A metal oxide-molecular sieve catalyst, its preparation method and application

Abstract

The present application relates to the field of catalyst preparation and technical application, in particular to a metal oxide-molecular sieve catalyst and its preparation method and application; the catalyst is formed by mixing two components M and Z, wherein component M is iron-based composite metal oxide, and Z is SAPO-34 molecular sieve; the mass ratio of M and Z is 0.5-2; the iron-based composite metal oxide is a spinel type metal oxide composed of three metal elements A, B and C, denoted as A a B b C c O x , wherein A is Zn, B is Fe, and C is one of Cr, Al and Mn; the molar ratio of a:b:c is 1:0.4-2:0-1.6; the metal oxide-molecular sieve catalyst according to the present application is applied to the reaction of CO2 hydrogenation to low-carbon olefins, which can significantly improve the CO2 conversion rate and the yield of low-carbon olefins. In addition, the iron-based composite metal oxide used in the catalyst is cheap and easy to obtain, which solves the problem of high cost of metal oxide industrial application.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation and technical application, specifically to a metal oxide-molecular sieve catalyst and its preparation method and application. Background Technology

[0002] Low-carbon olefins (C2O4) represented by ethylene, propylene, and butene = -C4 = CO2 is one of the most important chemical raw materials in the chemical industry and occupies an important position in modern organic chemistry. The conversion of CO2 as a carbon resource into high-value-added chemicals has attracted widespread attention, and the hydrogenation of CO2 to produce low-carbon olefins is one of the most effective ways to utilize CO2 resources.

[0003] In the CO2 hydrogenation to low-carbon olefins reaction, the methanol intermediate reaction pathway exhibits an olefin selectivity exceeding 80%, breaking the ASF distribution limitations of the traditional CO2-FT pathway and attracting widespread research attention. This methanol intermediate reaction pathway involves the design and construction of metal oxide-molecular sieve catalysts, enabling CO2 to first generate methanol or oxygen-containing intermediates on the metal oxide, followed by the transfer of these intermediates to the molecular sieve and C-C coupling to generate low-carbon olefins. The design and construction of highly efficient metal oxide-molecular sieve catalysts are the key technologies for this reaction pathway.

[0004] Because metal oxide components have weak CO2 activation capabilities, the CO2 conversion rate of metal oxide-molecular sieve catalysts is generally low. Furthermore, the competitive reaction on the metal oxide surface, the reverse water-gas reaction, leads to the generation of a significant amount of CO byproducts. Therefore, the yield of low-carbon olefins via the methanol intermediate pathway is generally lower than that via the CO2-FT pathway. For example, Carlo et al. (Applied Catalysis B: Environmental, 2017, 200, 530-542) used a K-promoted Fe catalyst for CO2-FT to produce low-carbon olefins, achieving a low-carbon olefin selectivity of approximately 35% and a yield of 13.7%. Wang Sen et al. (Chem, 2022, 8, 1-19) from the Shanxi Coal Chemistry Institute, Chinese Academy of Sciences, used Cr2O3 prepared by the sol-gel method coupled with SAPO-34 for CO2 hydrogenation to produce low-carbon olefins, achieving a low-carbon olefin selectivity of 95.7%, but a CO2 conversion rate of only 13% and a low-carbon olefin yield of only 7.9%. Chinese patent CN111889132B discloses InCrO... x The / H-SAPO-34 metal oxide-molecular sieve catalyst achieved a CO2 conversion of 33.6%, but the yield of low-carbon olefins was only 11.4%. Furthermore, ZnZrO2 is currently reported to have relatively excellent catalytic performance. x ,InZrO x ZnGaO xZnCrO x However, these methods are costly or potentially toxic, hindering the industrialization of the technology. In conclusion, the key to CO2 hydrogenation for producing low-carbon olefins lies in finding a highly efficient metal oxide-molecular sieve catalyst that offers high olefin yields at a low cost. Summary of the Invention

[0005] This invention overcomes the shortcomings of the prior art and provides a metal oxide-molecular sieve catalyst. The metal oxide-molecular sieve catalyst provided by this invention is used for the hydrogenation of CO2 to produce low-carbon olefins, and can effectively solve the problems of low CO2 conversion rate, low yield of low-carbon olefins and high cost of metal oxides.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: The first aspect of the present invention provides a metal oxide-molecular sieve catalyst, wherein the catalyst is composed of two components, M and Z, wherein component M is an iron-based composite metal oxide and Z is a SAPO-34 molecular sieve; the mass ratio of M to Z is 0.5 to 2:1.

