Composite catalysts, their preparation methods and applications

Abstract

This invention relates to the field of catalyst technology, and discloses a composite catalyst, its preparation method, and its application. The composite catalyst comprises a molecular sieve and a cobalt-based catalyst. Based on the total amount of the composite catalyst, the molecular sieve content is 2-35 wt%, and the cobalt-based catalyst content is 65-98 wt%. The cobalt-based catalyst comprises zirconium oxide and cobalt. Based on the total amount of the cobalt-based catalyst, the cobalt element content is 5-35 wt%, and the zirconium oxide content is 65-95 wt%. Based on the total amount of zirconium oxide, the content of zirconium oxide existing in monoclinic phase is above 50%. Using the composite catalyst provided by this invention in Fischer-Tropsch synthesis, high CO conversion and high jet fuel selectivity can be achieved at relatively low reaction temperatures.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a composite catalyst, its preparation method, and its application. Background Technology

[0002] Fischer-Tropsch synthesis (CO hydrogenation) can effectively convert syngas from non-petroleum carbon resources into liquid fuels and high-value chemicals. The product distribution of Fischer-Tropsch synthesis is constrained by the traditional ASF distribution model; except for methane, the selectivity of each target product exhibits a maximum value, particularly for low-carbon hydrocarbons (C4H2O). 2-4 ), gasoline (C 5-11 ), kerosene (C 8-16 ) and diesel (C 11-20 The maximum selectivity values ​​for the target products were 58%, 48%, 41%, and 40%, respectively. Failure to effectively improve the selectivity of each target product would place enormous pressure on subsequent separation and upgrading processes and hinder the efficient execution of the Fischer-Tropsch reaction itself. Compared to gasoline and diesel, jet fuel fractions have a moderate carbon number, and achieving a balance between high jet fuel selectivity and low methane selectivity has always been a research challenge.

[0003] For many years, researchers have been dedicated to optimizing the selectivity of Fischer-Tropsch synthesis products through the rational construction of catalysts. Li et al. successfully achieved the regulation of product selectivity by modulating the acidity and pore structure of mesoporous Y-type molecular sieves using Y-type molecular sieves as supports for cobalt nanoparticles, achieving selectivity of 74%, 72%, and 58% for gasoline, jet fuel, and diesel fractions, respectively (Nat. Catal. 2017, 1(10): 787-793). Wang et al. synthesized ZSM-5 molecular sieves with different acidities and mesoporous pore volumes by changing the concentration of TPAOH solution, and then loaded CoMn as the active component. They found that the molecular sieve treated with 0.5 M TPAOH solution had the largest mesoporous pore volume and suitable Brønsted acidity, achieving a selectivity of up to 50% for jet fuel (Ind. Eng. Chem. Res. 2021, 60, 5783-5791). Yang et al. prepared Y-modified β-zeolites using ion exchange and found that Co / Y-β catalysts with appropriate Y ratios could exhibit a jet fuel selectivity of 41.2% (Sustain. Energy Fuels 2020, 4 (7): 3528-3536). Cai et al. prepared SBA-15 zeolites with different Al / Si ratios and found that when the Al / Si ratio was 0.01, the cobalt-based catalyst could achieve a jet fuel selectivity as high as 52.4% (Ind. Eng. Chem. Res. 2018, 57, 3844−3854). Based on the results of existing literature, the Fischer-Tropsch synthesis technology for high-selectivity jet fuel preparation still has the inherent drawback of being difficult to achieve both high CO conversion and high jet fuel selectivity, and the reaction temperature is relatively high (250-260°C). How to achieve high-selectivity synthesis of jet fuel at low temperatures requires further research. Summary of the Invention

[0004] The purpose of this invention is to overcome the aforementioned problems in the prior art and provide a composite catalyst, its preparation method, and its application. When the composite catalyst provided by this invention is applied to Fischer-Tropsch synthesis, it can achieve both high CO conversion and high jet fuel selectivity at relatively low reaction temperatures.

[0005] To achieve the above objectives, the first aspect of the present invention provides a composite catalyst comprising a molecular sieve and a cobalt-based catalyst. Based on the total amount of the composite catalyst, the content of the molecular sieve is 2-35 wt%, the content of the cobalt-based catalyst is 65-98 wt%, and the cobalt-based catalyst comprises zirconium oxide and cobalt. Based on the total amount of the cobalt-based catalyst, the content of cobalt is 5-35 wt%, and the content of zirconium oxide is 65-95 wt%. Based on the total amount of zirconium oxide, the content of zirconium oxide existing in monoclinic phase is above 50%.

[0006] Preferably, the molecular sieve is a β molecular sieve.

[0007] The second aspect of the present invention provides a method for preparing the above-mentioned composite catalyst, the method comprising: mixing and grinding a molecular sieve and a cobalt-based catalyst, and then molding them; or, molding and pulverizing the molecular sieve and the cobalt-based catalyst separately, and then mixing them.

[0008] A third aspect of the present invention provides the application of the above-mentioned composite catalyst in the Fischer-Tropsch synthesis reaction, preferably in the Fischer-Tropsch synthesis reaction to produce jet fuel.

