A supported molybdenum carbide catalyst, its preparation method and use

Abstract

The application 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 MY molecular sieve, and the active component is molybdenum carbide; M is one or two of Co, Ni and Cu. A preparation method thereof is also disclosed, in which a molybdenum source solution is mixed with MY molecular sieve, dried, calcined, and then carbonized in a reducing mixed gas atmosphere to obtain the supported molybdenum carbide catalyst. The Y molecular sieve has good hydrothermal stability, a typical microporous structure, a large specific surface area, and can better disperse the active substance, so that more active components are exposed on the surface and participate in the reaction, and at the same time, smaller and more dispersed metal particles are obtained, which can effectively avoid the contact between the metal particles and the molybdenum carbide; on the other hand, the metal M is beneficial to H2 activation, improves the H2 dissociation capacity, and is helpful to remove the hydroxyl groups remaining on the surface of the molybdenum carbide during the reaction.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of catalysts, and particularly relates to a supported molybdenum carbide catalyst and a preparation method and application thereof. BACKGROUND

[0002] The massive use of carbon-based materials can quickly bring a large amount of energy to humans, but CO2 is also generated, and the continuous increase of CO2 concentration in the atmosphere will lead to global warming, extreme weather and frequent environmental problems such as ecological system destruction, but currently renewable energy such as wind energy and solar energy is still difficult to fully replace fossil fuels. In order to reduce the CO2 content, some researchers propose to capture and store CO2, but at the same time, CO2 exists as a cheap carbon source, and its conversion into other chemical products such as CO, CH4, alcohol or hydrocarbon substances is an effective way to realize resource utilization. Compared with other products, CO has relatively good application value in industrial production as a product of CO2 catalytic hydrogenation, and can be used again through Fischer-Tropsch synthesis to generate alcohol or hydrocarbon substances. The C=O bond energy in CO2 is high, which is difficult to activate, and the selectivity of the product in catalytic reduction is difficult to control, and the key problem to realize high selectivity and conversion rate of the target product is to find a suitable catalyst.

[0003] The noble metal catalyst such as the typical Pt-based catalyst has good H2 dissociation capacity and high catalytic activity, but the cost problem limits the application of the catalyst; the molybdenum carbide catalyst has the property of noble metal due to its unique electronic structure, and has high CO selectivity in the catalytic reduction of CO2, but in the process of participating in the reverse water gas shift reaction, the surface hydroxyl is easy to remain on the surface of the catalyst due to the relatively weak hydrogen dissociation capacity of the molybdenum carbide, which further causes deactivation.

[0004] In order to make the activity and stability of the molybdenum carbide catalyst better, on the one hand, a certain amount of metal is added, but too much contact between the metal and the molybdenum carbide will damage the surface structure of the molybdenum carbide, and then inhibit the reaction; on the other hand, a carrier is introduced into the catalyst to form a supported molybdenum carbide catalyst, so that the active sites are fully exposed, and the common carriers are Al2O3, SiO2, CeO2 and the like.

[0005] A catalyst with Al2O3 as the carrier and molybdenum carbide as the active component is disclosed in Chinese patent CN116571260A, which realizes high selectivity of target product alcohol under the condition of 3.0 MPa. In addition to common metal oxides, Chinese patent CN116219487A discloses a carbon-supported molybdenum carbide catalyst containing a single ruthenium atom, which realizes high dispersion of metal ruthenium and good catalytic effect. However, the preparation process of the catalyst needs the participation of a directing agent, and there are disadvantages such as complex preparation process, and the use of noble metal cannot be avoided. Chinese patent CN117884151A discloses a catalyst with carbon nanotubes as the carrier and molybdenum carbide as the active component. After the carrier is modified by an oxidizing agent (concentrated nitric acid or concentrated sulfuric acid) and loaded with molybdenum carbide, the molybdenum carbide is successfully encapsulated in the carbon nanotubes. The CO selectivity reaches more than 90% at 400℃, but the catalyst is slightly deactivated after a long time of reaction.

[0006] Therefore, to simultaneously improve the catalytic stability and activity of molybdenum carbide and reduce the cost, on the one hand, a cheap transition metal needs to be introduced to provide dissociated hydrogen atoms, and on the other hand, the contact between the transition metal and molybdenum carbide needs to be reduced. SUMMARY

[0007] The purpose of the present application is to provide a supported molybdenum carbide catalyst and its preparation method and application, so as to overcome the problems of poor stability of molybdenum carbide catalyst itself and easy residual of surface hydroxyl during reaction, and at the same time avoid the use of noble metal, realize the characteristics of high stability and high CO selectivity of the catalyst.

[0008] The present application is realized by 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] Further, the content of M is (1-5) wt%, and the content of molybdenum carbide is (2-20) wt%.