[0007] As a further limitation of the technical solution of the present invention, the iron-based composite metal oxide is a spinel-type metal oxide composed of three metal elements A, B, and C, denoted as A. a B b C c O x Where A is Zn, B is Fe, and C is one of Cr, Al, and Mn; a, b, and c represent the molar amounts of the three metallic elements; the molar ratio of a:b:c is 1:0.4~2:0~1.6; and the total oxidation state of all elements is zero.

[0008] A second aspect of this invention provides a method for preparing the aforementioned metal oxide-molecular sieve catalyst, comprising the following steps: S1. Weigh out water-soluble zinc salt, iron salt and third metal salt and dissolve them in deionized water to obtain a complex metal salt solution; S2. Weigh an appropriate amount of complexing agent and dissolve it in deionized water to prepare a complexing agent solution. S3. Add the composite metal salt solution obtained in step S1 dropwise to the complexing agent solution prepared in S2 until the metal ions are completely complexed. S4. Heat the complexed solution in an oil bath until a gel is formed; S5. Place the gel in an oven and dry it at a constant temperature to obtain a solid precursor; S6. Grind and calcine the obtained solid precursor to obtain iron-based composite metal oxide; S7. The iron-based composite metal oxide is mechanically mixed with SAPO-34 molecular sieve to obtain the catalyst.

[0009] As a further limitation of the technical solution of the present invention, the water-soluble zinc salt in step S1 is one of zinc nitrate, zinc chloride and zinc acetate; the water-soluble iron salt is ferric nitrate or ferric chloride; the third metal salt is at least one of nitrate, hydrochloride and oxalate; and the molar concentration of the resulting composite metal salt solution is 0.5~1 mol / L.

[0010] As a further limitation of the technical solution of the present invention, the complexing agent in step S2 is citric acid or glucose; the molar concentration of the obtained complexing agent solution is 1~3 mol / L.

[0011] As a further limitation of the technical solution of the present invention, the volume ratio of the composite metal salt solution to the complexing agent solution in step S3 is 1:1.

[0012] As a further limitation of the technical solution of the present invention, the heating temperature in step S4 is 70~90℃, and the constant temperature drying conditions in step S5 are 150~200℃ for 2~5 h.

[0013] As a further limitation of the technical solution of the present invention, the calcination temperature of the solid precursor in step S6 is 400~600℃ and the calcination time is 3~8h.

[0014] The third aspect of the present invention provides the application of the above-described metal oxide-molecular sieve catalyst in the CO2 hydrogenation to low-carbon olefins reaction, wherein the CO2 hydrogenation to low-carbon olefins reaction is carried out in a pressurized fixed-bed continuous flow reactor.

[0015] As a further limitation of the technical solution of the present invention, the reaction temperature is 350~400℃, the reaction pressure is 2~5Mpa, the reaction space velocity is 1800~9000mL / (g·h), and the H2 / CO2 ratio is 3 / 1~6 / 1.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) The metal oxide-molecular sieve catalyst described in this invention, when applied to the CO2 hydrogenation to produce low-carbon olefins, can significantly improve the CO2 conversion rate and the yield of low-carbon olefins. Its yield can reach up to 17.4%, which is not only significantly better than other metal oxide-molecular sieve catalysts in the prior art, but also significantly better than CO2-FT pathway catalysts, thus solving the problem of low low-carbon olefin yield in the CO2 hydrogenation to produce low-carbon olefins reaction using metal oxide-molecular sieve catalysts.

