Defect-state titanium dioxide supported catalyst, preparation method and application of defect-state titanium dioxide supported catalyst in methane and carbon dioxide co-conversion reaction

Abstract

The invention relates to the technical field of photocatalysis, in particular to a defect-state titanium dioxide supported catalyst, a preparation method and application of the defect-state titanium dioxide supported catalyst in a reaction for co-converting methane and carbon dioxide. The defect-state titanium dioxide supported catalyst comprises a carrier and metal Au supported on the surface of the carrier; the carrier is a defect-state titanium dioxide nanosheet with oxygen vacancies. According to the invention, the defect-state titanium dioxide nanosheet is used as a carrier, and after metal particles (Au) are loaded, the metal particles are used as capture centers of photo-induced electrons to promote spatial separation of photo-induced electron-hole pairs. In addition, the formed metal-carrier interface site effectively enhances the adsorption and activation of CH4 and CO2 by the photocatalyst. Moreover, the loaded high-electronegativity metal Au can also be used as a coupling site of methyl, so that high-yield C2H6 is obtained, and meanwhile, a corresponding CO product is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of photocatalysis, and in particular to a defective titanium dioxide supported catalyst, a preparation method and application in a co-conversion reaction of methane and carbon dioxide. Background Art

[0002] Methane and carbon dioxide are the two main greenhouse gases, accounting for about 90% of the total global emissions. At the same time, they are recognized as C1 raw materials with high bond energy for the production of high-value chemicals. Ethane is one of the components of natural gas and petroleum, and plays an important role in modern society. Moreover, ethane is a raw material for the production of ethylene, and a large part of the global plastic production depends on ethylene, so the supply of ethane directly affects the plastic and related industries. The co-conversion of CH4 and CO2 to ethane is not only conducive to alleviating the increasingly serious greenhouse effect, but also helps to meet the rapidly growing demand for ethane. However, since both CH4 and CO2 are highly symmetrical non-polar molecules, the thermal catalytic co-conversion of CH4 and CO2 often requires harsh high temperature and high pressure conditions, which easily induces many side reactions, such as carbon deposition. In addition, the thermal catalytic co-conversion of CH4 and CO2 often forms a syngas product, which requires additional Fischer-Tropsch reactions to be converted into high-value chemicals. Summary of the invention

[0003] In view of this, the technical problem to be solved by the present invention is to provide a defective titanium dioxide supported catalyst, a preparation method and an application in the co-conversion reaction of methane and carbon dioxide. The prepared defective titanium dioxide supported catalyst can catalyze the co-conversion of methane and carbon dioxide into ethane.

[0004] The present invention provides a defective titanium dioxide supported catalyst, comprising a support and metal Au supported on the surface of the support;

[0005] The carrier is a defective titanium dioxide nanosheet with oxygen vacancies.

[0006] Preferably, the loading amount of the metal Au is 1% to 3%.

[0007] Preferably, the thickness of the defective titanium dioxide nanosheet is 3-5 nm;

[0008] The average particle size of the metal Au is 1-8 nm.

[0009] The present invention provides a method for preparing the above-mentioned defective titanium dioxide supported catalyst, comprising the following steps:

[0010] S1) mixing titanium dioxide nanosheets and a salt solution of metal gold, and removing the solvent to obtain a mixed powder;

[0011] S2) calcining the mixed powder in a hydrogen and argon atmosphere to obtain a defective titanium dioxide supported catalyst.

[0012] Preferably, the titanium dioxide nanosheets are prepared according to the following method:

[0013] The titanium source compound and the acid compound are mixed and subjected to a hydrothermal reaction to obtain titanium dioxide nanosheets.

[0014] Preferably, the titanium source compound includes tetrabutyl titanate;

[0015] The acidic compound includes hydrofluoric acid;

[0016] The temperature of the hydrothermal reaction is 160-200° C.; the time of the hydrothermal reaction is 12-24 hours.

[0017] Preferably, the metal gold salt solution includes one or more of HAuCl4 solution and NaAuCl4 solution;

[0018] The calcination temperature is 300-500°C; the calcination time is 1-2h;

[0019] The heating rate of the calcination is 2-10 °C / min;

[0020] The hydrogen-argon atmosphere is a mixture of hydrogen and argon, and the volume content of hydrogen is 2% to 20%.

[0021] The present invention provides the use of the defective titanium dioxide supported catalyst or the defective titanium dioxide supported catalyst prepared by the above preparation method as a catalyst for the co-conversion of methane and carbon dioxide.

