A metal-supported boron-doped perovskite titanate photothermal catalyst, its preparation method, and its application in catalytic gas-phase ammonia synthesis.

Abstract

This invention relates to a metal-supported boron-doped perovskite titanate photothermal catalyst, its preparation method, and its application in catalytic gas-phase ammonia synthesis, belonging to the field of photothermal catalyst technology. The invention first synthesizes boron-doped perovskite titanate via a hydrothermal doping method. Then, a metal precursor is thoroughly and uniformly mixed with dried boron-doped barium titanate in a solvent, and the metal-supported boron-doped perovskite titanate photothermal catalyst is obtained through heating decomposition or chemical reduction. The photothermal catalyst of this invention requires low-cost equipment and instruments, is easy to operate, and has a low risk factor during preparation. The synthesis process is simple, the principle is clear, and the sample yield is high. The prepared catalyst exhibits strong photoresponsiveness and high surface reduction capacity. Furthermore, the catalytic reaction only requires visible light, making it environmentally friendly. The photothermal catalyst demonstrates high catalytic ammonia synthesis efficiency, maintaining good stability in the catalytic ammonia synthesis efficiency during seven cyclic reactions from temperature activation to photothermal catalysis.

Description

Technical Field

[0001] This invention belongs to the field of photothermal catalyst technology, specifically relating to a metal-supported boron-doped perovskite titanate photothermal catalyst, its preparation method, and its application in catalytic gas-phase ammonia synthesis. Background Technology

[0002] Nitrogen is widely distributed in nature. Apart from a small amount of mineral nitrates in the Earth's crust, nitrogen mainly exists as nitrogen gas, accounting for 78% of the atmosphere by volume. Nitrogen fixation is the primary way organisms utilize nitrogen. Since the last century, the Haber-Bosch process has been used to industrially synthesize ammonia from nitrogen. Nitrogen gas reacts with hydrogen under high temperature and pressure (350–450℃, 150–200 atm) to produce ammonia, which is widely used in various industries. However, with the overexploitation and use of fossil fuels, environmental damage and energy depletion have begun to limit human survival and development. The Haber-Bosch process no longer aligns with future industrial development trends. Therefore, researching green nitrogen fixation processes driven by new energy sources has practical significance and value.

[0003] Photovoltaic energy is an abundant, sustainable, and pollution-free source. Numerous studies have demonstrated the feasibility of nitrogen fixation under mild conditions using light energy as a driving force. However, the widely studied aqueous photocatalytic nitrogen fixation suffers from the difficulty of separating the ammonia and water products. Photocatalytic gas-phase nitrogen fixation avoids this problem while also enabling hydrogen storage through the synthesis of ammonia from hydrogen, thus aiding in the storage and utilization of hydrogen energy. Currently, photocatalytic gas-phase nitrogen fixation faces two main challenges: improving the utilization rate of light energy and designing inexpensive and efficient active sites.

[0004] In photocatalytic reactions, semiconductor catalysts absorb light energy to generate photogenerated electron-hole pairs. After separation, these electrons and holes transfer to active sites on the catalyst surface, where they redox reactants. By introducing defects, doping, or supporting co-catalysts, the composition, structure, and surface properties of semiconductor catalysts can be modulated to reduce the catalyst band gap, expand the catalyst's light absorption range, and construct highly efficient active sites on the catalyst surface to enhance the catalyst's reactivity. Summary of the Invention

[0005] The purpose of this invention is to provide a metal-supported boron-doped perovskite titanate photothermal catalyst, its preparation method, and its application in catalytic gas-phase ammonia synthesis.

