Catalyst for one-step hydrogenation of co2 to aromatics, and preparation method and application thereof

Abstract

The application discloses a catalyst for one-step hydrogenation of CO2 to arenes and a preparation method and application thereof. The catalyst has a core-shell structure, and comprises a core layer containing at least a metal oxide and a molecular sieve and a shell layer of silicon dioxide. The catalyst provided by the application can regulate a reaction path, sufficiently improve hydrogen-carbon conversion efficiency and atomic economy, and has the characteristics of high arene selectivity, high arene yield and low CO selectivity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of one-step hydrogenation of CO2 to produce aromatic hydrocarbons, and more particularly to a catalyst for one-step hydrogenation of CO2 to produce aromatic hydrocarbons, and a preparation method and application thereof. BACKGROUND

[0002] Aromatic hydrocarbons play an indispensable role in the national economy, and the traditional production route relies on non-renewable resources such as petroleum. With the increasing shortage of petroleum resources, more and more research is devoted to developing new routes for producing aromatic hydrocarbons to reduce dependence on petroleum resources. Carbon dioxide is widely present in nature, and the greenhouse effect caused by a large amount of carbon dioxide emitted in the process of fuel combustion and biological respiration is a serious environmental problem. Through carbon dioxide capture and catalytic conversion technology, carbon dioxide is used as a carbon source to produce aromatic hydrocarbons and other chemicals, which can realize the resource utilization of carbon dioxide, not only can reduce carbon emissions and relieve environmental pressure, but also can be used as a sustainable resource alternative.

[0003] The route of converting carbon dioxide to produce aromatic hydrocarbons includes a Fischer-Tropsch synthesis route and a conversion route via a methanol intermediate. The former converts carbon dioxide into carbon monoxide through a reverse water gas shift reaction, and the carbon monoxide is converted into hydrocarbons through a Fischer-Tropsch synthesis reaction. Since the product distribution of this process follows the Anderson-Schulz-Flory distribution, the selectivity of aromatic hydrocarbons is low. Another indirect synthesis route based on a methanol platform can draw on existing mature processes, but the production route is long and the equipment investment is high in actual production. In order to overcome the shortcomings of the above two routes, a catalyst with carbon dioxide hydrogenation activity and a catalyst with aromatization activity are coupled, which can realize one-step conversion of carbon dioxide and high selectivity of aromatic hydrocarbons.

[0004] CN201810476839.0 and Nature Communications 2018, 9, 3457 respectively report that a zinc aluminum spinel and an acidic molecular sieve coupled catalyst has achieved a near 80% aromatic hydrocarbon selectivity in a CO2 conversion system, but it is difficult to achieve high CO2 conversion and low CO selectivity at the same time, such as at a CO2 conversion rate of about 10%, the CO selectivity is about 60%, and the carbon conversion efficiency is low. CN107840778A provides a method for preparing aromatic hydrocarbons by hydrogenation of carbon dioxide, which uses an iron-based and modified or partially modified molecular sieve catalyst as a catalyst. This method for preparing aromatic hydrocarbons by hydrogenation of carbon dioxide improves the single-pass CO2 conversion rate, increases the selectivity of C 5+ hydrocarbons, and the selectivity of aromatic hydrocarbons in C 5+ hydrocarbons, but the selectivity of aromatic hydrocarbons is low. SUMMARY

[0005] The purpose of this invention is to overcome the shortcomings of low aromatic selectivity and low aromatic yield in the one-step CO2 hydrogenation to aromatics reaction in the prior art, and to provide a catalyst for the one-step CO2 hydrogenation to aromatics reaction, its preparation method, and its application. This catalyst regulates the reaction pathway, significantly improves hydrogen-carbon conversion efficiency and atom economy, and features high aromatic selectivity, high aromatic yield, and low CO selectivity.

[0006] To achieve the above objectives, the first aspect of the present invention provides a catalyst for one-step hydrogenation of CO2 to produce aromatics, the catalyst having a core-shell structure comprising a core layer containing at least a metal oxide and a molecular sieve and a shell layer containing silica.

[0007] Furthermore, the catalyst has a silica shell with a high degree of encapsulation, and its surface is basically free of unbonded metal hydroxyl groups.

[0008] Furthermore, to reflect the degree of coating on the catalyst surface, after correction based on the intensity of the metal-oxygen characteristic peak, the area of ​​the characteristic absorption peak of the metal hydroxyl group in the infrared spectrum of the catalyst without a coating shell (i.e., the catalyst with only the core layer of the catalyst of this invention and no shell layer) is taken as 1. The area of ​​the metal hydroxyl absorption peak in the infrared spectrum of the catalyst of this invention is less than 0.1. A metal hydroxyl absorption peak area of ​​less than 0.1 indicates that the exposure degree of metal hydroxyl groups is very low and the surface of the metal oxide is sufficiently modified, thereby achieving the effect of weakening side reactions such as reverse water-gas shift reaction on the surface of the metal oxide and inhibiting the formation of by-products such as CO.

[0009] Furthermore, an enhanced absorption peak of the characteristic silanol group attributable to silica was detected in the infrared spectrum of the catalyst. This enhanced absorption peak indicates a high degree of silica shell encapsulation, and that the silanol groups of silica can cover the metal hydroxyl groups, which is beneficial for mitigating side reactions.

[0010] Furthermore, based on the ratio of the area of ​​the characteristic absorption peak of silanol to the area of ​​the characteristic absorption peak of metal hydroxyl in the infrared spectrum of the catalyst, the relative content of silanol / metal hydroxyl in the catalyst is 4.0 to 10.0.

[0011] Furthermore, the mass ratio of the core layer to the shell layer in the catalyst is (4:1) to (40:1), for example, it can be 4:1, 6:1, 8:1, 10:1, 12:1, 14:1, 16:1, 18:1, 20:1, 22:1, 24:1, 26:1, 30:1, 32:1, 34:1, 36:1, or 40:1, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, and it is more preferably (8:1) to (20:1).

