A bifunctional catalyst and its application in preparation of glycolic acid methyl ester from dimethyl oxalate

Abstract

The application provides a bifunctional catalyst and application of the bifunctional catalyst in preparation of methyl glycolate from dimethyl oxalate by hydrogenation, the catalyst has a three-layer core-shell structure, the inner core is a dehydrogenation catalyst, the shell layer is a hydrogenation catalyst, and a separation layer between the inner core and the shell layer is a porous oxide layer with a gas channel; the dehydrogenation catalyst comprises an active component Cu and a non-noble metal auxiliary element M1; the hydrogenation catalyst comprises an active component Cu and a noble metal auxiliary element M2; and the porous oxide layer is also used as a solid carrier of the active component and the auxiliary element in the hydrogenation catalyst. The application can provide hydrogen in situ from methanol, cancels external hydrogen, uses methanol as a hydrogen source and a reactant at the same time, co-produces MF, spatially separates the hydrogenation catalyst and the dehydrogenation catalyst in the core-shell structure to avoid interference, uses a single catalyst and a single bed layer to simplify the process, and realizes continuous gas-phase coupling reaction under the condition of no external hydrogen by using a fixed bed for continuous gas-phase reaction, which is easy to be industrialized.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, and in particular to a bifunctional catalyst and its application in the hydrogenation of dimethyl oxalate to methyl glycolate. Background Technology

[0002] Methyl glycolate (MG) is a key monomer in the synthesis of polyglycolic acid (PGA), a biodegradable plastic. With the PGA market experiencing rapid growth in demand, producing MG from syngas (CO+H2) via the hydrogenation of dimethyl oxalate (DMO) is an important route that aligns with my country's resource endowment.

[0003] However, existing DMO hydrogenation to MG processes face three major technical bottlenecks: (1) Highly dependent on external hydrogen The hydrogenation reaction of DMO (dihydrogen monoxide) is: (COOCH3)2 + 2H2 → HOCH2COOCH3 + CH3OH, which requires a large amount of hydrogen gas. Industrially, hydrogen is mainly derived from the water-gas shift reaction of coal-to-syngas (CO + H2O → CO2 + H2), with approximately 10 tons of hydrogen produced as a byproduct for every ton of H2 produced. It has extremely high carbon emission intensity. At the same time, the conversion unit consumes a large amount of medium-pressure steam, accounting for 15-20% of the energy consumption of the entire plant.

[0004] (2) High energy consumption of methanol cycle In the existing process, methanol, as a solvent for DMO, needs to be recycled through a distillation column. The methanol recycling pipeline requires continuous steam tracing (to prevent DMO crystallization), and the steam consumption of the distillation column accounts for 15-20% of the total steam consumption of the unit. Furthermore, at low loads, low-quality methanol is discharged, causing material loss.

[0005] (3) High hydrogen-ester ratio, large equipment investment To prevent excessive hydrogenation and the formation of ethylene glycol, a high hydrogen-to-ester ratio is typically used industrially. The molar ratio is 80-100, which leads to a large hydrogen circulation volume, high compressor energy consumption, and large reactor volume.

[0006] In recent years, researchers have proposed a strategy of coupling methanol dehydrogenation with DMO hydrogenation: methanol dehydrogenation produces hydrogen gas. Methanol and methanol are used in situ for the hydrogenation of DMO. This approach eliminates the need for external hydrogen and upgrades methanol from a "solvent" to a "reactant," co-producing high-value-added MF. Zhao Chen et al. from East China Normal University achieved this coupled reaction in a one-pot high-pressure reactor, but the reactor reaction suffers from problems such as a sudden increase in hydrogen pressure and catalyst poisoning by the byproduct CO. No mature reports have yet been published on fixed-bed gas-phase coupled reaction systems. Mu Shifang et al. from Henan Polytechnic University conducted preliminary explorations of fixed-bed coupled reactions, but the active sites for dehydrogenation and hydrogenation were randomly distributed, resulting in mutual interference and low selectivity. Existing patents (such as CN121588835A) disclose catalysts and processes for the hydrogenation of DMO and methanol to MG, but these still rely on external hydrogen or use two independent catalysts in separate stages, failing to achieve true "hydrogen-free" and "single-catalyst single-bed" coupling.

