CO2 reduction reaction catalyst as well as supercritical alcohol heat preparation method and application thereof

Abstract

The invention relates to a CO2 reduction reaction catalyst and a supercritical alcohol heat preparation method and application thereof, and belongs to the technical field of CO2 reduction catalysis, and the CO2 reduction reaction catalyst comprises the following steps: S1, carrying out a reaction on an ethanol solution dispersed with tetrabutyl titanate in a first supercritical state, filtering, washing, and drying to obtain TiO2; s2, dispersing TiO2 obtained in S1 into ethanol containing chlorine salt again, reacting in a second supercritical state to enable chloride ions to be doped into TiO2 crystal lattices, filtering, washing and drying to obtain TiO2 / sc-Cl; and S3, dispersing the TiO2 / sc-Cl obtained in the step S2 in a silver salt solution, and continuously stirring under the irradiation of ultraviolet light to obtain Ag-TiO2 / sc-Cl. Compared with the prior art, the method has the advantages that Cl atoms are doped into TiO2 crystal lattices, Ag is deposited on the TiO2 crystal lattices, a Cl-Ag structure is obtained, the water activation process is remarkably improved, the process of CO2 activation and deep hydrogenation into ethylene is improved through active hydrogen species (* H) generated through water in-situ activation, use of a sacrificial agent is avoided, and the yield and selectivity of ethylene are effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of CO2 reduction catalysis, and particularly relates to a CO2 reduction reaction catalyst, a supercritical alcohol thermal preparation method thereof, and an application thereof. Background Art

[0002] Due to the high energy density of solar energy and its long-term stable supply performance, artificial photosynthesis (APS) is considered an effective, inexpensive, and environmentally friendly energy conversion method.

[0003] The two most important and challenging reactions in artificial photosynthesis are: 1. Photolysis of water to produce hydrogen and oxygen; 2. Photocatalytic reduction of carbon dioxide to hydrocarbon fuels such as methane and methanol. Since Honda and Fujishima et al. first reported the use of TiO2 semiconductors as electrodes to achieve photocatalytic water splitting in 1972, photocatalytic water splitting has been extensively studied by a large number of researchers. At the same time, photocatalytic CO2 reduction reaction is considered one of the best ways to overcome global warming and solve the energy crisis, and has attracted increasing attention in recent years.

[0004] However, compared with photocatalytic water splitting for hydrogen production, the CO2 photoreduction reaction is a more complex and difficult process. Due to the low photocatalytic efficiency and selectivity, and the limited number of available photocatalysts, the research progress of photocatalytic reduction of carbon dioxide to valuable hydrocarbons lags far behind that of photocatalytic water splitting, especially in terms of C-C coupling to prepare C2 products. Therefore, converting carbon dioxide and water into valuable hydrocarbons (such as ethylene) has great value and challenges.

[0005] Current CO2 photoreduction technologies for ethylene production often have problems such as the need to add sacrificial agents (such as triethylamine, triethanolamine, sodium sulfite, etc.), low ethylene yield and selectivity. Summary of the Invention

[0006] The purpose of the present invention is to provide a CO2 reduction reaction catalyst, a supercritical alcohol thermal preparation method thereof, and an application thereof in order to overcome at least one of the defects existing in the above-mentioned prior art. The present invention prepares chlorine-doped TiO2 nanoparticles by a supercritical alcohol thermal method, and then surface-loads Ag species by a photodeposition method, and successfully realizes the reduction of CO2 to ethylene using H2O as a reducing agent under the conditions of no sacrificial agent and normal pressure. Compared with other halogen elements, the chlorine atom has a suitable radius and can just be doped into the TiO2 lattice. Br and I cannot be doped into the TiO2 lattice because their atomic radii are too large, while F can be doped into the TiO2 lattice, but the obtained F-Ag is more unstable than the Cl-Ag bond and cannot exist stably.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] One of the objectives of the present invention is a supercritical alcohol thermal preparation method for a CO2 reduction reaction catalyst, comprising the following steps:

[0009] S1. React an ethanol solution dispersed with tetrabutyl titanate under a first supercritical state, filter, wash, and dry to obtain TiO2;

[0010] S2. Redisperse the TiO2 obtained in S1 in ethanol containing a chloride salt, react under a second supercritical state to allow chloride ions to be doped into the TiO2 lattice, filter, wash, and dry to obtain TiO2 / sc-Cl;

[0011] S3. Disperse the TiO2 / sc-Cl obtained in S2 in a silver salt solution, continuously stir under ultraviolet light irradiation to obtain Ag-TiO2 / sc-Cl.