[0012] Furthermore, the mass ratio of metal oxide to molecular sieve in the core layer of the catalyst is (1:10) to (10:1), for example, it can be 1:10, 1:9, 1:8, 1:7, 1:6, 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, and (1:3) to (3:1) is more preferred.

[0013] Furthermore, the metal element in the metal oxide component of the catalyst is selected from one or more of Cr, Mn, Zr, La, Ce, Al, Ti, Zn, In, and Ga, preferably one or more of Cr, Zr, Al, Zn, In, and Ga, and more preferably one or more of Zn-Cr, Zn-Al, Zn-Zr, In-Zr, Ga-Zr, Zn-Cr-Al, Zn-Ga-Zr, Zn-In-Zr, and Ga-In-Zr combinations. In this invention, the synergistic effect between the above-mentioned metals can promote the activation and hydrogenation reaction of CO2, thereby improving the CO2 conversion rate.

[0014] Furthermore, the molecules in the catalyst are screened from one or more of ZSM-5, ZSM-11, Silicalite-1, Silicalite-2, Beta, MOR, and USY, preferably one or more of ZSM-5, ZSM-11, Silicalite-1, and Silicalite-2, and more preferably one or more of ZSM-5 and Silicalite-1.

[0015] According to a preferred embodiment of the present invention, the catalyst contains Cr2O3 as the metal oxide, ZSM-5 as the molecular sieve, and silica as the shell, achieving outstanding technical effects in the one-step hydrogenation reaction of CO2 to produce aromatics. More preferably, the catalyst consists only of the above components.

[0016] According to a preferred embodiment of the present invention, the catalyst contains an In-Zr composite oxide as the metal oxide, ZSM-5 as the molecular sieve, and a silica shell, achieving outstanding technical results in the one-step hydrogenation reaction of CO2 to aromatics. More preferably, the catalyst consists only of the above components.

[0017] According to a preferred embodiment of the present invention, the catalyst contains a Zn-Cr composite oxide as the metal oxide, ZSM-5 as the molecular sieve, and a silica shell, achieving outstanding technical results in the one-step hydrogenation reaction of CO2 to produce aromatics. More preferably, the catalyst consists only of the above components.

[0018] A second aspect of the present invention provides a method for preparing the above-mentioned catalyst, comprising the following steps:

[0019] (1) Mix the metal salt solution with the precipitant solution and age it to obtain a metal precipitate;

[0020] (2) Disperse the metal precipitate and optional molecular sieve from step (1) in an alcohol solution, adjust the pH of the dispersion system to 6-8, and perform hydrothermal treatment to obtain precursor dispersion I.

[0021] (3) Optionally, the molecular sieve is added to the precursor dispersion I in step (2) to obtain precursor dispersion II;

[0022] (4) Mix precursor dispersion I and / or precursor dispersion II with silicon-modified solution, age and calcine to obtain catalyst;

[0023] Molecular sieves are added in step (2) and / or step (3).

[0024] Further, the metal salt mentioned in step (1) is at least one of a metal nitrate, a metal acetate, a metal carbonate, and a metal chloride. Further, the precipitant mentioned in step (1) is at least one of ammonia, ammonium carbonate, potassium carbonate, sodium carbonate, potassium hydroxide, and sodium hydroxide.

[0025] Furthermore, based on the theoretical amount of precipitant required for complete precipitation of metal cations being 1, the mixing ratio of the metal salt and precipitant in step (1) is 0.5 to 1.5, preferably 0.9 to 1.2.

[0026] In this invention, the mass concentration of the metal salt solution in step (1) is 5% to 70%, and the mass of the metal salt is the mass of the solute. In this invention, the mass concentration of the precipitant solution in step (1) is 2% to 30%, and the mass of the precipitant is the mass of the solute.

[0027] Furthermore, the mixing of the metal salt solution and the precipitant solution in step (1) is carried out using conventional methods in the art, preferably with the metal salt solution and the precipitant solution undergoing co-current precipitation.

[0028] Furthermore, the aging treatment in step (1) is carried out at 50-80°C for 1-24 hours.

[0029] Furthermore, step (1) also includes: after aging, optionally performing suction filtration, optional washing, optional filtering, and optional drying to obtain a metal precipitate. This invention does not impose any restrictions on the conditions for suction filtration, washing, filtering, and drying; those skilled in the art can freely choose these conditions.

[0030] Further, in step (2), the metal precipitate and optionally the molecular sieve are dispersed in an alcohol solution, wherein the liquid-to-solid mass ratio is 4–30:1. The volume ratio of solvent to alcohol in the alcohol solution is (1:10)–(50:1), and the solvent is preferably water.

[0031] Further, the alcohol mentioned in step (2) is selected from one or more of ethanol, propanol, isopropanol, butanol, and isobutanol.

[0032] Furthermore, the method for adjusting the pH of the dispersion system in step (2) can be any conventional method in the art, without any restrictions, such as adding one or more of ammonia, urea, acetic acid, hydrochloric acid, phosphate buffer solution, etc. to adjust the pH of the dispersion system.

[0033] Furthermore, in this invention, the hydrothermal treatment in step (2) is to enrich the surface of the metal precipitate with hydroxyl groups, so that these hydroxyl groups can be fully eliminated as silica deposition sites in subsequent steps.

[0034] Furthermore, in step (2), the hydrothermal treatment conditions are 90–120°C for 2–20 hours.

[0035] Further, based on the metal in the precursor dispersion I as oxides, the mass ratio of the molecular sieve added in step (2) and / or step (3) to the metal oxide is (1:10) to (10:1).

[0036] Furthermore, the silicon-containing modified solution in step (4) is a mixture of a silicon-containing modifier and an organic solvent.

[0037] Further, the silicon-containing modifier in step (4) is at least one of silica sol, methyl orthosilicate, ethyl orthosilicate, propyl orthosilicate, butyl orthosilicate, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, and ethyltriethoxysilane.

[0038] Furthermore, in step (4), the organic solvent is at least one of n-hexane, cyclohexane, n-heptane, and n-octane.