[0006] The preparation method of a metal-supported boron-doped perovskite titanate photothermal catalyst according to the present invention comprises the following steps:

[0007] (1) Boron-doped perovskite titanate was synthesized by hydrothermal doping method;

[0008] The hydrothermal method refers to a method of heating and dissolving an aqueous solution of a solid or liquid precursor in a sealed reaction vessel to recrystallize and form the target compound. Specifically, the method involves weighing a titanium-containing precursor, a boron-containing precursor, and a barium, strontium, or calcium-containing precursor and mixing them in deionized water until uniformly dispersed. The molar ratio of the titanium-containing precursor to the barium, strontium, or calcium-containing precursor is 1:1 to 5. The molar amount of the boron-containing precursor is 2% to 50% of that of the titanium-containing precursor. Sodium hydroxide with a molar ratio of 2 to 5:1 to the titanium-containing precursor is added to the above mixture. After stirring evenly, the mixture is transferred to a polytetrafluoroethylene reaction vessel and reacted at 220 to 240°C for 1.5 to 3.0 hours. After the reaction vessel cools to room temperature, the reaction product is washed multiple times with deionized water and vacuum dried at 20 to 30°C for 20 to 30 hours to obtain boron-doped perovskite titanate powder.

[0009] The titanium-containing precursors can be titanium dioxide, titanium tetrachloride, or tetrabutyl titanate; the boron-containing precursors can be boron trioxide, titanium boride, or boric acid; and the barium, strontium, or calcium-containing precursors can be barium chloride, barium hydroxide, strontium chloride, strontium hydroxide, calcium chloride, or calcium hydroxide.

[0010] The obtained perovskite titanate refers to an oxide with the general molecular formula ABO3, where A and B both represent metallic elements. A is an alkaline earth metal, such as Ca, Sr, Ba, etc., and B is the metal Ti.

[0011] (2) The metal precursor and the boron-doped perovskite titanate dried in step (1) are thoroughly and uniformly mixed in a solvent, and the metal-supported boron-doped perovskite titanate photothermal catalyst is obtained by heating decomposition or chemical reduction.

[0012] The metal precursor refers to a compound containing metallic iron, ruthenium, and platinum, and may further be iron pentacarbonyl, ruthenium trichloride, ruthenium dodecylcarbonyltriruthenium, chloroplatinic acid hexahydrate, etc.

[0013] The solvent is water or an organic solvent, such as methanol, ethanol, acetone, tetrahydrofuran, etc., and the concentration of the metal precursor in the solvent is 0.1 to 10 mg / mL.

[0014] The mass of the metal precursor is 0.05 to 10% of the mass of the boron-doped barium titanate titanate.

[0015] The aforementioned thermal decomposition refers to uniformly mixing the metal precursor with boron-doped perovskite titanate in a solvent, drying the solvent under vacuum, and then maintaining the mixture at 100–400°C for 1–10 hours.

[0016] The chemical reduction is carried out in two ways. One method is to uniformly mix the metal precursor with boron-doped perovskite titanate in a solvent and then reduce it under ultraviolet light for 15-30 min to obtain a metal-supported boron-doped perovskite titanate photothermal catalyst. The other method is to dry the solvent in a vacuum and then maintain it at 300-800℃ for 2-12 h in a reducing atmosphere such as hydrogen and carbon monoxide to obtain a metal-supported boron-doped perovskite titanate photothermal catalyst.

[0017] (3) Ammonia is synthesized in the gas phase by using a metal-supported boron-doped perovskite titanate photothermal catalyst under certain temperature and light conditions.

[0018] The temperature range is 0–400°C.

[0019] The illumination includes ultraviolet light, visible light, and near-infrared light, with a wavelength range of 190–2500 nm.

[0020] The aforementioned gas-phase ammonia synthesis refers to a mixture of nitrogen and hydrogen as reactants, with nitrogen comprising 20-30% by volume and a pressure of 0.1-50 atm.

[0021] This invention has the following significant advantages:

[0022] 1) The equipment and instruments required for the preparation of photothermal catalysts are low in cost, easy to operate, and have a low risk factor. The synthesis process is simple, the principle is clear, and the sample yield is high.

[0023] 2) The prepared photothermal catalyst has stable physicochemical properties, and the surface-supported metal morphology is nanoparticles with a diameter range of 1-5 nm.

