A method for preparing and applying a tungsten oxide-supported interstitial H-atom-doped photocatalyst

Abstract

This invention discloses a method for preparing and applying a tungsten oxide-supported interstitial H-atom-doped photocatalyst. The method involves preparing WO3 by high-temperature hydrothermal reduction of WCl6 dissolved in anhydrous ethanol, followed by photo-assisted in-situ reduction with lactic acid solution to synthesize H atoms interstitially doped into the interstitial spaces of the WO3 crystal lattice. The H atoms obtained in this invention... x WO3 exhibits high ammonia yield during photocatalytic nitrogen reduction and holds great promise for solar energy utilization and the conversion of dual-energy sources into high-value-added chemicals.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of photocatalytic nitrogen reduction, aiming at the shortcomings of traditional nitrogen fixation technology, such as high energy consumption and heavy pollution, and the bottleneck of current mild artificial nitrogen fixation technology, such as low yield, poor selectivity and system limitation. Specifically, it relates to the preparation method and application of tungsten oxide as a carrier interstitially doped with H atom photocatalyst. The modified catalyst can realize photocatalytic conversion of nitrogen and has high ammonia generation rate. The present application will provide a new efficient, green and mild nitrogen fixation technology, and also provide a new idea for the application and development of renewable solar energy. BACKGROUND

[0002] Ammonia is one of the most basic chemical raw materials in modern industrial and agricultural production, and is widely used in the synthesis of fertilizers, medicaments, explosives and resins. At the same time, due to its high hydrogen content, high volume energy density, low liquefaction pressure and transportation safety, it is also considered as a potential carbon-free energy carrier. The conversion of abundant N2 in the atmosphere into ammonia is not only crucial for the maintenance of life, but also plays an important role in the development of national economy. Although the raw materials are inexhaustible and inextinguishable, due to the high stability of N≡N bond (bond energy is as high as 940.95 KJ·mol -1 ), the process from nitrogen to ammonia (i.e. nitrogen fixation process (NRR)) is extremely difficult. The nitrogen fixation process can be generally divided into natural nitrogen fixation (including biological nitrogen fixation and lightning nitrogen fixation) and artificial nitrogen fixation. Among them, biological nitrogen fixation is to obtain nitrogen compounds by catalyzing multiple proton and electron transfer processes under environmental conditions by nitrogenase. This process is mild in conditions and efficient in reaction, and requires 6-24 ATP per mole of N2 reduction, which is the most ideal nitrogen fixation route. However, relying solely on natural nitrogen fixation cannot meet the growing demand for ammonia, and artificial nitrogen fixation has emerged as the main source of practical application needs. At present, the industrial scale artificial nitrogen fixation technology is mainly the Haber-Bosch method, which has a conversion efficiency of 20 %, realizes the intensification and scaling development of artificial nitrogen fixation, and directly promotes the unprecedented growth of global food production and population. Although this technology has undergone more than a hundred years of development, it still needs to be carried out under high temperature and high pressure conditions (350-550 ℃, 200-300 atm), and its annual average energy consumption accounts for 1-2 % of the world's total energy consumption, and the annual emission of greenhouse gas CO2 accounts for about 1.6 % of the total greenhouse gas, which undoubtedly aggravates environmental pollution and energy shortage. Therefore, it is necessary to develop green, low-consumption and efficient artificial nitrogen fixation technology to realize the sustainable development of human beings, which is also the focus of researchers and a great challenge.

[0003] Inspired by microbial nitrogen fixation in nature, electrocatalytic nitrogen fixation has attracted much attention and is considered a green and safe ammonia synthesis technology. However, this technology still faces problems such as low ammonia production rate, poor selectivity, low faradaic efficiency, and high applied bias voltage; at the same time, the system requires an external circuit and consumes additional electrical energy, and its applicability is limited. Therefore, how to directly utilize green renewable energy to replace the additional electrical energy consumed, while suppressing the competitive reaction of hydrogen reduction to hydrogen gas and improving nitrogen fixation efficiency and selectivity, is the key bottleneck problem currently facing mild artificial nitrogen fixation technology. To address these challenges, this invention effectively promotes the activation of nitrogen molecules, achieving efficient solar energy utilization for nitrogen reduction to generate ammonia. Summary of the Invention

[0004] To address the low efficiency and selectivity of current artificial nitrogen fixation technologies, this invention provides a method for preparing and applying a photocatalyst with interstitial H atom doping using tungsten oxide as a carrier. The HxWO3 obtained in this invention exhibits a high ammonia yield during photocatalytic nitrogen reduction, showing broad promise for solar energy utilization and conversion.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A photocatalyst based on WO3 as a support, incorporating H atoms interstitially into the interstitial spaces of tungsten oxide crystal lattice; wherein H... x In WO3, x is between 0.1 and 0.6.