[0039] Furthermore, in step (4), the volume ratio of the silicon modifier and the organic solvent is (1:10) to (1:1).

[0040] Further, in step (4), the volume ratio of precursor dispersion I and / or precursor dispersion II to silicon-modified solution is (1:4) to (4:1).

[0041] According to a preferred embodiment of the present invention, a surfactant is added in the step (4) of mixing precursor dispersion I and / or precursor dispersion II with silicon-modified solution. Preferably, precursor dispersion I and / or precursor dispersion II are mixed with surfactant and then mixed with silicon-modified solution.

[0042] Further, in step (4), the mass ratio of the catalyst contained in precursor dispersion I and / or precursor dispersion II to the surfactant is (10:1) to (50:1), based on the theoretical mass of the catalyst.

[0043] Further, the surfactant mentioned in step (4) is at least one of alkyltrimethylammonium salt, dialkyldimethylammonium salt, and alkyldimethylbenzylammonium salt, preferably at least one of tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, octadecyltrimethylammonium bromide, tetradecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, dimethyldiallylammonium bromide, and dimethyldiallylammonium chloride.

[0044] Furthermore, the aging treatment in step (4) is carried out at 20–70°C for 12–48 hours. The calcination conditions are calcination at 400–600°C for 2–6 hours.

[0045] Further, after aging in step (4), the product is dried. In this invention, drying is mainly to remove moisture from the surface of the mixture, to ensure the quality of the obtained catalyst material and improve the stability of the material. Conventional drying methods can be used, and preferably, the drying is vacuum drying.

[0046] The third aspect of the present invention provides the application of the above-mentioned catalyst in the one-step hydrogenation of CO2 to produce aromatics, wherein the catalyst is the catalyst provided in the first aspect or the catalyst prepared by the preparation method provided in the second aspect.

[0047] Furthermore, the application includes: using CO2 / H2 as raw material, contacting the raw material with the catalyst to react and obtain a stream containing hydrocarbon products.

[0048] Furthermore, the H2 / CO2 molar ratio in the raw gas is 2.0 to 6.0; preferably, the H2 / CO2 molar ratio is 2.5 to 4.0.

[0049] Further, the reaction conditions are: reaction temperature 300–550°C; and / or reaction pressure 1.0–8.0 MPa; and / or volume hourly space velocity 600–10000 h⁻¹. -1 .

[0050] In the one-step CO2 hydrogenation to hydrocarbons reaction system based on methanol synthesis using a metal oxide-molecular sieve coupled catalysis, CO2 and H2 first undergo a hydrogenation reaction on the surface of the metal oxide to generate a methanol intermediate. This methanol intermediate diffuses from the metal oxide surface into the molecular sieve, where it undergoes further aromatization to generate aromatics. The aromatization of the methanol intermediate is a multi-molecular reaction, and a higher concentration of methanol intermediate in the molecular sieve channels favors this reaction. Therefore, close contact between the metal oxide and the molecular sieve components facilitates the rapid migration of the methanol intermediate, contributing to improved CO2 conversion and aromatics selectivity in this system. Furthermore, a reverse water-gas shift (RWGS) reaction occurs on the metal oxide surface, which is one of the main side reactions in this system. This side reaction generates CO and H2O from CO2 and H2, reducing hydrogen and carbon atom utilization. How to suppress the RWGS reaction and improve aromatics selectivity at a higher CO2 conversion rate, thereby improving hydrogen-carbon conversion efficiency and atom economy, is the problem this invention aims to solve.

[0051] By employing the technical solution of this invention, surface modification of a combined catalyst of metal oxides and molecular sieves is applied to the one-step hydrogenation reaction of CO2 to produce aromatics. The CO selectivity is reduced to below 50%, significantly improving the selectivity of organic products, the yield of aromatics, and the utilization rate of hydrogen and carbon atoms, achieving excellent technical results. Attached Figure Description

[0052] Figure 1 These are the infrared spectra of the catalysts ZSM-5(100), Example 1, and Comparative Example 1;

[0053] in, Figure 1 In the example, (1) is ZSM-5(100) prepared in Example 1, and (2) and (3) are catalysts of Comparative Example 1 and Example 1, respectively;

[0054] Among them 3696cm -1 3657cm -1 3628cm -1 and 3596cm -1 The nearby peak is a characteristic peak of hydroxyl groups bonded to chromium; 3740 cm⁻¹ -1 The nearby peak is a characteristic peak of silanol; 3610 cm⁻¹ -1 The vicinity is a characteristic peak of hydroxyl groups in a silica-alumina bridge. Among them, (1) and (2) have been analyzed according to the characteristic peaks of the ZSM-5 molecular sieve framework (1500-2000 cm⁻¹). -1 (2) and (3) have been corrected according to the intensity of the chromium-oxygen vibration peak of chromium oxide. Detailed Implementation

[0055] The following embodiments will further illustrate the technical solutions provided by the present invention, but the scope of protection of the present invention is not limited to these embodiments.

[0056] In this invention, infrared testing is performed on a NICOLET 5700 infrared spectrometer equipped with an in-situ cell. An appropriate amount of sample is weighed, pressed into a self-supporting sheet, and placed in an infrared cell with CaF2 as the window. The sample is treated at 400°C under high vacuum for 2 hours, and then cooled to 200°C to acquire the spectrum.

[0057] In this invention, the post-reaction stream includes unconverted CO2 and H2, as well as hydrocarbon products, which are composed of C6 to C6 hydrocarbons. 10+ Aromatics and / or C1-C 5+ Hydrocarbon composition. The selectivity of each product is defined as the percentage (mol%) of each product in the total carbon number of the organic product. The specific calculation method is as follows:

[0058] CO2 conversion rate = (CO2 conversion amount / CO2 feed rate) × 100%

[0059] CO selectivity = (CO generation / CO2 conversion) × 100%

[0060] Total carbon number of organic products = Σ(amount of organic product i × number of carbon atoms in the molecule of organic product i),

[0061] Selectivity of organic product j = Amount of organic product j × Number of carbon atoms in organic product j molecule / Total number of carbon atoms in organic product j × 100%

[0062] Aromatic selectivity = C6 aromatic selectivity + C7 aromatic selectivity + C8 aromatic selectivity + C9 aromatic selectivity + C 10+ Aromatic selectivity,

[0063] Aromatics yield = CO2 conversion rate × (1 - CO selectivity) × aromatics selectivity × 100%.

