Catalytic material for water-gas shift reaction and preparation method and application thereof

Abstract

The present application belongs to the field of catalyst preparation and heterogeneous catalysis, and particularly relates to a catalytic material for water-gas shift reaction and a preparation method and application thereof. In the present application, molybdate is used as a raw material, and an easily decomposable cyanamide compound is used as a carbon source and a nitrogen source, so that efficient conversion from a bulk layered transition metal molybdenum oxide to a molybdenum carbide / molybdenum nitride nanosheet is realized, and a molybdenum carbide / molybdenum nitride composite molybdenum-based material with similar morphology is obtained. After being combined with Au, a material with catalytic capability for a water-gas shift reaction is obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of catalyst preparation and heterogeneous catalysis, and particularly relates to a catalytic material for a water-gas shift reaction and a preparation method and application thereof. BACKGROUND

[0002] Hydrogen energy is a clean, efficient, safe and sustainable new energy. At present, the most effective form of hydrogen energy is fuel cells. However, 95% of hydrogen production needs to be combined with hydrocarbon steam reforming, methanol cracking, coal gasification and natural gas synthesis gas processes. The synthesis gas contains a large amount of CO, and CO has a strong toxic effect on the Pt electrode in the fuel cell. The water-gas shift reaction can eliminate a large amount of CO while producing fuel H2, and becomes an important reaction for large-scale production of pure H2.

[0003] Traditional industrial water-gas reaction catalysts have many shortcomings: for example, Fe-based high-temperature (310-450℃) catalysts are limited by thermodynamic equilibrium, resulting in an impossible CO outlet concentration of less than 3%, and need to be pre-reduced, with the risk of spontaneous combustion when exposed to air; Cu-Zn-Al-based low-temperature (190-250℃) catalysts have very poor thermal stability and need strict pre-reduction activation; Co-Mo-based wide-temperature catalysts need a complicated sulfidation process, and are prone to desulfurization during use. Therefore, it is urgent to develop a new type of efficient water-gas shift catalyst for fuel cell systems.

[0004] Molybdenum-based materials have become a promising catalytic material in the catalysis field due to their rich valence states, low cost and high theoretical capacity. Among them, molybdenum carbide, as a unique new type of catalytic material, has been applied to various reactions due to its excellent performance. Ma et al. (Science, 2017, 357(6349): 389-393) reported an Au / α-MoC supported catalyst, which realized efficient catalysis of the water-gas shift reaction at low temperature, but the activity was lost by nearly half after 100h, and there were problems of poor temperature adaptability and narrow application range. At the same time, the existing synthesis method of molybdenum carbide involves multi-step ammoniation and carbonization or the use of a large amount of noble metal, and its preparation is severely limited by harsh synthesis conditions, which cannot be mass-produced, and it is imperative to develop a new synthesis method. Therefore, in view of the existing synthesis problems of molybdenum carbide, the present application provides a new preparation method for synthesizing molybdenum-based composite materials from the perspective of optimizing the process, but the catalytic performance of the catalyst for the water-gas shift reaction still needs to be further improved. SUMMARY

[0005] Based on the above research status, the application provides a kind of catalytic material for water gas shift reaction and its preparation method and application, by optimizing synthesis process, and can be effectively used in water gas shift reaction.

[0006] In the first aspect, the application provides a preparation method of a catalytic material for water gas shift reaction, comprising the following steps:

[0007] (1) Preparation of Mo-based composite material: mix molybdenum salt with cyanamide compound I, transfer to a tube furnace, and place cyanamide compound II upstream; then calcine under reducing atmosphere; after the reaction is completed, cool to room temperature under oxygen argon atmosphere;

[0008] (2) Preparation of catalytic material: add chloroauric acid and aqueous ammonia solution to the suspension of Mo-based composite material at the same time; age under stirring, then wash and dry to obtain the catalytic material for water gas shift reaction.

