A Cu / SiO2 catalyst with synergistic modification through complexation-dissolution-re-anchoring and its preparation method

Abstract

The application discloses a kind of complex dissolution-again anchoring synergic modification Cu / SiO2 Catalyst and its method.The method with ammonia evaporation method, hydrothermal method or urea precipitation method prepared catalyst precursor as processing object;After being dispersed in water, complex dissolution agent and amine group-containing silane coupling agent are sequentially added;Complex dissolution agent selectively dissolves low-active copper component and releases Cu 2+ , coupling agent is captured Cu 2+ By amine group, realize the re-anchoring of copper species by condensation of silane end and carrier;Finally, modified catalyst is obtained by drying and calcining.The method converts low-active copper component in situ into high-dispersion Cu-O-Si structure by the synergistic effect of "complex dissolution-anchoring", overcomes the limitation that low-active component cannot be removed by separate copper dissolution and separate coupling agent modification, and the activity, selectivity and stability of the obtained catalyst are significantly improved in dimethyl oxalate hydrogenation to prepare ethylene glycol.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, specifically a Cu / SiO2 catalyst with complexation-dissolution-re-anchoring synergistic modification and its preparation method. Background Technology

[0002] Ethylene glycol (EG) is an important chemical raw material, primarily used as a monomer in the production of polyester fibers and resins. In addition, EG is a key raw material for the production of automotive antifreeze, lubricants, and various fine chemicals. Developing a technology route for synthesizing EG from coal (CTEG) aligns with my country's resource endowment of "abundant coal, scarce oil, and limited gas," and is of strategic significance for ensuring energy security, optimizing the energy structure, and promoting the clean and efficient utilization of coal. In the CTEG route, the hydrogenation of dimethyl oxalate (DMO) to EG is the core reaction.

[0003] In the late 1970s, Japanese patents JP5323011 and JP5542971 first proposed a technical route for the hydrogenation of oxalate esters. In 1984, US patents US4585890 and US4440873 disclosed copper-silicon catalysts for the hydrogenation of oxalate esters; however, these catalysts had an excessively high hydrogen-to-ester ratio (>300), resulting in a correspondingly low liquid hourly space velocity (0.024 g / g·h). In 1986, ARCO Corporation in the United States used a Cu-Cr catalyst to convert dimethyl oxalate to ethylene glycol. In the early 1990s, the Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, completed a pilot test of the Cu-Cr catalyst for the hydrogenation of dimethyl oxalate esters. With technological advancements, hydrogenation catalysts have gradually transitioned from Cu-Cr to non-toxic Cu / SiO2-based catalysts.

[0004] Currently, Cu / SiO2-based catalysts have achieved industrial applications, but they still suffer from drawbacks such as high hydrogen-to-ester ratios, short catalyst lifetimes, and high selectivity for higher alcohol byproducts. Precise control of the size distribution, coordination environment, and valence state distribution of active components on the catalyst surface is crucial for further optimizing catalyst performance. Tianjin University (Ind. Eng. Chem. Res., 2023, 62, 10399-10408) proposed a method to modify the catalyst surface using silane coupling agents, controlling the acid-base relationship and the coordination state of copper, thereby reducing byproduct formation and achieving an EG selectivity of 95%. However, this modification process relies on organic groups on the catalyst surface, resulting in insufficient long-term reaction stability. The Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences (Mol. Catal., 2024, 565: 114290) proposed treating the catalyst precursor with EDTA to reconstruct the surface copper-silicon composition, ultimately improving EG selectivity (97%). However, this catalyst requires a hydrogen-to-ester ratio as high as 100, making it unsuitable for industrial application. Japan's Takashi Chemical Co., Ltd. (CN114450086A) disclosed an ammonia stripping process that involves adding precipitating agents such as urea or ammonium carbonate and surfactants. The aim is to construct more -Si-O-Cu-O-Si- structures, thereby controlling the valence state and coordination environment of copper. However, the introduction of surfactants not only leads to carbon residue covering the active sites on the catalyst surface, but also significantly increases wastewater treatment costs during production, resulting in low prospects for industrialization.