[0012] Further, in S1, the temperature of the first supercritical state is 250 - 300 °C, the pressure is 7 - 12 MPa, and the reaction time is 2 - 4 h.

[0013] Further, in S1, 1.0 - 10.0 g of tetrabutyl titanate is dispersed in every 100 ml of ethanol.

[0014] Further, in S2, the chloride salt is selected from one or more of NaCl, HCl, NH4Cl, and KCl.

[0015] Further, in S3, the silver salt is selected from one or more of AgNO3, silver acetylacetonate, and silver acetate.

[0016] Further, in S2, the temperature of the second supercritical state is 250 - 300 °C, the pressure is 7 - 12 MPa, and the reaction time is 2 - 4 h.

[0017] Further, in S2, every 100 ml of ethanol contains 0.01 - 1.00 g of the chloride salt.

[0018] Further, in S3, the solute concentration of the silver salt solution is 0.1 - 1000 mmol / L; the wavelength of the ultraviolet light is 280 - 400 nm, and the irradiation time is 2 - 4 h.

[0019] Another objective of the present invention is a CO2 reduction reaction catalyst prepared by the above-mentioned preparation method.

[0020] Another objective of the present invention is the application of the above-mentioned CO2 reduction reaction catalyst in improving the yield and selectivity of CO2 conversion to C2H4.

[0021] Compared with the prior art, the present invention dopes Cl atoms into the TiO2 lattice by using the supercritical alcohol thermal method, and then deposits Ag on the TiO2 lattice to obtain a Cl-Ag structure, which significantly improves the water activation process. The active hydrogen species (*H) generated in-situ by water activation is used to improve the CO2 activation and the process of deep hydrogenation to ethylene, avoiding the use of sacrificial agents and effectively improving the yield and selectivity of ethylene. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 XRD spectra of TiO2 and TiO2 / sc-0.1Cl in the present invention;

[0023] Figure 2 Raman spectra of TiO2 and TiO2 / sc-0.1Cl;

[0024] Figure 3 TEM images and particle size distributions of (a) TiO2 and (b) TiO2 / sc-0.1Cl;

[0025] Figure 4 Comparison of catalytic activities of Ag-TiO2 / sc-0.1Cl and Ag-TiO2;

[0026] Figure 5 Catalytic activity display of Ag-TiO2 / sc-0.1Cl catalyst with the extension of reaction time;

[0027] Figure 6 Effect of different Cl doping amounts on ethylene selectivity in Ag-TiO2 / sc-0.1Cl catalyst. DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0029] Example 1

[0030] This example provides a preparation method for a CO2 reduction reaction catalyst, and the specific steps are as follows:

[0031] (1) First, disperse 5.0 g of tetrabutyl titanate in 200 mL of ethanol, and maintain it for 3 h under supercritical conditions (260 °C, 10 MPa) to ensure the formation of TiO2. After filtration, washing, and drying, TiO2 is obtained;

[0032] (2) The 0.5 g of TiO2 obtained in (1) was dispersed again in 200 mL of ethanol containing 0.1 g of sodium chloride. Then, it was maintained under supercritical conditions (260 °C, 10 MPa) for 3 h to ensure that Cl was doped into the TiO2 lattice. After filtration, washing, and drying, the TiO2 / sc-0.1Cl catalyst was obtained.

[0033] (3) 0.1 g of the TiO2 / sc-0.1Cl catalyst obtained in (2) was dispersed in a 0.1 mmol / L AgNO3 solution. The suspension was placed under a 365 nm LED and continuously stirred and irradiated for 30 min, and then filtered, washed, and dried to obtain Ag-TiO2 / sc-0.1Cl. AgNO3 can also be replaced with any Ag salt / acid (such as silver acetylacetonate, silver acetate, etc.), and the 365 nm LED can also be replaced with an ultraviolet light source of any wavelength.

[0034] XRD patterns and Raman spectra showed that the characteristic peaks of TiO2 were significantly shifted after Cl doping compared to pure TiO2, indicating that Cl was successfully doped into the TiO2 lattice. See Figure 1-2 . Subsequent TEM images showed the nanosize of TiO2, which was polygonal, and the average particle sizes were 12.1 and 12.7 nm, respectively. See Figure 3 . These results clearly showed that Cl successfully entered the TiO2 lattice under supercritical conditions and had little effect on its morphology.

[0035] Example 2

[0036] Example 2 was basically the same as Example 1, except that the supercritical conditions in steps (1) and (2) were modified to a temperature of 250 °C and a pressure of 7 MPa.

