Preparation method of alkali halide doped alpha-Mo2C catalyst for reverse water gas reaction, catalyst and application thereof

Abstract

The invention belongs to the technical field of catalyst preparation, and relates to a preparation method of an alkali halide doped alpha-Mo2C catalyst for reverse water gas reaction, the catalyst and application of the catalyst, and the preparation method comprises the following steps: dissolving a molybdenum source and cane sugar in water according to a C / Mo molar ratio of 2-4, then adding an alkali halide according to a molar ratio of the alkali halide to Mo of 0.05-0.15, and carrying out a reaction for 2-4 hours; stirring until the solution is completely dissolved, and heating the solution at 110-130 DEG C for 8-12 hours to obtain a caramelized alkali halide doped molybdenum source intermediate; the preparation method comprises the following steps: fully grinding the raw materials, reducing at 450-550 DEG C in an H2 atmosphere for 18-23 hours, and then cooling to room temperature in an argon atmosphere to obtain the AMH-coated alpha-Mo2C catalyst. The prepared AMH-coated alpha-Mo2C catalyst is suitable for the field of reverse water gas reaction, and the excellent performance close to CO equilibrium yield can be achieved under the low-temperature condition of 400 DEG C.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation, and in particular relates to an alkali halide-doped α-Mo catalyst for reverse water gas reaction. 2 C catalyst preparation method, catalyst and application thereof. Background Art

[0002] The reverse water gas reaction (RWGS) is an important chemical reaction through which carbon dioxide (CO 2 ) can be converted into carbon monoxide (CO), providing synthesis gas (CO and H) for important chemical reactions such as Fischer-Tropsch synthesis. 2 ) raw materials. Since the RWGS reaction is an endothermic and reversible process, a higher reaction temperature (usually above 500 °C) can promote the 2 conversion and inhibit unfavorable methanation side reactions. However, high temperature conditions not only increase the equipment and energy costs in the reaction process, but also easily lead to catalyst deactivation. Therefore, how to achieve a near-equilibrium CO yield at a lower temperature, especially how to control the reaction temperature below 500°C, has become a key challenge in promoting the industrial application of the RWGS reaction. A near-equilibrium CO yield helps reduce the separation cost in actual CO production, thereby improving economic benefits.

[0003] At present, the catalysts that can achieve near-equilibrium CO yields below 500°C are mainly precious metal catalysts, such as platinum (Pt), ruthenium (Ru) and iridium (Ir). These catalysts have excellent catalytic performance and can achieve high CO selectivity at lower temperatures. However, due to the high cost of precious metals and the poor stability of the catalysts caused by the easy agglomeration of metal particles at high temperatures, their industrial application is limited. Therefore, the development of non-precious metal catalysts with high CO yields at lower temperatures, low cost and excellent stability has become the key to the industrialization of RWGS reactions.

[0004] In recent years, molybdenum carbide (Mo 2 C) has attracted extensive attention in RWGS reaction due to its excellent catalytic performance. 2 C has many crystal forms, the most common of which is α-Mo 2 C (fcc face-centered cubic structure) and β-Mo 2 C (hcp hexagonal close-packed structure). Studies have shown that compared to β-Mo 2 C, α-Mo 2 C exhibits better catalytic performance in the RWGS reaction. 2 C is in a thermodynamically metastable state, which is difficult to synthesize under conventional conditions and is easily transformed into the more thermodynamically stable β-Mo 2C, resulting in the deactivation of the catalyst. Although some studies have successfully synthesized pure phase α-Mo 2 C, and achieved a near-equilibrium CO yield above 500 °C, but the CO selectivity at lower temperatures (such as 400 °C) was still low, R Y / E (Actual CO yield / equilibrium yield) is only about 0.66. Therefore, how to design a catalyst that can achieve near-equilibrium CO yield, 100% CO selectivity, and excellent stability at lower temperatures remains a huge challenge for the commercialization of the RWGS reaction. Summary of the invention

[0005] The purpose of the present invention is to solve the problem of α-Mo 2 C is easily converted into β-Mo during the RWGS reaction 2 C and α-Mo 2 In order to solve the problem that the CO equilibrium yield is difficult to approach at temperatures below 500 °C, an alkali halide-doped α-Mo catalyst for the reverse water gas reaction was proposed. 2 The preparation method of C catalyst, catalyst and application thereof. The alkali halide-doped α-Mo 2 C catalyst (AMH@α-Mo 2 C catalyst) is suitable for the field of reverse water gas reaction and can achieve excellent performance close to the CO equilibrium yield under low temperature conditions of 400°C.

