Catalyst for synthesizing oxalic acid dimethyl ester hydrogenation to prepare glycollic acid methyl ester with additive complexing agent, its preparation method and application

Abstract

The application discloses a catalyst for synthesizing oxalic acid dimethyl ester hydrogenation to prepare glycollic acid methyl ester by adding a complexing agent, a preparation method and application thereof, the catalyst is a copper-silver bimetallic catalyst, the active component is copper species and silver species, the carrier is silicon dioxide, the copper-silver bimetallic catalyst structure is that silver species uniformly covers the surface of copper species in the form of a shell layer to form a core-shell structure, the core-shell structure is in the form of particles and is located on the carrier silicon dioxide, and copper and silicon dioxide form strong interaction. The catalyst precursor is synthesized by an ammonia evaporation method, copper particles with strong interaction with silicon dioxide are formed after reduction, and a copper-silver core-shell structure is synthesized by a replacement method, in the preparation process, different complexing agents are added, the pH value in the preparation process is changed, and the mass ratio of copper to silver is ensured to guarantee the compactness, uniformity and density of the silver shell layer. When the copper-silver bimetallic catalyst is used for the reaction of oxalic acid dimethyl ester hydrogenation to prepare glycollic acid methyl ester, the catalyst has low silver loading, high catalytic activity, high selectivity and high stability.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, and relates to bimetallic catalysts, particularly a catalyst for the hydrogenation of dimethyl oxalate to methyl glycolate with the addition of a complexing agent, its preparation method and application. The catalyst is used for the hydrogenation of dimethyl oxalate to methyl glycolate (MG). Background Technology

[0002] Methyl glycolate, with its unique molecular structure containing H, hydroxyl, and ester functional groups, possesses the chemical properties of both alcohols and esters. It can undergo carbonylation, hydrolysis, and oxidation reactions, making it an important chemical raw material widely used in many fields such as chemicals, pharmaceuticals, pesticides, feed, fragrances, and dyes.

[0003] my country's biodegradable material polyglycolic acid (PGA) industry is developing rapidly. PGA exhibits strong environmental degradability, breaking down into carbon dioxide and water in nature within 1-3 months. Given the huge demand, the large-scale production of methyl glycolate, the raw material for synthesizing PGA, is crucial. Traditional methyl glycolate production processes suffer from severe pollution and demanding reaction conditions, hindering large-scale production. In recent years, the coal-based route for producing methyl glycolate via the hydrogenation of dimethyl oxalate (DMO) has become one of the most promising coal chemical technologies in my country. It is expected that by controlling the distribution of hydrogenation reaction products, high-value-added biodegradable materials can be produced from coal. Furthermore, this process boasts high atom utilization and environmental friendliness, making it significant for promoting the high-end, diversified, and low-carbon development of my country's coal chemical industry.

[0004] Currently, copper-based and silver-based catalysts are commonly used in the hydrogenation of dimethyl oxalate to methyl glycolate. Compared to copper-based catalysts, silver-based catalysts have weaker hydrogenation capacity and weaker adsorption of methyl glycolate. Therefore, they can catalyze the highly selective hydrogenation of dimethyl oxalate to methyl glycolate, inhibiting its deep hydrogenation and exhibiting a high methyl glycolate yield, reaching over 85%. However, silver-based catalysts still have the following problems: 1. To ensure that the silver species exist as metallic silver and exhibit good catalytic activity, the silver loading of the catalyst is generally high, often greater than 10 wt.%, which is expensive and costly; 2. Silver has a low Taman temperature, and the reaction temperature easily leads to the agglomeration and sintering of silver particles, resulting in poor catalyst stability. If a support with strong interaction with the silver species is selected, the loss of electrons by silver leads to a significant decrease in its activity, and the acid-base sites on the support surface easily promote side reactions, reducing selectivity. Summary of the Invention

[0005] The purpose of this invention is to solve the problems of low selectivity of copper-based catalysts and high silver loading and poor stability of silver-based catalysts in the hydrogenation of dimethyl oxalate to methyl glycolate. Copper nanoparticles with strong interaction with the support silica are used as catalyst precursors. During the preparation process, a complexing agent is added to replace the metal on the surface of the copper particles with a monolayer of uniform silver species. This reduces the silver loading and promotes the stability of the catalyst without reducing the metallicity and activity of silver.

[0006] This invention successfully prepared a copper-silver bimetallic catalyst with a copper-silver core-shell structure through a substitution method and a complexing agent. When used in the hydrogenation reaction of dimethyl oxalate to methyl glycolate, it has the characteristics of simple preparation, high catalytic activity, high selectivity and high stability.

[0007] The technical solution adopted in this invention is:

[0008] A catalyst for the hydrogenation of dimethyl oxalate to methyl glycolate with an added complexing agent includes a support and active components. The active components are copper and silver species. The support is silica. The copper-silver bimetallic catalyst has the following structure: silver species uniformly cover the surface of copper species in the form of shells, forming a core-shell structure. The core-shell structure is located on the silica support in the form of particles, wherein copper and silica form a strong interaction. First, a copper-containing catalyst precursor is prepared. Then, the copper-containing catalyst precursor, silver salt, and complexing agent are mixed and treated to obtain the finished catalyst.

[0009] The core-shell structure here refers to the silver particles being uniformly dispersed on the surface of the copper particles, like a shell, ensuring that there is a shell layer of silver particles coating the outside of the copper particles. At the same time, the silver shell layer is also uniform and dense, which can ensure the uniform dispersion of Cu@Ag particles.

