Catalyst based on copper-zinc-aluminum core-shell structure as well as preparation method and application of catalyst

Abstract

The invention belongs to the technical field of catalysts, and relates to a copper-zinc-aluminum core-shell structure-based catalyst as well as a preparation method and application thereof. The catalyst comprises a core-shell structure and an auxiliary agent dispersed on the surface of the core-shell structure, the core-shell structure comprises an inner core of a Cu-Zn-Al active component and an outer shell wrapping the surface of the inner core, the outer shell is a ZrO2 and SiO2 composite oxide coating, the mass of the inner core accounts for 60-80% of the total mass of the catalyst, and the thickness of the outer shell is 50-200 nm; the auxiliary agent is CeO2, and the mass of the auxiliary agent is 1-5% of the total mass of the catalyst. Through cooperation of core-shell structure design and assistant modification, high activity, high stability and long service life of the catalyst under a temperature fluctuation working condition are realized, continuity of controllable atmosphere preparation is guaranteed, and industrial operation cost is reduced.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, and relates to a catalyst based on a copper-zinc-aluminum core-shell structure, its preparation method, and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] In industrial fields such as high-carbon steel heat treatment, the stable preparation of a controlled atmosphere is crucial for ensuring product quality. The ammonia-methanol coupled gasification process has become one of the mainstream technologies for controlled atmosphere preparation in this field due to its advantages such as readily available raw materials and controllable gas composition. The core of this process lies in the methanol cracking reaction, and Cu-Zn-Al based catalysts are widely used in this reaction system due to their high catalytic activity and low cost. However, in actual industrial production, the cracking reaction temperature of the ammonia-methanol coupled gasification process is easily affected by various factors such as the stability of raw material supply, the heat dissipation efficiency of the reaction unit, and adjustments to the operating load, inevitably resulting in significant temperature fluctuations. Under frequent and large temperature fluctuations (≥±50℃), the Cu particles of the traditional Cu-Zn-Al catalyst are prone to migration, agglomeration, and sintering. The pore structure of the support collapses, carbon deposits form, reducing the number of Cu active sites and the specific surface area of ​​the catalyst, leading to a sharp decline in catalytic activity. This results in a typically short catalyst lifespan, generally only a few hundred hours.

[0004] Frequent catalyst deactivation and replacement not only increase the operating costs of the ammonia-methanol coupled gasification process but also lead to unstable gasification efficiency and fluctuations in controllable atmosphere composition, thus affecting the product qualification rate of high-carbon steel heat treatment. Furthermore, frequent shutdowns for catalyst replacement reduce production continuity, further hindering the efficient industrial application of the ammonia-methanol coupled gasification process. Therefore, developing an ammonia-methanol coupled gasification catalyst system with excellent resistance to thermal fluctuations, a long service life, and the ability to maintain high cracking efficiency under fluctuating temperature conditions has become a pressing technical challenge in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a catalyst based on a copper-zinc-aluminum core-shell structure, its preparation method, and its application. Through the synergistic design of the core-shell structure and the modification of additives, the present invention achieves high activity, high stability, and long lifespan of the catalyst under temperature fluctuation conditions, ensuring the continuity of controlled atmosphere preparation and reducing industrial operating costs.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, a catalyst based on a copper-zinc-aluminum core-shell structure includes a core-shell structure and an additive dispersed on the surface of the core-shell. The core-shell structure includes a core of Cu-Zn-Al active components and an outer shell covering the surface of the core. The outer shell is a composite oxide coating of ZrO2 and SiO2. The mass of the core is 60-80% of the total catalyst mass, and the thickness of the outer shell is 50-200 nm. The additive is CeO2, and the mass of the additive is 1-5% of the total catalyst mass.

