SUPPORTED TRANSISTION METAL CARBIDE CATALYST AND ONE-STEP SYNTHESIS METHOD THEEFORE

Abstract

A supported transition metal carbide catalyst and a one-step synthesis method thereof are disclosed. The synthesis method includes: mixing a supporter, a transition metal precursor and a solid carbon source and then grinding to form a solid mixture; and putting the solid mixture into a reducing atmosphere, performing carbonization treatment and high-temperature programming thermal treatment in turn, and then at a protective atmosphere, cooling and passivating, so as to obtain the supported transition metal carbide catalyst. The synthesis method provided by the present application utilizes high-temperature solid solution reaction for further synthesis, which at least has the following advantages: the preparation process flow is simple so processes such as impregnation and carburization with gas carbon source can be avoided; different supporters used for catalyst modification, and the prepared catalyst has the characteristics of large outer surface area, rich notable metal-like catalytic property and the like.

Claims

1. A one-step method for synthesizing a supported transition metal carbide catalyst, comprising: mixing a supporter, a transition metal precursor and a solid carbon source to obtain a mixture and then grinding the mixture to form a solid mixture; and putting the solid mixture into a reducing atmosphere, performing a carbonization treatment on the solid mixture at 200-500° C. to obtain a carbonized mixture, then carrying out a high-temperature programming reduction carburization treatment on the carbonized mixture at 700-900° C., holding for 0.5-4 h at 700-900° C. to obtain a treated mixture, and then putting the treated mixture at a protective atmosphere, cooling and passivating the treated mixture, to obtain the supported transition metal carbide catalyst.

2. The one-step method for synthesizing the supported transition metal carbide catalyst according to claim 1, specifically comprising: at a temperature of 20-60° C., mixing the supporter, the transition metal precursor and the solid carbon source to obtain the mixture and then grinding the mixture for 5-60 min to form the solid mixture.

3. The one-step method for synthesizing the supported transition metal carbide catalyst according to claim 1, wherein a loading amount of the transition metal precursor on the supporter is 1 wt %-40 wt %, and a molar ratio of the transition metal precursor to the solid carbon source is 1:1-3.

4. The one-step method for synthesizing the supported transition metal carbide catalyst according to claim 1, wherein a material of the supporter comprises at least one selected from the group consisting of aluminum oxide, activated carbon and silicon oxide; and/or the transition metal precursor comprises at least one selected from the group consisting of ammonium heptamolybdate, ammonium tungstate and ferric nitrate; and/or the solid carbon source comprises at least one selected from the group consisting of glucose, citric acid and chitosan.

5. The one-step method for synthesizing the supported transition metal carbide catalyst according to claim 1, specifically comprising: putting the solid mixture in the reducing atmosphere, and heating the solid mixture to 200-500° C. at a heating rate of 1-30° C..Math.min.sup.−1 for the carbonization treatment.

6. The one-step method for synthesizing the supported transition metal carbide catalyst according to claim 5, specifically comprising: after the carbonization treatment, heating the carbonized mixture to 700-900° C. at a heating rate of 0.5-5° C..Math.min.sup.−1 to perform the high-temperature programming reduction carburization treatment for 0.5-4 h.

7. The one-step method for synthesizing the supported transition metal carbide catalyst according to claim 1, wherein the reducing atmosphere comprises a H.sub.2 atmosphere; and/or a flow of H.sub.2 used for forming the reducing atmosphere is 5-50 mL.Math.min.sup.−1.

8. The one-step method for synthesizing the supported transition metal carbide catalyst according to claim 1, wherein the protective atmosphere comprises a nitrogen atmosphere; and/or a flow of nitrogen used for forming the protective atmosphere is 50-1500 mL.Math.min.sup.−1.

9. A supported transition metal carbide catalyst, wherein the supported transition metal carbide catalyst is prepared by the one-step method according to claim 1.

10. The supported transition metal carbide catalyst according to claim 9, wherein the supported transition metal carbide catalyst comprises 1-20 wt % of molybdenum, and the supported transition metal carbide catalyst has a mesoporous structure, wherein a pore diameter of contained pores of the mesoporous structure is 4-6 nm, a total pore volume is 0.1-0.3 cm.sup.3.Math.g.sup.−1, and a specific surface area is 100-200 m.sup.2.Math.g.sup.−1.