[0010] The silver species constitute 1-10 wt.% of the total mass of the copper-silver bimetallic catalyst, and the copper species constitute 1-10 wt.% of the total mass of the copper-silver bimetallic catalyst. The reason for limiting the mass of the copper-silver bimetallic catalyst to the above range is as follows: 1. High silver content will result in uneven distribution of the silver shell layer on the particle surface, causing uneven particle size and thus decreased activity; 2. Increased silver content may also cause some silver to fail to participate in the formation of the core-shell structure, forming silver flocculents that grow freely outside the particles, causing some particles to agglomerate; 3. High copper content will result in excessively large particles, leading to decreased activity; 4. Increased copper content may also prevent the copper outer layer from being completely covered by silver, and exposed copper may easily catalyze the deep hydrogenation of methyl glycolate to ethylene glycol, resulting in decreased selectivity.

[0011] The copper-silver bimetallic catalyst has a specific surface area of ​​50-300 m². 2 / g, with an average pore volume of 0.4-1.7cm³. 3 / g, with an average pore size of 5-30nm. The particle size of the copper-silver bimetallic material is 1.0-10nm, and the thickness of the silver shell layer is 0.2-2nm; the particle size of the copper-silver bimetallic material is 1.0-8nm, and the thickness of the silver shell layer is 0.2-1nm.

[0012] Another object of the present invention is to provide a method for preparing a catalyst with a complexing agent for the hydrogenation of dimethyl oxalate to methyl glycolate, comprising the following steps:

[0013] (1) Dissolve copper nitrate in deionized water and add a certain volume of ammonia;

[0014] (2) Mix the two solutions obtained in step (1) and stir mechanically, and then add a certain amount of silica sol at a certain rate;

[0015] (3) Aging the solution obtained in step (2), then heating to evaporate ammonia, and filtering and washing the resulting mixed solution;

[0016] (4) The product obtained in step (3) is placed in an oven to dry, and then calcined at high temperature to obtain a catalyst precursor. The catalyst precursor is then subjected to reduction treatment.

[0017] (5) The catalyst precursor obtained in step (4) is mixed with silver nitrate, ethanol and complexing agent, and the pH value is adjusted. During this process, the solution is subjected to ultrasonic treatment and mechanical stirring.

[0018] (6) Centrifuge the solution obtained in step (5) and extract the Cu@Ag particles therein. Wash with ethanol and deionized water and dry to obtain the catalyst product.

[0019] The complexing agent is selected from any one of phenylalanine, tyrosine, L-histidine (L-His), gelatin, polyvinylpyrrolidone (PVP), glycine, dl-malic acid, citric acid or tannic acid;

[0020] The stirring time in step (2) is 30 min; the aging time in step (3) is 4 h, and the ammonia stripping temperature is 80℃; the drying conditions in step (4) are: drying temperature is 80-130℃, and drying time is 12-24 h; the reduction treatment conditions are 300℃, and hydrogen reduction is 4 h; the ambient temperature for mixing the catalyst precursor, silver nitrate, ethanol and complexing agent in step (5) is room temperature, i.e., 20-30℃; the drying conditions in step (6) are: drying temperature is 80-130℃, and drying time is 12-24 h.

[0021] The amount of silver nitrate added in step (5) is such that the copper-silver mass ratio is any one of 1:1, 2:1 and 1:2; the pH value of the solution is adjusted by adding alkaline substances in step (5), and the pH value of the adjusted solution is in the range of 8-12, preferably weakly alkaline.

[0022] Another object of the present invention is to provide an application of a catalyst for the hydrogenation of dimethyl oxalate to methyl glycolate, wherein the catalyst is used to catalyze the selective hydrogenation of dimethyl oxalate to methyl glycolate.

[0023] Specifically, the reaction involves introducing a mixture of gasified dimethyl oxalate and hydrogen into a reactor encapsulated with the aforementioned copper-silver bimetallic catalyst; the reaction pressure is 0.5-3.5 MPa; the reaction temperature is 180-240 °C; and the mass hourly space velocity (HSV) of dimethyl oxalate is 0.1-4.0 h⁻¹. -1 The hydrogen ester molar ratio is 60-150.

[0024] The preferred option is to use the catalyst prepared by the method of adding a complexing agent to synthesize a core-shell copper-silver bimetallic catalyst, and to use the catalyst to catalyze the selective hydrogenation of dimethyl oxalate to methyl glycolate.

[0025] Specifically, the reaction involves introducing a mixture of gasified dimethyl oxalate and hydrogen into a reactor encapsulated with the aforementioned copper-silver bimetallic catalyst; the reaction pressure is 0.5-3.5 MPa; the reaction temperature is 180-240 °C; and the mass hourly space velocity (HSV) of dimethyl oxalate is 0.1-4.0 h⁻¹. -1 The hydrogen ester molar ratio is 60-150.

[0026] The present invention has the following beneficial effects:

[0027] 1. This invention successfully prepared a bimetallic catalyst with a copper-silver core-shell structure. Here, the core-shell structure refers to the fact that silver particles are uniformly dispersed on the surface of copper particles like a shell, ensuring that there is a shell layer composed of silver particles coating the outside of the copper particles. At the same time, the silver shell layer also has the characteristics of uniformity and density, and can ensure the uniform dispersion of Cu@Ag particles.

[0028] 2. The copper-silver bimetallic catalyst of this invention exhibits high stability in the heterogeneous hydrogenation reaction of dimethyl oxalate. This is because: layered copper silicate is used as a precursor, which, after reduction, forms copper nanoparticles that strongly interact with silicon oxide. Ag species are located on the surface of the copper species. The interaction between copper and silicon oxide provides a basis for anchoring the silver species, which can prevent the sintering of silver particles and ensure that there is no problem of silver particle growth during long-term use, thereby improving its stability and greatly reducing the catalyst replacement cost in industry.

[0029] 3. The copper-silicon bimetallic catalyst of this invention exhibits low silver loading and high catalytic activity in the heterogeneous hydrogenation reaction of dimethyl oxalate. Compared to the silver loading of over 10 wt.% in existing technologies, the silver species loading in this invention is only 4-6 wt.%, yet the MG yield can reach over 90%. The low silver loading in this catalyst greatly improves silver utilization efficiency and significantly reduces catalyst production costs.