[0022] The present invention provides a method for co-converting methane and carbon dioxide, comprising the following steps:

[0023] The defective titanium dioxide supported catalyst or the defective titanium dioxide supported catalyst prepared by the preparation method is used to catalyze the photo-induced reaction of methane and carbon dioxide to obtain ethane and carbon monoxide.

[0024] Preferably, the light source of the illumination reaction is selected from any one of a xenon lamp, a high-pressure mercury lamp, an LED lamp or an iodine tungsten lamp;

[0025] The power of the light source in the light reaction is 100-1000 mW cm -2 ;

[0026] The light reaction time is 0.5~4 h;

[0027] The volume ratio of the methane to the carbon dioxide is 1:19-19:1.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present invention uses defective titanium dioxide nanosheets as carriers and loads metal particles (Au). The metal particles act as capture centers for photogenerated electrons, promoting the spatial separation of photogenerated electron-hole pairs. In addition, the metal-carrier interface sites formed effectively enhance the adsorption and activation of CH4 and CO2 by the photocatalyst. In addition, the loaded highly electronegative metal Au can also serve as a coupling site for methyl groups, thereby obtaining a high yield of C2H6 and the corresponding CO product. According to research, Au quantum dots loaded on defective titanium dioxide nanosheets obtained 2.6 mmol g in the photocatalytic co-conversion of CH4 and CO2 under mild conditions. -1 ethane yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The TiO2 nanosheets prepared in Comparative Example 1, the Au / TiO2 nanosheets prepared in Comparative Example 2, and the Au / TiO2-V prepared in Example 1 o XRD spectrum of nanosheets;

[0031] Figure 2 The Au / TiO2-V prepared in Example 1 o STEM images and particle size distribution of nanosheets;

[0032] Figure 3 The Au / TiO2-V prepared in Example 1 o Elemental distribution map of nanosheets;

[0033] Figure 4 The TiO2 nanosheets prepared in Comparative Example 1, the Au / TiO2 nanosheets prepared in Comparative Example 2, and the Au / TiO2-V prepared in Example 1 o XPS spectrum of nanosheets;

[0034] Figure 5 The TiO2 nanosheets prepared in Comparative Example 1, the Au / TiO2 nanosheets prepared in Comparative Example 2, and the Au / TiO2-V prepared in Example 1 o EPR spectrum of nanosheets;

[0035] Figure 6 The Au / TiO2-V prepared in Example 1 o AFM images of nanosheets and corresponding height distribution maps;

[0036] Figure 7 TEM images of the TiO2 nanosheets prepared in Comparative Example 1 and the Au / TiO2 nanosheets prepared in Comparative Example 2;

[0037] Figure 8 HRTEM image of the TiO2 nanosheet prepared in Comparative Example 1;

[0038] Fig. 9 The Au / TiO2 nanosheets prepared in Comparative Example 2 and the Au / TiO2-V prepared in Example 1 o Comparison chart of static photocurrent test of nanosheets;

[0039] Fig.10 The Au / TiO2 nanosheets prepared in Comparative Example 2 and the Au / TiO2-V prepared in Example 1 o Comparison chart of surface photovoltage test of nanosheets;

[0040] Fig.11 The Au / TiO2 nanosheets prepared in Comparative Example 2 and the Au / TiO2-V prepared in Example 1 o Comparison of photoluminescence tests of nanosheets;

[0041] Fig.12 The TiO2 nanosheets prepared in Comparative Example 1, the Au / TiO2 nanosheets prepared in Comparative Example 2, and the Au / TiO2-V prepared in Example 1 o UV-vis spectrum of nanosheets;

[0042] Fig.13 The Au / TiO2 nanosheets prepared in Comparative Example 2 and the Au / TiO2-V prepared in Example 1 o CO2-TPD spectrum of nanosheets;

[0043] Fig.14 The Au / TiO2 nanosheets prepared in Comparative Example 2 and the Au / TiO2-V prepared in Example 1 o CH4-TPD spectrum of nanosheets;

[0044] Fig.15 The Au / TiO2 nanosheets prepared in Comparative Example 2 and the Au / TiO2-V prepared in Example 1 o CO2 adsorption energy diagram of nanosheets;

[0045] Fig.16 The TiO2 nanosheets prepared in Comparative Example 1, the Au / TiO2 nanosheets prepared in Comparative Example 2, and the Au / TiO2-V prepared in Example 1 o Product distribution diagram of the photocatalytic co-conversion of CH4 and CO2 by nanosheets;

[0046] Fig.17 The Au / TiO2-V prepared in Example 1 oThe precipitation rate diagram of C2H6 under different Au mass fractions loaded on nanosheets;

[0047] Fig.18 The Au / TiO2-V prepared in Example 1 o Synchrotron radiation ultraviolet photoionization mass spectrum of the isotope labeling experiment of nanosheet photocatalytic co-conversion of CH4 and CO2. DETAILED DESCRIPTION

[0048] The present invention provides a defective titanium dioxide supported catalyst, comprising a support and metal Au supported on the surface of the support;

[0049] The carrier is a defective titanium dioxide nanosheet with oxygen vacancies.

