CN118719057A - A photocatalyst having a double metal atom site and its preparation method and application - Google Patents

Abstract

The invention relates to a photocatalyst with a bimetallic atom site, and a preparation method and application thereof. The photocatalyst having a bimetallic atom site includes: a CeO ₂ carrier, a bimetal atom supported on the CeO ₂ carrier; the bimetal atoms comprise a first metal atom selected from Au, ag and Pt and a second metal atom selected from Ag, in and Pd, and the first metal atom and the second metal atom are different.

Description

A photocatalyst having a double metal atom site and its preparation method and application

Technical Field

The present invention belongs to the technical field of photocatalysts, and in particular relates to a photocatalyst with double metal atom sites, a preparation method and an application thereof.

Background Art

Driven by solar energy, photocatalytic technology can convert CO ₂ into high-value-added carbon-containing fuels such as CO, HCOOH, CH ₄ and C ₂ H _6. Photocatalytic technology is expected to alleviate the depletion crisis faced by traditional fossil fuels, and at the same time mitigate environmental deterioration problems such as global warming and sea level rise caused by greenhouse gases. Therefore, photocatalytic CO ₂ reduction is of great significance. The conversion of CO ₂ to CH ₄ involves 8 electrons and 8 protons participating in the reaction, which is not conducive to the production of CH ₄ kinetically. Therefore, the production of highly selective CH ₄ in the process of photocatalytic CO ₂ reduction still faces great difficulties.

In order to improve the selectivity of _CH4 , there are currently two main solutions: 1. Starting from the reaction path. Generally, during the photocatalytic _CO2 reduction process, after the _CO2 molecule is adsorbed on the active site, it will undergo the transformation process of _CO2 →COOH→CO→CHO→ _CH2O → _CH3O → _CH4 . CO is an important intermediate in the production of _CH4 . If the site does not have a strong adsorption effect on it, it will desorb to form CO; if the site has a strong adsorption effect on it, but there are not enough protons and electrons to participate in the reaction, the transformation process of CO→CHO→ _CH2O → _CH3O → _CH4 will not occur, and _CH4 cannot be produced. Therefore, the production of _CH4 requires strong adsorption of CO and sufficient supply of protons and electrons. 2. Starting from _CO2 adsorption. The adsorption of _CO2 molecules by the active site of the catalyst is the first step of the reaction. In single-site catalysts, CO ₂ molecules are weakly connected to the active sites, which makes the intermediates (such as CO, CHO, CH ₂ O, and CH ₃ O) in the photocatalytic reaction process easily desorbed from the catalyst surface, making it difficult to form CH ₄ .

Summary of the invention

In view of the above problems, the object of the present invention is to provide a photocatalyst having dual metal atom sites and a preparation method and application thereof.

In the first aspect, the present invention provides a photocatalyst having a dual metal atom site, comprising: a _CeO2 carrier, and dual metal atoms loaded on the _CeO2 carrier; the dual metal atoms comprise a first metal atom selected from Au, Ag, and Pt and a second metal atom selected from Ag, In, and Pd, and the first metal atom and the second metal atom are different.

Preferably, the CeO ₂ carrier is a cubic fluorite structure crystal; the size of the CeO ₂ carrier is 50 to 200 nm.

Preferably, the mass of the bimetallic atoms is controlled to be 0.5-5wt% of the mass of the _CeO2 carrier, and the molar ratio of the first metal atom to the second metal atom is 1:(0.25-4).

In a second aspect, the present invention provides a method for preparing the above-mentioned photocatalyst having dual metal atomic sites, comprising: dispersing _CeO2 powder in water and adding an alkaline solution and stirring, then adding a precursor solution of a first metal atom and a precursor solution of a second metal atom, followed by aging, filtering, drying, grinding, and heat treatment under a reducing atmosphere to obtain the photocatalyst having dual metal atomic sites.

Preferably, the usage ratio of _CeO2 powder to water is 1g: (10-100)mL.

Preferably, the alkaline solution is selected from sodium hydroxide, (NH ₄ ) ₂ CO ₃ , NH ₄ HCO ₃ or ammonia solution, the concentration of the alkaline solution is 0.5-2M, and the usage ratio of the CeO ₂ powder to the alkaline solution is 1g: (10-100)mL.

Preferably, the precursor solution of the first metal atom is selected from chloroauric acid, silver nitrate or chloroplatinic acid solution, with a concentration of 0.06-30 mg/mL, and the amount added is 0.02-2 mL; the precursor solution of the second metal atom is selected from silver nitrate, indium nitrate or sodium chloropalladate, with a concentration of 0.06-30 mg/mL, and the amount added is 0.02-2 mL, preferably 0.03-1 mL.

