A coupling method for bifunctional catalysts in the synthesis of low-carbon olefins via CO2 hydrogenation and its application

Abstract

The application provides a method for synthesizing a bifunctional catalyst for CO2 hydrogenation into low-carbon olefins, comprising the following steps: A) tablet molding, crushing and screening of a composite oxide powder to obtain an oxide; the composite oxide powder is one or more of ZnO, ZrO2, In2O3 and ZrO2; tablet molding, crushing and screening of a molecular sieve powder to obtain a molecular sieve particle; B) physical mixing of the oxide and the molecular sieve particle to obtain a mixture; C) tablet molding, crushing and screening of the mixture to obtain the bifunctional catalyst. The method comprises the processes of molding, screening and secondary molding of the oxide and the molecular sieve. The bifunctional catalyst obtained by the secondary molding coupling method has excellent activity, high stability and high selectivity of target products, the selectivity of low-carbon olefins in the hydrocarbon product is as high as 87%, the selectivity of propylene is as high as 49.3%, and the deactivation rate of the catalyst is as low as 0.5%.

Description

Technical Field

[0001] This invention relates to the fields of CO2 utilization and catalysis technology, specifically to a coupling method for a bifunctional catalyst for the hydrogenation of CO2 to synthesize low-carbon olefins and its application. Background Technology

[0002] Carbon dioxide, as a non-toxic, economical, and renewable abundant carbon source, can be converted into fuels and chemicals, effectively alleviating environmental problems caused by excessive carbon dioxide emissions and addressing the issue of over-reliance on fossil fuels. Low-carbon olefins (including ethylene, propylene, and butene) are widely used as basic raw materials in the petrochemical and chemical industries to produce plastics, polymers, solvents, and chemicals. Utilizing renewable energy sources such as solar, wind, geothermal, and hydropower to generate renewable H2, which is then hydrogenated with CO2 to form liquid fuels or high-value-added chemicals, is a crucial pathway for carbon dioxide conversion and utilization, possessing significant economic and strategic value. Based on a reaction coupling strategy, the use of oxide / molecular sieve bifunctional catalysts can achieve highly selective synthesis of low-carbon olefin products from CO2 hydrogenation.

[0003] Currently, bifunctional catalytic systems for the hydrogenation of CO2 to low-carbon olefins mainly follow a reaction route using methanol as an intermediate. CO2 and H2 are first converted to methanol intermediates via formate on the surface of metal oxides (such as Cu, Zn, In, and Cr). Methanol then undergoes C-C bond coupling under the action of acidic molecular sieves to generate low-carbon olefins. This route can overcome the ASF distribution limitations of traditional Fischer-Tropsch synthesis reactions, significantly increasing the proportion of low-carbon olefins. Bifunctional systems have made some progress in the hydrogenation of CO2 to low-carbon olefins. Li et al. used a ZnZrO / SAPO tandem bifunctional catalyst for the hydrogenation of CO2 to low-carbon olefins, with the oxides and molecular sieves arranged in a particle-stacking manner, achieving 80% selectivity for low-carbon olefins, while the CO2 conversion rate was only 12.6% [ACS Catal.|(2017)7:8544]. Chinese patent CN 114433059 A discloses a catalyst for the synthesis of low-carbon olefin compounds by CO2 hydrogenation. The catalyst is constructed by mechanically mixing ZnO / Li-ZrO2 and SAPO-34 molecular sieve by ball milling. The catalyst has a CO2 conversion rate of 28.56%, a low-carbon olefin selectivity of up to 81.57%, and low selectivity for CO and CH4.

[0004] In summary, current bifunctional catalytic systems for the synthesis of low-carbon olefins via CO2 hydrogenation suffer from the problem that they cannot simultaneously improve both CO2 conversion rate and low-carbon olefin selectivity. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a bifunctional catalytic system for the synthesis of low-carbon olefins by CO2 hydrogenation, with high carbon dioxide conversion rate and low-carbon olefin selectivity.

[0006] This invention provides a method for synthesizing low-carbon olefins via CO2 hydrogenation using a bifunctional catalyst, comprising the following steps:

[0007] A) The composite oxide powder is compressed into tablets, crushed, and sieved to obtain oxides;

[0008] The composite oxide powder is one or more of ZnO, ZrO2, In2O3 and ZrO2;

[0009] Molecular sieve powder is compressed into tablets, crushed, and sieved to obtain molecular sieve particles.