[0050] Preferably, the loading amount of the metal Au is 1% to 3%. Experimental results show that controlling the loading amount of Au to 1% to 3% can obtain a C2H6 product with a higher precipitation rate.

[0051] Preferably, the thickness of the defective titanium dioxide nanosheet is 3-5 nm; including but not limited to 3 nm, 3.1 nm, 3.2 nm, 3.3 nm, 3.4 nm, 3.5 nm, 3.6 nm, 3.7 nm, 3.8 nm, 3.9 nm, 4.0 nm, 4.1 nm, 4.2 nm, 4.3 nm, 4.4 nm, 4.5 nm, 4.6 nm, 4.7 nm, 4.8 nm, 4.9 nm or 5 nm. The defective titanium dioxide nanosheet has excellent photosensitivity, and the abundant defect sites on the nanosheet can adjust the electronic structure and band structure of the titanium dioxide nanosheet, and serve as active sites for reactant adsorption. Controlling its thickness to 3-5 nm can effectively shorten the transmission distance of photogenerated carriers, improve the separation efficiency of photogenerated hole-electron pairs, and thus improve the catalytic performance. In the present invention, if the particle size of the loaded metal Au particles is too large, they will cover the surface of defective titanium dioxide nanosheets, reduce the adsorption sites in the subsequent actual photocatalysis, and aggravate the electron-hole recombination, resulting in reduced catalytic performance. Conversely, when the particle size is too small, it means that the amount of loaded metal is too low, which will also lead to poor catalytic performance. Therefore, the present invention preferably sets the average particle size of the metal Au particles to 1~8 nm, including but not limited to 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm or 8 nm.

[0052] Although a single titanium dioxide nanosheet has good photosensitivity, the recombination efficiency of photogenerated carriers is relatively high. The present invention uses defective titanium dioxide nanosheets as carriers and loads Au quantum dots as capture centers for photogenerated electrons to promote the spatial separation of electron-hole pairs.

[0053] In the present invention, the defective titanium dioxide nanosheet supported catalyst can be used as a photocatalyst to catalyze the co-conversion of CH4 and CO2 into C2H6 and CO, and by controlling the loading amount of metal particles, the conversion efficiency can be effectively improved. The present invention has found that when the mass fraction of the Au quantum dots loaded on the carrier is too low, the conversion efficiency will be low. Conversely, when the mass fraction of the Au quantum dots loaded on the carrier is too high, the conversion efficiency will also be low. Therefore, in the present invention, the mass ratio of the carrier to the metal Au loaded on the carrier is preferably (95~99.5): (0.5~5), more preferably (95~99): (1~5), including but not limited to 95: 5, 95.5: 4.5, 96: 4, 96.5: 3.5, 97: 3, 97.5: 2.5, 98: 2, 98.5: 1.5 or 99: 1, etc.

[0054] The present invention provides a method for preparing the above-mentioned defective titanium dioxide supported catalyst, comprising the following steps:

[0055] S1) mixing titanium dioxide nanosheets and a salt solution of metal gold, and removing the solvent to obtain a mixed powder;

[0056] S2) calcining the mixed powder in a hydrogen and argon atmosphere to obtain a defective titanium dioxide supported catalyst.

[0057] Preferably, the titanium dioxide nanosheets are prepared according to the following method:

[0058] The titanium source compound and the acid compound are mixed and subjected to a hydrothermal reaction to obtain titanium dioxide nanosheets.

[0059] The titanium source compound preferably includes tetrabutyl titanate.

[0060] The acidic compound preferably includes hydrofluoric acid.

[0061] The temperature of the hydrothermal reaction is preferably 160-200° C., more preferably 180-200° C.; the time of the hydrothermal reaction is preferably 12-24 h, more preferably 20-24 h.

[0062] In some specific embodiments of the present invention, the titanium dioxide nanosheets are prepared according to the following method:

[0063] Tetrabutyl titanate and hydrofluoric acid are mixed and subjected to hydrothermal reaction in a constant temperature oven at 160-200 °C. After the reactor is cooled naturally, the mixture is centrifuged, washed with anhydrous ethanol and deionized water for multiple times, and dried in an oven at 80 °C to obtain titanium dioxide nanosheets. The mixture is preferably mixed in a 50 mL reactor liner and fully mixed by magnetic stirring; the addition ratio of tetrabutyl titanate and hydrofluoric acid is preferably 25:1-25:4; and the drying time is preferably 12-24 h.