Preferably, the aging time is 0.5 to 10 hours, preferably 0.5 to 6 hours, and the temperature is 10 to 30° C.; the heat treatment temperature is 200 to 500° C., and the heat treatment time is 1 to 8 hours.

Preferably, the reducing gas is a mixed gas of high-purity H ₂ /Ar, wherein the volume fraction of H ₂ is 5-15 vol.%, and the purity of H ₂ and Ar is ≥99.9%.

In a third aspect, the present invention provides an application of the above-mentioned photocatalyst having bimetallic atom sites in solar fuel catalysis.

Beneficial Effects

1) The present invention adopts a simple deposition and precipitation thermal reduction method to prepare a nearly 100% CH ₄ highly selective CO ₂ reduction bimetallic site photocatalyst, and the preparation method is simple and easy;

2) The bimetallic site catalyst prepared by the present invention has excellent performance and has excellent photocatalytic _CO2 reduction performance under the condition that the total metal atom ratio is 0.5-5wt.%;

3) The bimetallic site catalyst prepared by the present invention has good stability and no obvious performance degradation after three cycles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an XRD spectrum of CeO _{2 and} photocatalyst samples prepared by examples and used in the examples and comparative examples and prepared by examples 1-4 and comparative examples 1-2;

FIG2 is a spherical aberration corrected HAADF-STEM image of the photocatalyst prepared in Example 1;

FIG3 is a photocurrent test characterization diagram of CeO ₂ carrier and photocatalyst sample prepared in Example 1;

FIG4 is an in-situ infrared spectrum of the CeO ₂ carrier and the photocatalyst sample prepared in Example 1;

FIG5 is a performance test diagram of the photocatalytic _CO2 reduction of _CeO2 carriers and the photocatalysts prepared in Examples 1-4 and Comparative Examples 1-2;

FIG6 is a performance cycle test diagram of the photocatalyst sample prepared in Example 1.

DETAILED DESCRIPTION

The present invention is further described below by way of embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, but not to limit the present invention.

The present invention provides a photocatalyst with a double metal atom site, the photocatalyst comprising: a _CeO2 carrier, and double metal atoms loaded on the _CeO2 carrier; the double metal atoms comprising a first metal atom selected from Au, Ag, and Pt and a second metal atom selected from Ag, In, and Pd, the first metal atom and the second metal atom are different.

_CeO2 is an oxygen ion conductor with easy generation of oxygen vacancies, making it a good candidate carrier material. The selection of the first metal is mainly based on its good conductivity and better adsorption of CO. The selection of the second metal is mainly based on its adsorption effect on protons.

In some embodiments, the _CeO2 carrier may be a cubic fluorite structure crystal.

The size of the _CeO2 carrier can be 50-200 nm. If the size is too large, the catalytic performance will be reduced; if the size is too small, it will cause serious agglomeration, thereby reducing the dispersion of the bimetal on the carrier.

In some embodiments, the mass of the dimetallic atoms can be controlled to be 0.5-5wt% of the mass of the CeO ₂ carrier. If the mass content of the dimetallic atoms is too high, the catalyst will be easily granulated, resulting in reduced catalytic performance; if the content is too low, the distance between the dimetallic atoms will be too far, resulting in failure to catalyze the generation of CH ₄ .

In some embodiments, the molar ratio of the first metal atom to the second metal atom can be controlled to be 1:(0.25-4). Controlling the molar ratio of the first and second metal atoms within an appropriate range can effectively enhance the synergistic catalytic effect of the two metal atoms. If one of the molar ratios is too large or too small, the selectivity of CH ₄ will be reduced, thereby producing more CO or H ₂ .

The photocatalyst with bimetallic atomic sites provided by the present invention anchors metal ions deposited on the surface of the nanocarrier _CeO2 through the electron-rich region generated around the oxygen vacancies, and bonds with O, has abundant active sites, and can effectively promote the improvement of catalytic activity. At the same time, the bimetallic sites have strong metal-carrier interactions in the catalyst, and the bimetallic sites are conducive to promoting carrier separation, photogenerated carrier generation, and photocurrent density generation.

