A catalyst for promoting carbon dioxide to olefin reaction by improving physical adsorption capacity

Abstract

The present application belongs to the field of CO2 chemical utilization and catalyst technology, and discloses a catalyst for promoting the CO2 to olefin reaction by improving the physical adsorption capacity, which comprises a CO2 hydrogenation catalyst and a CO2 physical adsorption catalyst, and the mass ratio of the CO2 hydrogenation catalyst to the CO2 adsorption catalyst is 1:1-5. The adsorption catalyst has the effect of significantly improving the CO2 physical adsorption capacity. In the present application, NaFe catalyst and mixed adsorption molecular sieve catalyst are used to carry out the CO2 hydrogenation to obtain olefin, the CO2 concentration on the surface of the catalyst is improved by the physical adsorption capacity of the adsorption molecular sieve, the CO2 adsorption amount is increased, the carbon-hydrogen ratio is further improved, the chemical reaction equilibrium is changed, the product selectivity is changed, and the product is mainly olefin. The method is different from the conventional chemical adsorption strategy, and is a new method for improving the conversion rate and target selectivity by physical adsorption, and the catalyst is simple to prepare and low in cost.

Description

Technical Field

[0001] This invention belongs to the field of CO2 chemical utilization and catalytic conversion technology, and in particular, it relates to the design and application of a catalyst that enhances the physical adsorption capacity of CO2 and promotes its hydrogenation to olefins reaction. Background Technology

[0002] Olefins are important basic chemicals and organic chemical raw materials, widely used in the synthesis of liquid fuels, plastics, and other fields. The direct production of olefins via CO2 catalytic hydrogenation is an effective means of reducing greenhouse gas emissions and alleviating oil resource shortages. Chemisorption is a prerequisite for catalytic reactions, and researchers typically improve the selectivity of target products by enhancing the chemisorption capacity and type of CO2, thereby altering the reaction pathway. Methods include modifying carbon-based metal catalysts, adding promoters, heteroatom hybridization, shape-selective catalysis, solid acid catalysis, surface functional groups, hydrophilic / hydrophobic modification, and adjusting the spatial distribution of active components. However, the influence of the catalyst's (or support's) physical adsorption capacity for CO2 on catalytic activity and reaction direction is often overlooked. For example, patent publication CN104437504A reports an iron-based catalyst modified with alkali metals or alkaline earth elements, achieving a low-carbon olefin selectivity of 60%. Patent publication CN114988977A describes the synthesis of olefins via CO / CO2 hydrogenation through a mixture of metal carbides and hydrophobic materials (such as activated carbon, graphite, or organic polymers as hydrophobic promoters). Zhang Long et al. (CN110327969A) developed a composite catalyst of nitrogen-doped metal oxides and molecular sieves, in which the molecular sieves were acidic catalysts such as SAPO-34, HZSM-5 and HY. The CO2 conversion rate was over 10% and the selectivity for low-carbon olefins reached 80%.

[0003] Type A and Type X molecular sieves are physisorbents of CO2, widely used in adsorption separation, but research on their catalytic applications is limited. For example, the catalytic pyrolysis of trioctylamine hydrochloride using 5A molecular sieves (Journal of East China University of Science and Technology, 2022, 48, 585-590) achieved a feed conversion rate of 99%. Hydrogen-exchanged 5A molecular sieves exhibit surface acidity, significantly reducing methane selectivity to as low as 0.2% in Fischer-Tropsch synthesis (Journal of Natural Gas Chemistry, 2009, 18, 187-190). Research on the catalytic performance of physisorbents in the hydrogenation of CO2 to olefins, especially in the synthesis of long-chain olefins, is extremely rare. CO2 is a typical acidic gas, and molecular sieves are commonly used industrially for its separation and purification. Literature reports that 5A molecular sieves can adsorb up to 94.38 cm⁻¹ of CO2 at 50℃. 3 / g, while the CO adsorption capacity is only 17.68cm³. 3 / g (Industrial Catalysis, 2019, 27, 82-84). Therefore, by using molecular sieves with adsorption capacity such as 5A, the CO2 concentration on the catalyst surface can be increased, thereby increasing the CO2 adsorption capacity, increasing the carbon-hydrogen ratio, and thus changing the chemical reaction equilibrium, and consequently altering the product selectivity. Looking at the current research status of CO2 hydrogenation to olefins both domestically and internationally, the following problems exist:

[0004] (1) CO2 hydrogenation products are wide-ranging. How to control and increase the concentration of CO2 on the catalyst surface plays a key role in the highly selective synthesis of olefins.