[0007] Based on the above, it can be seen that the existing DMO hydrogenation to MG production method has the following main drawbacks: it relies on water-gas shift for hydrogen production, resulting in high carbon emissions; methanol is only used as a solvent, resulting in high cycle energy consumption; the active sites for dehydrogenation and hydrogenation are randomly mixed and interfere with each other; two catalysts are loaded in stages, making the equipment complex; and the high-pressure autoclave reaction is difficult to make continuous. Summary of the Invention

[0008] Addressing the technical problems of existing technologies, such as dependence on exogenous hydrogen, high energy consumption in methanol cycling, and interference between active sites in dehydrogenation and hydrogenation, this invention proposes a bifunctional catalyst and its application in the hydrogenation of dimethyl oxalate to methyl glycolate. This catalyst enables: in-situ hydrogen supply from methanol, eliminating the need for exogenous hydrogen; methanol acting as both a hydrogen source and reactant, co-producing MF; spatial separation of the core-shell structure of the hydrogenation and dehydrogenation catalysts to avoid interference; a single catalyst and a single bed, simplifying the process; and a fixed-bed continuous gas-phase reaction, facilitating industrialization. In short, it achieves a continuous gas-phase coupled reaction under conditions without exogenous hydrogen.

[0009] The present invention proposes a bifunctional catalyst having a three-layer core-shell structure, wherein the core is a dehydrogenation catalyst, the shell is a hydrogenation catalyst, and the isolation layer between the core and the shell is a porous oxide with gas channels. The dehydrogenation catalyst includes an active component Cu and a non-precious metal auxiliary element M1; the hydrogenation catalyst includes an active component Cu and a precious metal auxiliary element M2; the porous oxide layer also serves as a support for the active component and auxiliary element in the hydrogenation catalyst.

[0010] In this invention, the catalyst has a three-layer core-shell structure: (1) Core: A highly active catalyst for the oxygen-free dehydrogenation of methanol is selected, at which methanol undergoes a dehydrogenation reaction: CH3OH → HCOOCH3 + 2H2 (Main reaction) CH3OH → CO + 2H2 (side reaction) (2) Shell: Select a catalyst with high selectivity for DMO hydrogenation; DMO undergoes hydrogenation at this site: (COOCH3)2 + 2H2→ HOCH2COOCH3 + CH3OH (3) Isolation layer: A porous oxide layer with gas channels and controllable thickness; its functions include: ① Physically separate the core and shell to prevent the two active components from migrating to each other or undergoing side reactions; ② Selective transmission The molecules (kinetic diameter 0.29 nm) are blocked from directly contacting the core by larger DMO and MG molecules, thus reducing undesirable reactions. ③ The porous structure provides hydrogen diffusion channels; ④ Used as a support for active components and auxiliary elements in shell catalysts.

[0011] Reaction pathway: The raw materials methanol and DMO first contact the shell layer. DMO is adsorbed on the surface of the shell catalyst, but at this time there is no hydrogen (or very little hydrogen), so the reaction does not occur; some methanol molecules diffuse through the pores of the shell and the isolation layer to the core surface, where they are dehydrogenated to form DMO. and MF / CO; generated The adsorbed DMO diffuses back into the shell, where it is hydrogenated to MG. MF and CO (as well as unreacted methanol) diffuse from the outside of the catalyst particles into the main gas stream and are discharged with the products.

[0012] Preferably, M1 is at least one of Zn, Cr or Mn; and M2 is at least one of Pd, Pt or Ru.

[0013] Preferably, the dehydrogenation catalyst is Cu-ZnO. or One of the following; the hydrogenation catalyst is at least one of Pd-Cu, Pt-Cu or Ru-Cu.

[0014] Preferably, in the dehydrogenation catalyst, the molar ratio of Cu to M1 is 1:0.5-2; in the hydrogenation catalyst, the molar ratio of Cu to M2 is 1:2-5.