11. The one-step method for synthesizing the supported transition metal carbide catalyst according to claim 2, wherein a material of the supporter comprises at least one selected from the group consisting of aluminum oxide, activated carbon and silicon oxide; and/or the transition metal precursor comprises at least one selected from the group consisting of ammonium heptamolybdate, ammonium tungstate and ferric nitrate; and/or the solid carbon source comprises at least one selected from the group consisting of glucose, citric acid and chitosan.

12. The one-step method for synthesizing the supported transition metal carbide catalyst according to claim 3, wherein a material of the supporter comprises at least one selected from the group consisting of aluminum oxide, activated carbon and silicon oxide; and/or the transition metal precursor comprises at least one selected from the group consisting of ammonium heptamolybdate, ammonium tungstate and ferric nitrate; and/or the solid carbon source comprises at least one selected from the group consisting of glucose, citric acid and chitosan.

13. The one-step method for synthesizing the supported transition metal carbide catalyst according to claim 5, wherein the reducing atmosphere comprises a H.sub.2 atmosphere; and/or a flow of H.sub.2 used for forming the reducing atmosphere is 5-50 mL.Math.min.sup.−1.

14. The one-step method for synthesizing the supported transition metal carbide catalyst according to claim 6, wherein the reducing atmosphere comprises a H.sub.2 atmosphere; and/or a flow of H.sub.2 used for forming the reducing atmosphere is 5-50 mL.Math.min.sup.−1.

15. The supported transition metal carbide catalyst according to claim 9, wherein the one-step method specifically comprises: at a temperature of 20-60° C., mixing the supporter, the transition metal precursor and the solid carbon source to obtain the mixture and then grinding the mixture for 5-60 min to form the solid mixture.

16. The supported transition metal carbide catalyst according to claim 9, wherein a loading amount of the transition metal precursor on the supporter is 1 wt %-40 wt %, and a molar ratio of the transition metal precursor to the solid carbon source is 1:1-3.

17. The supported transition metal carbide catalyst according to claim 9, wherein a material of the supporter comprises at least one selected from the group consisting of aluminum oxide, activated carbon and silicon oxide; and/or the transition metal precursor comprises at least one selected from the group consisting of ammonium heptamolybdate, ammonium tungstate and ferric nitrate; and/or the solid carbon source comprises at least one selected from the group consisting of glucose, citric acid and chitosan.

18. The supported transition metal carbide catalyst according to claim 9, wherein the one-step method specifically comprises: putting the solid mixture in the reducing atmosphere, and heating the solid mixture to 200-500° C. at a heating rate of 1-30° C..Math.min.sup.−1 for the carbonization treatment.

19. The supported transition metal carbide catalyst according to claim 18, wherein the one-step method specifically comprises: after the carbonization treatment, heating the carbonized mixture to 700-900° C. at a heating rate of 0.5-5° C..Math.min.sup.−1 to perform the high-temperature programming reduction carburization treatment for 0.5-4 h.

20. The supported transition metal carbide catalyst according to claim 9, wherein the reducing atmosphere comprises a H.sub.2 atmosphere; and/or a flow of H.sub.2 used for forming the reducing atmosphere is 5-50 mL.Math.min.sup.−1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1 is a microstructure graph of a supported transition metal carbide catalyst according to example 1 of the present application.

[0025] FIG. 2 is an element analysis graph of a supported transition metal carbide catalyst according to example 1 of the present application.

[0026] FIG. 3 is a N.sub.2 adsorption-desorption curve graph of a supported transition metal carbide catalyst according to example 1 of the present application.

[0027] FIG. 4 is an X-ray powder diffraction spectrogram of a supported transition metal carbide catalyst according to example 1 of the present application.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] In view of the defects in the prior art, the inventors put forward the technical solution of the present application through long-term researches and many practices. Next, the technical solution as well as the implementation process and principle thereof and the like will be further explained and described.

[0029] An embodiment of the present application provides a one-step method for synthesizing a supported transition metal carbide catalyst, comprising:

[0030] mixing a supporter, a transition metal precursor and a solid carbon source and then grinding to form a solid mixture; and

[0031] putting the solid mixture into a reducing atmosphere, carbonizing at 200-500° C., then carrying out high-temperature programming reduction carburization treatment at 700-900° C., and then at a protective atmosphere, cooling and passivating, so as to obtain the supported transition metal carbide catalyst.

