CN115448726A

CN115448726A - Method for enhancing catalytic performance of silicon carbide film material by acid etching

Info

Publication number: CN115448726A
Application number: CN202211079424.2A
Authority: CN
Inventors: 仲兆祥; 陈嘉豪; 邢卫红; 曾毅清
Original assignee: Nanjing Tech University
Current assignee: Nanjing Tech University
Priority date: 2022-09-05
Filing date: 2022-09-05
Publication date: 2022-12-09
Anticipated expiration: 2042-09-05
Also published as: CN115448726B

Abstract

The invention relates to a method for enhancing the catalytic performance of a silicon carbide film material by acid etching, which can significantly enhance the catalytic performance of the SiC film material by only immersing the SiC film material in an acid solution for a certain time and then drying. The method utilizes the acid corrosion resistance of the SiC membrane material, so that the acid solution only etches the catalytic component in the SiC membrane material, and the structure of the SiC membrane material cannot be damaged. The SiC catalytic membrane after acid etching can efficiently intercept dust and simultaneously carry out catalytic degradation on gas-phase pollutants such as nitrogen oxides, VOCs and the like, and has wide application prospect in the field of atmospheric pollution treatment.

Description

Method for enhancing catalytic performance of silicon carbide film material by acid etching

Technical Field

The invention belongs to the field of atmospheric pollution treatment, and particularly relates to a method for enhancing the catalytic performance of a silicon carbide film material by acid etching.

Background

Silicon carbide (SiC) ceramics have received much attention due to their good chemical resistance and thermal shock resistance. The SiC ceramic separation membrane prepared by sintering SiC ceramic shows great application potential in the field of gas-solid separation. Along with the stricter requirements on the treatment of industrial flue gas in recent years, more and more researches and attempts are made to couple the SiC ceramic separation membrane with other technologies to prepare a multifunctional SiC membrane material so as to realize the cooperative treatment of multiple pollutants in the flue gas. The SiC ceramic separation membrane is coupled with a catalytic technology to prepare the SiC catalytic membrane, so that dust and gas-phase pollutants (NO, VOCs and the like) can be effectively removed.

The prior patent reports that the SiC membrane material has catalytic activity mainly by coating or distributing catalytic components on the surface of the SiC membrane material or in the pore channels of a support body and calcining. However, although the impregnation method can produce the SiC catalyst membrane material, the production steps thereof are cumbersome. In addition, the bonding strength of the catalyst and the SiC ceramic membrane is poor, and the SiC catalytic membrane can face the risk of falling off of the catalyst. Therefore, at present, the SiC catalytic membrane material is prepared by adopting a blending sintering mode to improve the bonding strength of the catalyst and the carrier. The invention patent CN112028180A of China reports a SiC ceramic filter tube with a catalytic function. The ceramic catalytic filter tube is prepared by firstly preparing catalytic active particles, then mixing and pressing the catalytic active particles, siC ceramic raw material powder, polyethylene glycol, water and the like into a sintered preform, and finally performing gradient heating calcination. The Chinese invention patent CN111167491A uses metal carbonate and oxide as catalytic active components, and directly prepares the SiC catalytic film in one-time sintering. Although the SiC membrane material with catalytic activity can be prepared by blending and sintering, and the bonding strength between the catalyst and the SiC ceramic membrane is improved, the SiC membrane material has low catalytic efficiency and is difficult to meet the requirements of practical application. Therefore, the application prospect of the SiC membrane material is remarkably improved by improving the catalytic performance of the SiC membrane material through a post-treatment method.

Disclosure of Invention

The invention aims to remarkably improve the catalytic performance of the SiC membrane material in an acid etching mode. The acid solution etches the catalytic active components in the SiC membrane material into the catalytic active components with small particle sizes, so that the catalytic performance of the SiC membrane material can be further improved on the basis of the existing catalytic performance. In addition, the excellent chemical resistance of the SiC ceramic film makes it resistant to corrosion by acid solutions, thus maintaining high mechanical strength. The SiC membrane material after acid etching can remove ultrafine dust in industrial tail gas and simultaneously carry out NO treatment on the industrial tail gas _x And VOCs are subjected to high-efficiency catalytic degradation, so that the synergistic treatment of multiple pollutants is realized, and the method has a wide application prospect.