[0007] This invention uses a Cu-Zn-Al active component as the core, where Cu acts as the main active element, efficiently catalyzing the breaking of the CH bond in methanol; ZnO acts as a structural promoter, inhibiting Cu particle agglomeration; and Al2O3 acts as a support framework, enhancing the structural stability of the core. A composite oxide coating of ZrO2 and SiO2 serves as the outer shell. ZrO2 possesses excellent thermal stability and conductivity, buffering the thermal shock of temperature fluctuations to the core and inhibiting the sintering of the active component; SiO2 improves the pore structure and dispersibility of the outer shell, preventing coating cracking, and simultaneously enhancing the bonding force between the core and the shell. The synergistic effect of both protects the Cu-Zn-Al active component in the core from temperature fluctuations while maintaining the mass transfer and heat conduction conditions required for the catalytic reaction. CeO2 is used as a promoter, possessing good oxygen storage / release capabilities, which can adjust the oxygen species concentration on the catalyst surface and inhibit carbon deposition. Simultaneously, CeO2 synergizes with ZrO2, Cu, and other components, further enhancing the catalyst's anti-aging performance and structural stability.

[0008] Secondly, a method for preparing the catalyst according to the first aspect of the present invention includes the following steps: Copper, zinc, and aluminum salts are dissolved in water to prepare a mixed solution; ammonia or alkali metal hydroxides are added to the mixed solution to prepare hydroxide precipitates, which are then washed, dried, and calcined once to prepare Cu-Zn-Al oxide precursors; Zirconia precursors and silicon oxide precursors are dissolved in a solvent and hydrolyzed to form a sol. Cu-Zn-Al oxide precursors are then added to the sol for impregnation, allowing the sol to be adsorbed onto the surface of the Cu-Zn-Al oxide precursors. The sol is then converted into a composite oxide coating of ZrO2 and SiO2 through drying and secondary calcination, thereby forming a core-shell structure. The core-shell structure is added to a cerium salt solution and ultrasonically impregnated. Then, the impregnated core-shell structure is dried and calcined three times to convert the cerium salt impregnated in the core-shell structure into cerium oxide, thus obtaining the core-shell structure.

[0009] Thirdly, the application of the catalyst described in the first aspect of the present invention in catalytic methanol cracking to produce gas or catalytic ammonia-methanol coupling to produce gas.

[0010] The beneficial effects of this invention are as follows: 1. This invention uses a composite oxide coating of ZrO2 and SiO2 as the outer shell of the core-shell structure, which has high thermal conductivity and structural stability. It can effectively buffer and resist the impact of harsh temperature fluctuations in the reaction conditions, providing a physical protective barrier for the core active components. This avoids the migration, aggregation and sintering deactivation of the core active Cu particles due to sudden temperature rises and falls, and ensures the structural integrity of the catalyst under unsteady conditions.

[0011] 2. This invention uses Cu-Zn-Al active components as the core, combined with the oxygen regulation effect of CeO2 promoter, to synergistically ensure high activity and high selectivity in the methanol cracking reaction. Under actual operating conditions with temperature fluctuations, the catalyst can still maintain a methanol conversion rate of over 90%, and the selectivity of the target products (H2 and CO) is not less than 95%. The composition of the prepared gas is stable and controllable, fully meeting the stringent requirements for the composition of raw gas in the heat treatment of high-carbon steel.

[0012] 3. In the catalyst provided by this invention, the core-shell structure effectively inhibits the loss of active components through physical isolation; simultaneously, the introduction of CeO2 promoter further modifies and improves the catalyst's anti-aging performance. The two work synergistically to significantly inhibit the covering and sintering deactivation of active sites during the reaction process, and effectively suppress carbon deposition caused by side reactions. Experiments show that the service life of this catalyst is more than twice that of traditional Cu-Zn-Al catalysts, significantly reducing the catalyst replacement frequency of the reaction device.

