Preparation method of a photo-thermal carbon dioxide hydrogenation to methane catalyst

Abstract

The application discloses a preparation method of a photo-thermal carbon dioxide hydrogenation methane catalyst. The catalyst is prepared through processes of solvent-thermal crystallization for preparing a precursor, calcination for preparing carbon-coated titanium dioxide, and immersion reduction for preparing a product. The photo-thermal performance of metal oxide is improved by using the metal oxide and carbon-based material, and the material has good photo-thermal catalytic performance. The material is black as a whole due to the carbon material coated on the surface, has a relatively narrow band gap or rich surface defects, has a relatively wide spectral absorption rate and good photo-generated carrier separation efficiency, and finally has excellent photo-thermal catalytic performance.

Description

Technical Field

[0001] The present invention belongs to the field of photothermal catalytic carbon dioxide hydrogenation to methane, and particularly relates to a method for preparing a photothermal carbon dioxide hydrogenation to methane catalyst. Background Art

[0002] The massive consumption of fossil fuels by human activities and social development has caused serious environmental problems and energy crises across the globe. Green, low-carbon development is the general trend, and the world is striving towards carbon neutrality. Achieving the dual carbon goals requires reducing carbon dioxide emissions.

[0003] Currently, there are many methods for treating CO2, such as CCUS technology (carbon capture, utilization and storage). However, reducing carbon dioxide to value-added chemicals is one of the most promising sustainable technologies to address the global energy crisis and greenhouse effect. Carbon dioxide conversion can be achieved through a variety of catalytic methods, such as thermal catalysis, electrocatalysis, photocatalysis and photothermal catalysis. Among them, thermal catalytic carbon dioxide reduction has a relatively high energy cost and relatively low product selectivity; the electrocatalytic carbon dioxide reduction reaction barrier is relatively high, and the reaction kinetics are relatively slow; photocatalytic carbon dioxide reduction is limited by the use of solar energy, and the photocatalytic reaction rate is relatively low; however, photothermal carbon dioxide reduction has gradually become a hot topic of research due to its excellent characteristics. TiO2 is an excellent photocatalytic semiconductor material. Its energy band structure matches the CO2 reduction potential and can be reduced to a variety of products. However, it can only use ultraviolet light, which leads to its low utilization of the solar spectrum. The photothermal catalytic CO2 conversion efficiency is at a low level (in μmol g -1 h -1 within the scope).

[0004] Based on this, in order to solve the above existing problems, the present invention is proposed. Summary of the Invention

[0005] In response to the above technical problems, the present invention aims to provide a method for preparing a photothermal carbon dioxide hydrogenation to methane catalyst, which is prepared by the following processes: preparing a precursor by solvent thermal crystallization, preparing carbon-coated titanium dioxide by calcination, and preparing a product by impregnating agent reduction. The present invention uses a composite of metal oxides and carbon-based materials to significantly improve the photothermal performance of the metal oxides, thereby exhibiting good photothermal catalytic performance. Since the surface of the material is coated with carbon material, the material is black as a whole, generally has a narrow band gap or abundant surface defects, and thus has a wide spectral absorption rate and good photogenerated carrier separation efficiency, and ultimately exhibits excellent photothermal catalytic performance.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for preparing a catalyst for photothermal carbon dioxide hydrogenation to methane is carried out in the following order:

[0008] S1. Mix the tetrabutyl titanate solution and the isopropyl alcohol solution of hexamethylenetetramine, stir evenly, transfer the mixed solution to a crystallization kettle, and perform solvothermal crystallization at a crystallization temperature of 60 to 200° C. for 12 to 48 hours;

[0009] S2. After the solvothermal crystallization is completed, the solid is collected by filtration, washed with ethanol, dried, and then calcined in a tube furnace. The solid powder collected after calcination is carbon-coated titanium dioxide;

[0010] S3. Nickel oxide supported on nitrogen-doped carbon-coated titanium dioxide is obtained by an impregnation method, and then reduced under a reducing gas to prepare a metal nickel nanoparticle catalyst supported on nitrogen-doped carbon-coated titanium dioxide.