[0005] (2) Olefins will undergo secondary adsorption on the surface of molecular sieves, resulting in a large number of low-value-added products such as alkane products.

[0006] (3) Shape-selective catalysis effect of molecular sieves: control the pore structure of molecular sieves to maximize olefin selectivity. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a catalyst, method and application for promoting the carbon dioxide to olefins reaction by improving physical adsorption capacity.

[0008] The technical solution adopted by this invention to solve its technical problem is:

[0009] A catalyst that promotes the carbon dioxide-to-olefins reaction by enhancing physical adsorption capacity is disclosed. The catalyst comprises a CO2 hydrogenation catalyst and a CO2 physical adsorption catalyst, wherein the mass ratio of the CO2 hydrogenation catalyst to the CO2 adsorption catalyst is 1:1-5. The adsorption catalyst significantly enhances the physical adsorption capacity of CO2.

[0010] Furthermore, the CO2 hydrogenation catalyst is an iron-based catalyst FeNa, with a Na mass content of 1-10%, and is prepared by one or more of the following methods: co-precipitation, impregnation, and hydrothermal method.

[0011] Furthermore, the iron-based catalyst is prepared by an impregnation method, specifically including the following steps: iron salt and sodium salt are mixed in different proportions to form a mixed solution, and the mixed salt solution is impregnated on a support, wherein the support is one or more of Al2O3, SiO2, and TiO2; then it is dried and calcined in air, dried at 120°C for 12-24 hours, and calcined at 300-500°C for 6 hours.

[0012] Alternatively, the iron-based catalyst can also be prepared by precipitation method, specifically including the following steps: catalyst forming, flake forming, and sieving to a particle size of 20-40 mesh.

[0013] Furthermore, the CO2 physical adsorption catalyst is a microporous material with adsorption properties.

[0014] Furthermore, the adsorption-resistant microporous material is one or two of 3A, 4A, 5A, 10X, and 13X molecular sieves. The CO2 physical adsorption catalyst can be a commercial type A molecular sieve (including 3A, 4A, and 5A) or type X molecular sieve (10X, 13X).

[0015] Furthermore, the CO2 adsorption catalyst is prepared by reflux method, the specific steps of which include: mixing silicon source, aluminum source and strong base evenly at room temperature, loading into a three-necked flask, and then refluxing at 60-120℃ for 4-48h. The product is washed, dried and calcined at 500℃ for 5-10h to obtain CO2 adsorption catalyst.

[0016] Further, the silicon source is one or more of fumed SiO2, silicic acid, or sodium silicate; the aluminum source is one or more of sodium aluminate, aluminum sulfate, boehmite, aluminum nitrate, or kaolin; the strong base is one or two of NaOH and KOH; and the molar ratio of the silicon source, aluminum source, and strong base is 1-15:1:1-5.

[0017] The catalyst preparation method described above includes the following steps:

[0018] The reaction system is a high-pressure fixed bed, and the CO2 hydrogenation catalyst and CO2 adsorption catalyst are assembled in at least one of the following ways: physical mixing, two-stage mixing, and particle mixing.

[0019] The method of using the catalyst as described above includes the following steps:

[0020] The catalyst is reacted in a continuous fixed-bed reactor at a temperature of 200-350℃ and a pressure of 0.1-5MPa. The volume ratio of the feed gas H2 to CO2 is 1-3:1.

[0021] The application of catalysts as described above in promoting the carbon dioxide-to-olefins reaction.

[0022] The advantages and positive effects of this invention are as follows:

[0023] 1. This invention is carried out in a continuous fixed-bed reactor, which has the advantages of simple synthesis, low cost and high olefin selectivity. It achieves the matching of two process conditions, CO2 hydrogenation and CO2 physical adsorption, which is more conducive to the generation of higher value olefin products.