[0013] 4. The catalyst provided by this invention can improve the production continuity and operational stability of the ammonia-methanol coupled gasification process, reducing unplanned downtime caused by catalyst deactivation. This significantly reduces system downtime maintenance costs and catalyst procurement and replacement costs, improving overall production efficiency and economic benefits. Furthermore, the catalyst preparation process provided by this invention is simple, the raw materials are readily available, and the core-shell structure construction and additive modification methods are easy to control on a large scale, making it suitable for industrial-scale production. Attached Figure Description

[0014] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0015] Figure 1 The image shown is a transmission electron microscope (TEM) image of the core-shell structure prepared in Example 1 of this invention. Figure 2 The graph shows the performance test results of the catalyst prepared in Example 1 of this invention; Figure 3 The graph shows the performance test results of the catalyst prepared in Example 2 of this invention; Figure 4 The graph shows the performance test results of the catalyst prepared in Example 3 of this invention; Figure 5 This is a comparison chart of the cracking rates of the catalysts prepared in Comparative Example 1 and Examples 1-3 of the present invention. Detailed Implementation

[0016] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. 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 invention pertains.

[0017] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0018] In view of the shortcomings of traditional Cu-Zn-Al catalysts in the existing ammonia-methanol coupled gasification process, such as poor resistance to thermal fluctuations, easy deactivation, and short lifespan, in order to solve the above technical problems, this invention proposes a catalyst based on a copper-zinc-aluminum core-shell structure, its preparation method, and its application.

[0019] A typical embodiment of the present invention provides a catalyst based on a copper-zinc-aluminum core-shell structure, comprising a core-shell structure and an additive dispersed on the surface of the core-shell. The core-shell structure comprises a core of Cu-Zn-Al active components and an outer shell covering the surface of the core. The outer shell is a composite oxide coating of ZrO2 and SiO2. The mass of the core is 60-80% of the total catalyst, and the thickness of the outer shell is 50-200 nm. The additive is CeO2, and the mass of the additive is 1-5% of the total catalyst.

[0020] The Cu-Zn-Al active component described in this invention refers to a composite oxide containing Cu, Zn, and Al prepared by a co-precipitation method. In some embodiments, the molar ratio of Cu, Zn, and Al in the Cu-Zn-Al active component is (4~6):(2~3):(1~2). This ratio enables the Cu-Zn-Al active component to better ensure high activity in catalyzing methanol cracking.

[0021] In some embodiments, the molar ratio of ZrO2 to SiO2 in the composite oxide coating of ZrO2 and SiO2 is (3~5):(1~2). Performance is better under this ratio.

[0022] Another embodiment of the present invention provides a method for preparing the above-mentioned catalyst, comprising the following steps: Copper, zinc, and aluminum salts are dissolved in water to prepare a mixed solution; ammonia or alkali metal hydroxides are added to the mixed solution to prepare hydroxide precipitates, which are then washed, dried, and calcined once to prepare Cu-Zn-Al oxide precursors; Zirconia precursors and silicon oxide precursors are dissolved in a solvent and hydrolyzed to form a sol. Cu-Zn-Al oxide precursors are then added to the sol for impregnation, allowing the sol to be adsorbed onto the surface of the Cu-Zn-Al oxide precursors. The sol is then converted into a composite oxide coating of ZrO2 and SiO2 through drying and secondary calcination, thereby forming a core-shell structure. The core-shell structure is added to a cerium salt solution and ultrasonically impregnated. Then, the impregnated core-shell structure is dried and calcined three times to convert the cerium salt impregnated in the core-shell structure into cerium oxide, thus obtaining the core-shell structure.

[0023] The alkali metal hydroxides described in this invention can be sodium hydroxide, potassium hydroxide, etc. Ammonia is preferably added during the preparation of the hydroxide precipitate; the main reason for this is that the hydroxide precipitate prepared with ammonia can avoid introducing other cationic impurities, thereby ensuring the catalytic performance of the Cu-Zn-Al active component.

[0024] In some embodiments, during the preparation of the hydroxide precipitate, the pH is 7.0–8.0, the temperature is 60–80°C, and the time is 2–4 h. The hydroxide precipitate prepared under these conditions is more conducive to controlling the formation of Cu-Zn-Al oxide precursors (i.e., Cu-Zn-Al active components) with better catalytic morphology. In this invention, after forming the Cu-Zn-Al oxide precursor, it is dried and then calcined once; the drying conditions are: drying at 60–100°C for 12–24 h.

