Composite catalyst and method for directly converting synthesis gas to isobutane coproducing propane

Abstract

The present application belongs to the technical field of synthesis gas conversion, and particularly relates to a composite catalyst and a method for directly converting synthesis gas to prepare isobutane and coproduce propane. The composite catalyst comprises component I, component II and component III; the active component of the component I is Cu-based metal oxide; the component II is one or both of beta molecular sieve and Y molecular sieve; and the component III is one or both of SSZ-13 molecular sieve and SSZ-39 molecular sieve. The preparation process of the composite catalyst is simple and the conditions are mild; the reaction process has very high product yield and selectivity, the isobutane selectivity can reach 40-60%, the propane selectivity can reach 10-30%, the total selectivity of propane and isobutane reaches 70-85%, and the composite catalyst has good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of syngas conversion technology, specifically relating to a composite catalyst and a method for the direct conversion of syngas to prepare isobutane and propane. Background Technology

[0002] Driven by the global energy structure transformation and the demand for carbon emission reduction, the production of clean and low-carbon hydrocarbons via non-petroleum routes has become a core direction for the industry. Isobutane, as a high-value-added chemical raw material and a high-quality clean energy source, is widely used in alkylation, MTBE synthesis, and environmentally friendly refrigerants; propane is a core component of liquefied petroleum gas and a feedstock for chemical cracking. Traditionally, both rely on petroleum refining and natural gas light hydrocarbon recovery. However, facing inherent challenges such as strong raw material constraints, high costs, and insufficient supply stability, there is an urgent need to explore non-petroleum-based raw material routes and develop diversified new technologies for isobutane and propane production. Direct production of propane and isobutane from syngas can break free from dependence on petroleum routes and achieve independent and efficient production of low-carbon alkanes using diversified carbon sources such as coal, biomass, and waste organic matter, ensuring the security of chemical raw material and clean fuel supply. This technology shortens the process flow, improves atom economy and carbon utilization, helps reduce carbon emissions, and provides key technological support for green chemical industry and energy transformation. Early syngas-to-hydrocarbon synthesis primarily relied on Fischer-Tropsch (FTS) technology. However, this reaction follows a surface chain growth mechanism, and product distribution is limited by the Anderson-Schulz-Flory (ASF) distribution law, resulting in a wide range of carbon chain distributions in the products. When the chain growth probability is 0.55, the selectivity for C3 and C4 hydrocarbons reaches its highest value of only 31.9%, and the products are mainly straight-chain hydrocarbons with very low selectivity for isomeric hydrocarbons, complex byproducts, and high separation energy consumption. To overcome the selectivity bottleneck of traditional Fischer-Tropsch synthesis, bifunctional catalytic systems have become a core research focus in recent years. For example, the research team of Professor Pan Xiulian at the Dalian Institute of Chemical Physics achieved nearly 90% LPG selectivity using ZnCrAl metal oxides and SSZ-39 molecular sieves, but the products were mainly propane, with butane selectivity of less than 10% (J. EnergyChem., 2019, 36: 141-147). Fujimoto et al. achieved 68% selectivity for isoalkanes using a Co / SiO2 catalyst and a Pd-modified beta molecular sieve. However, the selectivity for isobutane was only 20.3%, propane only 5.6%, and methane more than 10% (Ind. Eng. Chem. Res. 2005, 44, 7329-7336). Therefore, there is a need to develop catalyst schemes that can replace Pd. Summary of the Invention

[0003] To address the above problems, this invention provides a composite catalyst and a method for the direct conversion of syngas to prepare isobutane and propane.

[0004] To achieve the above objectives, the technical solution of the present invention is as follows:

[0005] In one aspect, the present invention provides a composite catalyst comprising component I, component II, and component III; The active component of component I is a Cu-based metal oxide; Component II is one or both of beta molecular sieve and γ molecular sieve; Component III is one or both of SSZ-13 and SSZ-39 molecular sieves.

[0006] Based on the above technical solutions, the Cu-based metal oxide is a non-noble metal oxide / Cu reverse structure, represented by the formula MO / Cu, or a core-shell structure with Cu as the core and non-noble metal oxide as the shell, represented by the formula Cu@MO; in MO, M is one or more of Zn, Al, Cr, Ga, Zr, Ce, V, La, Fe, Pr, and In; in the Cu-based metal oxide, the mass fraction of Cu, calculated as CuO, is 10-83%.

