Coated bimetallic composite catalyst for preparing lactic acid through selective oxidation

Abstract

The invention discloses a coated bimetallic composite catalyst for preparing lactic acid through selective oxidation, and relates to a preparation method of a chemical catalyst, and the method prepares a novel carbon-coated Cu-X bimetallic composite catalyst through crystal phase regulation and control. The catalyst takes a Cu-MOFs material as a precursor, is formed by high-temperature calcination after a series of treatment, and has a unique crystal phase structure and active site distribution. A coated bimetallic catalyst which takes porous carbon (C) as a carrier and coats Cu and has a synergistic effect with double active centers of other metals is constructed, the expression of the coated bimetallic catalyst is Cu-X-C, and efficient selective oxidation from glycerol to lactic acid is realized in an intermittent reaction under an alkaline condition. Experimental results show that the catalyst enables the glycerin conversion rate to reach 100%, the lactic acid selectivity is improved to 96.44%, and the catalyst has good cycle stability and can be repeatedly used for more than 10 times. The invention provides an efficient, green and sustainable technical path for high-valued utilization of glycerol.

Description

Technical Field

[0001] The present invention relates to a method for preparing a catalyst, and more particularly to a coated bimetallic composite catalyst for the selective oxidation of glycerol to produce lactic acid. Background Art

[0002] Glycerol, also known as glycerin, is widely used in many fields such as food, cosmetics, medicine, chemical industry, coatings and energy, and has high utilization value. However, due to overcapacity, its price has dropped. Glycerol has three hydroxyl functional groups and can be converted into many high-value by-products through reactions such as dehydration, selective oxidation, hydrogenolysis, and transesterification, such as lactic acid, 1,2-propanediol, 1,3-dihydroxyacetone, acrolein, glycerol carbonate, etc. Among them, lactic acid is one of the most attractive high-value-added glycerol derivatives.

[0003] Lactic acid, also known as 2-hydroxypropionic acid, is widely used in fields such as materials and medicine. It can be used directly as a monomer to synthesize biodegradable lactic acid plastics and medical materials. The annual demand for lactic acid is increasing day by day and is expected to reach 1.96 million tons in 2025. At present, more than 90% of lactic acid production is produced by the fermentation method of bio-based carbohydrates. This method is time-consuming, cumbersome to operate, and the cost of enzymes is high. Therefore, using biomass as a resource to produce lactic acid by chemical methods has become a popular research topic in the past ten years. Glycerol, as a derivative of biomass resources, is one of the important raw materials for producing lactic acid.

[0004] In the research on the catalytic oxidation of glycerol to produce lactic acid, it is mainly divided into homogeneous catalysis and heterogeneous catalysis. In the research of heterogeneous catalysis, the selection of the catalyst is extremely important. In the research of the past ten years, noble metal catalysts have shown high catalytic performance under low-temperature reaction conditions, but the cost of noble metals is too high. Therefore, non-noble metal catalysts have become the research focus in recent years, among which Cu-based catalysts have shown excellent activity. According to reports, Cu 0 、Cu + 、Cu 2+All can be used as active sites, and the introduction of other metal elements can form a composite structure with the Cu element, produce a synergistic effect with Cu and play a role in stabilizing the structure. In today's technology, most of the supported copper-based catalysts for preparing lactic acid from glycerol are supported by molecular sieves, activated carbon and metal oxides. In recent years, the derivatization of MOFs materials has become a hot topic in research. After calcination and derivatization, high specific surface area materials of porous carbon-coated metal / bimetallic / metal oxide nanoparticles can be directly obtained. Among them, a study disclosed a Cu / ZnO / C catalyst, which, due to the synergistic effect of uniformly distributed Cu and ZnO active sites and the high specific surface area provided by porous C, achieved a glycerol conversion rate of 95.1% and a lactic acid selectivity of up to 84% (Journal of Catalysis Letters, 2024,154:1309-1321); However, its ZnO active site is a metal oxide active site, which is not stable under high temperature and strong alkaline conditions, and the number of cycles is only 4 times. Patent CN114751815A discloses a method for preparing lactic acid by selective oxidation of glycerol catalyzed by an ionic liquid-polymer supported Pd catalyst and a tin-containing mesoporous molecular sieve catalyst. The reaction is carried out under alkali-free conditions, avoiding cumbersome post-treatment processes, and the lactic acid yield is 85.86%.

