CN111185217A

CN111185217A - A kind of solid-phase preparation method and application of chromium-based carbon nitride catalyst

Info

Publication number: CN111185217A
Application number: CN202010070560.XA
Authority: CN
Inventors: 仲蕾; 应梦凡; 罗润; 孙建华; 周萍
Original assignee: Jiangsu University of Technology
Current assignee: Jiangsu University of Technology
Priority date: 2020-01-21
Filing date: 2020-01-21
Publication date: 2020-05-22

Abstract

The invention discloses a solid-phase preparation method and application of a chromium-based carbon nitride catalyst. During preparation, melamine, chromium trioxide and ammonium chloride are firstly added to an ethanol solution, and the final product can be obtained after grinding and calcining. product. The method is not only simple to operate and easy to obtain raw materials, but also the solid phase synthesis method changes the original bulk phase structure of melamine, so that the obtained final product is in the shape of a porous sheet. The porous sheet-like chromium-based carbon nitride catalyst is not only conducive to the dispersion of the active component chromium on the catalyst surface, but also to the adsorption of gas. At 300°C, the catalytic oxidation NO removal rate of the chromium-based carbon nitride catalyst can reach 80%.

Description

Solid phase method preparation method and application of chromium-based carbon nitride catalyst

Technical Field

The invention relates to the technical field of environment functional materials, in particular to a solid-phase method for preparing a chromium-based carbon nitride catalyst and application thereof.

Background

In recent years, with the rapid development of society, the environmental problems that follow become a problem that people have to look right at today and affect the sustainable development of all people. Among them, acid rain, ozone layer destruction, photochemical smog and greenhouse effect are some of the more prominent types of problems, and nitrogen oxide NOx is one of the main pollutants causing such problems, which has seriously threatened the living environment and health of human beings. At present, the emission limit of nitrogen oxides NOx in various countries in the world is more and more strict, and the total target of reducing the emission of the nitrogen oxides by 3 percent is clear in a government work report issued in 2019. Therefore, the reduction of the emission of nitrogen oxides NOx is important for the social development of China and the survival development of all human beings.

At present, the more economical flue gas denitration method used in industry is to oxidize NO in flue gas into NO₂By the use of NO₂The high solubility characteristic can further utilize alkaline substances to remove the nitrogen oxides, thereby achieving the purposes of completely removing the nitrogen oxides NOx and recycling the nitrogen oxides NOx. Regarding the oxidation of NO, there are classified into a catalytic oxidation method, a gas-phase oxidation method and a liquid-phase oxidation method depending on the oxidation mode. Among them, the gas-phase oxidation method and the liquid-phase oxidation method have problems of long reaction time, high operation cost, easy secondary pollution, and the like. The catalytic oxidation method has the characteristics of low investment and operation cost, good pollutant removal effect and stable performance, and has good development prospect. Among them, the core of the catalytic oxidation process is undoubtedly the preparation of the catalyst.

In recent years, the catalysts for catalytic oxidation of NO have been mainly used, including activated carbon catalysts, molecular sieve catalysts, noble metal catalysts, and metal oxide catalysts. Although the activated carbon catalyst has a large specific surface area and a good pore structure, the activated carbon catalyst has high NO oxidation efficiency only at low temperature, and the catalytic activity of the activated carbon catalyst is reduced along with the increase of the temperature; in addition, water vapor and SO in the flue gas₂The catalytic activity of the activated carbon catalyst is also affected to some extent. The molecular sieve catalyst has large specific surface area and uniform micropores, but the molecular sieve catalyst only shows higher catalytic activity at high temperature, and the NO oxidation rate is not high because of the limitation of thermodynamic equilibrium. Noble metals commonly used in noble metal catalystsMetals mainly comprise Pt, Pd, Au and the like, and are widely applied to the field of catalysis due to the excellent characteristics of high catalytic activity, high temperature resistance, corrosion resistance and the like, but noble metals are expensive and are not suitable for industrial mass production and application. Therefore, metal oxide catalysts, which are abundant in resource storage, relatively inexpensive in price, and have good catalytic activity, are receiving increasing attention.

The carbon nitride as a catalyst without metal components has the advantages of high thermal stability, chemical stability, certain acid and alkali resistance, low price, simple preparation, environmental protection and the like. Therefore, carbon nitride has important application prospects in the fields of energy conversion and environmental purification, and is more and more concerned by related fields. Therefore, the carbon nitride is taken as a carrier of the thermal catalytic denitration catalyst and has good development prospect. However, the structure of carbon nitride itself is not favorable for gas adsorption, and if the carbon nitride is not modified to a certain extent, the application of the carbon nitride in the field of catalytic oxidation of nitric oxide is necessarily greatly limited.

Disclosure of Invention

The invention aims to solve the defects in the prior art and provides a solid-phase method for preparing a chromium-based carbon nitride catalyst and application thereof.