[0007] As described above, the photocatalyst's nitrogen fixation activity was evaluated using a 300 W xenon lamp with a controlled wavelength (λ) range of 320–780 nm, and the reaction temperature was controlled at 25 °C. An ammonia yield of 32.95 μmol·g was achieved. −1 ·h −1 .

[0008] As described above, the preparation method and application of interstitial H-atom-doped photocatalysts using tungsten oxide as a support involve using WO3 as a precursor, calcining it in a muffle furnace at high temperature, and then introducing H atoms into the resulting product through photo-assisted in-situ reduction with lactic acid solution, thereby generating the final product, hydrogen tungsten bronze (H). x The specific preparation steps for WO3 are as follows:

[0009] (1) Synthesis of WO3 sample by hydrothermal reduction: First, 300 mg WCl6 was dissolved in 50 ml of anhydrous ethanol and transferred to a 100 ml stainless steel autoclave lined with polytetrafluoroethylene. The autoclave was heated at 200 °C for 24 hours. The sample was then removed and centrifuged multiple times with anhydrous ethanol and deionized water, respectively. After centrifugation, the sample was placed in a vacuum oven and dried at 60 °C for 12 hours. The product was collected and kept at 350 °C for 2 hours in a muffle furnace.

[0010] (2) Disperse the WO3 sample obtained in (1) in 80 ml of an aqueous solution containing 5%, 10%, 15%, and 20% lactic acid. Then irradiate with a 300 W Xe lamp for 30 minutes. Collect the precipitate by centrifugation and wash it several times with deionized water to remove lactic acid. Dry the sample in a vacuum oven at 60°C for 12 h to obtain the photocatalyst H with interstitial H atoms doped with tungsten oxide as a carrier. x WO3.

[0011] The aforementioned tungsten oxide-supported interstitial H-atom-doped photocatalyst is applied to the photocatalytic reduction of nitrogen to ammonia. The H atoms obtained in this invention... x WO3 exhibits high ammonia yield during photocatalytic nitrogen reduction and holds great promise for solar energy utilization and the conversion of dual-energy sources into high-value-added chemicals.

[0012] The significant advantages of this invention are:

[0013] This invention utilizes intermittent doping with a suitable proportion of H atoms, enabling H atoms to interact with O in WO3, forming oxygen vacancies that provide active sites for the chemisorption of N2 molecules. Simultaneously, the introduction of H atoms significantly enhances light absorption. Furthermore, the introduction of H atoms efficiently promotes the separation of photogenerated carriers, inhibits their recombination, and facilitates the aggregation of photogenerated electrons, thus promoting the multi-electron reaction in nitrogen reduction. This maintains a high ammonia generation rate during nitrogen reduction, demonstrating broad prospects for solar energy utilization and the conversion of dual-energy sources into high-value-added chemicals. Attached Figure Description

[0014] Figure 1 The WO3 obtained in Example 1, 5% H x WO3, 10%H x WO3, 15%H x WO3, 20%H x XRD pattern of WO3;

[0015] Figure 2 The WO3 obtained in Example 1, 15% H x TEM image of WO3;

[0016] Figure 3 The WO3 obtained in Example 1, 15% H x NMR spectrum of WO3 in solid state;

[0017] Figure 4 The WO3 obtained in Example 1, 15% H x WO3's EPR diagram;

[0018] Figure 5 The WO3 obtained in Example 1, 5% H xWO3, 10%H x WO3, 15%H x WO3, 20%H x Evaluation diagram of photocatalytic nitrogen reduction of WO3; Detailed Implementation

[0019] To make the above features and advantages of the present invention more apparent and understandable, specific embodiments are described below in conjunction with the accompanying drawings, but the present invention is not limited thereto.

[0020] Example 1

[0021] WO3, 5%H x WO3, 10%H x WO3, 15%H x WO3, 20%H x Preparation of WO3 catalysts

[0022] (1) First, 300 mg WCl6 was dissolved in 50 ml of anhydrous ethanol and transferred to a 100 ml stainless steel autoclave lined with polytetrafluoroethylene. The autoclave was heated at 200 °C for 24 hours. The sample was then removed and centrifuged multiple times with anhydrous ethanol and deionized water, respectively. After centrifugation, the sample was placed in a vacuum oven and dried at 60 °C for 12 hours. The sample was then collected and kept at 350 °C for 2 hours in a muffle furnace to obtain WO3 material.

[0023] (2) Disperse 60 mg of the WO3 sample obtained in (1) in 80 ml of aqueous solutions containing 5%, 10%, 15%, and 20% lactic acid. Then irradiate with a 300 W Xe lamp for 30 minutes. Collect the precipitate by centrifugation and wash it several times with deionized water to remove lactic acid. Dry the sample in a vacuum oven at 60 °C for 12 h to obtain 5% H2O. x WO3, 10%H x WO3, 15%H x WO3, 20%H x WO3.