[0030] 4. In the preparation process of the copper-silver bimetallic catalyst of this invention, different complexing agents and changes in the copper-silver mass ratio were added. The addition of complexing agents altered the uniformity of the silver shell layer in the core-shell structure; the change in the mass ratio altered the size of the copper particles and the thickness of the silver shell layer. This invention utilizes this method to control the size of the silver shell layer in Cu@Ag, thereby obtaining a core-shell copper-silver bimetallic catalyst with copper-silver bimetallic particle size of 1.0-10 nm and silver shell layer size of 0.2-2 nm, thus modifying the catalyst performance.

[0031] 5. This invention alters the particle size and core-shell structure formation of copper-silver bimetallic particles by regulating the pH value during the synthesis process.

[0032] 6. The copper-silver bimetallic catalyst obtained in this invention has the advantages of readily available raw materials, mild reaction conditions, simple and controllable process, stable structure, strong operability, and good industrial application prospects when used in the heterogeneous hydrogenation reaction of dimethyl oxalate. Attached Figure Description

[0033] Figure 1 The molecular formula of the complexing agent in the embodiments of this invention;

[0034] Figure 2 This is a high-resolution TEM image of the Cu@Ag structure of the copper-silver bimetallic catalyst in this invention.

[0035] Figure 3 This is a stability test of the catalysts in the comparative and example examples of this invention. Detailed Implementation

[0036] The present invention will be further described below through embodiments, but is not limited to these embodiments. Experimental methods not specifically described in the embodiments generally use conventional conditions and conditions described in manuals, or conditions recommended by the manufacturer. The general equipment, materials, reagents, etc., used are all commercially available unless otherwise specified.

[0037] The methods for evaluating the online reduction and catalytic effect of the catalyst in this embodiment and the comparative example are as follows:

[0038] In this invention, the hydrogenation reaction of dimethyl oxalate is carried out in a fixed-bed reactor. 0.5 g of catalyst is loaded and reduced at 300 °C in a hydrogen atmosphere at 2.5 MPa with a gas flow rate of 80 mL / min for 4 h. The mixture is then cooled to the reaction temperature, and the dimethyl oxalate solution is vaporized and mixed with hydrogen before entering the reaction system. The hydrogen-to-ester ratio is 80. The hydrogenation reaction is carried out at 2.5 MPa, 210 °C, or 225 °C. The products after the reaction are analyzed by gas chromatography, and the conversion rate of dimethyl oxalate and the selectivity and yield of methyl glycolate are calculated. Since the hydrogenation reaction of dimethyl oxalate is a series reaction, and methyl glycolate is the intermediate hydrogenation product, the difference in selectivity for the intermediate product can only be reflected when the conversion rate is not 100%. Therefore, the reaction space velocity was adjusted to achieve a conversion rate of 98.5%. In the stability evaluation process, in order to fully utilize all active sites to participate in the reaction and prevent the situation where the catalyst is deactivated but the conversion rate is still 100%, the stability evaluation needs to be carried out under conditions where the conversion rate is not 100%. In order to characterize the thermal stability of the catalyst, the atmosphere was switched during the reaction, and the catalyst was subjected to high-temperature heat treatment at 350°C under nitrogen for 20 hours before the feed was continued to test the catalyst performance.

[0039] The specific experimental conditions for the catalysts in the comparative examples and each embodiment are shown in Table 1 below, and the activity data are shown in Table 2.

[0040] Comparative Example 1

[0041] Preparation of copper-silver bimetallic catalyst (synthesized at 25℃, without complexing agent, co-impregnation method, copper-silver mass ratio 1:1). This comparative example is the preparation of copper-silver bimetallic catalyst synthesized at 25℃ without complexing agent, as shown in the following details:

[0042] A certain mass of silver nitrate (AgNO3) and copper nitrate (Cu(NO3)2·3H2O) was dissolved in 150 mL of deionized water and stirred at room temperature, protected from light. Then, a corresponding mass of dried fumed silica was slowly added, and the mixture was stirred vigorously for 20 h under light-protected conditions. The mixture was then rotary evaporated at 40 °C to remove excess water. The resulting solid was dried in an oven at 110 °C for 15 h and calcined in a muffle furnace at 400 °C for 4 h. The resulting catalyst was reduced in H2 at 300 °C for 4 h before use. This comparative catalyst, under the above online reduction conditions and catalyst evaluation method, showed a 1.0 h reduction rate. -1 The reaction was carried out under the following conditions. The catalyst remained stable for 250 hours. After 20 hours of high-temperature heat treatment, the yield decreased by 11.0%, and between 270 and 500 hours, the yield decreased from 38.7% to 11.6%.

[0043] Comparative Example 2

[0044] Preparation of copper-silver bimetallic catalyst (synthesized at 25℃, without complexing agent, by displacement method, copper-silver mass ratio 1:1)

[0045] This comparative example is the preparation of the copper-silver bimetallic catalyst (comparative sample 2) synthesized at 25℃ without the addition of a complexing agent, as detailed below:

[0046] Preparation of catalyst precursors by ammonia stripping:

[0047] A certain amount of Cu(NO3)2·H2O was weighed and dissolved in 150 mL of deionized water, and mixed with a certain volume of ammonia (25 wt.%) to form a copper ammonia solution. After stirring for 30 min to homogenize, a certain amount of silica sol was added dropwise to the copper ammonia solution at a certain rate and aged for 4 h. Then, the solution was heated to 80 °C to begin ammonia evaporation, which was stopped when the pH of the solution dropped to 6-7. The mixed solution was filtered and washed with deionized water. The obtained sample was dried in an oven at 110 °C for 12 h, calcined in a muffle furnace at 400 °C for 4 h, and then reduced at 300 °C in an H2 atmosphere for 4 h to obtain a catalyst precursor with a Cu loading of 10 wt.%.