[0005] Current research primarily relies on the complexation of copper components with organic additives to modify catalyst surfaces. However, this process often suffers from limited control effects, and difficulties arise due to the introduction of residual carbon and the gradual decomposition of organic groups over prolonged reactions. Theoretical studies have revealed that Cu / SiO2-based catalysts prepared by ammonia stripping precipitation exhibit a wide dispersion of copper particles, including large-sized copper components with weak metal-support interactions. This portion of copper readily sintersulates and aggregates after reduction, and also serves as an active center for carbon chain growth in the coking reaction. Therefore, further development of this technology is needed to research and develop highly stable and active hydrogenation catalysts for efficient application in the hydrogenation of dimethyl oxalate to ethylene glycol. Summary of the Invention

[0006] The purpose of this invention is to address the issues of low dispersion of physically adsorbed CuO particles and their tendency to migrate and agglomerate into large, inactive Cu particles during subsequent calcination and reduction processes in existing Cu / SiO2 catalysts prepared by ammonia stripping. 0To address the problem of insufficient catalyst activity and long-term stability, this paper provides a Cu / SiO2 catalyst with synergistic modification through complexation-dissolution-re-anchoring and its preparation method. This method, through the synergistic effect of "complexation-dissolution-anchoring," transforms the low-activity copper component in situ into a highly dispersed Cu-O-Si structure, overcoming the limitations of easy copper loss from dissolution alone and the inability of single coupling agent modification to remove low-activity components. The resulting catalyst exhibits significantly improved activity, selectivity, and stability in the hydrogenation of dimethyl oxalate to ethylene glycol.

[0007] To achieve the above-mentioned objectives, the specific technical solution of this invention is as follows: A method for preparing a complex-dissolution-re-anchoring synergistic modified Cu / SiO2 catalyst includes the following steps: (1) The catalyst precursor obtained by supporting copper on SiO2 is dispersed in water, and a complexing solvent is added under stirring to selectively dissolve the low-activity CuO or Cu(OH)2 particles on the catalyst surface, releasing Cu 2+ Ions, forming soluble copper complex ions; (2) Add an amino-silane coupling agent solution to the substance obtained in step (1) to carry out the reaction; during the reaction, the amino end of the amino-silane coupling agent undergoes coordination exchange or competitive coordination with the copper complex ions released in step (2) to capture free Cu. 2+ After hydrolysis, its silane end condenses with the silanol groups on the surface of the SiO2 support to form Si-O-Si covalent bonds, thus re-anchoring the copper species to the support surface. (3) The substance (slurry) obtained in step (2) is subjected to solvent removal, drying, calcination and reduction to obtain modified Cu / SiO2 catalyst.

[0008] Preferably, in step (1) of a method for preparing a complex-dissolve-re-anchor synergistic modified Cu / SiO2 catalyst, the method of loading copper onto a SiO2 support to obtain a catalyst precursor includes, but is not limited to, ammonia stripping, urea precipitation, and hydrothermal synthesis.

[0009] Preferably, in step (1) of a method for preparing a complexing-dissolution-reanchoring synergistic modified Cu / SiO2 catalyst, the complexing solvent is ammonia or an organic amine; wherein, the organic amine includes one or more of ethylenediamine, triethanolamine, ethylenediaminetetraacetic acid and their salts; after adding the complexing solvent, the catalyst is treated at 40-80°C for 0.5-2.0 hours.

[0010] Preferably, in step (1) of a method for preparing a complexing-dissolution-re-anchoring synergistic modified Cu / SiO2 catalyst, when ammonia is used as the complexing solvent, the concentration of ammonia is 0.05-0.5 mol / L and the treatment time is 5-60 minutes.

[0011] The ammonia concentration is more preferably 0.1–0.3 mol / L, and the treatment time is more preferably 10–30 minutes.

[0012] When using ethylenediaminetetraacetic acid or its salts as a complexing solvent, the amount should be controlled at n(EDTA) / n(Cu) = 0.005 to 0.05, and the treatment time should be 5 to 30 minutes.

[0013] Preferably, in step (2) of a method for preparing a complex-dissolve-re-anchor synergistic modified Cu / SiO2 catalyst, the amino-containing silane coupling agent is an organosilicon compound containing at least one amino group and at least one hydrolyzable alkoxy group, preferably one or more of N-[3-(methoxysilane)propyl]ethylenediamine, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-[3-(trimethoxysilyl)propyl]ethylenediamine and polyamine silane coupling agents containing multiple amino groups.

[0014] Preferably, the amount of the amino-containing silane coupling agent is 0.1 to 5 wt% of the dry basis mass of the catalyst, more preferably 0.5 to 2 wt%.

[0015] Preferably, in step (2) of the preparation method of a complexation-dissolution-re-anchoring synergistic modification of Cu / SiO2 catalyst, the amino-silane coupling agent is added in the form of a pre-hydrolysis solution; the pre-hydrolysis method is as follows: the amino-silane coupling agent is mixed with an alcohol-water mixed solvent at a mass ratio of 1:(8-20), and hydrolyzed at room temperature for 10-60 minutes; the mass ratio of alcohol to water in the alcohol-water mixed solvent is 4:1-8:1, and the alcohol is methanol or ethanol.