[0024] 2. The catalyst of this invention is a combination of a CO2 hydrogenation catalyst and a CO2 physical adsorption catalyst. By adding adsorption-type molecular sieve catalysts (A-type, X-type molecular sieves, etc.), this catalyst exhibits a strong physical adsorption capacity for the raw material CO2, increasing the CO2 concentration on the catalyst surface and thus increasing the C / H ratio. This results in the product being predominantly unsaturated hydrocarbons (olefins), significantly improving the selectivity of the target product olefins. Simultaneously, this catalyst is simple and easy to prepare, further reducing catalyst costs.

[0025] 3. The essence of this invention is to alter the chemical equilibrium and product selectivity by increasing the concentration of reactants on the catalyst surface. A NaFe catalyst is used in combination with an adsorption-type molecular sieve catalyst for the hydrogenation of CO2 to olefins. The physical adsorption capacity of the molecular sieve increases the CO2 concentration on the catalyst surface, leading to increased CO2 adsorption and thus a higher C-H ratio, thereby shifting the chemical equilibrium to the right and altering the product selectivity. This method differs from conventional chemisorption strategies; it is a novel approach that improves conversion rate and target selectivity through physical adsorption, and the catalyst preparation is simple and inexpensive. Attached Figure Description

[0026] Figure 1 The image shows the CO2 physical adsorption isotherm spectrum at 25°C for the 4A molecular sieve sample obtained in Example 3 of this invention (the CO2 adsorption capacity of this 4A molecular sieve sample is 2.8 × 10⁻⁶). -3 mol / g);

[0027] Figure 2 The image shows the CO2 physical adsorption isotherm spectrum at 25°C for the 5A molecular sieve sample obtained in Example 4 of this invention (the CO2 adsorption capacity of this 5A molecular sieve sample is 3.0 × 10⁻⁶). -3 mol / g);

[0028] Figure 3 The image shows the CO2 physical adsorption isotherm spectrum at 25°C for the 13X molecular sieve sample obtained in Example 5 of this invention (the CO2 adsorption capacity of this 13X molecular sieve sample is 4.2 × 10⁻⁶). -3 mol / g);

[0029] Figure 4 This is the CO2 physical adsorption isotherm spectrum of the Al2O3 sample at 25℃ in this invention (the CO2 adsorption capacity of this Al2O3 sample is 3.1 × 10⁻⁶). -4 mol / g);

[0030] Figure 5 The image shows the CO2 physical adsorption isotherm spectrum of the Fe / Al2O3 sample at 25℃ in this invention (the CO2 adsorption capacity of this Fe / Al2O3 sample is 2.3 × 10⁻⁶). -4 mol / g);

[0031] Figure 6 The image shows the CO2 physical adsorption isotherm spectrum of the NaFe / Al2O3 sample at 25℃ in this invention (the CO2 adsorption capacity of this NaFe / Al2O3 sample is 3.2 × 10⁻⁶). -4 mol / g);

[0032] Figure 7 This is a schematic diagram of the catalytic reaction pathway of the catalyst of the present invention. Detailed Implementation

[0033] The present invention will be further described below with reference to the embodiments. The following embodiments are descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0034] The various experimental operations involved in the specific embodiments are all conventional techniques in the field. For parts not specifically annotated in this document, those skilled in the art can refer to various commonly used reference books, scientific and technological documents or related instructions and manuals prior to the filing date of this invention to carry out the operations.

[0035] A catalyst that promotes the carbon dioxide-to-olefins reaction by enhancing physical adsorption capacity is disclosed. The catalyst comprises a CO2 hydrogenation catalyst and a CO2 physical adsorption catalyst, wherein the mass ratio of the CO2 hydrogenation catalyst to the CO2 adsorption catalyst is 1:1-5. The adsorption catalyst significantly enhances the physical adsorption capacity of CO2.

[0036] Preferably, the CO2 hydrogenation catalyst is an iron-based catalyst FeNa, with a Na mass content of 1-10%, and the catalyst is prepared by one or more of the following methods: co-precipitation, impregnation, and hydrothermal method.