[0011] As a limitation of the present invention:

[0012] (1) In step S1, the molar ratio of tetrabutyl titanate to hexamethylenetetramine is 0.3 to 3:1.

[0013] (2) In step S2, the drying temperature is 60-120° C., and the drying time is 6-24 hours.

[0014] (3) In step S2, the calcination temperature is 400-800°C, the calcination time is 2-4 hours, and the calcination atmosphere is N2 or Ar.

[0015] (4) In step S3, the process of the impregnation method is as follows:

[0016] A nickel nitrate hexahydrate aqueous solution is prepared, a nitrogen-doped carbon-coated titanium dioxide carrier is ground into powder, and the powder is dissolved in the aqueous solution, wherein the mass ratio of the nickel nitrate hexahydrate to the nitrogen-doped carbon-coated titanium dioxide carrier is 0.05-3.3:1, ultrasonic stirring is performed to uniformly mix the nickel nitrate hexahydrate aqueous solution, and then the nickel nitrate hexahydrate aqueous solution is added dropwise to the nitrogen-doped carbon-coated titanium dioxide carrier aqueous solution, and the mixture is placed at room temperature for 6-24 hours and then dried. After drying, the mixture is ground into powder and calcined to obtain titanium dioxide carrier-loaded nickel oxide.

[0017] (V) In step S3, the reducing gas is a 10% Vol H2 / Ar mixed gas, the reducing temperature is 400-700°C, and the reducing time is 0.5-3h.

[0018] As a further limitation of the present invention,

[0019] (1) In step S3, the drying temperature is 60-120° C., and the drying time is 6-24 hours.

[0020] (2) In step S3, the calcination temperature is 400-800°C, the calcination time is 2-4 hours, and the calcination atmosphere is N2 or Ar.

[0021] The present invention also has a limitation that the metal nickel nanoparticle catalyst loaded on nitrogen-doped carbon-coated titanium dioxide has a flower ball structure, the carrier is nitrogen-doped carbon-coated titanium dioxide, the active component includes metal nickel nanoparticles located on the carrier, based on the total mass of the catalyst, the Ni loading amount is 0.1 to 40 wt%, and the size of the active component metal nickel nanoparticles is 5 to 20 nm.

[0022] In the present invention, the size of Ni is affected by the proportion of the titanium source, the content and distribution of carbon. The size of the Ni nanoparticles of the present invention is small, and the small particle size is achieved through the strong interaction between the metal particles and the carrier, which will lay a good foundation for the later catalytic process. In the catalytic process of photothermal carbon dioxide methanation, the photothermal conversion ability of TiO2 is used to transfer the generated thermal electrons and photogenerated electrons, and then these electrons are transferred to the TiO2 surface, causing CO2 to decompose into CO*. Then, because Ni metal easily adsorbs and dissociates hydrogen, H2 is dissociated into H atoms by Ni NPs. At the same time, the transferred electrons pass through the nitrogen-doped carbon coating layer to reach the Ni metal surface, accelerating the dissociation of H2, and finally participating in the hydrogenation reaction of the CO* intermediate to produce methane.

[0023] The above technical solution of the present invention is taken as a whole, and the various steps are closely related and influence each other, which jointly determine the morphological characteristics and performance of the product.

[0024] The above technical solution has the following advantages or beneficial effects:

[0025] 1. In the photothermal carbon dioxide hydrogenation to methane catalyst of the present invention, the active component nickel metal nanoparticles are uniformly dispersed on the nitrogen-doped carbon-coated titanium dioxide carrier, thereby enhancing the interaction strength between the active component Ni and the carrier, reducing the Ni particle size, and inhibiting the sintering of Ni particles under high temperature conditions, thereby increasing the activity and stability of the catalyst.

[0026] 3. The Ni-TiO2@NC catalyst prepared by the present invention has good photothermal and photoelectric conversion capabilities. At 275°C, the full spectrum (1200mW / cm 2 ) irradiation, the reaction raw material space velocity is 12000ml / g cat Under the condition of ·h, the conversion rate of carbon dioxide is as high as 71.6%, which is about twice that of the condition without light, and the methane yield is as high as 65.3mmol / g cat ·h, which is about 1.9 times that under the condition without light addition, and the selectivity of the product methane is greater than 99%.