[0009] This invention obtains a composite catalyst by mixing a supported cobalt-based catalyst with a molecular sieve phase, which effectively achieves high selectivity in the preparation of jet fuel at 220°C. By adjusting the composite ratio and method, the ratio, proximity, and synergistic mechanism of metal active sites and acidic sites can be effectively changed, which is beneficial to changing the secondary isomerization cracking effect of heavy hydrocarbon products. As a result, the catalyst exhibits excellent selectivity for jet fuel fractions. The composite catalyst provided by this invention is a highly promising catalyst for the high-selectivity preparation of jet fuel. Attached Figure Description

[0010] Figure 1 These are the XRD patterns of zirconium oxide from Examples 1, 5, and Comparative Example 1. Detailed Implementation

[0011] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0012] The first aspect of this invention provides a composite catalyst comprising a molecular sieve and a cobalt-based catalyst. Based on the total amount of the composite catalyst, the molecular sieve content is 2-35 wt%, the cobalt-based catalyst content is 65-98 wt%, and the cobalt-based catalyst comprises zirconium oxide and cobalt. Based on the total amount of the cobalt-based catalyst, the cobalt element content is 5-35 wt%, and the zirconium oxide content is 65-95 wt%. Based on the total amount of zirconium oxide, the zirconium oxide content existing in monoclinic phase is above 50%.

[0013] In this invention, the contents of molecular sieves, cobalt, and zirconium oxide were determined by XRF testing. The type of molecular sieve was determined by X-ray diffraction (XRD).

[0014] In this invention, the crystal form of the zirconium oxide can be determined by X-ray diffraction (XRD). In the XRD pattern of standard monoclinic zirconium oxide (m-ZrO2), the characteristic diffraction peaks at 2θ of 24.1°, 27.9°, and 31.4° can be attributed to (110) of m-ZrO2, respectively. (111) crystal plane (JCPDS 001-0750); In the XRD pattern of standard tetragonal zirconia (t-ZrO2), the characteristic diffraction peaks at 2θ of 30.5°, 35.6°, 51.0°, and 60.5° can be attributed to the (101), (110), (200), and (211) crystal planes of t-ZrO2 (JCPDS 002-0733), respectively. Through the formula... ×100%, the content of monoclinic zirconium oxide was calculated ( X m ).in, and These represent m-ZrO2 in the XRD pattern. The fitting intensity (fitting peak area) of the (111) crystal plane. The fitting intensity (fitting peak area) of the t-ZrO2 (101) crystal plane in the XRD spectrum represents the fitting intensity (fitting peak area).

[0015] According to a preferred embodiment of the present invention, based on the total amount of the composite catalyst, the content of the molecular sieve is 10-20 wt%, and the content of the cobalt-based catalyst is 80-90 wt%. This preferred embodiment is more conducive to achieving both high CO conversion and jet fuel selectivity in the catalyst. When the molecular sieve content is low, the content of heavy hydrocarbons in the Fischer-Tropsch reaction products is high, and the jet fuel selectivity is low. When the molecular sieve content is high, the cobalt-based active sites may be covered by the molecular sieve, leading to a significant decrease in CO conversion.

[0016] Preferably, the total acid content of the composite catalyst is 50-400 μmol / g, more preferably 100-300 μmol / g. In this invention, the total acid content of the composite catalyst is determined by ammonia-programmed temperature desorption (NH3-TPD). Specifically, 200 mg of a 40-60 mesh sample is weighed and placed in a reaction tube, and heated to 400°C at a rate of 10 °C / min under a high-purity He atmosphere and held for 2 hours. This pretreatment process is to remove surface-adsorbed water and other impurities. Subsequently, the temperature is lowered to 100°C, and the atmosphere is switched to an NH3 / He mixture (NH3 volume ratio of 5%) for pulse adsorption until saturation. Finally, the atmosphere is switched back to He gas for purging, and after the baseline stabilizes, the temperature is increased to 600°C at a rate of 10 °C / min to collect data.

[0017] There is no particular limitation on the shape of the composite catalyst, as long as it meets the above composition. It can be adapted to the specific application. Preferably, the composite catalyst is a particulate catalyst with a particle size of 20-40 mesh.

[0018] This invention allows for a wide range of molecular sieve types. Preferably, the molecular sieve is selected from at least one of β-molecular sieve, Y-molecular sieve, and ZSM-5 molecular sieve, and more preferably, β-molecular sieve. During their research, the inventors discovered that combining β-molecular sieve with the cobalt-based catalyst is more beneficial for improving the CO conversion rate and jet fuel selectivity of the composite catalyst under low-temperature conditions.

[0019] Preferably, the SiO2 / Al2O3 molar ratio of the molecular sieve is 3-200, more preferably 10-90.

[0020] Preferably, the molecular sieve is a Y molecular sieve, and the SiO2 / Al2O3 molar ratio of the Y molecular sieve is 4-10.

[0021] Preferably, the molecular sieve is a ZSM-5 molecular sieve, and the SiO2 / Al2O3 molar ratio of the ZSM-5 molecular sieve is 30-150.