[0006] The technical solution of the present invention is:

[0007] The present invention protects an alkali halide-doped α-Mo for reverse water gas reaction 2 The preparation method of C catalyst comprises the following steps:

[0008] (1) dissolving a molybdenum source and sucrose in water at a C / Mo molar ratio of 2 to 4, then adding an alkali halide at a molar ratio of alkali halide to Mo of 0.05 to 0.15, stirring until completely dissolved, and heating the solution at 110 to 130° C. for 8 to 12 hours to obtain a caramelized alkali halide-doped molybdenum source intermediate;

[0009] (2) The caramelized alkali halide-doped molybdenum source intermediate is fully ground and heated in H 2 The alkali halide-doped α-Mo was obtained by reducing the α-Mo in an argon atmosphere for 18 to 23 hours and then cooling the α-Mo in an argon atmosphere to room temperature. 2 C catalyst (AMH@α-Mo 2 C catalyst).

[0010] Further, the molybdenum source is (NH 4 ) 6Mo 7 O 24 ·4H 2 O.

[0011] Furthermore, the alkali halide is any one or more of KI, KCl, KBr, KF, NaI, NaCl, NaBr, and NaF.

[0012] Furthermore, the flow rate of the hydrogen is 2Lkg -1 min -1 .

[0013] Furthermore, the solution in step (1) is heated at 120° C. for 10 h.

[0014] Furthermore, the molybdenum source intermediate in step (2) is heated at 500°C in H 2 Reduce in atmosphere for 20 h; heating rate is 10 °C min -1 .

[0015] The present invention also protects the alkali halide-doped α-Mo prepared by any of the preparation methods described above. 2 C catalyst.

[0016] The present invention also protects the alkali halide doped α-Mo as described in claim 7 2 Application of C catalyst in reverse water gas reaction.

[0017] Furthermore, the temperature of the reverse water gas reaction is 350-700°C, and the reverse water gas reaction uses H 2 With CO 2 is the reaction gas, the H 2 With CO 2 The volume ratio is (1-4):1, GHSV = 9-54 L kg -1 min -1 .

[0018] Preferably, the temperature of the reverse water gas reaction is 400°C.

[0019] The present invention proposes for the first time that 2 C doped with alkali halide, named AMH@α-Mo 2 C. The study found that alkali halide doping into α-Mo 2 C can effectively improve α-Mo 2 The stability of C makes it difficult to be replaced by H in the reverse water gas reaction. 2 Overreduction to β-Mo 2C and deactivation. This new catalyst can achieve a nearly balanced CO yield and 100% CO selectivity in a wide reaction temperature range of 400-700°C, especially at a low temperature of 400°C, with excellent performance.

[0020] At gas hourly space velocity GHSV = 18Lkg -1 min -1 Under the condition of 2 C at 400℃ R Y / E The results show that the addition of halogens effectively promotes the H 2 activation, thereby increasing the CO 2 The alkali metal elements are converted into 2 More amorphous oxygen is fixed on the C surface, which inhibits the occurrence of methanogenic side reactions, thereby achieving a near-equilibrium CO yield at 400 °C. Further experiments showed that AMH@α-Mo 2 The preparation process of C has been successfully scaled up to the kilogram scale, which demonstrates that the catalyst has important potential for industrial applications.

[0021] Beneficial effects of the present invention:

[0022] (1) The present invention provides an alkali halide-doped α-Mo for reverse water gas reaction 2 The preparation method of C catalyst comprises the following steps: firstly, sucrose and (NH 4 ) 6 Mo 7 O 24 ·4H 2 O and alkali halide caramelization reaction in one step to obtain alkali halide doped molybdenum source intermediate, and then high temperature hydrogen reduction and carburization to obtain alkali halide doped α-Mo 2 C catalyst, namely AMH@α-Mo 2 C catalyst. This preparation method uses cheap sucrose as a carbon source and (NH 4 ) 6 Mo 7 O 24 ·4H 2 O can be obtained by caramelization reaction and hydrogen reduction at 500℃ to obtain α-Mo 2 C; can replace the traditional one that requires high temperature above 700℃ to generate α-Mo 2 C methane deposition method, greatly reducing α-Mo 2 The preparation cost of C.