[0064] The titanium dioxide nanosheets are then mixed with a salt solution of metallic gold.

[0065] The metal gold salt solution preferably includes one or more of HAuCl4 solution and NaAuCl4 solution.

[0066] In some specific embodiments of the present invention, the above step S1) is specifically:

[0067] The titanium dioxide nanosheets and the metal gold salt solution are mixed and stirred, and evaporated to dryness at 80-120°C to obtain a mixed powder.

[0068] The evaporation temperature is more preferably 80-120°C, and more preferably 100-120°C.

[0069] The obtained mixed powder is then calcined.

[0070] The calcination temperature is preferably 300-500° C., more preferably 400-450° C.; the calcination time is preferably 1-2 hours.

[0071] The heating rate of the calcination is preferably 2-10°C / min, more preferably 2°C / min.

[0072] The hydrogen-argon atmosphere is a mixture of hydrogen and argon, and the volume content of hydrogen is preferably 2% to 20%, more preferably 5%.

[0073] The present invention selects hydrogen and argon atmosphere as the calcination atmosphere. H2 not only reduces the metal Au ions adsorbed on the titanium dioxide nanosheets to metal quantum dots, but also preferentially stimulates abundant oxygen vacancies around the metal quantum dots, thereby obtaining titanium dioxide nanosheets loaded with Au quantum dots and abundant oxygen vacancies. The content of hydrogen affects the size of the formed Au quantum dots and the concentration of the formed oxygen vacancies.

[0074] After the above reaction is completed, the present invention preferably stores the obtained defective titanium dioxide nanosheet supported catalyst in a vacuum desiccator for subsequent characterization and application.

[0075] In the present invention, the point values ​​listed above are merely for enumeration and are not limited thereto. Other point values ​​within the numerical range are applicable. To avoid complexity, they will not be described one by one.

[0076] The defective titanium dioxide nanosheet supported catalyst provided by the present invention is prepared by simple conventional means such as hydrothermal reaction and calcination, which is easy to operate, has a short synthesis time, and is convenient for large-scale production. o The results of ultraviolet-visible near-infrared diffuse reflectance spectroscopy (UV-vis), static photocurrent test and photoluminescence (PL) test showed that the Au / TiO2-V nanosheets provided by the present invention o Compared with the single TiO2 nanosheet catalyst, the nanosheet catalyst not only effectively increases the light absorption, but also significantly improves the separation efficiency of photogenerated carriers and reduces the recombination efficiency of electron-hole pairs. o The Au / TiO2-V nanosheets were found to have a good thermal conductivity and good thermal conductivity. o Compared with a single TiO2 nanosheet catalyst, the desorption temperature of CO2 and CH4 is significantly increased by the nanosheet catalyst, which indicates that the adsorption capacity of CO2 and CH4 is significantly enhanced, which is beneficial to improving the catalytic efficiency of photocatalytic co-conversion of CH4 and CO2.

[0077] Based on this, the present invention provides the use of the above-mentioned defective titanium dioxide supported catalyst or the defective titanium dioxide supported catalyst prepared by the above-mentioned preparation method as a catalyst for the co-conversion of methane and carbon dioxide.

[0078] The present invention aims at the problem that the co-conversion of CH4 and CO2 in the prior art is inefficient and has many side reactions, and provides a method for co-converting methane and carbon dioxide, comprising the following steps:

[0079] The defective titanium dioxide supported catalyst or the defective titanium dioxide supported catalyst prepared by the preparation method is used to catalyze the photo-induced reaction of methane and carbon dioxide to obtain ethane and carbon monoxide.

[0080] Specifically, the defective titanium dioxide supported catalyst is subjected to light irradiation reaction in a flowing mixed atmosphere of CH4 and CO2 to obtain ethane and carbon monoxide.

[0081] The light source for the photoreaction is preferably any one of a xenon lamp, a high pressure mercury lamp, an LED lamp or an iodine tungsten lamp, more preferably a xenon lamp.

[0082] The power of the light source in the illumination reaction is preferably 100-1000 mW cm -2, more preferably 500-800 mW cm -2 .

[0083] The light irradiation reaction time is preferably 0.5 to 4 h, more preferably 1 to 2 h, including but not limited to 1 h, 1.5 h or 2 h.