[0022] Preferably, the molecular sieve is a β molecular sieve, the β molecular sieve is an all-silica molecular sieve, or its SiO2 / Al2O3 molar ratio is 10-90, more preferably 20-80.

[0023] According to a preferred embodiment of the present invention, the mesoporous pore volume of the β molecular sieve accounts for 20-100% of the total pore volume, preferably 30-60%.

[0024] The mesopore volume and total pore volume of the β molecular sieve were obtained by nitrogen physical adsorption-desorption test.

[0025] According to a preferred embodiment of the present invention, the β molecular sieve has a medium-strong acid content of 200-850 μmol / g, preferably 500-700 μmol / g.

[0026] The acid content of the medium-strong acid in the β-zeolite was obtained by NH3-TPD testing. Specifically, 200 mg of 40-60 mesh sample was weighed and placed in a reaction tube. The sample was heated to 400°C at a rate of 10 °C / min under a high-purity He atmosphere and held for 2 hours. This pretreatment was to remove surface-adsorbed water and other impurities. The temperature was then lowered to 100°C, and the atmosphere was switched to an NH3 / He mixture (NH3 volume ratio of 5%) for pulse adsorption until saturation. Finally, the atmosphere was switched back to He gas for purging, and after the baseline stabilized, the temperature was increased to 600°C at a rate of 10 °C / min to collect data. The acid content of the medium-strong acid could be calculated from the high-temperature desorption peak (desorption temperature greater than 300°C) after peak separation of the NH3-TPD spectrum.

[0027] According to a preferred embodiment of the present invention, the specific surface area of ​​the β molecular sieve is 400-800 m². 2 / g, preferably 450-650 m 2 / g.

[0028] In this invention, the specific surface area is obtained by nitrogen physical adsorption-desorption test.

[0029] The present invention uses β molecular sieves with specific mesoporous pore volume ratio, specific surface area and medium-strong acid content, combined with cobalt-based catalysts, which is more conducive to promoting the diffusion of intermediate species and products and secondary reactions, thereby effectively improving the selectivity of jet fuel fractions.

[0030] The present invention does not have any particular limitation on the source of the molecular sieve, which can be obtained commercially or prepared by existing methods.

[0031] According to a preferred embodiment of the present invention, based on the total amount of cobalt-based catalyst, the cobalt content is 16-30 wt%, for example, 16 wt%, 18 wt%, 20 wt%, 22 wt%, 24 wt%, 26 wt%, 28 wt%, or 30 wt%, and the zirconium oxide content is 70-84 wt%, for example, 70 wt%, 72 wt%, 74 wt%, 76 wt%, 78 wt%, 80 wt%, 82 wt%, or 84 wt%.

[0032] According to the present invention, the cobalt-based catalyst is preferably composed of zirconium oxide and the active component cobalt.

[0033] The present invention does not particularly limit the form in which cobalt exists. It can exist in an oxidized state, a reduced state, or a partially oxidized and partially reduced state. Catalysts containing cobalt in different forms are all within the protection scope of the present invention.

[0034] In this invention, preferably, the content of zirconium oxide existing in monoclinic phase is 70-100% based on the total amount of zirconium oxide. This preferred embodiment is more conducive to improving the CO conversion rate and jet fuel selectivity of the composite catalyst.

[0035] According to a preferred embodiment of the present invention, the method for preparing the cobalt-based catalyst includes the following steps:

[0036] (1) Zirconia was prepared by hydrothermal method;

[0037] (2) The cobalt precursor is introduced into the zirconium oxide by impregnation, followed by drying and calcination.

[0038] The present invention does not have any particular limitation on the method of preparing zirconium oxide by hydrothermal method in step (1), as long as the zirconium oxide with the crystal form described above can be obtained. Preferably, step (1) includes: reacting zirconium salt precursor solution and precipitant under hydrothermal conditions, and then drying and calcining.

[0039] Preferably, the zirconium salt precursor includes at least one selected from zirconium nitrate, zirconium oxynitrate, zirconium oxychloride, zirconium chloride, and zirconium acetate. This invention uses zirconium oxynitrate as an example for illustrative purposes, but the invention is not limited thereto.

[0040] According to the present invention, preferably, the solvent in the zirconium salt precursor solution includes water and optionally an alcohol, with the water content being 90-100% by volume based on the total amount of solvent. By controlling the water content in the solvent, it is more advantageous to obtain a catalyst with improved performance.

[0041] The present invention has a wide range of choices for the alcohols, and various alcohols commonly used can be used in the present invention, such as C1-C5 alcohols, including but not limited to methanol, ethanol or propanol, with methanol being preferred.

[0042] Preferably, the precipitant is selected from at least one of urea, ammonia, ammonium carbonate and hexadecyltrimethylammonium chloride, more preferably urea.

[0043] According to the present invention, preferably, the molar ratio of the precipitant to the zirconium salt precursor is 3-30, more preferably 8-12.

[0044] According to the present invention, preferably, the hydrothermal conditions include: a hydrothermal temperature of 100-250 °C, more preferably 120-200 °C; and a hydrothermal time of 10-30 hours, more preferably 20-24 hours. The hydrothermal conditions of this preferred embodiment are more conducive to obtaining perfectly crystalline zirconia and to improving the Fischer-Tropsch synthesis performance of the catalyst.