[0017] (2) The metal oxide described in this invention exists in a spinel structure, and the three metal elements interact within the spinel structure to form a stable FeO. x Site. Other Fe-based catalysts in the prior art typically use FeO. xIt exists in both FeO and FeC forms, possessing both CO2 activation and CC coupling capabilities, and is generally used in Fischer-Tropsch reactions. This invention, however, constructs a ternary metal spinel structure to control the existence of Fe species, ensuring that all Fe species exist as FeO. x It exists in the form of [specific substance], thus possessing only CO2 activation capability. When coupled with SAPO-34, it can catalyze the hydrogenation of CO2 to low-carbon olefins via a novel reaction pathway, thereby improving CO2 conversion and low-carbon olefin yield.

[0018] (3) The metal oxide-molecular sieve catalyst described in this invention is applied to the CO2 hydrogenation to produce low-carbon olefins reaction. CO2 first reacts with FeO. x At the site, it transforms into a CO intermediate species, and then in ZnO x This invention provides a novel and more efficient CO-methanol intermediate reaction pathway by converting CO intermediates to methanol intermediates at specific sites, compared to the existing technology where CO2 is directly converted to methanol intermediates on metal oxides. This pathway improves CO2 conversion rate and low-carbon olefin yield.

[0019] (4) Compared with other metal oxides in the prior art, the iron-based composite metal oxide used in the catalyst of the present invention is inexpensive and readily available, which solves the problem of high cost in industrial application of metal oxides. Attached Figure Description

[0020] Figure 1 The images show the XRD patterns of the catalysts prepared in Examples 2, 5, and 6 of this invention, corresponding from top to bottom to ZnFeAlO4, ZnFeMnO4, and ZnFeCrO4 catalysts.

[0021] Figure 2 The reaction evaluation results for Application Examples 2, 5, and 6 are shown, corresponding to ZnFeAlO4, ZnFeMnO4, and ZnFeCrO4 catalysts from right to left. Detailed Implementation

[0022] The present invention will be further described below with reference to specific embodiments. Example 1

[0023] Weigh out 4.46 g of zinc nitrate hexahydrate, 2.42 g of ferric nitrate nonahydrate, and 9.01 g of aluminum nitrate nonahydrate, and dissolve them in 50 mL of deionized water. Dissolve 17.29 g of citric acid in 50 mL of deionized water. Add the metal salt solution dropwise to the citric acid, stir at room temperature for 30 min, and then heat the precursor in an oil bath to 50–120 °C until gel formation. Dry the wet gel at 100–250 °C for 2–5 h, and calcine the dried solid in a muffle furnace at 300–800 °C for 3–9 h to obtain the composite metal oxide ZnFe. 0.4 Al1.6 O4. Then ZnFe 0.4 Al 1.6 O4 composite metal oxide and SAPO-34 molecular sieve (silicon-to-aluminum ratio = 0.01) were uniformly mixed in a mortar at a mass ratio of 1:1. The resulting composite was pressed into tablets, crushed, and sieved at 15 MPa to obtain ZnFe. 0.4 Al 1.6 O4 / SAPO-34 catalyst. Example 2

[0024] Weigh out 4.46 g of zinc nitrate hexahydrate, 6.06 g of ferric nitrate nonahydrate, and 5.63 g of aluminum nitrate nonahydrate, and dissolve them in 50 mL of deionized water. Dissolve 17.29 g of citric acid in 50 mL of deionized water. Add the metal salt solution dropwise to the citric acid, stir at room temperature for 30 min, and then heat the precursor in an oil bath to 50-120 °C until gel formation. Dry the wet gel at 100-250 °C for 2-5 h, and calcine the dried solid in a muffle furnace at 300-800 °C for 3-9 h to obtain the composite metal oxide ZnFe1Al1O4. Then, mix the ZnFe1Al1O4 composite metal oxide with SAPO-34 molecular sieve (silicon-to-aluminum ratio = 0.01) in a mortar at a mass ratio of 1:1. Press the resulting composite into tablets at 15 MPa, crush, and sieve to obtain the ZnFe1Al1O4 / SAPO-34 catalyst, the XRD pattern of which is shown below. Figure 1 As shown. Example 3