[0032] In some embodiments, the method can comprise the following steps:

[0033] (1) carrying out ultrasonic fusion on the supporter, the transition metal precursor and the solid carbon source, then putting into a mortar to be evenly and mechanically ground to obtain a solid mixture;

[0034] (2) carrying out carburization and high-temperature programming thermal treatment on the solid mixture in turn at the reducing atmosphere at the thermal treatment temperature of 700-900° C. for 0.5-4 h, and then at a protective atmosphere, cooling and passivating, so as to obtain the supported transition metal carbide catalyst.

[0035] Further, the method specifically comprises: mixing the supporter, the transition metal precursor and the solid carbon source at the temperature of 20-40° C. and then grinding for 5-60 min to form the solid mixture.

[0036] Preferably, the loading amount of the transition metal precursor on the supporter is 1 wt %-40 wt %.

[0037] Preferably, a molar ratio of transition metal precursor to solid carbon source is 1:1-3.

[0038] Further, the material of the supporter comprises any one or a combination of more than two of aluminum oxide, activated carbon and silicon oxide, but is not limited thereto.

[0039] Further, the transition metal precursor comprises any one or a combination of more than two of ammonium heptamolybdate, ammonium tungstate and ferric nitrate, but is not limited thereto.

[0040] Further, the solid carbon source comprises any one or a combination of more than two of glucose, citric acid and chitosan, but is not limited thereto.

[0041] Further, the method specifically comprises: putting the solid mixture in the reducing atmosphere, heating to 200-500° C. at the heating rate of 1-30° C..Math.min.sup.−1 for carbonization treatment.

[0042] More further, the method also comprises: after the carbonization treatment, heating the obtained mixed reactant to 700-900° C. at the heating rate of 0.5-5° C..Math.min.sup.−1 in the reducing atmosphere to undergo high-temperature programming thermal treatment for 0.5-4 h.

[0043] Further, the reducing atmosphere comprises H.sub.2 atmosphere;

[0044] Preferably, the flow of H.sub.2 used for forming the reducing atmosphere is 5-50 mL.Math.min.sup.−1.

[0045] Further, the protective atmosphere comprises nitrogen atmosphere.

[0046] Preferably, the flow of nitrogen used for forming the protective atmosphere is 50-1500 mL.Math.min.sup.−1.

[0047] An embodiment of the present application also provides the supported transition metal carbide catalyst prepared by any above-mentioned method.

[0048] Further, the catalyst comprises 1-20 wt % of molybdenum element, and meanwhile the catalyst has a mesoporous structure in which the pore diameter of the contained pores is 4-6 nm, the total pore volume is 0.1-0.3 cm.sup.3.Math.g.sup.−1, and the specific surface area is 100-200 m.sup.2.Math.g.sup.−1.

[0049] The preparation process flow of the supported transition metal carbide catalyst provided by an embodiment of the present application is simple, can further prepare the molybdenum carbide catalyst, so processes such as impregnation and carburization with a gas carbon source (methane and ethane) can be avoided; the supported transition metal carbide catalyst is available in raw materials, low in cost and stable in product, has large outer surface area, rich notable metal-like property and good application prospect, and catalyst modification is easily carried out.

[0050] The technical solution of the present application will be further described in combination with several examples below.

[0051] Example 1 A method for preparing a supported transition metal carbide catalyst comprises the following steps:

[0052] (1) at the temperature of 20-60° C., weighing 1 g of alumina supporter, 0.1225 g of ammonium heptamolybdate and 0.0460 g of glucose, mixing, and then grinding for 10 min to obtain a solid mixture.

[0053] (2) putting the mixture in a reducing atmosphere, heating to 300° C. at the heating rate of 10° C..Math.min.sup.−1 for carbonization treatment, heating to 800° C. at the heating rate of 1° C..Math.min.sup.−1 for high-temperature programming thermal treatment, holding for 1 h at 800° C., wherein the reducing atmosphere is hydrogen atmosphere, and the flow of hydrogen used for forming the hydrogen atmosphere is 30 mL.Math.min.sup.−1; and passivating using a protective atmosphere in the process of cooling, wherein the protective atmosphere is nitrogen atmosphere, and the flow of nitrogen used for forming the protective atmosphere is 100 mL.Math.min.sup.−1, thereby obtaining a supported transition metal carbide catalyst.