[0007] Based on the above technical solution, component II has the characteristics of a moderately strong acid, and the amount of moderately strong acid sites is 0.1-1.0 mol / kg.

[0008] Based on the above technical solution, component III has the characteristics of a moderately strong acid, and the amount of moderately strong acid sites is 0.1-1.0 mol / kg.

[0009] The temperature range corresponding to the peak apex of the NH3-TPD desorption peak for moderately strong acids is 200-500℃; acetone is used as the probe molecule. 13 The C-NMR chemical shift is in the range of 210-220 ppm.

[0010] The acid strength is defined by the NH3-TPD peak and includes three types of acidity: weak acid, moderately strong acid, and strong acid. The NH3-TPD method is based on the desorption peak position of NH3. The position of the desorption peak refers to the position of the desorption peak. Under standard test conditions, with a sample mass w to carrier gas flow rate f ratio (w / f) = 100 g·h / L and a heating rate of 10℃ / min, the TCD records the thermal conductivity signal of desorbed NH3 and plots the desorption curve. Based on the peak position of the curve, the inorganic solid is divided into three acid strengths: weak acid refers to acid sites with an NH3 desorption temperature less than 275℃; moderately strong acid refers to acid sites with an NH3 desorption temperature between 275-500℃; and strong acid refers to acid sites with an NH3 desorption temperature greater than 500℃.

[0011] Based on the above technical solution, component II is one or two of metal-modified beta molecular sieves and Y molecular sieves, and component III is one or two of non-precious metal-modified SSZ-13 molecular sieves and SSZ-39 molecular sieves, wherein the non-precious metals are one or two of Cu, Zn, Ga, Zr, Ce, Co, Fe, and Ni.

[0012] Based on the above technical solution, the weight ratio of component I to component II is 0.3-3:1; the weight ratio of component II to component III is 0.3-3:1.

[0013] Based on the above technical solutions, the combination of component I, component II and component III is a physical mixing method, including one of solid phase ultrafine powder mixing, particle mixing, sheet forming and extrusion forming.

[0014] The second aspect of the present invention provides a method for the direct conversion of syngas to prepare isobutane and co-produce propane, using syngas as a reaction raw material, and under the action of the above-mentioned composite catalyst, isobutane is obtained and propane is produced simultaneously.

[0015] Based on the above technical solution, the synthesis gas is an H2 / CO mixture, with a molar ratio of H2 to CO of 0.5-4; the reaction conditions are: synthesis gas pressure of 2-8 MPa, reaction temperature of 200-320 ℃, and space velocity of 1000-8000 ml / g. cat / h.

[0016] Based on the above technical solution, the method involves a conversion reaction in a fixed bed to produce isobutane, while simultaneously producing propane.

[0017] The beneficial effects of this invention are as follows: 1. The catalyst used in this invention is a multifunctional composite catalyst. Component I is a metal oxide used to activate CO to generate oxygen-containing compound intermediates. Components II and III utilize the confined catalytic effect of molecular sieves to convert the target product into isobutane and propane. Using components I, II, and III individually cannot fully achieve the function of this invention. Using component I alone does not generate the target product; using component II, III, or a combination of II and III alone cannot activate and convert syngas; using I+II or I+III can achieve syngas conversion, but the product composition is singular and cannot simultaneously produce isobutane and propane; only when the three components work synergistically can the function of this invention be achieved.

[0018] 2. In the catalyst of the present invention, the Cu-based metal oxide of component I has a metal oxide / Cu reverse phase structure or a Cu@metal oxide core-shell structure, which has better stability compared with traditional Cu-based catalysts.

[0019] 3. The method provided by this invention can co-produce propane while generating isobutane, and propane is a key raw material for the preparation of propylene, polypropylene, and various fine chemicals. The products isobutane and propane can be separated by a simple method. Therefore, the technology of this invention can simultaneously obtain two very important chemical raw materials, which can also be directly used as high-quality liquefied petroleum gas fuel.

[0020] 4. The preparation process of the composite catalyst of the present invention is simple and the conditions are mild; and the reaction process has a high product yield and selectivity, with isobutane selectivity reaching 40-60%, propane selectivity reaching 10-30%, and the total selectivity of propane and isobutane reaching 70-85%, which has good application prospects. Detailed Implementation

[0021] The present invention will be further illustrated below by way of embodiments, but the scope of the claims of the present invention is not limited to these embodiments. Furthermore, the embodiments only provide some conditions for achieving this objective, but do not imply that these conditions must be met to achieve this objective.

