CN112076777A - For CO2Reduced photocatalyst and preparation method thereof - Google Patents
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Images
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/24—Nitrogen compounds
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
- B01D53/86—Catalytic processes
- B01D53/8671—Removing components of defined structure not provided for in B01D53/8603 - B01D53/8668
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/20—Carbon compounds
- B01J27/22—Carbides
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- B01J35/39—
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- B01J35/61—
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/40—Carbon monoxide
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2257/00—Components to be removed
- B01D2257/50—Carbon oxides
- B01D2257/504—Carbon dioxide
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
- Y02C20/00—Capture or disposal of greenhouse gases
- Y02C20/20—Capture or disposal of greenhouse gases of methane
Abstract
The invention relates to a method for preparing CO2The invention relates to a reduced photocatalyst and a preparation method thereof, and the photocatalyst is prepared from g-C3N4The composite material is prepared by high-temperature calcination and partial oxidation after being compounded with transition metal carbide, has Z-type carrier transmission characteristics, reduces the hole electron recombination rate of the formed Z-type heterojunction, and separates the oxidation reaction and the reduction reaction on the catalyst, thereby improving the photocatalytic CO2Reduction efficiency and stability. The catalysisThe photo-thermal effect caused by the large specific surface area and the strong light absorption strength of the agent enables the photocatalytic activity to be improved, and products such as CO are easy to desorb on the surface of the agent, thereby being beneficial to the reutilization of active sites and enhancing the stability of the photocatalyst. The catalyst of the invention is used for photocatalysis of CO2The method has the advantages of good application prospect in the reduction field, cheap raw materials, simple preparation method and operation, and suitability for large-scale production.
Description
Technical Field
The invention belongs to photocatalytic CO2The field of utilization, in particular to a method for preparing CO2Reduced photocatalysts and methods of making the same.
Technical Field
CO2Capture and utilization are always the hot topics of human research. CO 22Is the root of the global greenhouse effect, and can be used as a C source to be used as a raw material for various energy reactions, thereby being resistant to CO2The fuel material with high potential energy is prepared by carrying out collection and resource utilization, and has quite high research value.
At present, CO2The trapping mainly comprises three technical schemes, namely pre-combustion trapping, oxygen-enriched combustion and post-combustion trapping, and the three methods are mature at present and CO is generated in the global range2Capturing items and capturing capabilities are growing rapidly. However, CO2The capturing technical scheme generally has the defects of higher cost, larger influence of local policy on profit and income and the like, and the captured CO is2The degree of utilization of (a) also becomes a necessary consideration for the entire capture project. At present, large scale CO2The sealing in the ground is still the main treatment method, but the method has the existence of CO2Secondary leakage and damage to geological structures. In contrast, although CO2The resource utilization technology is still in the laboratory stage, but has great research value.
CO2Structurally stable, typically by catalytic hydrogenation, to higher energy species, e.g. CO2And H2、H2O or CH4And the like, to produce hydrocarbons, alcohols, dimethyl ether, carboxylic acids, and the like. The reaction catalysis mode is also divided into a plurality of modes, including thermal catalysis, electrocatalysis, photocatalysis and the like, wherein the photocatalysis mode has the advantages of environmental protection, low reaction energy consumption, mild conditions and the like, and is favored by researchers. Photocatalyst catalysis of CO2The reduction activity is high or low, and is related to many factors, such as the type and number of active sites on the surface of the catalyst, the adsorption capacity of the catalyst on reaction substances, the electron hole transfer rate of the catalyst, and the like.
Aiming at the key points capable of improving the catalytic activity of the photocatalyst, transition metal carbide and g-C are combined through reasonable modification design3N4Carrying out composite modification and further calcining to prepare the photocatalyst. The catalyst is applied to photocatalysis of CO at room temperature2And CH4The reaction shows higher catalytic activity and stability, and the yield of CO after four hours of the reaction is bulk g-C3N4More than 4 times, researches show that the transfer type of the photo-generated carriers on the catalyst is Z-type electron transport, which not only improves the transport rate of photo-generated electron holes and prolongs the service life of the photo-generated electron holes, but also enables the electron holes with high reactivity to be reserved. In addition, the catalyst has higher light absorption intensity, and due to the photo-thermal effect, when the catalyst is irradiated by light, the temperature of the catalytic surface of the catalyst is increased, so that reactants on the surface of the catalyst are easier to activate, and the products are easier to desorb.