[0025] In some embodiments, the temperature of a single firing is 400~550°C. Specifically, the firing time is 3~5 hours.

[0026] The precursor of zirconium oxide described in this invention is generally a zirconium salt, and the precursor of silicon oxide is generally an organosilicon compound. In some embodiments, zirconium oxychloride and tetraethyl orthosilicate are added to an aqueous ethanol solution to dissolve, the pH is adjusted to 3-4 with acid, and hydrolysis is performed to form ZrO2-SiO2 sol.

[0027] In some embodiments, the Cu-Zn-Al oxide precursor is added to the sol for impregnation at a temperature of 50–70°C for 4–6 hours. Studies have shown that under these conditions, the ZrO2-SiO2 sol can be better impregnated onto the surface of the Cu-Zn-Al oxide precursor, thereby improving the synergistic effect of the core-shell structure. Specifically, the drying temperature after impregnation is 60–120°C for 8–12 hours.

[0028] In some embodiments, the temperature of the secondary calcination is 500~600℃. Specifically, the secondary calcination time is 2~3 hours.

[0029] In this invention, when the core-shell structure is impregnated with a cerium salt solution, ultrasonic treatment is used to better impregnate the cerium salt to the interface between the core and the shell, as well as to the surface of the shell, thereby improving its effectiveness. In some embodiments, the ultrasonic impregnation time is 1-2 hours.

[0030] The drying conditions for the impregnated core-shell structure are: drying at 80~120℃ for 6~8 hours.

[0031] In some embodiments, the temperature for the three firings is 400~500℃. Specifically, the firing time for the three firings is 2~3 hours.

[0032] A third embodiment of the present invention provides an application of the above-mentioned catalyst in catalytic methanol cracking to produce gas or ammonia-methanol coupled gas production.

[0033] The target gases for catalytic methanol cracking gas production in this invention are hydrogen and carbon monoxide. The target gases for ammonia-methanol coupled gas production in this invention are nitrogen, hydrogen, and carbon monoxide. In ammonia-methanol coupled gas production, ammonia and air undergo a combustion reaction to produce nitrogen and water, simultaneously releasing heat to provide heat for the methanol cracking reaction.

[0034] To enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples. Unless otherwise specified in the embodiments, all raw materials are industrial-grade conventional raw materials.

[0035] Example 1: Weigh out 60.5g of copper nitrate, 31.2g of zinc nitrate, and 22.8g of aluminum nitrate, and dissolve them in 500mL of deionized water to obtain a mixed salt solution. Slowly add ammonia solution dropwise, control the pH to 7.5, stir the reaction at 70℃ for 3h, wash and filter the precipitate, dry it at 90℃ for 24h, and calcine it at 500℃ for 4h to obtain core particles with a Cu:Zn:Al molar ratio of 5:2.5:1.5.

[0036] Weigh out 45.3g of ZrOCl2 8H₂O and 18.6g of tetraethyl orthosilicate were dissolved in 200mL of an ethanol-water mixture (volume ratio 1:1). The pH was adjusted to 3.5 with nitric acid, and the mixture was stirred and hydrolyzed for 1.5h to obtain a sol. Core particles ground to 200 mesh were added to the sol, and the mixture was stirred and impregnated at 60℃ for 5h, dried at 120℃ for 10h, and calcined at 550℃ for 2.5h to form a shell layer on the core surface. The molar ratio of ZrO₂ to SiO₂ was 4:1.5, and the coating thickness was 100nm (e.g., ...). Figure 1 (As shown); Take 8.7g of Ce(NO3)3·6H2O, dissolve it in 100mL of deionized water, place the coated particles into Ce(NO3)3 solution, ultrasonically impregnate for 1.5h, dry at 110℃ for 7h, and calcine at 450℃ for 2.5h to obtain the target catalyst, wherein the mass proportions of the core, shell and promoter are 70%, 27% and 3%, respectively.

