Supported molybdenum carbide catalyst and preparation method and application thereof

Abstract

The invention belongs to the technical field of catalysts, and relates to a supported molybdenum carbide catalyst, which comprises a carrier and an active component, the carrier is an MY molecular sieve, and the active component is molybdenum carbide; and M is one or two of Co, Ni and Cu. The preparation method comprises the following steps: mixing a molybdenum source solution with the MY molecular sieve, drying, calcining, and carbonizing in a reducing mixed gas atmosphere to obtain the supported molybdenum carbide catalyst. The Y molecular sieve is good in hydrothermal stability, has a typical microporous structure, is relatively large in specific surface area, and can well disperse active substances, so that more active components are exposed on the surface and participate in the reaction, meanwhile, relatively small and relatively dispersed metal particles are obtained, and the metal particles can be effectively prevented from being in contact with molybdenum carbide; and on the other hand, the metal M is beneficial to H2 activation, the dissociation capacity of H2 is improved, and hydroxyl remaining on the surface of molybdenum carbide in the reaction process can be removed.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and in particular relates to a supported molybdenum carbide catalyst and a preparation method and application thereof. Background Art

[0002] The extensive use of carbon-based materials can quickly bring a lot of energy to humans, but CO2 is also produced. The continuous increase in the concentration of CO2 in the atmosphere will lead to frequent environmental problems such as global temperature rise, extreme weather and ecosystem destruction. However, renewable energy such as wind power and solar energy are still difficult to fully replace fossil fuels. In order to reduce the CO2 content, some researchers have proposed to capture and store CO2, but at the same time, CO2 exists as a cheap carbon source. Converting it into other chemical products, such as CO, CH4, alcohols or hydrocarbons, is an effective way to achieve resource utilization. In comparison, CO, as a product of CO2 catalytic hydrogenation, has relatively good application value in industrial production and can be used again through Fischer-Tropsch synthesis to generate alcohols or hydrocarbons. The C=O bond energy in CO2 is high, making it difficult to activate, and the product selectivity is difficult to control in catalytic reduction. The key issue to achieve high selectivity and conversion rate of the target product is to find a suitable catalyst.

[0003] Precious metal catalysts such as typical Pt-based catalysts have good H2 dissociation ability and high catalytic activity, but cost issues make this catalyst have certain limitations in application; Molybdenum carbide catalysts have precious metal-like properties due to their unique electronic structure and maintain high CO selectivity in CO2 catalytic reduction, but in the process of participating in the reverse water gas shift reaction, due to the relatively weak ability of Molybdenum carbide to dissociate hydrogen, the surface hydroxyl groups are easily left on the catalyst surface, causing deactivation.

[0004] In order to make the molybdenum carbide catalyst more active and stable, on the one hand, a certain amount of metal is added, but excessive contact between metal and molybdenum carbide will destroy the surface structure of molybdenum carbide, thereby inhibiting the reaction; on the other hand, a carrier is introduced into the catalyst to form a supported molybdenum carbide catalyst to fully expose the active sites. Common carriers are Al2O3, SiO2, CeO2, etc.

[0005] Chinese patent CN116571260A discloses a catalyst with Al2O3 as carrier and molybdenum carbide as active component, which achieves high selectivity of target product alcohol under 3.0MPa conditions. In addition to this common metal oxide, Chinese patent CN116219487A discloses a carbon-supported molybdenum carbide catalyst containing ruthenium single atoms, which achieves high dispersion of metal ruthenium and good catalytic effect. The preparation of the catalyst requires the participation of a guiding agent, and there are disadvantages such as a complicated preparation process, and the presence of ruthenium still does not avoid the use of precious metals. Chinese patent CN117884151A discloses a catalyst with carbon nanotubes as carrier and molybdenum carbide as active component, and uses an oxidant (concentrated nitric acid or concentrated sulfuric acid) to modify the carrier and load molybdenum carbide, and successfully encapsulates molybdenum carbide in carbon nanotubes, and CO selectivity reaches more than 90% when reacting at 400°C, but the catalyst is slightly deactivated after a long reaction time.