[0015] Preferably, the porous oxide layer is mesoporous. Mesoporous or mesoporous At least one of them.

[0016] Preferably, the core particle size is 10-500 nm; the shell thickness is 5-300 nm; the isolation layer thickness is 20-200 nm, and the pore size is 2-10 nm.

[0017] This invention also proposes a method for preparing the above-mentioned bifunctional catalyst, comprising: (1) The aqueous solution containing Cu and M1 soluble salts was subjected to a co-precipitation reaction, and after drying, calcination and reduction, the core of the dehydrogenation catalyst was obtained. (2) The core of the dehydrogenation catalyst is dispersed in an ethanol-water solution containing a template agent and an oxide precursor for a sol-gel reaction. After calcination to remove the template agent, an isolation layer is formed on the surface of the core. (3) The core of the isolation layer is immersed in an aqueous solution containing Cu and M2 precursor salt, and then dried, roasted and reduced to form a shell of hydrogenation catalyst on the surface of the isolation layer, which is the bifunctional catalyst.

[0018] This invention also proposes the application of the above-mentioned bifunctional catalyst in the hydrogenation of dimethyl oxalate to methyl glycolate from methanol with in-situ hydrogen supply.

[0019] Preferably, a feed liquid comprising methanol and dimethyl oxalate is passed into a fixed-bed reactor packed with the multiphase catalyst, and a hydrogenation reaction is carried out under conditions without external hydrogen to obtain methyl glycolate.

[0020] Preferably, the hydrogenation reaction temperature is 240-300℃, the pressure is 0.5-2.5 MPa, and the liquid hourly space velocity of dimethyl oxalate is [missing value]. The mass ratio of methanol to dimethyl oxalate is 1-4:1.

[0021] This invention also proposes a process system for the hydrogenation of dimethyl oxalate to methyl glycolate using methanol with in-situ hydrogen donation, comprising: Raw material mixing tank, used to mix methanol and dimethyl oxalate to form a raw material liquid; A fixed-bed reactor, connected to a feed mixing tank, is filled with the bifunctional catalyst described in any one of claims 1-5, for hydrogenating the feed liquid to obtain gaseous reaction products; A cooler, connected to a fixed-bed reactor, is used to condense gaseous reaction products into liquid reaction products; A gas-liquid separator, connected to a cooler, is used to separate liquid-phase reaction products into gas and liquid phases; A distillation column, connected to a gas-liquid separator, is used to separate the liquid phase into methyl glycolate, methyl formate, and unreacted methanol and dimethyl oxalate. The circulation system, connected to the distillation column, is used to return unreacted methanol and dimethyl oxalate to the feed mixing tank.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Elimination of external hydrogen supply: In-situ dehydrogenation of methanol to supply hydrogen, eliminating the need for water-gas conversion to produce hydrogen, and the entire process is completed. Emissions reduced by more than 80%; (2) Methanol value-added conversion: Methanol is converted from a low-value solvent into a high-value reactant, and methyl formate is produced as a co-product, with 0.45 tons of MF produced as a byproduct per ton of MG; (3) Reduce methanol cycle energy consumption: methanol consumption is reduced by about 66%, and steam consumption is reduced by 51%; (4) The catalyst is highly innovative: the core-shell structure separates the active sites for dehydrogenation and hydrogenation, avoiding mutual interference, and the MG selectivity is ≥92%; (5) Simplified equipment: single catalyst, single bed, no need for segmented filling, easy to modify existing equipment; (6) Continuous gas phase fixed bed process: It overcomes the disadvantages of batch reaction which is difficult to make continuous and the pressure rises sharply, and has industrialization prospects. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the process system described in this invention. Detailed Implementation