The invention is realized by the following technical scheme:

a method for enhancing the catalytic performance of a silicon carbide film material by acid etching comprises the following steps:

(1) Weighing catalytic active components with certain particle sizes according to a certain proportion, placing the catalytic active components into a ball milling tank, adding a solvent at a certain rotating speed, carrying out wet ball milling for a certain time, and drying to obtain mixed catalytic active powder;

(2) Mixing catalytic active powder, siC aggregate with certain particle size and active carbon powder in certain proportion at certain rotation speed for certain time;

(3) Screening the mixed powder by using a stainless steel screen to obtain mixed powder with uniform particle size;

(4) Mixing and stirring the mixed powder and a binder according to a certain proportion, carrying out cold isostatic pressing, and then calcining at a certain temperature to obtain a SiC membrane material;

(5) Preparing an acid solution according to a certain molar ratio, then placing the prepared SiC membrane material in the acid solution for soaking for a certain time, taking out the soaked SiC membrane material, and drying at a certain temperature to obtain the SiC membrane material with enhanced catalytic performance.

And further:

the catalytically active component and the particle size of step (1) are respectively strontium carbonate particle size 300-500 nm, titanium dioxide particle size 20-30 nm, tricobalt tetroxide particle size 50-200 nm, cobaltous oxide particle size 50-200 nm; the selected proportion is strontium carbonate: titanium dioxide: cobaltosic oxide or the molar ratio of cobaltosic oxide = (0-1): (0-0.6): (0.4-1); the solvent is deionized water or absolute ethyl alcohol; the speed of rotation of the ball mill used is 200-300 rpm, the ball milling time is 4-6 h, and the drying temperature is 80-120 ℃.

The grain size of the SiC powder used in step (2) is 40-200 μm, and the average grain size of the carbon powder is 20 μm; the mass ratio of the selected materials is as follows: siC aggregate: the mass ratio of the activated carbon powder =1: (7.5-19): (1.5-5); the speed of rotation of the ball mill is 200-300 r/min and the mixing time is 2-4 h.

Step (4) using a binder of 6-8% by mass of PVA solution, the mass ratio of binder to SiC powder being 1 (9-19); the pressure of the cold isostatic pressure is 8-10 MPa, the dwell time is 10-15 s; the calcination temperature is 500 ℃ hold 2-4 h, continuing to 1070-1350 ℃ hold 2-4 h.

The acid solution in the step (5) is any one of acetic acid, hydrochloric acid, sulfuric acid, phosphoric acid or nitric acid; the concentration of the acid solution is 1-2 mol/L, the immersion time is 1-2 h, the drying temperature is 100-120 ℃, and the drying time is 8-12 h.

The silicon carbide film material with enhanced catalytic performance can be used for deep treatment of industrial tail gas pollutants.

The invention has the beneficial effects that:

1. the surface of the catalytic active component in the SiC membrane material is etched by adopting the acid solution to form the catalytic active component with small particle size, so that the catalytic performance of the SiC membrane material can be further improved on the basis of the existing catalytic performance.

2. The acid etching utilizes the chemical corrosion resistance of the SiC membrane material, so that the acid solution only etches the catalytic active component, and the property of the SiC membrane material is not influenced.

3. The acid solution adopted by the acid etching has wide source and low price. The etching process is safe and simple and is easy to amplify.

4. The acid etching method has certain universality and can be used for ceramic film materials made of other same raw materials.

5. The SiC membrane material after acid etching has high catalytic performance, can remove dust and gas phase pollutants simultaneously, and has wide prospect in the field of gas purification.

Drawings

Fig. 1 is an SEM image of the SiC film material prepared by acid etching as described in example 1.

Fig. 2 is a graph showing the nitrogen oxide oxidation performance of the SiC film material prepared by the acid etching described in example 1.

Fig. 3 is a dust removal performance diagram of the SiC film material prepared by the acid etching described in example 1.

Fig. 4 is an XRD pattern of the SiC film material prepared by acid etching as described in example 2.

Fig. 5 is a TEM image of the SiC film material prepared by acid etching as described in example 2.

Fig. 6 is an SEM image of the SiC film material prepared by acid etching described in example 3.

Fig. 7 is a graph showing the nitrogen oxide oxidation performance of the SiC film material prepared by the acid etching described in example 4.