[0024] 3) The prepared catalyst exhibits strong photoresponsiveness and high surface reduction capacity; furthermore, the catalytic reaction requires only visible light to drive it, making it environmentally friendly. The photothermal catalyst demonstrates high efficiency in ammonia synthesis. Under visible light irradiation conditions with a system pressure of 0.2 atm and a wavelength above 400 nm, and a maximum reaction temperature of 150℃, the photothermal ammonia synthesis rate reaches 3202 μg / g / h, which is higher than that of Ru@K2Ta2O under the same conditions. 6-x The photothermal catalyst (published in Angewandte Chemie International Edition, titled "Defect Pyrochlore-Type Mott–Schottky Photocatalysts for Enhanced Ammonia Synthesis at Low Pressure") achieved 1.8 times the ammonia synthesis efficiency. In seven cycles, the photothermal catalytic ammonia synthesis efficiency of the catalyst remained relatively stable, and the surface properties of the catalyst were well maintained during the reaction process. Attached Figure Description

[0025] Figure 1 The XRD patterns of BaTiO3, B-BaTiO3-1, and B-BaTiO3 in Example 1 demonstrate that the synthesized barium titanate and boron-doped barium titanate are both pure-phase perovskite structures.

[0026] Figure 2 The XPS images of barium titanate (BaTiO3) with perovskite structure and barium boron-doped perovskite structure (B-BaTiO3) in Example 1 show that boron was successfully doped into barium titanate.

[0027] Figure 3 The UV-Vis absorption spectra of BaTiO3, B-BaTiO3-1, and B-BaTiO3 prepared in Example 1 are shown. The test data prove that the boron-doped samples have enhanced light absorption in the visible light region, and the higher the doping ratio, the higher the visible light absorption.

[0028] Figure 4 The image shows a TEM image of Ru / B-BaTiO3 in Example 2. Ruthenium metal is loaded on the catalyst surface in the form of nanoparticles (darker spots on the crystal surface). The diameter of the ruthenium metal (inset) is mainly between 1.5 and 2.0 nm.

[0029] Figure 5 XPS images of Ru on the surface of Ru / B-BaTiO3 and Ru / BaTiO3 samples in Example 2 not only demonstrate the successful loading of ruthenium, but the smaller binding energy also proves that the ruthenium on the surface of Ru / B-BaTiO3 samples has a higher electron density and stronger reducing power.

[0030] Figure 6 The figure shows the reaction rate of the catalyst sample in Example 3 for photothermal catalytic gas-phase ammonia synthesis at 150°C under visible light irradiation. The results show that Ru / B-BaTiO3 has the highest photothermal catalytic activity for ammonia synthesis.

[0031] Figure 7 The figure shows the experimental data of photothermal catalytic gas-phase ammonia synthesis at 150°C for barium boron titanate samples with different ruthenium mass ratios in Example 4. The results show that the barium boron titanate with a ruthenium loading mass ratio of 5% has the highest photothermal catalytic ammonia synthesis activity.

[0032] Figure 8 The figure shows the cyclic experimental data of the photothermal catalytic ammonia synthesis reaction of Ru / B-BaTiO3 in Example 5. The experimental data proves that the catalytic ammonia synthesis efficiency of Ru / B-BaTiO3 remained highly stable in seven photothermal reaction cycles. Detailed Implementation

[0033] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0034] Example 1:

[0035] Barium titanate was synthesized using a hydrothermal method. 0.89 g of titanium tetrachloride and 3.34 g of barium chloride dihydrate were weighed and mixed in 40 mL of deionized water, stirring until completely dissolved. 2.00 g of sodium hydroxide was weighed and added to the homogeneous mixture. The mixture was then transferred to a 55 mL polytetrafluoroethylene (PTFE) reactor and reacted in a 230 °C oven for 2 hours. After the reactor cooled to room temperature, the reaction product was washed several times with deionized water and dried in a vacuum drying oven at 25 °C for 24 hours to obtain approximately 1.50 g of white barium titanate (BaTiO3) powder.