[0005] The catalyst currently used to catalyze glycerol to produce lactic acid still has problems such as poor stability, low number of cycles, and the lactic acid yield still needs to be improved. Therefore, the present invention prepares a Cu-X-MOFs catalyst to solve these problems. Summary of the invention

[0006] The purpose of the present invention is to provide a coated bimetallic composite catalyst for selective oxidation preparation of lactic acid, which is a coated bimetallic composite catalyst for catalyzing the oxidation of glycerol to prepare lactic acid, and solves the problems of poor cycle stability and low lactic acid yield in the current reaction of preparing lactic acid from glycerol.

[0007] The objective of the present invention is achieved through the following technical solutions: First, the present invention provides a coated bimetallic composite catalyst with Cu and X (X is at least one of transition metals such as Fe, Co, Ni, and Zn) as active centers and a porous carbon material (C) as a carrier. 0 and X 0 It is evenly dispersed and coated in the porous carbon material to form a stable bimetallic active center structure, which significantly improves the activity, selectivity and cycle stability of the catalyst.

[0008] In the present invention, the catalyst uses Cu-MOFs (metal-organic framework materials) as a precursor, introduces an X metal salt solution by an impregnation method, and is then prepared by high-temperature calcination. The Cu-MOFs precursor is synthesized by a hydrothermal method using a copper salt solution and an organic ligand solution as raw materials. Among them, the type of copper salt solution, the choice of organic ligand, and the hydrothermal reaction conditions (such as temperature and time) will all affect the morphology and structure of the Cu-MOFs precursor, and thus affect the performance of the final catalyst. The addition amount of the X metal is regulated according to a certain ratio with reference to the amount of Cu to achieve an optimized configuration of the bimetallic active centers.

[0009] As a preferred embodiment, the copper salt solution is an aqueous solution of copper nitrate, the organic ligand solution is an ethanol solution of trimesic acid, the hydrothermal reaction temperature is 80-120 °C, and the hydrothermal reaction time is 24-36 h. By regulating the hydrothermal conditions, a Cu-MOFs precursor with a high specific surface area and a uniform pore structure can be obtained, laying a foundation for the subsequent preparation of the catalyst.

[0010] The present invention also finds that the calcination temperature has a significant impact on the performance of the catalyst. As the calcination temperature increases, the lattice spacing of Cu 0 increases, which helps to improve the adsorption capacity of glycerol on the catalyst surface, thereby enhancing the conversion rate of glycerol. In addition, the calcination temperature also affects the crystal structure and surface properties of the catalyst, and thus regulates its catalytic activity.

[0011] Furthermore, the present invention finds that the content of the X metal element has an important impact on the performance of the catalyst. As the proportion of the X metal element increases, the conversion rate of glycerol gradually decreases, while the selectivity of lactic acid shows a trend of first increasing and then decreasing. By optimizing the addition ratio of the X metal element, an efficient conversion of glycerol to lactic acid can be achieved.

[0012] In addition, the present invention also reveals a heterojunction composite structure formed between Cu 0 and X 0 . This structure promotes the synergistic effect of the bimetallic active centers, not only improving the conversion rate of glycerol, but also significantly enhancing the selectivity of lactic acid. The formation of the heterojunction structure also enhances the stability of the catalyst, enabling it to maintain a high catalytic activity even after multiple cycles of use.