[0024] Example 2

[0025] Catalyst performance evaluation

[0026] In the evaluation process of photocatalytic nitrogen reduction to ammonia, 20 mg of catalyst was added to a quartz reactor (100 mL), and 60 mL of deionized water was added. Nitrogen gas was purged for 1 h in the dark, with the flow rate controlled at 60 mL / min. -1 After ventilation was completed, the photocatalytic reduction of nitrogen to ammonia was evaluated using a 300 W xenon lamp with a wavelength (λ) controlled within the range of 320–780 nm. The nitrogen flow rate was maintained at 60 mL / min throughout the process. -1The reaction temperature was controlled at 25 °C, and the concentration of ammonium ions in the final liquid product was detected by cation chromatography.

[0027] Figure 1 The obtained WO3, 5%H x WO3, 10%H x WO3, 15%H x WO3, 20%H x XRD pattern of WO3 catalyst. From Figure 1 As can be seen, no other assigned X-ray diffraction peaks were detected, indicating that interstitial doping of H atoms did not cause changes in the WO3 structure.

[0028] Figure 2 For the obtained WO3, 15% H x Transmission electron microscope image of WO3 catalyst. From Figure 2 Very distinct lattice fringes can be seen, all belonging to the 020 crystal plane, WO3, 15% H x The interplanar spacing of WO3 is 0.378 and 0.382 nm, respectively.

[0029] Figure 3 For the obtained WO3, 15% H x The solid-state NMR spectrum of WO3 shows that, compared to WO3 at 15% H2O, [the NMR spectrum is missing from the original text]. x The presence of H at different positions in the structure of WO3 proves that H has been successfully doped into the interstitial spaces of WO3 and bonded to O, existing in the form of W-OH.

[0030] Figure 4 For the obtained WO3, 15% H x The EPR diagram of WO3 shows that H atoms are doped into the interstitial spaces of the tungsten oxide lattice. The H atoms interact with O, creating oxygen defects.

[0031] Figure 5 The obtained WO3, 5%H x WO3, 10%H x WO3, 15%H x WO3, 20%H x Evaluation chart of photocatalytic nitrogen reduction of WO3. From Figure 4 It can be seen that WO3, 5%H x WO3, 10%H x WO3, 15%H x WO3, 20%H x The ammonium formation rates of WO3 were 0.84, 4.16, 18.28, 32.95, and 9.98 μmol·g, respectively. −1 ·h −1The introduction of H atoms into interstitial spaces creates oxygen vacancies, thereby exposing more unsaturated metal sites to promote the adsorption and activation of nitrogen molecules.

[0032] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. Use of a tungsten oxide supported interstitially doped H atom photocatalyst in the reduction of nitrogen, characterized in that, The interstitially doped H atom photocatalyst with tungsten oxide as a carrier is applied to photocatalysis under ultraviolet visible light, and an ultraviolet visible light photocatalytic nitrogen reduction system; The photocatalyst is H-doped WO3, in which H atoms are interstitially doped into the interstices of the tungsten oxide crystal lattice on the basis of WO3 as the carrier; the photocatalyst is H x WO3, wherein x is 0.1-0.6; The photocatalyst takes WO3 as a precursor, is calcined at high temperature in a muffle furnace, and is introduced with H atoms by photo-assisted in-situ reduction of the obtained product in a lactic acid solution, so that a final product hydrogen tungsten bronze H x WO3; The preparation method of the photocatalyst specifically comprises the following steps: (1) WO3 sample is synthesized by a hydrothermal reduction method: first, WCl6 is dissolved in anhydrous ethanol and transferred into a polytetrafluoroethylene-lined stainless steel autoclave, heated at 200 ℃ for 24 hours; the sample is taken out, centrifuged with anhydrous ethanol and deionized water for several times, and then the sample is placed in a vacuum oven and heated at 60 ℃ for 12 hours; the product is collected and kept in a muffle furnace at 350 ℃ for 2 hours; (2) H x The WO3 sample was synthesized by a photo-assisted in-situ reduction method: the WO3 sample obtained in (1) was dispersed in a 15% volume fraction of lactic acid aqueous solution; then a 300 W Xe lamp was used for irradiation for 30 minutes; the precipitate was collected by centrifugation and washed with deionized water multiple times to remove lactic acid; the sample was dried in a vacuum oven at 60°C for 12h, thus obtaining a photo-catalyst H x WO3; the ratio of the WO3 sample to the lactic acid aqueous solution was 3:4 mg / mL.

2. Use according to claim 1, characterized in that: In step (1), the ratio of the amount of WCl6 to the amount of anhydrous ethanol is 6:1 mg / mL.

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