[0045] According to the present invention, the hydrothermal reaction is carried out under closed conditions. The present invention does not particularly limit the equipment used for carrying out the hydrothermal reaction; for example, it can be a hydrothermal reactor, including but not limited to a polytetrafluoroethylene liner within a stainless steel hydrothermal reactor, which is then sealed and placed in an oven for the reaction.

[0046] Preferably, the calcination conditions in step (1) include: a calcination temperature of 300-700°C, preferably 400-500°C; a calcination time of 2-10 hours, preferably 3-8 hours; a calcination heating rate of 1-5 °C / min; and preferably an atmosphere of air, nitrogen, or argon.

[0047] According to the present invention, preferably, before the calcination in step (1), the hydrothermal reaction product is further washed and dried. The washing and drying methods and conditions can be carried out according to conventional techniques in the art. Preferably, in the washing method, after the hydrothermal process is completed, the supernatant is discarded, and the precipitate is washed repeatedly with water and ethanol multiple times, for example, 2-10 times. Preferably, the drying method is forced-air drying or vacuum drying; the drying temperature is 50-150°C, preferably 80-120°C; and the drying time is 4-48 hours, preferably 8-16 hours.

[0048] According to the present invention, preferably, the method further includes grinding the dried product after drying in step (1) and then calcining it.

[0049] By controlling the solvent, hydrothermal reaction conditions, precipitant, and zirconium precursor ratio in the above zirconium oxide process, the zirconium oxide crystal phase type and ratio can be effectively controlled, resulting in a catalyst with better Fischer-Tropsch synthesis performance.

[0050] In this invention, there is no particular limitation on the impregnation method. It can be impregnation of equal volume or impregnation of excess volume, but it is preferred to impregnate of equal volume.

[0051] According to a preferred embodiment of the present invention, the introduction of a cobalt precursor into the zirconium oxide by impregnation specifically includes: impregnating the zirconium oxide with an impregnation solution containing the cobalt precursor, and then performing the drying and calcination described in step (2).

[0052] The present invention does not particularly limit the type of cobalt precursor, but preferably, the cobalt precursor is selected from at least one of cobalt nitrate, cobalt acetate and cobalt chloride.

[0053] Those skilled in the art can select the concentration of the impregnation solution containing the cobalt precursor based on the target cobalt content.

[0054] The present invention has a wide range of choices for the drying method and conditions in step (2). Preferably, the drying method is blower drying or vacuum drying, the drying temperature is 50-150°C, preferably 80-120°C, and the drying time is 4-48 hours, preferably 8-16 hours.

[0055] According to the present invention, preferably, the calcination conditions in step (2) include: a calcination temperature of 300-500 °C, preferably 350-450 °C; a calcination time of 2-8 hours, preferably 4-6 hours; a calcination heating rate of 1-5 °C / min; and preferably an atmosphere of air, nitrogen, argon or nitric oxide.

[0056] In this invention, the roasting in steps (1) and (2) can be carried out independently in a tube furnace or a muffle furnace.

[0057] According to a preferred embodiment of the present invention, the calcination temperature during the zirconium oxide preparation process (i.e., the calcination temperature described in step (1)) does not exceed 500 °C, and the calcination temperature after cobalt loading (i.e., the calcination temperature described in step (2)) is not higher than the calcination temperature during the zirconium oxide preparation process. More preferably, the calcination temperature during the zirconium oxide preparation process is 400-500 °C, and the calcination temperature after cobalt loading is 0-100 °C lower than the calcination temperature during the zirconium oxide preparation process. The preferred method of using the carrier calcination conditions can ensure the stability of the zirconium oxide crystal phase and pore structure of the carrier, and the preferred method of using the calcination conditions after cobalt loading can ensure the stability of the carrier after cobalt loading. If the above preferred range is not met, for example, if the calcination temperature of the carrier is too high, it will cause the collapse of the pore structure and a significant decrease in the specific surface area, thereby affecting the subsequent cobalt dispersion. If the calcination temperature after cobalt loading is too high, it will damage the carrier structure and cause cobalt particles to agglomerate.

[0058] This invention does not particularly limit the preparation method of the composite catalyst, and can use various methods conventionally used in the art. This invention provides a method for preparing the composite catalyst described in the first aspect above, which includes: mixing and grinding a molecular sieve and a cobalt-based catalyst, and then molding them; or, molding and pulverizing the molecular sieve and the cobalt-based catalyst separately, and then mixing them. Preferably, the preparation method of the composite catalyst includes: mixing and grinding a molecular sieve and a cobalt-based catalyst, and then molding them. In this preferred embodiment, mixing the molecular sieve and the cobalt-based catalyst, and then grinding and molding them together, is more conducive to the effective contact between the metal active sites and the acidic sites of the molecular sieve, thus more conducive to improving the CO conversion rate and jet fuel selectivity of the prepared composite catalyst.

[0059] According to a specific embodiment of the present invention, the preparation method includes: mixing molecular sieve powder and cobalt-based catalyst powder in a certain proportion, grinding (which can be done in a mortar or ball mill) until uniform, then molding and pulverizing, and finally sieving to obtain a composite catalyst with a particle size that meets the requirements.