[0024] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1

[0026] This embodiment proposes a bifunctional catalyst with a three-layered core-shell structure, and the specific preparation method includes: (1) Core particles of Cu / ZnO dehydrogenation catalyst 12.1g and 7.4g Dissolved in 100 mL of deionized water, ammonia (25%) was added to pH=11 to form a copper-zinc ammonia complex solution. The solution was stirred and aged for 2 h, then heated to 90 °C to evaporate the ammonia until pH=7. The solution was filtered, washed, dried at 110 °C for 12 h, and calcined at 450 °C for 4 h to obtain Cu-ZnO composite powder (Cu:Zn molar ratio 2:1). The obtained powder was then... Reduced at 300℃ for 2 hours in an atmosphere to obtain core particles (Cu / ZnO dehydrogenation catalyst, with an average particle size of about 20 nm). (2) Covering mesopores layer of isolation layer 5g of the above-mentioned core particles were ultrasonically dispersed in 150mL of ethanol-water (1:1) mixture containing 1.5g of CTAB. 10mL of tetraethyl orthosilicate (TEOS) was added, and ammonia was added dropwise to adjust the pH to 9. The mixture was stirred at room temperature for 24h, centrifuged, washed with ethanol, dried at 110℃, and calcined at 550℃ for 5h to remove CTAB, forming mesopores on the surface of the core particles. The isolation layer of the layer (thickness approximately 50 nm, mesopore diameter approximately 5 nm); (3) Shell of supported Pd-Cu hydrogenation catalyst The above mesopores The core particles after layering are impregnated with a solution containing (Contains 0.2g of Pd) and In a 50 mL aqueous solution containing 0.4 g of Cu, the mixture was sonicated for 30 min, evaporated at 85 °C to remove water, dried at 110 °C for 12 h, calcined at 450 °C for 4 h, and then... Reduction at 350℃ for 3 hours in a (5:1) atmosphere, in a mesoporous environment. A shell layer for the Pd-Cu hydrogenation catalyst is formed on the surface of the isolation layer, yielding the final catalyst (Pd loading approximately 2 wt%, Cu loading approximately 4 wt%, Pd:Cu molar ratio approximately 1:3), which is the bifunctional catalyst (Cu-ZnO@mesoporous). ), denoted as catalyst A.

[0027] Example 2

[0028] This embodiment proposes a bifunctional catalyst, which also has a three-layer core-shell structure. The specific preparation method is the same as in Example 1, except that in step (1) an equimolar amount is used. replace The final catalyst is obtained, denoted as catalyst A-1.

[0029] Example 3

[0030] This embodiment proposes a bifunctional catalyst, which also has a three-layer core-shell structure. The specific preparation method is the same as in Example 1, except that in step (3) an equal amount of replace The final catalyst is obtained, denoted as catalyst A-2.

[0031] Comparative Example 1 This comparative example presents a bifunctional catalyst (physical mixing), and the specific preparation method includes: (1) Cu / ZnO dehydrogenation catalyst: 12.1g and 7.4g Dissolved in 100 mL of deionized water, ammonia (25%) was added to pH=11 to form a copper-zinc ammonia complex solution. The solution was stirred and aged for 2 h, then heated to 90 °C to evaporate the ammonia until pH=7. The solution was filtered, washed, dried at 110 °C for 12 h, and calcined at 450 °C for 4 h to obtain Cu-ZnO composite powder (Cu:Zn molar ratio 2:1). The obtained powder was then... The Cu / ZnO dehydrogenation catalyst (average particle size about 20 nm) was obtained by reduction at 300 °C for 2 h in a (10:1) atmosphere. (2) Hydrogenation catalyst: Add 10 mL of tetraethyl orthosilicate (TEOS) to 150 mL of an ethanol-water (1:1) mixture containing 1.5 g of CTAB, adjust the pH to 9 by adding ammonia dropwise, stir at room temperature for 24 h, centrifuge, wash with ethanol, dry at 110 °C, and calcine at 550 °C for 5 h to obtain... Particles; the aforementioned Particles impregnated with containing (Contains 0.2g of Pd) and In a 50 mL aqueous solution containing 0.4 g of Cu, the mixture was sonicated for 30 min, evaporated at 85 °C to remove water, dried at 110 °C for 12 h, calcined at 450 °C for 4 h, and then... Reduced at 350℃ for 3 hours in a (5:1) atmosphere to obtain Hydrogenation catalyst; (3) Bifunctional catalyst: 5g of the above Cu / ZnO dehydrogenation catalyst and the above After simple physical mixing of the hydrogenation catalysts, the bifunctional catalyst is obtained, denoted as catalyst B.