[0013] The present invention finds that Cu and X particles are uniformly distributed on the surface and inside of C, and the introduction of the X metal makes the Cu-X heterojunction structure more stable in combination with C, which makes its structure and chemical properties more stable, and significantly increases the number of recyclable times.

[0014] Preferably, Cu 0 and X 0The ratio is optimally (1 - 3):1, and the calcination temperature at this time is 400 - 600 °C.

[0015] Second, the present invention provides a specific preparation method of the catalyst, including: A. Mix the copper salt solution and the organic ligand solution into a reactor, and obtain the Cu-MOFs precursor by hydrothermal method or precipitation method, and dry it for later use.

[0016] B. Take a certain amount of the Cu-MOFs precursor and add it to a salt solution containing a certain amount of metal X for impregnation. After a period of time, filter by suction, wash, and dry to obtain the Cu-X-MOFs precursor for later use.

[0017] Calcine the Cu-X-MOFs precursor in an inert reducing gas atmosphere to obtain the catalyst, denoted as Cu-X@C.

[0018] In the step A, the concentrations of both the copper salt solution and the organic ligand solution are 0.1 mol / L - 0.5 mol / L, the reaction temperature is 30 - 150 °C, the reaction time is 12 - 36 h, the drying temperature is 50 - 70 °C, and the drying time is 6 - 24 h.

[0019] In the step A, the copper salts include copper nitrate and copper iodide. The organic ligands include trimesic acid, 4,5-dicyanoimidazole, and terephthalic acid.

[0020] In the step B, the inert reducing gas is a mixture of N2 and H2, the H2 content is 10 - 40%, the calcination temperature is 300 - 600 °C, the heating rate is 1 - 4 °C / min, and the constant temperature time is 1 - 4 h.

[0021] Third, the present invention provides the application of the catalyst in the catalytic selective oxidation of glycerol to prepare lactic acid, and the highest glycerol conversion rate of 100% and lactic acid selectivity of 96.44% are obtained. The specific steps are as follows: A. Add the glycerol aqueous solution, the Cu-X@C catalyst, and KOH into a high-pressure reactor with magnetic stirring, and close the valve to seal the reactor.

[0022] B. Continuously stir and heat up, and naturally cool to room temperature after reacting for a certain time.

[0023] C. Centrifuge the reaction mixture, wash the lower solid catalyst with deionized water for later use, acidify the upper clear liquid with acid, and filter for product analysis.

[0024] In the step A, the concentration of the glycerol aqueous solution is 10 - 30 wt.%, the mass ratio of glycerol to the catalyst is (3.3 - 10):1, and the molar ratio of KOH to glycerol is (0.9 - 1.5):1.

[0025] In step B, the stirring speed is 400 - 600 rmp, the reaction time is 4 - 8 h, and the heating rate is 5 ℃ / min.

[0026] In step C, the pH value of the supernatant is adjusted to 1 - 2 with 1 mol / L H2SO4, filtered through a 0.45 μm filter membrane, and then analyzed using a liquid chromatograph.

[0027] The beneficial effects of the present invention are as follows: 1. The coated bimetallic composite catalyst of the present invention has high catalytic activity. In the reaction of catalytic selective oxidation of glycerol to prepare lactic acid, the lactic acid yield reaches over 90%. It has high stability, and the number of recyclable times reaches over 10 times.

[0028] 2. By constructing a Cu - X@C catalyst with C - coated Cu 0 and X 0 dual active sites, high stability and high recyclability under alkaline conditions can be achieved. Crystal regulation is carried out by changing the calcination temperature to increase the adsorption energy of glycerol on the catalyst surface, and by changing the ratio of X metal to Cu to increase the 0 dual - metal synergistic effect between Cu 0 and X. Through the above two points, high conversion rate of glycerol and high yield of lactic acid can be achieved. And the preparation method of the catalyst is simple and the cost is low, which is beneficial to industrialization and has good development prospects. Specific Embodiments