Fig. 8 is a dust removal performance diagram of the SiC film material prepared by the acid etching described in example 4.

Fig. 9 is a graph showing the NO reduction performance of the SiC film material prepared by the sulfuric acid etching described in example 5.

Detailed Description

The present invention is explained in further detail below with reference to examples, which are only for illustrating the present invention, but the embodiments of the present invention are not limited thereto.

Example 1

The method for enhancing the catalytic performance of the silicon carbide film material by acid etching comprises the following preparation steps:

(1) The powder with the corresponding mass is weighed according to the mol ratio of the strontium carbonate, the titanium dioxide and the cobaltosic oxide of 1: 0.6: 0.4. Pouring the weighed powder intoAnd (3) simultaneously adding an ethanol solution into the ball milling tank to submerge the powder, and then carrying out wet ball milling for 6 hours at the rotating speed of 200 revolutions per minute. Drying at 120 ℃ to obtain SrTi _0.6 Co _0.4 O _3-δ (STC, strontium titanium cobalt) precursor powder. -500 nm of strontium carbonate particle size 300-500 nm, titanium dioxide particle size 20-30 nm, three-cobalt oxide particle size 50-200 nm, cobalt oxide particle size 50-200 nm.

(2) Mixing STC precursor powder, 40-micron SiC particles and activated carbon powder according to the mass ratio of 1:7.5:1.5 weighing the powder with the corresponding mass, then placing the powder into a mixing tank, and mixing for 4 hours at 200 revolutions per minute.

(3) Screening the mixed powder by using a stainless steel screen mesh to obtain mixed powder with uniform particle size;

(4) According to the mass ratio of the PVA solution to the mixed powder of 1:9, 6wt.% of PVA solution is weighed, then the PVA solution is dripped into the mixed powder for mixing and stirring, a cold isostatic press is adopted for maintaining the pressure for 15s at 8MPa to form the mixed powder, then the formed mixed powder is placed at 500 ℃ for heat preservation for 2h, and then the heat preservation is carried out for 2h at 1070 ℃ to obtain the SiC membrane material.

(5) Preparing 1mol/L nitric acid solution, then placing the SiC membrane material in the nitric acid solution for dipping for 1h, taking out the SiC membrane material and drying at 100 ℃ for 12h to obtain the SiC membrane material with enhanced catalytic performance.

Fig. 1 is an SEM image of the SiC film material after acid etching. It can be seen that micron-sized STC catalyst was formed on the SiC particles after the primary sintering. After etching by acid solution, lots of Co is generated on the surface of the STC catalyst ₃ O ₄ And TiO ₂ And (3) nanoparticles. The acid etched SiC film material had an NO oxidation efficiency of 65% (fig. 2) and a dust rejection of 100% (fig. 3) in a synergistic dust and nitrogen oxide removal test.

Example 2

(1) The powder with the corresponding mass is weighed according to the mol ratio of the strontium carbonate, the titanium dioxide and the cobaltosic oxide of 1: 0.6: 0.4. And pouring the weighed powder into a ball milling tank, adding deionized water to submerge the powder, and performing wet ball milling for 4 hours at the rotating speed of 300 revolutions per minute. Drying at 80 ℃ to obtain STC precursor powder. Strontium carbonate particle size 300-500 nm, titanium dioxide particle size 20-30 nm, tricobalt-oxide particle size 50-200 nm, cobaltic-oxide particle size 50-200 nm.

(2) Mixing STC precursor powder, 40-micron SiC particles and activated carbon powder according to the mass ratio of 1:9:2.5 weighing the powder with the corresponding mass, then placing the powder into a mixing tank, and mixing for 2 hours at 300 revolutions per minute.

(4) According to the mass ratio of the PVA solution to the mixed powder of 1:11.5, 6wt.% of PVA solution is weighed, then the PVA solution is dripped into the mixed powder for mixing and stirring, a cold isostatic press is adopted for keeping the pressure for 10s under 10MPa to form the mixed powder, then the formed mixed powder is placed at 500 ℃ for heat preservation for 4h, and then the heat preservation is carried out for 4h at 1070 ℃ to obtain the SiC membrane material.

(5) Preparing 1mol/L phosphoric acid solution, then placing the SiC membrane material in the phosphoric acid solution for dipping for 2h, taking out the SiC membrane material and drying at 120 ℃ for 8h to obtain the SiC membrane material with enhanced catalytic performance.