[0060] In the method provided by the present invention, the molding can be any of the molding methods conventionally used in the art, such as tablet molding, extrusion molding, and preferably tablet molding.

[0061] According to another specific embodiment of the present invention, the preparation method includes: molding and crushing molecular sieve powder and cobalt-based catalyst powder respectively, sieving them, and then physically mixing the two types of particles with the same mesh size in a certain proportion to obtain a composite catalyst.

[0062] According to a preferred embodiment of the present invention, the preparation method of the composite catalyst further includes a reduction step. The reduction is primarily a reduction of the cobalt-based catalyst. This reduction can be carried out during the preparation of the cobalt-based catalyst, i.e., in step (2), a cobalt precursor is introduced into the zirconium oxide using an impregnation method, followed by drying and calcination, and then reduction. Alternatively, reduction can be carried out after mixing with molecular sieves. Preferably, the reduction is carried out after mixing with molecular sieves.

[0063] According to a preferred embodiment of the present invention, the reduction conditions preferably include: being carried out in a hydrogen-containing atmosphere, a reduction temperature of 300-500 °C, preferably 400-450 °C, a pressure of 0.1-1 MPa, preferably 0.1-0.5 MPa, and a time of 3-15 hours, preferably 5-10 hours. More preferably, the hydrogen-containing atmosphere is a pure hydrogen atmosphere.

[0064] According to the present invention, preferably, the reduction temperature of the cobalt-based catalyst or composite catalyst is not lower than 350°C and not higher than the calcination temperature after cobalt loading during the preparation of the cobalt-based catalyst, and more preferably 0-50°C lower. This preferred embodiment is more advantageous for improving the CO conversion rate and jet fuel selectivity of the catalyst.

[0065] A third aspect of this invention provides the application of the above-described composite catalyst in the Fischer-Tropsch synthesis reaction, preferably in the Fischer-Tropsch synthesis reaction to produce jet fuel. Using the composite catalyst provided by this invention in the Fischer-Tropsch synthesis reaction results in improved CO conversion and jet fuel selectivity.

[0066] The present invention does not particularly limit the composition of the jet fuel, and has conventional illustrations, for example, the jet fuel has 8-16 carbon atoms.

[0067] Preferably, the conditions for the Fischer-Tropsch synthesis reaction include: an H2 / CO volume ratio of 1-2 in the reactant gas, a reaction temperature of 200-250°C, preferably 210-230°C, a reaction pressure of 1.5-4 MPa, and a reaction volume hourly space velocity of 1000-10000 h⁻¹. -1 The composite catalyst provided by this invention can reduce the temperature of the Fischer-Tropsch synthesis reaction to a certain extent, for example, it can achieve highly selective preparation of jet fuel at 220°C.

[0068] The present invention will be described in detail below through embodiments.

[0069] In the following examples and comparative examples, the crystal form and content of each crystal form of the zirconium oxide were determined by X-ray diffraction (XRD). The total acidity of the composite catalyst was determined by NH3-TPD. The mesopore volume and total pore volume of the molecular sieve were obtained by nitrogen physical adsorption-desorption test. The acidity of the medium-strong acid in the molecular sieve was obtained by NH3-TPD test. Specific test conditions are as described in the detailed embodiments section above and will not be repeated here.

[0070] The contents of molecular sieve, cobalt, and zirconium oxide were calculated using the feed ratio.

[0071] Example 1

[0072] (1) Preparation of the support zirconium oxide: Weigh 7.376 g of zirconium nitrate, dissolve it in 150 mL of deionized water, stir evenly, then add 15.4 g of urea, stir the mixture evenly, pour it into a 200 mL polytetrafluoroethylene liner, seal the stainless steel reactor, and place it in an oven at 160 °C for 24 hours. After the reactor cools down, discard the supernatant, wash the precipitate repeatedly with water and ethanol more than 5 times, and dry it in a forced-air oven at 120 °C for 12 hours. Grind the dried powder, calcine it in a muffle furnace, introduce air, raise the temperature to 400 °C at a rate of 2 °C / min, and calcine at 400 °C for 3 hours to obtain the support named Z1. Its XRD pattern is shown below. Figure 1 As shown, from Figure 1 It can be seen that pure monoclinic zirconium oxide can be obtained by using pure water as a solvent.

[0073] (2) Preparation of supported cobalt-based catalyst: Take 2g of Z1 and measure its water absorption rate. Then, calculate the amount of cobalt nitrate and deionized water according to the water absorption rate and cobalt loading (16 wt%). Add the prepared cobalt nitrate solution dropwise to Z1. After the excess solvent is evaporated by rotary evaporation, dry it in an oven at 120 °C and then put it into a tube furnace. Air is introduced and the temperature is raised to 400 °C at a heating rate of 2 °C / min. Keep it for 4 hours to obtain the C1 catalyst.

[0074] (3) Preparation of composite catalyst: C1 powder and β molecular sieve powder (properties shown in Table 1) were physically mixed at a mass ratio of 9 / 1, ground evenly in a mortar, and then pressed into tablets and pulverized and sieved to 20-40 mesh to obtain the final catalyst, named M1. The total acid content of the composite catalyst is listed in Table 1.