[0048] Preparation of copper-silver bimetallic catalysts:

[0049] The catalyst precursor obtained by the ammonia stripping method was reduced at 300℃ for 4 hours in an H2 atmosphere. A certain amount of AgNO3 was weighed and dissolved in a small amount of deionized water to obtain a mixed solution. A certain volume of ethanol was added to a three-necked flask, which was connected to a Schlenk line and purged with nitrogen at room temperature to remove air from the system. Then, a certain amount of the reduced catalyst precursor was added, followed by a certain volume of AgNO3 solution (mass ratio Cu:Ag = 1:1). The mixture was stirred and mixed for 90 minutes in the dark. The mixed solution was then filtered and washed with deionized water. Finally, the obtained sample was dried in an oven at 110℃ for 12 hours to obtain the catalyst.

[0050] This comparative catalyst, under the aforementioned online reduction conditions and catalyst evaluation methods, was tested at 1.0 h. -1 The reaction was carried out under the following conditions. The catalyst remained stable for 250 hours. After 20 hours of high-temperature heat treatment, the yield decreased by 9.1%, and between 270 and 500 hours, the yield decreased from 44.5% to 23.9%.

[0051] Example 1

[0052] Preparation of a copper-silver bimetallic catalyst (synthesized at 25℃, with the addition of phenylalanine as a complexing agent, by displacement method, copper-silver mass ratio 1:1)

[0053] This comparative example was synthesized at 25℃. Sample 1 was prepared using a copper-silver bimetallic catalyst with the addition of the complexing agent phenylalanine, as detailed below:

[0054] Preparation of catalyst precursors by ammonia stripping:

[0055] 7.6 g of Cu(NO3)2·H2O was weighed and dissolved in 150 mL of deionized water, and then mixed with 25.9 mL of ammonia solution (25 wt.%) to form a copper-ammonia solution. After stirring for 30 min to homogenize, 50 mL of silica sol was added dropwise to the copper-ammonia solution at a certain rate (e.g., 1 drop per second) and aged for 4 h. Then, the solution was heated to 80 °C to begin ammonia evaporation, which was stopped when the pH of the solution dropped to 6-7. The mixed solution was filtered and washed with deionized water (using a Buchner funnel). The obtained sample was dried in an oven at 110 °C for 12 h, calcined in a muffle furnace at 400 °C for 4 h, and then reduced at 300 °C in an H2 atmosphere for 4 h to obtain a catalyst precursor with a Cu loading of 10 wt.%.

[0056] Preparation of copper-silver bimetallic catalysts:

[0057] The catalyst precursor obtained by the ammonia stripping method was reduced at 300℃ for 4 hours in an H2 atmosphere. 0.4 g of AgNO3 was weighed and dissolved in a small amount of deionized water to obtain a mixed solution, which was then set aside.

[0058] A certain volume of ethanol was added to a three-necked flask, which was then connected to a Schlenk line and purged with nitrogen at room temperature to remove air from the system. Then, 4 g of the reduced catalyst precursor was added, along with 10 g / L phenylalanine (sufficient complexing agent), and a certain volume of AgNO3 solution (prepared above, with a Cu:Ag mass ratio of 1:1). The mixture was stirred and mixed in the dark for 90 min. The solution was then filtered and washed with deionized water. Finally, the obtained sample was dried in a 110℃ oven for 12 h (vacuum drying) to obtain the catalyst.

[0059] This comparative catalyst, under the aforementioned online reduction conditions and catalyst evaluation methods, was tested at 1.0 h. -1 The reaction was carried out under the following conditions. The catalyst remained stable for 250 hours. After 20 hours of high-temperature heat treatment, the yield decreased by 5.5%, and between 270 and 500 hours, the yield decreased from 91.7% to 88.7%.

[0060] Example 2

[0061] Preparation of a copper-silver bimetallic catalyst (synthesized at 25°C, with the addition of tyrosine as a complexing agent, by displacement method, copper-silver mass ratio 1:1)

[0062] This embodiment describes the preparation of copper-silver bimetallic catalyst sample 2. The only difference between this sample and sample 1 in Example 1 is that tyrosine was added as a complexing agent during the preparation of the copper-silver bimetallic catalyst in this embodiment. The specific preparation process is as follows:

[0063] The catalyst precursor obtained by the ammonia stripping method was reduced in H2 atmosphere at 300℃ for 4 hours. A certain amount of AgNO3 was weighed and dissolved in a small amount of deionized water to obtain a mixed solution for later use.

[0064] A certain volume of ethanol was added to a three-necked flask, which was then connected to a Schlenk line and purged with nitrogen at room temperature to remove air from the system. Then, a certain amount of reduced catalyst precursor, 10 g / L tyrosine, and a certain volume of AgNO3 solution (prepared above, with a Cu:Ag ratio of 1:1) were added. The mixture was stirred and mixed in the dark for 90 min. The resulting solution was then filtered and washed with deionized water. Finally, the sample was dried in a 110℃ oven for 12 h to obtain the catalyst.

[0065] In this embodiment, the catalyst was subjected to the above-described online reduction conditions and catalyst evaluation method for 1.0 h. -1 The reaction was carried out under the following conditions, and the catalyst yield values ​​are shown in Table 2.