[0084] The volume ratio of the methane to the carbon dioxide is preferably 1:19-19:1, more preferably 1:1.

[0085] In some embodiments of the present invention, the method for co-converting CH4 and CO2 preferably comprises the following steps:

[0086] Weigh an appropriate amount of the above-prepared defective titanium dioxide nanosheet catalyst loaded with Au metal quantum dots, add an appropriate amount of deionized water for ultrasonic dispersion, and then apply it on a quartz surface dish by drop coating. Then, after drying on a heater, place it in a photocatalytic reactor with openings on both ends, pass flowing CH4 and CO2 mixed gas, and irradiate with light. In the present invention, the photocatalytic reactor can be a gas-solid phase reactor with a quartz window, and the CH4 and CO2 mixed gas is preferably obtained by mixing high-purity methane (≥99.9%) and high-purity carbon dioxide (≥99.9%) through a gas mixing system.

[0087] The experimental results of photocatalytic co-conversion of CH4 and CO2 showed that the defective titanium dioxide nanosheets loaded with 1.86 wt% Au quantum dots (named Au / TiO2-V o Nanosheets) were used as photocatalysts in the photocatalytic co-conversion of CH4 and CO2. After 1.5 h of reaction, 2.6 mmol g -1 h -1 The ethane precipitation rate is much higher than that of Au-loaded titanium dioxide nanosheets. Although single defective titanium dioxide nanosheets have good photosensitivity, they have weak visible light capture ability, poor photogenerated carrier separation efficiency, and weak adsorption and activation ability for CH4 and CO2. The original TiO2 nanosheets hardly produce ethane.

[0088] In order to further illustrate the present invention, the following is a detailed description in conjunction with the embodiments. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the invention.

[0089] All raw materials of the present invention have no particular limitation on their sources, and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0090] Example 1

[0091] This embodiment provides an Au / TiO2-V oPreparation method of nanosheet photocatalyst and its application in photocatalytic co-conversion of CH4 and CO2 to produce ethane:

[0092] Use a pipette to transfer 12.5 mL of tetrabutyl titanate (Sinopharm Chemical Reagent Co., Ltd., purity ≥99%) and 1.5 mL of hydrofluoric acid (Sinopharm Chemical Reagent Co., Ltd., content ≥40%) into the lining of a 50 mL reactor, and stir for 10 min to ensure full mixing. Then put the lining into the outer shell of the stainless steel reactor, tighten it, and put it into a constant temperature oven (Shanghai Jinghong Experimental Equipment Co., Ltd., DHG-9036Y) to react at 200 °C for 24 h. After natural cooling, collect the solid obtained by the reaction by centrifugation, and wash it with ethanol and deionized water three times respectively. Then put it into an 80 °C oven and dry it overnight to obtain a dry white powder. 500 mg of the obtained white powder was weighed and dispersed in 20 mL of deionized water, and 2 mL of HAuCl4 aqueous solution was added. The mixture was stirred at 500 rpm for 24 h, and then the water was completely evaporated at 100 °C. After the obtained powder was fully ground, the temperature was increased from room temperature to 400 °C at a rate of 2 °C / min in a 5% H2 / Ar environment and maintained for 1 h. The purple powder sample was Au / TiO2-V o Nanosheets.

[0093] The obtained Au / TiO2-V o The nanosheets were characterized using an X-ray powder diffractometer (Philips X'Pert Pro Superdiffractometer), a high-resolution transmission electron microscope (JEOL-2010 TEM), an X-ray photoelectron spectrometer (ESCALAB250), and an electron paramagnetic resonance spectrometer (JEOL JES-FA200). The mass fraction of Au was determined using inductively coupled plasma emission spectroscopy (measured to be 1.86%). The obtained XRD diffraction pattern is shown in Figure 1 The scanning transmission electron microscopy (STEM) image and the corresponding particle size distribution are shown in Figure 2 As shown in Figure AB, the element distribution diagram is as follows Figure 3 As shown, the X-ray photoelectron spectroscopy (XPS) is as follows Figure 4 As shown, the obtained EPR spectrum is as follows Figure 5 As shown, the atomic force probe microscope (AFM) image and the corresponding height distribution diagram are shown in Figure 6 From the above characterization, it can be seen that Au quantum dots are uniformly dispersed on the titanium dioxide nanosheets with abundant oxygen vacancies.