[0016] Preferably, in step (2) of the method for preparing a complex-dissolve-re-anchor synergistic modified Cu / SiO2 catalyst, an amino-silane coupling agent solution is added, and the reaction is continued at 10-80°C for 0.5-12 hours, more preferably at 40-80°C for 2-8 hours.

[0017] Preferably, in step (3) of a method for preparing a complexed dissolution-re-anchoring synergistic modified Cu / SiO2 catalyst, the calcination conditions are calcination at 400-500°C for 3-8 hours, more preferably calcination at 400-450°C for 3-4 hours.

[0018] Preferably, in a method for preparing a complex-dissolve-re-anchor synergistic modified Cu / SiO2 catalyst, in step (3), the reduction atmosphere is hydrogen or a hydrogen-containing mixture, and the reduction temperature is 200-300℃, more preferably 200-240℃.

[0019] This invention protects a modified Cu / SiO2 catalyst prepared by the steps or combinations of the methods described above.

[0020] This invention also protects the application of the modified Cu / SiO2 catalyst described above in the hydrogenation of dimethyl oxalate to ethylene glycol.

[0021] Preferably, the reaction conditions are as follows: temperature 180–200°C, pressure 2–3 MPa, molar ratio of H2 to DMO 50–200, and liquid hourly space velocity (LHSV) of DMO 0.5–2 h⁻¹. -1 .

[0022] This invention discovers: Treating Cu / SiO2 precursors with complexing solvents such as ammonia, ethylenediamine, and ethylenediaminetetraacetic acid (EDTA) alone can selectively dissolve some unstable CuO particles and release Cu. 2+ Ions play a certain role in surface reconstruction, but the dissolved Cu 2+ If the ions are not stabilized in time, they are very likely to re-aggregate into large CuO particles during subsequent drying or calcination, or even be lost during washing, resulting in the loss of active components, limited dispersion improvement effect, and unstable and difficult-to-control performance gains from individual modification.

[0023] When Cu / SiO2 precursors are modified using amine-containing silane coupling agents such as KH-792 alone, the amine groups on the coupling agent molecules can react with Cu. 2+ Coordination with the silane end allows for condensation with the silanol groups on the SiO2 support surface after hydrolysis, forming Si-O-Si covalent bonds, which provide a certain anchoring effect for copper species. However, coupling agent modification alone cannot effectively eliminate the large CuO particles already present in the precursor. These large CuO particles will still transform into easily sintered, low-activity Cu after calcination and reduction. 0 The location of the site limits further improvements in catalyst dispersion and stability. Furthermore, modification with a single coupling agent affects the overall coordination environment of copper species and Cu. + / Cu 0 The ability to regulate the ratio is limited, resulting in a small increase in catalytic activity.

[0024] The core innovation of this invention lies in the continuous and synergistic completion of the two processes, "complexation dissolution" and "covalent re-anchoring," within the same reaction system. The complexation solvent first selectively dissolves physically adsorbed CuO particles, converting them into free Cu. 2+ Complexing ions remove "bad copper"; subsequently, an amino-containing silane coupling agent is introduced, utilizing its amino terminal to bind with Cu. 2+ Its strong coordination ability allows it to competitively capture Cu from copper complexes formed by complexing solvents. 2+Simultaneously, by utilizing the hydrolysis and condensation of its silane ends to form Si-O-Si covalent bonds, the captured copper species are firmly anchored to the surface of the SiO2 support, achieving in-situ transformation of "bad copper" into "good copper." This synergistic mechanism of "first removal, then anchoring" overcomes the limitations of treating copper species with complexing solvents alone, which cannot stabilize copper species, and treating large CuO particles with coupling agents alone, which cannot eliminate them. It achieves improved copper species dispersion, coordination environment, and Cu... + / Cu 0 Multi-dimensional synchronous optimization of proportions.

[0025] Compared with existing technologies, the beneficial effects of the present invention are as follows: (1) Through the synergistic effect of the complexing solvent and the amino-silane coupling agent, a series reaction of "dissolution-re-anchoring" was achieved in the same system. The complexing solvent converted low-activity large-particle CuO into soluble Cu. 2+ Complex ions overcome the limitation of single coupling agent modification in eliminating existing large CuO particles; amino-containing silane coupling agents, through competitive coordination of amino groups and covalent anchoring at the silane end, release dissolved CuO particles. 2+ In-situ fixation on the carrier surface overcomes the shortcomings of single complexing solvent treatment, which cannot stabilize copper species and easily leads to loss or re-aggregation of active components. The synergy of the two achieves in-situ directional transformation of "bad copper" into "good copper", and the quality of the active center is significantly better than any single modification method.