[0025] Weigh out 4.46 g of zinc nitrate hexahydrate, 9.70 g of ferric nitrate nonahydrate, and 2.25 g of aluminum nitrate nonahydrate, and dissolve them in 50 mL of deionized water. Dissolve 17.29 g of citric acid in 50 mL of deionized water. Add the metal salt solution dropwise to the citric acid, stir at room temperature for 30 min, and then heat the precursor in an oil bath to 50–120 °C until gel formation. Dry the wet gel at 100–250 °C for 2–5 h, and calcine the dried solid in a muffle furnace at 300–800 °C for 3–9 h to obtain the composite metal oxide ZnFe. 1.6 Al 0.4 O4. Then ZnFe 1.6 Al 0.4 O4 composite metal oxide and SAPO-34 molecular sieve (silicon-to-aluminum ratio = 0.01) were uniformly mixed in a mortar at a mass ratio of 1:1. The resulting composite was pressed into tablets, crushed, and sieved at 15 MPa to obtain ZnFe. 1.6 Al 0.4 O4 / SAPO-34 catalyst. Example 4

[0026] Weigh out 4.46 g of zinc nitrate hexahydrate, 10.91 g of ferric nitrate nonhydrate, and 1.13 g of aluminum nitrate nonhydrate, and dissolve them in 50 mL of deionized water. Dissolve 17.29 g of citric acid in 50 mL of deionized water. Add the metal salt solution dropwise to the citric acid, stir at room temperature for 30 min, and then heat the precursor in an oil bath to 50–120 °C until gel formation. Dry the wet gel at 100–250 °C for 2–5 h, and calcine the dried solid in a muffle furnace at 300–800 °C for 3–9 h to obtain the composite metal oxide ZnFe. 1.8 Al 0.2 O4. Then ZnFe 1.8 Al 0.2 O4 composite metal oxide and SAPO-34 molecular sieve (silicon-to-aluminum ratio = 0.01) were uniformly mixed in a mortar at a mass ratio of 1:1. The resulting composite was pressed into tablets, crushed, and sieved at 15 MPa to obtain ZnFe. 1.8 Al 0.2 O4 / SAPO-34 catalyst. Example 5

[0027] Weigh 4.46 g of zinc nitrate hexahydrate, 6.06 g of ferric nitrate nonahydrate, and 3.57 g of chromium nitrate nonahydrate and dissolve them in 50 mL of deionized water. Dissolve 17.29 g of citric acid in 50 mL of deionized water. Add the metal salt solution dropwise to the citric acid, stir at room temperature for 30 min, and then heat the precursor in an oil bath to 50-120 °C until gelation occurs. Dry the wet gel at 100-250 °C for 2-5 h, and calcine the dried solid in a muffle furnace at 300-800 °C for 3-9 h to obtain the composite metal oxide ZnFeCrO4. Then, mix the ZnFeCrO4 composite metal oxide with SAPO-34 molecular sieve (silicon-to-aluminum ratio = 0.01) in a mortar at a mass ratio of 1:1. The resulting composite is pressed into tablets, crushed, and sieved at 15 MPa to obtain the ZnFeCrO4 / SAPO-34 catalyst, the XRD pattern of which is shown below. Figure 1 As shown. Example 6

[0028] Weigh 4.46 g of zinc nitrate hexahydrate, 6.06 g of ferric nitrate nonahydrate, and 4.31 g of manganese nitrate hexahydrate and dissolve them in 50 mL of deionized water. Dissolve 17.29 g of citric acid in 50 mL of deionized water. Add the metal salt solution dropwise to the citric acid, stir at room temperature for 30 min, and then heat the precursor in an oil bath to 50-120 °C until gel formation. Dry the wet gel at 100-250 °C for 2-5 h, and calcine the dried solid in a muffle furnace at 300-800 °C for 3-9 h to obtain the composite metal oxide ZnFeMnO4. Then, mix the ZnFeMnO4 composite metal oxide with SAPO-34 molecular sieve (silicon-to-aluminum ratio = 0.01) in a mortar at a mass ratio of 1:1. Press the resulting composite into tablets at 15 MPa, crush, and sieve to obtain the ZnFeMnO4 / SAPO-34 catalyst, the XRD pattern of which is shown below. Figure 1 As shown.