[0094] Comparative Example 1

[0095] Use a pipette to transfer 12.5 mL of tetrabutyl titanate (Sinopharm Chemical Reagent Co., Ltd., purity ≥99%) and 1.5 mL of hydrofluoric acid (Sinopharm Chemical Reagent Co., Ltd., content ≥40%) into the lining of a 50 mL reactor, and stir for 10 minutes to ensure full mixing. Then put the lining into the outer shell of the stainless steel reactor, tighten it, and put it into a constant temperature oven (Shanghai Jinghong Experimental Equipment Co., Ltd., DHG-9036Y) to react at 200 °C for 24 h. After natural cooling, collect the solid obtained by the reaction by centrifugation, and wash it with ethanol and deionized water three times respectively. Then put it into an 80 °C oven and dry it overnight to obtain a dry white powder as TiO2 nanosheets.

[0096] The obtained TiO2 nanosheets were characterized using an X-ray powder diffractometer (Philips X'Pert Pro Superdiffractometer), a high-resolution transmission electron microscope (JEOL-2010 TEM), an X-ray photoelectron spectrometer (ESCALAB250), and an electron paramagnetic resonance spectrometer (JEOL JES-FA200). The obtained XRD diffraction pattern is as follows: Figure 1 As shown in the transmission electron microscope (TEM) Figure 7 As shown in a, the high-resolution transmission electron microscopy image is Figure 8 As shown, the X-ray photoelectron spectroscopy (XPS) is as follows Figure 4 The obtained EPR spectrum is shown in Figure 5 As shown above, it can be seen that comparative example 1 successfully synthesized titanium dioxide nanosheets without oxygen vacancies.

[0097] Comparative Example 2

[0098] Use a pipette to transfer 12.5 mL of tetrabutyl titanate (Sinopharm Chemical Reagent Co., Ltd., purity ≥99%) and 1.5 mL of hydrofluoric acid (Sinopharm Chemical Reagent Co., Ltd., content ≥40%) into the lining of a 50 mL reactor, and stir for 10 min to ensure thorough mixing. Then put the lining into the stainless steel reactor shell, tighten it, and put it into a constant temperature oven (Shanghai Jinghong Experimental Equipment Co., Ltd., DHG-9036Y) to react at 200 ℃ for 24 h. After natural cooling, collect the solid obtained by the reaction by centrifugation, and wash it with ethanol and deionized water three times respectively. Then put it in an 80 ℃ oven to dry overnight to obtain a dry white powder. Weigh 100 mg of white powder and disperse it in 100 mL of deionized water and disperse it ultrasonically. Add 0.4 mL of HAuCl4 aqueous solution and stir at 500 rpm for 24 h. Then add freshly prepared sodium borohydride solution dropwise, then collect the solid obtained by centrifugation and wash it with water three times. After drying in an oven at 80 °C overnight, the obtained pink solid powder is Au / TiO2 nanosheets.

[0099] The obtained Au / TiO2 nanosheets were characterized using an X-ray powder diffractometer (Philips X'Pert Pro Superdiffractometer), a high-resolution transmission electron microscope (JEOL-2010 TEM), an X-ray photoelectron spectrometer (ESCALAB250), and an electron paramagnetic resonance spectrometer (JEOL JES-FA200). The mass fraction of Au was determined by inductively coupled plasma emission spectroscopy (measured to be 1.89%). The obtained XRD diffraction pattern is as follows: Figure 1 As shown in the transmission electron microscope (TEM) Figure 7 As shown in Figure b, the X-ray photoelectron spectroscopy (XPS) is as follows Figure 4 The obtained EPR spectrum is shown as Figure 5 As shown in the above characterization, it can be seen that Au quantum dots are uniformly dispersed on the titanium dioxide nanosheets without oxygen vacancies.

[0100] Optical characterization

[0101] Static photocurrent test: Au / TiO2 nanosheets prepared in Comparative Example 2 and Au / TiO2-V prepared in Example 1 o Taking Au / TiO2 nanosheets as an example, 5 mg Au / TiO2 nanosheets, Au / TiO2-V oNanosheets, add 2 mL of ethanol and sonicate for 10 min, take 300 μL of the dispersion and drop it on 2 cm*1 cm FTO conductive glass (drop coating area is 1 cm*1 cm), and dry it under an infrared lamp. Then use a Zahner electrochemical workstation (Zahner PP211) to perform photocurrent testing, using 0.5 mol / L Na2SO4 solution as the electrolyte, and a three-electrode system with a carbon rod as the counter electrode, a silver chloride electrode as the reference electrode, and ITO glass as the working electrode. The test results are shown in Fig. 9 .