[0037] Preferably, the preparation method of the iron-based catalyst FeNa adopts an impregnation method, specifically including the following steps: iron salt and sodium salt are mixed in different proportions to form a mixed solution, and the mixed salt solution is impregnated on a support, wherein the support is one or more of Al2O3, SiO2, and TiO2; then it is dried and calcined in air, dried at 120°C for 12-24 h, and calcined at 300-500°C for 6 h to obtain the FeNa catalyst;

[0038] Alternatively, the iron-based catalyst FeNa can be prepared by precipitation, specifically including the following steps: catalyst forming, flake forming, and sieving to a particle size of 20-40 mesh.

[0039] Preferably, the CO2 physical adsorption catalyst is a microporous material with adsorption properties.

[0040] Preferably, the adsorption-resistant microporous material is one or two of 3A, 4A, 5A, 10X, and 13X molecular sieves. The CO2 adsorption catalyst may be a commercial type A molecular sieve (including 3A, 4A, and 5A) or type X molecular sieve (10X, 13X).

[0041] Preferably, the CO2 adsorption catalyst is prepared by reflux method, the specific steps of which include: mixing silicon source, aluminum source and strong base evenly at room temperature, loading into a three-necked flask, and then refluxing at 60-120℃ for 4-48h. The product is washed, dried and calcined at 500℃ for 5-10h to obtain CO2 adsorption catalyst.

[0042] Preferably, the silicon source is one or more of fumed SiO2, silicic acid, or sodium silicate; the aluminum source is one or more of sodium aluminate, aluminum sulfate, boehmite, aluminum nitrate, or kaolin; the strong base is one or two of NaOH and KOH; and the molar ratio of the silicon source, aluminum source, and strong base is 1-15:1:1-5.

[0043] The catalyst preparation method described above includes the following steps:

[0044] The reaction system is a high-pressure fixed bed, and the CO2 hydrogenation catalyst and CO2 adsorption catalyst are assembled in at least one of the following ways: physical mixing, two-stage mixing, and particle mixing.

[0045] The method of using the catalyst as described above includes the following steps:

[0046] The catalyst is reacted in a continuous fixed-bed reactor at a temperature of 200-350℃ and a pressure of 0.1-5MPa. The volume ratio of the feed gas H2 to CO2 is 1-3:1.

[0047] The application of catalysts as described above in promoting the carbon dioxide-to-olefins reaction.

[0048] Specifically, the relevant preparation and testing methods are as follows:

[0049] like Figure 4 , Figure 6 As shown, the CO2 adsorption capacities of Fe / Al2O3 and NaFe / Al2O3 catalysts are 2.3*10⁻⁶. -4 and 3.2*10 -4 The CO2 concentration was significantly lower than that of adsorption-type molecular sieves (4A, 5A, and 13X) by mol / g. This demonstrates that adsorption-type molecular sieves significantly enhance CO2 adsorption capacity, thereby increasing the CO2 concentration on the catalyst surface, which plays a crucial role in improving CO2 conversion and olefin selectivity.

[0050] A catalyst that promotes the carbon dioxide-to-olefins reaction by enhancing physical adsorption capacity, such as Figure 7 As shown, the catalyst comprises a CO2 hydrogenation catalyst (FeNa) and a CO2 physical adsorption catalyst (type A or X molecular sieve). In the following examples, the reaction temperature is 300°C, the pressure is 3.0 MPa, the feed gas volume ratio is H2 / CO2 = 3:1, the mass ratio of the CO2 hydrogenation catalyst to the CO2 adsorption catalyst is 1:1-3, and the catalyst loading method is a physical mixture of FeNa catalyst and adsorption molecular sieve.

[0051] Example 1

[0052] 18.1 g of Fe(NO3)3·9H2O, 100 mL of deionized water, and 10 g of Al2O3 support were placed in a flask and rotary evaporated at 80 °C. The mixture was then calcined in air at 350 °C for 6 h to obtain a Fe / Al2O3 catalyst with a 20% Fe loading. The results are as follows: Figure 4 , Figure 5 As shown in Table 1.

[0053] Example 2

[0054] 18.1 g Fe(NO3)3·9H2O, 0.754 g NaNO3, 100 mL deionized water, and 10 g Al2O3 support were placed in a flask and subjected to rotary evaporation at 80 °C. The mixture was then calcined in air at 350 °C for 6 h to obtain a FeNa / Al2O3 catalyst with a Fe content of 20% and a Na content of 2%. After adding Na as a promoter to the Fe / Al2O3 catalyst, the olefin selectivity increased from 25.1% to 46.5%, with low-carbon olefins (ethylene, propylene, and butene, denoted as O2-4) predominating. The results are as follows... Figure 6 As shown in Table 1.