[0027] 4. The present invention adopts a solvent thermal crystallization method to prepare a catalyst precursor, and the obtained catalyst precursor is subjected to high-temperature calcination and hydrogen reduction to prepare a loaded Ni-TiO2@NC catalyst. Compared with the Ni-TiO2 catalyst, the activity and stability of the Ni-TiO2@NC catalyst prepared by the solvent thermal crystallization method in the present invention are greatly improved. In addition, the selectivity of the product has also undergone a fundamental change from methane to carbon monoxide. The Ni-TiO2@NC catalyst prepared by the present invention has good photothermal and photoelectric conversion capabilities, which is very beneficial for photothermal carbon dioxide methanation.

[0028] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 XRD patterns of Ni / TiO2, Ni / 0.25-TiO2@NC, Ni / 0.5-TiO2@NC, Ni / 1.0-TiO2@NC, and Ni / 1.5-TiO2@NC catalysts prepared in comparative example and examples 1-4, respectively;

[0030] Figure 2 Scanning electron micrographs of NiO / TiO2 prepared in Comparative Example 1 and NiO / 0.5-TiO2@NC catalysts prepared in Example 2;

[0031] Figure 3 Transmission electron micrographs of NiO / TiO2 prepared in Comparative Example 1 and NiO / 0.5-TiO2@NC catalysts prepared in Example 2;

[0032] Figure 4 High-resolution transmission electron microscopy images and mapping images of NiO / TiO2 prepared in Comparative Example 1 and NiO / 0.5-TiO2@NC catalysts prepared in Example 2;

[0033] Figure 5 H2-TPR spectra of Ni / 0.25-TiO2@NC, Ni / 0.5-TiO2@NC, Ni / 1.0-TiO2@NC, and Ni / 1.5-TiO2@NC catalysts prepared in Examples 1-4, respectively;

[0034] Figure 6 CO2-TPD spectra of Ni / 0.25-TiO2@NC, Ni / 0.5-TiO2@NC, Ni / 1.0-TiO2@NC, and Ni / 1.5-TiO2@NC catalysts prepared in Examples 1-4, respectively;

[0035] Figure 7In situ XPS spectra of Ni / TiO2 and Ni / 0.5-TiO2@NC catalysts prepared in Comparative Example 1 and Example 2, respectively;

[0036] Figure 8 Transient photocurrent graphs and fluorescence spectra of Ni / 0.25-TiO2@NC, Ni / 0.5-TiO2@NC, Ni / 1.0-TiO2@NC, and Ni / 1.5-TiO2@NC catalysts prepared in Examples 1-4, respectively;

[0037] Figure 9 The carbon dioxide conversion rate and carbon monoxide selectivity of the TiO2@NC catalyst prepared in Comparative Example 2 at different temperatures, with and without light;

[0038] Figure 10 The carbon dioxide conversion rates and methane selectivities of the Ni / 0.25-TiO2@NC, Ni / 0.5-TiO2@NC, Ni / 1.0-TiO2@NC, and Ni / 1.5-TiO2@NC catalysts prepared in Examples 1-4, respectively, at different temperatures with and without light addition;

[0039] Figure 11 The absolute methane yields of Ni / 0.25-TiO2@NC, Ni / 0.5-TiO2@NC, Ni / 1.0-TiO2@NC, and Ni / 1.5-TiO2@NC catalysts prepared in Examples 1-4 at 275°C with and without light addition are shown;

[0040] Figure 12 Carbon dioxide conversion rates of Ni / 0.25-TiO2@NC, Ni / 0.5-TiO2@NC, Ni / 1.0-TiO2@NC, and Ni / 1.5-TiO2@NC catalysts prepared in Examples 1-4, respectively, under different light intensities;