[0026] (2) The amino group of the amino-silane coupling agent is related to Cu 2+ The strong coordination ability of N-coordinates alters the coordination chemistry of copper species. The introduction of N-coordinates enhances the ligand field strength, resulting in Cu in the precursor... 2+ It exists in a more stable chelated state. Although the N coordination is removed after calcination, the anchoring effect is retained, promoting the formation of a highly dispersed Cu-O-Si interface. + / (Cu + +Cu 0 A better ratio promotes Cu + -Cu 0 Synergistic catalytic effect enhances catalyst activity.

[0027] (3) The modification process is carried out under mild conditions, which has minimal impact on the macroscopic texture and pore distribution of the catalyst. The coupling agent is uniformly anchored on the inner surface of the pores in the form of monomolecules or oligomers without clogging the pores, thus achieving a balance between optimizing the active center and protecting the support framework.

[0028] (4) The modification methods described in this invention can be flexibly combined according to the characteristics of the catalyst system and process conditions. They have a wide range of applications and are easy to combine with existing, but not limited to, ammonia precipitation methods, and have good industrialization prospects. Detailed Implementation

[0029] A method for preparing a complex-dissolution-re-anchoring synergistic modified Cu / SiO2 catalyst includes the following steps: (1) Prepare Cu / SiO2 catalyst precursor by deposition precipitation, ion exchange or hydrothermal synthesis; disperse the obtained precursor in water, add a complexing solvent while stirring, and treat at 40-80℃ for 0.5-2.0 hours, using the complexing solvent to treat Cu 2+ Its coordination ability selectively dissolves unstable physically adsorbed CuO particles, releasing Cu 2+ Ions form soluble copper complex ions, while preserving the copper silicate and Cu-O-Si interface units to the greatest extent possible; (2) Add an aminosilane coupling agent solution to the substance (slurry) obtained in step (1) and continue the reaction at 10-80°C for 0.5-12 hours; the amino end of the aminosilane coupling agent undergoes coordination exchange or competitive coordination with the copper complex ions released in step (1), capturing free Cu. 2+ After hydrolysis, its silane end condenses with the silanol groups on the surface of the SiO2 support to form Si-O-Si covalent bonds, thus re-anchoring the copper species to the support surface. (3) The substance (slurry) obtained in step (2) is subjected to ammonia stripping or direct drying and calcination to obtain a modified Cu / SiO2 catalyst.

[0030] In step (1), the complexing solvent is capable of reacting with Cu. 2+ One or more of the amine compounds or ammonia molecules that form soluble complexes, preferably ammonia, ethylenediamine, triethanolamine, ethylenediaminetetraacetic acid and their salts.

[0031] In step (1), the amount of complexing solvent and the treatment conditions are adjusted according to its complexing strength: when using reversible complexing solvents such as ammonia, the concentration of ammonia is 0.05-0.5 mol / L, preferably 0.1-0.3 mol / L, and the treatment time is 10-30 minutes; when using strong irreversible complexing solvents such as EDTA, the amount of solvent is controlled in a low ratio range of n(EDTA) / n(Cu)≤0.05, and the treatment time is 5-30 minutes.

[0032] In step (2), the amino-containing silane coupling agent is an organosilicon compound containing at least one amino group and at least one hydrolyzable alkoxy group, preferably one or more of N-[3-(methoxysilane)propyl]ethylenediamine (KH-792), γ-aminopropyltriethoxysilane (APTES), γ-aminopropyltrimethoxysilane (APTMS), N-[3-(trimethoxysilyl)propyl]ethylenediamine and polyamine-containing polyamine silane coupling agents, and the amount of coupling agent used is 0.1 to 5 wt% of the dry basis mass of the catalyst, preferably 0.5 to 2 wt%.

[0033] In step (2), the amino-silane coupling agent is added in the form of a pre-hydrolyzed solution. The pre-hydrolyzed method is as follows: the amino-silane coupling agent is mixed with an alcohol-water mixed solvent at a mass ratio of 1:(8-20) and hydrolyzed at room temperature for 10-60 minutes. The mass ratio of alcohol to water in the alcohol-water mixed solvent is 4:1-8:1, and the alcohol is methanol or ethanol.

[0034] In step (2), the reaction temperature is preferably 40-80℃ and the reaction time is preferably 2-8 hours.

[0035] In step (3), the ammonia stripping temperature is 85-95℃ until the pH drops to 6-7; the roasting conditions are 400-500℃ for 3-8 hours.

[0036] The modified Cu / SiO2 catalyst described herein, compared to the unmodified catalyst, exhibits larger Cu particles... 0 The grains have essentially disappeared, and the dispersion of the Cu component has increased; Cu + / (Cu + +Cu 0 The proportion of oxalate increased, while the pore structure remained essentially unchanged. Performance tests were conducted on the hydrogenation of dimethyl oxalate to ethylene glycol using this catalyst, showing an oxalate conversion rate of >99% and an ethylene glycol selectivity of 94-97%.