[0064]

Example 1

[0065] Cr₂O₃ was prepared by precipitation. 52.66 g of chromium nitrate was dissolved in 70 mL of deionized water, and 19.91 g of ammonium carbonate was dissolved in 94.0 mL of deionized water. Under vigorous stirring, the chromium nitrate solution and the ammonium carbonate solution were added dropwise to 10 mL of deionized water at rates of 5 mL / min and 6.7 mL / min, respectively. After precipitation, the mother liquor was aged in a 70 °C water bath for 3 h, then filtered and washed with deionized water until neutral. The resulting metal precipitate was dispersed in 5 times its mass of an ethanol solution (water to ethanol volume ratio of 1:1), and the pH was adjusted to 7. The solution was then hydrothermally treated at 105 °C for 10 h to obtain a Cr₂O₃ precursor dispersion. ZSM-5 molecular sieve with a Si / Al molar ratio of 100 was synthesized by hydrothermal method, denoted as ZSM-5(100). Based on the Cr2O3 in the Cr2O3 precursor dispersion, 10.0 g of ZSM-5(100) was added to the Cr2O3 precursor dispersion and mixed thoroughly, with a mass ratio of Cr2O3 to ZSM-5(100) of 1:1, to obtain the catalyst precursor dispersion. 13.88 g of tetraethyl orthosilicate was dissolved in 24 mL of n-hexane and mixed thoroughly with the catalyst precursor dispersion. The mixture was aged at 25 °C for 24 h, vacuum dried at 80 °C, and calcined at 500 °C for 4 h to obtain a core-shell structured catalyst with SiO2 as the shell layer. The mass ratio of the combined catalyst in the core layer to the SiO2 in the shell layer was 5.0, denoted as [Cr2O3 / ZSM-5(100)(1:1)]@SiO2(5.0).

[0066] The surface hydroxyl groups of ZSM-5(100) and [Cr2O3 / ZSM-5(100)(1:1)]@SiO2(5.0) were characterized by infrared spectroscopy, as shown below. Figure 1 As shown in (1) and (3), an infrared absorption peak was detected at 3610 cm⁻¹ in ZSM-5 (100). -1 Nearby silicic aluminum bridged hydroxyl groups, and 3740cm -1 In the infrared spectrum of [Cr2O3 / ZSM-5(100)(1:1)]SiO2(5.0), the characteristic peaks of silanols are significantly enhanced, while the intensity of the characteristic peaks of hydroxyl groups bonded to chromium is greatly weakened, except that the basic characteristic peaks of ZSM-5(100) are basically retained.

[0067] The obtained core-shell structured catalyst was granulated and packed into a reactor, using a H2 / CO2 mixture with a molar ratio of 3.0 as feedstock, and subjected to a space velocity of 1200 h⁻¹. -1The reaction was carried out at a temperature of 350℃ and a pressure of 4.0MPa. The catalyst was pretreated with H2 at 380℃ for 2 hours before the reaction. The results of the metal hydroxyl content (based on Comparative Example 1, i.e., the area / content of the characteristic metal hydroxyl peak in the infrared spectrum of the catalyst without a shell), the relative content of silanol / metal hydroxyl groups, CO2 conversion, CO selectivity, aromatic selectivity, and aromatic yield are shown in Table 1.

[0068]

Example 2

[0069] The method is the same as in Example 1, except that the mass ratio of the core catalyst to the shell SiO2 is 10.0. The resulting core-shell catalyst is denoted as [Cr2O3 / ZSM-5(100)(1:1)]@SiO2(10.0).

[0070]

Example 3

[0071] The method is the same as in Example 1, except that the metal oxide in the core catalyst is a Zn-Cr oxide with a Zn / Cr molar ratio of 1 / 2, denoted as 1Zn-2Cr. The 1Zn-2Cr precipitate is prepared by precipitation. 7.89 g of zinc acetate and 34.41 g of chromium nitrate are dissolved in 75 mL of deionized water. 70.0 g of ammonia (25 wt%) is diluted with 47.5 mL of deionized water. Under vigorous stirring, the metal salt solution and the precipitant solution are added dropwise to 15 mL of deionized water at rates of 3.75 mL / min and 5 mL / min, respectively, in a parallel flow. After precipitation, the mother liquor is aged in a constant temperature water bath at 50 °C for 24 h, then filtered without additional washing. The resulting core-shell structured catalyst is denoted as [1Zn-2Cr / ZSM-5(100)(1:1)]@SiO2(5.0).

[0072]

Example 4

[0073] The method is the same as in Example 1, except that the metal oxide in the core-shell catalyst is an In-Zr oxide with an In / Zr molar ratio of 1 / 6, denoted as 1In-6Zr. The 1In-6Zr precipitate is prepared by precipitation. 4.36 g of indium nitrate and 29.39 g of zirconium nitrate are dissolved in 600 mL of deionized water, and 11.09 g of sodium hydroxide is dissolved in 420.0 mL of deionized water. Under vigorous stirring, the metal salt solution and the precipitant solution are added dropwise to 30 mL of deionized water at rates of 10 mL / min and 7 mL / min, respectively, in a parallel flow. After precipitation, the mother liquor is aged in an 80°C constant temperature water bath for 1 h, and then filtered and washed with deionized water until neutral. The resulting core-shell structure catalyst is denoted as [1In-6Zr / ZSM-5(100)(1:1)]@SiO2(5.0).

