A bifunctional catalyst for one-step production of p-xylene from carbon dioxide hydrogenation, a preparation method and application thereof

Abstract

The application discloses a bifunctional catalyst for preparing p-xylene from carbon dioxide and hydrogen in one step, a preparation method and application, relates to the technical field of catalysts for preparing p-xylene from carbon dioxide and hydrogen, and opens up a new way for selectively hydrogenating carbon dioxide into high-value p-xylene; the application comprises alkali metal modified FeMn oxides and ZSM-5 capsule zeolites, and is used for converting CO2 into p-xylene through one-step hydrogenation; in the alkali metal modified FeMn oxides, Mn is dispersed on the oxide phase of Fe; the ZSM-5 capsule zeolites are subjected to hydrothermal treatment with a TPAOH solution, and the external passivated Bronsted acid sites of the ZSM-5 capsule zeolites can inhibit the structuralization reaction of dimethylbenzene; the bifunctional catalyst can realize the conversion of carbon dioxide into p-xylene in one step, has high carbon dioxide conversion rate, high space-time yield of p-xylene, and long catalyst service life.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of carbon dioxide hydrogenation to produce p-xylene catalysts, in particular to a bifunctional catalyst for one-step carbon dioxide hydrogenation to produce p-xylene, a preparation method and application. BACKGROUND

[0002] Aromatic hydrocarbons are the most critical platform molecules in chemical production processes, and play a pivotal role in human production and life. Benzene, toluene and xylene, as important chemical raw materials or solvents, are widely used in industries such as dye industry, pesticide production, perfume manufacturing, paint manufacturing, paint spraying, pharmaceutical manufacturing, shoe manufacturing, furniture manufacturing, etc. As an important monomer, it can also produce a series of important chemicals and polymers, including phenol, aniline, styrene, resin, polyester and nylon. P-terephthalic acid (PTA) derived from p-xylene can be polymerized to produce polyethylene terephthalate (PET), which is closely related to people's life. However, most of the aromatic hydrocarbons used in current chemical production are produced by catalytic reforming of naphtha and high-energy chemical production. In addition, the separation of benzene, toluene and xylene isomers is also an extremely energy-consuming process. Therefore, it is urgent to develop a method for directly synthesizing p-xylene from non-petroleum, in order to alleviate the great pressure on resources caused by the decline in crude oil prices.

[0003] For a period of time, researchers have proposed several ways to synthesize p-xylene from non-petroleum molecules, including CO / CO2 hydrogenation, methanol aromatization, benzene / toluene methylation and alkane aromatization. Direct hydrogenation of carbon dioxide molecules containing one carbon atom to produce p-xylene containing eight carbon atoms is a highly green carbon conversion method. However, the direct, efficient and green synthesis of p-xylene is challenging. Coupling methanol synthesis catalysts with specific zeolites to construct bifunctional catalysts can directly convert carbon dioxide through a methanol-mediated pathway to produce aromatic hydrocarbons. However, the methanol-mediated pathway usually has a low CO2 conversion rate (5%-30%) and a high CO selectivity (20%-80%). This is due to the limitation of thermodynamic equilibrium, which is difficult to meet the requirements of industrial production. Iron-based catalysts can also be coupled with zeolites to construct bifunctional catalysts, which can also efficiently produce aromatic hydrocarbons through an improved Fischer-Tropsch synthesis (FTS) pathway. Generally, the FTS pathway is to generate C n H 2n intermediates on iron-based catalysts through reverse water gas shift (RWGS) and FTS reactions, and then perform olefin oligomerization and aromatization reactions on acid zeolites to generate aromatic hydrocarbons. The key to this process is to form C n H 2nThe intermediates and the grafting transformation have a great influence on the aromatic hydrocarbon selectivity of the final product. Due to the control of the Anderson-Schulz-Flory (ASF) law, the FTS reaction usually shows a wider product distribution, so the selectivity of light olefins is usually low.