[0013] The present application also discloses a preparation method of a supported molybdenum carbide catalyst, comprising the following processes:

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

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

[0016] The molybdenum source is dissolved in a solvent to obtain a molybdenum source solution;

[0017] S2, the molybdenum source solution is mixed with the MY molecular sieve, dried, calcined, and carbonized 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 acetylacetone.

[0020] The solvent is water or ethanol.

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

[0022] Further, 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℃, and the time is 2-6h.

[0024] Deionized water or anhydrous ethanol is used for washing several times, the drying temperature is 50-100℃, and the drying time is 4-12h.

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

[0026] The drying is specifically drying at 50-80℃ for 6-12h.

[0027] The calcination temperature is 400-600℃, 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 temperature rising rate is 2-5℃ / min, the carbonization temperature is 600-800℃, and the holding time is 2-6h, to obtain the supported molybdenum carbide catalyst.

[0030] Further, the calcination process is calcination at 500℃ for 2-5h, and the carbonization process is rising from room temperature to 680℃ at a rate of 2-5℃ / min and holding for 2-6h.

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

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

[0033] The application discloses a supported molybdenum carbide catalyst, takes MY molecular sieve as a carrier, takes molybdenum carbide as an active component, and constructs the molecular sieve supported molybdenum carbide catalyst. On one hand, the Y molecular sieve has good hydrothermal stability, a typical microporous structure, and a larger specific surface area, can better disperse the active substance, and then makes more active components exposed on the surface and participate in the reaction, and meanwhile, smaller and more dispersed metal particles are obtained, so that the contact between the metal particles and the molybdenum carbide can be effectively avoided. On the other hand, the metal M is beneficial to H2 activation, improves the H2 dissociation capacity, and is helpful to remove the residual hydroxyl on the surface of the molybdenum carbide in the reaction process. The synergistic effect of the two makes the catalyst provided by the application have higher CO selectivity and stability in the reverse water gas shift reaction.

[0034] The prepared supported molybdenum carbide catalyst in the application plays the synergistic effect between the molybdenum carbide and the metal, further promotes the improvement of the catalytic activity and stability, reduces the reaction temperature in the application of the reverse water gas shift reaction to a certain extent, reduces the energy loss in the reaction process, avoids the use of noble metals, reduces the industrial utilization cost, the active component in the catalyst has high stability and is not easy to be deactivated, and the preparation method is simple and low in cost.

[0035] The application further discloses a preparation method of the supported molybdenum carbide catalyst. The metal M is first loaded into the carrier by using an ion exchange method, and then the active component molybdenum carbide is introduced, so that the catalyst preparation process is simple, raw materials are easy to obtain, the contact between the metal and the molybdenum carbide can be effectively avoided, the dispersity of the metal is improved, and the improvement of the catalytic activity is further promoted. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 The XRD characterization graph of the catalyst prepared in the application;

[0037] Figure 2 The CO2 conversion rate graph of the catalyst prepared in the examples 1-7 and the comparative example 1 in the reaction;

[0038] Figure 3 The CO selectivity graph of the catalyst prepared in the examples 1-7 and the comparative example 1 in the reaction;

[0039] Figure 4 The CO2 conversion rate graph of the catalyst prepared in the example 2 under the reaction at 300 DEG C. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical scheme and advantages of the application clearer and more apparent, the following further describes in detail in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the application, and are not used to limit the application, that is, the described examples are only a part of the examples of the application, but not all the examples.

[0041] The components shown in the description and drawings of the application can be arranged and designed in a variety of different configurations, therefore, the detailed description of the embodiments of the application provided in the following drawings is not intended to limit the scope of the application claimed, but merely represents a selected embodiment of the application. Based on the drawings and embodiments of the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the application.

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

[0043] The application discloses a preparation method of a supported molybdenum carbide catalyst.

[0044] S1, the carrier Y molecular sieve is added to a metal salt solution, and is fully mixed to obtain a suspension;

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

[0046] The molybdenum source is dissolved in a solvent to obtain a molybdenum source solution;

[0047] S2, the molybdenum source solution is mixed with the MY molecular sieve, dried, calcined, and subjected to carbonization under a reducing mixed gas atmosphere to obtain the supported molybdenum carbide catalyst.

[0048] The prepared supported molybdenum carbide catalyst comprises a carrier and an active component.

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

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

[0051] The features and performances of the application are further described in detail in combination with the following embodiments.

[0052] Unless otherwise specified, the raw materials used in the embodiments of the application are purchased through commercial channels.

[0053] Example 1

[0054] Take 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 under 80°C water bath for 2 h, filter and wash with deionized water, dry at 100°C for 4 h, to obtain CoY molecular sieve;

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

[0056] Take 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] Transfer the catalyst precursor to a 60°C oven and dry for 12 h, and calcine at 550°C for 3 h, then transfer the calcined catalyst to a quartz bottle reactor, and raise the temperature from room temperature to 680°C at a rate of 2.5°C / min under CH4 / H2 mixed gas, and keep the temperature for 2 h, to obtain a CoY supported molybdenum carbide catalyst, which is denoted as catalyst sample A.