[0054] The supported transition metal carbide catalyst prepared in this example is named Mo.sub.2C/Al.sub.2O.sub.3, its microstructure refers to FIG. 1, and the contents of various elements are shown in Table 1 and FIG. 2.

TABLE-US-00001 TABLE 1 Element Analysis Table Of Supported Transition Metal Carbide Catalyst In Example 1 Of The Present Application Elements Weight percent (%) Atom percent (%) C K 7.16 11.73 O K 44.43 54.69 Al K 45.04 32.88 Mo L 3.38 0.69 Total 100.00 100.00

[0055] As shown in Table 1 and FIG. 2, the supported transition metal carbide catalyst in example 1 contains Mo and C, and it can be seen from FIG. 1 that the method can prepare the supported transition metal carbide catalyst with a good crystal form, which is Mo.sub.2C (JCPDS35-0787) (Journal of Solid State Chemistry, 2012, 194 (194): 19-22.) with a hexagonal crystal system. FIG. 3 shows a supported transition metal carbide catalyst in example 1 and a scanning electron microscope thereof. It can be seen that the surface of the supported transition metal carbide catalyst in example 1 of the present application is supported with a molybdenum carbide catalyst, and the total pore volume is 0.1985 cm.sup.3.Math.g-1, the specific surface area is 109.0253 m.sup.2.Math.g-1, the pore diameter of the mesoporous structure is 4.9319 nm, and the content of molybdenum element is 3.38 wt %. It can be seen from FIG. 4 that the molybdenum carbide catalyst can be well prepared in example 1 of the present application.

[0056] Example 2 A method for preparing a supported transition metal carbide catalyst comprises the following steps:

[0057] (1) at the temperature of 20-60° C., weighing 0.1151 g of ammonium tungstate and 1 g of chitosan, mixing, and grinding for 10 min to obtain a solid mixture.

[0058] (2) putting the mixture in a reducing atmosphere, heating to 300° C. at the heating rate of 10° C..Math.min.sup.−1 for carbonization treatment, heating to 900° C. at the heating rate of 1° C..Math.min.sup.−1 for high-temperature programming thermal treatment, wherein the protective atmosphere includes nitrogen atmosphere, the flow of hydrogen used for forming the reducing atmosphere is 100 mL.Math.min.sup.−1, and the activated carbon is a reducing agent; and passivating using the protective atmosphere in the process of cooling, wherein the protective atmosphere is nitrogen atmosphere, and the flow of nitrogen used for forming the protective atmosphere is 100 mL.Math.min.sup.−1, thereby obtaining a supported transition metal carbide catalyst. The supported transition metal carbide catalyst prepared in this example is named W.sub.xC/Al.sub.2O.sub.3, and x is 1 or 2.

[0059] Example 3 A method for preparing a supported transition metal carbide catalyst comprises the following steps:

[0060] (1) at the temperature of 20-60° C., weighing 1 g of alumina supporter, 0.5235 g of ferric nitrate and 0.0856 g of glucose, mixing, and grinding for 10 min to obtain a solid mixture.

[0061] (2) putting the mixture in a reducing atmosphere, heating to 300° C. at the heating rate of 10° C..Math.min.sup.−1 for carbonization treatment, heating to 800° C. at the heating rate of 1° C..Math.min.sup.−1 for high-temperature programming thermal treatment, wherein the reducing atmosphere is hydrogen atmosphere, and the flow of hydrogen used for forming the reducing atmosphere is 30 mL.Math.min.sup.−1; and passivating using a protective atmosphere in the process of cooling, wherein the protective atmosphere is nitrogen atmosphere, and the flow of nitrogen used for forming the protective atmosphere is 100 mL.Math.min.sup.−1, thereby obtaining a supported transition metal carbide catalyst. The supported transition metal carbide catalyst prepared in this example is named Fe.sub.xC/Al.sub.2O.sub.3.