[0102] Combining the Au / TiO2 nanosheets prepared in Comparative Example 2 and the Au / TiO2-V prepared in Example 1 o The surface photovoltage (SPV) test and photoluminescence (PL) spectrum test of the nanosheets, such as Fig.10 and Fig.11 Compared with the defect-free Au / TiO2 nanosheets, Au / TiO2-V o It exhibits a high efficiency of photogenerated carrier separation and effectively inhibits the recombination of photogenerated carriers.

[0103] The pure TiO2 nanosheets prepared in Comparative Example 1, the Au / TiO2 nanosheets prepared in Comparative Example 2, and the Au / TiO2-V prepared in Example 1 were o The nanosheets were characterized by ultraviolet-visible near-infrared diffuse reflectance (UV-vis) spectroscopy. Fig.12 .Depend on Fig.12 It can be seen that the surface plasmon resonance effect of Au enhances the absorption of the catalyst in the photosensitive region (400-800 nm). Enhancing the absorption of light is beneficial to improving the separation efficiency of photogenerated carriers, thereby improving the catalytic activity.

[0104] Characterization of CO2 and CH4 adsorption capacity

[0105] The Au / TiO2 nanosheets prepared in Comparative Example 2 and the Au / TiO2-V prepared in Example 1 o The nanosheets were tested for CO2 and CH4 temperature programmed desorption (CO2-TPD, CH4-TPD) respectively, and the results were as follows Fig.13 and Fig.14 As shown. Au / TiO2-V o The nanosheets exhibited higher CO2 and CH4 desorption temperatures than Au / TiO2 nanosheets, proving that Au / TiO2-V o The nanosheets exhibited excellent adsorption capacity for both CO2 and CH4, which laid the foundation for the co-conversion of CO2 and CH4.

[0106] In addition, by comparing the Au / TiO2 nanosheets prepared in Comparative Example 2 and the Au / TiO2-V prepared in Example 1 o Theoretical simulation of CO2 adsorption on nanosheets shows that CO2 is adsorbed on Au / TiO2-V o At the nanosheet metal-support interface, C and O in the CO2 molecule can bond with the electron-rich Au and electron-deficient Ti, respectively, greatly enhancing CO2 adsorption. Fig.15 , Au / TiO2-V o It exhibits an extremely low CO2 adsorption energy of -0.54 eV, and the enhanced adsorption capacity of the reactants is beneficial to increasing the catalytic efficiency.

[0107] Photocatalytic application example: Photocatalytic co-conversion of CH4 and CO2 to produce ethane

[0108] 10 mg of pure TiO2 nanosheets prepared in Comparative Example 1, Au / TiO2 nanosheets prepared in Comparative Example 2, and Au / TiO2-V prepared in Example 1 were taken respectively. o The nanosheets were added to 3 mL of deionized water and ultrasonically dispersed. The resulting dispersion was droplet coated on a quartz dish and dried on a heater at 70 °C. The dried quartz dish was transferred to the bottom of the Zhongjiao Jinyuan photocatalytic reactor. High-purity Ar gas was first introduced at a total flow rate of 20 mL / min for 30 min to remove air and other impurities adsorbed on the surface of the catalyst in the device. Then the Ar gas was converted to 10 mL / min of high-purity CO2 and 10 mL / min of high-purity CH4. The two gases were mixed through a gas mixing system and then introduced into the photocatalytic reactor. The light source was a 300 W Xe lamp (CEL-HXF300, Beijing Zhongjiao Jinyuan Technology Co., Ltd.). The gas obtained after the reaction was collected with a gas collection bag and then injected into a gas chromatograph for quantification (Agilent GC-7890B equipped with a TDX-01 column, thermal conductivity detector (TCD) and flame ionization detector (FID)).

[0109] The TiO2 nanosheets in Comparative Example 1, the Au / TiO2 nanosheets in Comparative Example 2, and the Au / TiO2-V in Example 1 o The product distribution diagram of the photocatalytic co-conversion of CH4 and CO2 by nanosheets is shown in Fig.16 .from Fig.16 It can be seen that TiO2 nanosheets produce almost no ethane, while Au / TiO2 nanosheets exhibit a higher C2H6 precipitation rate, indicating that the loaded Au species is conducive to driving the formation of C2H6. o The nanosheets further increased the ethane evolution rate to 2.6 mmol g -1 h -1, which is about 3 times that of Au / TiO2 nanosheets. In addition, it can be found that the precipitation rate of CO products has increased significantly. It can be speculated that the introduced oxygen vacancies enhance the adsorption and activation ability of CO2. Subsequently, the effect of the mass fraction of Au on the ethane generation rate was further tested, such as Fig.17 The precipitation rate of C2H6 shows a volcanic trend with the increase of Au mass fraction. When the mass fraction of Au is 1.86%, the precipitation rate of C2H6 reaches the highest. With the further increase of Au mass fraction, the precipitation rate of ethane begins to decrease significantly. This may be due to the excessive loading of Au quantum dots, which blocks the TiO2 substrate and reduces light absorption. Therefore, controlling the loading amount of Au at 1%~3% can obtain C2H6 products with a higher precipitation rate.