[0010] B) Physically mix the oxide and molecular sieve particles to obtain a mixture;

[0011] C) Compress the mixture into tablets, crush them, and sieve them to obtain the final product.

[0012] Preferably, the composite oxide powder in step A) is one of ZnO-ZrO2, In2O3-ZrO2, and In2O3-ZnO-ZrO2; and the molecular sieve powder is one or more of SAPO-18, SAPO-20, and SAPO-34.

[0013] Preferably, the pressure for tableting in step A) is 10–40 MPa;

[0014] The pressure for tablet compression in step C) is 10-40 MPa.

[0015] Preferably, the oxide has a mesh size of 20 to 100 mesh; the molecular sieve particles have a mesh size of 20 to 100 mesh.

[0016] Preferably, the mass ratio of the oxide and molecular sieve particles physically mixed in step B) is 1:2 to 2:1.

[0017] Preferably, the low-carbon olefin bifunctional catalyst has a mesh size of 40 to 80 mesh.

[0018] Preferably, the composite oxide powder in step A) is synthesized by co-precipitation; the molecular sieve powder is synthesized by hydrothermal method.

[0019] This invention provides the application of the bifunctional catalyst for low-carbon olefins described in any one of the above-mentioned methods in the reaction of CO2 hydrogenation to synthesize low-carbon olefins.

[0020] This invention provides a method for synthesizing low-carbon olefins by CO2 hydrogenation, comprising:

[0021] The low-carbon olefin bifunctional catalyst described in any of the above technical solutions is obtained by reacting CO2 after pretreatment with an inert gas.

[0022] Preferred,

[0023] The pretreatment specifically involves pretreatment at 360–400°C for 1–3 hours in a pure Ar or N2 atmosphere;

[0024] The reaction pressure is 1–5 MPa, the reaction temperature is 340–400 °C, and the reaction space velocity is 1500–12000 mL gcat. -1 h -1 The volume ratio of H2 to CO2 in the feed gas is 2 to 5;

[0025] The reaction is carried out in a continuous flow high-pressure fixed-bed reactor;

[0026] The low-carbon olefins are C2 to C4 olefins.

[0027] Compared with existing technologies, this invention provides a method for synthesizing low-carbon olefins via CO2 hydrogenation, comprising the following steps: A) pressing, crushing, and sieving a composite oxide powder to obtain an oxide; the composite oxide powder is one or more of ZnO, ZrO2, In2O3, and ZrO2; pressing, crushing, and sieving a molecular sieve powder to obtain molecular sieve particles; B) physically mixing the oxide and molecular sieve particles to obtain a mixture; C) pressing, crushing, and sieving the mixture to obtain the final product. The method of this invention includes the forming, sieving, and secondary forming processes of the oxide and molecular sieve. The bifunctional catalyst obtained by the secondary forming coupling method of this invention exhibits excellent activity, high stability, and high selectivity for the target product, with a low-carbon olefin selectivity of up to 87% and a propylene selectivity of up to 49.3% among hydrocarbon products, and a catalyst deactivation rate as low as 0.5%. Detailed Implementation

[0028] This invention provides a coupling method for a bifunctional catalyst used in the hydrogenation of CO2 to synthesize low-carbon olefins and its application. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and fall within the scope of this invention. The method and application of this invention have been described through preferred embodiments. Those skilled in the art can clearly modify or appropriately change and combine the method and application described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0029] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural.

[0030] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items.

[0031] The purpose of this invention is to solve the problem that the current bifunctional catalytic system for the synthesis of low-carbon olefins by CO2 hydrogenation cannot simultaneously improve the carbon dioxide conversion rate and the low-carbon olefin selectivity. The invention provides a coupling method for a bifunctional catalytic system, which involves secondary molding of oxides and molecular sieves to construct a bifunctional catalyst and applying it to the reaction of carbon dioxide hydrogenation to synthesize low-carbon olefins.