[0036] Boron-doped barium titanate was synthesized using a hydrothermal method. 0.89 g of titanium tetrachloride, a certain amount of titanium boride (0.17 g of 5% molar percentage TiB2 and 0.68 g of 20% molar percentage TiB2), and 3.34 g of barium chloride dihydrate were weighed and mixed in 40 mL of deionized water, stirred until completely dissolved. The molar amounts of titanium boride were 5% and 20% of titanium tetrachloride. 2.00 g of sodium hydroxide was weighed and added to the homogeneous mixture. The mixture was stirred and transferred to a 55 mL polytetrafluoroethylene (PTFE) reactor, and reacted in a 230 °C oven for 2 hours. After the reactor cooled to room temperature, the reaction product was washed several times with deionized water and dried in a vacuum drying oven at 25 °C for 24 hours, yielding approximately 1.3 g and 1.2 g of blue powders of boron-doped barium titanate (B-BaTiO3-1 and B-BaTiO3), respectively. Samples with a 5% molar percentage of TiB2 were labeled B-BaTiO3-1 and TiB2. The sample with a 20% molar ratio was labeled as B-BaTiO3.

[0037] In this embodiment, BaTiO3, B-BaTiO3-1, and B-BaTiO3 were prepared, and the XRD, XPS, and UV-Vis spectra of the prepared materials were tested. Figure 1 As shown, XRD data confirm that all synthesized samples have a pure-phase perovskite crystal structure; Figure 2 As shown, XPS confirms that boron is doped into barium titanate; Figure 3 As shown, the visible light absorption capacity of the sample increases with the increase of boron doping ratio.

[0038] Example 2:

[0039] 300 mg of BaTiO3 and 30 mg of dodecyltriruthenium were weighed and uniformly mixed in 10 mL of anhydrous ultradry tetrahydrofuran solution. The solvent was dried under vacuum and the temperature was raised to 150 °C and held for 1 h to obtain approximately 0.31 g of ruthenium-supported barium titanate (Ru / BaTiO3).

[0040] 300 mg of B-BaTiO3 and 30 mg of dodecyltriruthenium were weighed and uniformly mixed in 10 mL of anhydrous ultra-dry tetrahydrofuran solution. The solvent was dried under vacuum and the temperature was raised to 150 °C and held for 1 h to obtain approximately 0.31 g of ruthenium-supported barium boron titanate (Ru / B-BaTiO3).

[0041] In this embodiment, ruthenium was loaded onto the surfaces of BaTiO3 and B-BaTiO3, and Ru / B-BaTaO3 was characterized by TEM, while Ru / BaTiO3 and Ru / B-BaTaO3 were characterized by XPS. Figure 4 As shown, the TEM image confirms that ruthenium was successfully loaded onto the surface of B-BaTaO3. Statistical analysis shows that the diameter of most ruthenium nanoparticles on the B-BaTaO3 surface is between 1.5 and 2 nm. Figure 5 As shown, XPS tests demonstrate that ruthenium nanoparticles on the surface of B-BaTaO3 have a smaller binding energy and stronger reducing power than ruthenium nanoparticles on the surface of BaTaO3.

[0042] Example 3:

[0043] 100 mg of B-BaTiO3 and 3 mg of chloroplatinic acid hexahydrate were weighed and mixed evenly in 40 mL of methanol. Metal reduction loading was carried out under ultraviolet light for 20 min. After filtration and drying, about 0.1 g of platinum-loaded barium boron titanate (Pt / B-BaTiO3) was obtained.

[0044] BaTiO3 and Ru / BaTiO3 were respectively added 3-1Ru / BaTiO3, Ru / B-BaTiO3, and Pt / B-BaTiO3 were respectively spread evenly at the bottom of five quartz reactors. Air was removed from the reactors by vacuuming, and then the reactors were heated to 200℃ and held for 2 hours to remove residual solvents and impurities from the catalyst surface. Next, a 0.2 atm H2 / N2 mixture (volume ratio 3:1) was introduced into each of the five quartz reactors. The reactors were placed in a room temperature environment (20℃~30℃) and irradiated with the same visible light source (λ>400nm) for 5 minutes to carry out the catalytic gas-phase ammonia synthesis reaction. The catalyst surface naturally heated up under the light, reaching a temperature of 150℃ within the reaction time. The ammonia gas produced by the reaction was absorbed by 2 mL of deionized water to obtain an aqueous solution of ammonium ions. The concentration of the ammonium ion aqueous solution was obtained using ultraviolet spectroscopy, and the ammonia synthesis reaction rate of each catalyst was calculated based on the concentration. The reaction results are as follows: Figure 6 As shown, Ru / B-BaTiO3 exhibits the highest photothermal catalytic efficiency for ammonia synthesis (column 4).