[0029] The present invention will be further specifically described below in conjunction with embodiments, but the present invention is by no means limited to these embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. In addition, in the following embodiments, unless otherwise specified, all are commercially available conventional raw materials and conventional methods used by those skilled in the art. Example 1

[0030] This example first provides a preparation method of the catalyst, and the steps are as follows: 0.246 g of Cu(NO3)2·3H2O is added to 30 mL of deionized water and completely dissolved to be recorded as solution A. 0.210 g of trimesic acid is added to 30 mL of ethanol and completely dissolved to be recorded as solution B. Solution A is slowly dropped into solution B, stirred evenly for 10 min, added to a hydrothermal reactor, and hydrothermally reacted at 110 ℃ for 24 h. After the reaction is completed, it is taken out for suction filtration and dried at 70 ℃ for 12 h. Cu - BTC is obtained for standby.

[0031] 0.9 g of Cu-BTC was added to 10 ml of 0.36 mol / L aqueous Ni(NO3)2 solution and impregnated for 24 h. The mixture was filtered by suction, washed three times with ethanol: aqueous solution (v:v = 1:1), and dried in an oven at 70 °C for 12 h to obtain Cu-Ni2-BTC for standby.

[0032] Cu-Ni2-BTC was placed in a tubular furnace and heated to 450 °C at a rate of 1 °C / min in a 20% H2 / N2 atmosphere, and kept at a constant temperature for 2 h to obtain Cu-Ni2@C-450 for standby.

[0033] This example further provides a method for catalyzing glycerol to prepare lactic acid, and the steps are as follows: 0.2 g of the catalyst prepared above was added to the inner lining of a high-pressure reactor, 10 g of 20 wt.% glycerol aqueous solution was added, 1.34 g of solid KOH was added, and the mixture was stirred evenly. The reactor was sealed and maintained at a stirring rate of 500 rmp, heated to 190 °C at a rate of 5 °C / min, and kept at a constant temperature for 6 h. After the reaction was completed, it was naturally cooled to room temperature.

[0034] The mixture after the reaction was centrifuged to recover the lower-layer catalyst. The supernatant was taken and acidified with 1 mol / L H2SO4 to adjust the pH to 1-2, and a mixture of glycerol and the product was obtained for product analysis.

[0035] Among them, the product was obtained from the liquid chromatography analysis results. The glycerol conversion rate was 100%, and the lactic acid selectivity was 94.80%. Example 2

[0036] This example first provides a method for preparing a catalyst, which is different from Example 1 in that heating to 450 °C at a rate of 1 °C / min in a 20% H2 / N2 atmosphere was replaced by heating to 300 °C at a rate of 1 °C / min in a 20% H2 / N2 atmosphere. The obtained catalyst was denoted as Cu-Ni2@C-300.

[0037] This example further provides a method for catalyzing glycerol to prepare lactic acid, and the steps are the same as those in Example 1.

[0038] Among them, the product was obtained from the liquid chromatography analysis results. The glycerol conversion rate was 78.44%, and the lactic acid selectivity was 88.21%. Example 3

[0039] This example first provides a method for preparing a catalyst, which is different from Example 1 in that heating to 600 °C at a rate of 1 °C / min in a 20% H2 / N2 atmosphere is replaced by heating to 600 °C at a rate of 1 °C / min in a 20% H2 / N2 atmosphere, and the obtained catalyst is denoted as Cu-Ni2@C-600.

[0040] This example further provides a method for catalytically preparing lactic acid from glycerol, and the steps are the same as those in Example 1.

[0041] Among them, the product is obtained through the analysis result of liquid chromatography. The glycerol conversion rate is 96.47%, and the lactic acid selectivity is 96.44%. Example 4

[0042] This example first provides a method for preparing a catalyst, which is different from Example 1 in that 10 ml of 0.36 mol / L Ni(NO3)2 aqueous solution is replaced by 10 ml of 0.18 mol / L Ni(NO3)2 aqueous solution, and the obtained catalyst is denoted as Cu-Ni1@C-450.