[0032] This invention provides a method for synthesizing low-carbon olefins via CO2 hydrogenation using a bifunctional catalyst, comprising the following steps:

[0033] A) The composite oxide powder is compressed into tablets, crushed, and sieved to obtain oxides;

[0034] The composite oxide powder is one or more of ZnO, ZrO2, In2O3 and ZrO2;

[0035] Molecular sieve powder is compressed into tablets, crushed, and sieved to obtain molecular sieve particles.

[0036] B) Physically mix the oxide and molecular sieve particles to obtain a mixture;

[0037] C) Compress the mixture into tablets, crush them, and sieve them to obtain the final product.

[0038] The method for preparing a bifunctional catalyst for the synthesis of low-carbon olefins via CO2 hydrogenation provided by this invention first involves preparing composite oxide powder and molecular sieve powder, respectively.

[0039] According to the present invention, the composite oxide powder is one or more of ZnO, ZrO2, In2O3 and ZrO2; preferably, the composite oxide powder is one of ZnO-ZrO2, In2O3-ZrO2 and In2O3-ZnO-ZrO2.

[0040] The composite oxide powder described in this invention is synthesized by a co-precipitation method. This invention does not limit the specific operation of the aforementioned co-precipitation method; methods well-known to those skilled in the art are acceptable.

[0041] According to the present invention, the molecular sieve powder is one or more of SAPO-18, SAPO-20 and SAPO-34.

[0042] The molecular sieve powder described in this invention is preferably synthesized by a hydrothermal method. This invention does not limit the specific operation of the aforementioned hydrothermal method; methods well-known to those skilled in the art are acceptable.

[0043] The composite oxide powder is compressed into tablets, crushed, and sieved to obtain the oxide. The compression pressure is preferably 10–40 MPa; more preferably 12–38 MPa; and most preferably 15–35 MPa.

[0044] The present invention does not limit the specific operations of crushing and sieving, as those well known to those skilled in the art are acceptable. Preferably, the oxide powder obtained by sieving has a mesh size of 20-100 mesh; more preferably 30-90 mesh; and most preferably 40-80 mesh.

[0045] Molecular sieve powder is compressed into tablets, crushed, and sieved to obtain molecular sieve particles.

[0046] The compression pressure is preferably 10-40 MPa; more preferably 12-38 MPa; and most preferably 15-35 MPa.

[0047] The present invention does not limit the specific operations of crushing and sieving, as those well known to those skilled in the art are acceptable. Preferably, the molecular sieve particles obtained by sieving are 20-100 mesh; more preferably 30-90 mesh; and most preferably 40-80 mesh.

[0048] The oxide and molecular sieve particles are physically mixed to obtain a mixture.

[0049] In one preferred embodiment of the present invention, the mass ratio of the physical mixture of the oxide and the molecular sieve particles is 1:2 to 2:1.

[0050] In one preferred embodiment of the present invention, the mass ratio of the physical mixture of the oxide and the molecular sieve particles is 1:2 to 1:1.

[0051] In one preferred embodiment of the present invention, the mass ratio of the physical mixture of the oxide and the molecular sieve particles is 1:1 to 2:1.

[0052] In one preferred embodiment of the present invention, the mass ratio of the oxide and the molecular sieve particles physically mixed is 1:1.

[0053] The mixture is pressed into tablets, crushed, and sieved to obtain the final product.

[0054] The compression pressure is preferably 10-40 MPa; more preferably 12-38 MPa; and most preferably 15-35 MPa.

[0055] The present invention does not limit the specific operations of crushing and sieving, as those well known to those skilled in the art are acceptable. Preferably, the molecular sieve particles obtained by sieving are 20-100 mesh; more preferably 30-90 mesh; and most preferably 40-80 mesh.

[0056] The coupling method of the two-stage molding of this invention is simple to prepare, inexpensive, and can enhance the physical strength of bifunctional catalysts, making it suitable for large-scale production.

[0057] This invention provides the application of the bifunctional catalyst for low-carbon olefins described in any one of the above-mentioned methods in the reaction of CO2 hydrogenation to synthesize low-carbon olefins.

[0058] The aforementioned low-carbon olefins are C2 to C4 olefins.