[0075] Example 2

[0076] (1) Preparation of carrier zirconia: Same as in Example 1.

[0077] (2) Preparation of supported cobalt-based catalyst: Take 2g of Z1 and measure its water absorption rate. Then, calculate the amount of cobalt nitrate and deionized water according to the water absorption rate and cobalt loading (25 wt%). Add the prepared cobalt nitrate solution dropwise to Z1. After the excess solvent is evaporated by rotary evaporation, dry it in an oven at 120 °C and then put it into a tube furnace. Air is introduced and the temperature is raised to 400 °C at a heating rate of 2 °C / min. Keep it for 4 hours to obtain the C2 catalyst.

[0078] (3) Preparation of composite catalyst: C2 powder and β molecular sieve powder (properties shown in Table 1) were physically mixed at a mass ratio of 4 / 1, ground evenly in a mortar, and then pressed into tablets and pulverized and sieved to 20-40 mesh to obtain the final catalyst, named M2. The total acid content of the composite catalyst is listed in Table 1.

[0079] Example 3

[0080] C1 was prepared according to the method in Example 1, except that C1 powder and β molecular sieve powder were mixed in a 2 / 1 mass ratio, and the resulting catalyst was named M3.

[0081] Example 4

[0082] C1 was prepared according to the method in Example 1, except that C1 powder and β molecular sieve powder were respectively pressed into tablets and pulverized and sieved to obtain two kinds of particles with a mesh size of 20-40. The two kinds of particles were then physically mixed in a mass ratio of 9 / 1 to obtain the final catalyst M4.

[0083] Example 5

[0084] (1) Preparation of the support zirconia: Following the method of Example 1, except that the hydrothermal treatment used a mixed solution (water and methanol volume ratio of 10 / 90), the support was named Z2, and its XRD pattern is shown below. Figure 1 As shown, from Figure 1 It can be seen that Z2 exhibits characteristic diffraction peaks of both monoclinic and tetragonal zirconium oxide phases. Calculations show that the monoclinic phase accounts for 70.4%.

[0085] (2) Preparation of supported cobalt-based catalyst: Take 2g of Z2 and measure its water absorption rate. Then, calculate the amount of cobalt nitrate and deionized water according to the water absorption rate and cobalt loading (16 wt%). Add the prepared cobalt nitrate solution dropwise to Z2. After the excess solvent is evaporated by rotary evaporation, dry it in an oven at 120 °C and then put it into a tube furnace. Air is introduced and the temperature is raised to 400 °C at a heating rate of 2 °C / min. Keep it for 4 hours to obtain the C3 catalyst.

[0086] (3) Preparation of composite catalyst: C3 powder and β molecular sieve powder (properties are shown in Table 1) are physically mixed in a mass ratio of 9 / 1, ground evenly in a mortar, and then pressed into tablets and pulverized and sieved to 20-40 mesh to obtain the final catalyst named M5.

[0087] Example 6

[0088] The method of Example 1 was followed, except that the β molecular sieve was replaced with an equal mass of HY molecular sieve, and the resulting catalyst was named M6.

[0089] Comparative Example 1

[0090] (1) Preparation of the support zirconium oxide: Weigh 7.376 g of zirconium nitrate, dissolve it in 150 mL of methanol, stir evenly, then add 15.4 g of urea, stir the mixture evenly, pour it into a 200 mL polytetrafluoroethylene liner, seal the stainless steel reactor, and place it in an oven for hydrothermal treatment at 160 °C for 24 hours. After the reactor cools down, discard the supernatant, wash the precipitate repeatedly with water and ethanol more than 5 times, and dry it in a forced-air oven at 120 °C for 12 hours. Grind the dried powder, calcine it in a muffle furnace, introduce air, raise the temperature to 400 °C at a rate of 2 °C / min, and calcine at 400 °C for 3 hours to obtain the support named Z3. Its XRD pattern is shown below. Figure 1 As shown, from Figure 1 It can be seen that the tetragonal zirconium oxide prepared using pure methanol solvent is pure.

[0091] (2) Preparation of supported cobalt-based catalyst: Take 2g of Z3 and measure its water absorption rate. Then, calculate the amount of cobalt nitrate and deionized water according to the water absorption rate and cobalt loading (16 wt%). Add the prepared cobalt nitrate solution dropwise to Z3. After the excess solvent is evaporated by rotary evaporation, dry it in an oven at 120 °C and then put it into a tube furnace. Air is introduced and the temperature is raised to 400 °C at a heating rate of 2 °C / min. Keep it for 4 hours to obtain C4 catalyst.

[0092] (3) Preparation of composite catalyst: C4 powder and β molecular sieve powder (properties shown in Table 1) were physically mixed at a mass ratio of 9 / 1, ground evenly in a mortar, and then pressed into tablets and pulverized and sieved to 20-40 mesh to obtain the final catalyst, named M7. The total acid content of the composite catalyst is listed in Table 1.

[0093] Table 1

[0094]

[0095] Test case

[0096] The performance of the catalysts prepared in the above examples and comparative examples was evaluated.

