperature; (4) Centrifuging the reaction solution to obtain the reaction product, and then washing it repeatedly with deionized water and anhydrous ethanol; (5) placing the washed reaction product in a constant temperature drying oven and drying it at 120 °C overnight, and cooling it after drying to obtain surface-modified mesoporous silica (SiO2-m); (6) Weigh the surface-modified mesoporous silica (SiO2-m) and disperse it in a mixed solution of deionized water and anhydrous ethanol. Stir it magnetically at room temperature for 30 to 90 min to completely dissolve and disperse it. This is referred to as solution A. (7) Weigh 2-methylimidazole, silver nitrate (AgNO3) and nitrate of additive M (Fe, Co, Ni, Cu), dissolve them in anhydrous ethanol solution, and stir them magnetically at room temperature for 30-90 min to completely dissolve and disperse them. This is referred to as solution B. (8) Mix solution A and solution B and stir them magnetically at room temperature for 30 to 90 minutes to thoroughly mix them; The obtained solution was transferred into a 200 mL polytetrafluoroethylene-lined stainless steel autoclave and placed in an oven for reaction at 120 °C for 12 h, and then naturally cooled to room temperature; The reaction product is obtained by centrifuging the solution after the reaction, and then washed repeatedly with deionized water and anhydrous ethanol alternately; (10) The washed reaction product was placed in a constant temperature drying oven and dried at 80 °C overnight. The dried product was placed in a muffle furnace and calcined at 450 °C for 4-9 h and cooled to obtain the Ag-MOF-M / SiO2-m catalyst.

2. The method for preparing a catalyst for preparing methyl glycolate by hydrogenating dimethyl oxalate as claimed in claim 1, characterized in that: In steps (1) and (2), the mass ratio of hexadecyltrimethylammonium bromide (CTAB):triethanolamine (TEA):deionized water (H2O):tetraethyl orthosilicate (TEOS):anhydrous ethanol (EtOH) is 1:(8-12):(0.3-0.6):(1-4):(1-5).

3. The method for preparing a catalyst for preparing methyl glycolate by hydrogenating dimethyl oxalate as claimed in claim 1, characterized in that In step (3), (3-aminopropyl)triethoxysilane is added in a mass ratio of (3-aminopropyl)triethoxysilane:mixed solution of 1:(30-300).

4. The method for preparing a catalyst for preparing methyl glycolate by hydrogenating dimethyl oxalate as claimed in claim 1, characterized in that In step (6), the volume ratio of deionized water to anhydrous ethanol is 1:(0.5~3).

5. The method for preparing a catalyst for preparing methyl glycolate by hydrogenating dimethyl oxalate as claimed in claim 1, characterized in that: The process and steps of using the catalyst in preparing methyl glycolate from dimethyl oxalate are as follows: (1) The catalyst is loaded into a fixed bed continuous reactor for reduction, and after the reduction is completed, the reaction temperature is cooled to 100-300° C., and then hydrogen and dimethyl oxalate are introduced at a molar ratio of 20:1-100:1 to react to obtain methyl glycolate, wherein the liquid hourly space velocity of dimethyl oxalate is 0.1-5.0 h -1 ; The hydrogen pressure is 0.5~5.0MPa; The catalyst is required to be reduced with hydrogen before use, and the reduction conditions are hydrogen pressure of 0.5~5.0MPa and hydrogen space velocity of 100~150h -1 , reduction temperature 150~400℃, reduction time 2~16h; (2) After the reduction is completed, the reaction temperature is cooled to 100~300℃, and then the reaction raw materials are added for hydrogenation reaction. The reaction pressure is controlled to be 0.5MPa~5.0MPa, the reaction temperature is 100℃~300℃, and the liquid space velocity of dimethyl oxalate is 0.1~5.0h -1 , dimethyl oxalate is dissolved in methanol, the mass ratio of methanol to dimethyl oxalate is 5-15, and the molar ratio of hydrogen to dimethyl oxalate is 20-100.

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