[0037] The catalyst was loaded into a fixed-bed reactor, and the reaction temperature was set to 250–350 °C, the pressure to be 0.2 MPa, and the space velocity to be 1.2 h⁻¹. -1 Under the test conditions, the methanol conversion rate was ≥93.2%; the H2 selectivity was ≥96.5%, such as... Figure 2 As shown, the activity decay rate was 4.8% and the carbon deposition was 0.3wt% after 500 hours of continuous operation.

[0038] Example 2: The catalyst preparation method is the same as in Example 1, except that the ratio of core raw materials is changed to a Cu:Zn:Al molar ratio of 4:3:1. 48.4 g of copper nitrate, 37.4 g of zinc nitrate, and 15.2 g of aluminum nitrate were weighed and dissolved in 500 mL of deionized water to obtain a mixed salt solution. Ammonia solution was slowly added dropwise, controlling the pH at 7.5. The reaction was stirred at 70°C for 3 hours. After washing and filtering the precipitate, it was dried at 90°C for 24 hours and calcined at 500°C for 4 hours to obtain the core particles. The molar ratio of ZrO2 to SiO2 in the shell layer was 4:1.5, and the coating thickness was 100 nm. The mass percentages of the catalyst core, shell layer, and promoters were 65%, 30%, and 5%, respectively.

[0039] The test conditions were the same as in Example 1, with the reaction temperature set at 250~350℃, pressure at 0.2MPa, and space velocity at 2.0h. -1 Under the test conditions, the methanol conversion rate was ≥91.8%, and the target product selectivity was ≥95.8%. Figure 3 As shown, the activity decay rate was 5.5% after 500 hours of continuous operation; the carbon deposition was 0.4 wt%.

[0040] Example 3: The catalyst preparation method is the same as in Example 1, except that the raw material ratio is changed so that the molar ratio of Cu, Zn, and Al is 6:2:2. 72.6 g of copper nitrate, 24.9 g of zinc nitrate, and 30.4 g of aluminum nitrate were weighed and dissolved in 500 mL of deionized water to obtain a mixed salt solution. Ammonia solution was slowly added dropwise, controlling the pH to 7.5. The reaction was carried out at 70°C with stirring for 3 hours. After washing and filtering the precipitate, it was dried at 90°C for 24 hours and calcined at 500°C for 4 hours to obtain the core particles. The molar ratio of ZrO2 to SiO2 in the shell layer was 5:2, and the coating thickness was 50 nm. The mass percentages of the catalyst core, shell layer, and promoters were 75%, 20%, and 5%, respectively.

[0041] The test conditions were the same as in Example 1, with the reaction temperature set at 250~350℃, pressure at 0.2MPa, and space velocity at 2.2h. -1 Under the test conditions, the methanol conversion rate was ≥94.5%, and the target product selectivity was ≥97.2%. Figure 4 As shown, after 500 hours of continuous operation, the activity decay rate was 4.2% and the carbon deposition was 0.4 wt%.

[0042] Comparative example: Weigh out 45.3g of ZrOCl2 8H2O and 18.6g of tetraethyl orthosilicate were dissolved in 200mL of ethanol-water mixed solvent (volume ratio 1:1), the pH was adjusted to 3.5 with nitric acid, and the mixture was stirred and hydrolyzed for 1.5h to obtain a sol. The sol was then dried at 120℃ and calcined at 550℃ to obtain a ZrO2-SiO2 support.

[0043] A co-precipitation-impregnation method was used to mix a mixed salt solution of copper nitrate, zinc nitrate, and aluminum nitrate with a ZrO2-SiO2 support. The pH was adjusted to 7.5 with urea, and the mixture was stirred at 70℃ for 2 hours. After drying and calcination, a supported catalyst was obtained. The molar ratio of Cu, Zn, and Al was 5:2.5:1.5, the ZrO2:SiO2 ratio in the ZrO2-SiO2 support was 4:1.5, and the mass ratio of active component to support was 7:3.