[0022] Unless otherwise specified, the materials used in the embodiments of the present invention can be obtained commercially or prepared according to conventional methods known to those skilled in the art.

[0023] I. Preparation of Catalyst Component I: Cu-based Metal Oxide Preparation of reverse-phase ZnO / Cu: Preparation of solution A: Cu(NO3)2 3H2O and Zn(NO3)2 Dissolve 6H2O in 150 mL of anhydrous ethanol at a target molar ratio and sonicate until clear; Preparation of solution B: Add excess oxalic acid dihydrate (H2C2O4) 2H2O (molar amount of which is 1.05 times the total amount of metal) dissolved in 480 mL of anhydrous ethanol; Solution B was added dropwise to solution A at a rate of 5 mL / min, and the mixture was stirred continuously to obtain a light blue gel slurry. The mixture was stirred and aged for 2 h. After centrifugation, it was washed three times with anhydrous ethanol, dried at 60 °C for 12 h, and calcined at 450 °C for 2 h in air to obtain a reverse-phase ZnO / Cu structure, denoted as I-1, in which the mass fraction of Cu (calculated as CuO) was 53%.

[0024] The reverse-phase structures ZnLaO / Cu, GaAlO / Cu, ZnZrO / Cu, CeZnAlO / Cu, ZnVO / Cu, ZrO / Cu, ZnAlO / Cu, CrO / Cu, FeAlO / Cu, PrCrO / Cu, and InO / Cu were prepared using similar methods. The specific names and the mass fraction of Cu (calculated as CuO) are shown in Table 1.

[0025] Preparation of core-shell structured Cu@ZnO: (1) Preparation of CuO nanoparticles: Add 0.3 g of polyvinylpyrrolidone to 50 ml of 0.1 mol / L copper nitrate solution and stir magnetically for 30 min at room temperature until completely dissolved; add 2 mol / L NaOH solution dropwise to the above solution while stirring vigorously until the pH of the system is 12-13 and a sky-blue flocculent precipitate is formed instantly. Continue stirring for 30 min, transfer the mixture to a polytetrafluoroethylene-lined hydrothermal reactor, seal it tightly and place it in an oven. Heat the oven to 140 ℃ and keep it at a constant temperature for 10 h. After the reaction is completed, centrifuge the product, wash it with deionized water and anhydrous ethanol, dry it at 60 ℃ for 12 h, and calcine it in a muffle furnace at 400 ℃ in air atmosphere for 2 h to obtain CuO nanoparticles; (2) Cu@ZnO was prepared by deposition precipitation method: a certain amount of the above CuO nanoparticles were placed in a 0.1 mol / L zinc nitrate solution and ultrasonically dispersed at room temperature. Under vigorous stirring, 1 mol / L NaOH aqueous solution was added dropwise to the above mixture until the pH of the system was 7-7.5. The stirring was continued for 30 min. The product was centrifuged, washed with deionized water, dried at 60℃ for 12 h, and calcined at 400℃ for 2 h in a muffle furnace under air atmosphere to obtain Cu@ZnO with core-shell structure, denoted as I-13, in which the mass fraction of Cu was 51% (calculated as CuO).

[0026] Cu@GaCrO, denoted as I-14, was prepared by a similar method, wherein the mass fraction of Cu was 37% (calculated as CuO).

[0027] In comparison, CuZnO was prepared by co-precipitation: 16.70 g of copper nitrate trihydrate and 16.43 g of zinc nitrate hexahydrate were weighed and dissolved in deionized water to prepare a mixed metal salt solution. Separately, 15.83 g of sodium carbonate was weighed and dissolved to prepare a precipitant solution. 100 mL of deionized water was added to a three-necked flask as the base solution. The temperature was maintained at 60 °C and stirred continuously. The metal salt solution and sodium carbonate precipitant solution were added dropwise in parallel flow. The pH of the system was maintained at around 7.5 throughout the process. After the addition was completed, the mixture was stirred and aged at a constant temperature for 2 h. Then, it was filtered and the precipitate was washed several times with warm deionized water to remove sodium ions and nitrate ions. The resulting filter cake was dried in an oven at 110 °C for 12 h. The dried sample was placed in a muffle furnace and calcined at 350 °C for 4 h in air at a heating rate of 2 °C / min to obtain CuZnO, denoted as I-15, with a Cu mass fraction (calculated as CuO) of 55%.

