CN104743529B - Synthesis method of tungsten nitride with high catalytic performance - Google Patents

Abstract

The invention discloses a method for preparing nanometer tungsten nitride, belonging to the technical field of powder metallurgy preparation. Firstly, the tungsten oxide precursor is synthesized and prepared by solution method, and then the tungsten oxide precursor is nitrided in ammonia gas to obtain tungsten nitride powder with nanoscale crystal grains, and the powder particle size is 30-120nm. The invention solves the problems that the traditional preparation method is difficult to obtain ultrafine nanocrystalline powder and the preparation time is long, and the obtained tungsten nitride powder has the advantages of controllable particle size, low cost, high utilization rate of raw material powder, and remarkable catalytic performance.

Description

A kind of synthesis method of tungsten nitride with high catalytic performance

technical field

The invention belongs to the technical field of powder metallurgy preparation, and particularly provides a preparation method of nanocrystalline tungsten nitride powder.

Background technique

The refractory metal tungsten not only has excellent performance as a single substance, but also its compounds tungsten oxide, tungsten sulfide, and tungsten nitride are also widely used. Among them, tungsten nitride is a new type of catalytic material, which has better performance than sulfide catalysts in hydrodesulfurization and hydrodenitrogenation. The hydrogenolysis of the ring has high selectivity, which can greatly reduce the hydrogen consumption in the process, and has great industrial significance. These processes traditionally use noble metals as catalysts. Thus, the desire to use nitrides instead of noble metals has driven research into the synthesis and catalysis of such catalysts.

At the same time, the current research shows that when the material reaches the nanometer size, its optical, thermal, electrical, magnetic, mechanical and even chemical properties will change significantly accordingly, and it has superior performance that ordinary materials do not have. Similarly, when the grain size of tungsten nitride reaches the nanometer level, its catalytic performance is also greatly improved. On the other hand, because violet tungsten has the highest oxygen vacancy defect in tungsten oxide and has high surface activity, it is currently widely used in the preparation of ultrafine tungsten powder, cemented carbide WC, etc. Therefore, the preparation of nanocrystalline tungsten nitride can be obtained by preferentially preparing violet tungsten and then subsequent nitriding.

At present, the preparation method of nanoscale tungsten nitride is mainly to prepare tungsten oxide precursor by sol-gel method, spray pyrolysis method, rotary kiln calcination method, etc., and then pass it into ammonia gas for nitriding. Liu Bingfa (Journal of Nanchang University: Engineering Edition, 2006,28(3):235-238.) used ammonium metatungstate as raw material, and prepared WO ₃ precursor with an average particle size of 0.64μm by spraying granulation and then calcining. Powder, and then screen out the particles of about 100nm to be nitrided under the condition of pure ammonia. Although the method can prepare tungsten nitride powder smaller than 100nm, the powder making rate is very low. Chen (Journal of Solid State Chemistry, 2011, 184(2):455-462.) mixed tungstic acid and octylamine for 24 hours, then fed ammonia gas after 48 hours of reaction, and calcined at 650-800°C to prepare WN. The WN prepared by this method is in the shape of short rods and fine grains, but the preparation time is too long and the preparation cost is relatively high. Therefore, it is necessary to develop a new preparation method for tungsten nitride with high catalytic performance.

Contents of the invention

The purpose of the present invention is to provide a new method for preparing nano-tungsten nitride, which solves the problems of too long preparation time and high preparation cost.

The invention directly uses tungstate ammonium metatungstate as a raw material, has the characteristics of short process and low cost, and the prepared tungsten nitride has controllable particle size and excellent catalytic performance.

Processing step of the present invention is as follows:

1. Raw materials: The raw materials used are ammonium metatungstate, ammonium nitrate, auxiliary agent and ethylenediaminetetraacetic acid;

2. Solution preparation: dissolve the selected raw materials in water according to a certain ratio, and mix them evenly;

3. Precursor preparation: Heat the aqueous solution obtained in step (2). With the volatilization of the aqueous solution, the solution will bubble after concentration and release a large amount of gas, and a violent redox reaction will occur within tens of seconds to form a precursor powder.

4. Preparation of tungsten nitride: calcining the precursor obtained in step (3) at a temperature of 650°C to 900°C in an ammonia atmosphere for 1 to 2 hours to obtain pure, porosity and particle size controlled Nano tungsten nitride powder.

Wherein in step (2), the molar ratio of ammonium nitrate to tungsten source is 12-36; the molar ratio of auxiliary agent to tungsten source is 5-15; the molar ratio of EDTA to tungsten source is 0.5-1.

The advantages of the present invention are:

1. Directly use tungstate ammonium metatungstate as raw material, short process, low cost, simple and fast process, suitable for large-scale production;

2. By controlling the type and proportion of raw materials, the reaction process of precursor preparation can be controlled, and the particle size and pore structure of the precursor can be controlled;

3. A large amount of gas is generated during the reaction process of the present invention, which effectively controls the contact between the reactant and oxygen during the reaction process, and plays an important role in the formation of the precursor violet tungsten powder;

4. The precursor powder has high reactivity, which can reduce the heat treatment temperature and increase the heat treatment speed;

5. The particle size and pore structure of the obtained tungsten nitride can be controlled by the nitriding temperature of ammonia gas. So as to achieve the purpose of improving the catalytic performance.