[0043] This example further provides a method for catalytically preparing lactic acid from glycerol, and the steps are the same as those in Example 1.

[0044] Among them, the product is obtained through the analysis result of liquid chromatography. The glycerol conversion rate is 100%, and the lactic acid selectivity is 90.88%. Example 5

[0045] This example first provides a method for preparing a catalyst, which is different from Example 1 in that 10 ml of 0.36 mol / L Ni(NO3)2 aqueous solution is replaced by 10 ml of 0.54 mol / L Ni(NO3)2 aqueous solution, and the obtained catalyst is denoted as Cu-Ni3@C-450.

[0046] This example further provides a method for catalytically preparing lactic acid from glycerol, and the steps are the same as those in Example 1.

[0047] Among them, the product is obtained through the analysis result of liquid chromatography. The glycerol conversion rate is 94.81%, and the lactic acid selectivity is 95.27%. Example 6

[0048] This example first provides a method for preparing a catalyst, which is different from Example 1 in that 10 ml of 0.36 mol / L Ni(NO3)2 aqueous solution is replaced by 10 ml of 0.72 mol / L Ni(NO3)2 aqueous solution, and the obtained catalyst is denoted as Cu-Ni4@C-450.

[0049] This example further provides a method for catalyzing glycerol to prepare lactic acid, and the steps are the same as those in Example 1.

[0050] Among them, the product is obtained from the liquid chromatography analysis results. The glycerol conversion rate is 90.54%, and the lactic acid selectivity is 92.11%. Example 7

[0051] This example first provides a method for preparing a catalyst, and the steps are as follows: Add 0.246 g of Cu(NO3)2·3H2O to 30 mL of deionized water. After complete dissolution, it is denoted as solution A. Add 0.166 g of terephthalic acid to 30 mL of N,N-dimethylformamide. After complete dissolution, it is denoted as solution B. Slowly drip solution A into solution B. After mixing evenly, stir for 10 min, add it to a hydrothermal reactor, and conduct hydrothermal reaction at 150 °C for 36 h. After the reaction is completed, take it out and perform suction filtration, and dry it at 60 °C for 12 h. Obtain Cu-BDC for standby.

[0052] Add 0.9 g of Cu-BDC to 10 ml of 0.36 mol / L Ni(NO3)2 aqueous solution and impregnate for 24 h. Filter the mixed solution, and wash it 3 times with ethanol:aqueous solution (v:v = 1:1). Place it in an oven and dry it at 70 °C for 12 h to obtain Cu-Ni2-BDC for standby.

[0053] Place Cu-Ni2-BDC in a tubular furnace, heat it to 450 °C at a rate of 1 °C / min in a 20% H2 / N2 atmosphere, and keep it at a constant temperature for 2 h to obtain Cu-Ni2@C-450BDC for standby.

[0054] This example further provides a method for catalyzing glycerol to prepare lactic acid, and the steps are the same as those in Example 1.

[0055] Among them, the product is obtained from the liquid chromatography analysis results. The glycerol conversion rate is 90.24%, and the lactic acid selectivity is 82.97%. Example 8

[0056] This example first provides a method for preparing a catalyst, and the steps are as follows: Add 9.5 g of CuI to 500 mL of deacetonitrile. After complete dissolution, it is denoted as solution A. Add 5.9 g of 4,5-dicyanoimidazole to solution A, add triethylamine until no white precipitate is formed, filter it, collect the precipitate, place it in 50 mL of acetonitrile, age it at 30 °C for 12 h, filter it to collect the precipitate, and dry it at 50 °C for 12 h to obtain Cu-DCI.