[0055] Example 3

[0056] FeNa / Al2O3 particles and 4A molecular sieve particles prepared by reflux method were mixed at a mass ratio of 1:2, wherein the particle size of both FeNa / Al2O3 and 4A catalyst was 20-40 mesh.

[0057] Preparation of 4A molecular sieve: 33.3g of NaAlO2, 11.1g of silica, 16.6g of NaOH and 20g of deionized water were placed in a three-necked flask, and stirring and reflux were started. The stirring speed was 600rpm, the temperature was set at 80℃, and crystallization was carried out for 6h. The reactants were filtered to separate solid and liquid. The filter cake was washed with water until neutral. The filter cake was placed in a 120℃ oven to dry the moisture and then passed through a 20-40 mesh sieve to obtain the 4A molecular sieve catalyst.

[0058] The adsorption curve of CO2 physical adsorption isotherm at 25℃ for the 4A molecular sieve sample is shown below. Figure 1 As shown in Table 1, from Figure 1 As can be seen, compared with Fe / Al2O3 and NaFe / Al2O3 catalysts, the CO2 adsorption capacity of 4A molecular sieve increased by an order of magnitude, the CO2 conversion rate was slightly improved, and the olefin selectivity was further increased to 52.6% (compared with catalyst in Example 2), which proves the important role of adsorption molecular sieves in improving olefin selectivity.

[0059] Meanwhile, by comparing Examples 1, 2 and 3, it can be seen that the synergistic use of the CO2 hydrogenation catalyst and the CO2 physical adsorption catalyst in this invention can greatly improve the physical adsorption capacity of the prepared catalyst. The CO2 hydrogenation catalyst and the CO2 physical adsorption catalyst in the catalyst of this invention have a synergistic effect.

[0060] Example 4

[0061] FeNa / Al2O3 particles were mixed with 5A molecular sieve particles prepared by reflux method (the same method as the preparation of 4A molecular sieve in Example 3) at a mass ratio of 1:2, wherein both FeNa / Al2O3 and 5A catalyst particles were 20-40 mesh. Compared to 4A molecular sieve, 5A molecular sieve has slightly larger pores, resulting in a higher H2 concentration within the 4A molecular sieve. This also facilitates the desorption of olefins from the catalyst, further improving the olefin selectivity to 55.9%. The results are as follows... Figure 2 As shown in Table 1.

[0062] Meanwhile, by comparing Examples 1, 2 and 4, it can be seen that the synergistic use of the CO2 hydrogenation catalyst and the CO2 physical adsorption catalyst in this invention can greatly improve the physical adsorption capacity of the prepared catalyst. The CO2 hydrogenation catalyst and the CO2 physical adsorption catalyst in the catalyst of this invention have a synergistic effect.

[0063] Example 5

[0064] FeNa / Al2O3 particles were mixed with 13X molecular sieve particles prepared by reflux method (the same method as the preparation of 4A molecular sieve in Example 3) at a mass ratio of 1:2, wherein both FeNa / Al2O3 and 13X catalyst particles had a particle size of 20-40 mesh. The 13X molecular sieve exhibited a larger pore size and higher physical adsorption capacity for CO2, achieving an olefin selectivity of 56.4%. The results are as follows... Figure 3 As shown in Table 1.

[0065] Meanwhile, by comparing Examples 1, 2 and 3, it can be seen that the synergistic use of the CO2 hydrogenation catalyst and the CO2 physical adsorption catalyst in this invention can greatly improve the physical adsorption capacity of the prepared catalyst. The CO2 hydrogenation catalyst and the CO2 physical adsorption catalyst in the catalyst of this invention have a synergistic effect.

[0066] Example 6

[0067] FeNa / Al2O3 particles were mixed with 13X molecular sieve particles prepared by reflux method (the same method as the preparation of 4A molecular sieve in Example 3) at a mass ratio of 1:1, wherein the particle size of both FeNa / Al2O3 and 13X catalyst was 20-40 mesh. The increase in olefin selectivity was not significant with increasing molecular sieve content. The results are shown in Table 1.