Disclosure of Invention
The technical problem solved by the invention is to provide a catalyst for CO by a designed catalyst preparation scheme2Reduced photocatalysts and methods of making the same. In terms of catalytic activity, the composite catalyst has Z-type carrier transmission characteristics, the transmission rate and the service life of a photon-generated electron hole are improved, and most of electron holes with high reaction activity are reserved; in addition, the catalyst has stronger light absorption intensity and larger specific surface area. The optical performance and the physical and chemical performance are combined, so that the catalyst has higher photocatalytic activity and stability. In the aspect of catalyst preparation, the preparation method is cheap, simple to operate and suitable for large-scale production.
The technical scheme adopted by the invention is as follows:
for CO2A reduced photocatalyst and a method of making the same, the photocatalyst characterized by:
(1) from transition metal oxides, transition metal carbides, g-C3N4And (4) forming.
(2) The material has Z-type carrier transmission characteristics, higher electron hole transmission rate and reactivity, stronger light absorption intensity and larger specific surface area.
The preparation method comprises the step of mixing the transition metal carbide with g-C by using a wet chemical method3N4The method is characterized by comprising the following steps of:
(1) g to C3N4Dispersing the powder into a mixed solution of absolute ethyl alcohol and deionized water, adding the transition metal carbide into the mixed solution, carrying out ultrasonic and stirring treatment to obtain a mixed solution, and evaporating the mixed solution under the stirring condition to obtain a catalyst precursor.
(2) And grinding the catalyst precursor into powder, placing the powder into a reaction furnace for high-temperature calcination, and simultaneously keeping the oxygen atmosphere state in the reaction furnace to finally obtain the photocatalyst.
In the photocatalyst, the transition metal of the transition metal carbide in the characteristic (1) may be a metal such as Ti, Zr, Ta, V, Hf, Nb, Cr, Sc, or the like.
The photocatalyst is characterized in that in the step (1), the transition metal oxide is prepared by oxidizing transition metal carbide under the high-temperature calcination condition, and the oxidation degree of the transition metal carbide can be adjusted by controlling the calcination temperature and time.
In the preparation method, in the step (1), the volume ratio of the absolute ethyl alcohol to the deionized water is 0-4.
The preparation method comprises the step (1) of mixing the transition metal carbide and g-C3N4The mass and dosage ratio of (1): 5-1: 20.
in the preparation method, in the step (1), the total time of the ultrasonic treatment and the stirring is 0.5-2 hours, and the stirring speed is 500-1200 r/min.
In the preparation method, in the step (2), the calcining temperature is 300-600 ℃, and the calcining time is 2-5 hours.
In the preparation method, in the step (2), oxygen or air is introduced into the oxygen atmosphere, and the volume concentration of the oxygen is 0-100%.
The reducing agent used in the reduction reaction can be methane, water and hydrogen.
Use of the photocatalyst, CO2And the volume ratio of the reducing agent is 1-10.
The invention has the following characteristics:
by reacting a transition metal carbide with g-C3N4And compounding and further calcining to prepare the photocatalyst. The catalyst has Z-type carrier transmission characteristic, strong light absorption intensity and large specific surface area. The preparation method of the catalyst is cheap, simple to operate and suitable for large-scale production.
The catalyst is applied to the photocatalytic reaction, and has the following advantages:
(1) because the catalyst has Z-type carrier transmission characteristics, the transmission rate of photogenerated electron holes is improved, the service life of the photogenerated electron holes is prolonged, and the electron holes with high reactivity are reserved, so that the photocatalytic activity of the photogenerated electron holes is improved.
(2) The catalyst has higher light absorption intensity, and has higher surface temperature under illumination due to photo-thermal effect, so that reactants on the surface of the catalyst are easy to activate, and products are easy to desorb, thereby improving the photocatalytic activity and stability.
Drawings
FIG. 1 shows 450- (25) TiC-TiO2/g-C3N4The preparation process is shown in the figure.
FIG. 2 shows 450- (25) TiC-TiO2/g-C3N4X-ray single crystal diffraction pattern (XRD).
FIG. 3 shows 450- (25) TiC-TiO2/g-C3N4And g-C3N4Ultraviolet-visible absorption spectrum (UV-vis), and a calculated forbidden band width map.
FIG. 4 shows 450- (25) TiC-TiO2/g-C3N4And 450- (20) TNPs/g-C3N4Graph of light absorption intensity versus experimental light source wavelength range.
FIG. 5 shows 450- (25) TiC-TiO2/g-C3N4And 450- (20) TNPs/g-C3N4The fluorescence spectrum of (a).
FIG. 6 shows 450- (25) TiC-TiO2/g-C3N4The "Z" heterojunction mechanism diagram of (1).
FIG. 7 is a view of a photocatalytic device.
Detailed description of the invention
The present invention will be further described with reference to the following examples.