[0006] Therefore, in order to simultaneously improve the catalytic stability and activity of molybdenum carbide and reduce the cost, on the one hand, it is necessary to introduce cheap transition metals to provide dissociated hydrogen atoms, and on the other hand, to reduce the contact between transition metals and molybdenum carbide. Summary of the invention

[0007] The purpose of the present invention is to provide a supported molybdenum carbide catalyst and a preparation method and application thereof, so as to overcome the problems of poor stability of the molybdenum carbide catalyst itself and easy residual hydroxyl groups on the surface during the reaction, while avoiding the use of precious metals, and achieving the characteristics of high stability and high CO selectivity of the catalyst.

[0008] The present invention is achieved through the following technical solutions:

[0009] A supported molybdenum carbide catalyst, comprising a carrier and an active component;

[0010] The carrier is MY molecular sieve, and the active component is molybdenum carbide;

[0011] M is one or two of Co, Ni, and Cu.

[0012] Furthermore, the content of M is (1-5) wt%; the content of molybdenum carbide is (2-20) wt%.

[0013] The present invention also discloses a method for preparing a supported molybdenum carbide catalyst, comprising the following steps:

[0014] S1, adding carrier Y molecular sieve to the metal salt solution, mixing thoroughly to obtain a suspension;

[0015] The suspension is subjected to ion exchange, filtration, washing and drying to obtain MY molecular sieve;

[0016] dissolving a molybdenum source in a solvent to obtain a molybdenum source solution;

[0017] S2. Mixing the molybdenum source solution with the MY molecular sieve, drying, and calcining, and carbonizing the mixture under a reducing mixed gas atmosphere to obtain a supported molybdenum carbide catalyst.

[0018] Further, in S1, the metal element in the metal salt solution is one or two of Co, Ni, and Cu;

[0019] The molybdenum source is molybdenum oxide, ammonium molybdate or molybdenum acetylacetonate;

[0020] The solvent is water or ethanol;

[0021] The Y molecular sieve is HY molecular sieve or NaY molecular sieve.

[0022] Furthermore, in S1, the concentration of the metal salt solution is 0.01-0.05 mol / L.

[0023] Further, in S1, the ion exchange water bath temperature is 50-90°C and the time is 2-6h;

[0024] Wash several times with deionized water or anhydrous ethanol, the drying temperature is 50-100℃, and the drying time is 4-12h.

[0025] Further, in S2, the mixing is specifically: stirring and mixing under magnetic stirring, and the mixing temperature is 60-80° C.;

[0026] The drying is specifically: drying at 50-80° C. for 6-12 hours;

[0027] The calcination temperature is 400-600°C and the time is 2-5h.

[0028] Further, in S2, the reducing mixed gas used in the carbonization process is one of C2H6 / H2, CH4 / H2, and CO / H2;

[0029] The heating rate is 2-5°C / min, the carbonization temperature is 600-800°C, and the insulation time is 2-6h to obtain a supported molybdenum carbide catalyst.

[0030] Furthermore, the calcination process is calcined at 500° C. for 2-5 hours; the carbonization process is heated from room temperature to 680° C. at 2-5° C. / min and kept warm for 2-6 hours.

[0031] The invention also discloses the application of the supported molybdenum carbide catalyst in the reverse water-gas shift reaction.

[0032] Compared with the prior art, the present invention has the following beneficial technical effects:

[0033] The present invention discloses a supported molybdenum carbide catalyst, which uses MY molecular sieve as a carrier and molybdenum carbide as an active component to construct a molecular sieve-supported molybdenum carbide catalyst. On the one hand, the Y molecular sieve has good hydrothermal stability, a typical microporous structure, and a large specific surface area, which can better disperse active substances, thereby exposing more active components to the surface and participating in the reaction, and at the same time obtaining smaller and more dispersed metal particles, which can effectively avoid the contact between metal particles and molybdenum carbide; on the other hand, metal M is conducive to H2 activation, improves H2 dissociation ability, and helps to remove the hydroxyl groups remaining on the surface of molybdenum carbide during the reaction. The synergistic effect of the two makes the catalyst provided by the present invention have higher CO selectivity and stability in the reverse water gas shift reaction.