[0058] Example 2

[0059] Take 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 under 80°C water bath for 4 h, filter and wash with deionized water, and dry at 70°C for 6 h, to obtain CoY molecular sieve;

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

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

[0062] Transfer the catalyst precursor to a 70°C oven and dry for 6 h, and calcine at 550°C for 3 h, then transfer the calcined catalyst to a quartz bottle reactor, and raise the temperature from room temperature to 680°C at a rate of 2.5°C / min under CH4 / H2 mixed gas, and keep the temperature for 4 h, to obtain a CoY supported molybdenum carbide catalyst, which is denoted as catalyst sample B.

[0063] Example 3

[0064] Take 4.3 mL of 0.02 mol / L copper nitrate solution, take 0.5 g of NaY molecular sieve and place it in the cobalt nitrate solution for ion exchange, stir under 80°C water bath for 4 h, filter and wash with deionized water, and dry at 70°C for 6 h, to obtain CuY molecular sieve;

[0065] Take 0.1 g of ammonium molybdate and dissolve it in 20 mL of deionized water, stir and dissolve thoroughly at 70°C, to prepare an ammonium molybdate solution;

[0066] 0.3g of CuY molecular sieve was weighed and placed in the ammonium molybdate solution, and after stirring and drying at 70°C, a catalyst precursor was obtained;

[0067] The catalyst precursor was transferred to a 60°C oven and dried for 12h, and calcined at 500°C for 3h. The calcined catalyst was transferred to a quartz bottle reactor, and was heated from room temperature to 680°C at a heating rate of 2.5°C / min under CH4 / H2mixed gas, and was kept at 680°C for 2h, to obtain a CuY supported molybdenum carbide catalyst, which was recorded as catalyst sample C.

[0068] Example 4

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

[0070] Example 5

[0071] 6.5mL of a 0.02mol / L nickel nitrate solution and a 0.5g HY molecular sieve were weighed and placed in the mixed salt solution for ion exchange, and were stirred in a water bath at 80°C for 2h. After filtration and washing with deionized water, the CoNiY molecular sieve was dried at 70°C for 6h.

[0072] 0.1g of ammonium molybdate was dissolved in 20mL of deionized water, and was stirred at 70°C until dissolved to obtain an ammonium molybdate solution;

[0073] 0.3g of CoNiY molecular sieve was weighed and placed in the ammonium molybdate solution, and after stirring and drying at 70°C, the catalyst precursor was transferred to a 70°C oven and dried for 12h, and was calcined at 500°C for 3h. The calcined catalyst was transferred to a quartz bottle reactor, and was heated from room temperature to 630°C at a heating rate of 2.5°C / min under CH4 / H2mixed gas, and was kept at 630°C for 4h, to obtain a CoNiY supported molybdenum carbide catalyst, which was recorded as catalyst sample E.

[0074] Example 6

[0075] The preparation steps were basically the same as in Example 5, except that 8.6mL and 8mL of a 0.02mol / L cobalt nitrate solution and a copper nitrate solution were weighed, to obtain a CoCuY molecular sieve. 0.086g of molybdenum oxide was dissolved in 46mL of deionized water, to obtain a CoCuY supported molybdenum carbide catalyst, which was recorded as sample F.

[0076] Example 7

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

[0078] Comparative Example 1

[0079] 0.1 g of ammonium molybdate was dissolved in 20 mL of water to prepare an ammonium molybdate solution. The solution was stirred and dissolved thoroughly in a water bath at 70 °C. 0.3 g of NaY molecular sieve was weighed and placed in the ammonium molybdate solution. After stirring and drying at 70 °C, the solution was transferred to a 60 °C oven and dried for 12 h. The solution was then calcined at 550 °C for 3 h. 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. The temperature was maintained for 2 h to obtain the catalyst Mo2C / Y.

[0080] Activity testing procedure: 100 mg of catalyst sample was weighed and placed in a 20 mm diameter fixed-bed quartz reactor for reverse water-gas shift reaction performance testing. The tail gas and feed gas after the reaction were analyzed using gas chromatography. Catalyst activity was expressed as CO2 conversion rate and CO selectivity. The CO2:H2 ratio in the feed gas was 4:1, the feed gas flow rate was 20 mL / min, the reaction temperature range was 200-400℃, the heating rate was 10℃ / min, and the reaction pressure was atmospheric pressure. The catalyst sample was tested at reaction temperature intervals of 50℃. The test results are as follows: Figures 2-3 As shown.