[0074]

Example 5

[0075] Zn-Cr oxide with a Zn / Cr molar ratio of 2 / 1, denoted as 2Zn-1Cr, was prepared by precipitation. 12.50 g of zinc nitrate and 8.40 g of chromium nitrate were dissolved in 40 mL of deionized water, and 9.0 g of potassium hydroxide was dissolved in 30 mL of deionized water. Under vigorous stirring, the metal salt solution and the precipitant solution were added dropwise to 5 mL of deionized water at rates of 0.67 mL / min and 0.5 mL / min, respectively, in a parallel stream. After precipitation, the mother liquor was aged in a 60℃ constant-temperature water bath for 5 h, then filtered and washed with deionized water until neutral. The resulting metal precipitate was dispersed in 25 times its mass of an ethanol solution (water to ethanol volume ratio of 2:1), and the pH was adjusted to 7.5. The solution was then hydrothermally treated at 90℃ for 8 h to obtain a 2Zn-1Cr precursor dispersion. ZSM-5 molecular sieve with a Si / Al molar ratio of 200, denoted as ZSM-5(200), was synthesized hydrothermally. Based on the 2Zn-1Cr oxide in the 2Zn-1Cr precursor dispersion, 50.0g of ZSM-5(200) was added to the 2Zn-1Cr precursor dispersion and mixed thoroughly at a mass ratio of 1:10 between 2Zn-1Cr and ZSM-5(200) to obtain the catalyst precursor dispersion. 4.77 g of tetraethyl orthosilicate was dissolved in 40 mL of n-hexane and thoroughly mixed with the catalyst precursor dispersion. The mixture was aged at 40 °C for 18 h, vacuum dried at 80 °C, and calcined at 480 °C for 5 h to obtain a core-shell catalyst with a SiO2 shell. In the core catalyst, the metal oxide was 2Zn-1Cr, the molecular sieve was ZSM-5(200), and the mass ratio of the metal oxide to the molecular sieve was 1:10. The mass ratio of the core catalyst to the shell SiO2 was 40.0. The resulting core-shell catalyst was denoted as [2Zn-1Cr / ZSM-5(200)(1:10)]@SiO2(40.0). The core-shell catalyst was granulated and packed into a reactor. A H2 / CO2 mixture with a molar ratio of 3.5 was used as feedstock, and the reactor was calcined at a space velocity of 800 h⁻¹. -1 The reaction was carried out at a temperature of 320℃ and a pressure of 7.0MPa. The catalyst was pretreated with H2 at 380℃ for 2 hours before the reaction.

[0076]

Example 6

[0077] ZrO2 was prepared by precipitation. 174.52 g of zirconium nitrate was dissolved in 2000 mL of deionized water, and 90.49 g of sodium carbonate was dissolved in 1000 mL of deionized water. Under vigorous stirring, the metal salt solution and the precipitant solution were added dropwise to 100 mL of deionized water at a rate of 50 mL / min and 25 mL / min, respectively. After precipitation, the mother liquor was aged in a constant temperature water bath at 70 °C for 10 h, then filtered and washed with deionized water until neutral. The resulting metal precipitate was dispersed in a butanol solution of 10 times its mass (the volume ratio of water to butanol in the solution was 1:10), and the pH was adjusted to 8. The solution was then hydrothermally treated at 120 °C for 18 h to obtain a ZrO2 precursor dispersion. ZSM-5 molecular sieve with a Si / Al molar ratio of 30 was synthesized by hydrothermal method, denoted as ZSM-5(30). Based on ZrO2 in the ZrO2 precursor dispersion, 5.0 g of ZSM-5(30) was added to the ZrO2 precursor dispersion and mixed thoroughly, with a ZrO2 to ZSM-5(30) mass ratio of 10:1, to obtain the catalyst precursor dispersion. 47.67 g of tetraethyl orthosilicate was dissolved in 200 mL of n-hexane and mixed thoroughly with the catalyst precursor dispersion. The mixture was aged at 30 °C for 20 h, vacuum dried at 90 °C, and calcined at 550 °C for 3 h to obtain a core-shell structure catalyst with SiO2 as the shell layer. In the core layer catalyst, the metal oxide is ZrO2 and the molecular sieve is ZSM-5(30). The mass ratio of metal oxide to molecular sieve in the core layer is 10:1. The mass ratio of core layer catalyst to shell SiO2 is 4.0. The obtained core-shell structure catalyst is denoted as [ZrO2 / ZSM-5(30)(10:1)]@SiO2(4.0).

[0078]

Example 7

[0079] The method of Example 3 is followed, except that the molecular sieves in the core catalyst are ZSM-5 (100) and ZSM-11 (100) in a mass ratio of 2 / 1. The resulting core-shell catalyst is denoted as [1Zn-2Cr / ZSM-5 (100)&ZSM-11 (100) (1:1)]@SiO2 (5.0).

[0080]

Example 8

[0081] The method described in Example 3 differs in that the 1Zn-2Cr precursor dispersion was prepared by dispersing the metal precipitate in four times its mass of an isopropanol solution (the volume ratio of water to isopropanol in the solution was 45:1), adjusting the pH to 6.0, and then hydrothermally treating it at 110°C for 20 hours to obtain the 1Zn-2Cr precursor dispersion. The resulting core-shell structured catalyst is denoted as [1Zn-2Cr(IPA) / ZSM-5(100)(1:1)]@SiO2(5.0).

[0082]

Example 9

[0083] The method described in Example 3 differs in that the SiO2-containing shell layer was introduced by dissolving 10.14 g of methyl orthosilicate in 30 mL of cyclohexane and thoroughly mixing it with the combined catalyst precursor dispersion. The mixture was then aged at room temperature for 24 h, vacuum dried at 80 °C, and calcined at 500 °C for 4 h to obtain a core-shell structured catalyst with SiO2 on its surface. The resulting core-shell structured catalyst is denoted as [1Zn-2Cr / ZSM-5(100)(1:1)]@SiO2(TMOS, 5.0).

[0084]

Example 10

[0085] The method of Example 4 differs in that: based on the theoretical mass of catalyst contained in the catalyst precursor dispersion, a surfactant, hexadecyltrimethylammonium bromide, is added to the catalyst precursor dispersion at a mass ratio of 50:1, and then mixed with a silicon-modified solution. The resulting core-shell structured catalyst is denoted as [1In-6Zr / ZSM-5(100)(CTAB,1:1)]@SiO2(5.0).