Fig. 4 is an XRD pattern of the SiC film material before and after the acid etching. It can be seen that the peak of the SiC film material before and after the acid etching hardly changed, indicating that the material structure of the SiC film material did not change. The TEM chart of FIG. 5 shows that acid etching promotes in-situ generation of Co in SiC film material ₃ O ₄ And TiO ₂ And (3) nanoparticles. However, no Co is observed in the XRD pattern ₃ O ₄ And TiO ₂ The characteristic peak associated with the nanoparticles may be due to the fact that the lower amount of nanoparticles generated results in lower peak intensity and thus mainly appears as a characteristic peak of SiC.

Example 3

(1) Weighing corresponding mass of powder according to the mol ratio of strontium carbonate, titanium dioxide and cobaltosic oxide of 0: 1. And pouring the weighed powder into a ball milling tank, simultaneously adding an ethanol solution to submerge the powder, and performing wet ball milling for 5 hours at the rotating speed of 250 revolutions per minute. Drying at 100 ℃ to obtain the catalytic active powder.

(2) Mixing catalytic active powder with 200 mu m SiC particles and active carbon powder according to the mass ratio of 1:19:5 weighing the powder with the corresponding mass, then placing the powder into a mixing tank, and mixing for 3 hours at 250 revolutions per minute.

(4) According to the mass ratio of the PVA solution to the mixed powder of 1:19, weighing 8wt.% of PVA solution, then dropwise adding the PVA solution into the mixed powder, mixing and stirring, keeping the pressure for 15s at 8MPa by using a cold isostatic press to form the mixed powder, then placing the formed mixed powder at 500 ℃ for heat preservation for 3h, and then preserving the heat at 1350 ℃ for 3h and calcining to obtain the SiC membrane material.

(5) Preparing 1mol/L hydrochloric acid solution, then placing the SiC membrane material in the hydrochloric acid solution for soaking for 1h, taking out the SiC membrane material, and drying at 100 ℃ for 10h to obtain the SiC membrane material with enhanced catalytic performance.

Fig. 6 is an SEM image of the SiC film material after acid etching. It can be seen that the neck bonding of the SiC film material remains after acid etching, while corrosion of the particle surface occurs. This result indicates that the acid solution is only applied to the bulk Co on the surface of the SiC particles ₃ O ₄ Etching and etching it into Co with small grain size ₃ O ₄ Thereby improving the catalytic performance of the membrane material.

Example 4

(1) Weighing the powder with corresponding mass according to the molar ratio of the strontium carbonate, the titanium dioxide and the cobaltous oxide of 0: 1. And pouring the weighed powder into a ball milling tank, adding deionized water to submerge the powder, and performing wet ball milling for 4 hours at the rotating speed of 200 revolutions per minute. Drying at 120 ℃ to obtain the catalytic activity powder.

(2) Mixing catalytic active powder with 40 mu m SiC particles and active carbon powder according to the mass ratio of 1:9:2.5 weighing the powder with the corresponding mass, then placing the powder into a mixing tank, and mixing for 4 hours at 300 revolutions per minute.

(4) According to the mass ratio of the PVA solution to the mixed powder of 1:15.7 and 8wt.% of PVA solution is weighed, then the PVA solution is dripped into the mixed powder to be mixed and stirred, a cold isostatic press is adopted to maintain the pressure for 10s under 10MPa to form the mixed powder, then the formed mixed powder is placed at 500 ℃ for heat preservation for 4h, and then the heat preservation is carried out at 1350 ℃ for 4h to calcine, thus obtaining the SiC membrane material.

(5) Preparing 2mol/L acetic acid solution, then placing the SiC membrane material in the acetic acid solution for soaking for 2h, taking out the SiC membrane material, and drying at 120 ℃ for 12h to obtain the SiC membrane material with enhanced catalytic performance.

Fig. 7 and 8 are respectively a NO oxidation performance graph and a dust entrapment performance graph of the SiC film material after acid etching. It can be seen that the SiC film material after acid etching has an NO oxidation rate of 83% and a dust entrapment efficiency of 100%. Compared with the SiC membrane material before acid etching, the catalytic performance of the SiC membrane material is obviously improved, and the method for effectively improving the catalytic performance of the SiC membrane material by acid etching is verified.