[0032] Comparative Example 2 This comparative example presents a bifunctional catalyst (without an isolation layer), and the specific preparation method includes: (1) Cu / ZnO dehydrogenation catalyst: 12.1g and 7.4g Dissolved in 100 mL of deionized water, ammonia (25%) was added to pH=11 to form a copper-zinc ammonia complex solution. The solution was stirred and aged for 2 h, then heated to 90 °C to evaporate the ammonia until pH=7. The solution was filtered, washed, dried at 110 °C for 12 h, and calcined at 450 °C for 4 h to obtain Cu-ZnO composite powder (Cu:Zn molar ratio 2:1). The obtained powder was then... The Cu / ZnO dehydrogenation catalyst (average particle size about 20 nm) was obtained by reduction at 300 °C for 2 h in a (10:1) atmosphere. (2) Bifunctional catalyst: 5g of the above Cu / ZnO dehydrogenation catalyst was impregnated with a solution containing... (Contains 0.2g of Pd) and In a 50 mL aqueous solution containing 0.4 g of Cu, the mixture was sonicated for 30 min, evaporated at 85 °C to remove water, dried at 110 °C for 12 h, calcined at 450 °C for 4 h, and then... (5:1) Reduction at 350℃ for 3h in an atmosphere to form a shell of Pd-Cu hydrogenation catalyst on the surface of Cu / ZnO dehydrogenation catalyst, thus obtaining the bifunctional catalyst (Cu-ZnO@Pd-Cu), denoted as catalyst C.

[0033] Comparative Example 3 This comparative example proposes a bifunctional catalyst (without gas channels in the isolation layer), and the specific preparation method includes: (1) Core particles of Cu / ZnO dehydrogenation catalyst 12.1g (0.05 mol) and 7.4 g Dissolved in 100 mL of deionized water, ammonia (25%) was added to pH=11 to form a copper-zinc ammonia complex solution. The solution was stirred and aged for 2 h, then heated to 90 °C to evaporate the ammonia until pH=7. The solution was filtered, washed, dried at 110 °C for 12 h, and calcined at 450 °C for 4 h to obtain Cu-ZnO composite powder (Cu:Zn molar ratio 2:1). The obtained powder was then... Reduction at 300℃ for 2 hours in a (10:1) atmosphere yields core particles, which are the Cu / ZnO dehydrogenation catalyst; (2) Covering mesopores layer of isolation layer 5g of the above-mentioned core particles were ultrasonically dispersed in 150mL of ethanol-water (1:1) mixture, 10mL of tetraethyl orthosilicate (TEOS) was added, and ammonia was added dropwise to adjust the pH to 9. The mixture was stirred at room temperature for 24h, centrifuged, washed with ethanol, dried at 110℃, and calcined at 550℃ for 5h to form a dense core on the surface of the core particles. The isolation layer of the layer; (3) Shell of supported Pd-Cu hydrogenation catalyst The above-mentioned dense The core particles after layering are impregnated with a solution containing (Contains 0.2g of Pd) and In a 50 mL aqueous solution containing 0.4 g of Cu, the mixture was sonicated for 30 min, evaporated at 85 °C to remove water, dried at 110 °C for 12 h, calcined at 450 °C for 4 h, and then... (5:1) Reduction at 350℃ for 3 hours in a dense atmosphere A shell layer for the Pd-Cu hydrogenation catalyst is formed on the surface of the isolation layer, resulting in the final catalyst, which is the bifunctional catalyst. Let it be denoted as catalyst D.

