Photocatalyst, method for preparing and using the same, and method for photocatalytic reduction of no to ammonia

Abstract

The application relates to the field of photocatalysis, and discloses a photocatalyst, a preparation method and application thereof, and a method for reducing NO to generate ammonia by photocatalysis. x MoO 3‑y , a Pd element and a Cu element, 0 < x < 1, 0 < y < 3, wherein the content of the Pd element is 5-12 mol%, and the content of the Cu element is 0.9-9 mol% based on the total amount of the photocatalyst. The photocatalyst has improved catalytic activity and selectivity.

Description

Technical Field

[0001] This invention relates to the field of photocatalysis, specifically to photocatalysts, their preparation methods and applications, and a method for photocatalytic reduction of NO to ammonia. Background Technology

[0002] Nitrogen oxides (NO) x NOx is a major greenhouse gas and air pollutant that causes environmental and health problems. Currently, NOx... x Reduction technologies include selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR), but these processes are carried out at high temperatures (SCR >150℃, SNCR >800℃), requiring considerable energy. Nitric oxide (NO) is the form of NO in flue gas. x NO is a major component of fertilizers, formed through combustion processes in chemical plants, power plants, and other facilities. While existing thermocatalytic methods have made significant efforts to lower temperatures, achieving high NO removal rates at room temperature remains challenging. Furthermore, ammonia (NH3) is not only a major component of fertilizers but also an important "green" energy carrier for storing H2. To date, the most common industrial method for NH3 synthesis is the classic Haber-Bosch process, which requires extreme conditions of high temperature and high pressure. Therefore, photocatalytic reduction of NO to ammonia at room temperature is crucial for addressing the energy and environmental crises facing humanity. However, due to the weak adsorption capacity of NO at active sites and the numerous side reactions, the development of highly active and selective photocatalysts is particularly urgent.

[0003] CN107790127A relates to a Pt-Ag / WO3 plasma photocatalyst, its preparation method, and its application. This photocatalyst is obtained by modifying WO3 photocatalytic material with Pt-Ag noble metal alloy nanoparticles exhibiting plasmon resonance. This plasma photocatalyst demonstrates high utilization efficiency for ultraviolet and visible light from sunlight. Furthermore, by altering the composition of the noble metal alloy Pt-Ag, the band structure of the photocatalytic material can be tuned, thereby improving the photocatalytic performance. The photocatalyst prepared in this application exhibits good photocatalytic removal efficiency for low concentrations of NO gas, and the photocatalytic removal reaction is carried out at room temperature, making the operation simple and energy-efficient. Its drawbacks include: Pt and Ag are both noble metals, resulting in high preparation costs; WO3 semiconductors lack localized electrons, leading to low catalytic efficiency; and the yield and selectivity for generating the high-value-added product NH3 are not high.

[0004] Currently reported plasma photocatalysts exhibit weak adsorption of gas molecules, lack of local electrons, and low catalytic efficiency. In recent years, introducing oxygen vacancies (OVs) with abundant local electrons into semiconductors has been considered an effective method for capturing and activating CO2, O2, or N2. Professor Zhang's team has reported for the first time that the oxygen vacancies in BiOBr nanosheets possess abundant local electrons, which can significantly promote the adsorption and activation of N2, improving the efficiency of N2 reduction to NH3 under visible light irradiation (MAO C, WANG J, ZOU Y, et al. Hydrogen Spillover to Oxygen Vacancy of TiO2). 2-x H y / Fe:Breaking the Scaling Relationship of Ammonia Synthesis[J].Journal of the American Chemical Society,2020,142(41):17403-17412.). Compared with other plasma semiconductors, hydrogen-molybdenum bronze (H) with abundant OVs x MoO 3-y It exhibits strong plasmon absorption in the visible light spectrum, which is caused by strong localized surface plasmon resonance (LSPR). However, in photocatalytic reactions, H... x MoO 3-y OVs on the surface are easily oxidized by holes in the valence band, leading to the termination of gas molecule activation and low catalytic efficiency. Summary of the Invention

[0005] The purpose of this invention is to overcome the aforementioned problems in the prior art and to provide a photocatalyst, its preparation method and application, as well as a method for photocatalytic reduction of NO to ammonia, wherein the photocatalyst has improved catalytic activity and selectivity.

[0006] To achieve the above objectives, a first aspect of the present invention provides a photocatalyst, the photocatalyst comprising H x MoO 3-y The photocatalyst contains Pd and Cu elements, with 0 < x ≤ 1 and 0 ≤ y < 3. The Pd content is 5-12 mol%, and the Cu content is 0.9-9 mol%, based on the total amount of the photocatalyst.

[0007] Preferably, the total molar content of Pd and Cu elements is 10-13%, more preferably 11-12%.