[0068] Example 7

[0069] FeNa / Al2O3 particles were mixed with commercial 13X molecular sieve particles at a mass ratio of 1:3, with both FeNa / Al2O3 and 13X catalyst having a particle size of 20-40 mesh. The increase in olefin selectivity was not significant with increasing molecular sieve content. The results are shown in Table 1.

[0070] Comparative Example 1

[0071] FeNa / Al2O3 particles were mixed with commercial Silicalite-1 molecular sieve particles at a mass ratio of 1:2, with both FeNa / Al2O3 and Silicalite-1 catalysts having a particle size of 20-40 mesh. Compared to the acid-free all-silica molecular sieve (S1) catalyst, which is a non-adsorption molecular sieve catalyst, its olefin selectivity was significantly lower, at only 43.7%. This comparison demonstrates that adsorption molecular sieves play a crucial role in olefin selectivity. The results are shown in Table 1.

[0072] Comparative Example 2

[0073] FeNa / Al2O3 particles were mixed with commercial ZSM-5 molecular sieve particles at a mass ratio of 1:2, with both FeNa / Al2O3 and ZSM-5 catalysts having a particle size of 20-40 mesh. Compared with the significantly acidic ZSM-5 molecular sieve, the conversion rate was comparable to catalysts such as 4A, but the olefin selectivity was only 35.3%, because olefins were converted to isoalkanes and cracking products under the acidic catalysis of the molecular sieve. The results are shown in Table 1.

[0074] Table 1. Catalytic activity and product selectivity of each catalytic reaction

[0075]

[0076] Meanwhile, by comparing Examples 1-7 and Comparative Examples 1-2, it can be seen that the synergistic use of CO2 hydrogenation catalyst and CO2 physical adsorption catalyst in this invention can greatly improve the physical adsorption capacity of the prepared catalyst. The CO2 hydrogenation catalyst and CO2 physical adsorption catalyst in the catalyst of this invention have a synergistic effect.

[0077] Although embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the scope of the invention is not limited to the contents disclosed in the embodiments.

Claims

1. A catalyst that promotes the carbon dioxide-to-olefins reaction by enhancing physical adsorption capacity, characterized in that: The catalyst includes a CO2 hydrogenation catalyst and a CO2 physical adsorption catalyst, with a mass ratio of 1:1-5. The CO2 hydrogenation catalyst is an iron-based catalyst FeNa, with a Na mass content of 1-10%. The preparation method of the iron-based catalyst FeNa adopts an impregnation method, specifically including the following steps: iron salt and sodium salt are mixed in different proportions to form a mixed solution, and the mixed salt solution is impregnated on a support, wherein the support is one or more of Al2O3, SiO2, and TiO2; then it is dried and calcined in air, dried at 120℃ for 12-24h, and calcined at 300-500℃ for 6h to obtain the FeNa catalyst; The CO2 physical adsorption catalyst is a microporous material with adsorption properties; The adsorption-resistant microporous material is one or two of the molecular sieves 3A, 4A, 5A, 10X, and 13X; The CO2 adsorption catalyst was prepared by reflux method. The specific steps included: mixing silicon source, aluminum source and strong base evenly at room temperature, loading into a three-necked flask, and then refluxing at 60-120℃ for 4-48h. The product was washed, dried and calcined at 500℃ for 5-10h to obtain the CO2 adsorption catalyst. The silicon source is one or more of fumed SiO2, silicic acid, or sodium silicate; the aluminum source is one or more of sodium aluminate, aluminum sulfate, boehmite, aluminum nitrate, or kaolin; the strong base is one or two of NaOH and KOH; the molar ratio of the silicon source, aluminum source, and strong base is 1-15:1:1-5. The CO2 hydrogenation catalyst and CO2 adsorption catalyst are assembled by particle mixing.

2. The method of using the catalyst as described in claim 1, characterized in that: The method includes the following steps: The catalyst is reacted in a continuous fixed-bed reactor at a temperature of 200-350℃ and a pressure of 0.1-5MPa. The volume ratio of the feed gas H2 to CO2 is 1-3:

1.

3. The application of the catalyst as described in claim 1 in promoting the carbon dioxide to olefins reaction.

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