[0009] In the application, molybdate is used as raw material, and easily decomposable cyanamide compound is used as carbon source and nitrogen source, to realize efficient conversion from bulk phase layered transition metal molybdenum oxide to molybdenum carbide / molybdenum nitride nanosheet, and obtain molybdenum carbide / molybdenum nitride composite molybdenum-based material with similar morphology. When carbonizing and nitriding under hydrogen / argon reducing atmosphere, by controlling the position and content of cyanamide compound II, different types of molybdenum-based composite materials can be obtained, and performance test in water gas device verifies that the catalytic material has certain catalytic activity in water gas reaction.

[0010] The application innovatively proposes to use cyanamide compound to provide N source and C source gas by thermal decomposition, and simultaneously use the strong reducing property of H2 to simulate the role of NH3 in the ammoniation process and the carburizing of CH4 in the carbonization process, to generate molybdenum-based composite material of molybdenum nitride / molybdenum carbide by one-step method. The method can control the proportion of the two substances, and by changing the proportion of cyanamide compound put upstream and downstream, the proportion of molybdenum nitride and molybdenum carbide in the final product can be adjusted.

[0011] Further, the mass ratio of the molybdenum salt to cyanamide compound I is 1:(1-2).

[0012] Further, the mass ratio of cyanamide compound II to cyanamide compound I is (2-3):1.

[0013] Further, in step (1), the molybdenum salt includes one or more of molybdenum chloride, ammonium molybdate and phosphomolybdic acid.

[0014] Further, the molybdenum salt is ammonium molybdate tetrahydrate.

[0015] Further, in step (1), the cyanamide compound comprises one or more of dicyandiamide and melamine.

[0016] Further, the cyanamide compound is melamine.

[0017] Further, in step (1), the calcination process specifically comprises: heating at a rate of 3-6℃ / min to 500-700℃ under a reducing atmosphere, and calcining for 2-4h; and then heating at a rate of 1-3℃ / min to 700-800℃, and calcining for 1-2h.

[0018] Further, in step (1), the reducing atmosphere is 10vol.% H2 / Ar.

[0019] Further, in step (1), the heating rate is preferably 4-5℃ / min, and more preferably 5℃ / min; the first reduction calcination temperature is preferably 600-700℃, and the calcination time is preferably 3-4h; and the second calcination temperature is preferably 800℃, and the calcination time is preferably 1h.

[0020] Further, in step (2), the control temperature is 60-100℃, and the pH is 9-10, and as a preference, the control temperature is 80℃, and the adjusted pH is 9.3.

[0021] Further, in step (2), the concentration of the chloroauric acid solution is 0.002-0.003mol / L, and the concentration of the ammonia solution is 0.01-0.1mol / L, and as a preference, the concentration of the chloroauric acid is 0.0025mol / L, and the concentration of the ammonia solution is 0.05mol / L.

[0022] Further, in step (2), the aging time is 2-4h, and the drying temperature is 100-110℃, and as a preference, the aging time is 3h, and the drying temperature is 105℃.

[0023] In a second aspect, the present application provides a catalytic material prepared by the above preparation method, wherein the catalytic material is an Au-molybdenum carbide / nitride material, Au is loaded on the molybdenum carbide / nitride material, the content of Au is 0.5%-10% of the total mass of the catalyst, preferably 0.8%-10%, and more preferably 1-5wt%; and the molybdenum carbide / nitride material mainly comprises MoC, Mo3N2, and part of MoN.

[0024] In a third aspect, the present application provides an application of the above catalytic material in water-gas shift.

[0025] The catalyst is used in carbon monoxide water coal gas shift reaction, and the catalyst does not need to be reduced in advance when applied in water coal gas shift reaction. The water coal gas shift reaction conditions are: water and CO are essential components in the reaction gas, the raw material gas (12.5% CO and 87.5% N2), mass space velocity 16000-24000 mL·h -1 ·g -1 催化剂 The ratio of water vapor to raw material gas is kept at 1:1 to enter the gas chromatograph equipped with a thermal conductivity detector (TCD).