[0034] The supported molybdenum carbide catalyst prepared by the present invention exerts the synergistic effect between molybdenum carbide and metal to further promote the improvement of catalytic activity and stability. In the application of reverse water gas shift reaction, the reaction temperature is reduced to a certain extent, the energy loss of the reaction process is reduced, and the use of precious metals is avoided, thereby reducing industrial utilization costs. The active components in the catalyst are highly stable and not easy to deactivate, and the preparation method is simple and the cost is low.

[0035] The present invention also discloses a method for preparing a supported molybdenum carbide catalyst. The preparation method first uses an ion exchange method to load the metal M into a carrier, and then introduces the active component molybdenum carbide. The catalyst preparation process is simple and the raw materials are easily available. The contact between the metal and the molybdenum carbide can be effectively avoided, while the dispersibility of the metal is improved, further promoting the improvement of the catalytic activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 XRD characterization diagram of the catalyst prepared by the present invention;

[0037] Figure 2 The graph of CO2 conversion rate in the reaction of the catalyst prepared in Examples 1-7 and Comparative Example 1;

[0038] Figure 3 The CO selectivity diagram of the catalysts prepared in Examples 1-7 and Comparative Example 1 in the reaction;

[0039] Figure 4 This is a graph showing the CO2 conversion rate of the catalyst prepared in Example 2 at 300°C. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the present invention more clear, the following is further described in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the embodiments described are only part of the embodiments of the present invention, not all embodiments.

[0041] The components described and shown in the drawings and embodiments of the present invention may be arranged and designed in various configurations. Therefore, the detailed description of the embodiments of the present invention provided in the following drawings is not intended to limit the scope of the claimed invention, but merely represents a selected embodiment of the present invention. Based on the drawings and embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0042] It should be noted that the terms "comprises", "includes" or any other variations are intended to cover non-exclusive inclusion, so that a process, element, method, article or equipment that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to the process, element, method, article or equipment.

[0043] The present invention discloses a method for preparing a supported molybdenum carbide catalyst, comprising the following steps:

[0044] S1, adding carrier Y molecular sieve to the metal salt solution, mixing thoroughly to obtain a suspension;

[0045] The suspension is subjected to ion exchange, filtration, washing and drying to obtain MY molecular sieve;

[0046] dissolving a molybdenum source in a solvent to obtain a molybdenum source solution;

[0047] S2. Mixing the molybdenum source solution with the MY molecular sieve, drying, and calcining, and carbonizing the mixture under a reducing mixed gas atmosphere to obtain a supported molybdenum carbide catalyst.

[0048] The supported molybdenum carbide catalyst prepared by the present invention comprises a carrier and an active component;

[0049] The carrier is MY molecular sieve, the active component is molybdenum carbide; M is one or two of Co, Ni and Cu.

[0050] The content of M is (1-5) wt%; the loading amount of molybdenum carbide is (2-20) wt%.

[0051] The features and performances of the present invention are further described in detail below in conjunction with the embodiments.

[0052] Unless otherwise specified, the raw materials used in the examples of the present invention were purchased from commercial sources.