[0004] In order to improve the hydrogenation activity and the proportion of light olefins, a series of additives are often added to the iron-based catalyst to activate CO2 and optimize the olefin selectivity. In the process of producing p-xylene by carbon dioxide hydrogenation, p-xylene is formed in the micropore of ZSM-5 zeolite, but the p-xylene in the product will isomerize into other isomers during the diffusion process, or be externally alkylated into heavy aromatics, and the product selectivity and space-time yield of p-xylene cannot be satisfactory. On the other hand, the intercrystalline medium diffusion in the micropore of the zeolite limits the medium diffusion of reactant and product molecules, leading to inevitable carbon deposition, which in turn leads to rapid deactivation of the catalyst. Therefore, it is a major challenge to design and develop a new bifunctional catalyst with high CO2 conversion and p-xylene selectivity, as well as excellent p-xylene space-time yield and stability. SUMMARY

[0005] The purpose of the present application is to provide a bifunctional catalyst for one-step production of p-xylene by carbon dioxide hydrogenation, a preparation method and application, which opens up a new way for selective hydrogenation of carbon dioxide to produce high-value p-xylene.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical solution: a bifunctional catalyst for one-step production of p-xylene by carbon dioxide hydrogenation, comprising alkali metal modified FeMn oxide and ZSM-5 capsule zeolite, for one-step hydrogenation to convert CO2 into p-xylene; wherein in the alkali metal modified FeMn oxide, Mn is dispersed on the oxide phase of Fe; the ZSM-5 capsule zeolite is treated by TPAOH solution hydrothermal treatment, and the external passivated Bronsted acid sites can inhibit the p-xylene structuring reaction.

[0007] Preferably, the mass ratio of ZSM-5 capsule zeolite to alkali metal modified FeMn oxide is 1:(0.5-1.5).

[0008] Preferably, the alkali metal is one or more of lithium, sodium and potassium.

[0009] A preparation method of a bifunctional catalyst for one-step production of p-xylene by carbon dioxide hydrogenation, comprising the following specific contents:

[0010] Fe(NO3)3·9H2O and Mn(NO3)2·6H2O are dissolved in deionized water according to the designed ratio of Fe and Mn to obtain solution A, and a basic solution for co-precipitation is prepared and recorded as solution B. Under stirring, the two aqueous solutions A and B are simultaneously added into a beaker, and the temperature and pH value of the reaction are controlled to obtain the product FeMn by co-precipitation. An alkali metal salt solution is added into the obtained FeMn, and the mixture is fully mixed by ultrasonic treatment to obtain an alkali metal modified FeMn oxide.

[0011] The reactants are prepared, i.e. tetraethoxysilane (TEOS), aluminum nitrate, tetrapropylammonium hydroxide (TPAOH) and ethanol (EtOH) are dissolved in distilled water, and the obtained clear solution is transferred into a reaction kettle after stirring. The reaction obtains a ZSM-5 zeolite with a hollow hierarchical porous structure, and the ZSM-5 zeolite is hydrothermally treated by adding a TPAOH aqueous solution, filtered, washed and calcined to obtain a ZSM-5 capsule zeolite.

[0012] The alkali metal modified FeMn oxide is mixed with the ZSM-5 capsule zeolite in a certain proportion to obtain a target catalyst product.

[0013] Preferably, in the preparation process of the ZSM-5 capsule zeolite, the reactants are tetraethoxysilane and aluminum nitrate which are converted into SiO2 and Al2O3 respectively, and the molar ratio of SiO2:Al2O3:H2O:TPAOH:EtOH is =1:X:50:0.24:4, wherein X is adjusted according to the required Si / Al ratio, and the Si / Al ratio is (10-1500):1.

[0014] Preferably, in the preparation process of the ZSM-5 capsule zeolite, the clear solution obtained after the reactants are dissolved and stirred is transferred into a polytetrafluoroethylene sealed autoclave, and the reaction is carried out in an oven at 150-180℃ for 12-48h. The hydrothermal treatment process by adding a TPAOH aqueous solution includes: treating the ZSM-5 zeolite with a TPAOH aqueous solution at 150-180℃, the concentration of the TPAOH aqueous solution is 0.2M, and the amount of the TPAOH aqueous solution used per gram of the ZSM-5 zeolite is 5mL, and the treatment time is 12-48h. After filtration, washing, drying at 80-120℃ for 5-10h and calcination, the calcination conditions are calcination in static air at 450-600℃ for 2-6h.