[0045] Example 4:

[0046] (1) Weigh 300 mg of B-BaTiO3 and 12 mg of dodecyltriruthenium carbonyl and mix them evenly in 10 mL of anhydrous ultra-dry tetrahydrofuran solution. The solvent is dried under vacuum and the temperature is raised to 150 °C and held for 1 h to obtain about 0.3 g of ruthenium-loaded barium boron titanate with a mass ratio of 2% of dodecyltriruthenium carbonyl to B-BaTiO3 (the mass fraction of metallic ruthenium in dodecyltriruthenium carbonyl is calculated as 50%).

[0047] (2) Weigh 300 mg of B-BaTiO3 and 30 mg of dodecyltriruthenium carbonyl and mix them evenly in 10 mL of anhydrous ultra-dry tetrahydrofuran solution. The solvent is dried under vacuum, and the temperature is raised to 150 °C and held for 1 h to obtain approximately 0.31 g of barium boron doped titanate supported on ruthenium carbonyl triruthenium and B-BaTiO3 at a mass ratio of 5%.

[0048] (3) Weigh 300 mg of B-BaTiO3 and 60 mg of dodecyltriruthenium carbonyl and mix them evenly in 10 mL of anhydrous ultra-dry tetrahydrofuran solution. The solvent is dried under vacuum and the temperature is raised to 180 °C and held for 2 h under vacuum to obtain about 0.32 g of barium boron titanate supported on metallic ruthenium carbonyl triruthenium and B-BaTiO3 in a mass ratio of 10%.

[0049] Boron-doped barium titanate catalysts with different mass ratios were spread evenly at the bottom of three quartz reactors. The reactors were then evacuated and heated to 200°C for 2 hours to remove other gases and residual solvents and impurities from the catalyst surface. Next, a 0.2 atm H2 / N2 mixture (volume ratio 3:1) was introduced into each quartz reactor. The reactors were placed in a room temperature environment (20°C–30°C) and irradiated with the same visible light source (λ>400nm) for 5 minutes to carry out the catalytic gas-phase ammonia synthesis reaction. The catalyst surface naturally heated up under the light, reaching a temperature of 150°C within the reaction time. The reaction efficiency of photothermal catalysts with different ruthenium ratios was compared.

[0050] In this embodiment, different mass ratios of dodecyltriruthenium carbonyl were supported on B-BaTiO3, and the photothermal catalytic synthesis rate of the prepared catalyst was compared. Figure 7 As shown, the highest efficiency of photothermal catalytic synthesis of ammonia was achieved by barium boron titanate with a mass ratio of 5% to ruthenium dodecyltriruthenium and B-BaTiO3 (Column 3), indicating that under this condition, the ruthenium-supported barium boron titanate exhibited the strongest photothermal catalytic activity for ammonia synthesis.

[0051] Example 5:

[0052] Ru / B-BaTiO3 (ruthenium dodecylcarbonyl triruthenium to B-BaTiO3 mass ratio 5%) was evenly spread on a substrate with a volume of 72 cm³. 3 A sealed quartz reactor was evacuated and heated to 200°C for 2 hours to remove other gases and residual solvents and impurities from the catalyst surface. A H2 / N2 mixture (volume ratio 3:1) at a total pressure of 0.2 atm was introduced into the quartz reactor, and a photothermal catalytic gas-phase ammonia synthesis reaction was carried out under visible light irradiation for 5 minutes. After yield testing, the reaction system was evacuated again, heated to 200°C for 2 hours, cooled to room temperature, and then a H2 / N2 mixture (volume ratio 3:1) at a total pressure of 0.2 atm was introduced into the quartz reactor. A photothermal catalytic gas-phase ammonia synthesis reaction was carried out under visible light irradiation for 10 minutes. This process was repeated multiple times to test the cyclic performance of the photothermal catalyst.

[0053] like Figure 8 As shown, Ru / B-BaTiO3 (ruthenium dodecylcarbonyl to B-BaTiO3 mass ratio 5%) maintained a relatively stable ammonia synthesis rate in seven photothermal catalytic cycle experiments.