[0110] Furthermore, in order to identify the sources of C2H6 and CO in the product, isotope labeling experiments were carried out, and the product was detected using a synchrotron radiation ultraviolet photoionization mass spectrometer. Fig.18 ,use 13 C-labeled CH4 and unlabeled CO2 were used as reaction gases to obtain 13 C-labeled 13 C2H6 and some of its fragment peaks, as well as unlabeled CO, prove that C2H6 in the product comes from CH4 oxidation, while CO in the product comes from CO2 reduction.

[0111] According to the above embodiments and comparative examples, the Au quantum dot-loaded defective titanium dioxide nanosheets prepared by the present invention are used as photocatalysts to achieve high-performance simultaneous conversion of CH4 and CO2 into valuable fuels. CH4 and CO2 can react with the photogenerated holes and electrons generated by the photocatalyst, respectively, to thereby be converted. According to spectroscopy tests, it is shown that metal-loaded defective titanium dioxide nanosheets have stronger light absorption capacity and electron-hole separation efficiency, and thus have good photocatalytic properties. In addition, defective titanium dioxide-loaded catalysts have stronger CH4 and CO2 adsorption capacity, which lays the foundation for achieving simultaneous conversion of CH4 and CO2. This invention provides valuable guidance for exploring the preparation of high-performance photocatalysts for co-conversion of CH4 and CO2.

[0112] The above embodiments are only used to help understand the method and core idea of ​​the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A defective titanium dioxide supported catalyst, It is characterized in that It includes a carrier and metal Au loaded on the surface of the carrier; The carrier is a defective titanium dioxide nanosheet with oxygen vacancies.

2. The defective titanium dioxide supported catalyst according to claim 1, It is characterized in that The loading amount of the metal Au is 1% to 3%.

3. The defective titanium dioxide supported catalyst according to claim 1, It is characterized in that The thickness of the defective titanium dioxide nanosheet is 3-5 nm; The average particle size of the metal Au is 1-8 nm.

4. The method for preparing the defective titanium dioxide supported catalyst according to any one of claims 1 to 3, It is characterized in that The following steps are involved: S1) mixing titanium dioxide nanosheets and a salt solution of metal gold, and removing the solvent to obtain a mixed powder; S2) calcining the mixed powder in a hydrogen and argon atmosphere to obtain a defective titanium dioxide supported catalyst.

5. The preparation method according to claim 4, It is characterized in that The titanium dioxide nanosheets are prepared according to the following method: The titanium source compound and the acid compound are mixed and subjected to a hydrothermal reaction to obtain titanium dioxide nanosheets.

6. The preparation method according to claim 5, It is characterized in that The titanium source compound includes tetrabutyl titanate; The acidic compound includes hydrofluoric acid; The temperature of the hydrothermal reaction is 160-200° C.; the time of the hydrothermal reaction is 12-24 hours.

7. The preparation method according to claim 4, It is characterized in that The metal gold salt solution includes HAuCl 4 Solution, NaAuCl 4 One or more of the solutions; The calcination temperature is 300-500°C; the calcination time is 1-2h; The heating rate of the calcination is 2-10 °C / min; The hydrogen-argon atmosphere is a mixture of hydrogen and argon, and the volume content of hydrogen is 2% to 20%.

8. Use of the defective titanium dioxide supported catalyst according to any one of claims 1 to 3 or the defective titanium dioxide supported catalyst prepared by the preparation method according to any one of claims 4 to 7 as a catalyst for the co-conversion of methane and carbon dioxide.

9. A method for co-converting methane and carbon dioxide, It is characterized in that The following steps are involved: The defective titanium dioxide supported catalyst described in any one of claims 1 to 3 or the defective titanium dioxide supported catalyst prepared by the preparation method described in any one of claims 4 to 7 is used to catalyze the photoreaction of methane and carbon dioxide to obtain ethane and carbon monoxide.

10. The method according to claim 9, It is characterized in that The light source of the illumination reaction is selected from any one of a xenon lamp, a high-pressure mercury lamp, an LED lamp or an iodine tungsten lamp; The power of the light source in the light reaction is 100-1000 mW cm -2 ; The light reaction time is 0.5~4 h; The volume ratio of the methane to the carbon dioxide is 1:19-19:1.

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