[0028] Table 1. Metal types and Cu content of component I in this invention

[0029] II. Preparation of Catalyst Component II The molecular sieve of this invention can be a commercially available beta or γ molecular sieve with an acid density that meets the requirements of this invention, or it can be a self-synthesized molecular sieve. The moderately strong acid described in this invention can be tested by solid-state NMR spectroscopy (H-N), NH3-TPD, infrared spectroscopy, chemical titration, etc. However, the methods for testing acidity are not limited to the above methods.

[0030] Preparation of beta molecular sieve: Weigh 6.4 g NaOH and 8.52 g NaAlO2, add 216 g deionized water, stir at 60℃ for 30 min until clear, to prepare aluminum alkali solution; weigh 288 g 25% TEAOH aqueous solution to prepare template solution, pour aluminum alkali solution into template solution, slowly add 333.3 g 30 wt% acidic silica sol, stir for 2 h to form gel, age at room temperature for 12 h, then load into reaction vessel, statically crystallize at 150 ℃ for 72 h, cool and filter, wash with 60 ℃ hot water until the filtrate pH 7-8 and conductivity <200 μS / cm, dry at 110 ℃ to obtain Na-Beta; weigh an appropriate amount of Na-Beta, add 1 mol / L NH4NO3 solution (1 g molecular sieve corresponds to 10 mL solution), stir and exchange twice at 80 ℃, dry, and calcine in air in stages at 550 ℃ for 4 hours. h, yielded H-type Beta molecular sieve, denoted as II-1, with a medium-strong acid content of 0.67 mmol / g.

[0031] Preparation of Y molecular sieve: Commercial USY molecular sieve, denoted as II-2, was used, with a medium-strong acid content of 0.54 mmol / g.

[0032] II-1 was modified with non-precious metals by impregnation: 0.395 g of copper nitrate trihydrate was dissolved in 15 ml of water, 10 g of I-1 molecular sieve was added to the above solution, stirred, air-dried at room temperature, dried at 100℃, and calcined in air at 350℃ for 2 h to obtain Cu-modified beta molecular sieve Cu / beta, denoted as II-3, in which the Cu content (calculated as CuO) was 1.3% and the amount of moderately strong acid was 0.43 mmol / g.

[0033] Zn-modified beta molecular sieves Zn / Beta, Ga-modified beta molecular sieves Ga / beta, Zr-modified beta molecular sieves Zr / beta, Ce-modified Y molecular sieves Ce / Y, Co-modified Y molecular sieves Co / Y, Fe-modified Y molecular sieves Fe / Y, and Ni-modified Y molecular sieves Ni / Y were prepared using similar methods and are designated as II-4, II-5, II-6, II-7, II-8, II-9, and II-10, respectively.

[0034] In comparison, Zn-modified low-acidity beta molecular sieves were prepared: II-1 molecular sieve was subjected to dealumination treatment. 10 g of II-1 molecular sieve was placed in 100 ml of 9 mol / L nitric acid solution and placed in an 80℃ water bath for 20 h of stirring for dealumination treatment. The product was washed several times until neutral, dried overnight at 110℃, and calcined in air at 500℃ for 5 h to obtain low-acidity beta molecular sieves. Subsequently, Zn-modified low-acidity beta molecular sieves were prepared using a similar impregnation method, wherein the Zn content (calculated as ZnO) was 1.5%, denoted as II-11, and the medium-strong acidity was 0.01 mmol / g.

[0035] The modified metal content and medium-strong acid content of component II are shown in Table 2.

[0036] Table 2. Molecular sieve types and moderately strong acidity properties of component II

[0037] III. Preparation of Catalyst Component III The moderately strong acids described in this invention can be tested using methods such as solid-state NMR spectroscopy (H-N), NH3-TPD, infrared spectroscopy, and chemical titration. However, the methods for testing acidity are not limited to those described above.