[0066] Example 3

[0067] Preparation of a copper-silver bimetallic catalyst (synthesized at 25°C, with the addition of complexing agent L-histidine, by substitution method, copper-silver mass ratio 1:1)

[0068] This embodiment describes the preparation of copper-silver bimetallic catalyst sample 3. The only difference between this sample and sample 2 in Example 2 is that L-histidine was added as a complexing agent during the preparation of the copper-silver bimetallic catalyst in this embodiment. The specific preparation process is as follows:

[0069] The catalyst precursor obtained by the ammonia stripping method was reduced in H2 atmosphere at 300℃ for 4 hours. A certain amount of AgNO3 was weighed and dissolved in a small amount of deionized water to obtain a mixed solution for later use.

[0070] A certain volume of ethanol was added to a three-necked flask, which was then connected to a Schlenk line and purged with nitrogen at room temperature to remove air from the system. Then, a certain amount of the reduced catalyst precursor was added, along with 10 g / L L-histidine and a certain volume of AgNO3 solution (prepared above, with a Cu:Ag ratio of 1:1). The mixture was stirred and mixed in the dark for 90 min. The resulting solution was then filtered and washed with deionized water. Finally, the sample was dried in a 110°C oven for 12 h to obtain the catalyst.

[0071] In this embodiment, the catalyst was subjected to the above-described online reduction conditions and catalyst evaluation method for 1.0 h. -1 The reaction was carried out under the following conditions, and the catalyst yield values ​​are shown in Table 2.

[0072] Example 4

[0073] Preparation of a copper-silver bimetallic catalyst (synthesized at 25°C, with the addition of complexing agent gelatin, displacement method, copper-silver mass ratio 1:1)

[0074] This embodiment describes the preparation of copper-silver bimetallic catalyst sample 4. The only difference between this sample and sample 3 in Example 3 is that gelatin was added as a complexing agent during the preparation of the copper-silver bimetallic catalyst in this embodiment. The specific preparation process is as follows:

[0075] The catalyst precursor obtained by the ammonia stripping method was reduced in H2 atmosphere at 300℃ for 4 hours. A certain amount of AgNO3 was weighed and dissolved in a small amount of deionized water to obtain a mixed solution for later use.

[0076] A certain volume of ethanol was added to a three-necked flask, which was then connected to a Schlenk line and purged with nitrogen at room temperature to remove air from the system. Then, a certain amount of the reduced catalyst precursor, 10 g / L gelatin, and a certain volume of AgNO3 solution (prepared above, with a Cu:Ag ratio of 1:1) were added. The mixture was stirred and mixed in the dark for 90 min. The resulting solution was then filtered and washed with deionized water. Finally, the sample was dried in a 110℃ oven for 12 h to obtain the catalyst.

[0077] In this embodiment, the catalyst was subjected to the above-described online reduction conditions and catalyst evaluation method for 1.0 h. -1 The reaction was carried out under the following conditions, and the catalyst yield values ​​are shown in Table 2.

[0078] Example 5

[0079] Preparation of copper-silver bimetallic catalyst (synthesized at 25℃, with the addition of complexing agent PVP, displacement method, copper-silver mass ratio 1:1)

[0080] This embodiment describes the preparation of copper-silver bimetallic catalyst sample 5. The only difference between this sample and sample 4 in Example 4 is that PVP was added as a complexing agent during the preparation of the copper-silver bimetallic catalyst in this embodiment. The specific preparation process is as follows:

[0081] The catalyst precursor obtained by the ammonia stripping method was reduced in H2 atmosphere at 300℃ for 4 hours. A certain amount of AgNO3 was weighed and dissolved in a small amount of deionized water to obtain a mixed solution for later use.

[0082] A certain volume of ethanol was added to a three-necked flask, which was then connected to a Schlenk line and purged with nitrogen at room temperature to remove air from the system. Then, a certain amount of reduced catalyst precursor, 10 g / L PVP, and a certain volume of AgNO3 solution (prepared above, with a Cu:Ag ratio of 1:1) were added. The mixture was stirred and mixed in the dark for 90 min. The resulting solution was then filtered and washed with deionized water. Finally, the sample was dried in a 110℃ oven for 12 h to obtain the catalyst.

[0083] In this embodiment, the catalyst was subjected to the above-described online reduction conditions and catalyst evaluation method for 1.0 h. -1 The reaction was carried out under the following conditions, and the catalyst yield values ​​are shown in Table 2.

[0084] Example 6

[0085] Preparation of a copper-silver bimetallic catalyst (synthesized at 25°C, with the addition of glycine as a complexing agent, by displacement method, copper-silver mass ratio 1:1)

[0086] This embodiment describes the preparation of copper-silver bimetallic catalyst sample 6. The only difference between this sample and sample 5 in Example 5 is that glycine was added as a complexing agent during the preparation of the copper-silver bimetallic catalyst in this embodiment. The specific preparation process is as follows:

[0087] The catalyst precursor obtained by the ammonia stripping method was reduced in H2 atmosphere at 300℃ for 4 hours. A certain amount of AgNO3 was weighed and dissolved in a small amount of deionized water to obtain a mixed solution for later use.

[0088] A certain volume of ethanol was added to a three-necked flask, which was then connected to a Schlenk line and purged with nitrogen at room temperature to remove air from the system. Then, a certain amount of the reduced catalyst precursor, 10 g / L glycine, and a certain volume of AgNO3 solution (prepared above, with a Cu:Ag ratio of 1:1) were added. The mixture was stirred and mixed in the dark for 90 min. The resulting solution was then filtered and washed with deionized water. Finally, the sample was dried in a 110℃ oven for 12 h to obtain the catalyst.

[0089] In this embodiment, the catalyst was subjected to the above-described online reduction conditions and catalyst evaluation method for 1.0 h. -1 The reaction was carried out under the following conditions, and the catalyst yield values ​​are shown in Table 2.