[0062] Example 4 A method for preparing a supported transition metal carbide catalyst comprises the following steps:

[0063] (1) this step is the same as that in example 1, but the molar ratio of transition metal precursor to solid carbon source is 1:3;

[0064] (2) putting the mixture in a reducing atmosphere, heating to 200° C. at the heating rate of 30° C..Math.min.sup.−1 for carbonization treatment, heating to 900° C. at the heating rate of 5° C..Math.min.sup.−1 for high-temperature programming thermal treatment, and holding for 0.5 h at 900° C., wherein the reducing atmosphere is hydrogen atmosphere, and the flow of hydrogen used for forming the reducing atmosphere is 5 mL.Math.min.sup.−1; and passivating using a protective atmosphere in the process of cooling, wherein the protective atmosphere is nitrogen atmosphere, and the flow of nitrogen used for forming the protective atmosphere is 1500 mL.Math.min.sup.−1, thereby obtaining a supported transition metal carbide catalyst.

[0065] Example 5 A method for preparing a supported transition metal carbide catalyst comprises the following steps:

[0066] (1) this step is the same as that in example 1, but a molar ratio of transition metal precursor to solid carbon source is 1:3;

[0067] (2) putting the mixture in a reducing atmosphere, heating to 500° C. at the heating rate of 30° C..Math.min.sup.−1 for carbonization treatment, heating to 700° C. at the heating rate of 0.5° C..Math.min.sup.1 for high-temperature programming thermal treatment, and holding for 4 h at 700° C., wherein the reducing atmosphere is a hydrogen atmosphere, and the flow of hydrogen used for forming the reducing atmosphere is 50 mL.Math.min.sup.−1; and passivating using a protective atmosphere in the process of cooling, wherein the protective atmosphere is nitrogen atmosphere, and the flow of nitrogen used for forming the protective atmosphere is 50 mL.Math.min.sup.−1, thereby obtaining a supported transition metal carbide catalyst.

Comparative Example 1

[0068] the method in this comparative example is the same as that in example 1, and the difference is that step (1) is not contained, the alumina supporter is directly used to replace the mixture to carry out operation in step (2).

Comparative Example 2

[0069] Step (1) is the same as that in example 1.

[0070] Step (2) differs from that of example 1 that the mixture is put in the reducing atmosphere, heated to 300° C. at the heating rate of 10° C..Math.min.sup.−1 for carbonization treatment, and then rapidly heated to 800° C. for thermal treatment.

[0071] Wherein, in comparative example 1, the supporter Al.sub.2O.sub.3 is used as blank control. In the heat treatment step of comparative example 2, the carburization and reduction processes can not be sufficiently carried out due to too fast heating (the heating rate is about 40° C..Math.min.sup.−1), and the supported catalyst prepared at this rate cannot obtain molybdenum carbide or a small amount of molybdenum carbide.

[0072] In addition, the inventors of this case also perform corresponding tests with reference to examples 1-3 based on other raw materials and process conditions mentioned in this specification, and find that corresponding supported carbide catalysts can also be prepared through these tests, and meanwhile these catalysts also have ideal catalytic performances.

[0073] The preceding examples of the present application provide the method for preparing the supported transition metal carbide catalyst by utilizing high temperature solid fusion reaction. The preparation method is simple in process, so the introduction of a gas carbon source (methane and ethane) and other flammable gases is avoided in the process of preparation, so as to reduce the dangerousness of the operation process. Furthermore, the catalyst can be conveniently modified by further adjusting the content of the precursor and the content of the solid carbon source, the compositions and properties of the obtained supported transition metal carbide catalyst can be controlled, and the catalysis behavior of the formed catalyst is further adjusted. The obtained supported transition metal carbide catalyst is safe, easy to control, environmental-friendly, low in cost, high in preparation efficiency, high in product quality and high in yield. The supported transition metal carbide catalyst prepared in the preceding examples of the present application contains small molybdenum carbide particles and large specific surface, is beneficial to reactant diffusion and exposure of active sites, and meanwhile the molybdenum carbide catalyst with a small amount of surface area carbon can be obtained by helping the uniform reaction of the precursor via mechanical grinding. Moreover, catalyst modification is conveniently carried out, which is beneficial to improvement of properties of the catalyst. The obtained supported transition metal carbide catalyst has good application and industrialization prospect.

[0074] It should be understood that the above examples are only for illustrating the technical concept and features of the present application for the purpose of enabling those familiar with the technology to understand the content of the present application and implement it accordingly, but not limit the protective scope of the present application. All equivalent changes or modifications made according to the spirit of the present application shall fall within the scope of protection of the present application.