Example 5

(1) Weighing the powder with corresponding mass according to the molar ratio of the strontium carbonate, the titanium dioxide and the cobaltous oxide of 0: 1. And pouring the weighed powder into a ball milling tank, adding an ethanol solution to the powder, and performing wet ball milling for 4 hours at the rotating speed of 200 revolutions per minute. Drying at 120 ℃ to obtain the catalytic activity powder.

(2) Mixing the catalytic activity powder with 40 mu m SiC particles and active carbon powder according to the mass ratio of 1:9:2.5 weighing the powder with the corresponding mass, then placing the powder into a mixing tank, and mixing for 4 hours at 300 revolutions per minute.

(5) Preparing 1mol/L sulfuric acid solution, then placing the SiC membrane material in the sulfuric acid solution for soaking for 2h, taking out the SiC membrane material, and drying at 120 ℃ for 12h to obtain the SiC membrane material with enhanced catalytic performance.

FIG. 9 is a diagram of NO reduction performance of SiC membrane material after sulfuric acid etching. Because the sulfuric acid contains sulfate radicals, the surface of the SiC membrane material can be deposited with sulfate radicals after the sulfuric acid is etched, so that the redox performance of the SiC membrane material is reduced. But the sulfate can improve the acid sites and the acid content of the SiC membrane material. Therefore, the SiC film material after sulfuric acid etching has a NO reduction rate of 78%.

Claims

1. A method for enhancing the catalytic performance of a silicon carbide film material by acid etching is characterized by comprising the following preparation steps:

weighing catalytic active components with certain particle sizes according to a certain proportion, placing the catalytic active components into a ball milling tank, adding a solvent at a certain rotating speed, performing wet ball milling for a certain time, and drying to obtain mixed catalytic active powder;

mixing catalytic active powder, siC aggregate with certain particle size and active carbon powder in certain proportion at certain rotation speed for certain time;

screening the mixed powder by using a stainless steel screen to obtain mixed powder with uniform particle size;

mixing and stirring the mixed powder and a binder according to a certain proportion, carrying out cold isostatic pressing, and then calcining at a certain temperature to obtain a SiC membrane material;

preparing an acid solution according to a certain molar ratio, then placing the prepared SiC membrane material in the acid solution for soaking for a certain time, taking out the soaked SiC membrane material and drying at a certain temperature to obtain the SiC membrane material with enhanced catalytic performance.

2. A method according to claim 1 wherein the catalytically active component and the particle size of step (1) are respectively strontium carbonate particle size 300-500 nm, titanium dioxide particle size 20-30 nm, three-cobalt-oxide particle size 50-200 nm, two-cobalt-oxide particle size 50-200 nm, respectively; the selected proportion is strontium carbonate: titanium dioxide: cobaltosic oxide or cobaltosic oxide in molar ratio = (0-1): (0-0.6): (0.4-1); the solvent is deionized water or absolute ethyl alcohol; the speed of rotation of the ball mill used is 200-300 rpm, the ball milling time is 4-6 h, and the drying temperature is 80-120 ℃.

3. The method as claimed in claim 1, wherein the SiC powder used in step (2) has a particle size of 40-200 μm, and the carbon powder has an average particle size of 20 μm; the mass ratio of the catalytic active powder is as follows: siC aggregate: the mass ratio of the activated carbon powder =1: (7.5-19): (1.5-5); the speed of rotation set by the ball mill is 200-300 rpm, the mixing time is 2-4 h.

4. A method according to claim 1 wherein the binder used in step (4) is a 6-8% by mass PVA solution, the mass ratio of binder to SiC powder being 1 (9-19); the pressure of the cold isostatic pressure is 8-10 MPa, the dwell time is 10-15 s; the calcination temperature is 500 ℃ hold 2-4 h, continuing to 1070-1350 ℃ hold 2-4 h.

5. The method for acid etching to enhance the catalytic performance of silicon carbide film material as claimed in claim 1, wherein the acid solution in step (5) is any one of acetic acid, hydrochloric acid, sulfuric acid, phosphoric acid or nitric acid; the concentration of acid solution is 1-2 mol/L, the immersion time is 1-2 h, the drying temperature is 100-120 c, and the drying time is 8-12 h.