Claims

1. A method for preparing a metal-supported boron-doped perovskite titanate photothermal catalyst, comprising the following steps: (1) Boron-doped perovskite titanate was synthesized by hydrothermal doping. Weigh out titanium-containing precursors, boron-containing precursors, and barium, strontium, or calcium-containing precursors and mix them in deionized water. Stir until uniformly dispersed to obtain a mixed solution. The molar ratio of titanium-containing precursors to barium, strontium, or calcium-containing precursors is 1:1~5, and the molar amount of boron-containing precursors is 2%~50% of that of titanium-containing precursors. Weigh out sodium hydroxide at a molar ratio of 2~5:1 with the titanium-containing precursors and add it to the mixed solution. After stirring evenly, transfer the solution to a polytetrafluoroethylene (PTFE) reactor and react at 220~240 °C for 1.5~3.0 hours. After the reactor cools to room temperature, wash the reaction product several times with deionized water for 20~30 minutes. Vacuum drying at ℃ for 20-30 hours yields boron-doped perovskite titanate powder; the titanium-containing precursor is titanium dioxide, titanium tetrachloride, or tetrabutyl titanate; the boron-containing precursor is boron trioxide, titanium boride, or boric acid; and the barium, strontium, or calcium-containing precursor is barium chloride, barium hydroxide, strontium chloride, strontium hydroxide, calcium chloride, or calcium hydroxide. (2) The metal precursor and the boron-doped perovskite titanate dried in step (1) are thoroughly and uniformly mixed in a solvent, and the metal-supported boron-doped perovskite titanate photothermal catalyst is obtained by heating decomposition or chemical reduction; the metal precursor is iron pentacarbonyl, ruthenium trichloride, ruthenium dodecyl carbonyl or chloroplatinic acid hexahydrate; the solvent is water or an organic solvent, and the organic solvent is methanol, ethanol, acetone or tetrahydrofuran; the concentration of the metal precursor in the solvent is 0.1~10 mg / mL, and the mass of the metal precursor is 0.05~10% of the mass of the barium boron titanate titanate.

2. The method for preparing a metal-supported boron-doped perovskite titanate photothermal catalyst as described in claim 1, characterized in that: In step (2), the thermal decomposition refers to uniformly mixing the metal precursor and boron-doped perovskite titanate in a solvent, drying the solvent under vacuum, and then maintaining the mixture at 100~400 ℃ for 1~10 h to obtain a metal-supported boron-doped perovskite titanate photothermal catalyst.

3. The method for preparing a metal-supported boron-doped perovskite titanate photothermal catalyst as described in claim 1, characterized in that: In step (2), the chemical reduction involves uniformly mixing the metal precursor with boron-doped perovskite titanate in a solvent and reducing it under ultraviolet light for 15-30 min to obtain a metal-supported boron-doped perovskite titanate photothermal catalyst; or drying the solvent in a vacuum and then maintaining it at 300-800 °C for 2-12 h in a hydrogen or carbon monoxide reducing atmosphere to obtain a metal-supported boron-doped perovskite titanate photothermal catalyst.

4. A metal-supported boron-doped perovskite titanate photothermal catalyst, characterized in that: It is prepared by the method described in any one of claims 1 to 3.

5. The application of the metal-supported boron-doped perovskite titanate photothermal catalyst according to claim 4 in the catalytic gas-phase synthesis of ammonia.

6. The application of the metal-supported boron-doped perovskite titanate photothermal catalyst as described in claim 5 in the catalytic gas-phase ammonia synthesis, characterized in that: It utilizes a metal-supported boron-doped perovskite titanate photothermal catalyst to catalyze the gas-phase synthesis of ammonia under certain temperature and light conditions.

7. The application of the metal-supported boron-doped perovskite titanate photothermal catalyst as described in claim 6 in the catalytic gas-phase ammonia synthesis, characterized in that: The temperature range is 0~400 ℃, and the light source is ultraviolet, visible or near-infrared light with a wavelength range of 190~2500 nm; gas phase ammonia synthesis refers to the reaction of all reactants being gases, which are a mixture of nitrogen and hydrogen, with the volume percentage of nitrogen in the mixture being 20~30% and the gas pressure being 0.1~50 atm.

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