[0008] Preferably, the molar ratio of Pd to Cu is 1-10:1.

[0009] A second aspect of this invention provides a method for preparing a photocatalyst, the method comprising the following steps:

[0010] (1) Provide a mixture containing molybdenum precursor, Pd precursor, Cu precursor, structure directing agent, reducing agent and ion exchanger;

[0011] (2) The precursor material obtained from the mixture in step (1) is washed and then calcined in a hydrogen atmosphere.

[0012] Preferably, the preparation of the mixture in step (1) includes:

[0013] (1-1) Mix the molybdenum precursor dispersion with the Pd precursor and Cu precursor;

[0014] (1-2) Mix the mixture obtained in step (1-1) with the structure directing agent, reducing agent and ion exchanger.

[0015] The third aspect of the present invention provides a photocatalyst prepared by the method described in the second aspect.

[0016] The fourth aspect of this invention provides the application of the above-mentioned photocatalyst in the photocatalytic reduction of NO to ammonia.

[0017] The fifth aspect of the present invention provides a method for photocatalytic reduction of NO to ammonia, the method comprising: reacting a photocatalyst with a gas containing NO under light irradiation conditions, wherein the photocatalyst is the photocatalyst described in the first or third aspect above.

[0018] The photocatalyst provided by this invention uses H x MoO 3-y Pd and Cu elements combine to form H x MoO 3-y Electrons enriched on surface OVs can be rapidly transferred to PdCu alloys through Schottky junctions under illumination. This not only improves the stability of OVs, but also serves as an active site to regulate the surface and electronic structure of PdCu alloys. By integrating different components, it exhibits a synergistic multi-level coupling effect, thereby improving photocatalytic activity and ammonia selectivity.

[0019] The photocatalyst of this invention exhibits an NH3 selectivity of nearly 98.0% and a yield of 28.2 molg under full-spectrum irradiation. cat -1 h -1 This catalyst exhibits a high photogenerated carrier separation efficiency, can process NO gas of varying concentrations with high selectivity for NH3 across the entire NO concentration range, and demonstrates excellent stability, good alkali resistance, and resistance to heavy metals. The photocatalyst preparation method provided by this invention is simple, environmentally friendly, and suitable for large-scale production and application. Attached Figure Description

[0020] Figure 1 PdCu / H prepared in Example 1 x MoO 3-y Transmission electron microscopy (TEM) image of the photocatalyst;

[0021] Figure 2 PdCu / H prepared in Example 1 x MoO 3-y TEM image and corresponding energy-dispersive X-ray spectrum (EDS) of the photocatalyst;

[0022] Figure 3 X-ray diffraction (XRD) patterns of the photocatalysts prepared in Examples 1-3 and Comparative Examples 1-3;

[0023] Figure 4 X-ray photoelectron spectroscopy (XPS) spectra of the photocatalysts prepared in Examples 1-3 and Comparative Examples 1-3; wherein (a) is the Mo 3d XPS spectrum of the photocatalyst prepared in Comparative Example 1, (b) is the Mo 3d XPS spectrum of the photocatalyst prepared in Comparative Example 2, (c) is the Mo 3d XPS spectrum of the photocatalyst prepared in Comparative Example 3, (d) is the Mo 3d XPS spectrum of MoO3, (e) is the Mo 3d XPS spectrum of the photocatalyst prepared in Example 1, (f) is the Mo 3d XPS spectrum of the photocatalyst prepared in Example 2, and (g) is the Mo 3d XPS spectrum of the photocatalyst prepared in Example 3.

[0024] Figure 5 X-ray photoelectron spectroscopy (XPS) spectra of the photocatalysts prepared in Examples 1-3 and Comparative Examples 1-3; wherein (a) is the O 1s XPS spectrum of the photocatalyst prepared in Comparative Example 1, (b) is the O 1s XPS spectrum of the photocatalyst prepared in Comparative Example 2, (c) is the O 1s XPS spectrum of the photocatalyst prepared in Comparative Example 3, (d) is the O 1s XPS spectrum of MoO3, (e) is the O 1s XPS spectrum of the photocatalyst prepared in Example 1; (f) is the O 1s XPS spectrum of the photocatalyst prepared in Example 2, and (g) is the O 1s XPS spectrum of the photocatalyst prepared in Example 3.