[0097] Using the cobalt-based catalyst prepared in the examples and comparative examples as the calculation basis, 1g of cobalt-based catalyst (20-40 mesh) was taken and mixed with quartz sand at a ratio of 1:10. This mixture was then packed into a fixed-bed reactor with a reaction tube inner diameter of 18 mm and a constant-temperature zone length of 40 mm. Subsequently, the catalyst was reduced in situ using pure hydrogen gas at a reduction temperature of 400°C, a pressure of 0.1 MPa, and a reduction time of 10 hours. The Fischer-Tropsch reaction feedstock gas had an H2 / CO volume ratio of 2, a reaction temperature of 220°C, a reaction pressure of 2 MPa, and a reaction volume hourly space velocity (based on the cobalt-based catalyst) of 4800 h⁻¹. -1 The feed gas and reaction gaseous products were analyzed online using an Agilent 7890A gas chromatograph, while the liquid products were collected, separated, and weighed using both hot and cold traps before offline analysis. All performance evaluation results are shown in Table 2.

[0098] Table 2 Fischer-Tropsch performance of composite catalysts

[0099]

[0100] As shown in Table 2, the jet fuel selectivity of Examples 1-3 is as high as 59-62%, indicating that the addition of molecular sieves can effectively control the secondary cracking of heavy hydrocarbons to generate middle fractions. However, in Example 3, the molecular sieve content is 33%, which may affect the contact between the active sites and reactant molecules in the cobalt-based catalyst, thus significantly reducing its selectivity. In Example 4, the performance tested by particle mixing showed that the CO conversion rate and jet fuel selectivity were significantly lower than those of the powder-mixed catalyst, indicating that the contact mode between the molecular sieve and the metal catalyst in the composite catalyst has a significant impact on catalytic performance. This is because the proximity of the acidic sites on the molecular sieve and the metal active sites on the metal catalyst affects the secondary reaction of intermediate products. If the distance between the two sites increases during particle mixing, it is not conducive to the formation of middle fractions. Compared with β molecular sieves, HY molecular sieves have significantly reduced amounts of medium-strong acids and a lower proportion of mesopores, which is not conducive to the cracking and diffusion of intermediate species. Therefore, at a lower reaction temperature, Example 6 exhibits poor CO conversion rate and jet fuel selectivity. When pure methanol is used as a solvent, pure tetragonal zirconium oxide is obtained. This catalyst exhibits a relatively low CO conversion rate, indicating that using tetragonal zirconium oxide as a support is not conducive to improving the performance of the Fischer-Tropsch reaction.

[0101] The preferred embodiments of the present invention have been described in detail above; however, 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 combinations of 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 composite catalyst, characterized in that, The composite catalyst comprises molecular sieves and cobalt-based catalysts. Based on the total amount of the composite catalyst, the molecular sieve content is 2-35 wt%, the cobalt-based catalyst content is 65-98 wt%, and the cobalt-based catalyst comprises zirconium oxide and cobalt. Based on the total amount of the cobalt-based catalyst, the cobalt element content is 5-35 wt%, and the zirconium oxide content is 65-95 wt%. Based on the total amount of zirconium oxide, the zirconium oxide content existing in monoclinic phase is above 50%. The molecular sieve is a β molecular sieve; The mesoporous pore volume of the β-molecular sieve accounts for 20-100% of the total pore volume; The β molecular sieve has a medium-strong acid content of 200-850 μmol / g.

2. The composite catalyst according to claim 1, wherein, Based on the total amount of the composite catalyst, the content of the molecular sieve is 10-20 wt%, and the content of the cobalt-based catalyst is 80-90 wt%.

3. The composite catalyst according to claim 1, wherein, The total acid content of the composite catalyst is 50-400 μmol / g.

4. The composite catalyst according to claim 3, wherein, The total acidity of the composite catalyst is 100-300 μmol / g.

5. The composite catalyst according to claim 1, wherein, The composite catalyst is a particulate catalyst with a particle size of 20-40 mesh.

6. The composite catalyst according to claim 1, wherein, The SiO2 / Al2O3 molar ratio of the molecular sieve is 3-200.

7. The composite catalyst according to claim 6, wherein, The SiO2 / Al2O3 molar ratio of the molecular sieve is 10-90.

8. The composite catalyst according to claim 1, wherein, The mesoporous pore volume of the β molecular sieve accounts for 30-60% of the total pore volume; And / or, the amount of the medium-strong acid in the β-zeolite is 500-700 μmol / g; And / or, the specific surface area of ​​the β molecular sieve is 400-800 m². 2 / g; And / or, the β molecular sieve is an all-silica molecular sieve, or its SiO2 / Al2O3 molar ratio is 20-80.

9. The composite catalyst according to claim 8, wherein, The specific surface area of ​​the β molecular sieve is 450-650 m². 2 / g.

10. The composite catalyst according to claim 1, wherein, Based on the total amount of cobalt-based catalyst, the cobalt content is 16-30 wt%, and the zirconium oxide content is 70-84 wt%. And / or, based on the total amount of zirconium oxide, the content of zirconium oxide existing in the monoclinic phase is 70-100%.

