阅读说明：本技术 一种用于氨合成的碳化钼/氧化铈催化剂及其制备方法 (Molybdenum carbide/cerium oxide catalyst for ammonia synthesis and preparation method thereof ) 是由 林炳裕 方笔耘 柳方明 倪军 林建新 江莉龙 于 2019-10-28 设计创作，主要内容包括：本发明公开了一种用于氨合成的碳化钼/氧化铈催化剂及其制备方法,其是以氧化铈为载体,将钼前驱体引入到氧化铈颗粒上,在含碳混合气中高温碳化,得到所述用于氨合成的碳化钼/氧化铈催化剂,本发明制备方法简单,成本低廉,所得催化剂具有较高的氨合成活性,且其不需要添加钌活性组分,具有较好的应用前景。(The invention discloses a molybdenum carbide/cerium oxide catalyst for ammonia synthesis and a preparation method thereof, wherein cerium oxide is used as a carrier, a molybdenum precursor is introduced onto cerium oxide particles, and the cerium oxide particles are carbonized at high temperature in a carbon-containing mixed gas to obtain the molybdenum carbide/cerium oxide catalyst for ammonia synthesis.)

1. A molybdenum carbide/cerium oxide catalyst for ammonia synthesis is characterized in that the catalyst is CeO₂As a carrier, Mo₂C is formed by active components; wherein the molybdenum content is 5wt.% to 75 wt.%.

2. A process for preparing the Mo/Ce carbide/Ce oxide catalyst used for synthesizing ammonia includes such steps as dissolving the Mo precursor in the ammonia solution to obtain Mo precursor solution, introducing it to the Ce oxide particles, heat treating, and high-temp carbonizing in the mixed gas containing carbon.

3. The method of claim 2, wherein the molybdenum precursor is one or a mixture of ammonium molybdate and molybdic acid.

4. The method of preparing a molybdenum carbide/cerium oxide catalyst according to claim 2, wherein the aqueous ammonia solution has a concentration of 2wt.% to 15 wt.%.

5. The method for preparing the molybdenum carbide/cerium oxide catalyst according to claim 2, wherein the heat treatment is performed in an oxygen-containing mixed gas at a treatment temperature of 30 to 600 ℃ for 0.2 to 10 hours;

the oxygen-containing mixed gas contains 3% ~ 100% of oxygen by volume and is specifically gas composed of air or oxygen and 0 group inert gas.

6. The method of claim 2, wherein the carbon-containing gas mixture comprises 10 to 50% by volume of carbon-containing gas, 40 to 90% by volume of hydrogen gas, and the balance of one or more of nitrogen gas and group 0 inert gas;

the carbon-containing gas is one or more of methane, ethane, propane, acetylene and propyne.

7. The method of claim 2, wherein the temperature of the high temperature carbonization is 300-1000 ℃ and the carbonization time is 0.5-10 h.

Technical Field

The invention belongs to the technical field of material preparation, and particularly relates to a molybdenum carbide/cerium oxide catalyst for ammonia synthesis and a preparation method thereof.

Background

In the ammonia synthesis reaction, the traditional industrial iron-based catalyst must operate under the condition of high temperature and high pressure (> 15 MPa, >450 ℃) for synthesizing ammonia, and the ton energy consumption is high.

The dissociation of nitrogen-nitrogen bonds in ammonia synthesis reactions is generally considered to be a reaction rate controlling step, and molybdenum has a better nitrogen dissociation ability than iron ruthenium, and thus has been sought as an active component of ammonia synthesis catalysts. Aika et al (Molybdenum nitride and carbide catalysts for ammonia synthesis. applied catalysis A: General 219 (2001) 141-147) found that pure Molybdenum carbide has higher catalytic activity than Molybdenum nitride and is more suitable as an active component of an ammonia synthesis catalyst. However, the pure molybdenum carbide catalyst has a low specific surface area and a few pore channels, which are not favorable for the adsorption, reaction and diffusion of reactants and products on the catalyst, so the ammonia synthesis performance of the catalyst cannot be fully exerted. As an important rare earth oxide, cerium oxide has the characteristics of high thermal stability, rich and adjustable oxygen defects and unique electronic property, can be applied to multiple fields of catalysis, electrochemistry, optics and the like, and is an important carrier material and an important catalyst active component. The invention takes cerium oxide as a carrier, molybdenum carbide grows in situ on the cerium oxide, and the molybdenum carbide serving as an active component for supporting and dispersing the catalyst is utilized to prepare the molybdenum carbide-cerium oxide ammonia synthesis catalyst, wherein the ammonia synthesis reaction activity of the catalyst is equivalent to that of a cerium oxide loaded ruthenium-based catalyst, and the catalyst has good application prospect.

Disclosure of Invention

The invention aims to provide a molybdenum carbide-cerium oxide catalyst for ammonia synthesis, which has high ammonia synthesis activity, does not need to add a ruthenium active component, and has good application prospect.

In order to achieve the purpose, the invention adopts the following technical scheme:

a Mo carbide/Ce oxide catalyst for ammonia synthesis is CeO₂As a carrier, Mo₂C is formed by active components; wherein the molybdenum content is 5wt.% to 75 wt.%.

The preparation method of the molybdenum carbide/cerium oxide catalyst comprises the following steps:

(1) dissolving a molybdenum precursor in an ammonia water solution to prepare a molybdenum precursor solution;

(2) introducing a molybdenum precursor solution onto cerium oxide particles to obtain a mixture of the molybdenum precursor solution and the cerium oxide particles;

(3) putting the mixture obtained in the step (2) into oxygen-containing mixed gas for heat treatment;

(4) and (4) putting the mixture after the heat treatment into carbon-containing mixed gas for high-temperature carbonization.

The precursor of the molybdenum in the step (1) is any one of ammonium molybdate and molybdic acid or a mixture of the two. The concentration of the aqueous ammonia solution is 2wt.% to 15 wt.%.

The heat treatment in the step (3) is carried out in oxygen-containing mixed gas, the treatment temperature is 30-600 ℃, the treatment time is 0.2-10 h, the volume content of oxygen in the oxygen-containing mixed gas is 3% ~ 100%, and the oxygen is specifically air or gas consisting of oxygen and 0 group inert gas.

In the carbon-containing mixed gas in the step (4), the volume content of carbon-containing gas is 10-50%, the volume content of hydrogen is 40-90%, and the balance is one or more of nitrogen and group 0 inert gas;

the carbon-containing gas is one or more of methane, ethane, propane, acetylene and propyne.

The temperature of the high-temperature carbonization in the step (4) is 300-1000 ℃, and the carbonization time is 0.5-10 h.

The invention has the following remarkable advantages:

the invention prepares the molybdenum carbide/cerium oxide catalyst by in-situ growing molybdenum carbide on cerium oxide particles. The catalyst has low preparation cost, does not need to add ruthenium active components, but has the ammonia synthesis activity equivalent to that of a ruthenium-based ammonia synthesis catalyst, thereby having better application prospect.

Drawings

FIG. 1 is an XRD pattern of a sample of the catalyst obtained in examples 1 to 3 and comparative examples 1 to 2.

Detailed Description

In order to make the present invention more comprehensible, the technical solutions of the present invention are further described below with reference to specific embodiments, but the present invention is not limited thereto.