[0038] Preparation of SSZ-13 molecular sieve: Weigh an appropriate amount of NaOH and dissolve it in deionized water. Add TMAdaOH and choline chloride in a certain ratio and stir thoroughly before adding seed crystals; then add Al2(SO4)3. Add 18H2O and stir vigorously for 30 min. After stirring, add an appropriate amount of silica and continue stirring for 2 h to obtain a uniform gel. Transfer the gel to a 100 mL crystallization vessel and crystallize at 160 °C. o Crystallization was carried out at C for 4 days; after crystallization, the resulting product was filtered, washed, and then subjected to 120°C. o Dry at C for 12 h, and finally dry the product at 550 °C. o Na-SSZ-13 molecular sieve, denoted as III-1, was obtained by calcination in air at C for 5 hours. This molecular sieve contains virtually no moderately strong acids, with an acid content of only 0.005 mmol / g. Na-SSZ-13 molecular sieve III-1 was reacted with 1 mol / L NH4Cl solution at 80°C. o After exchanging at C for 2 h, the mixture was washed with deionized water until neutral. This process was repeated three times to obtain H-SSZ-13 molecular sieve, denoted as III-2, with a medium-strong acid content of 0.46 mmol / g.

[0039] Preparation of SSZ-39 molecular sieve: Commercial SSZ-39 molecular sieve, denoted as III-3, was used, with a medium-strong acid content of 0.67 mmol / g.

[0040] III-2 was modified with non-precious metals by impregnation: 0.801 g of copper nitrate trihydrate was dissolved in 26 ml of water, 20 g of III-2 molecular sieve was added to the above solution, stirred, air-dried at room temperature, dried at 100℃, and calcined in air at 300℃ for 4 h to obtain Cu-modified SSZ-13 molecular sieve Cu / SSZ-13, denoted as III-4, in which Cu content was 1.2% (calculated as CuO) and the amount of moderately strong acid was 0.40 mmol / g.

[0041] Zn-modified SSZ-13 molecular sieves (Zn / SSZ-13), Ga-modified SSZ-13 molecular sieves (Ga / SSZ-13), Zr-modified SSZ-13 molecular sieves (Zr / SSZ-13), Ce-modified SSZ-39 molecular sieves (Ce / SSZ-39), Co-modified SSZ-39 molecular sieves (Co / SSZ-39), Fe-modified SSZ-39 molecular sieves (Fe / SSZ-39), and Ni-modified SSZ-39 molecular sieves (Ni / SSZ-39) were prepared using similar methods and are designated as III-5, III-6, III-7, III-8, III-9, III-10, and III-11, respectively.

[0042] In comparison, Ga-modified low-acidity SSZ-13 molecular sieve was prepared: 0.1 g of gallium nitrate was dissolved in water, a certain amount of III-1 molecular sieve was added to the above solution, stirred, air-dried at room temperature, dried at 100℃, and calcined in air at 300℃ for 4 h to obtain Ga-modified SSZ-13 molecular sieve Ga / SSZ-13, denoted as III-12, in which Ga content was 0.5% as Ga2O3 and the medium-strong acidity was 0.004 mmol / g.

[0043] The modified metal content and medium-strong acid content of component III are shown in Table 3.

[0044] Table 3. Molecular sieve types and moderately strong acidity properties of component III

[0045] IV. Preparation of Composite Catalysts The composite catalyst was prepared by methods such as solid-phase ultrafine powder mixing, particle mixing, tablet forming, and extrusion forming. Specific preparation parameters and composition are shown in Table 4.

[0046] Table 4. Preparation and parameter characteristics of the composite catalyst of the present invention

[0047] V. Performance Testing The composite catalyst prepared above was loaded into a fixed-bed reactor equipped with a gas mass flow meter and an online product analysis chromatograph (the reactor tail gas was directly connected to the chromatograph's injection valve for periodic real-time sampling and analysis). Before the reaction, the catalyst was reduced at 280°C for 2 h under a hydrogen atmosphere. The syngas was an H2 / CO mixture. The reaction evaluation conditions and results of the catalyst of this invention and the comparative catalyst in the fixed bed are shown in Table 4. CO conversion rate, % = number of moles of CO consumed in the reaction / number of moles of CO fed into the reaction; Isobutane selectivity, % = number of moles of CO consumed in the reaction to produce isobutane / number of moles of CO consumed in the reaction to produce all hydrocarbon products; Propane selectivity, % = number of moles of CO consumed in the reaction to produce propane / number of moles of CO consumed in the reaction to produce all hydrocarbon products; Isobutane and propane selectivity, % = Isobutane selectivity, % + Propane selectivity, % Deactivation rate, % / h = (CO conversion rate after 220 h of reaction - CO conversion rate after 20 h of reaction) / 200.