The technical scheme of the invention is as follows: a solid phase method for preparing a chromium-based carbon nitride catalyst comprises the following steps:

(1) adding melamine, chromic oxide and ammonium chloride into an ethanol solution, and grinding;

(2) and (3) taking out the sample ground in the step (1), calcining, and taking out the calcined sample to obtain the chromium-based carbon nitride catalyst.

Further, the melamine used in the step 1 is a carbon nitride precursor, the chromium oxide is a chromium source, the ammonium chloride is a pore-forming agent, and the ratio of the amounts of the three substances is 400: 1-10: 1500.

Further, the calcination process in step 2 is carried out in a muffle furnace, specifically, the calcination is carried out after the temperature is raised to 500-540 ℃ at the speed of 2-3 ℃/min, and the temperature is kept for 2-6 h.

The chromium-based carbon nitride catalyst prepared by the method can be applied to the field of flue gas denitration, and can efficiently catalyze and oxidize NO.

The invention has the beneficial effects that:

1. the method comprises the steps of preparing a chromium-based carbon nitride catalyst by a solid phase method by taking melamine as a carbon nitride precursor, chromium oxide as a chromium source and ammonium chloride as a pore-forming agent; the solid-phase synthesis method changes the original bulk phase structure of melamine, so that the obtained final product is in a porous sheet shape, which is beneficial to the dispersion of active component chromium on the surface of the catalyst and the adsorption of gas, and when the solid-phase synthesis method is used in the field of flue gas denitration, the removal rate of NO in the catalytic oxidation of the prepared chromium-based carbon nitride catalyst can reach 80% at 300 ℃;

2. the invention mainly adopts the solid phase synthesis method to prepare the chromium-based carbon nitride catalyst, has simple operation and easily obtained raw materials, and is suitable for laboratories and industrial expanded production application.

Drawings

FIG. 1 is an XRD spectrum of a chromium-based carbonitride catalyst prepared in examples 1-4 and a catalyst CN prepared in comparative example 1;

FIG. 2 is SEM images of chromium-based carbonitride catalysts prepared in examples 1-4 and catalyst CN prepared in comparative example 1;

FIG. 3 is a graph of NO removal versus temperature for chromium-based carbonitride catalysts prepared in examples 1-4 and catalyst CN prepared in comparative example 1.

Detailed Description

The following examples further illustrate the present invention but are not to be construed as limiting the invention. Modifications and substitutions to methods, procedures, or conditions of the invention may be made without departing from the spirit of the invention.

Example 1 preparation of chromium-based carbonitride catalyst a

Step 1: 3.3062 g of melamine, 0.0203 g of chromium trioxide and 5.0654 g of ammonium chloride are added to 5mL of ethanol solution and ground;

step 2: and (3) taking out the sample ground in the step (1), putting the sample into a muffle furnace for calcination (the calcination condition is that the temperature is increased to 520 ℃ at the speed of 2.4 ℃/min and is kept for 4 hours), and taking out the sample obtained by calcination to obtain the final product, namely the chromium-based catalyst, which is recorded as the catalyst a.

Example 2 preparation of chromium-based carbonitride catalyst b

Step 1: 3.3163 g of melamine, 0.0507 g of chromium trioxide and 5.0562 g of ammonium chloride are added into 5mL of ethanol solution and ground;

step 2: and (3) taking out the sample ground in the step (1), putting the sample into a muffle furnace for calcination (the calcination condition is that the temperature is increased to 520 ℃ at the speed of 2.4 ℃/min and is kept for 4 hours), and taking out the sample obtained by calcination to obtain a final product, namely the chromium-based catalyst, which is recorded as the catalyst b.

Example 3 preparation of chromium-based carbonitride catalyst c

Step 1: 3.3361 g of melamine, 0.0824 g of chromium trioxide and 5.0323 g of ammonium chloride are added into 5mL of ethanol solution and ground;

step 2: and (3) taking out the sample ground in the step (1), putting the sample into a muffle furnace for calcination (the calcination condition is that the temperature is increased to 520 ℃ at the speed of 2.4 ℃/min and is kept for 4 hours), and taking out the sample obtained by calcination to obtain a final product, namely the chromium-based catalyst, which is recorded as the catalyst c.

Example 4 preparation of chromium-based carbonitride catalyst d

Step 1: 3.3589 g of melamine, 0.1016 g of chromium trioxide and 5.0063 g of ammonium chloride are added to 5mL of ethanol solution and ground;

step 2: and (3) taking out the sample ground in the step (1), putting the sample into a muffle furnace for calcination (the calcination condition is that the temperature is increased to 520 ℃ at the speed of 2.4 ℃/min and is kept for 4 hours), and taking out the sample obtained by calcination to obtain a final product, namely the chromium-based catalyst, which is recorded as catalyst d.

Comparative example 1 preparation of catalyst CN

The procedure is essentially the same as in example 1, except that "0.0203 g of chromium oxide" in step 1 is omitted and the product obtained is designated as catalyst CN.