[0037] Based on the specific implementation methods, 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, 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.

[0038] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0039] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this description, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0040] In this invention, some conventional operating equipment, devices and components have been omitted or only briefly described.

[0041] Unless otherwise specified in the examples, the conditions shall be performed according to the standard conditions or the conditions recommended by the manufacturer.

[0042] In this application, unless otherwise specified, % refers to mass fraction.

[0043] Example 1: A method for preparing a Cu / SiO2 catalyst with complexation-dissolution-re-anchoring synergistic modification includes the following steps: (1) At room temperature and stirring speed of 350 rpm, 30 g Cu(NO3)·3H2O was added to 500 mL of deionized water and dissolved completely. Then concentrated ammonia was added until the solution pH=11 to obtain a copper ammonia solution.

[0044] (2) Disperse 30g of silica powder in 500g of deionized water and stir continuously at 600 rpm for 120min. Adjust the pH of the dispersion to 7.0 with ammonia water to obtain the silicon source.

[0045] (3) Slowly add the silicon source from step (2) into the solution from step one, and age it for 4 hours at room temperature and stirring speed of 350 rpm.

[0046] (4) Heat the mixture obtained in step (3) to 90°C and stir continuously to carry out ammonia precipitation. Stop the reaction when the pH is less than 7.0.

[0047] (5) After filtering and washing the slurry obtained in step (4), the filter cake is redispersed in 500 mL of deionized water and 50 g of dilute ammonia (3 wt%) is added. The mixture is reacted at 60 °C for 60 min.

[0048] (6) Dissolve 0.6g of KH792 silane coupling agent in 100mL of methanol-water solution, wherein the mass ratio of methanol to water is 1:3. Stir the above solution at room temperature and 300rpm for 40min to achieve pre-hydrolysis.

[0049] (7) Slowly add the pre-hydrolyzed solution obtained in (6) to the mixed slurry in (5) and react at 90°C for 2 hours. After the reaction is complete, filter and wash the slurry until the pH of the filtrate is 7.0.

[0050] (8) The obtained filter cake was dried at 100℃ for 12h, calcined at 450℃ for 4h, and then pressed, crushed and sieved to obtain the Cu / SiO2 catalyst. The structural properties and performance test results of the catalyst are shown in Table 1 and Table 2.

[0051] Example 2: A method for preparing a Cu / SiO2 catalyst with complexation-dissolution-re-anchoring synergistic modification includes the following steps: (1) Dissolve 30g Cu(NO3)·3H2O and 55g urea in 650 mL of deionized water at room temperature and stirring speed of 350 rpm.

[0052] (2) Disperse 30g of silica powder in 500g of deionized water and stir continuously at 600 rpm for 120min. Adjust the pH of the dispersion to 3.0~4.0 with dilute nitric acid to obtain the silicon source.

[0053] (3) Slowly add the silicon source from step (2) into the solution from step (1) and age it for 4 hours at room temperature and stirring speed of 350 rpm.

[0054] (4) Heat the mixture from step (3) to 90°C and reflux for 24 hours.

[0055] (5) After filtering and washing the slurry obtained in step (4), the filter cake is redispersed in 500 mL of deionized water and 50 g of dilute ammonia (3 wt%) is added. The mixture is reacted at 60 °C for 60 min.

[0056] (6) Dissolve 0.6g of KH792 silane coupling agent in 100mL of methanol-water solution, wherein the mass ratio of methanol to water in the methanol-water solution is 1:3. Stir the above solution at room temperature and 300rpm for 40min to achieve pre-hydrolysis.

[0057] (7) Slowly add the pre-hydrolyzed solution obtained in step (6) to the mixed slurry in (5) and react at 90°C for 2 hours. After the reaction is complete, filter and wash the slurry until the pH of the filtrate is 7.0.

[0058] (8) The obtained filter cake was dried at 100℃ for 12h, calcined at 450℃ for 4h, and then pressed, crushed and sieved to obtain the Cu / SiO2 catalyst.

[0059] Example 3: A method for preparing a Cu / SiO2 catalyst with complexation-dissolution-re-anchoring synergistic modification includes the following steps: (1) At room temperature and stirring speed of 350 rpm, 30g Cu(NO3)·3H2O and 85g concentrated ammonia water were dissolved together in 500 mL of deionized water.

[0060] (2) Disperse 30g of silica powder in 500g of deionized water and stir continuously at 600 rpm for 120min. Adjust the pH of the dispersion to 7.0 with ammonia water to obtain the silicon source.

[0061] (3) Slowly add the silicon source from step (2) into the solution from step one, and age it for 4 hours at room temperature and stirring speed of 350 rpm.