[0086]

Example 11

[0087] The method of Example 4 differs in that: based on the theoretical mass of catalyst contained in the catalyst precursor dispersion, a surfactant, dimethyl diallyl ammonium chloride, is added to the catalyst precursor dispersion at a mass ratio of 10:1, and then mixed with a silicon-modified solution. The resulting core-shell structured catalyst is denoted as [1In-6Zr / ZSM-5(100)(DMDAAC,1:1)]@SiO2(5.0).

[0088] Comparative Example 1

[0089] Cr₂O₃ was prepared by precipitation. 52.66 g of chromium nitrate was dissolved in 70 mL of deionized water, and 19.91 g of ammonium carbonate was dissolved in 94.0 mL of deionized water. Under vigorous stirring, the chromium nitrate solution and the ammonium carbonate solution were added dropwise to 10 mL of deionized water at rates of 5 mL / min and 6.7 mL / min, respectively. After precipitation, the mother liquor was aged in a constant temperature water bath at 70 °C for 3 h, then filtered, washed with deionized water until neutral, vacuum dried at 80 °C, and calcined at 500 °C for 4 h to obtain Cr₂O₃.

[0090] The catalyst was obtained by thoroughly mixing Cr2O3 and ZSM-5(100) (same as in Example 1) at a mass ratio of 1:1. The surface hydroxyl groups of the catalyst were characterized by infrared spectroscopy, as shown in the attached figure. Figure 1As shown in (2). In the Cr2O3 / ZSM-5(100) catalyst, in addition to retaining the characteristic peaks of silanol bridged hydroxyl groups and silanol groups of ZSM-5(100), at 3696 cm⁻¹... -1 3657cm -1 3628cm -1 3596cm -1 A strong characteristic peak of hydroxyl groups bonded to chromium was detected nearby. The catalyst, after being granulated and compressed, was packed into a reactor using a H2 / CO2 mixture with a molar ratio of 3.0 as feedstock, and reacted at a space velocity of 1200 h⁻¹. -1 The reaction was carried out at a temperature of 350℃ and a pressure of 4.0MPa. The catalyst was pretreated with H2 at 380℃ for 2 hours before the reaction. The results of the catalyst's metal hydroxyl content, relative silanol / metal hydroxyl content, CO2 conversion, CO selectivity, aromatic selectivity, and aromatic yield are shown in Table 1.

[0091] Comparative Example 2

[0092] Cr2O3 was prepared by precipitation. 52.66 g of chromium nitrate was dissolved in 70 mL of deionized water, and 19.91 g of ammonium carbonate was dissolved in 94.0 mL of deionized water. Under vigorous stirring, the chromium nitrate solution and the ammonium carbonate solution were added dropwise to 10 mL of deionized water at rates of 5 mL / min and 6.7 mL / min, respectively. After precipitation, the mother liquor was aged in a 70°C constant-temperature water bath for 3 h, then filtered, washed with deionized water until neutral, vacuum dried at 80°C, and calcined at 700°C for 10 h to obtain Cr2O3. High-temperature, long-term calcination removed some of the hydroxyl groups in Cr2O3. A combined catalyst was obtained by thoroughly mixing Cr2O3-700 and ZSM-5(100) (same as in Example 1) at a mass ratio of 1:1. The combined catalyst was granulated and packed into a reactor. Using a H2 / CO2 mixture with a molar ratio of 3.0 as feedstock, the reactor was flaked at a space velocity of 1200 h⁻¹. -1 The reaction was carried out at a temperature of 350℃ and a pressure of 4.0MPa. The catalyst was pretreated with H2 at 380℃ for 2 hours before the reaction. The results of the catalyst's metal hydroxyl content, relative silanol / metal hydroxyl content, CO2 conversion, CO selectivity, aromatic selectivity, and aromatic yield are shown in Table 1.

[0093] Comparative Example 3

[0094] Cr2O3 was prepared by precipitation method. 52.66 g of chromium nitrate was dissolved in 70 mL of deionized water, and 19.91 g of ammonium carbonate was dissolved in 94.0 mL of deionized water. Under vigorous stirring, the chromium nitrate solution and the ammonium carbonate solution were added dropwise to 10 mL of deionized water at a rate of 5 mL / min and 6.7 mL / min, respectively. After precipitation, the mother liquor was aged in a constant temperature water bath at 70 °C for 3 h, then filtered and washed with deionized water until neutral. The resulting filter cake was dispersed in a mixed solution of 5 times its mass of deionized water and ethanol (volume ratio of water to ethanol was 1:1), and the pH was adjusted to 7. The solution was then hydrothermally treated at 105 °C for 10 h to obtain a Cr2O3 precursor dispersion. 6.94 g of tetraethyl orthosilicate was dissolved in 24 mL of n-hexane and thoroughly mixed with a Cr2O3 precursor dispersion. The mixture was aged at 30 °C for 24 h, dried under vacuum at 80 °C, and calcined at 500 °C for 4 h to obtain modified Cr2O3 with a SiO2 shell. The mass ratio of Cr2O3 to SiO2 was 5.0, denoted as Cr2O3-SiO2(5.0). ZSM-5 molecular sieve with a Si / Al molar ratio of 100 was synthesized by hydrothermal method, denoted as ZSM-5(100) (same as Example 1). 6.94 g of tetraethyl orthosilicate was dissolved in 24 mL of n-hexane, and 10.0 g of ZSM-5(100) was added and mixed thoroughly. The mixture was aged at 30 °C for 24 h, dried under vacuum at 80 °C, and calcined at 500 °C for 4 h to obtain modified ZSM-5(100) with a shell of SiO2. The mass ratio of ZSM-5(100) to SiO2 was 5.0, and it was denoted as ZSM-5(100)-SiO2(5.0).