[0029] Application Examples 1-6 The composite iron-based metal oxide-molecular sieve catalysts prepared in Examples 1-6 were treated at 380°C and atmospheric pressure for 2 hours under a N2 atmosphere, and then applied to the catalytic hydrogenation of CO2 to produce low-carbon olefins. The reaction conditions were: reaction temperature 370°C, reaction pressure 3 MPa, H2 / CO2 = 3, and reaction space velocity 3600 mL / (g·h), corresponding to Application Examples 1-6 respectively. The reaction evaluation results are shown in Table 1, and the reaction evaluation graphs for Application Examples 2, 5, and 6 are shown in Figure 6. Figure 2 As shown.

[0030] Application Example 7 The composite iron-based metal oxide-molecular sieve catalyst prepared in Example 1 was treated at 380°C and atmospheric pressure for 2 hours in a N2 atmosphere, and then applied to the catalytic hydrogenation of CO2 to produce low-carbon olefins. The reaction conditions were: reaction temperature 400°C, reaction pressure 3 MPa, H2 / CO2=3, and reaction space velocity 3600 mL / (g·h), corresponding to Application Example 7. The reaction evaluation results are shown in Table 1.

[0031] Application Example 8 The composite iron-based metal oxide-molecular sieve catalyst prepared in Example 1 was treated at 380°C and atmospheric pressure for 2 hours in a N2 atmosphere, and then applied to the catalytic hydrogenation of CO2 to produce low-carbon olefins. The reaction conditions were: reaction temperature 370°C, reaction pressure 3 MPa, H2 / CO2=3, and reaction space velocity 1800 mL / (g·h), corresponding to application example 8. The reaction evaluation results are shown in Table 1.

[0032] Application Example 9 The composite iron-based metal oxide-molecular sieve catalyst prepared in Example 1 was treated at 380°C and atmospheric pressure for 2 hours in a N2 atmosphere, and then applied to the catalytic reaction of CO2 hydrogenation to produce low-carbon olefins. The reaction conditions were: reaction temperature 380°C, reaction pressure 4 MPa, H2 / CO2=4, and reaction space velocity 3600 mL / (g·h), corresponding to application example 9. The reaction evaluation results are shown in Table 1.

[0033] Comparative Example 1 Weigh 4.46 g of zinc nitrate hexahydrate and 5.63 g of aluminum nitrate nonahydrate and dissolve them in 50 mL of deionized water. Dissolve 11.53 g of citric acid in 50 mL of deionized water. Add the metal salt solution dropwise to the citric acid, stir at room temperature for 30 min, and then heat the precursor in an oil bath to 50–120 °C until gel formation. Dry the wet gel at 100–250 °C for 2–5 h, and calcine the dried solid in a muffle furnace at 300–800 °C for 3–9 h to obtain the composite metal oxide ZnAlO. x Then ZnAlO x The composite metal oxide and SAPO-34 molecular sieve (silicon-to-aluminum ratio = 0.01) were uniformly mixed in a mortar at a mass ratio of 1:1. The resulting composite was pressed into tablets, crushed, and sieved at 15 MPa to obtain ZnAlO. x / SAPO-34 catalyst.

[0034] The metal oxide-molecular sieve catalyst prepared in Comparative Example 1 was treated at 380℃ and atmospheric pressure for 2h in a N2 atmosphere, and then applied to the catalytic hydrogenation of CO2 to produce low-carbon olefins. The reaction conditions were: reaction temperature 380℃, reaction pressure 4MPa, H2 / CO2=4, and reaction space velocity 3600mL / (g·h). The reaction evaluation results are shown in Table 1.