[0026] Compared with the prior art, the present application has the following beneficial effects:

[0027] (1) The Au-molybdenum carbide / molybdenum nitride composite material is synthesized by direct calcination method, and it is proved that it has certain catalytic ability for water coal gas shift reaction;

[0028] (2) The preparation method of the catalytic material provided by the present application has simple procedure and low cost, and has broad application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 It is a preparation process schematic diagram of the molybdenum carbide / molybdenum nitride composite catalytic material of the present application.

[0030] Figure 2 It is an XRD diagram of the catalyst prepared in Examples 1-4.

[0031] Figure 3 It is an XRD diagram of the catalyst prepared in Comparative Examples 1-5.

[0032] Figure 4 It is a water coal gas shift reaction evaluation data diagram of the catalyst prepared in Examples 1-4 and Comparative Examples 1, 2 and 5. DETAILED DESCRIPTION

[0033] In order for those skilled in the art to better understand the present application, the technical solutions of the present application will be described in detail below in combination with specific embodiments. It should be pointed out that the following detailed description is exemplary and only a part of the embodiments of the present application, but not all.

[0034] Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts shall belong to the scope of protection of the present application.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Experimental materials used in the embodiments of the present application are all conventional experimental materials in the art, and can be purchased through commercial channels. The experimental methods without detailed conditions are carried out according to the conventional experimental methods or according to the operation instructions recommended by the suppliers.

[0036] Example 1

[0037] A method for preparing a catalytic material for a water-gas shift reaction, using a preparation method as shown in Figure 1 , comprising the following steps:

[0038] Catalyst preparation: 2g of (NH4)6Mo7O 24 4H2O was accurately weighed, mixed with 2g of melamine and ground uniformly, and then sent into a tube furnace, while a porcelain boat containing 4g of melamine was placed at the upper end of the gas inlet, then heated to 600℃ at a rate of 5℃ / min under a 10vol.% H2 / Ar atmosphere, and kept for 2h, then heated to 700℃ at a rate of 1℃ / min, and kept for 1h; then, during the cooling process, 1vol.% O2 / Ar was passed, and after cooling to room temperature, it was taken out, and the obtained powder solid was recorded as a Mo-based composite material. 0.5g of the Mo-based composite material was uniformly dispersed in 150mL of water by ultrasonic treatment, 20.7mL of a HAuCl4(0.0025mol / L) solution was taken according to the Au content of 2% in the catalyst, and 100mL of NH3·H2O(0.05mol / L) was taken at the same time. Under the conditions of controlling the temperature(80℃) and pH(9-9.3), the HAuCl4(0.0025mol / L) and NH3·H2O(0.05mol / L) solutions were simultaneously added dropwise into the suspension by a peristaltic pump. After aging for 3h with stirring, it was washed with deionized water for 6 times, and dried at 80℃ for 12h to obtain a 2wt% Au / Mo-based composite material, which was used without any reduction.

[0039] Example 2

[0040] Catalyst preparation: 2g of (NH4)6Mo7O 24 4H2O was accurately weighed, mixed with 2g of melamine and ground uniformly, and then sent into a tube furnace, while a porcelain boat containing 4g of melamine was placed at the upper end of the gas inlet, then heated to 600℃ at a rate of 5℃ / min under a 10vol.% H2 / Ar atmosphere, and kept for 2h, then heated to 700℃ at a rate of 1℃ / min, and kept for 1h; then, during the cooling process, 1vol.% O2 / Ar was passed, and after cooling to room temperature, it was taken out, and the obtained powder solid was recorded as a Mo-based composite material. 0.5g of the Mo-based composite material was uniformly dispersed in 150mL of water by ultrasonic treatment, 20.7mL of a HAuCl4(0.0025mol / L) solution was taken according to the Au content of 2% in the catalyst, and 100mL of NH3·H2O(0.05mol / L) was taken at the same time. Under the conditions of controlling the temperature(80℃) and pH(9-9.3), the HAuCl4(0.0025mol / L) and NH3·H2O(0.05mol / L) solutions were simultaneously added dropwise into the suspension by a peristaltic pump. After aging for 3h with stirring, it was washed with deionized water for 6 times, and dried at 80℃ for 12h to obtain a 2wt% Au / Mo-based composite material, which was used without any reduction.