11. The composite catalyst according to claim 1, wherein, The preparation method of the cobalt-based catalyst includes the following steps: (1) Zirconia was prepared by hydrothermal method; (2) The cobalt precursor is introduced into the zirconium oxide by impregnation, followed by drying and calcination.

12. The composite catalyst according to claim 11, wherein, Step (1) includes reacting the zirconium salt precursor solution and the precipitant under hydrothermal conditions, followed by drying and calcination.

13. The composite catalyst according to claim 12, wherein, The zirconium salt precursor includes at least one of zirconium nitrate, zirconium oxynitrate, zirconium oxychloride, zirconium chloride, and zirconium acetate.

14. The composite catalyst according to claim 12, wherein, The solvent in the zirconium salt precursor solution includes water and optional alcohol, with the water content being 90-100% by volume based on the total amount of solvent.

15. The composite catalyst according to claim 12, wherein, The precipitant is selected from at least one of urea, ammonia, ammonium carbonate, and hexadecyltrimethylammonium chloride.

16. The composite catalyst according to claim 12, wherein, The molar ratio of the precipitant to the zirconium salt precursor is 3-30.

17. The composite catalyst according to claim 16, wherein, The molar ratio of the precipitant to the zirconium salt precursor is 8-12.

18. The composite catalyst according to claim 12, wherein, The hydrothermal conditions include: a hydrothermal temperature of 100-250°C and a hydrothermal time of 10-30 hours.

19. The composite catalyst according to claim 18, wherein, The hydrothermal conditions include: a hydrothermal temperature of 120-200°C and a hydrothermal time of 20-24 hours.

20. The composite catalyst according to claim 12, wherein, The drying conditions include using forced-air drying or vacuum drying, with a drying temperature of 50-150°C and a drying time of 4-48 hours.

21. The composite catalyst according to claim 20, wherein, The drying conditions include using forced-air drying or vacuum drying, with a drying temperature of 80-120 °C and a drying time of 8-16 hours.

22. The composite catalyst according to claim 12, wherein, The calcination conditions in step (1) include: calcination temperature of 300-700°C; calcination time of 2-10 hours; calcination heating rate of 1-5 °C / min; and atmosphere of air, nitrogen or argon.

23. The composite catalyst according to claim 22, wherein, The roasting conditions in step (1) include: roasting temperature of 400-500°C; roasting time of 3-8 hours.

24. The composite catalyst according to claim 11, wherein, The calcination conditions in step (2) include: calcination temperature of 300-500°C; calcination time of 2-8 hours; calcination heating rate of 1-5 °C / min; and atmosphere of air, nitrogen, argon or nitric oxide.

25. The composite catalyst according to claim 24, wherein, The roasting conditions in step (2) include: roasting temperature of 350-450℃; roasting time of 4-6 hours.

26. The composite catalyst according to claim 1, wherein, The calcination temperature during the zirconium oxide preparation process does not exceed 500 °C, and the calcination temperature after cobalt loading is not higher than the calcination temperature during the zirconium oxide preparation process.

27. The composite catalyst according to claim 26, wherein, The calcination temperature during the preparation of zirconium oxide is 400-500°C, and the calcination temperature after loading cobalt is 0-100°C lower than the calcination temperature during the preparation of zirconium oxide.

28. A method for preparing the composite catalyst according to any one of claims 1-27, the method comprising: The molecular sieve and cobalt-based catalyst are mixed and ground, and then shaped; or the molecular sieve and cobalt-based catalyst are shaped and crushed separately, and then mixed.

29. The preparation method according to claim 28, wherein, The preparation method further includes reducing the obtained composite catalyst.

30. The preparation method according to claim 29, wherein, The reduction conditions include: being carried out in a hydrogen-containing atmosphere, at a reduction temperature of 300-500 °C, a pressure of 0.1-1 MPa, and a time of 3-15 hours.

31. The preparation method according to claim 30, wherein, The reduction conditions include: being carried out in a hydrogen-containing atmosphere, at a reduction temperature of 400-450 °C, a pressure of 0.1-0.5 MPa, and a time of 5-10 hours.

32. The preparation method according to claim 29, wherein, The reduction temperature of the composite catalyst is not lower than 350°C and not higher than the calcination temperature after cobalt loading during the preparation of the cobalt-based catalyst.

33. The preparation method according to claim 32, wherein, The reduction temperature of the composite catalyst is 0-50°C lower than the calcination temperature after cobalt loading in the preparation process of cobalt-based catalysts.

34. The use of the composite catalyst according to any one of claims 1-27 in the Fischer-Tropsch synthesis reaction.

35. The application according to claim 34, wherein, The Fischer-Tropsch synthesis reaction is the Fischer-Tropsch synthesis reaction for producing jet fuel.

36. The application according to claim 34, wherein, The conditions for the Fischer-Tropsch synthesis reaction include: an H2 / CO volume ratio of 1-2 in the reactant gas, a reaction temperature of 200-250°C, a reaction pressure of 1.5-4 MPa, and a reaction volume hourly space velocity of 1000-10000 h⁻¹. -1 .

37. The application according to claim 36, wherein, The reaction temperature is 210-230°C.

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