[0090] Example 7

[0091] Preparation of a copper-silver bimetallic catalyst (synthesized at 25℃, with the addition of complexing agent dl-malic acid, displacement method, copper-silver mass ratio 1:1)

[0092] This embodiment describes the preparation of copper-silver bimetallic catalyst sample 7. The only difference between this sample and sample 6 in Example 6 is that dl-malic acid was added as a complexing agent during the preparation of the copper-silver bimetallic catalyst in this embodiment. The specific preparation process is as follows:

[0093] The catalyst precursor obtained by the ammonia stripping method was reduced in H2 atmosphere at 300℃ for 4 hours. A certain amount of AgNO3 was weighed and dissolved in a small amount of deionized water to obtain a mixed solution for later use.

[0094] A certain volume of ethanol was added to a three-necked flask, which was then connected to a Schlenk line and purged with nitrogen at room temperature to remove air from the system. Then, a certain amount of the reduced catalyst precursor was added, along with 10 g / L dl-malic acid and a certain volume of AgNO3 solution (prepared above, with a Cu:Ag ratio of 1:1). The mixture was stirred and mixed in the dark for 90 min. The resulting solution was then filtered and washed with deionized water. Finally, the sample was dried in a 110℃ oven for 12 h to obtain the catalyst.

[0095] In this embodiment, the catalyst was subjected to the above-described online reduction conditions and catalyst evaluation method for 1.0 h. -1 The reaction was carried out under the following conditions, and the catalyst yield values ​​are shown in Table 2.

[0096] Example 8

[0097] Preparation of a copper-silver bimetallic catalyst (synthesized at 25°C, with the addition of citric acid as a complexing agent, by displacement method, copper-silver mass ratio 1:1)

[0098] This embodiment describes the preparation of copper-silver bimetallic catalyst sample 8. The only difference between this sample and sample 7 in Example 7 is that citric acid was added as a complexing agent and potassium carbonate was added to adjust the pH of the solution to 8 during the preparation process. The specific preparation process is as follows:

[0099] The catalyst precursor obtained by the ammonia stripping method was reduced in H2 atmosphere at 300℃ for 4 hours. A certain amount of AgNO3 was weighed and dissolved in a small amount of deionized water to obtain a mixed solution for later use.

[0100] A certain volume of ethanol was added to a three-necked flask, which was then connected to a Schlenk line and purged with nitrogen at room temperature to remove air from the system. Then, a certain amount of the reduced catalyst precursor was added, along with 10 g / L citric acid and a certain volume of AgNO3 solution (prepared above, with a Cu:Ag ratio of 1:1). The mixture was stirred and mixed in the dark for 90 min. The resulting solution was then filtered and washed with deionized water. Finally, the sample was dried in a 110°C oven for 12 h to obtain the catalyst.

[0101] In this embodiment, the catalyst was subjected to the above-described online reduction conditions and catalyst evaluation method for 1.0 h. -1 The reaction was carried out under the following conditions, and the catalyst yield values ​​are shown in Table 2.

[0102] Example 9

[0103] Preparation of a copper-silver bimetallic catalyst (synthesized at 25℃, with the addition of complexing agent tannic acid, by displacement method, copper-silver mass ratio 1:1)

[0104] This embodiment describes the preparation of copper-silver bimetallic catalyst sample 9. The only difference between this sample and sample 8 in Example 8 is that tannic acid was added as a complexing agent during the preparation of the copper-silver bimetallic catalyst in this embodiment. The specific preparation process is as follows:

[0105] The catalyst precursor obtained by the ammonia stripping method was reduced in H2 atmosphere at 300℃ for 4 hours. A certain amount of AgNO3 was weighed and dissolved in a small amount of deionized water to obtain a mixed solution for later use.

[0106] A certain volume of ethanol was added to a three-necked flask, which was then connected to a Schlenk line and purged with nitrogen at room temperature to remove air from the system. Then, a certain amount of reduced catalyst precursor, 10 g / L tannic acid, and a certain volume of AgNO3 solution (prepared above, with a Cu:Ag ratio of 1:1) were added. The mixture was stirred and mixed in the dark for 90 min. The resulting solution was then filtered and washed with deionized water. Finally, the sample was dried in a 110℃ oven for 12 h to obtain the catalyst.

[0107] In this embodiment, the catalyst was subjected to the above-described online reduction conditions and catalyst evaluation method for 1.0 h. -1 The reaction was carried out under the following conditions, and the catalyst yield values ​​are shown in Table 2.

[0108] Examples 10-13

[0109] The effects of different pH values ​​on the copper-silver bimetallic catalyst (synthesized at 25℃ with the addition of complexing agent tannic acid, displacement method, copper-silver mass ratio 1:1) and its catalytic activity were investigated.

[0110] The only difference from Example 9 is that the solution pH is 9, 10, 11, and 12.

[0111] Examples 10-13: Catalysts were subjected to the above-described online reduction conditions and catalyst evaluation methods, and the reaction was carried out at 1.0 h. -1 The reaction was carried out under the following conditions, and the catalyst yield values ​​are shown in Table 2.

[0112] Examples 14 and 15

[0113] Preparation of copper-silver bimetallic catalysts (synthesized at 25℃, with the addition of complexing agent glycine, by displacement method)

[0114] The effects of different copper-silver mass ratios on copper-silver bimetallic catalysts and their effects on catalyst activity were investigated.

[0115] The only difference from Example 6 is that the Cu:Ag ratios are 2:1 and 1:2, respectively.

[0116] In Examples 14 and 15, the catalysts were subjected to the above-described online reduction conditions and catalyst evaluation methods for 1.0 h. -1 The reaction was carried out under the following conditions, and the catalyst yield values ​​are shown in Table 2.

[0117] Example 16

[0118] Preparation of a copper-silver bimetallic catalyst (synthesized at 25℃, with the addition of phenylalanine as a complexing agent, by displacement method, copper-silver mass ratio 1:1)

[0119] The effects of high temperature and high space velocity on the selectivity of copper-silver bimetallic catalysts were investigated.