[0081] Depend on Figures 2-3 It can be seen that, within the test temperature range of 200-400℃, the catalyst AG prepared in Examples 1-7 significantly improved the CO2 conversion rate compared with the catalyst Mo2C / Y prepared in Comparative Example 1. Among them, catalyst B showed the best catalytic effect, achieving a conversion rate of 23% at a reaction temperature of 400℃, which is about three times higher than the conversion rate at the same temperature. Within the temperature range of 200-250℃, except for catalysts B and G, the other catalysts showed low selectivity for the product CO. However, within the temperature range of 300-400℃, the CO selectivity remained above 80%. Therefore, it can be concluded that the supported molybdenum carbide catalyst provided by this invention improves the activity of the molybdenum carbide catalyst in the reverse water-gas shift reaction, exhibits good catalytic effect, and shows high CO selectivity at reaction temperatures above 300℃.

[0082] X-ray diffraction analysis was performed on the catalysts prepared in Examples 1-7, and the results were as follows: Figure 1The XRD diffraction chart shows that the synthesized molybdenum carbide crystal phase is beta phase, and no characteristic peak of metal Co is observed, indicating that the Co in the catalyst has good dispersibility.

[0083] The catalyst sample B prepared in Example 2 was subjected to stability test at 300 DEG C, and the test result is shown in the following table. Figure 4 As shown in the table, it can be seen that the catalyst has good stability in the stability test, and the deactivation phenomenon is not obvious, indicating that the catalyst prepared by the present application can maintain structural stability and catalytic activity for a long time when used in the reverse water gas shift reaction.

[0084] The reverse water gas shift (RWGS) reaction is a key step for converting carbon dioxide (CO2) into high-value-added chemicals and fuels such as methanol, low-carbon olefins, aromatic hydrocarbons and gasoline by hydrogenation. The prepared supported molybdenum carbide catalyst improves the catalytic activity in the application of low-temperature reverse water gas shift reaction, reduces the energy consumption in the reaction process to a certain extent, avoids the use of noble metals, reduces the industrial utilization cost, and further promotes the improvement of catalytic activity and stability by playing the synergistic effect between molybdenum carbide and metal. The active component in the catalyst has high stability and is not easy to deactivate, and the preparation method is simple and low in cost.

[0085] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application but not to limit it, although the present application has been described in detail with reference to the above examples, those skilled in the art should understand that: the specific embodiments of the present application can still be modified or replaced by the same, without departing from the spirit and scope of the present application. Any modification or equivalent replacement, which is not included in the scope of protection of the claims of the present application.

Claims

1. A supported molybdenum carbide catalyst characterized in that, The active component is carbonized molybdenum; The carrier is MY molecular sieve, and the active component is carbonized molybdenum; M is one or two of Co, Ni and Cu; The preparation method of the supported carbonized molybdenum catalyst comprises the following steps: S1, adding the carrier Y molecular sieve into a metal salt solution, mixing thoroughly to obtain a suspension; The suspension is subjected to ion exchange, filtration, washing and drying to obtain the MY molecular sieve; The molybdenum source is dissolved in a solvent to obtain a molybdenum source solution; S2, mixing the molybdenum source solution with the MY molecular sieve, drying, calcining, and carbonizing under a reducing mixed gas atmosphere to obtain the supported carbonized molybdenum catalyst; 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 acetylacetone; The solvent is water or ethanol; The Y molecular sieve is HY molecular sieve or NaY molecular sieve.

2. The supported molybdenum carbide catalyst of claim 1, wherein, In S1, the concentration of the metal salt solution is 0.01-0.05 mol / L.

3. The supported molybdenum carbide catalyst of claim 1, wherein the molybdenum carbide is present in an amount of 5 to 50 wt%. In S1, the ion exchange water bath temperature is 50-90℃, and the time is 2-6h; The deionized water or anhydrous ethanol is washed for several times, the drying temperature is 50-100℃, and the drying time is 4-12h.

4. The supported molybdenum carbide catalyst of claim 1, wherein the molybdenum carbide is present in an amount of 5 to 50 wt%. In S2, the mixing is specifically mixing under magnetic stirring, and the mixing temperature is 60-80℃; The drying is specifically drying at 50-80℃ for 6-12h; The calcining temperature is 400-600℃, and the time is 2-5h.

5. The supported molybdenum carbide catalyst of claim 1, wherein, 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℃ / min, the carbonization temperature is 600-800℃, and the holding time is 2-6h to obtain the supported carbonized molybdenum catalyst.

6. The supported molybdenum carbide catalyst of claim 1, wherein the molybdenum carbide is present in an amount of 5 to 50 wt%. The calcining process is calcining at 500℃ for 2-5h, and the carbonization process is heating from room temperature to 680℃ at a rate of 2-5℃ / min and holding for 2-6h.

7. The supported carbonized molybdenum catalyst according to any one of claims 1-6 is applied in the reverse water gas shift reaction.

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