[0059] This invention provides a method for synthesizing low-carbon olefins by CO2 hydrogenation, comprising:

[0060] The low-carbon olefin bifunctional catalyst described in any of the above technical solutions is obtained by reacting CO2 after pretreatment with an inert gas.

[0061] The method for synthesizing low-carbon olefins by CO2 hydrogenation provided by the present invention firstly pretreats the low-carbon olefin bifunctional catalyst described in any of the above technical solutions at 360-400°C for 1-3 hours in a pure Ar or N2 atmosphere; preferably, pretreating at 370-400°C for 1-2.5 hours in a pure Ar atmosphere; more preferably, pretreating at 380-400°C for 1-2 hours in a pure Ar atmosphere.

[0062] After pretreatment, the reaction begins. The reaction pressure is 1-5 MPa and the reaction temperature is 340-400℃; preferably, the reaction pressure is 1-4 MPa and the reaction temperature is 350-390℃; more preferably, the reaction pressure is 2-4 MPa and the reaction temperature is 360-380℃.

[0063] The reaction space velocity is 1500–12000 mL gcat. -1 h -1 Preferably, the reaction space velocity is 2000–10000 mL gcat. -1 h -1 More preferably, the reaction space velocity is 3000–9000 mL gcat. -1 h -1 .

[0064] The volume ratio of H2 to CO2 in the feed gas is 2 to 5. Specifically, it can be 2, 3, 4, or 5.

[0065] The above reaction is preferably carried out in a continuous flow high-pressure fixed-bed reactor.

[0066] This invention provides a method for a bifunctional catalyst for the direct synthesis of low-carbon olefins via CO2 hydrogenation, comprising the following steps: A) pressing, crushing, and sieving a composite oxide powder to obtain an oxide; the composite oxide powder is one or more of ZnO, ZrO2, In2O3, and ZrO2; pressing, crushing, and sieving a molecular sieve powder to obtain molecular sieve particles; B) physically mixing the oxide and molecular sieve particles to obtain a mixture; C) pressing, crushing, and sieving the mixture to obtain the final product. The bifunctional catalyst coupling method proposed in this invention involves secondary shaping of the oxide and molecular sieve components to maintain a suitable coupling distance, which is beneficial for the mass transfer of reaction intermediates and slows down the secondary hydrogenation of olefins generated by carbon-carbon coupling at oxygen vacancies and strongly acidic sites on the molecular sieve to produce alkanes. Therefore, when used in the direct synthesis of low-carbon olefins via CO2 hydrogenation, the selectivity for low-carbon olefins is significantly improved. Simultaneously, the improved coupling method also enhances the selectivity of propylene and the stability of the catalyst.

[0067] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0068] To further illustrate the present invention, the following describes in detail, with reference to embodiments, a coupling method for a bifunctional catalyst for the synthesis of low-carbon olefins using CO2 hydrogenation, and its application.

[0069] Example 1:

[0070] This embodiment provides a coupling method for a bifunctional catalyst used in the hydrogenation of CO2 to synthesize low-carbon olefins and its application, specifically including the following steps:

[0071] S1. Weigh out 5g of ZnO-ZrO2 composite oxide powder synthesized by coprecipitation method and 5g of SAPO-34 molecular sieve powder synthesized by hydrothermal method.

[0072] S2. The ZnO-ZrO2 powder and SAPO-34 powder from step S1 are respectively compressed, crushed and sieved to obtain particles with a particle size of 40-60 mesh, wherein the compression pressure is 15 MPa.

[0073] S3. Thoroughly mechanically mix the ZnO-ZrO2 and SAPO-34 particles obtained in step S2, with the mass ratio of oxide to molecular sieve being 1:1.

[0074] S4. The mixed particles obtained in step S3 are compressed, crushed and sieved to obtain bifunctional catalyst particles with a particle size of 40-60 mesh, wherein the pressure for tableting is 15 MPa.

[0075] Activity evaluation:

[0076] The bifunctional catalyst obtained by secondary molding in this embodiment was evaluated for its catalytic activity in the synthesis of low-carbon olefins via carbon dioxide hydrogenation. The activity evaluation process is as follows:

[0077] 1.0 g of the bifunctional catalyst synthesized in Example 1 was weighed and placed in a continuous flow high-pressure fixed-bed reactor. Pretreatment was performed at 400 °C for 1 h in a pure Ar atmosphere. After pretreatment, the reaction was initiated at a pressure of 3.0 MPa, a temperature of 380 °C, and a space velocity of 9000 mLg. cat -1 h -1 The volume ratio of H2 to CO2 in the feed gas was 3.0. The reaction products were detected online by gas chromatography, and the results are shown in Table 1.