[0023] (2) In the present invention, doping with halogen ions can effectively improve the α-Mo 2 C in the reverse water gas reaction 2 Activation efficiency, thereby improving CO 2 The conversion rate is close to the equilibrium conversion rate. Alkali metal ions are doped into α-Mo 2 C can effectively inhibit the occurrence of methanogenesis side reactions, thereby ensuring 100% CO selectivity.

[0024] (3) The alkali halide prepared by the present invention is doped into α-Mo 2 AMH@α-Mo 2 The C catalyst can achieve excellent performance close to the CO equilibrium yield at 400 °C, which is a typical case of pure α-Mo 2 C cannot achieve this. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 for KI@α-Mo 2 C at 400~700℃, 1~4bar, CO 2 :H 2 =1:1, GHSV = 18Lkg -1 min -1 CO selectivity and yield performance diagram under different conditions;

[0026] Figure 2 for KI@α-Mo 2 C at 400°C, 4 bar, CO 2 :H 2 =1:1, GHSV = 36L kg -1 min -1 X-ray diffraction (XRD) patterns before and after 1000 hours of reaction under the same conditions;

[0027] Figure 3 The newly prepared KI@α-Mo 2 Transmission electron microscopy (TEM) image and particle size distribution of C;

[0028] Figure 4 for KI@α-Mo 2 C at 400°C, 4 bar, CO 2 :H 2 =1:1, GHSV = 36L kg -1 min -1 TEM image and particle size distribution diagram after 1000 hours of reaction under the same conditions. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] In order to further understand the present invention, the present invention will be further described in conjunction with the accompanying drawings and embodiments.

[0031] Example 1

[0032] This embodiment provides an alkali halide doped α-Mo for reverse water gas reaction 2 The preparation method of C catalyst comprises the following steps:

[0033] (1) Caramelization process: (NH 4 ) 6 Mo 7 O 24 ·4H 2 O and sucrose were dissolved in deionized water with a molar ratio of C / Mo of 3.5; KI was then added with a molar ratio of KI to Mo of 0.11, and the resulting solution was stirred evenly until completely dissolved; the solution was transferred to a beaker, occupying one-fifth of the volume of the beaker to prevent overflow during the subsequent caramelization process; and then placed in an oven at 120°C and heated for 10 hours to obtain a caramelized KI-doped molybdenum source intermediate.

[0034] (2)H 2 Reduction and carburization process: The caramelized KI-doped molybdenum source intermediate was fully ground and placed in a quartz tube, which was sealed and filled with quartz wool at both ends. Then, the tube was heated at 500 °C (heating rate was 10 °C min -1 ) in H 2 atmosphere for 20 hours, the corresponding molybdenum source intermediate H 2 The reduction flow is 2Lkg -1 min -1 ; H occurred during this process 2 Reduction and carbonization reactions; the sample was then cooled to room temperature in an argon atmosphere to obtain KI@α-Mo 2 C catalyst.

[0035] The KI@α-Mo 2 C catalyst is used in the reverse water gas reaction.

[0036] The catalyst is loaded into the reaction tank and is first reduced and activated before the reverse water gas reaction. The steps are as follows: 2The catalyst was reduced and activated (GHSV = 9 L kg -1 min -1 ), the reduction temperature is 600℃, and the -1 The heating rate was increased from room temperature to 600°C and maintained at 600°C for 3 h for activation treatment.

[0037] Activated KI@α-Mo 2 The C catalyst is used in the reverse water gas reaction. The steps are as follows: turn off the temperature rise, wait for the temperature to naturally drop to 400°C and maintain, then switch to the reaction gas H 2 :CO 2 =1:1, GHSV = 18L kg -1 min -1 , to carry out the reverse water gas reaction.

[0038] Test Example 1

[0039] KI@α-Mo prepared in Example 1 2 C catalyst was tested experimentally.

[0040] During the test, the catalyst was loaded into the reaction tank and H 2 The catalyst was reduced and activated (GHSV = 9 L kg -1 min -1 ), the reduction temperature is 600℃ (heating rate is 10℃min -1 ) and maintained at 600 °C for 3 h; then, the temperature was turned off and the temperature dropped to 400 °C naturally, and the reaction gas was switched to H 2 :CO 2 =1:1, GHSV = 18L kg -1 min -1 The reaction pressure was controlled to 1 bar, 2 bar, 3 bar, and 4 bar respectively. After 60 min of reaction, the outlet gas composition was collected in the gas phase to record the catalytic activity of the catalyst at 400 °C and different pressures.