[0048] Table 5. Specific applications and effect data of catalysts

[0049] Comparative Example 1, using only component I, showed a very low CO conversion rate, and no isobutane or propane was found in the products. Comparative Example 2, using only components II and III, without component I, showed a CO conversion rate of 0. Comparative Example 3, using only components I and II, showed very low propane selectivity. Comparative Example 4, using only components I and III, showed very low isobutane selectivity. Comparative Examples 5 and 6, although using composite catalysts of components I, II, and III, also showed low selectivity for the target products due to the low amount of moderately strong acid in either component II or III. Conversely, Examples 1-16, using composite catalysts of component I and appropriately balanced amounts of moderately strong acid in components II and III, exhibited high CO conversion rates and target product selectivity, demonstrating the importance of composite catalysts.

[0050] Compared with Examples 1 and 13, the catalyst component I in Comparative Example 7 was CuZnOI-15 prepared by ordinary co-precipitation. Although the Cu content was similar, its deactivation rate was significantly higher than that of Example 1, which used reverse-phase ZnO / Cu, and Example 13, which used Cu@ZnO with a core-shell structure. This indicates that Cu-based metal oxides with reverse-phase structures and metal oxides with core-shell structures have better anti-sintering properties and catalyst stability.

[0051] The components II and III used in Examples 15 and 16 were not modified with metals and also exhibited high CO conversion and target product selectivity. However, compared with Examples 2 and 7, their target product selectivity was slightly lower under similar reaction conditions.

[0052] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A composite catalyst, characterized in that: Includes component I, component II, and component III; The active component of component I is a Cu-based metal oxide; Component II is one or both of beta molecular sieve and γ molecular sieve; Component III is one or both of SSZ-13 molecular sieve and SSZ-39 molecular sieve.

2. The composite catalyst according to claim 1, characterized in that: The Cu-based metal oxide is a non-noble metal oxide / Cu reverse structure, represented by the formula MO / Cu, or a core-shell structure with Cu as the core and non-noble metal oxide as the shell, represented by the formula Cu@MO; in MO, M is one or more of Zn, Al, Cr, Ga, Zr, Ce, V, La, Fe, Pr, and In; in the Cu-based metal oxide, the mass fraction of Cu, calculated as CuO, is 10-83%.

3. The composite catalyst according to claim 1, characterized in that: Component II is characterized by being a moderately strong acid, with the amount of moderately strong acid sites being 0.1-1.0 mol / kg.

4. The composite catalyst according to claim 1, characterized in that: Component III is characterized by being a moderately strong acid, with the amount of moderately strong acid sites being 0.1-1.0 mol / kg.

5. The composite catalyst according to claim 1, characterized in that: Component II is one or two of metal-modified beta molecular sieves and Y molecular sieves, and component III is one or two of non-precious metal-modified SSZ-13 molecular sieves and SSZ-39 molecular sieves, wherein the non-precious metal is one or two of Cu, Zn, Ga, Zr, Ce, Co, Fe, and Ni.

6. The composite catalyst according to claim 1, characterized in that: The weight ratio of component I to component II is 0.3-3:1; the weight ratio of component II to component III is 0.3-3:

1.

7. The composite catalyst according to claim 1, characterized in that: The combination of components I, II and III is a physical mixing method, including one of solid-phase ultrafine powder mixing, particle mixing, sheet forming and extrusion forming.

8. A method for the direct conversion of syngas to prepare isobutane and co-produce propane, using syngas as a reactant and under the action of a catalyst, to obtain isobutane and simultaneously produce propane, characterized in that: The catalyst is the composite catalyst according to any one of claims 1-7.

9. The method according to claim 8, characterized in that: The syngas is an H2 / CO mixture with a molar ratio of H2 to CO of 0.5-4; the reaction conditions are: syngas pressure of 2-8 MPa, reaction temperature of 200-320 ℃, and space velocity of 1000-8000 ml / g. cat / h.

10. The method according to claim 8, characterized in that: The method involves a conversion reaction carried out in a fixed bed to produce isobutane, while simultaneously producing propane.

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