[0015] Preferably, the designed ratio of Fe and Mn is the molar ratio of Fe and Mn of 10:1, 9:1 or 8:1; and solution B uses one or more of ammonium nitrate, ammonium carbonate, sodium hydroxide or potassium hydroxide solution, and the concentration is 0.1-2M.

[0016] Preferably, the reaction temperature and pH are controlled at 50-100 DEG C and 6.0-9.0 respectively in the preparation process of the alkali metal modified FeMn oxide; the alkali metal modification is carried out by impregnation method, and the alkali metal salt solution used is alkali metal carbonate solution; after the alkali metal salt solution is added, ultrasonic treatment is continued for more than 1 hour;

[0017] More preferably in the above preferred scheme, the reaction temperature and pH are 70-80 DEG C and 7.0-8.0 respectively, the alkali metal salt solution is K2CO3 solution, and the potassium loading in the alkali metal modified FeMn oxide is not more than 2wt%.

[0018] A bifunctional catalyst for one-step preparation of p-xylene from carbon dioxide hydrogenation is applied to catalyze the preparation of p-xylene from carbon dioxide hydrogenation, and the catalyst is pretreated by hydrogen, and then is contacted with a raw gas containing carbon dioxide to complete the carbon dioxide hydrogenation to prepare p-xylene under reaction conditions, and in the carbon dioxide hydrogenation reaction, the one-time conversion rate of carbon dioxide is more than 40%, and the CO2 hydrogenation STY of p-xylene can reach 41.7g·kg cat -1 ·h -1 .

[0019] Compared with the prior art, the bifunctional catalyst for one-step preparation of p-xylene from carbon dioxide hydrogenation, the preparation method and the application have the beneficial effects that:

[0020] 1. The bifunctional catalyst for one-step preparation of p-xylene from carbon dioxide hydrogenation, the preparation method and the application use ZSM-5 capsule zeolite and alkali metal modified FeMn oxide to construct a new type of bifunctional catalyst for one-step conversion of carbon dioxide hydrogenation to p-xylene, and in the case that the one-time conversion rate of carbon dioxide is more than 40%, the space-time yield of p-xylene is significantly improved and can be as high as 41.7g·kg cat -1 ·h -1 , the alkali metal modified FeMn oxide is responsible for converting carbon dioxide through the RWGS reaction and generating C n H 2n intermediate products through the FTS reaction, and the C n H 2n is sent to the ZSM-5 capsule zeolite to be converted into p-xylene and inhibit the isomerization of the product in the diffusion process, and the bifunctional catalyst of the application opens up the practical industrial application prospect of selective conversion of carbon dioxide to p-xylene.

[0021] 2. In the bifunctional catalyst for one-step preparation of p-xylene from carbon dioxide hydrogenation, the preparation method and the application, the increase of the basicity on the surface of the alkali metal modified FeMn oxide catalyst significantly enhances the CO2 adsorption capacity, thereby affecting the carbonization rate of iron and improving the content of intermediate low-carbon olefins.

[0022] 3. The bifunctional catalyst for one-step preparation of para-xylene from carbon dioxide and hydrogen, the preparation method and the application, the ZSM-5 capsule zeolite is obtained by treating HZSM-5 zeolite molecular sieve, TPA + Internal dissolution of zeolite is more likely to occur when the zeolite is treated with an alkali solution, and a continuous dissolution process of internal Si and Al materials to the outside of the zeolite gradually leads to the formation of a hollow hierarchical porous structure. The present application covers part of the acid sites with amorphous SiO2 dissolved from the interior of the zeolite, thereby affecting the number of acid sites on the surface of the ZSM-5 zeolite molecular sieve and improving the catalytic performance.