[0057] 0.9 g of Cu-DCI was added to 10 ml of 0.36 mol / L aqueous Ni(NO3)2 solution and impregnated for 24 h. The mixed solution was filtered by suction and washed 3 times with ethanol: aqueous solution (v:v = 1:1), and then dried in an oven at 70 °C for 12 h to obtain Cu-Ni2-DCI for standby. Cu-DCI was placed in a tubular furnace and heated to 450 °C at a rate of 1 °C / min in an atmosphere of 20% H2 / N2, and kept at a constant temperature for 2 h to obtain Cu-Ni2@C-450DCI for standby.

[0058] This example further provides a method for catalyzing glycerol to prepare lactic acid, and the steps are the same as those in Example 1.

[0059] Among them, the product was obtained through the analysis results of liquid chromatography. The glycerol conversion rate was 100%, and the lactic acid selectivity was 90.84%. Example 9

[0060] This example first provides a method for preparing a catalyst, and the steps are the same as those in Example 1.

[0061] This example further provides a method for catalyzing glycerol to prepare lactic acid, and the difference from Example 1 is that heating to 190 °C at a rate of 5 °C / min is replaced by heating to 180 °C at a rate of 5 °C / min.

[0062] Among them, the product was obtained through the analysis results of liquid chromatography. The glycerol conversion rate was 96.27%, and the lactic acid selectivity was 90.59%.

[0063] Example 10: This example first provides a method for preparing a catalyst, and the steps are the same as those in Example 1.

[0064] This example further provides a method for catalyzing glycerol to prepare lactic acid, and the difference from Example 1 is that heating to 190 °C at a rate of 5 °C / min is replaced by heating to 200 °C at a rate of 5 °C / min.

[0065] Among them, the product was obtained through the analysis results of liquid chromatography. The glycerol conversion rate was 100%, and the lactic acid selectivity was 89.89%.

[0066] Example 11: This example first provides a method for preparing a catalyst, and the steps are the same as those in Example 1.

[0067] This example further provides a method for catalyzing glycerol to prepare lactic acid, and the difference from Example 1 is that maintaining the constant temperature for 6 h is replaced by maintaining the constant temperature for 4 h.

[0068] Among them, the product is obtained from the liquid chromatography analysis results, with the glycerol conversion rate being 96.33% and the lactic acid selectivity being 77.25%.

[0069] Example 12: This example first provides a method for preparing the catalyst, and the steps are the same as those in Example 1.

[0070] This example further provides a method for catalyzing glycerol to prepare lactic acid. The difference from Example 1 is that maintaining the constant temperature for 6 h is replaced by maintaining the constant temperature for 8 h.

[0071] Among them, the product is obtained from the liquid chromatography analysis results, with the glycerol conversion rate being 100% and the lactic acid selectivity being 86.53%.

[0072] Example 13: This example first provides a method for preparing the catalyst, and the steps are the same as those in Example 1.

[0073] This example further provides a method for catalyzing glycerol to prepare lactic acid. The difference from Example 1 is that 10 g of 20 wt.% glycerol aqueous solution is replaced by 10 g of 10 wt.% glycerol aqueous solution.

[0074] Among them, the product is obtained from the liquid chromatography analysis results, with the glycerol conversion rate being 100% and the lactic acid selectivity being 91.93%.

[0075] Example 14: This example first provides a method for preparing the catalyst, and the steps are the same as those in Example 1.

[0076] This example further provides a method for catalyzing glycerol to prepare lactic acid. The difference from Example 1 is that 10 g of 20 wt.% glycerol aqueous solution is replaced by 10 g of 30 wt.% glycerol aqueous solution.

[0077] Among them, the product is obtained from the liquid chromatography analysis results, with the glycerol conversion rate being 95.19% and the lactic acid selectivity being 83.54%.

[0078] Example 15: This example first provides a method for preparing the catalyst. The difference from Example 1 is that 10 ml of 0.36 mol / L Ni(NO3)2 aqueous solution is replaced by 10 ml of 0.36 mol / L Co(NO3)2 aqueous solution, and the obtained catalyst is denoted as Cu-Co2@C-450.

[0079] This example further provides a method for catalyzing glycerol to prepare lactic acid, and the steps are the same as those in Example 1.