[0095] The catalyst was prepared by thoroughly mixing Cr2O3-SiO2(5.0) and ZSM-5(100)-SiO2(5.0) at a mass ratio of 1:1. After granulation and tableting, the catalyst was loaded into a reactor. A mixture of H2 / CO2 with a molar ratio of 3.0 was used as feed gas, and the reactor was subjected to a space velocity of 1200 h⁻¹. -1 The reaction was carried out at a temperature of 350℃ and a pressure of 4.0MPa. The catalyst was pretreated with H2 at 380℃ for 2 hours before the reaction. The results of the catalyst's metal hydroxyl content, relative silanol / metal hydroxyl content, CO2 conversion, CO selectivity, aromatic selectivity, and aromatic yield are shown in Table 1.

[0096] Comparative Example 4

[0097] Cr₂O₃ was prepared by precipitation. 52.66 g of chromium nitrate was dissolved in 70 mL of deionized water, and 19.91 g of ammonium carbonate was dissolved in 94.0 mL of deionized water. Under vigorous stirring, the chromium nitrate solution and the ammonium carbonate solution were added dropwise to 10 mL of deionized water at rates of 5 mL / min and 6.7 mL / min, respectively. After precipitation, the mother liquor was aged in a constant temperature water bath at 70 °C for 3 h, then filtered, washed with deionized water until neutral, vacuum dried at 80 °C, and calcined at 500 °C for 4 h to obtain Cr₂O₃. ZSM-5 molecular sieve with a Si / Al molar ratio of 100 was synthesized by hydrothermal method, denoted as ZSM-5(100) (same as Example 1). 6.94 g of tetraethyl orthosilicate was dissolved in 24 mL of n-hexane, and 10.0 g of ZSM-5(100) was added and mixed thoroughly. The mixture was aged at 30 °C for 24 h, vacuum dried at 80 °C, and calcined at 500 °C for 4 h to obtain modified ZSM-5(100) with a SiO2 shell. The mass ratio of ZSM-5(100) to SiO2 was 5.0, denoted as ZSM-5(100)-SiO2(5.0). Cr2O3 and ZSM-5(100)-SiO2(5.0) were thoroughly mixed at a mass ratio of 1:1 to obtain a catalyst. The catalyst was granulated and packed into a reactor. A mixture of H2 / CO2 with a molar ratio of 3.0 was used as feedstock, and the reactor was calcined at a space velocity of 1200 h⁻¹. -1 The reaction was carried out at a temperature of 350℃ and a pressure of 4.0MPa. The catalyst was pretreated with H2 at 380℃ for 2 hours before the reaction. The results of the catalyst's metal hydroxyl content, relative silanol / metal hydroxyl content, CO2 conversion, CO selectivity, aromatic selectivity, and aromatic yield are shown in Table 1.

[0098] Comparative Example 5

[0099] Cr2O3 was prepared by precipitation method: 52.66 g of chromium nitrate was dissolved in 70 mL of deionized water, and 19.91 g of ammonium carbonate was dissolved in 94.0 mL of deionized water. Under vigorous stirring, the chromium nitrate solution and the ammonium carbonate solution were added dropwise to 10 mL of deionized water at a rate of 5 mL / min and 6.7 mL / min, respectively. After precipitation, the mother liquor was aged in a constant temperature water bath at 70 °C for 3 h, then filtered and washed with deionized water until neutral. The resulting filter cake was dispersed in a mixed solution of 5 times its mass of deionized water and ethanol (volume ratio of water to ethanol was 1:1), and the pH was adjusted to 7. The solution was then hydrothermally treated at 105 °C for 10 h to obtain a Cr2O3 precursor dispersion. 6.94 g of tetraethyl orthosilicate was dissolved in 24 mL of n-hexane and thoroughly mixed with a Cr2O3 precursor dispersion. The mixture was aged at 30 °C for 24 h, vacuum dried at 80 °C, and calcined at 500 °C for 4 h to obtain modified Cr2O3 with a SiO2 shell. The mass ratio of Cr2O3 to SiO2 was 5.0, denoted as Cr2O3-SiO2(5.0). Cr2O3-SiO2(5.0) and ZSM-5(100) (same as in Example 1) were thoroughly mixed at a mass ratio of 1:1 to obtain a catalyst. The catalyst was granulated and packed into a reactor. A H2 / CO2 mixture with a molar ratio of 3.0 was used as feedstock, and the reactor was ignited at a space velocity of 1200 h⁻¹. -1 The reaction was carried out at a temperature of 350℃ and a pressure of 4.0MPa. The catalyst was pretreated with H2 at 380℃ for 2 hours before the reaction. The results of the catalyst's metal hydroxyl content, relative silanol / metal hydroxyl content, CO2 conversion, CO selectivity, aromatic selectivity, and aromatic yield are shown in Table 1.

[0100] Comparative Example 6

[0101] Cr₂O₃ was prepared by precipitation. 52.66 g of chromium nitrate was dissolved in 70 mL of deionized water, and 19.91 g of ammonium carbonate was dissolved in 94.0 mL of deionized water. Under vigorous stirring, the chromium nitrate solution and the ammonium carbonate solution were added dropwise to 10 mL of deionized water at rates of 5 mL / min and 6.7 mL / min, respectively. After precipitation, the mother liquor was aged in a 70℃ water bath for 3 h, then filtered and washed with deionized water until neutral. The resulting metal precipitate was dispersed in 5 times its mass of an ethanol solution (water to ethanol volume ratio of 1:1), and the pH was adjusted to 7 to obtain a Cr₂O₃ precursor dispersion. ZSM-5 molecular sieve with a Si / Al molar ratio of 100 was synthesized by hydrothermal method, denoted as ZSM-5(100). Based on the Cr2O3 in the Cr2O3 precursor dispersion, 10.0 g of ZSM-5(100) was added to the Cr2O3 precursor dispersion and mixed thoroughly, with a mass ratio of Cr2O3 to ZSM-5(100) of 1:1, to obtain the catalyst precursor dispersion. 13.88 g of tetraethyl orthosilicate was dissolved in 24 mL of n-hexane and mixed thoroughly with the catalyst precursor dispersion. The mixture was aged at 25 °C for 24 h, vacuum dried at 80 °C, and calcined at 500 °C for 4 h to obtain a core-shell structured catalyst with SiO2 as the shell layer. The mass ratio of the combined catalyst in the core layer to the SiO2 in the shell layer was 5.0, denoted as [Cr2O3 / ZSM-5(100)(without hydrothermal treatment, 1:1)]@SiO2(5.0).