[0023] 4. The bifunctional catalyst for one-step preparation of para-xylene from carbon dioxide and hydrogen, the preparation method and the application, the average STY in a continuous catalytic reaction of 50 hours is more than 20 g·kg cat -1 ·h -1 , which can maintain a high space-time yield for a long time, significantly prolongs the catalyst life under high space-time yield compared with the rapid deactivation of existing zeolite catalysts. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 XRD comparison patterns of FeMn and Fe2O3 with different iron-manganese ratios;

[0025] Figure 2 HRTEM image of HZSM-5 zeolite obtained in Example 2;

[0026] Figure 3 HRTEM image of ZSM-5 capsule zeolite obtained in Example 2;

[0027] Figure 4 Nitrogen adsorption and desorption curves of HZSM-5 zeolite and ZSM-5 capsule zeolite obtained in Example 2;

[0028] Figure 5 Al2p XPS precision spectrum of the surface of HZSM-5 zeolite and ZSM-5 capsule zeolite obtained in Example 2;

[0029] Figure 6 Fourier transform infrared spectrum of di-tert-butylpyridine adsorbed on HZSM-5 zeolite and ZSM-5 capsule zeolite obtained in Example 2;

[0030] Figure 7 XRD patterns of HZSM-5 zeolite and ZSM-5 capsule zeolite. DETAILED DESCRIPTION

[0031] A bifunctional catalyst for one-step preparation of p-xylene from carbon dioxide and hydrogen, comprising alkali metal modified FeMn oxide and ZSM-5 capsule zeolite, for one-step hydrogenation of CO2 into p-xylene, for reference, the mass ratio of ZSM-5 capsule zeolite to alkali metal modified FeMn oxide is preferably 1:(0.5-1.5); wherein in the alkali metal modified FeMn oxide, Mn is dispersed on the oxide phase of Fe; the ZSM-5 capsule zeolite is treated by TPAOH solution by hydrothermal treatment, and the external passivated Bronsted acid sites can inhibit the xylene structuring reaction.

[0032] The alkali metal is one or more of lithium, sodium and potassium.

[0033] The preparation method of the above-mentioned catalyst comprises the following specific contents:

[0034] 1) Preparation of alkali metal modified FeMn oxide:

[0035] Fe(NO3)3·9H2O and Mn(NO3)2·6H2O are dissolved in deionized water according to the designed Fe / Mn ratio to obtain solution A, and an alkaline solution for co-precipitation is recorded as solution B, which can be one or more of ammonium nitrate, ammonium carbonate, sodium hydroxide, potassium hydroxide, etc., and the concentration can be 1M, as long as co-precipitation can be achieved, under stirring conditions, A and B two aqueous solutions are added into a beaker at the same time, the reaction temperature and pH value are controlled, the co-precipitation product is recorded as FeMn, for reference, the reaction temperature and pH can be controlled at 50-100℃ and 6.0-9.0, more preferably, it can be further controlled at 70-80℃ and 7.0-8.0; alkali metal salt solution is added to the prepared FeMn, and ultrasonic treatment is continuously carried out to fully mix to obtain alkali metal modified FeMn oxide, which can be added for more than 1 hour after the addition of alkali metal salt solution, this step is to modify the alkali metal by impregnation, and the alkali metal salt solution can be an alkali metal carbonate solution;

[0036] In a more preferred embodiment, the alkali metal salt solution is K2CO3 solution, in order to obtain better catalytic performance, the weight of potassium loaded in the alkali metal modified FeMn oxide can be controlled to be less than 2wt%.

[0037] After alkali metal modification, the surface basicity of the product can be increased, the CO2 adsorption capacity can be obviously enhanced, thereby affecting the carbonization rate of iron, and improving the content of intermediate low-carbon olefin catalytic performance;

[0038] 2) Preparation of ZSM-5 capsule zeolite:

[0039] Preparation of reactants, i.e. dissolving tetraethoxysilane (TEOS), aluminum nitrate, tetrapropylammonium hydroxide (TPAOH) and ethanol (EtOH) in distilled water, after stirring, the obtained clear solution is transferred into a reaction kettle (optionally a polytetrafluoroethylene sealed autoclave), and the reaction is carried out to obtain ZSM-5 zeolite with hollow hierarchical porous structure. For reference, the reaction conditions can be controlled as follows: the reaction is carried out in an oven at 150-180℃ for 12-48h, and then the obtained ZSM-5 zeolite is hydrothermally treated by adding TPAOH aqueous solution. Optionally, the ZSM-5 zeolite is treated by TPAOH aqueous solution at 150-180℃, the concentration of TPAOH aqueous solution is 0.2M, the amount of TPAOH aqueous solution used per gram of ZSM-5 zeolite is 5mL, and the treatment time is 12-48h. After filtration and washing, the template agent is removed by calcination, and finally the ZSM-5 capsule zeolite is obtained. Optionally, after filtration and washing, the ZSM-5 capsule zeolite is dried at 80-120℃ for 5-10h and then calcined. The calcination conditions can be as follows: calcination in static air at 450-600℃ for 2-6h.