[0120] Compared to Example 1, the only difference is that the reaction conditions were changed to 225°C and 2.0 h. -1 .

[0121] Example 16: The catalyst was subjected to the above-described online reduction conditions and catalyst evaluation method at 225°C for 2.0 h. -1 The reaction was carried out under the following conditions, and the catalyst yield values ​​are shown in Table 2.

[0122] Comparative Examples 1 and 2 show that the catalyst in Comparative Example 1, synthesized at room temperature using the co-impregnation method, had a yield of only 49.7%. In contrast, the catalyst prepared using the substitution method in Comparative Example 2 exhibited increased activity, with the MG yield rising to 53.6%. Therefore, the substitution method in the preparation of copper-silver bimetallic catalysts allows for better anchoring of copper and silver species through strong interactions, enhancing catalyst activity, improving the directional selectivity of methyl glycolate, and enhancing catalyst stability. This also reduces catalyst replacement costs in industrial applications.

[0123] Comparative Example 2 and Example 1 show that the catalyst in Comparative Example 2, synthesized at room temperature without a complexing agent, exhibits low activity, with a selectivity of only 62.1% and a yield of only 53.6%. In Example 1, however, the addition of a complexing agent significantly increases the catalyst activity, raising the selectivity to 98.7%, the MG yield to over 90%, and the space-time yield from 5.1 g·g⁻¹. cat -1 ·h -1 Increased to 9.3 g·g cat -1 ·h -1 Therefore, introducing a complexing agent during the preparation of copper-silver bimetallic catalysts enhances catalyst activity, improves the directional selectivity of methyl glycolate, and strengthens catalyst stability. This can reduce catalyst replacement costs in industrial applications.

[0124] As shown in Examples 1-9, different complexing agents were added during the preparation process. The catalyst selectivity and MG yield changed under the action of different complexing agents, indicating that different complexing agents have different effects on the synthesis of copper-silver bimetallic catalysts.

[0125] Comparative Examples 2 and 3 show that the synthesis temperature was changed during the preparation process, and the MG yield and space-time yield of the catalysts prepared in Comparative Examples 2 and 3 were also different under the reaction conditions, indicating that the synthesis temperature has an impact on the preparation of copper-silver bimetallic catalysts.

[0126] As can be seen from Examples 9-13, the pH changed during the preparation of the copper-silver bimetallic catalyst in Examples 9-13, and the MG yield and space-time yield of the prepared catalyst under the reaction conditions also differed, indicating that pH has an impact on the preparation of the copper-silver bimetallic catalyst.

[0127] As can be seen from Examples 6 and 14 and 15, the copper-silver mass ratio changed during the preparation of the copper-silver bimetallic catalyst in Examples 4 and 14 and 15. The MG yield and space-time yield of the prepared catalyst under the reaction conditions also differed, indicating that the copper-silver mass ratio has an impact on the preparation of the copper-silver bimetallic catalyst.

[0128] Table 1. Preparation conditions and particle size of each catalyst

[0129]

[0130] Table 2. Activity data of each catalyst for the heterogeneous hydrogenation reaction of dimethyl oxalate.

[0131]

[0132] Through Examples 1-9 in Table 1-2 and Figure 1 It is evident that phenylalanine is the most effective chelating agent. This is because phenylalanine itself contains amino and hydroxyl groups that can form bonds with Ag, anchoring Ag species. Furthermore, the amino and hydroxyl structures of phenylalanine are located on the side chain, bypassing the cyclic structure of the chelating agent itself and preventing intermolecular aggregation. Therefore, phenylalanine is more effective as a chelating agent.

[0133] As shown in Examples 9-13 of Table 1-2, pH=11 yielded the best results during the preparation process. This is because weak alkalinity promotes the reduction of silver ions, and at pH approximately 11, more functional groups, such as hydroxyl or carbonyl groups, can form bonds with Ag, resulting in interactions. Conversely, higher alkalinity tends to cause the deposition of some silver anions. Therefore, pH=11 is the most effective.

[0134] Through Examples 6 and 14, 15 in Table 1-2 and Figure 2 It can be seen that the Cu:Ag ratio of 1:1 is the most effective in the preparation process. This is because when the Ag content is low, not all the metallic Cu species are coated with Ag, resulting in low catalytic selectivity. When the Ag content is high, Ag species agglomerate during the displacement process, and Ag nanoparticles grow, failing to coat Cu with Ag. Therefore, the Cu:Ag ratio of 1:1 is the most effective.

[0135] Compared with Example 16, the catalyst exhibits higher selectivity for MG and better space-time yield at high space velocity and high reaction temperature. This is because high space velocity and high reaction temperature can keep the catalyst in the MG generation stage during the DMO hydrogenation process, thus inhibiting the deep hydrogenation process.

[0136] Comparative Examples 1 and 2 and Examples 1-9 in Tables 1-2 and... Figure 3 As can be seen, introducing a complexing agent during catalyst synthesis can enhance the catalyst's activity and stability.

[0137] The catalyst prepared by adding a complexing agent in this invention features mild conditions, a simple preparation process, readily available raw materials, low cost, and excellent catalytic performance. In practical industrial applications, it can be used alone for the production of methyl glycolate, a high-value and high-demand product, maintaining a methyl glycolate yield of over 90% even at high space velocities. Furthermore, the catalyst's stability is greatly improved, significantly extending its lifespan, reducing losses from catalyst replacement in industrial applications, and lowering its industrialization costs.