The bimetallic site is tightly bonded to the C and O atoms in the CO ₂ molecule to form a strong CM ₁ -M ₂ -O bridge adsorption, thereby inhibiting the desorption of the intermediate product and efficiently promoting the generation of CH _4. The bimetallic atomic site photocatalyst provided by the present invention promotes the generation of *CH ₂ intermediates by adsorbing H* and CO* by two metals respectively, and synergistically achieves the generation of CH ₄ .

The present invention introduces bimetallic sites into the CeO ₂ carrier through a simple deposition and settling thermal reduction method, thereby achieving photocatalytic CO ₂ reduction with nearly 100% selectivity to produce CH ₄ .

The following is an exemplary description of a method for preparing a photocatalyst having dual metal atom sites provided by the present invention. The preparation method may include the following steps: dispersing _CeO2 powder in water and adding an alkaline solution and stirring; then, adding a precursor solution of a first metal atom and a precursor solution of a second metal atom; then, aging, filtering, drying, grinding, and heat treating in a reducing atmosphere to obtain the photocatalyst having dual metal atom sites.

In some embodiments, the preparation of the nano _CeO2 powder can adopt the following process: dissolving cerium nitrate hexahydrate (Ce( _NO3 ) ₃ · _6H2O ) in ethylene glycol, and controlling the molar ratio of the cerium nitrate hexahydrate to ethylene glycol to be 1:(0.5-5), preferably 1:3; then, performing a solvent thermal reaction at 100-200°C (such as 150°C) for 3-35h; washing and drying; and calcining at 80-400°C for 0.5-8h, preferably 2-4h, to obtain the nano _CeO2 powder.

As an example, the preparation of the nano CeO ₂ powder adopts the following process: dissolving 0.1 mol of cerium nitrate hexahydrate (Ce(NO ₃ ) ₃ ·6H ₂ O) in 10 ml of ethylene glycol; then, performing a solvent thermal reaction at 150° C. for 24 hours; washing with deionized water three times, drying at 60° C. for 12 hours; and calcining at 200° C. for 2 hours to obtain the nano CeO ₂ powder.

In some embodiments, the usage ratio of the CeO ₂ powder and water can be controlled to be 1 g: (10-100) mL.

The alkaline solution may be selected from sodium hydroxide, (NH ₄ ) ₂ CO ₃ , NH ₄ HCO ₃ or ammonia solution. The concentration of the alkaline solution may be 0.5-2M. The usage ratio of the CeO ₂ powder and the alkaline solution may be controlled to be 1 g: (10-100) mL.

The dosage relationship between the _CeO2 powder, water and alkaline solution will affect the actual effect of the final photocatalyst. If the powder dispersion concentration is too high, the diatoms cannot be evenly dispersed to achieve the expected effect; if the alkaline solution concentration is too high, it will lead to excessive oxygen vacancies on the _CeO2 surface, forming electron-hole recombination centers and reducing catalytic activity.

In some embodiments, the precursor solution of the first metal atom can be selected from chloroauric acid, silver nitrate or chloroplatinic acid solution, the concentration can be 0.06-30 mg/mL, and the added amount can be 0.02-2 mL; the precursor solution of the second metal atom can be selected from silver nitrate, indium nitrate or sodium chloropalladate, the concentration can be 0.06-30 mg/mL, and the added amount can be 0.02-2 mL, preferably 0.03-1 mL.

In some embodiments, the aging time may be 0.5 to 10 hours, preferably 0.5 to 6 hours, and the temperature may be 10 to 30° C. The aging can fully combine the bimetallic ions with the carrier without causing the migration and nucleation of metal atoms to form metal particles, thereby effectively controlling the size of the bimetallic atoms.

In some embodiments, the heat treatment temperature may be 200 to 500° C., and the heat treatment time may be 1 to 8 hours. Through the heat treatment, the metal atoms and the carrier can be bonded in the form of chemical bonds, and the connection is tight.

The reducing gas may be a mixed gas of high-purity H ₂ /Ar, wherein the volume fraction of H ₂ may be controlled to be 5-15 vol.%, and the purity of H ₂ and Ar may be ≥99.9%.

The photocatalyst with double metal atom sites obtained by the preparation method provided by the present invention can be applied in the field of solar fuel catalysis.

Example 1

Preparation of bimetallic atomic site photocatalyst Ag _0.6 In _0.4 /CeO ₂ .