[0053] Example 1

[0054] Measure 26.2 mL of 0.01 mol / L cobalt nitrate solution, take 0.5 g of HY molecular sieve and place it in the cobalt nitrate solution for ion exchange, stir it in a water bath at 80°C for 2 h, filter it and wash it with deionized water, and dry it at 100°C for 4 h to obtain CoY molecular sieve;

[0055] Weigh 0.19 g of molybdenum acetylacetonate and dissolve it in 50 mL of water to prepare a solution;

[0056] Weigh 0.3 g of CoY molecular sieve and place it in the above solution, stir and dry at 70° C. to obtain a catalyst precursor;

[0057] The catalyst precursor was transferred to a 60°C oven and dried for 12 hours, and calcined at 550°C for 3 hours. The calcined catalyst was transferred to a quartz bottle reactor, and the temperature was increased from room temperature to 680°C at a heating rate of 2.5°C / min under a CH4 / H2 mixed gas, and kept warm for 2 hours to obtain a CoY-loaded molybdenum carbide catalyst, which was recorded as catalyst sample A.

[0058] Example 2

[0059] Measure 22.3 mL of 0.02 mol / L cobalt nitrate solution, take 0.5 g of NaY molecular sieve and place it in the cobalt nitrate solution for ion exchange, stir in a water bath at 80°C for 4 h, filter and wash with deionized water, and dry at 70°C for 6 h to obtain CoY molecular sieve;

[0060] Weigh 0.1 g of ammonium molybdate and dissolve it in 20 mL of deionized water to prepare an ammonium molybdate solution;

[0061] Weigh 0.3 g of CoY molecular sieve and place it in an ammonium molybdate solution, stir and dry at 70° C. to obtain a catalyst precursor;

[0062] The catalyst precursor was transferred to a 70°C oven and dried for 6 hours, and calcined at 550°C for 3 hours. The calcined catalyst was transferred to a quartz bottle reactor, and the temperature was increased from room temperature to 680°C at a heating rate of 2.5°C / min under a CH4 / H2 mixed gas, and kept warm for 4 hours to obtain a CoY-loaded molybdenum carbide catalyst, which was recorded as catalyst sample B.

[0063] Example 3

[0064] 4.3 mL of 0.02 mol / L copper nitrate solution was measured, and 0.5 g of NaY molecular sieve was placed in the cobalt nitrate solution for ion exchange, stirred in a water bath at 80°C for 4 h, filtered and washed with deionized water, and dried at 70°C for 6 h to obtain CuY molecular sieve;

[0065] Weigh 0.1 g of ammonium molybdate and dissolve it in 20 mL of deionized water. Stir and dissolve it fully at 70°C to prepare an ammonium molybdate solution.

[0066] Weigh 0.3 g of CuY molecular sieve and place it in an ammonium molybdate solution, stir and dry at 70° C. to obtain a catalyst precursor;

[0067] The catalyst precursor was transferred to a 60°C oven and dried for 12 hours, and calcined at 500°C for 3 hours. The calcined catalyst was placed in a quartz bottle reactor and heated from room temperature to 680°C at a heating rate of 2.5°C / min under a CH4 / H2 mixed gas, and kept warm for 2 hours to obtain a CuY-loaded molybdenum carbide catalyst, which was recorded as catalyst sample C.

[0068] Example 4

[0069] The preparation steps are basically the same as those in Example 1, except that the 26.2 mL of cobalt nitrate solution in Example 1 is replaced with 26.3 mL of nickel nitrate solution of the same concentration to obtain a NiY-supported molybdenum carbide catalyst, which is recorded as catalyst sample D.

[0070] Example 5

[0071] 6.5 mL of 0.02 mol / L nickel nitrate and cobalt nitrate solutions were measured respectively, and 0.5 g of HY molecular sieve was placed in the mixed salt solution for ion exchange, stirred in a water bath at 80°C for 2 h, filtered and washed with deionized water, and dried at 70°C for 6 h to obtain CoNiY molecular sieve;

[0072] Weigh 0.1 g of ammonium molybdate and dissolve it in 20 mL of deionized water. Stir and dissolve it fully at 70°C to prepare an ammonium molybdate solution.