[0041] Example 3

[0042] Catalyst preparation: 2g of (NH4)6Mo7O 24• 4H2O, 4 g of melamine was added and ground with it, and then put into the tube furnace, at the same time, a porcelain boat containing 8 g of melamine was placed at the upper end of the gas inlet, then heated to 550 °C at a rate of 4 °C / min under 10 vol.% H2 / Ar atmosphere, and kept for 3 h, then heated to 800 °C at a rate of 3 °C / min, and kept for 2 h, and the subsequent steps were the same as in Example 1.

[0043] Example 4

[0044] Catalyst preparation: 2 g of (NH4)6Mo7O24·4H2O was accurately weighed, and then mixed with 4 g of melamine and ground, and then put into the tube furnace, at the same time, a porcelain boat containing 8 g of melamine was placed at the upper end of the gas inlet, then heated to 550 °C at a rate of 4 °C / min under 10 vol.% H2 / Ar atmosphere, and kept for 3 h, then heated to 800 °C at a rate of 3 °C / min, and kept for 2 h, and the subsequent steps were the same as in Example 1. 24 • 4H2O, 4 g of melamine was added and ground with it, and then put into the tube furnace, at the same time, a porcelain boat containing 8 g of melamine was placed at the upper end of the gas inlet, then heated to 550 °C at a rate of 4 °C / min under 10 vol.% H2 / Ar atmosphere, and kept for 3 h, then heated to 800 °C at a rate of 3 °C / min, and kept for 2 h, and the subsequent steps were the same as in Example 1.

[0045] Comparative Example 1

[0046] The process of Example 1 was repeated, and the only difference compared with Example 1 was that no melamine was added upstream in the catalyst preparation process, and the calcined support was simply ground and tested for water-gas shift.

[0047] Comparative Example 2

[0048] The process of Example 1 was repeated, and the only difference compared with Example 1 was that melamine was added upstream in the catalyst preparation process, but no melamine was mixed with ammonium molybdate tetrahydrate.

[0049] Comparative Example 3

[0050] The process of Example 1 was repeated, and the only difference compared with Example 1 was that the mass of melamine added upstream in the catalyst preparation process was reduced to 2 g, and the amount of melamine mixed with ammonium molybdate tetrahydrate remained unchanged.

[0051] Comparative Example 4

[0052] The process of Example 1 was repeated, and the only difference compared with Example 1 was that the mass of melamine added upstream in the catalyst preparation process remained unchanged, and the amount of melamine mixed with ammonium molybdate tetrahydrate was increased to 6 g.

[0053] Comparative Example 5

[0054] The process of Example 1 was repeated, and the only difference compared with Example 1 was that the mass of melamine added upstream in the catalyst preparation process was increased to 6 g, and the amount of melamine mixed with ammonium molybdate tetrahydrate was also increased to 6 g.

[0055] The XRD pattern of the obtained material was determined, as shown in Figure 1. Figure 2As shown, the diffraction peaks of Example 1, Example 2, Example 3, Example 4 mainly represent MoC, Mo3N2 and part of MoN, indicating that the obtained substance is a molybdenum-based composite material of molybdenum carbide / molybdenum nitride. The main substance of Comparative Example 1, Comparative Example 3, Comparative Example 4 and Comparative Example 5 is Mo2C, and the main substance of Comparative Example 2 is MoO2, indicating that changing the position and content of the cyanamide compound I and II can obtain molybdenum-based composite materials with different types.