[0041] Then at 10℃min -1 The temperature was raised to 500°C at a rate of 1 bar, 2 bar, 3 bar, and 4 bar, and the reaction pressure was controlled to be 1 bar, 2 bar, 3 bar, and 4 bar, respectively. After each reaction for 60 min, the outlet gas composition was collected from the gas phase to record the catalytic activity of the catalyst at 500°C and different pressures.

[0042] Similarly, the catalytic performance of the catalyst was tested at 600°C and 700°C under different pressures (1 to 4 bar).

[0043] from Figure 1 The performance test chart shows that KI@α-Mo 2C catalyst at 400-700°C, 1-4 bar, H 2 :CO 2 =1:1, GHSV = 18L kg -1 min -1 Under the conditions of , the products showed excellent performance close to the CO equilibrium yield.

[0044] from Figure 2 The XRD pattern of KI@α-Mo 2 C at 400 °C, 4 bar, reaction gas H 2 :CO 2 =1:1, GHSV = 36Lkg -1 min -1 After 1000 hours of reverse water gas reaction stability test under the conditions of 2 C crystal form, but not transformed into β-Mo with worse performance 2 C crystal form.

[0045] Figure 3 The newly prepared KI@α-Mo 2 C catalyst and Figure 4 KI@α-Mo after 1000 hours of reverse water gas reaction stability test 2 TEM image of C catalyst shows that KI@α-Mo 2 C only experienced grain growth before and after 1000 hours of reaction, but no crystal change occurred. These indicate that KI doped α-Mo 2 C plays a significant role in its performance and crystal stability.

[0046] Example 2

[0047] This embodiment provides an alkali halide doped α-Mo for reverse water gas reaction 2 The preparation method of C catalyst comprises the following steps:

[0048] (1) Caramelization process: (NH 4 ) 6 Mo 7 O 24 ·4H 2 O and sucrose were dissolved in deionized water with a molar ratio of C / Mo of 3.5; KCl was then added with a molar ratio of KCl to Mo of 0.05, and the resulting solution was stirred evenly until completely dissolved; the solution was transferred to a beaker, occupying one-fifth of the volume of the beaker to prevent overflow during the subsequent caramelization process; and then placed in an oven at 110°C and heated for 8 hours to obtain a caramelized KCl-doped molybdenum source intermediate.

[0049] (2)H 2Reduction and carburization process: The caramelized KCl-doped molybdenum source intermediate was fully ground and placed in a quartz tube, which was sealed and filled with quartz wool at both ends. Then, it was heated at 450 °C (heating rate of 10 °C min -1 ) in H 2 atmosphere for 18 hours, the corresponding molybdenum source intermediate H 2 The reduction flow rate is 2L kg -1 min -1 ; H occurred during this process 2 Reduction and carbonization reactions; the sample was then cooled to room temperature in an argon atmosphere to obtain KCl@α-Mo 2 C catalyst.

[0050] The KCl@α-Mo 2 C catalyst is used in the reverse water gas reaction.

[0051] The catalyst was loaded into the reaction tank and, before the reverse water gas reaction, H 2 The catalyst was reduced and activated (GHSV = 9 L kg -1 min -1 ), the reduction temperature is 600℃, and the -1 The heating rate was raised from room temperature to 600 °C and kept at 600 °C for 3 h. Then, the heating was turned off and the temperature dropped to 400 °C naturally. The reaction gas (H 2 :CO 2 =2:1, GHSV = 18Lkg -1 min -1 ) to carry out the reverse water gas reaction.

[0052] Example 3

[0053] This embodiment provides an alkali halide doped α-Mo for reverse water gas reaction 2 The preparation method of C catalyst comprises the following steps:

[0054] (1) Caramelization process: (NH 4 ) 6 Mo 7 O 24 ·4H 2 O and sucrose were dissolved in deionized water with a molar ratio of C / Mo of 3.5; KBr was then added with a molar ratio of KBr to Mo of 0.15, and the resulting solution was stirred evenly until completely dissolved; the solution was transferred to a beaker, occupying one-fifth of the volume of the beaker to prevent overflow during the subsequent caramelization process; and then placed in an oven at 130°C and heated for 12 hours to obtain a caramelized KBr-doped molybdenum source intermediate.