[0025] Figure 6X-ray photoelectron spectroscopy (XPS) spectra of the photocatalysts prepared in Examples 1-3 and Comparative Examples 1-2; wherein (a) is the Pd 3d XPS spectrum of the photocatalysts prepared in Example 1 and Comparative Example 1, (b) is the Pd 3d XPS spectrum of the photocatalysts prepared in Examples 2-3, (c) is the Cu 2p XPS spectrum of the photocatalysts prepared in Examples 1 and Comparative Example 2, and (d) is the Cu 2p XPS spectrum of the photocatalysts prepared in Examples 2-3;

[0026] Figure 7 The UV / Vis-NIR diffuse reflectance spectra of the photocatalysts prepared in Example 1 and Comparative Examples 1-3 after reduction with H2 at 350 °C;

[0027] Figure 8 The electron spin resonance (ESR) spectra of the photocatalysts prepared in Example 1 and Comparative Examples 1-3 are shown.

[0028] Figure 9 The yields of NH3 and NH2OH of the photocatalysts prepared in Examples 1-5 and Comparative Examples 1-3 under full-spectrum light irradiation;

[0029] Figure 10 The apparent quantum yield of the photocatalyst prepared in Example 1 as a function of wavelength under monochromatic light irradiation in the UV-vis diffuse reflectance spectrum.

[0030] Figure 11 The yields of NH3 and NH2OH of the photocatalysts prepared in Example 1 and Comparative Examples 1-3 under different light conditions;

[0031] Figure 12 The photocatalytic activity of the photocatalyst prepared in Example 1 under different NO concentrations;

[0032] Figure 13 Cyclic experiments were conducted on the photocatalytic production of NH3 by the photocatalyst prepared in Example 1.

[0033] Figure 14 The photocatalytic activity of the photocatalysts prepared in Example 1 and Comparative Examples 1-3 in alkali metal solution;

[0034] Figure 15 The photocatalytic activity of the photocatalysts prepared in Example 1 and Comparative Examples 1-3 in heavy metal solutions. Detailed Implementation

[0035] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0036] In this invention, the H x MoO 3-y As is conventional in the art, this invention is not particularly limited thereto, and it may also be referred to as hydrogen molybdenum bronze.

[0037] The first aspect of the present invention provides a photocatalyst, the photocatalyst comprising H x MoO 3-y The photocatalyst contains Pd and Cu elements, with 0 < x ≤ 1 and 0 ≤ y < 3. The Pd content is 5-12 mol%, and the Cu content is 0.9-9 mol%, based on the total amount of the photocatalyst.

[0038] According to a preferred embodiment of the present invention, based on the total amount of photocatalyst, the content of Pd element is 5.5-12 mol%, and the content of Cu element is 1-6 mol%.

[0039] Preferably, the total molar content of Pd and Cu elements is 10-13%, more preferably 11-12%. Using this preferred embodiment, the total molar content of Pd and Cu elements not only improves the catalytic performance of the photocatalyst but also helps control costs.

[0040] In the photocatalyst described in this invention, the contents of Pd and Cu were determined by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0041] In this invention, H in the photocatalyst x MoO 3-y The presence of [a specific substance] can be determined by XRD (X-ray diffraction). The values ​​of x and y can also be determined by comparing the XRD pattern of the photocatalyst with a standard pattern.

[0042] Preferably, the molar ratio of Pd to Cu is 0.5-12:1, more preferably 1-10:1, for example, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1. This preferred embodiment can achieve a synergistic effect of plasma resonance and PdCu alloying to promote ammonia synthesis.

[0043] According to the present invention, preferably, Pd and Cu elements are present at least partially in the form of a PdCu alloy. This preferred embodiment is more advantageous for the interaction of PdCu and H. x MoO 3-y The photocatalyst provides a synergistic effect to improve ammonia synthesis. It should be noted that the photocatalyst provided by this invention does not exclude the possibility that some Pd and Cu elements exist in other forms (e.g., elemental forms).

[0044] According to a preferred embodiment of the present invention, Pd and Cu are dispersed in H x MoO 3-y On the nanosheet, Pd and Cu elements are preferably present at least partially in the form of alloy nanoparticles.

[0045] According to a preferred embodiment of the present invention, dispersed in H x MoO 3-y The size of the PdCu particles on the nanosheets is 2-10 nm.

[0046] There are no particular limitations on the form of the PdCu particles, such as spherical.

[0047] The morphology of the photocatalyst can be determined by TEM characterization. Figure 1 It can be seen that in H x MoO 3-y PdCu nanoparticles with a size (~5 nm) and a shape similar to spheres were deposited on the nanosheet.

[0048] In this invention, the presence of Pd and Cu elements in the form of a PdCu alloy can be determined by TEM and corresponding energy-dispersive X-ray spectroscopy (EDS), for example, by... Figure 2 It can be seen that PdCu / H x MoO 3-y In the hybrid, Pd and Cu elements have the same spatial distribution. Figure 1 and Figure 2 This fully demonstrates the formation of the PdCu alloy.

[0049] According to the present invention, preferably, no Pd and Cu diffraction peaks are present in the XRD pattern of the photocatalyst. In the photocatalyst having this preferred characteristic, Pd and Cu are highly dispersed in H₂O. x MoO 3-y This allows the catalyst to have further improved ammonia synthesis performance.