[0062] (4) Transfer the mixture from step (3) into a hydrothermal reactor, heat it to 120°C, and react for 24 hours.

[0063] (5) After filtering and washing the slurry obtained in step (4), the filter cake is redispersed in 500 mL of deionized water and 50 g of dilute ammonia (3 wt%) is added. The mixture is reacted at 60 °C for 60 min.

[0064] (6) Dissolve 0.6g of KH792 silane coupling agent in 100mL of methanol / water solution, wherein the mass ratio of methanol to water is 1 / 3. Stir the above solution at room temperature and 300rpm for 40min to achieve pre-hydrolysis.

[0065] (7) Slowly add the pre-hydrolyzed solution obtained in step (6) to the mixed slurry in (5) and react at 90°C for 2 hours. After the reaction is complete, filter and wash the slurry until the pH of the filtrate is 7.0.

[0066] (8) The obtained filter cake was dried at 100℃ for 12h, calcined at 450℃ for 4h, and then pressed, crushed and sieved to obtain the Cu / SiO2 catalyst.

[0067] Example 4: A method for preparing a Cu / SiO2 catalyst with complexation-dissolution-re-anchoring synergistic modification is provided. The preparation steps are basically the same as those in Example 1, except that the silica dispersion in step (2) is replaced with 100 g of silica sol.

[0068] Example 5: A method for preparing a Cu / SiO2 catalyst with complexation-dissolution-reanchoring synergistic modification is provided. The preparation steps are basically the same as those in Example 1, except that step (5) is changed to 1.6 g of EDTA instead of 50 g of dilute ammonia (3wt%), which is then added to the redispersed slurry and reacted at 60°C for 60 min.

[0069] Example 6: A method for preparing a Cu / SiO2 catalyst with complexation-dissolution-re-anchoring synergistic modification is provided. The preparation steps are basically the same as those in Example 1, except that step (5) is changed to replacing 50 g of dilute ammonia (3wt%) with 0.6 g of ethylenediamine, which is then added to the redispersed slurry and reacted at 60°C for 60 min.

[0070] Example 7: A method for preparing a Cu / SiO2 catalyst with complexation-dissolution-re-anchoring synergistic modification is provided. The preparation steps are basically the same as those in Example 1, except that the silane coupling agent in step (6) is replaced with APTMS, and the amount added is 0.8 g.

[0071] Comparative Example 1: A method for preparing a Cu / SiO2 catalyst with synergistic modification through complexation-dissolution-re-anchoring includes the following steps: (1) At room temperature and stirring speed of 350 rpm, 30 g Cu(NO3)·3H2O was added to 500 mL of deionized water and dissolved completely. Then concentrated ammonia was added until the solution pH=11 to obtain a copper ammonia solution.

[0072] (2) Disperse 30g of silica powder in 500g of deionized water and stir continuously at 600 rpm for 120min. Adjust the pH of the dispersion to 7.0 with ammonia water to obtain the silicon source.

[0073] (3) Slowly add the silicon source from step (2) into the solution from step one, and age it for 4 hours at room temperature and stirring speed of 350 rpm.

[0074] (4) Heat the mixture obtained in step (3) to 90°C and stir continuously to carry out ammonia precipitation. Stop the reaction when the pH is less than 7.0.

[0075] (5) After filtering and washing the slurry obtained after the reaction in step (4), dry it at 100°C for 12 hours, calcine it at 450°C for 4 hours, and obtain the Cu / SiO2 catalyst after pressing, crushing and sieving.

[0076] Comparative Example 2: A method for preparing a Cu / SiO2 catalyst with complexation-dissolution-re-anchoring synergistic modification is provided. The preparation steps are basically the same as those in Example 1, except that the secondary ammonia stripping reaction in step (7) is carried out directly after step (5).

[0077] Comparative Example 3: A method for preparing a Cu / SiO2 catalyst with complexation dissolution-re-anchoring synergistic modification is provided. The preparation steps are basically the same as those in Example 1, except that no complexing solvent is added in step (5), and step (6) and subsequent steps are carried out directly.

[0078] Comparative Example 4: A method for preparing a Cu / SiO2 catalyst with synergistic modification through complexation-dissolution-re-anchoring includes the following steps: (1) At room temperature and stirring speed of 350 rpm, 30 g Cu(NO3)·3H2O was added to 500 mL of deionized water and dissolved completely. Then concentrated ammonia was added until the solution pH=11 to obtain a copper ammonia solution.

[0079] (2) Disperse 30g of silica powder in 500g of deionized water and stir continuously at 600 rpm for 120min. Adjust the pH of the dispersion to 7.0 with ammonia water to obtain the silicon source.