[0055] (2)H2 Reduction and carburization process: The caramelized KBr-doped molybdenum source intermediate was fully ground and placed in a quartz tube, which was sealed and filled with quartz wool at both ends. Then, the tube was heated at 550 °C (heating rate was 10 °C min -1 ) in H 2 atmosphere for 23 hours, the corresponding molybdenum source intermediate H 2 The reduction flow rate is 2L kg -1 min -1 ; H occurred during this process 2 Reduction and carbonization reactions; the sample was then cooled to room temperature in an argon atmosphere to obtain KBr@α-Mo 2 C catalyst.

[0056] The KBr@α-Mo 2 C catalyst is used in the reverse water gas reaction.

[0057] The catalyst was loaded into the reaction tank and, before the reverse water gas reaction, H 2 The catalyst was reduced and activated (GHSV = 9 L kg -1 min -1 ), the reduction temperature is 600℃, and the -1 The heating rate was raised from room temperature to 600 °C and kept at 600 °C for 3 h. Then, the heating was turned off and the temperature dropped to 350 °C naturally. The reaction gas (H 2 :CO 2 =1:1, GHSV = 9Lkg -1 min -1 ) to carry out the reverse water gas reaction.

[0058] Example 4

[0059] This embodiment provides an alkali halide doped α-Mo for reverse water gas reaction 2 The preparation method of C catalyst comprises the following steps:

[0060] (1) Caramelization process: 4 ) 6 Mo 7 O 24 ·4H 2 O and sucrose were dissolved in deionized water with a molar ratio of C / Mo of 2; NaI was then added with a molar ratio of NaI to Mo of 0.11, and the resulting solution was stirred evenly until completely dissolved; the solution was transferred to a beaker, occupying one-fifth of the volume of the beaker to prevent overflow during the subsequent caramelization process; and then placed in an oven at 120°C and heated for 10 hours to obtain a caramelized NaI-doped molybdenum source intermediate.

[0061] (2)H2 Reduction and carburization process: The caramelized NaI-doped molybdenum source intermediate was fully ground and placed in a quartz tube, which was sealed and filled with quartz wool at both ends. Then, the tube was heated at 500 °C (heating rate was 10 °C min -1 ) in H 2 atmosphere for 20 hours, the corresponding molybdenum source intermediate H 2 The reduction flow rate is 2L kg -1 min -1 ; H occurred during this process 2 Reduction and carbonization reactions; the sample was then cooled to room temperature in an argon atmosphere to obtain NaI@α-Mo 2 C catalyst.

[0062] The NaI@α-Mo 2 C catalyst is used in the reverse water gas reaction.

[0063] The catalyst was loaded into the reaction tank and, before the reverse water gas reaction, H 2 The catalyst was reduced and activated (GHSV = 9 L kg -1 min -1 ), the reduction temperature is 600℃, and the -1 The heating rate was raised from room temperature to 600 °C and kept at 600 °C for 3 h. Then, the heating was turned off and the temperature dropped to 450 °C naturally. The reaction gas (H 2 :CO 2 =2:1, GHSV = 36Lkg -1 min -1 ) to carry out the reverse water gas reaction.

[0064] Example 5

[0065] This embodiment provides an alkali halide doped α-Mo for reverse water gas reaction 2 The preparation method of C catalyst comprises the following steps:

[0066] (1) Caramelization process: (NH 4 ) 6 Mo 7 O 24 ·4H 2 O and sucrose were dissolved in deionized water with a molar ratio of C / Mo of 3; NaCl was then added with a molar ratio of NaCl to Mo of 0.11, and the resulting solution was stirred evenly until completely dissolved; the solution was transferred to a beaker, occupying one-fifth of the volume of the beaker to prevent overflow during the subsequent caramelization process; and then placed in an oven at 115°C and heated for 9 hours to obtain a caramelized NaCl-doped molybdenum source intermediate.

[0067] (2)H 2 Reduction and carburization process: The caramelized NaCl-doped molybdenum source intermediate was fully ground and placed in a quartz tube, which was sealed and filled with quartz wool at both ends. Then, the tube was heated at 470 °C (heating rate was 10 °C min -1 ) in H 2 atmosphere for 19 hours, the corresponding molybdenum source intermediate H 2 The reduction flow rate is 2L kg -1 min -1 ; H occurred during this process 2 Reduction and carbonization reactions; the sample was then cooled to room temperature in an argon atmosphere to obtain NaCl@α-Mo 2 C catalyst.

[0068] The NaCl@α-Mo 2 C catalyst is used in the reverse water gas reaction.