Description of drawings

Fig. 1 is the XRD pattern of tungsten nitride powder;

Fig. 2 is a scanning electron microscope observation photo of tungsten nitride powder (where a is x2,000, b is x9,000 times).

detailed description

Example 1

Weigh 0.01 mol of ammonium metatungstate ((NH ₄ ) ₆ H ₂ W ₁₂ O ₄₀ ), 0.24 mol of ammonium nitrate (NH ₄ NO ₃ ), 0.072 mol of urea (CO(NH ₂ ) ₂ ), and Diaminetetraacetic acid (EDTA) 0.005mol. Dissolve the raw material powder in an appropriate amount of deionized water and stir until completely dissolved, then heat at a constant temperature of 200°C, and react after the solution is evaporated to dryness to obtain the precursor tungsten oxide powder. Nitriding the precursor at 650°C in ammonia gas and keeping it warm for 2 hours to obtain tungsten nitride with a diameter of 30-80nm.

Example 2

Weigh 0.01 mol of ammonium metatungstate ((NH ₄ ) ₆ H ₂ W ₁₂ O ₄₀ ), 0.24 mol of ammonium nitrate (NH ₄ NO ₃ ), 0.072 mol of urea (CO(NH ₂ ) ₂ ), and Diaminetetraacetic acid (EDTA) 0.005mol. Dissolve the raw material powder in an appropriate amount of deionized water and stir until completely dissolved, then heat at a constant temperature of 200°C, and react after the solution is evaporated to dryness to obtain the precursor tungsten oxide powder. Nitriding the precursor at 750°C in ammonia gas and keeping it warm for 2 hours to obtain tungsten nitride with a diameter of 30-100nm.

Example 3

Weigh ammonium metatungstate ((NH ₄ ) ₆ H ₂ W ₁₂ O ₄₀ ) 0.01mol, ammonium nitrate (NH ₄ NO ₃ ) 0.3mol, citric acid (C ₆ H ₈ O ₇ ) 0.072mol according to the reaction measurement ratio, Ethylenediaminetetraacetic acid (EDTA) 0.005mol. Dissolve the raw material powder in an appropriate amount of deionized water and stir until completely dissolved, then heat at a constant temperature of 200°C, and react after the solution is evaporated to dryness to obtain the precursor tungsten oxide foam. Nitriding the precursor at 900°C in ammonia gas and keeping it warm for 1 hour to obtain tungsten nitride with a diameter of 50-100nm.

Example 4

Weigh 0.01 mol of ammonium metatungstate ((NH ₄ ) ₆ H ₂ W ₁₂ O ₄₀ ), 0.24 mol of ammonium nitrate (NH ₄ NO ₃ ), 0.1 mol of citric acid (C ₆ H ₈ O ₇ ) according to the reaction measurement ratio, Ethylenediaminetetraacetic acid (EDTA) 0.005mol. Dissolve the raw material powder in an appropriate amount of deionized water and stir until completely dissolved, then heat at a constant temperature of 200°C, and react after the solution is evaporated to dryness to obtain the precursor tungsten oxide powder. Nitriding the precursor at 650°C in ammonia gas and keeping it warm for 2 hours to obtain tungsten nitride with a diameter of 50-80nm.

Example 5

Weigh 0.01 mol of ammonium metatungstate ((NH ₄ ) ₆ H ₂ W ₁₂ O ₄₀ ), 0.24 mol of ammonium nitrate (NH ₄ NO ₃ ), 0.072 mol of glycine (C ₂ H ₅ NO ₂ ), and Diaminetetraacetic acid (EDTA) 0.005mol. Dissolve the raw material powder in an appropriate amount of deionized water and stir until completely dissolved, then heat at a constant temperature of 200°C, and react after the solution is evaporated to dryness to obtain the precursor tungsten oxide powder. Nitriding the precursor at 750°C in ammonia gas and keeping it warm for 2 hours to obtain tungsten nitride with a diameter of 50-100nm.

Claims (2)

1. A synthetic method of high catalytic performance tungsten nitride, characterized in that it has the following steps: (1) Raw material: Ammonium metatungstate, ammonium nitrate, auxiliary agent and ethylenediaminetetraacetic acid are used as raw materials; (2) Solution preparation: Dissolve the selected raw materials in water according to a certain ratio and mix them evenly; the molar ratio of ammonium nitrate to ammonium metatungstate is 12-36; the molar ratio of auxiliary agent to ammonium metatungstate is 5-15 ; The molar ratio of ethylenediaminetetraacetic acid to ammonium metatungstate is 0.5-1; (3) Precursor preparation: heat the aqueous solution obtained in step (2), and as the aqueous solution volatilizes, the solution bubbles after concentration and releases a large amount of gas, and a violent redox reaction occurs within a few seconds to form a Porous precursor powder; (4) Preparation of tungsten nitride: Nitriding the precursor obtained in step (3) under an ammonia atmosphere to obtain a pure, porosity and particle size-controlled nano-tungsten nitride powder; the nitriding temperature under an ammonia atmosphere The temperature is 650℃～900℃, and the nitriding time is 1～2h. 2. the synthetic method of a kind of high catalytic performance tungsten nitride according to claim 1 is characterized in that the auxiliary agent in the step (1) is at least one wherein of urea, glycine, malic acid, thiourea, citric acid .