[0040] For reference, if tetraethoxysilane and aluminum nitrate are converted into SiO2 and Al2O3 respectively, the molar ratio of SiO2:Al2O3:H2O:TPAOH:EtOH is preferably =1:X:50:0.24:4, wherein X is adjusted according to the required Si / Al ratio, and the Si / Al ratio can be further preferred as (10-1500):1. (The Si / Al ratio described in the present application is a conventional index for describing the chemical composition of the molecular sieve, which refers to the molar ratio of silicon element to aluminum element.)

[0041] Finally, the alkali metal modified FeMn oxide is mixed with the ZSM-5 capsule zeolite in a certain proportion to obtain the target catalyst product.

[0042] In a more preferred embodiment, when preparing the alkali metal modified FeMn oxide, the molar ratio of Fe to Mn can be 10:1, 9:1 or 8:1, which can be adjusted according to the needs. For reference, see Figure 1 After the introduction of manganese, no peak belonging to manganese oxide is detected because manganese is well dispersed in the oxide phase of Fe.

[0043] The above-mentioned catalyst can be applied to the preparation of p-xylene by the hydrogenation of carbon dioxide. Specifically, after the catalyst is pretreated by hydrogen, it is contacted with a raw gas containing carbon dioxide, and under the reaction conditions, the hydrogenation of carbon dioxide to produce p-xylene can be completed in one step. The principle is that the intermediate olefin produced by the catalysis of the alkali metal modified FeMn oxide undergoes aromatization reaction through the ZSM-5 capsule zeolite. In the carbon dioxide hydrogenation reaction, the once-through conversion rate of carbon dioxide is more than 40%, and the CO2 hydrogenation STY of p-xylene can reach 41.7g·kg cat -1 ·h -1 .

[0044] Example 1:

[0045] This example is the preparation of alkali modified FeMn oxide, the specific preparation method is as follows:

[0046] Alkali modified FeMn oxide (Fe / Mn molar ratio of 9:1) was prepared by co-precipitation method. Specifically, a certain amount of Fe(NO3)3·9H2O and Mn(NO3)2·6H2O was dissolved in deionized water to obtain solution A, and 1M ammonium nitrate solution was selected as solution B. Under stirring, solutions A and B were simultaneously added to a beaker, and the temperature and pH value were controlled at 60-70°C and about 6.0-7.0, respectively. The obtained catalyst was recorded as FeMn.

[0047] FeMn was treated by adding K2CO3 solution and ultrasonic treatment to make it fully mixed and continue to ultrasonic for more than 1 hour. The concentration and amount of K2CO3 solution were controlled, and the weight of potassium loaded in the alkali modified FeMn oxide was 1wt%, recorded as 1wt% K-FeMn.

[0048] Example 2:

[0049] This example is the preparation of ZSM-5 capsule zeolite, the specific preparation method is as follows:

[0050] HZSM-5 zeolite with Si / Al of 100 was prepared by hydrothermal method. The preparation method is as follows: tetraethoxysilane (TEOS), aluminum nitrate, 25% tetrapropylammonium hydroxide (TPAOH) and ethanol (EtOH) were dissolved in distilled water, and after conversion of TEOS and aluminum nitrate into SiO2 and Al2O3, the molar ratio of SiO2:Al2O3:H2O:TPAOH:EtOH was 1:0.005:50:0.24:4, and after magnetic stirring, the obtained clear solution was transferred to a sealed autoclave, and placed in an oven at 180°C for 24 hours. After filtration, washing and drying at 100°C for 5 hours, the obtained intermediate zeolite was recorded as HZSM-5 (as Figures 2 to 7 recorded as HZSM-5 in ).