Claims

1. A catalyst for synthesizing glycollic acid methyl ester by hydrolyzing dimethyl oxalate, the catalyst being a copper-silver bimetallic catalyst characterized in that: The catalyst comprises a carrier and active components, the active components are copper species and silver species, and the carrier is silicon dioxide; the silver species accounts for 1-10 wt.% of the total mass of the catalyst, and the copper species accounts for 1-10 wt.% of the total mass of the catalyst; First, a copper-containing catalyst precursor is prepared, and then the copper-containing catalyst precursor, a silver salt and a complexing agent are mixed and treated to obtain a catalyst product; The preparation process of the catalyst precursor comprises the following steps: dissolving a copper salt in water, adding ammonia water, stirring uniformly, and then dropping silicon sol; after aging treatment, ammonia is evaporated by heating, and after completion, the product is filtered and washed; after washing, the product is dried and then calcined to obtain the catalyst precursor, and reduction treatment is performed; The structure of the catalyst is that the silver species covers the surface of the copper species in the form of a shell layer to form a core-shell structure.

2. The catalyst for synthesizing oxalic acid dimethyl ester by adding complexing agent for preparing glycollic acid methyl ester by hydrogenation according to claim 1, characterized in that: The catalyst has a specific surface area of 50-300 m 2 / g, an average pore volume of 0.4-1.7 cm 3 / g, and an average pore diameter of 5-30 nm.

3. The catalyst for synthesizing oxalic acid dimethyl ester hydrogenation to prepare glycollic acid methyl ester by adding complexing agent according to claim 2, characterized in that: The core-shell structure is in the form of particles and is located on the carrier silicon dioxide, and copper and silicon oxide form a strong interaction.

4. The catalyst for synthesizing oxalic acid dimethyl ester by hydrogenation to prepare methyl glycolate by adding a complexing agent according to claim 3, characterized in that: The particle size of the copper-silver bimetallic catalyst is 1.0-10 nm, and the thickness of the silver shell layer is 0.2-2 nm.

5. The catalyst for synthesizing oxalic acid dimethyl ester by hydrogenation to prepare methyl glycolate by adding a complexing agent according to claim 3, characterized in that: The particle size of the copper-silver bimetallic catalyst is 1.0-8 nm, and the thickness of the silver shell layer is 0.2-1 nm.

6. A process for the preparation of a catalyst for the synthesis of methyl glycolate by hydro genation of dimethyl oxalate with the addition of a complexing agent as claimed in claim 1 or 2 or 3 or 4 or 5, characterized in that: It comprises the following steps: Dissolve the copper salt in water, add ammonia water, stir uniformly, and then drop the silicon sol; After aging treatment, ammonia is evaporated by heating, and after completion, the product is filtered and washed; After washing, the product is dried and then calcined to obtain the catalyst precursor, and reduction treatment is performed; The catalyst precursor, a silver salt, ethanol and a complexing agent are mixed, the pH value is adjusted, copper-silver particles are extracted after centrifugation, and the catalyst product is obtained after cleaning and drying.

7. The method for preparing a catalyst for synthesizing oxalic acid dimethyl ester hydrogenation to prepare glycollic acid methyl ester by adding a complexing agent according to claim 6, characterized in that: The aging treatment time is 4 hours, and the ammonia evaporation temperature is 80 degrees Celsius.

8. The method for preparing a catalyst for synthesizing oxalic acid dimethyl ester hydrogenation to prepare glycollic acid methyl ester by adding a complexing agent according to claim 6, characterized in that: The drying conditions of the washed product are: the temperature is 80-130 degrees Celsius, and the drying time is 12-24 hours.

9. The method for preparing a catalyst for synthesizing oxalic acid dimethyl ester hydrogenation to prepare glycollic acid methyl ester by adding a complexing agent according to claim 6, characterized in that: The temperature after mixing the catalyst precursor, the silver salt, ethanol and the complexing agent is room temperature.

10. The method for preparing a catalyst for synthesizing oxalic acid dimethyl ester hydrogenation to prepare glycollic acid methyl ester by adding a complexing agent according to claim 6, characterized in that: The copper salt is copper nitrate.

11. The method for preparing a catalyst for synthesizing oxalic acid dimethyl ester hydrogenation to prepare glycollic acid methyl ester by adding a complexing agent according to claim 7 or 8 or 9, characterized in that: The copper salt is copper nitrate.

12. The preparation method of the catalyst for synthesizing oxalic acid dimethyl ester by hydrogenation to prepare methyl glycolate by adding a complexing agent according to claim 11, characterized in that: The complexing agent is any one of phenylalanine, tyrosine, L-histidine, gelatin, polyvinylpyrrolidone, glycine, dl-malic acid, citric acid or tannic acid.

13. The method for preparing a catalyst for synthesizing oxalic acid dimethyl ester hydrogenation to prepare glycollic acid methyl ester by adding a complexing agent according to claim 12, characterized in that: The mass ratio of copper to silver is any one of 1:1, 2:1 or 1:

2.

14. The method for preparing a catalyst for synthesizing oxalic acid dimethyl ester hydrogenation to prepare glycollic acid methyl ester by adding a complexing agent according to claim 12 or 13, characterized in that: The pH value is adjusted to weak alkalinity.

15. Use of a catalyst for the synthesis of methyl glycolate by hydrogenation of dimethyl oxalate to which a complexing agent has been added, as claimed in claim 1 or 2 or 3 or 4 or 5, or of a catalyst prepared according to the method for the synthesis of methyl glycolate by hydrogenation of dimethyl oxalate to which a complexing agent has been added, as claimed in claim 10 or 11 or 12 or 13 or 14, characterized in that: The catalyst is used to catalyze the selective hydrogenation of oxalic acid dimethyl ester to generate methyl glycolate; Specifically, mixed gaseous oxalic acid dimethyl ester and hydrogen are introduced into a reactor encapsulating the copper-silver bimetallic catalyst to perform reaction. The reaction pressure is 0.5-3.5 MPa; the reaction temperature is 180-240 ℃; the mass space velocity of dimethyl oxalate is 0.1-4.0 h -1 ; and the molar ratio of hydrogen ester is 60-150.

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