[0041] Figure 13 The apparent activation energies of Ni / 0.25-TiO2@NC, Ni / 0.5-TiO2@NC, Ni / 1.0-TiO2@NC, and Ni / 1.5-TiO2@NC catalysts prepared in Examples 1-4, respectively, under light-added and light-free conditions;

[0042] Figure 14 The change in carbon dioxide conversion rate with reaction time at 275°C under alternating light and dark conditions for the Ni / 0.25-TiO2@NC, Ni / 0.5-TiO2@NC, Ni / 1.0-TiO2@NC, and Ni / 1.5-TiO2@NC catalysts prepared in Examples 1-4, respectively. DETAILED DESCRIPTION

[0043] The following embodiments are merely some of the embodiments of the present invention, rather than all of them. Therefore, the detailed description of the embodiments of the present invention provided below is not intended to limit the scope of the claimed invention, but rather merely represents selected embodiments of the present invention. All other embodiments derived by those skilled in the art based on the embodiments of the present invention without creative effort are intended to fall within the scope of protection of the present invention.

[0044] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments, unless otherwise specified, are all conventional methods in the art.

[0045] (1) Preparation of catalyst

[0046] Example 1: Preparation method of Ni / 0.25-TiO2@NC catalyst

[0047] The catalyst preparation process of this embodiment is as follows:

[0048] S1. Mix the tetrabutyl titanate solution and the isopropyl alcohol solution of hexamethylenetetramine (0.561 g of hexamethylenetetramine, 0.25 mL of tetrabutyl titanate, and 50 mL of isopropyl alcohol solution), stir for 30 min until uniform, transfer the mixed solution to a crystallization kettle, and perform solvothermal crystallization at a crystallization temperature of 60°C for 48 h;

[0049] S2. After the solvothermal crystallization is completed, the solid is collected by filtration, washed with ethanol, and dried at a drying temperature of 120°C for 6 hours. After drying, it is placed in a tube furnace under a nitrogen atmosphere at a calcination temperature of 400°C for 3 hours. The solid powder collected after calcination is nitrogen-doped carbon-coated titanium dioxide;

[0050] S3. Nickel oxide supported on nitrogen-doped carbon-coated titanium dioxide is obtained by an impregnation method. The process of the impregnation method is as follows:

[0051] Take 0.05g of nickel nitrate hexahydrate and prepare it into 1.5mL of solution. Weigh 0.99g of nitrogen-doped carbon-coated titanium dioxide support and grind it into powder, and dissolve it in aqueous solution. Stir it evenly with ultrasonic stirring. Then, add the nickel nitrate hexahydrate aqueous solution dropwise to the nitrogen-doped carbon-coated titanium dioxide support aqueous solution. After placing it at room temperature for 15h, transfer it to an oven at 80°C and dry it for 6h. After drying, grind it into powder and calcine it at a calcination temperature of 800°C and a calcination time of 3h in a N2 atmosphere.

[0052] After calcination, it was placed in a reactor and introduced with a 10% Vol H2 / Ar mixed gas at 400°C for 3 hours to obtain Ni / 0.25-TiO2@C, wherein the Ni loading in the final catalyst was 0.1 wt%.

[0053] Example 2: Preparation method of Ni / 0.5-TiO2@C catalyst

[0054] The catalyst preparation process of this embodiment is as follows:

[0055] S1. Mix the tetrabutyl titanate solution and the isopropyl alcohol solution of hexamethylenetetramine (0.561 g hexamethylenetetramine, 0.5 mL tetrabutyl titanate, 50 mL isopropyl alcohol solution), stir for 30 min until uniform, transfer the mixed solution to a crystallization kettle, and perform solvothermal crystallization at a crystallization temperature of 200°C for 12 h;

[0056] S2. After the solvothermal crystallization is completed, the solid is collected by filtration, washed with ethanol, and dried at a drying temperature of 100°C for 12 hours. After drying, it is placed in a tube furnace under an argon atmosphere at a calcination temperature of 800°C for 4 hours. The solid powder collected after calcination is nitrogen-doped carbon-coated titanium dioxide;