[0044] The test conditions were the same as in Example 1, with the reaction temperature set at 250~350℃, the pressure at 0.2MPa, and the space velocity at 1.2h. -1 Under the test conditions, the initial methanol conversion rate was 94.5%, and after 500 hours, the methanol conversion rate was 68.5%, the activity decay rate was 25.6%, and the carbon deposition was 1.8 wt%. Figure 5 As shown.

[0045] The catalyst of this invention exhibits significantly better stable operating time, catalytic activity, and resistance to degradation than the comparative example under temperature fluctuations of ±50℃. The comparative example, lacking a core-shell structure, cannot buffer the impact of temperature fluctuations, resulting in rapid sintering and deactivation of the active components.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A catalyst based on a copper-zinc-aluminum core-shell structure, characterized in that, The catalyst comprises a core-shell structure and an additive dispersed on the surface of the core-shell. The core-shell structure includes a core of Cu-Zn-Al active components and an outer shell covering the surface of the core. The outer shell is a composite oxide coating of ZrO2 and SiO2. The mass of the core is 60-80% of the total catalyst mass, and the thickness of the outer shell is 50-200 nm. The additive is CeO2, and the mass of the additive is 1-5% of the total catalyst mass.

2. The catalyst as described in claim 1, characterized in that, In the Cu-Zn-Al active component, the elemental molar ratio of Cu, Zn, and Al is (4~6):(2~3):(1~2).

3. The catalyst as described in claim 1, characterized in that, In the composite oxide coating of ZrO2 and SiO2, the molar ratio of ZrO2 to SiO2 is (3~5):(1~2).

4. A method for preparing the catalyst according to any one of claims 1 to 3, characterized in that, Includes the following steps: Copper, zinc, and aluminum salts are dissolved in water to prepare a mixed solution; ammonia or alkali metal hydroxides are added to the mixed solution to prepare hydroxide precipitates, which are then washed, dried, and calcined once to prepare Cu-Zn-Al oxide precursors; Zirconia precursors and silicon oxide precursors are dissolved in a solvent and hydrolyzed to form a sol. Cu-Zn-Al oxide precursors are then added to the sol for impregnation, allowing the sol to be adsorbed onto the surface of the Cu-Zn-Al oxide precursors. The sol is then converted into a composite oxide coating of ZrO2 and SiO2 through drying and secondary calcination, thereby forming a core-shell structure. The core-shell structure is added to a cerium salt solution and ultrasonically impregnated. Then, the impregnated core-shell structure is dried and calcined three times to convert the cerium salt impregnated in the core-shell structure into cerium oxide, thus obtaining the core-shell structure.

5. The preparation method according to claim 4, characterized in that, During the preparation of hydroxide precipitate, the pH is 7.0~8.0, the temperature is 60~80℃, and the time is 2~4h.

6. The preparation method according to claim 4, characterized in that, Zirconium oxychloride and tetraethyl orthosilicate were dissolved in an aqueous ethanol solution, and the pH was adjusted to 3-4 with acid to carry out hydrolysis, forming a ZrO2-SiO2 sol.

7. The preparation method according to claim 4, characterized in that, The Cu-Zn-Al oxide precursor is added to the sol for impregnation at a temperature of 50~70℃ for 4~6h.

8. The preparation method according to claim 4, characterized in that, The ultrasonic impregnation time is 1~2 hours.

9. The preparation method according to claim 4, characterized in that, The temperature for the first firing is 400~550℃; Alternatively, the temperature for the second firing is 500~600℃; Alternatively, the temperature for the three firings is 400~500℃.

10. The application of the catalyst according to any one of claims 1 to 3 in catalytic methanol cracking to produce gas or catalytic ammonia-methanol coupling to produce gas.

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