[0102] The obtained core-shell structured catalyst was granulated and packed into a reactor, using a H2 / CO2 mixture with a molar ratio of 3.0 as feedstock, and subjected to a space velocity of 1200 h⁻¹. -1 The reaction was carried out at a temperature of 350℃ and a pressure of 4.0MPa. The catalyst was pretreated with H2 at 380℃ for 2 hours before the reaction. The results of the catalyst's metal hydroxyl content, relative silanol / metal hydroxyl content, CO2 conversion, CO selectivity, aromatic selectivity, and aromatic yield are shown in Table 1.

[0103] Table 1

[0104]

[0105]

[0106] As can be seen from the results in Table 1, the catalyst provided by this invention can suppress the reverse water-gas shift reaction. Compared with existing oxide-molecular sieve catalysts without surface treatment, or catalysts that only treat oxides or molecular sieves, it has outstanding technical effects of significantly reducing CO selectivity and increasing aromatic yield.

[0107] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A catalyst for one-step hydrogenation of CO2 to aromatics, the catalyst having a core-shell structure comprising a core layer containing at least a metal oxide and a molecular sieve and a shell layer containing silica; Taking the area of ​​the characteristic absorption peak of the metal hydroxyl group in the infrared spectrum of a catalyst with only a core layer and no shell layer as 1, the area of ​​the absorption peak of the metal hydroxyl group in the infrared spectrum of the catalyst is less than 0.

1. The relative content of silanol / metallol in the catalyst is 4.0~10.0, calculated by the ratio of the area of ​​the characteristic absorption peak of silanol to that of the characteristic absorption peak of metall in the infrared spectrum of the catalyst. The metal element in the metal oxide component of the catalyst is selected from one or more of Cr, Zr, Al, Zn, In, and Ga; the molecules in the catalyst are screened from ZSM-5.

2. The catalyst according to claim 1, characterized in that, The mass ratio of the core layer to the shell layer in the catalyst is (4:1) to (40:1); the mass ratio of the metal oxide to the molecular sieve in the core layer of the catalyst is (1:10) to (10:1).

3. The catalyst according to claim 2, characterized in that, The mass ratio of the core layer to the shell layer in the catalyst is (8:1) to (20:1).

4. The catalyst according to claim 2, characterized in that, The mass ratio of metal oxide to molecular sieve in the core layer of the catalyst is (1:3) to (3:1).

5. A method for preparing the catalyst according to any one of claims 1-4, comprising the following steps: (1) Mix the metal salt solution with the precipitant solution and age it to obtain a metal precipitate; (2) Disperse the metal precipitate from step (1) in an alcohol solution, adjust the pH of the dispersion system to 6-8, and perform hydrothermal treatment to obtain precursor dispersion I; (3) Add the molecular sieve to the precursor dispersion I in step (2) to obtain precursor dispersion II; (4) Mix precursor dispersion I and / or precursor dispersion II with silicon-modified solution, age and calcine to obtain catalyst.

6. The preparation method according to claim 5, characterized in that, The metal salt in step (1) is at least one of metal nitrate, metal acetate, metal carbonate, and metal chloride; the precipitant is at least one of ammonia, ammonium carbonate, potassium carbonate, sodium carbonate, potassium hydroxide, and sodium hydroxide.

7. The preparation method according to claim 5, characterized in that, The aging process in step (1) is carried out at 50-80°C for 1-24 hours.

8. The preparation method according to claim 5, characterized in that, In step (2), the metal precipitate and optional molecular sieve are dispersed in an alcohol solution, wherein the liquid-to-solid mass ratio is 4-30:1; wherein the volume ratio of solvent to alcohol in the alcohol solution is (1:10)-(50:1); the alcohol is selected from one or more of ethanol, propanol, isopropanol, butanol, and isobutanol.

9. The preparation method according to claim 5, characterized in that, In step (2), the hydrothermal treatment conditions are 90~120℃ for 2~20h.

10. The preparation method according to claim 5, characterized in that, The mass ratio of the molecular sieve added in step (2) and / or step (3) to the mass of the metal oxide is (1:10) to (10:1), based on the metal in precursor dispersion I as oxide.

11. The preparation method according to claim 5, characterized in that, The silicon-containing modified solution in step (4) is a mixture of a silicon-containing modifier and an organic solvent; the silicon-containing modifier is at least one of silica sol, methyl orthosilicate, ethyl orthosilicate, propyl orthosilicate, butyl orthosilicate, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, and ethyltriethoxysilane; the organic solvent is at least one of n-hexane, cyclohexane, n-heptane, and n-octane.

12. The preparation method according to claim 5, characterized in that, In step (4), a surfactant is added to the process of mixing precursor dispersion I and / or precursor dispersion II with the silicon-modified solution. The surfactant is at least one of alkyl trimethylammonium salt, dialkyl dimethylammonium salt, and alkyl dimethyl benzylammonium salt.

13. The preparation method according to claim 5, characterized in that, The aging conditions in step (4) are 12-48 h at 20-70 °C; the roasting conditions are 2-6 h at 400-600 °C.

14. The application of the catalyst according to any one of claims 1-4 in the one-step hydrogenation of CO2 to aromatics.

15. The application according to claim 14, characterized in that, The application includes: using CO2 / H2 as raw material, reacting the raw material with the catalyst to obtain a stream containing hydrocarbon products.

16. The application according to claim 15, characterized in that, The H2 / CO2 molar ratio in the feed gas is 2.0~6.0; the reaction conditions are: reaction temperature 300~550℃; reaction pressure 1.0~8.0 MPa; volume hourly space velocity 600~10000 h⁻¹ -1 .

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