[0034] Application examples The application of the above-mentioned bifunctional catalyst in the hydrogenation of dimethyl oxalate to methyl glycolate from methanol using in-situ hydrogen donation includes: (1) The fixed bed reactor (inner diameter 12mm, length 500mm, constant temperature section 200mm) is filled with the above-mentioned bifunctional catalyst, the catalyst bed height is about 80mm, and the top and bottom are filled with quartz sand; (2) Methanol (purity ≥ 99.5%) and dimethyl oxalate (purity ≥ 99%) are mixed at a mass ratio of 2.5:1 and heated to 60°C to completely dissolve DMO to obtain a clear raw material solution; (3) The clarified feed solution was fed into the heater (preheated to 175℃) at a flow rate of 0.5 mL / min using a high-pressure metering pump, and then into the fixed-bed reactor. The reaction temperature was 270℃, the reaction pressure was 1.5 MPa (controlled by the back pressure valve), and the liquid hourly space velocity (LHSV) of dimethyl oxalate was [missing value]. No additional hydrogen is introduced. The gas at the reactor outlet is cooled to 0-5°C by a condenser, and the gas and liquid are separated. The liquid phase is collected and sampled for analysis, and the gas phase is collected and analyzed using a gas bag. (4) The above gas phase mainly contains CO and a small amount of MF vapor, after the gas phase is washed with water to absorb MF, the remaining gas It can be sent to the CO conversion section or directly burned, where CO can be purified for DMO synthesis; the above liquid phase mainly contains MG, MF, unreacted methanol and trace amounts of DMO. The liquid phase is distilled under reduced pressure (0.06 MPa) at a top temperature of 55-65℃ to distill off MF (purity ≥99%), and methanol is distilled off at a temperature of 85-95℃ in the column (for recycling). MG (purity ≥98%) is obtained from the bottom of the column.

[0035] Referring to the application example, the bifunctional catalysts were selected as catalysts A, A-1, A-2, B, C, and D, respectively. The conversion rate and selectivity of MG obtained under different catalysts are shown in Table 1 below: Table 1 Results of the catalyst on the hydrogenation of dimethyl oxalate to methyl glycolate

[0036] As shown in Table 1 above, the bifunctional catalyst of the present invention avoids direct contact between dehydrogenation and hydrogenation active sites due to spatial separation, significantly suppresses the excessive hydrogenation side reaction (EG formation), and improves MG selectivity to over 90%.

[0037] Referring to the application example, catalyst A is used to fix... With a methanol / DMO ratio of 2.5:1, the effects of reaction temperature and pressure on catalyst activity were investigated, and the results are shown in Table 2 below: Table 2. Effects of reaction temperature and pressure on the hydrogenation of dimethyl oxalate to dimethyl carbonate.

[0038] As shown in Table 2 above, catalyst A exhibits the best performance at 270℃ and 1.5MPa.

[0039] Referring to the application example, catalyst A was used, the reaction temperature was fixed at 270℃, the system pressure was 1.5 MPa, and the methanol / DMO ratio was 2.5. The reaction effect of catalyst A was verified by periodic sampling and analysis after 100 hours of stable operation. The results are shown in Table 3 below: Table 3 Continuous stability test results of catalyst A

[0040] As shown in Table 3 above, the activity of catalyst A decreased slightly (conversion rate decreased by 1.4% and selectivity decreased by 1.9%), mainly due to surface carbon accumulation, which can be restored through periodic air regeneration.

[0041] Reference Figure 1 The present invention also proposes a process system for the hydrogenation of dimethyl oxalate to methyl glycolate using methanol with in-situ hydrogen donation, comprising: Raw material mixing tank, used to mix methanol and dimethyl oxalate to form a raw material liquid; A heater, connected to a raw material mixing tank, is used to bring the raw material liquid to a preheating temperature; A fixed-bed reactor, connected to a heater, is filled with the bifunctional catalyst and used to hydrogenate the feed liquid to obtain gas-phase reaction products; A cooler, connected to a fixed-bed reactor, is used to condense gaseous reaction products into liquid reaction products; A gas-liquid separator, connected to a cooler, is used to separate liquid-phase reaction products into a gas phase (such as homogenized carbon) and a liquid phase; A distillation column, connected to a gas-liquid separator, is used to separate the liquid phase into methyl glycolate, methyl formate, and unreacted methanol and dimethyl oxalate. The circulation system, connected to the distillation column, is used to return unreacted methanol and dimethyl oxalate to the feed mixing tank.