[0051] Then 5g HZSM-5 zeolite was placed in 25mL 0.2M TPAOH aqueous solution in an oven at 180°C for 48 hours. Finally, it was calcined in a muffle furnace at 550°C for 5 hours to obtain ZSM-5 capsule zeolite (as Figures 3 to 7 recorded as Hollow ZSM-5 in ).

[0052] As an important part of the catalyst, the structure of the zeolite directly affects the distribution of the final product of carbon dioxide hydrogenation. For example, Figure 2 and 3As shown, HZSM-5 zeolite consists of elliptical particles approximately 3 μm in size. TPAOH-treated ZSM-5 capsule zeolite exhibits rounded rectangular shapes with a small amount of amorphous SiO2 on the surface, and cavities are formed within the zeolite. This indicates that TPAOH treatment significantly shortens the pore length and creates a large hollow structure within HZSM-5. Figure 4 In the N2 adsorption-desorption isotherms of HZSM-5 and ZSM-5 capsule zeolites, it is shown that the desorption branch of the zeolite has an H2 hysteresis loop, which abruptly occurs at around P / P0 = 0.45. (TPA) + Internal dissolution is more likely to occur in zeolites when treated with alkaline solutions. The continuous dissolution of Si and Al from the inside of the zeolite to the outside gradually leads to the formation of a hollow structure. The Al 2p XPS spectra of HZSM-5 and ZSM-5 capsule zeolites are shown below. Figure 5 As shown, the signal at 75 eV indicates the presence of aluminum on the zeolite surface. Notably, the aluminum signal on the ZSM-5 capsule zeolite surface is very low, indicating a reduced aluminum content. Fourier transform infrared spectroscopy analysis of the adsorbed di-tert-butylpyridine (DTBPy) further supports this finding. Figure 6 This further clarified the number of external Brønsted acid sites. Larger probe molecules could not enter the pores of the ZSM-5 capsule zeolite. The low signal intensity of the ZSM-5 capsule zeolite indicates that TPAOH treatment suppressed external Brønsted acid sites. Attenuating external acidic sites is beneficial for improving the selectivity for xylene. Furthermore, Figure 7 The XRD results show that the treated ZSM-5 capsule zeolite catalyst remains stable.

[0053] Example 3:

[0054] 1 wt% K-FeMn from Example 1 was mixed with HZSM-5 and Hollow ZSM-5 from Example 2 at a mass ratio of 1:1 to prepare two catalysts. The CO2 hydrogenation performance of each catalyst was tested. Before the reaction, each catalyst was pretreated by reduction at 300–400°C under hydrogen atmosphere for 6–8 hours. After cooling to room temperature, the feed gas (H2 / CO2 = 3) was introduced into the reactor. Typical reaction pressures and temperatures were 3.0–4.0 MPa and 300–400°C, respectively. For 0.3 g of catalyst, GHSV = 8000 (mL g·kg⁻¹). cat -1 ·h -1 The catalytic performance results of the two catalysts for converting carbon dioxide are shown in Tables 1 and 2 below:

[0055] Table 1. Distribution of hydrocarbon products from CO2 hydrogenation of the catalyst

[0056]

[0057] Table 2. CO2 hydrogenation aromatics product distribution for catalysts

[0058]

[0059] B, T, OX, MX, PX and A(C 9+ ) represent the respective selectivity in all products, where B = benzene, T = toluene, E = ethylbenzene, OX = o-xylene, MX = m-xylene, PX = p-xylene. PX / X is the C mole ratio of PX to all xylenes.

[0060] As shown in Table 1 and Table 2, although 1wt% K-FeMn / HZSM-5 exhibited good aromatics selectivity, the C 9+ The ratio of aromatics products was the highest, with m-xylene dominating in xylenes. The STY of p-xylene was 17.8 g-kg cat -1 ·h -1 over 1wt% K-FeMn / HZSM-5 catalyst. In contrast, when 1wt% K-FeMn / ZSM-5 capsule zeolite was used for the reaction, the content of p-xylene in the product was significantly increased, and the STY of p-xylene reached 41.7 g-kg cat -1 ·h -1 Therefore, the use of ZSM-5 capsule zeolite treated with TPAOH for an appropriate time in the composite catalyst is crucial for the synthesis of p-xylene in the process.