[0080] Among them, the product was obtained by liquid chromatography analysis. The conversion rate of glycerol was 96.87%, and the selectivity of lactic acid was 95.83%.

[0081] Experimental Example The catalyst Cu-Ni2@C-450 prepared in Example 1 was used in the present invention to verify its recycling effect in the catalytic preparation of lactic acid from glycerol, as follows: 0.2 g of the above catalyst, 10 g of 20 wt.% aqueous glycerol solution and 1.34 g of solid KOH were added to a high-pressure reactor. The reactor was sealed and maintained at a stirring rate of 500 rmp, heated to 190 °C at a rate of 5 °C / min, and kept at a constant temperature for 6 h. After the reaction was completed, it was naturally cooled to room temperature. The reaction mixture was centrifuged, and the supernatant was added with 1 mol / L H2SO4 for acidification to adjust the pH to 1-2 to obtain a mixture of glycerol and the product for product analysis. The lower-layer catalyst was recovered and washed with deionized water until the pH was about 7. The above operation was carried out for 10 cycles of experiments, and the experimental analysis results are shown in Table 1.

[0082] Table 1 Number of cycles Glycerol conversion rate (%) Lactic acid yield (%) 1 100.00 94.80 2 100.00 94.40 3 100.00 94.51 4 100.00 94.27 5 99.20 92.87 6 96.56 90.44 7 95.41 89.21 8 95.62 90.93 9 94.38 88.12 10 94.33 88.03 As can be seen from Table 1, when recycled to the 10th time, the yield of lactic acid can still be maintained above 85%, indicating that Cu-Ni2@C-450 has high stability and high recyclability.

[0083] It can be seen from the examples and experimental examples that in the application of the Cu-X@C catalyst prepared in the present invention in the catalytic preparation of lactic acid from glycerol, the highest yield of lactic acid reaches 94.80%, and the number of recyclable times reaches more than 10 times, indicating that it has high catalytic activity and recyclability and has good industrial prospects.

Claims

1. A coated bimetallic composite catalyst for the selective oxidation to prepare lactic acid, characterized in that, The described catalyst has the expression Cu-X@C. The catalyst is composed of a composite material of Cu, X, and porous carbon (C), where X is selected from at least one of Fe, Co, Ni, and Zn. Cu and X are uniformly distributed on the surface and inside of the C support, and the molar ratio of Cu to X is (1 to 5):

1. The described core-shell bimetallic composite catalyst has a Cu element content of 20 wt.% to 60 wt.% and an X element content of 5 wt.% to 30 wt.%. The preparation process of the core-shell bimetallic composite catalyst is as follows: 1) After mixing the Cu metal salt solution and the organic ligand solution, react at a temperature of 30 to 150 °C to obtain a Cu-MOFs precursor; 2) Take the Cu-MOFs precursor, add the X metal salt solution for impregnation, then filter by suction and wash with the solution, and place it in an oven to dry to obtain a Cu-X-MOFs precursor; 3) Calcinate the Cu-X-MOFs precursor in an inert reducing gas atmosphere at 300 to 600 °C. The calcination heating-up time is 4 to 10 h, and the constant-temperature time is 1 to 3 h to obtain the described catalyst; When the above core-shell bimetallic composite catalyst is applied in the selective catalytic oxidation of glycerol to lactic acid, mix the aqueous glycerol solution and the above catalyst into a high-pressure reactor, add KOH, and react in a sealed oxygen-containing atmosphere; the concentration of the aqueous glycerol solution is 10 wt.% to 30 wt.%; the molar ratio of KOH to glycerol is (1 to 1.5):1; the catalyst accounts for 5 to 20% of the mass of glycerol.

2. The coated bimetallic composite catalyst for the preparation of lactic acid by selective oxidation according to claim 1, wherein The reaction temperature during the described application is 120 to 200 °C; the reaction time is 2 to 6 h.