[0056] Catalytic performance test: The WGS catalytic performance of the catalyst was tested in a gas-solid phase catalytic reaction fixed bed device. The test steps were as follows: 0.15 g of the catalyst (60-80 mesh) was placed on the quartz cotton layer of a quartz glass tube (inner diameter of 7 mm). The temperature at the center of the bed and the temperature of the reactor wall were monitored by thermocouples. The catalyst was not subjected to any pre-reduction treatment. The raw gas (12.5% CO and 87.5% N2) was fed at a flow rate of 40 mL / min, which was converted to a mass space velocity of 20000 mL·h -1 ·g -1 The catalyst was introduced into 82℃ H2O, and the ratio of steam to raw gas was kept at 1:1. The residual water at the outlet was removed by a condenser before entering the gas chromatograph (GC2060) equipped with a thermal conductivity detector (TCD). The catalytic activity was measured at a range of 200-400℃, and the catalytic activity was measured every 50℃, and each temperature was kept for about 1h. No methane was generated during the reaction. The specific results are shown in Table 1. Figure 4 .

[0057] Figure 4 The activity data graphs of Example 1, Example 2, Example 4, Example 5 and Comparative Example 1, Comparative Example 3, Comparative Example 5 are shown in the figure. As can be seen from the figure, the conversion rates of the catalyst sample of Example 1 at 350℃ and 400℃ are 39.2% and 64.8% respectively, the conversion rates of the catalyst of Example 2 at 350℃ and 400℃ are 36.6% and 56.7% respectively, the conversion rates of the catalyst of Example 3 at 350℃ and 400℃ are 40.7% and 46.5% respectively, and the conversion rates of the catalyst of Example 4 at 350℃ and 400℃ are 40.6% and 42.5% respectively. However, the conversion rates of Comparative Example 1 and Comparative Example 2 at 350℃ and 400℃ are generally lower than 20%, the conversion rates of Comparative Example 3 at 350℃ and 400℃ are 25.1% and 27.6% respectively, and therefore, it is shown that Example 1 and Example 2 have much higher catalytic activity than Comparative Example 1, Comparative Example 3 and Comparative Example 5, indicating that the Au-molybdenum carbide / molybdenum nitride composite material has better water-gas catalytic activity than single Mo2C.

Claims

1. A method for preparing a catalytic material for water-gas shift reaction, characterized in that: Includes the following steps: (1) Preparation of Mo-based composite material: Molybdenum salt and cyanamide compound I were mixed and transferred to a tube furnace, with cyanamide compound II placed upstream of the tube furnace; then, under a reducing atmosphere, the temperature was raised to 500-700℃ at a rate of 3-6℃ / min and calcined for 2-4h; then, the temperature was raised to 700-800℃ at a rate of 1-3℃ / min and calcined for 1-2h; after the reaction was completed, the mixture was cooled to room temperature under an oxygen-argon atmosphere to obtain the Mo-based composite material. The mass ratio of the molybdenum salt to cyanamide compound I is 1:(1~2). The mass ratio of cyanamide compound II to cyanamide compound I is (2~3):1; The Mo-based composite material mainly includes MoC, Mo3N2 and some MoN; (2) Preparation of catalytic material: Chloroauric acid and ammonia solution were added to the suspension of Mo-based composite material; aged under stirring, then washed and dried to obtain catalytic material for water-gas shift reaction.

2. The preparation method according to claim 1, characterized in that: In step (1), the molybdenum salt includes one or more of molybdenum chloride, ammonium molybdate, and phosphomolybdic acid.

3. The preparation method according to claim 1, characterized in that: In step (1), the cyanamide compound includes one or more of dicyandiamide and melamine.

4. The catalytic material prepared by the method described in claim 1.

5. The application of the catalytic material as described in claim 4, or the catalytic material prepared by the preparation method as described in any one of claims 1 to 3, in water-gas shift reaction.

Images