[0035] Comparative Example 2 Weigh 4.46 g of zinc nitrate hexahydrate and 3.57 g of chromium nitrate nonahydrate and dissolve them in 50 mL of deionized water. Dissolve 11.53 g of citric acid in 50 mL of deionized water. Add the metal salt solution dropwise to the citric acid, stir at room temperature for 30 min, and then heat the precursor in an oil bath to 50–120 °C until gelation occurs. Dry the wet gel at 100–250 °C for 2–5 h, and calcine the dried solid in a muffle furnace at 300–800 °C for 3–9 h to obtain the composite metal oxide ZnCrO. x Then, the ZnCrOx composite metal oxide and SAPO-34 molecular sieve (silicon-to-aluminum ratio = 0.01) were uniformly mixed in a mortar at a mass ratio of 1:1. The resulting composite was pressed into tablets, crushed, and sieved at 15 MPa to obtain ZnCrO. x / SAPO-34 catalyst.

[0036] The metal oxide-molecular sieve catalyst prepared in Comparative Example 2 was treated at 380℃ and atmospheric pressure for 2h in a N2 atmosphere, and then applied to the catalytic hydrogenation of CO2 to produce low-carbon olefins. The reaction conditions were: reaction temperature 380℃, reaction pressure 4MPa, H2 / CO2=4, and reaction space velocity 3600mL / (g·h). The reaction evaluation results are shown in Table 1.

[0037] Comparative Example 3 Weigh 4.46 g of zinc nitrate hexahydrate and 6.44 g of zirconium nitrate pentahydrate and dissolve them in 50 mL of deionized water. Dissolve 11.53 g of citric acid in 50 mL of deionized water. Add the metal salt solution dropwise to the citric acid, stir at room temperature for 30 min, and then heat the precursor in an oil bath to 50–120 °C until gel formation. Dry the wet gel at 100–250 °C for 2–5 h, and calcine the dried solid in a muffle furnace at 300–800 °C for 3–9 h to obtain the composite metal oxide ZnZrO. x Then ZnZrO x The composite metal oxide and SAPO-34 molecular sieve (silicon-to-aluminum ratio = 0.01) were uniformly mixed in a mortar at a mass ratio of 1:1. The resulting composite was pressed into tablets, crushed, and sieved at 15 MPa to obtain ZnZrO. x / SAPO-34 catalyst.

[0038] The metal oxide-molecular sieve catalyst prepared in Comparative Example 3 was treated at 380℃ and atmospheric pressure for 2h in a N2 atmosphere, and then applied to the catalytic hydrogenation of CO2 to produce low-carbon olefins. The reaction conditions were: reaction temperature 380℃, reaction pressure 4MPa, H2 / CO2=4, and reaction space velocity 3600mL / (g·h). The reaction evaluation results are shown in Table 1.

[0039] Comparative Example 4 Weigh 0.064 g of sodium nitrate and 6.06 g of ferric nitrate nonahydrate into 50 mL of deionized water. Dissolve 5.76 g of citric acid in 50 mL of deionized water. Add the metal salt solution dropwise to the citric acid, stir at room temperature for 30 min, and then heat the precursor in an oil bath to 50–120 °C until gel formation. Dry the wet gel at 100–250 °C for 2–5 h, and calcine the dried solid in a muffle furnace at 300–800 °C for 3–9 h to obtain the Na-Fe metal catalyst.

[0040] The metal oxide-molecular sieve catalyst prepared in Comparative Example 4 was treated at 350℃ and atmospheric pressure for 2h in an H2 atmosphere, and then applied to the catalytic hydrogenation of CO2 to produce low-carbon olefins. The reaction conditions were: reaction temperature 320℃, reaction pressure 3MPa, H2 / CO2=3, and reaction space velocity 1800mL / (g·h). The reaction evaluation results are shown in Table 1.