[0080] (3) Slowly add the silicon source from step (2) into the solution from step one, and age it for 4 hours at room temperature and stirring speed of 350 rpm.

[0081] (4) Heat the mixture obtained in step (3) to 90°C and stir continuously to carry out ammonia precipitation. Stop the reaction when the pH is less than 7.0.

[0082] (5) After filtering and washing the slurry obtained after the reaction in step (4), dry it at 100°C for 12 hours to obtain the precursor powder of the catalyst after drying.

[0083] (6) Disperse the powder obtained in step (5) in 500 mL of deionized water and add 50 g of dilute ammonia (3 wt%), and react at 60 °C for 60 min.

[0084] (6) Dissolve 0.6g of KH792 silane coupling agent in 100mL of methanol / water solution, wherein the mass ratio of methanol to water is 1 / 3. Stir the above solution at room temperature and 300rpm for 40min to achieve pre-hydrolysis.

[0085] (7) Slowly add the pre-hydrolyzed solution obtained in step (6) to the mixed slurry in (5) and react at 90°C for 2 hours. After the reaction is complete, filter and wash the slurry until the pH of the filtrate is 7.0.

[0086] (8) The obtained filter cake was dried at 100℃ for 12h, calcined at 450℃ for 4h, and then pressed, crushed and sieved to obtain the Cu / SiO2 catalyst.

[0087] Comparative Example 5: A method for preparing a Cu / SiO2 catalyst with synergistic modification through complexation-dissolution-re-anchoring includes the following steps: (1) At room temperature and stirring speed of 350 rpm, 30 g Cu(NO3)·3H2O was added to 500 mL of deionized water and dissolved completely. Then concentrated ammonia was added until the solution pH=11 to obtain a copper ammonia solution.

[0088] (2) Disperse 30g of silica powder in 500g of deionized water and stir continuously at 600 rpm for 120min. Adjust the pH of the dispersion to 7.0 with ammonia water to obtain the silicon source.

[0089] (3) Slowly add the silicon source from step (2) into the solution from step one, and age it for 4 hours at room temperature and stirring speed of 350 rpm.

[0090] (4) Heat the mixture obtained in step (3) to 90°C and stir continuously to carry out ammonia precipitation. Stop the reaction when the pH is less than 7.0.

[0091] (5) After filtering and washing the slurry obtained after the reaction in step (4), dry it at 100°C for 12 hours and calcine it at 450°C for 4 hours to obtain the precursor powder after calcination of the catalyst.

[0092] (6) Disperse the powder obtained in step (5) in 500 mL of deionized water and add 50 g of dilute ammonia (3 wt%), and react at 60 °C for 60 min.

[0093] (6) Dissolve 0.6g of KH792 silane coupling agent in 100mL of methanol / water solution, wherein the mass ratio of methanol to water is 1 / 3. Stir the above solution at room temperature and 300rpm for 40min to achieve pre-hydrolysis.

[0094] (7) Slowly add the pre-hydrolyzed solution obtained in (6) to the mixed slurry in (5) and react at 90°C for 2 hours. After the reaction is complete, filter and wash the slurry until the pH of the filtrate is 7.0.

[0095] (8) The obtained filter cake was dried at 100℃ for 12h, calcined at 450℃ for 4h, and then pressed, crushed and sieved to obtain the Cu / SiO2 catalyst.

[0096] The catalysts prepared in the examples and comparative examples were measured. Specific surface area, pore size, and pore volume were calculated from N2 adsorption-desorption curves using the BET method, employing an automated specific surface area analyzer (APSP 2460, Micromeritics). Copper content was determined using inductively coupled plasma optical emission spectrometry (ICP-OES, Agilent). The valence state distribution of surface copper components was determined using X-ray photoelectron spectroscopy (XPS, Thermo Fisher Scientific).

[0097] Table 1. Physical properties of the catalyst

[0098] The catalyst performance was tested in a pressurized fixed-bed reactor. Prior to the reaction, the catalyst was reduced at 230°C for 4 hours in a 10 v.% H2 / N2 mixture. The reaction conditions were: LHSV = 1.0 h. -1 The reaction was carried out at 3.0 MPa, 200℃, with a hydrogen-to-ester molar ratio of 60, and the liquid-phase feed was a 15 wt% DMO methanol solution. The reaction tail gas was collected after condensation and analyzed by gas chromatography (Agilent 7890S). The reaction performance of the above catalyst is shown in Table 2.