[0061] In addition, this example also carried out a 1wt% K-FeMn / ZSM-5 capsule zeolite catalyst life experiment, and the experimental results showed that the average STY within 50 hours of continuous catalytic reaction was more than 20 g-kg cat -1 ·h -1 .

[0062] Example 4:

[0063] This example is to study the effect of Si / Al on the target catalyst product during the preparation of ZSM-5 capsule zeolite. Based on Example 2, the amount of aluminum nitrate was adjusted to prepare different ZSM-5 capsule zeolites, which were mixed with 1wt% K-FeMn1:1 prepared in Example 1 to obtain catalysts with different Si / Al. The test results are shown in Table 3 and Table 4. For convenience, FeMn represents 1wt% K-FeMn, and ZSM-5 capsule represents ZSM-5 capsule zeolite.

[0064] Table 3. CO2 hydrogenation hydrocarbons product distribution for catalysts

[0065]

[0066] Table 4. CO2 hydrogenation aromatics product distribution over catalysts

[0067]

[0068] B, T, OX, MX, PX and A(C 9+ ) represent the respective selectivity in all products, where B = benzene, T = toluene, E = ethylbenzene, OX = o-xylene, MX = m-xylene, PX = p-xylene. PX / X is the C mole ratio of PX to all xylenes.

[0069] As can be seen from the table, the FeMn / ZSM-5 capsule (Si / Al = 25) catalyst has the highest aromatics selectivity, but the product is mainly C 9+ The aromatics are mainly xylene, and the content of m-xylene is the highest, and the ratio of p-xylene is only 2.9%. After increasing the Si / Al, the CO2 conversion and CO selectivity change little, but the selectivity of light alkanes decreases sharply, the selectivity of CH4 increases, the selectivity of light olefins increases, and the selectivity of aromatics directly decreases. In fact, the HZSM-5 zeolite with high Si / Al has not enough acid sites for the aromatization of olefins, so the corresponding catalyst shows low selectivity of aromatics and p-xylene. More obviously, the trend of the selectivity of light olefins and aromatics is opposite, which indicates that the aromatics are generated from light olefins. On the other hand, in terms of detailed aromatics distribution, when the Si / Al increases from 25 to 1500, the selectivity of p-xylene first increases and then decreases, and similarly, the p-X / X ratio (mole ratio of p-xylene to all xylenes) first increases and then decreases, and the selectivity of C 9+ The selectivity of aromatics also decreases with the increase of Si / Al; as described above, light olefins can start the arylization reaction at the acid sites of the zeolite, and the acidity of the zeolite has a great influence on the catalytic performance. When the hollow HZSM-5 zeolite with Si / Al ratio of 100 is used, the aromatization selectivity reaches 39.7%, the p-xylene selectivity reaches 8.6%, and the p-X / X ratio reaches 62.7%, and the p-xylene space-time yield is the highest at this time.

[0070] The above only describes preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, and any changes or replacements within the technical range disclosed by the present application can be easily thought of by those skilled in the art, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be defined by the protection scope defined in the claims.

[0071] The parts not described in the present application are the known technology of those skilled in the art.

Claims

1. A bifunctional catalyst for one-step production of para-xylene by hydrogenation of carbon dioxide, characterized by: The application relates to a catalyst for converting CO2 into para-xylene in one step, which comprises alkali metal modified FeMn oxide and ZSM-5 encapsulated zeolite; wherein in the alkali metal modified FeMn oxide, Mn is dispersed in the oxide phase of Fe; the ZSM-5 encapsulated zeolite is treated by TPAOH solution, and the external passivated Bronsted acid sites can inhibit the xylene structuralization reaction. The mass ratio of the ZSM-5 encapsulated zeolite to the alkali metal modified FeMn oxide is 1:(0.5-1.5). The alkali metal is one or more of lithium, sodium and potassium.