[0069] The catalyst was loaded into the reaction tank and, before the reverse water gas reaction, H 2 The catalyst was reduced and activated (GHSV = 9 L kg -1 min -1 ), the reduction temperature is 600℃, and the -1 The heating rate was raised from room temperature to 600 °C and kept at 600 °C for 3 h. Then, the heating was turned off and the temperature dropped to 500 °C naturally. The reaction gas (H 2 :CO 2 =3:1, GHSV = 18Lkg -1 min -1 ) to carry out the reverse water gas reaction.

[0070] Example 6

[0071] This embodiment provides an alkali halide doped α-Mo for reverse water gas reaction 2 The preparation method of C catalyst comprises the following steps:

[0072] (1) Caramelization process: 4 ) 6 Mo 7 O 24 ·4H 2 O and sucrose were dissolved in deionized water with a molar ratio of C / Mo of 4; then NaBr was added with a molar ratio of NaBr to Mo of 0.11, and the obtained solution was stirred evenly until it was completely dissolved; the solution was transferred to a beaker, occupying one-fifth of the volume of the beaker to prevent overflow during the subsequent caramelization process; and then it was placed in an oven at 125°C and heated for 11 hours to obtain a caramelized NaBr-doped molybdenum source intermediate.

[0073] (2)H 2 Reduction and carburization process: The caramelized NaBr-doped molybdenum source intermediate was fully ground and placed in a quartz tube, which was sealed and filled with quartz wool at both ends. Then, the tube was heated at 520 °C (heating rate of 10 °C min -1 ) in H 2 atmosphere for 22 hours, the corresponding molybdenum source intermediate H 2 The reduction flow rate is 2L kg -1 min -1 ; H occurred during this process 2 Reduction and carbonization reactions; the sample was then cooled to room temperature in an argon atmosphere to obtain NaBr@α-Mo 2 C catalyst.

[0074] The NaBr@α-Mo 2 C catalyst is used in the reverse water gas reaction.

[0075] The catalyst was loaded into the reaction tank and, before the reverse water gas reaction, H 2 The catalyst was reduced and activated (GHSV = 9 L kg -1 min -1 ), the reduction temperature is 600℃, and the -1 The heating rate was increased from room temperature to 600 °C and kept at 600 °C for 3 h; then, the temperature was increased to 700 °C and the reaction gas (H 2 :CO 2 =4:1, GHSV = 54L kg -1 min -1 ) to carry out the reverse water gas reaction.

[0076] The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still modify the technical solutions described in the above embodiments, or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, modification, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing an alkali halide-doped α-Mo2C catalyst for reverse water gas reaction, characterized in that: The following steps are involved: (1) dissolving a molybdenum source and sucrose in water at a C / Mo molar ratio of 2 to 4, then adding an alkali halide at a molar ratio of alkali halide to Mo of 0.05 to 0.15, stirring until completely dissolved, and heating the solution at 110 to 130° C. for 8 to 12 hours to obtain a caramelized alkali halide-doped molybdenum source intermediate; (2) The caramelized alkali halide-doped molybdenum source intermediate is fully ground, reduced in a H2 atmosphere at a temperature of 450 to 550°C for 18 to 23 hours, and then cooled to room temperature in an argon atmosphere to obtain an alkali halide-doped α-Mo2C catalyst.

2. The preparation method according to claim 1, characterized in that: The molybdenum source is (NH4)6Mo7O 24 ·4H2O.

3. The preparation method according to claim 1, characterized in that: The alkali halide is any one or more of KI, KCl, KBr, KF, NaI, NaCl, NaBr, and NaF.

4. The preparation method according to claim 1, characterized in that: The flow rate of the hydrogen is 2Lkg -1 min -1 .

5. The preparation method according to claim 1, characterized in that: The solution in step (1) is heated at 120° C. for 10 h.

6. The preparation method according to claim 1, characterized in that: The molybdenum source intermediate in step (2) is reduced in a H2 atmosphere at 500°C for 20h; the heating rate is 10°C min -1 .

7. An alkali halide-doped α-Mo2C catalyst prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the alkali halide-doped α-Mo2C catalyst according to claim 7 in the reverse water gas reaction.

9. The use according to claim 8, characterized in that: The temperature of the reverse water gas reaction is 350-700°C. The reverse water gas reaction uses H2 and CO2 as reaction gases. The volume ratio of H2 to CO2 is (1-4):1, and GHSV=9-54Lkg -1 min -1 .

10. The use according to claim 9, characterized in that: The temperature of the reverse water gas reaction is 400°C.

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