[0057] S3. Nickel oxide supported on nitrogen-doped carbon-coated titanium dioxide is obtained by an impregnation method. The process of the impregnation method is as follows:

[0058] Take 0.396g of nickel nitrate hexahydrate and prepare it into 1.5mL of solution. Weigh 0.92g of nitrogen-doped carbon-coated titanium dioxide support and grind it into powder, dissolve it in aqueous solution, stir it evenly with ultrasound, then add the nickel nitrate hexahydrate aqueous solution dropwise to the nitrogen-doped carbon-coated titanium dioxide support aqueous solution, place it at room temperature for 6h, transfer it to a 120℃ oven and dry it for 24h, grind it into powder and roast it after drying, the roasting temperature is 450℃, the roasting time is 4h, the roasting atmosphere is argon, and after roasting, place it in a reactor and pass 10% Vol H2 / Ar mixed gas at 500℃ for 1h to obtain Ni / 0.25-TiO2@C, where the Ni loading in the final catalyst is 8wt%.

[0059] Example 3: Preparation method of Ni / 1.0-TiO2@NC catalyst

[0060] The catalyst preparation process of this embodiment is as follows:

[0061] S1. Mix the tetrabutyl titanate solution and the isopropyl alcohol solution of hexamethylenetetramine (0.561 g of hexamethylenetetramine, 1.0 mL of tetrabutyl titanate, and 50 mL of isopropyl alcohol solution), stir for 30 min until uniform, transfer the mixed solution to a crystallization kettle, and perform solvothermal crystallization at a crystallization temperature of 150° C. for 16 h;

[0062] S2. After the solvothermal crystallization is completed, the solid is collected by filtration, washed with ethanol, and dried at a drying temperature of 80°C for 15 hours. After drying, it is placed in a tube furnace under an argon atmosphere at a calcination temperature of 600°C for 2 hours. The solid powder collected after calcination is nitrogen-doped carbon-coated titanium dioxide;

[0063] S3. Nickel oxide supported on nitrogen-doped carbon-coated titanium dioxide is obtained by an impregnation method. The process of the impregnation method is as follows:

[0064] Take 1.982g of nickel nitrate hexahydrate and prepare it into 1.5mL of solution. Weigh 0.6g of nitrogen-doped carbon-coated titanium dioxide support and grind it into powder, dissolve it in aqueous solution, stir it evenly with ultrasound, then add the nickel nitrate hexahydrate aqueous solution dropwise to the nitrogen-doped carbon-coated titanium dioxide support aqueous solution, place it at room temperature for 24h, transfer it to a 60°C oven and dry it for 12h, grind it into powder after drying, and calcine it at a calcination temperature of 400°C and a calcination time of 4h in an argon atmosphere. After calcination, place it in a reactor and introduce 10% Vol H2 / Ar mixed gas at 700°C for 0.5h to obtain a NiO / 1.0-TiO2@NC catalyst, wherein the Ni loading in the final catalyst is 40wt%.

[0065] Example 4: Preparation method of Ni / 1.5-TiO2@NC catalyst

[0066] S1. Mix the tetrabutyl titanate solution and the isopropyl alcohol solution of hexamethylenetetramine (0.561 g of hexamethylenetetramine, 1.5 mL of tetrabutyl titanate, and 50 mL of isopropyl alcohol solution), stir for 30 min until uniform, transfer the mixed solution to a crystallization kettle, and perform solvothermal crystallization at a crystallization temperature of 100°C for 20 h;

[0067] S2. After the solvothermal crystallization is completed, the solid is collected by filtration, washed with ethanol, and dried at a drying temperature of 60°C for 24 hours. After drying, it is placed in a tube furnace under an argon atmosphere at a calcination temperature of 700°C for 3 hours. The solid powder collected after calcination is nitrogen-doped carbon-coated titanium dioxide;

[0068] S3. Nickel oxide supported on nitrogen-doped carbon-coated titanium dioxide is obtained by an impregnation method. The process of the impregnation method is as follows:

[0069] Take 0.396g of nickel nitrate hexahydrate and prepare it into 1.5mL of solution. Weigh 0.92g of nitrogen-doped carbon-coated titanium dioxide support and grind it into powder, dissolve it in aqueous solution, stir it evenly with ultrasound, then add the nickel nitrate hexahydrate aqueous solution dropwise to the nitrogen-doped carbon-coated titanium dioxide support aqueous solution, place it at room temperature for 18h, transfer it to a 100℃ oven and dry it for 6h. After drying, grind it into powder and calcine it at 700℃ for 2h in argon atmosphere. After calcination, place it in a reactor and introduce 10% Vol H2 / Ar mixed gas at 700℃ for 0.5h to obtain Ni / 1.5-TiO2@NC catalyst, where the Ni loading in the final catalyst is 8wt%.

[0070] Comparative Example 1: Preparation of Ni / TiO2 catalyst

[0071] (1) Weigh 0.561 g of hexamethylenetetramine and 0.5 mL of tetrabutyl titanate, mix and dissolve them in 50 mL of isopropanol solution, stir for 30 min, then transfer to a 200 °C oven and dry for 12 h to obtain a brown solid, which is then ground and calcined in a muffle furnace at 800 °C for 4 h, and then cooled to obtain a white titanium dioxide carrier.

[0072] (2) Weigh 0.396 g of nickel nitrate hexahydrate to prepare a 1.5 mL solution, weigh 0.92 g of a titanium dioxide carrier, and add the prepared nickel nitrate hexahydrate solution dropwise to the titanium dioxide carrier with a pipette until the mixture is uniform. After standing at room temperature for 6 h, transfer the mixture to a 120°C oven and dry it for 24 h. Then, calcine it in a muffle furnace at 450°C for 4 h to obtain titanium dioxide-supported NiO (NiO / TiO2). The mixture is then placed in a reactor and introduced with a 10% Vol H2 / Ar mixed gas at 500°C for 1 h to obtain Ni / TiO2, wherein the final Ni loading is 8 wt% based on the total mass of the catalyst.

[0073] Comparative Example 2: Preparation of TiO2@NC catalyst

[0074] Weigh 0.561g hexamethylenetetramine and 0.5mL tetrabutyl titanate, mix and dissolve them in 50mL of isopropanol solution, stir for 30min, then transfer to a 200℃ oven and dry for 12h to obtain a brown solid. After grinding, place it in a tube furnace at 800℃ and calcine for 4h in the calcination atmosphere of N2 or Ar. Cool down to obtain a brown-yellow nitrogen-doped carbon-coated titanium dioxide support (TiO2@NC).

[0075] (2) Catalyst characterization

[0076] The products prepared in the above examples and comparative examples were subjected to a series of performance characterizations. Figure 1Shown are XRD patterns of the Ni / TiO2, Ni / 0.25-TiO2@NC, Ni / 0.5-TiO2@NC, Ni / 1.0-TiO2@NC, and Ni / 1.5-TiO2@NC catalysts. The patterns reveal the presence of both rutile and anatase crystalline phases. After treatment in a reducing atmosphere, characteristic diffraction peaks of nickel metal were observed, demonstrating successful nickel loading.

[0077] Figure 2 and Figure 3 These are the SEM and TEM images of NiO / TiO2 and NiO / 0.5-TiO2@NC catalysts, respectively. It can be seen that after nitrogen-doped carbon coating, the catalyst presents a spherical morphology, which increases its specific surface area.

[0078] Figure 4 These are the HRTEM and mapping images of NiO / TiO2 and NiO / 0.5-TiO2@NC catalysts. It can be seen from the figure that the Ni element in NiO / 0.5-TiO2@NC is more evenly distributed than that in NiO / TiO2. It can also be seen that the C and N elements are evenly distributed around it.

[0079] Figure 5 Shown are the H2-TPR diagrams of Ni / TiO2, Ni / 0.25-TiO2@NC, Ni / 0.5-TiO2@NC, Ni / 1.0-TiO2@NC, and Ni / 1.5-TiO2@NC catalysts. It can be seen from the figure that the nickel metal in the Ni / 0.5-TiO2@NC catalyst has a strong interaction with its carrier, is not prone to sintering during the reaction, and has good cycle stability.