[0078] Example 2:

[0079] This embodiment provides a coupling method for a bifunctional catalyst used in the hydrogenation of CO2 to synthesize low-carbon olefins and its application, specifically including the following steps:

[0080] S1. Weigh out 5g of ZnO-ZrO2 composite oxide powder synthesized by coprecipitation method and 5g of SAPO-34 molecular sieve powder synthesized by hydrothermal method.

[0081] S2. The ZnO-ZrO2 powder and SAPO-34 powder from step S1 are respectively compressed, crushed and sieved to obtain particles with a particle size of 60-80 mesh, wherein the pressure for tableting is 15 MPa.

[0082] S3. Thoroughly mechanically mix the ZnO-ZrO2 and SAPO-34 particles obtained in step S2, with the mass ratio of oxide to molecular sieve being 1:1.

[0083] S4. The mixed particles obtained in step S3 are compressed, crushed and sieved to obtain bifunctional catalyst particles with a particle size of 40-60 mesh, wherein the pressure for tableting is 15 MPa.

[0084] Activity evaluation:

[0085] The bifunctional catalyst obtained by secondary molding in this embodiment was used to evaluate the catalytic activity of carbon dioxide hydrogenation to synthesize low-carbon olefins. The activity evaluation process is as follows:

[0086] 1.0 g of the bifunctional catalyst synthesized in Example 2 was weighed and placed in a continuous flow high-pressure fixed-bed reactor. Pretreatment was performed at 400 °C for 1 h in a pure Ar atmosphere. After pretreatment, the reaction was initiated at a pressure of 3.0 MPa, a temperature of 380 °C, and a space velocity of 9000 mLg. cat -1 h -1 The volume ratio of H2 to CO2 in the feed gas was 3.0. The reaction products were detected online by gas chromatography, and the results are shown in Table 1.

[0087] Example 3:

[0088] This embodiment provides a coupling method for a bifunctional catalyst used in the hydrogenation of CO2 to synthesize low-carbon olefins and its application, specifically including the following steps:

[0089] S1. Weigh out 5g of ZnO-ZrO2 composite oxide powder synthesized by coprecipitation method and 5g of SAPO-34 molecular sieve powder synthesized by hydrothermal method.

[0090] S2. The ZnO-ZrO2 powder and SAPO-34 powder from step S1 are respectively compressed, crushed and sieved to obtain particles with a particle size of 80-100 mesh, wherein the pressure for tableting is 15 MPa.

[0091] S3. Thoroughly mechanically mix the ZnO-ZrO2 and SAPO-34 particles obtained in step S2, with the mass ratio of oxide to molecular sieve being 1:1.

[0092] S4. The mixed particles obtained in step S3 are compressed, crushed and sieved to obtain bifunctional catalyst particles with a particle size of 40-60 mesh, wherein the pressure for tableting is 15 MPa.

[0093] Activity evaluation:

[0094] The bifunctional catalyst obtained by secondary molding in this embodiment was used to evaluate the catalytic activity of carbon dioxide hydrogenation to synthesize low-carbon olefins. The activity evaluation process is as follows:

[0095] 1.0 g of the bifunctional catalyst synthesized in Example 3 was weighed and placed in a continuous flow high-pressure fixed-bed reactor. Pretreatment was performed at 400 °C for 1 h in a pure Ar atmosphere. After pretreatment, the reaction was initiated at a pressure of 3.0 MPa, a temperature of 380 °C, and a space velocity of 9000 mLg. cat -1 h -1 The volume ratio of H2 to CO2 in the feed gas was 3.0. The reaction products were detected online by gas chromatography, and the results are shown in Table 1.