[0073] Weigh 0.3 g of CoNiY molecular sieve and place it in an ammonium molybdate solution. After stirring and drying at 70°C, transfer it to a 70°C oven and dry it for 12 hours. Calcined it at 500°C for 3 hours. Transfer the calcined catalyst to a quartz bottle reactor and heat it from room temperature to 630°C at a heating rate of 2.5°C / min under a CH4 / H2 mixed gas. Keep it warm for 4 hours to obtain a CoNiY-loaded molybdenum carbide catalyst, which is recorded as catalyst sample E.

[0074] Example 6

[0075] The preparation steps are basically the same as those in Example 5, except that: 8.6 mL and 8 mL of 0.02 mol / L cobalt nitrate and copper nitrate solutions are measured respectively to obtain CoCuY molecular sieves, and 0.086 g of molybdenum oxide is weighed and dissolved in 46 mL of deionized water to obtain a CoCuY-loaded molybdenum carbide catalyst, which is recorded as sample F.

[0076] Example 7

[0077] The preparation steps are basically the same as those in Example 5, except that: 13 mL and 11.9 mL of 0.01 mol / L nickel nitrate and copper nitrate solutions are measured respectively to obtain NiCuY molecular sieve, 0.086 g of molybdenum oxide is weighed and dissolved in 46 mL of deionized water, and finally a NiCuY-loaded molybdenum carbide catalyst is obtained, which is recorded as sample G.

[0078] Comparative Example 1

[0079] Weigh 0.1 g of ammonium molybdate and dissolve it in 20 mL of water to prepare an ammonium molybdate solution. Stir and dissolve it in a 70°C water bath. Weigh 0.3 g of NaY molecular sieve and place it in the ammonium molybdate solution. Stir and dry it at 70°C, then transfer it to a 60°C oven and dry it for 12 h. Calcine it at 550°C for 3 h. Put the calcined catalyst into a quartz bottle reactor, and heat it from room temperature to 680°C at a heating rate of 2.5°C / min under a CH4 / H2 mixed gas, and keep it warm for 2 h to obtain the catalyst Mo2C / Y.

[0080] Activity test process: Weigh 100 mg of catalyst sample and place it in a fixed bed quartz reactor with a diameter of 20 mm to test the performance of the reverse water gas shift reaction. Use a gas chromatograph to analyze and detect the tail gas and raw gas after the reaction. The catalyst activity is expressed by CO2 conversion rate and CO selectivity. The CO2:H2 ratio in the reaction raw gas is 4:1, the raw gas flow rate is 20 mL / min, the reaction temperature range is 200-400°C, the heating rate is 10°C / min, the reaction pressure is normal pressure, and the catalyst sample is tested for activity at a reaction temperature of 50°C. The test results are as follows: Figure 2-3 shown.

[0081] Depend on Figure 2-Figure 3 It can be seen that within the test temperature range of 200-400°C, the catalysts AG prepared in Examples 1-7 have a significantly improved conversion rate for CO2 compared to the catalyst Mo2C / Y prepared in Comparative Example 1, among which the catalytic effect of the real catalyst B is the best, and the conversion rate reaches 23% when the reaction temperature is 400°C, which is about 3 times higher than the conversion rate at the same temperature. Within the temperature range of 200-250°C, except for catalysts B and G, the selectivity of the remaining catalysts for the product CO is not high, but within the temperature range of 300-400°C, the CO selectivity remains above 80%, so it can be explained that the supported molybdenum carbide catalyst provided by the present invention improves the activity of the molybdenum carbide catalyst in the reverse water gas shift reaction, has a good catalytic effect, and when the reaction temperature is above 300°C, the product CO selectivity is high.

[0082] The catalysts prepared in Examples 1-7 were subjected to X-ray diffraction analysis to obtain the following Figure 1The XRD diffraction pattern shown clearly shows that the synthesized molybdenum carbide crystal phase is β phase, and no characteristic peak of metal Co is observed, indicating that the Co dispersion in the catalyst is good.