2. A process for preparing a bifunctional catalyst for one-step production of para-xylene by hydrogenation of carbon dioxide according to claim 1, characterized in that, The application comprises the following specific contents: Fe (NO3)3.9H2O and Mn (NO3)2.6H2O are dissolved in deionized water to obtain solution A, and an alkaline solution for co-precipitation is prepared and recorded as solution B; under stirring, the two aqueous solutions A and B are simultaneously added into a beaker, and the temperature and pH value of the reaction are controlled; the product is recorded as FeMn; alkali metal salt solution is added into the prepared FeMn, and the alkali metal modified FeMn oxide is obtained by continuously ultrasonic treating and fully mixing; Reactants are prepared, that is, tetraethoxysilane (TEOS), aluminum nitrate, tetrapropylammonium hydroxide (TPAOH) and ethanol (EtOH) are dissolved in distilled water, and the obtained clear solution is transferred into a reaction kettle after stirring; the ZSM-5 zeolite with a hollow hierarchical porous structure is obtained by reaction; TPAOH aqueous solution is added for hydrothermal treatment; after filtration and washing, the ZSM-5 encapsulated zeolite is obtained by calcination; The alkali metal modified FeMn oxide is mixed with the ZSM-5 encapsulated zeolite in a certain proportion to obtain the target catalyst product.

3. The method of claim 2, wherein: In the preparation process of the ZSM-5 encapsulated zeolite, the molar ratio of SiO2, Al2O3, H2O, TPAOH and EtOH is 1:X:50:0.24:4, wherein X is adjusted according to the required Si / Al ratio, and the Si / Al ratio is (10-1500):

1.

4. The method of claim 2, wherein: In the preparation process of the ZSM-5 encapsulated zeolite, the clear solution obtained after the reactants are dissolved and stirred is transferred into a polytetrafluoroethylene sealed autoclave, and the reaction is carried out in an oven at 150-180 DEG C for 12-48 h; the hydrothermal treatment process of adding TPAOH aqueous solution includes: treating the ZSM-5 zeolite with TPAOH aqueous solution at 150-180 DEG C, the concentration of the TPAOH aqueous solution is 0.2 M, the amount of TPAOH aqueous solution used per gram of ZSM-5 zeolite is 5 mL, and the treatment time is 12-48 h; after filtration and washing, the ZSM-5 encapsulated zeolite is dried at 80-120 DEG C for 5-10 h and then calcined, and the calcination conditions are as follows: calcination is carried out in static air at 450-600 DEG C for 2-6 h.

5. The method of claim 2, wherein: The designed Fe / Mn ratio is the molar ratio of Fe and Mn, which is 10:1, 9:1 or 8:1; solution B adopts one or more of ammonium nitrate, ammonium carbonate, sodium hydroxide or potassium hydroxide solution, and the concentration is 1 M.

6. The method of claim 2, wherein: The reaction temperature and pH are controlled at 50-100 DEG C and 6.0-9.0 respectively in the preparation process of the alkali metal modified FeMn oxide; the alkali metal modification is carried out by impregnation method, and the alkali metal salt solution used is alkali metal carbonate solution; after adding the alkali metal salt solution, ultrasonic treatment is continued for more than 1 hour.

7. The method of claim 6, wherein: The reaction temperature and pH are 70-80 DEG C and 7.0-8.0 respectively, the alkali metal salt solution is K2CO3 solution, and the weight of the loaded potassium in the alkali metal modified FeMn oxide is not more than 2wt%.

8. The bifunctional catalyst for one-step production of p-xylene from carbon dioxide hydrogenation according to claim 1, or the target catalyst product prepared by the preparation method according to any one of claims 2 to 7, applied to catalyze the production of p-xylene from carbon dioxide hydrogenation, characterized in that: The catalyst is pretreated by hydrogen, and then is contacted with a raw gas containing carbon dioxide to complete the preparation of p-xylene by carbon dioxide hydrogenation under reaction conditions. In the carbon dioxide hydrogenation reaction, the one-time conversion rate of carbon dioxide is more than 40%, and the CO2 hydrogenation STY of p-xylene can reach 41.7 g·kg cat -1 ·h -1 .

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