[0096] Example 4:

[0097] This embodiment provides a coupling method for a bifunctional catalyst used in the hydrogenation of CO2 to synthesize low-carbon olefins and its application, specifically including the following steps:

[0098] S1. Weigh out 5g of ZnO-ZrO2 composite oxide powder synthesized by coprecipitation method and 5g of SAPO-34 molecular sieve powder synthesized by hydrothermal method.

[0099] S2. The ZnO-ZrO2 powder and SAPO-34 powder from step S1 are respectively compressed, crushed and sieved to obtain particles with a particle size of 20-40 mesh, wherein the pressure for tableting is 15 MPa.

[0100] S3. Thoroughly mechanically mix the ZnO-ZrO2 and SAPO-34 particles obtained in step S2, with the mass ratio of oxide to molecular sieve being 1:1.

[0101] S4. The mixed particles obtained in step S3 are compressed, crushed and sieved to obtain bifunctional catalyst particles with a particle size of 40-60 mesh, wherein the pressure for tableting is 15 MPa.

[0102] Activity evaluation:

[0103] The bifunctional catalyst obtained by secondary molding in this embodiment was used to evaluate the catalytic activity of carbon dioxide hydrogenation to synthesize low-carbon olefins. The activity evaluation process is as follows:

[0104] 1.0 g of the bifunctional catalyst synthesized in Example 4 was weighed and placed in a continuous flow high-pressure fixed-bed reactor. Pretreatment was performed at 400 °C for 1 h in a pure Ar atmosphere. After pretreatment, the reaction was initiated at a pressure of 3.0 MPa, a temperature of 380 °C, and a space velocity of 9000 mLg. cat -1 h -1 The volume ratio of H2 to CO2 in the feed gas was 3.0. The reaction products were detected online by gas chromatography, and the results are shown in Table 1.

[0105] Comparative Example 1:

[0106] To verify the promoting effect of the secondary molding coupling method on the activity of bifunctional catalysts in the synthesis of low-carbon olefins from CO2 hydrogenation, Comparative Example 1 uses a conventional coupling method of particle packing to compose a bifunctional catalyst, specifically including the following steps:

[0107] S1. Weigh out 5g of ZnO-ZrO2 composite oxide powder synthesized by coprecipitation method and 5g of SAPO-34 molecular sieve powder synthesized by hydrothermal method.

[0108] S2. The ZnO-ZrO2 powder and SAPO-34 powder from step S1 are respectively compressed, crushed and sieved to obtain particles with a particle size of 40-60 mesh, wherein the compression pressure is 15 MPa.

[0109] S3. Thoroughly mechanically mix the ZnO-ZrO2 and SAPO-34 particles obtained in step S2, with the mass ratio of oxide to molecular sieve being 1:1.

[0110] Activity evaluation:

[0111] The bifunctional catalyst obtained from particle packing in this comparative example was evaluated for its catalytic activity in the synthesis of low-carbon olefins via carbon dioxide hydrogenation. The activity evaluation procedure is as follows:

[0112] 1.0 g of the bifunctional catalyst synthesized in Comparative Example 1 was weighed and placed in a continuous flow high-pressure fixed-bed reactor. Pretreatment was performed at 400 °C for 1 h under a pure Ar atmosphere. After pretreatment, the reaction was initiated at a pressure of 3.0 MPa, a temperature of 380 °C, and a space velocity of 9000 mLg / g. cat -1 h -1 The volume ratio of H2 to CO2 in the feed gas was 3.0. The reaction products were detected online by gas chromatography, and the results are shown in Table 1.

[0113] Comparative Example 2:

[0114] To verify the promoting effect of the secondary molding coupling method on the activity of bifunctional catalysts in the CO2 hydrogenation synthesis of low-carbon olefins, in Comparative Example 2, oxides and molecular sieves were coupled in a dual-bed packing manner to form a bifunctional catalyst, specifically including the following steps:

[0115] S1. Weigh out 5g of ZnO-ZrO2 composite oxide powder synthesized by coprecipitation method and 5g of SAPO-34 molecular sieve powder synthesized by hydrothermal method.

[0116] S2. The ZnO-ZrO2 powder and SAPO-34 powder from step S1 are respectively compressed, crushed and sieved to obtain particles with a particle size of 40-60 mesh, wherein the compression pressure is 15 MPa.