[0083] The stability test of the catalyst sample B prepared in Example 2 was carried out at 300°C. The test results are as follows: Figure 4 As shown, it can be seen that the catalyst has good stability in the stability test and the deactivation phenomenon is not obvious, which means that when the catalyst prepared by the present invention is used for the reverse water-gas shift reaction, it can maintain structural stability and catalytic activity for a long time.

[0084] The reverse water gas shift (RWGS) reaction is a key step in converting carbon dioxide (CO2) into high value-added chemicals and fuels such as methanol, light olefins, aromatics and gasoline by hydrogenation. The supported molybdenum carbide catalyst prepared by the present invention improves the catalytic activity in the application of low-temperature reverse water gas shift reaction, reduces the energy consumption of the reaction process to a certain extent, avoids the use of precious metals, reduces the cost of industrial utilization, and plays a synergistic role between molybdenum carbide and metals to further promote the improvement of catalytic activity and stability. The active components in the catalyst are highly stable and not easy to deactivate, and the preparation method is simple and low in cost.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A supported molybdenum carbide catalyst, characterized in that including a carrier and an active component; The carrier is MY molecular sieve, and the active component is molybdenum carbide; M is one or two of Co, Ni, and Cu.

2. A supported molybdenum carbide catalyst according to claim 1, characterized in that The content of M is (1-5) wt%; the content of molybdenum carbide is (2-20) wt%.

3. The method for preparing a supported molybdenum carbide catalyst according to claim 1 or 2, characterized in that: The process includes: S1, adding carrier Y molecular sieve to the metal salt solution, mixing thoroughly to obtain a suspension; The suspension is subjected to ion exchange, filtration, washing and drying to obtain MY molecular sieve; dissolving a molybdenum source in a solvent to obtain a molybdenum source solution; S2. Mixing the molybdenum source solution with the MY molecular sieve, drying, and calcining, and carbonizing the mixture under a reducing mixed gas atmosphere to obtain a supported molybdenum carbide catalyst.

4. The method for preparing a supported molybdenum carbide catalyst according to claim 3, characterized in that: In S1, the metal element in the metal salt solution is one or two of Co, Ni, and Cu; The molybdenum source is molybdenum oxide, ammonium molybdate or molybdenum acetylacetonate; The solvent is water or ethanol; The Y molecular sieve is HY molecular sieve or NaY molecular sieve.

5. The method for preparing a supported molybdenum carbide catalyst according to claim 3, characterized in that: In S1, the concentration of the metal salt solution is 0.01-0.05 mol / L.

6. The method for preparing a supported molybdenum carbide catalyst according to claim 3, characterized in that: In S1, the ion exchange water bath temperature is 50-90°C and the time is 2-6h; Wash several times with deionized water or anhydrous ethanol, the drying temperature is 50-100℃, and the drying time is 4-12h.

7. The method for preparing a supported molybdenum carbide catalyst according to claim 3, characterized in that: In S2, the mixing specifically comprises: stirring and mixing under magnetic stirring, and the mixing temperature is 60-80° C.; The drying is specifically: drying at 50-80° C. for 6-12 hours; The calcination temperature is 400-600°C and the time is 2-5h.

8. The method for preparing a supported molybdenum carbide catalyst according to claim 3, characterized in that: In S2, the reducing mixed gas used in the carbonization process is one of C2H6 / H2, CH4 / H2, and CO / H2; The heating rate is 2-5°C / min, the carbonization temperature is 600-800°C, and the insulation time is 2-6h to obtain a supported molybdenum carbide catalyst.

9. The method for preparing a supported molybdenum carbide catalyst according to claim 3, characterized in that: The calcination process is calcined at 500° C. for 2-5 hours; the carbonization process is heated from room temperature to 680° C. at 2-5° C. / min and kept warm for 2-6 hours.

10. Use of the supported molybdenum carbide catalyst according to claim 1 or 2 in the reverse water gas shift reaction.

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