[0042] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A bifunctional catalyst, characterized in that, The catalyst has a three-layer core-shell structure, with the core being a dehydrogenation catalyst, the shell being a hydrogenation catalyst, and the isolation layer between the core and the shell being a porous oxide layer with gas channels. The dehydrogenation catalyst includes an active component Cu and a non-precious metal auxiliary element M1; the hydrogenation catalyst includes an active component Cu and a precious metal auxiliary element M2; the porous oxide layer also serves as a support for the active component and auxiliary element in the hydrogenation catalyst.

2. The bifunctional catalyst according to claim 1, characterized in that, M1 is at least one of Zn, Cr, or Mn; M2 is at least one of Pd, Pt, or Ru; The dehydrogenation catalyst is Cu-ZnO. or One of the following; the hydrogenation catalyst is at least one of Pd-Cu, Pt-Cu or Ru-Cu.

3. The bifunctional catalyst according to claim 2, characterized in that, In the dehydrogenation catalyst, the molar ratio of Cu to M1 is 1:0.5-2; in the hydrogenation catalyst, the molar ratio of Cu to M2 is 1:2-5.

4. The bifunctional catalyst according to any one of claims 1-3, characterized in that, The porous oxide layer is mesoporous. Mesoporous or mesoporous At least one of them.

5. The bifunctional catalyst according to any one of claims 1-3, characterized in that, The core particle size is 10-500nm; the shell thickness is 5-300nm; the isolation layer thickness is 20-200nm, and the pore size is 2-10nm.

6. A method for preparing a bifunctional catalyst according to any one of claims 1-5, characterized in that, include: (1) The aqueous solution containing Cu and M1 soluble salts was subjected to a co-precipitation reaction, and after drying, calcination and reduction, the core of the dehydrogenation catalyst was obtained. (2) The core of the dehydrogenation catalyst is dispersed in an ethanol-water solution containing a template agent and an oxide precursor for a sol-gel reaction. After calcination to remove the template agent, an isolation layer is formed on the surface of the core. (3) The core of the isolation layer is immersed in an aqueous solution containing Cu and M2 precursor salt, and then dried, roasted and reduced to form a shell of hydrogenation catalyst on the surface of the isolation layer, which is the bifunctional catalyst.

7. The use of the bifunctional catalyst according to any one of claims 1-5 in the hydrogenation of dimethyl oxalate to methyl glycolate from methanol with in-situ hydrogen donation.

8. The application according to claim 7 in the hydrogenation of dimethyl oxalate to methyl glycolate using methanol with in-situ hydrogen supply, characterized in that, A feed liquid containing methanol and dimethyl oxalate is passed into a fixed-bed reactor packed with the heterogeneous catalyst, and a hydrogenation reaction is carried out under conditions without external hydrogen to obtain methyl glycolate.

9. The application according to claim 7 or 8 in the hydrogenation of dimethyl oxalate to methyl glycolate via in-situ hydrogen donation from methanol, characterized in that, The hydrogenation reaction was carried out at a temperature of 240-300℃ and a pressure of 0.5-2.5 MPa, with a liquid hourly space velocity (LISH) of dimethyl oxalate being [missing value]. The mass ratio of methanol to dimethyl oxalate is 1-4:

1.

10. A process system for the hydrogenation of dimethyl oxalate to methyl glycolate using methanol with in-situ hydrogen donation, characterized in that, include: Raw material mixing tank, used to mix methanol and dimethyl oxalate to form a raw material liquid; A fixed-bed reactor, connected to a feed mixing tank, is filled with the bifunctional catalyst described in any one of claims 1-5, for hydrogenating the feed liquid to obtain gaseous reaction products; A cooler, connected to a fixed-bed reactor, is used to condense gaseous reaction products into liquid reaction products; A gas-liquid separator, connected to a cooler, is used to separate liquid-phase reaction products into gas and liquid phases; A distillation column, connected to a gas-liquid separator, is used to separate the liquid phase into methyl glycolate, methyl formate, and unreacted methanol and dimethyl oxalate. The circulation system, connected to the distillation column, is used to return unreacted methanol and dimethyl oxalate to the feed mixing tank.

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