[0080] Figure 6 The CO2-TPD diagrams of Ni / TiO2, Ni / 0.25-TiO2@NC, Ni / 0.5-TiO2@NC, Ni / 1.0-TiO2@NC, and Ni / 1.5-TiO2@NC catalysts are shown. It can be seen from the figure that the Ni / 0.5-TiO2@NC catalyst has more medium-strength basic sites, which is conducive to the adsorption and activation of carbon dioxide.

[0081] Figure 7 The in-situ XPS spectra of Ni / TiO2 and Ni / 0.5-TiO2@NC catalysts prepared in Comparative Example 1 and Example 2 respectively. It can be seen from the figure that after the addition of light, the nickel in the Ni / 0.5-TiO2@NC catalyst moves toward the direction of low binding energy, indicating that the electron cloud density of nickel increases and the rate of hydrogen dissociation is accelerated. At the same time, the Ti 3+ The ratio of becomes larger, indicating that the carrier has more oxygen vacancies, which is conducive to the adsorption and activation of more carbon dioxide.

[0082] Figure 8 The transient photocurrent diagrams and fluorescence spectra of Ni / 0.25-TiO2@NC, Ni / 0.5-TiO2@NC, Ni / 1.0-TiO2@NC, and Ni / 1.5-TiO2@NC catalysts prepared in Examples 1, 2, 3, and 4, respectively, show that the recombination efficiency of photogenerated electron-hole pairs in the Ni / 0.5-TiO2@NC catalyst is significantly reduced, indicating that the catalyst has good photoelectric conversion ability.

[0083] Figure 9 The carbon dioxide conversion rate and carbon monoxide selectivity of the TiO2@NC catalyst prepared in Comparative Example 2 at different temperatures with and without light. The figure shows that the TiO2@NC catalyst has almost no catalytic performance, and before nickel metal is loaded, the product selectivity of its TiO2@NC carrier is carbon monoxide.

[0084] (3) Catalyst evaluation

[0085] The catalyst prepared above was pressed into tablets and sieved to obtain catalyst particles of 20 to 40 mesh. The particles were loaded into a fixed bed tubular reactor with a length of 40 cm.

[0086] First, the catalyst prepared above was reduced with 10% Vol H2 / Ar for 1 h, and then a mixture of carbon dioxide, hydrogen and nitrogen was introduced to carry out the reaction. The reaction temperature was 275°C, the pressure was normal pressure, the catalyst mass was 0.16 g, and the carbon dioxide, hydrogen and nitrogen mixture (volume ratio CO2:H2:N2=1:4:2) was 32 mL / min.

[0087] The reaction data looks like this:

[0088] Figure 10 The carbon dioxide conversion rates of Ni / 0.25-TiO2@NC, Ni / 0.5-TiO2@NC, Ni / 1.0-TiO2@NC, and Ni / 1.5-TiO2@NC catalysts at different temperatures with and without light. As can be seen from the figure, after nickel loading, the selectivity of the product changes from carbon monoxide to methane. It can also be seen that Ni / 0.5-TiO2@NC has the best catalytic performance. At 275°C, the carbon dioxide conversion rate is 71.6%, which is about twice that of the condition without light.

[0089] Figure 11The absolute methane yields of Ni / 0.25-TiO2@NC, Ni / 0.5-TiO2@NC, Ni / 1.0-TiO2@NC, and Ni / 1.5-TiO2@NC catalysts at 275°C with and without light. The methane yield of Ni / 0.5-TiO2@NC catalyst is 65.3 mmol / g cat ·h, which is about 1.9 times that under no light conditions.

[0090] Figure 12 The carbon dioxide conversion rates of Ni / 0.25-TiO2@NC, Ni / 0.5-TiO2@NC, Ni / 1.0-TiO2@NC, and Ni / 1.5-TiO2@NC catalysts under different light intensities. It can be seen from the figure that with the increase of light intensity, the catalytic performance of carbon dioxide also increases, indicating that the catalyst has a good light response.