[0099] Table 2 Catalyst Performance Overview

[0100] Table 1 shows that the catalyst modified by this method is similar to the unmodified catalyst in terms of pore properties and copper content. This indicates that the "complexation-dissolution-re-anchoring" modification method described in this patent does not significantly alter the pore structure of the catalyst itself, nor does it cause severe copper loss. Simultaneously, the Cu content on the catalyst surface... + The increased content indicates that some of the large, easily reducible copper oxide particles on the catalyst surface were redispersed on the catalyst surface in a coordination form with stronger support-metal interactions. Table 2 shows that the modified catalyst exhibits significantly improved ethylene glycol selectivity and significantly reduced byproduct selectivity.

[0101] Therefore, it can be concluded that the catalyst modification preparation method described in this invention can regulate the distribution and chemical environment of the copper component in the active center, improve the utilization efficiency of copper, and thus improve the selectivity of the target product of the catalyst. Furthermore, this method is easy to operate, has a wide range of applicability, and possesses broad application potential.

[0102] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.

[0103] This background section is provided to generally present the context of the invention. The work of the currently named inventors, the work to the extent described in this background section, and aspects of this section that did not constitute prior art at the time of application are neither expressly nor impliedly acknowledged as prior art to the invention.

Claims

1. A method for preparing a complex-dissolution-re-anchoring synergistic modification of Cu / SiO2 catalyst, characterized in that, Includes the following steps: (1) The catalyst precursor obtained by supporting copper on SiO2 is dispersed in water, and a complexing solvent is added under stirring to selectively dissolve the low-activity CuO or Cu(OH)2 particles on the catalyst surface, releasing Cu 2+ Ions, forming soluble copper complex ions; (2) Add an amino-silane coupling agent solution to the substance obtained in step (1) to carry out the reaction; during the reaction, the amino end of the amino-silane coupling agent undergoes coordination exchange or competitive coordination with the soluble copper complex ions released in step (2), capturing free Cu. 2+ The silane end of the aminosilane coupling agent is hydrolyzed and condenses with the silanol groups on the surface of the SiO2 support to form Si-O-Si covalent bonds, thereby re-anchoring copper to the support surface. (3) The substance obtained in step (2) is subjected to solvent removal, drying, calcination and reduction to obtain the modified Cu / SiO2 catalyst.

2. The method according to claim 1, characterized in that: In step (1), the method used to obtain the catalyst precursor by loading copper onto the SiO2 support includes, but is not limited to, ammonia stripping, urea precipitation and hydrothermal synthesis; the complexing solvent is ammonia or an organic amine, wherein the organic amine includes one or more of ethylenediamine, triethanolamine, ethylenediaminetetraacetic acid and their salts.

3. The method according to claim 1, characterized in that: In step (2), the amino-containing silane coupling agent is an organosilicon compound containing at least one amino group and at least one hydrolyzable alkoxy group; selected from one or more of N-[3-(methoxysilane)propyl]ethylenediamine, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-[3-(trimethoxysilyl)propyl]ethylenediamine and polyamine-containing silane coupling agents; the amount of amino-containing silane coupling agent is 0.1 to 5 wt% of the dry basis mass of the catalyst.

4. The method according to claim 1, characterized in that: In step (2), the reaction temperature is 10-80℃ and the reaction time is 0.5-12 hours.

5. The method according to claim 1, characterized in that: In step (3), the calcination conditions are 400-500℃ for 3-8 hours.

6. The method according to claim 1, characterized in that: In step (3), the atmosphere for reduction is hydrogen or a hydrogen-containing mixture, and the reduction temperature is 200-300°C.

7. The method according to claim 2, characterized in that, In step (1), when ammonia is used as the complexing solvent, the concentration of ammonia is 0.05-0.5 mol / L and the treatment time is 5-60 minutes; when ethylenediaminetetraacetic acid or its salts are used as the complexing solvent, the amount is controlled to be n(EDTA) / n(Cu) = 0.005-0.05 and the treatment time is 5-30 minutes.

8. The method according to claim 3, characterized in that: In step (2), the amino-silane coupling agent is added in the form of a pre-hydrolyzed solution; the pre-hydrolyzed method is as follows: the amino-silane coupling agent is mixed with an alcohol-water mixed solvent at a mass ratio of 1:8 to 20, and hydrolyzed at room temperature for 10 to 60 minutes; the mass ratio of alcohol to water in the alcohol-water mixed solvent is 4:1 to 8:1; the alcohol is methanol or ethanol.

9. A modified Cu / SiO2 catalyst, characterized in that: Prepared by the method according to any one of claims 1 to 8.

10. The application of the modified Cu / SiO2 catalyst according to claim 9 in the hydrogenation of dimethyl oxalate to ethylene glycol, characterized in that, The reaction conditions were: temperature 180–200℃, pressure 2–3 MPa; molar ratio of H2 to DMO 50–200; and liquid hourly space velocity (LIHSV) of DMO 0.5–2 h⁻¹. -1 .

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