[0037] Example 3

[0038] Example 2 was basically the same as Example 1, except that the supercritical conditions in steps (1) and (2) were modified to a temperature of 280 °C and a pressure of 10 MPa.

[0039] Example 4

[0040] Example 2 was basically the same as Example 1, except that the supercritical conditions in steps (1) and (2) were modified to a temperature of 300 °C and a pressure of 12 MPa.

[0041] Application Example

[0042] 2 mg of the catalyst was dispersed on a glass fiber membrane. After dropping 0.15 mL of water, it was placed in a sealed glass reactor. After thoroughly exhausting the air, 101 kPa of CO2 gas was filled, and the reaction was carried out under (simulated) natural light for 2 hours. The gas after the reaction was detected by chromatography.

[0043] The above catalysts were respectively tested using the Ag-TiO2 / sc-0.1Cl catalyst prepared in Example 1 and the existing Ag-TiO2 catalyst. The main product of the existing Ag-TiO2 catalyst was CO, with only small amounts of ethylene and methane being produced. However, on the Ag-TiO2 / sc-0.1Cl catalyst doped with supercritical Cl, the main product was C2H4, and the yield and selectivity were 244 μmol / g cat / h and 64.3%, as shown in Figure 4 . This phenomenon indicates that Ag-TiO2 doped with supercritical Cl can significantly promote the process of CO→C2H4. As Figure 5 shown, under the catalysis of Ag-TiO2 / sc-0.1Cl, as the reaction time extended, the yields of CO, CH4, and C2H4 continuously increased, further demonstrating the significant change in selectivity under Cl doping. As Figure 6 shown, as the Cl doping amount increased, the C2H4 selectivity first increased and then decreased. When 0.1 g of NaCl was selected, the C2H4 selectivity was the highest, further indicating the significant change in Cl doping on ethylene selectivity.

[0044] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention in any other form. Any person skilled in the art may use the technical content disclosed above to make changes or modifications into equivalent embodiments with equivalent changes. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the technical solution content of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A supercritical alcohol thermal preparation method for a CO2 reduction reaction catalyst, characterized in that, It includes the following steps: S1. React the ethanol solution dispersed with tetrabutyl titanate under the first supercritical state, filter, wash, and dry to obtain TiO2; S2. Redisperse the TiO2 obtained in S1 in ethanol containing chloride salt, and react under the second supercritical state to allow chloride ions to be doped into the TiO2 lattice, filter, wash, and dry to obtain TiO2 / sc-Cl; S3. Disperse the TiO2 / sc-Cl obtained in S2 in a silver salt solution, and continuously stir under ultraviolet light irradiation to obtain Ag-TiO2 / sc-Cl.

2. The supercritical alcohol thermal preparation method of a CO2 reduction reaction catalyst according to claim 1, characterized in that, In S1, the temperature of the first supercritical state is 250 - 300 °C, the pressure is 7 - 12 MPa, and the reaction time is 2 - 4 h.

3. The supercritical alcohol thermal preparation method of a CO2 reduction reaction catalyst according to claim 1, characterized in that, In S1, 1.0 - 10.0 g of tetrabutyl titanate is dispersed in every 100 ml of ethanol.

4. The supercritical alcohol thermal preparation method of a CO2 reduction reaction catalyst according to claim 1, wherein In S2, the chloride salt is selected from one or more of NaCl, HCl, NH4Cl, and KCl.

5. The supercritical alcohol thermal preparation method of a CO2 reduction reaction catalyst according to claim 1, characterized in that, In S3, the silver salt is selected from one or more of AgNO3, silver acetylacetonate, and silver acetate.

6. The supercritical alcohol thermal preparation method of a CO2 reduction reaction catalyst according to claim 1, characterized in that, In S2, the temperature of the second supercritical state is 250 - 300 °C, the pressure is 7 - 12 MPa, and the reaction time is 2 - 4 h.

7. The supercritical alcohol thermal preparation method of a CO2 reduction reaction catalyst according to claim 1, characterized in that, In S2, every 100 ml of ethanol contains 0.01 - 1.00 g of chloride salt.

8. The supercritical alcohol thermal preparation method of a CO2 reduction reaction catalyst according to claim 1, characterized in that, In S3, the solute concentration of the silver salt solution is 0.1 - 1000 mmol / L; the wavelength of the ultraviolet light is 280 - 400 nm, and the irradiation time is 2 - 4 h.

9. A CO2 reduction reaction catalyst, characterized in that, It is prepared by using the preparation method described in any one of claims 1 - 8.

10. Application of a CO2 reduction reaction catalyst as described in claim 9 in improving the yield and selectivity of CO2 conversion to C2H4.

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