[0117] S3. The ZnO-ZrO2 and SAPO-34 particles obtained in step S2 are sequentially packed into the reaction tube, with ZnO-ZrO2 in the upper layer and SAPO-34 in the lower layer, separated by quartz sand. The mass ratio of oxide to molecular sieve is 1:1.

[0118] Activity evaluation:

[0119] The bifunctional catalyst obtained from the dual-bed loading in this comparative example was evaluated for its catalytic activity in the synthesis of low-carbon olefins via carbon dioxide hydrogenation. The activity evaluation procedure is as follows:

[0120] 0.5 g each of ZnO-ZrO2 and SAPO-34 particles from step S2 were weighed and loaded into a continuous flow high-pressure fixed-bed reactor using a dual-bed coupling method. The reactor was pretreated at 400 °C for 1 h in a pure Ar atmosphere. After pretreatment, the reaction was initiated at a pressure of 3.0 MPa, a temperature of 380 °C, and a space velocity of 9000 mLg / g. cat -1 h -1 The volume ratio of H2 to CO2 in the feed gas was 3.0. The reaction products were detected online by gas chromatography, and the results are shown in Table 1.

[0121] Analysis of the activity data in Table 1 shows that in Example 2, the carbon dioxide conversion rate reached as high as 30.9%, and the selectivity for low-carbon olefins reached as high as 86.5%, with propylene selectivity reaching as high as 49.29%. In contrast, the selectivity for low-carbon olefins using conventional particle packing and dual-bed loading coupling methods is far lower than that of secondary molding. The catalyst reactivity obtained from Examples 1-4 and Comparative Examples 1-2 indicates that, using the secondary molding coupling method and matching conditions proposed in this invention, the bifunctional catalyst exhibits optimal activity for carbon dioxide hydrogenation to low-carbon olefins, and also demonstrates high catalyst stability and a low deactivation rate.

[0122] Table 1

[0123]

[0124] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a bifunctional catalyst for the hydrogenation of CO2 to synthesize low-carbon olefins, characterized in that, Includes the following steps: A) The composite oxide powder is compressed into tablets, crushed, and sieved to obtain oxides; The composite oxide powder is one of ZnO-ZrO2, In2O3-ZrO2, and In2O3-ZnO-ZrO2; the molecular sieve powder is compressed into tablets, crushed, and sieved to obtain molecular sieve particles; the molecular sieve powder is one or more of SAPO-18, SAPO-20, and SAPO-34; the compression pressure is 10~40MPa. B) Physically mix the oxide and molecular sieve particles to obtain a mixture; the mass ratio of the physically mixed oxide and molecular sieve particles is 1:2 to 2:

1. C) The mixture is compressed into tablets, crushed, and sieved to obtain the tablets; the compression pressure is 10~40MPa.

2. The method according to claim 1, characterized in that, The oxide has a mesh size of 20-100 mesh; the molecular sieve particles have a mesh size of 20-100 mesh.

3. The method according to claim 1, characterized in that, The low-carbon olefin bifunctional catalyst has a mesh size of 40-80 mesh.

4. The method according to claim 1, characterized in that, Step A) The composite oxide powder is synthesized by co-precipitation method; the molecular sieve powder is synthesized by hydrothermal method.

5. The application of the low-carbon olefin bifunctional catalyst prepared by the method according to any one of claims 1 to 4 in the reaction of CO2 hydrogenation to synthesize low-carbon olefins.

6. A method for synthesizing low-carbon olefins by CO2 hydrogenation, characterized in that, include: The low-carbon olefin bifunctional catalyst prepared by the method according to any one of claims 1 to 4 is pretreated with an inert gas and then mixed with the feed gas to react, thereby obtaining low-carbon olefins.

7. The method according to claim 6, characterized in that, The pretreatment specifically involves pretreatment at 360–400°C for 1–3 hours in a pure Ar or N2 atmosphere; The reaction pressure is 1–5 MPa, the reaction temperature is 340–400 °C, and the reaction space velocity is 1500–12000 mLg. cat -1 h -1 The volume ratio of H2 to CO2 in the feed gas is 2 to 5; The reaction is carried out in a continuous flow high-pressure fixed-bed reactor; The low-carbon olefins are C2 to C4 olefins.

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