[0041] Table 1

[0042] C2 in Table 1 = -C4 = This refers to low-carbon olefin products with 2-4 carbon atoms, C2 0 -C4 0 This refers to low-carbon olefin products with 2-4 carbon atoms, C5. + This indicates hydrocarbon products with 5 or more carbon atoms. CO byproducts are not included when calculating hydrocarbon selectivity.

[0043] From the data in Table 1 and Figure 2 It can be seen that the ZnFe1Al1O4 / SAPO-34 catalyst described in Example 2, in the CO2 hydrogenation to low-carbon olefins reaction, CO2 The conversion rate can reach up to 41.5%, and the yield of low-carbon olefins is 18%, which is far higher than other types of metal oxide-molecular sieve catalysts under the same reaction conditions, such as Comparative Examples 1-3; it is also higher than CO2. Catalysts for the -FT reaction pathway, such as Comparative Example 4. Therefore, the novel iron-based composite metal oxide-molecular sieve catalyst of this invention exhibits excellent CO2... It improves conversion rate and low-carbon olefin yield, and effectively solves the problem that the low-carbon olefin yield of metal oxide-molecular sieve catalysts is lower than that of CO2-FT pathway catalysts.

Claims

1. The application of a metal oxide-molecular sieve catalyst in the CO2 hydrogenation to produce low-carbon olefins, characterized in that, The CO2 hydrogenation to produce low-carbon olefins reaction is carried out in a pressurized fixed-bed continuous flow reactor; The metal oxide-molecular sieve catalyst is composed of two components, M and Z, wherein component M is an iron-based composite metal oxide and Z is a SAPO-34 molecular sieve; the mass ratio of M to Z is 0.5~2:

1. The iron-based composite metal oxide is a spinel-type metal oxide composed of three metal elements, A, B, and C, denoted as A. a B b C c O x Where A is Zn, B is Fe, and C is one of Cr, Al, and Mn; a, b, and c represent the molar amounts of the three metallic elements; the molar ratio of a:b:c is 1:0.4~2:0.2~1.6; and the total oxidation state of all elements is zero.

2. The application according to claim 1, characterized in that, The catalyst reaction conditions are: reaction temperature 350~400℃, reaction pressure 2~5MPa, reaction space velocity 1800~9000mL / (g·h), H2 / CO2 = 3 / 1~6 / 1.

3. The application according to claim 1, characterized in that, The preparation method of the metal oxide-molecular sieve catalyst includes the following steps: S1. Weigh out water-soluble zinc salt, iron salt and third metal salt and dissolve them in deionized water to obtain a complex metal salt solution; S2. Weigh an appropriate amount of complexing agent and dissolve it in deionized water to prepare a complexing agent solution; S3. Add the composite metal salt solution obtained in step S1 dropwise to the complexing agent solution prepared in S2 until the metal ions are completely complexed. S4. Heat the complexed solution in an oil bath until a gel is formed; S5. Place the gel in an oven and dry it at a constant temperature to obtain a solid precursor; S6. Grind and calcine the obtained solid precursor to obtain iron-based composite metal oxide; S7. The iron-based composite metal oxide is mechanically mixed with SAPO-34 molecular sieve to obtain the catalyst.

4. The application according to claim 3, characterized in that, The water-soluble zinc salt in step S1 is one of zinc nitrate, zinc chloride, and zinc acetate; the water-soluble iron salt is ferric nitrate or ferric chloride; the third metal salt is at least one of nitrate, hydrochloride, and oxalate; and the molar concentration of the resulting composite metal salt solution is 0.5~1 mol / L.

5. The application according to claim 3, characterized in that, The complexing agent in step S2 is citric acid or glucose; the molar concentration of the resulting complexing agent solution is 1~3 mol / L.

6. The application according to claim 3, characterized in that, In step S3, the volume ratio of the composite metal salt solution to the complexing agent solution is 1:

1.

7. The application according to claim 3, characterized in that, In step S4, the heating temperature is 70~90℃, and in step S5, the constant temperature drying conditions are 150~200℃ for 2~5 hours.

8. The application according to claim 3, characterized in that, In step S6, the solid precursor is calcined at a temperature of 400~600℃ for 3~8h.

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