Example 1: composite catalyst TiC-TiO2/g-C3N4The preparation method of (1). 0.25g g-C3N4Dispersing in a beaker filled with 30mL of deionized water, weighing 25mgTiC, putting into the mixed solution, performing ultrasonic treatment for 10min and stirring for 10min, wherein the stirring speed is 1000rad/min, transferring the mixed solution into a water bath kettle, and performing water bath evaporation at 80 ℃ and the rotating speed is 500 rad/min. After the solid is evaporated to dryness, taking out the residual solid, grinding the solid, then placing the ground solid in a muffle furnace for calcination, wherein the calcination temperature is 450 ℃, the heating rate is 5 ℃/min, and the calcination time is 3h, so that the TiC part is oxidized into TiO2The obtained sample is marked as 450- (25) TiC-TiO2/g-C3N4. FIG. 1 shows 450- (25) TiC-TiO2/g-C3N4The preparation process is shown in a brief diagram.
Comparative example 1: 8g of the uniformly ground melamine are placed in a crucible and placed in a tube furnace N2Calcining for 3h at 550 ℃ in the atmosphere, wherein the heating rate is 5 ℃/min. After calcination, the mixture was ground thoroughly to give a pale yellow powder, and the sample obtained was designated bulk g-C3N4。
Comparative example 2: the difference from example 1 is that in the preparation of the catalyst, the reaction is carried out in the direction of g-C3N420mg of TiO was added to the mixture2The nanoparticles (5-7 nm) were calcined in a muffle furnace for 2h, and the obtained sample was recorded as 450- (20) TNPs/g-C3N4。
Example 2: the preparation method is the same as that of example 1, and the difference is that during the preparation of the catalyst, the catalyst is directly added to g-C3N4Adding 10mg TiC and15mg TiO2nanoparticles (5-7 nm) in a tube furnace N2Calcining for 3h at 550 ℃ in the atmosphere, wherein the heating rate is 5 ℃/min, TiC is not oxidized, and the obtained sample is recorded as 450-TiC/TiO2/g-C3N4。
Example 3: the preparation method is the same as that of example 1, and the difference is that in the preparation process of the catalyst, the calcination temperature in a muffle furnace is 400 ℃, and the obtained sample is marked as 400- (25) TiC-TiO2/g-C3N4。
Example 4: and testing the optical characteristics of the photocatalyst. As can be seen from FIG. 2, after the final calcination process, 450- (25) TiC-TiO2/g-C3N4Most of TiC is converted into TiO2But still a small portion of TiC is not converted. As can be seen from FIG. 3, 450- (25) TiC-TiO2/g-C3N4Has certain response to visible light and is calculated to obtain 450- (25) TiC-TiO2/g-C3N4Has a forbidden band width of 2.66eV relative to g-C3N4The forbidden band width is narrowed. As can be seen from FIG. 4, 450- (25) TiC-TiO2/g-C3N4And 450- (20) TNPs/g-C3N4The former has higher light absorption intensity under the irradiation of experimental light source (wavelength range of 320-780 nm). FIG. 5 is a fluorescence spectrum clearly showing 450- (25) TiC-TiO2/g-C3N4The electron transfer rate of (A) is higher than that of (A) 450- (20) TNPs/g-C3N4Fast, this is benefited from in 450- (25) TiC-TiO2/g-C3N4In the figure, TiC with good conductivity acts as a bridge to accelerate the transfer of photo-generated electron holes and form a Z-type heterojunction electron transport mechanism, and the specific transport mechanism can be seen in figure 6.
Example 5: photocatalytic activity comparative experiment. Photocatalytic CO2And CH4The reaction apparatus is shown in figure 7, and the reaction is carried out at room temperature. 50mg of photocatalyst is put into a reactor, the reactor is vacuumized after being filled and sealed, and CO is distributed through three paths of gas distribution2And CH4Charging raw material gas with a ratio of 2:1 into a reactor, and vacuumizing the reactor when the raw material gas is charged to a certain pressureThe treatment was carried out so as to purge the interior of the reactor, then 15kPa gas was introduced into the reactor, and then the circulation pump was turned on to circulate the gas in the reactor for 30 min. And then, turning on a light source to react, and sampling and detecting the gas in the reactor every 30min in the reaction process, wherein the total reaction time is 4 h. Wherein the light source of the simulated sunlight is a 300W xenon lamp (320nm-780 nm). During the reaction, CO is the main product, and the reaction results are shown in Table 1.
TABLE 1 comparison of catalytic effects of comparative and examples
Example 6: and testing the stability of the photocatalyst. The experimental method is the same as the comparative experiment of the photocatalytic activity, and the difference is that for 450- (20) TNPs/g-C3N4Catalyst, optimized CO2And CH4The ratio was 2:1 and the optimized reaction pressure was 30 kPa. For 450- (25) TiC-TiO2/g-C3N4Catalyst, CO2And CH4The ratio was 1:1, the reaction pressure was 40kPa, the total reaction time was 12 hours, and the results of comparison of the photocatalytic stability are shown in Table 2.