0.2 g of CeO ₂ powder was put into 10 mL of deionized water and ultrasonicated for 30 min to completely disperse the CeO ₂ powder in the water; after the ultrasonic dispersion was completed, 10 mL of 0.5 M ammonium carbonate solution was added and stirred for 30 min to fully mix it; then, 0.15 mL of AgNO ₃ solution (5 mg/mL) and 0.2 mL of In(NO ₃ ) ₃ solution (10 mg/mL) were added dropwise at the same time; then, the mixture was aged for 8 hours under stirring; after AgNO ₃ and In(NO ₃ ) ₃ were fully in contact with CeO ₂ , the solid was collected by filtration, dried in an oven at 60°C for 8 hours, and ground into powder; the powder was heat treated at 200°C for 2 hours in a reducing atmosphere of high-purity H ₂ /Ar mixed gas (H ₂ : 5 vol.%) to obtain a bimetallic atomic site photocatalyst Ag _0.6 In _0.4 /CeO ₂ .

Example 2

Preparation of bimetallic atomic site photocatalyst Ag _0.4 In _0.6 /CeO ₂ .

0.2 g of CeO ₂ powder was put into 10 mL of deionized water and ultrasonicated for 30 min to completely disperse the CeO ₂ powder in the water; after the ultrasonic dispersion was completed, 10 mL of 0.5 M ammonium carbonate solution was added and stirred for 30 min to fully mix it; then, 0.1 mL of AgNO ₃ solution (10 mg/mL) and 0.3 mL of In(NO ₃ ) ₃ solution (10 mg/mL) were added dropwise at the same time; then, the mixture was aged for 8 hours under stirring; after AgNO ₃ and In(NO ₃ ) ₃ were fully in contact with CeO ₂ , the solid was collected by filtration, dried in an oven at 60°C for 8 hours, and ground into powder; the powder was heat treated at 250°C for 3 hours in a reducing atmosphere of high-purity H ₂ /Ar mixed gas (H ₂ : 10 vol.%) to obtain a bimetallic atomic site photocatalyst Ag _0.4 In _0.6 /CeO ₂ .

Example 3

Preparation of bimetallic atomic site photocatalyst Ag _0.2 In _0.8 /CeO ₂ .

0.2 g of CeO ₂ powder was put into 10 mL of deionized water and ultrasonicated for 30 min to completely disperse the CeO ₂ powder in the water; after the ultrasonic dispersion was completed, 10 mL of 1 M sodium hydroxide solution was added and stirred for 30 min to fully mix it; then, 0.05 mL of AgNO ₃ solution (10 mg/mL) and 0.4 mL of In(NO ₃ ) ₃ solution (10 mg/mL) were added dropwise at the same time; then, the mixture was aged for 10 hours under stirring; after AgNO ₃ and In(NO ₃ ) ₃ were fully in contact with CeO ₂ , the solid was collected by filtration, dried in an oven at 60°C for 6 hours, and ground into powder; the powder was heat treated at 280°C for 2 hours in a reducing atmosphere of high-purity H ₂ /Ar mixed gas (H ₂ : 15 vol.%) to obtain a bimetallic atomic site photocatalyst Ag _0.2 In _0.8 /CeO ₂ .

Example 4

Preparation of bimetallic atomic site photocatalyst Ag _0.8 In _0.2 /CeO ₂ .

0.2 g of CeO ₂ powder was placed in 10 mL of deionized water and ultrasonicated for 30 min to completely disperse the CeO ₂ powder in the water; after the ultrasonic dispersion was completed, 10 mL of 1 M sodium hydroxide solution was added and stirred for 30 min to fully mix it; then, 0.2 mL of AgNO ₃ solution (8 mg/mL) and 0.1 mL of In(NO ₃ ) ₃ solution (10 mg/mL) were added dropwise at the same time; then, the mixture was aged for 4 hours under stirring; after AgNO ₃ and In(NO ₃ ) ₃ were fully in contact with CeO ₂ , the solid was collected by filtration, dried in an oven at 60°C for 10 hours, and ground into powder; the powder was heat treated at 200°C for 2.5 hours in a reducing atmosphere of high-purity H ₂ /Ar mixed gas (H ₂ : 5 vol.%) to obtain the metal atom site photocatalyst Ag _0.8 In _0.2 /CeO ₂ .

Comparative Example 1

Preparation of single metal atom site photocatalyst Ag/CeO ₂ .

The preparation method is similar to that of Example 1, with the main difference being that only the precursor AgNO ₃ solution of the first metal atom is added to obtain a single metal atom site photocatalyst Ag/CeO ₂ .

Comparative Example 2

Preparation of single metal atom site photocatalyst In/CeO ₂ .