[0091] Figure 13 The apparent activation energy of Ni / 0.25-TiO2@NC, Ni / 0.5-TiO2@NC, Ni / 1.0-TiO2@NC, and Ni / 1.5-TiO2@NC catalysts under light and no light conditions indicates that adding light can reduce the activation energy of the reaction and promote the reaction.

[0092] Figure 14 The carbon dioxide conversion rates of Ni / 0.25-TiO2@NC, Ni / 0.5-TiO2@NC, Ni / 1.0-TiO2@NC, and Ni / 1.5-TiO2@NC catalysts prepared in Examples 1, 2, 3, and 4, respectively, changed with reaction time at 275°C under alternating conditions of light and darkness. After 2880 minutes, there was almost no significant decrease in the carbon dioxide conversion rate, indicating that the activity and stability of the catalyst were improved after carbon coating, and the addition of light was more conducive to the methanation of carbon dioxide.

[0093] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. Application of a catalyst for producing methane from carbon dioxide by photothermal hydrogenation, characterized in that: The preparation method of the catalyst is carried out in the following steps in sequence: S1. Mix the tetrabutyl titanate solution and the isopropyl alcohol solution of hexamethylenetetramine, stir evenly, transfer the mixed solution to a crystallization kettle, and perform solvothermal crystallization at a crystallization temperature of 60-200 °C for 12-48 h; S2. After the solvothermal crystallization is completed, the solid is collected by filtration, washed with ethanol, dried, and then calcined in a tube furnace. The solid powder collected after calcination is nitrogen-doped carbon-coated titanium dioxide; S3. Nickel oxide supported on nitrogen-doped carbon-coated titanium dioxide is obtained by an impregnation method, and then reduced under a reducing gas to prepare a metal nickel nanoparticle catalyst supported on nitrogen-doped carbon-coated titanium dioxide.

2. The use according to claim 1, characterized in that In step S1, the molar ratio of tetrabutyl titanate to hexamethylenetetramine is 0.3-3:

1.

3. The use according to claim 1, characterized in that In step S2, the drying temperature is 60-120° C., and the drying time is 6-24 h.

4. The use according to claim 1, characterized in that In step S2, the calcination temperature is 400-800°C, the calcination time is 2-4 hours, and the calcination atmosphere is N2 or Ar.

5. The use according to claim 1, characterized in that Step S3, the process of the impregnation method is as follows: A nickel nitrate hexahydrate aqueous solution is prepared, a nitrogen-doped carbon-coated titanium dioxide support is ground into powder, and the powder is dissolved in the aqueous solution, the mass ratio of the nickel nitrate hexahydrate to the nitrogen-doped carbon-coated titanium dioxide support is 0.05-3.3:1, ultrasonic stirring is performed to uniformly add the nickel nitrate hexahydrate aqueous solution dropwise into the nitrogen-doped carbon-coated titanium dioxide support aqueous solution, and the mixture is placed at room temperature for 6-24 hours and then dried. After drying, the mixture is ground into powder and calcined to obtain nitrogen-doped carbon-coated titanium dioxide support-loaded nickel oxide.

6. The use according to claim 5, characterized in that The drying temperature is 60-120° C., and the drying time is 6-24 hours.

7. The use according to claim 5, characterized in that The calcination temperature is 400-800° C., the calcination time is 2-4 h, and the calcination atmosphere is N 2 or Ar.

8. The use according to claim 1, characterized in that In step S3, the reducing gas is a 10% Vol H2 / Ar mixed gas, the reduction temperature is 400-700°C, and the reduction time is 0.5-3 h.

9. The use according to any one of claims 1 to 8, characterized in that The catalyst of metal nickel nanoparticles supported on nitrogen-doped carbon-coated titanium dioxide has a flower ball-like structure. The support is nitrogen-doped carbon-coated titanium dioxide. The active component includes metal nickel nanoparticles located on the support. Based on the total mass of the catalyst, the Ni loading amount is 0.1 to 40wt%, and the size of the active component metal nickel nanoparticles is 5 to 20 nm.

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