TABLE 2 comparison of photocatalytic stability results
As is clear from Table 1, 450- (25) TiC-TiO2/g-C3N4Catalyst CO production is bulk g-C3N43.3 times of the catalyst, because of 450- (25) TiC-TiO2/g-C3N4In the process of calcining the catalyst, the TiC surface is oxidized into TiO2So that the types and the number of the reaction sites on the surface of the catalyst are more than those of bulk g-C3N4. In addition, the former catalyst forms a stable heterojunction, which accelerates the mobility rate of photogenerated carriers, increases the survival time of their photogenerated carriers, and thus improves the catalytic activity.
From the aspect of catalyst structure, 450- (25) TiC-TiO2/g-C3N4And 450- (20) TNPs/g-C3N4Can be regarded as TiO2And g-C3N4So that their catalytic sites do not differ much. However, the former CO yield was 450- (20) TNPs/g-C3N4The catalyst is 1.7 times (Table 1), the catalytic activity and the stability of the catalyst are higher than those of the catalyst of2/g-C3N4The transmission rate of the photogenerated electron and the hole is higher than 450- (20) TNPs/g-C3N4The "Z" heterojunction electron transport mechanism, which increases the transport rate of photogenerated electron holes, prolongs their lifetime, and retains highly reactive electron holes. In addition, the results of ultraviolet-visible absorption spectroscopy (UV-vis) show that, in the wavelength range of laboratory simulated light source, 450- (25) TiC-TiO2/g-C3N4The absorption intensity of the light is higher than 450- (20) TNPs/g-C3N4A catalyst, which has a higher surface temperature under light irradiation, so that reactants on the surface of the catalyst are easily activated and products are easily desorbed, thereby catalyzing CO2For reduction, the catalyst may be CO2Provides more effective reaction sites and can timely desorb the generated products: CO and H2And the like. Therefore, the key points of higher photocatalytic activity and stability are provided.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The invention relates to a method for preparing CO2A reduced photocatalyst and a method of making the same, the photocatalyst characterized by:
(1) the photocatalyst consists of transition metal oxide and transition metal oxideCarbide of transition metal, g-C3N4And (4) forming.
(2) Electrons on the conduction band of the transition metal oxide and g-C3N4Holes in the valence band are recombined on the transition metal carbide, so that the Z-type heterojunction formed by the catalyst has Z-type carrier transmission characteristics.
The preparation method comprises the step of mixing the transition metal carbide with g-C by using a wet chemical method3N4The method is characterized by comprising the following steps of:
(1) g to C3N4Dispersing the powder into a mixed solution of absolute ethyl alcohol and deionized water, adding the transition metal carbide into the mixed solution, carrying out ultrasonic and stirring treatment to obtain a mixed solution, and evaporating the mixed solution under the stirring condition to obtain a catalyst precursor.
(2) And grinding the catalyst precursor into powder, placing the powder into a reaction furnace for high-temperature calcination, and simultaneously keeping the oxygen atmosphere state in the reaction furnace to finally obtain the photocatalyst.
2. The photocatalyst as claimed in claim 1, wherein the transition metal of the transition metal carbide in the feature (1) is a metal selected from the group consisting of Ti, Zr, Ta, V, Hf, Nb, Cr, Sc, and the like.
3. The photocatalyst as claimed in claim 1, wherein the transition metal oxide in the feature (1) is prepared by oxidizing a transition metal carbide under high-temperature calcination conditions, and the degree of oxidation of the transition metal carbide can be adjusted by controlling the calcination temperature and time.
4. The method according to claim 1, wherein in the step (1), the volume ratio of the absolute ethyl alcohol to the deionized water is 0 to 4.
5. The method according to claim 1, wherein in the step (1), the peroxide is usedCarbide of transition metal and g-C3N4The mass and dosage ratio of (1): 5-1: 20.
6. the method according to claim 1, wherein in the step (1), the total time of the ultrasonic treatment and the stirring is 0.5 to 2 hours, and the stirring rate is 500 to 1200 rpm.
7. The method according to claim 1, wherein in the step (2), the calcination temperature is 300 to 600 ℃ and the calcination time is 2 to 5 hours.
8. The method according to claim 1, wherein in the step (2), the oxygen atmosphere is introduced with oxygen or air, and the volume concentration of oxygen is 0 to 100%.
9. The use of the photocatalyst of claim 1, wherein the reducing agent used in the reduction reaction is selected from the group consisting of methane, water, and hydrogen.
10. Use of a photocatalyst as claimed in claim 1, wherein said CO is2And the volume ratio of the reducing agent is 1-10.
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