The preparation method is similar to that of Example 1, with the main difference being that only the precursor In(NO ₃ ) ₃ solution of the second metal atom is added to obtain a single metal atom site photocatalyst In/CeO ₂ .

Figure 1 shows the XRD spectra of _CeO2 prepared and used in the examples and comparative examples and the photocatalyst samples prepared in Examples 1-4 and Comparative Examples 1-2. It can be seen from the figure that the _CeO2 carriers are all cubic fluorite structure phases.

Figure 2 is a spherical aberration corrected HAADF-STEM image of the photocatalyst prepared in Example 1. It can be seen from the figure that the bimetallic sites are evenly distributed in the carrier _CeO2 , indicating that the bimetallic site catalyst was successfully prepared.

Figure 3 is a photocurrent test characterization diagram of _CeO2 carrier and photocatalyst sample prepared in Example 1. It can be seen from the figure that the photocurrent density of the bimetallic site catalyst is enhanced, indicating that the bimetallic site is conducive to promoting the generation of photogenerated carriers and improving the photocatalytic activity.

Figure 4 is an in-situ infrared spectrum of the _CeO2 carrier and the photocatalyst sample prepared in Example 1. It can be seen from the figure that the bimetallic active sites promote the generation of * _CH2 intermediate species and directly promote the generation of _CH4 .

Figure 5 is a performance test diagram of the photocatalyst catalyzed CO ₂ reduction prepared by CeO ₂ carrier and Examples 1-4 and Comparative Examples 1-2. It can be seen from the figure that the bimetallic active site catalyst achieves nearly 100% CH ₄ production.

Figure 6 is a performance cycle test diagram of the photocatalyst sample prepared in Example 1. It can be seen from the figure that the dual metal site catalyst has good stability.

Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims (10)

1. A photocatalyst with a double metal atom site, characterized in that it comprises: a _CeO2 carrier, and double metal atoms loaded on the _CeO2 carrier; the double metal atoms comprise a first metal atom selected from Au, Ag, and Pt and a second metal atom selected from Ag, In, and Pd, and the first metal atom and the second metal atom are different. 2. The photocatalyst with dual metal atom sites according to claim 1, characterized in that the _CeO2 carrier is a cubic fluorite structure crystal; and the size of the _CeO2 carrier is 50 to 200 nm. 3. The photocatalyst with dual metal atom sites according to claim 1 or 2, characterized in that the mass of the dual metal atoms is controlled to be 0.5-5wt% of the mass of the _CeO2 carrier, and the molar ratio of the first metal atom to the second metal atom is 1:(0.25-4). 4. A method for preparing a photocatalyst having dual metal atom sites according to any one of claims 1 to 3, characterized in that it comprises: dispersing _CeO2 powder in water and adding an alkaline solution and stirring, then adding a precursor solution of a first metal atom and a precursor solution of a second metal atom, followed by aging, filtering, drying, grinding, and heat treatment under a reducing atmosphere to obtain the photocatalyst having dual metal atom sites. 5. The preparation method according to claim 4, characterized in that the dosage ratio of the _CeO2 powder to water is 1 g: (10-100) mL. 6. The preparation method according to claim 4 or 5, characterized in that the alkaline solution is selected from sodium hydroxide _, ( _NH4 ) _2CO3 , _NH4HCO3 or _ammonia solution, the concentration of the alkaline solution is 0.5-2M, and the dosage ratio of the _CeO2 powder and the alkaline solution is 1g: (10-100)mL. 7. The preparation method according to any one of claims 4 to 6, characterized in that the precursor solution of the first metal atom is selected from chloroauric acid, silver nitrate or chloroplatinic acid solution, with a concentration of 0.06-30 mg/mL, and the amount added is 0.02-2 mL; the precursor solution of the second metal atom is selected from silver nitrate, indium nitrate or sodium chloropalladate, with a concentration of 0.06-30 mg/mL, and the amount added is 0.02-2 mL, preferably 0.03-1 mL. 8. The preparation method according to any one of claims 4-7, characterized in that the aging time is 0.5 to 10 hours, preferably 0.5 to 6 hours, and the temperature is 10 to 30°C; the heat treatment temperature is 200 to 500°C, and the heat treatment time is 1 to 8 hours. 9. The preparation method according to any one of claims 4 to 8, characterized in that the reducing gas is a mixed gas of high-purity _H2 /Ar, wherein the volume fraction of _H2 is 5-15 vol.%, and the purity of _H2 and Ar is ≥99.9%. 10. Use of the photocatalyst having bimetallic atomic sites according to claim 1 in solar fuel catalysis.