Characterization test of the relevant properties:

FIG. 1 is an XRD pattern of chromium-based catalysts prepared in examples 1-4 (corresponding to a-d in the figures, respectively) and catalyst CN prepared in comparative example 1; in which the catalyst CN prepared in comparative example 1 exhibited two characteristic peaks at 13.0 ° and 27.3 °, whereas in examples 1 to 4, the characteristic diffraction peaks of chromium trioxide were exhibited in the catalyst due to the addition of chromium trioxide. With the increase of the addition amount of the chromium sesquioxide, the characteristic peak of the chromium sesquioxide in the catalyst is gradually enhanced. Meanwhile, the diffraction peak of the carbon nitride does not change, which shows that the addition of the chromium oxide in the catalyst does not change the structure of the carbon nitride of the catalyst carrier, and the chromium-based catalyst prepared by the method has good stability.

FIG. 2 is an SEM image of each of the catalysts prepared in examples 1-4 (corresponding in sequence to b-e in FIG. 2) and comparative example 1 (a in FIG. 2); the catalyst CN prepared in the comparative example 1 is obvious in agglomeration and has a certain thickness, the catalysts prepared in the examples 1 to 4 are flaky and are uniformly dispersed, and the catalyst b with the best flaky structure is more favorable for dispersing active component chromium on the surface of the catalyst and adsorbing gas compared with the catalyst CN, so that the catalyst lays a foundation for the application in the field of flue gas denitration.

Catalytic oxidation of NO experiment

The chromium-based carbon nitride catalysts prepared in examples 1 to 4 and the catalyst CN prepared in comparative example 1 were used for the activity evaluation experiment for catalytic oxidation of NO.

The experiments were divided into 5 groups: respectively placing 0.1500 g of catalyst a, 0.1500 g of catalyst b, 0.1500 g of catalyst c, 0.1500 g of catalyst d and 0.1500 g of catalyst CN in the center of a cylindrical reactor, and plugging two ends of the cylindrical reactor with quartz wool; the mixed gas consists of 13.3 percent, 10 percent and 70 percent of O by volume fraction₂NO and N₂The composition is that after being stabilized at normal temperature for 1 h, the temperature is raised from 250 ℃ to 400 ℃ under the same atmosphere condition, test points are taken every 50 ℃, each test point is kept for 15 min, and the concentration of nitrogen oxide NOx at an outlet is measured and analyzed by a testo 340 type flue gas analyzer。

Fig. 3 is a graph showing NO removal rate versus temperature change of each of the catalysts prepared in examples 1 to 4 and comparative example 1, and it can be seen from the graph that the denitration performance of the chromium-based carbon nitride catalysts (catalyst a, catalyst b, catalyst c and catalyst d) prepared in examples 1 to 4 is greatly improved compared to that of catalyst CN, wherein the denitration performance of catalyst b is the best, and the NO removal rate reaches 80% at 300 ℃; the denitration performance of the catalyst c is inferior, and the NO removal rate reaches 53.27% at 300 ℃; the denitration performance of the catalyst a is the next time, and the NO removal rate reaches 34.65% at 300 ℃; the denitration performance of the catalyst d is the worst, and the NO removal rate is only 23.71% at 300 ℃.

It can also be seen from the graph that the denitration performance of the chromium-based carbon nitride catalyst prepared in the example section meets thermodynamic equilibrium, that is, according to the thermodynamic equilibrium, the NO removal rate gradually increases with the increase of temperature, and when the removal rate reaches the maximum value, the NO removal rate gradually decreases with the increase of temperature, so that the highest catalytic efficiency exists.

The foregoing illustrates and describes the principles, general features, and advantages of the present invention. However, the above description is only an example of the present invention, the technical features of the present invention are not limited thereto, and any other embodiments that can be obtained by those skilled in the art without departing from the technical solution of the present invention should be covered by the claims of the present invention.

Claims

1. a solid-phase preparation method of chromium-based carbon nitride catalyst, is characterized in that, comprises the following steps:

(1) Add melamine, chromium trioxide and ammonium chloride to the ethanol solution and grind;

(2) The sample ground in step 1 is taken out and then calcined, and the calcined sample is taken out to obtain a chromium-based carbon nitride catalyst.

2. the solid-phase preparation method of a kind of chromium-based carbon nitride catalyst as claimed in claim 1, is characterized in that, the melamine used in step 1 is carbon nitride precursor, and chromium oxide is chromium source, chlorine Ammonium is a pore-forming agent, and the ratio of the three substances is 400:1~10:1500.

3. the solid-phase method preparation method of a kind of chromium-based carbon nitride catalyst as claimed in claim 1, is characterized in that, the calcination process in step 2 is to carry out in muffle furnace, specifically is 2-3 ℃/ The temperature was raised to 500-540 °C at a rate of min, followed by calcination, and the temperature was kept for 2-6 h.

4. the application of the chromium-based carbon nitride catalyst prepared by the solid phase method preparation method of a chromium-based carbon nitride catalyst in the field of flue gas denitration as claimed in any one of claims 1-3, is characterized in that, The chromium-based carbon nitride catalyst has the ability to efficiently catalyze the oxidation of NO.