[0050] According to the present invention, preferably, as characterized by XPS, in the photocatalyst, (O -OH +O H2O ) / O total The molar ratio is 0.6-0.65, preferably 0.6-0.63; wherein, O-OH O is a -OH group that coordinates with the Mo atom. H2O O is a -OH2 group coordinated with the Mo atom. total The total number of oxygen-containing groups is [missing information]. The photocatalyst provided by this invention has a higher [missing information] (O2 ... -OH +O H2O ) / O total The ratio indicates that the H in the photocatalyst provided by this invention... + It has a higher degree of intercalation and exhibits better catalytic performance when applied to ammonia synthesis.

[0051] In this invention, (O -OH +O H2O ) / O total The molar ratio can be obtained by X-ray photoelectron spectroscopy (XPS) using the peak area ratio. Specifically, according to the O 1s XPS spectrum of the photocatalyst, there are three peaks, namely -OH2(O) coordinated with Mo atoms at 532.4 eV. H2O ) group, and -OH group (O) coordinated to a Mo atom at 531.4 eV. -OH ) and the O atom coordinating groups at 530.85 eV (O latt ), O total For O H2O O -OH O latt The sum of .

[0052] According to a preferred embodiment of the present invention, the photocatalyst, after reduction with H2 at 350°C and subjected to UV / Vis-NIR diffuse reflection, exhibits an LSPR absorption peak at 540 nm ± 2 nm. This indicates that the PdCu alloy can promote the generation of oxygen vacancies in MoO3 during H overflow, thereby inducing a stronger plasma absorption peak.

[0053] A second aspect of this invention provides a method for preparing a photocatalyst, the method comprising the following steps:

[0054] (1) Provide a mixture containing molybdenum precursor, Pd precursor, Cu precursor, structure directing agent, reducing agent and ion exchanger;

[0055] (2) The precursor material obtained from the mixture in step (1) is washed and then calcined in a hydrogen atmosphere.

[0056] According to the method provided by the present invention, preferably, the photocatalyst prepared by the method comprises H x MoO 3-y Pd and Cu elements, preferably Pd and Cu elements are present at least partially in the form of PdCu alloy.

[0057] The present invention does not have any particular limitation on the way the mixture is provided in step (1). The principle is to facilitate the dispersion of each substance. As long as a mixture in which each substance is uniformly dispersed can be obtained, the performance of the catalyst can be further improved.

[0058] Preferably, the preparation of the mixture in step (1) includes:

[0059] (1-1) Mix the molybdenum precursor dispersion with the Pd precursor and Cu precursor;

[0060] (1-2) Mix the mixture obtained in step (1-1) with the structure directing agent, reducing agent and ion exchanger.

[0061] Preferably, step (1-1) includes mixing the molybdenum precursor and water, and then heating in a water bath under stirring conditions to obtain the molybdenum precursor dispersion.

[0062] According to a preferred embodiment of the present invention, the concentration of the molybdenum precursor in its aqueous solution is 10-30 g / L.

[0063] According to a preferred embodiment of the present invention, the conditions for water bath heating include: water bath temperature of 70-90°C and heating time of 20-40 min.

[0064] The above-described preferred embodiments are more conducive to obtaining a molybdenum precursor dispersion with better dispersibility.

[0065] The mixing of the molybdenum precursor dispersion with the Pd and Cu precursors in step (1-1) is preferably carried out under stirring conditions.

[0066] According to a preferred embodiment of the present invention, the method further includes, before step (1-2), allowing the mixture obtained in step (1-1) to stand (preferably for 0.5-5 hours), and then proceeding to step (1-2). There is no particular limitation on the standing time, as long as it allows for sufficient dispersion and loading of the Pd and Cu active components onto the molybdenum precursor substrate.

[0067] The mixing described in steps (1-2) is preferably carried out under stirring conditions (e.g., magnetic stirring).

[0068] The present invention does not impose any particular limitations on the above stirring conditions, but rather on the conditions that are more conducive to dispersion. Those skilled in the art can make appropriate selections based on the specific type of material.

[0069] According to the method provided by the present invention, the types of structure-directing agent, reducing agent, and ion exchanger are selected to enable the preparation of H-containing... x MoO 3-y The catalysts are based on Pd and Cu elements.

[0070] Preferably, the structure-directing agent is a directing agent that facilitates the formation of a PdCu alloy. More preferably, the structure-directing agent is an alloy structure-directing agent, preferably polyvinylpyrrolidone (PVP).

[0071] In this invention, the reducing agent is used to reduce Pd and Cu ions. Preferably, the reducing agent is L-ascorbic acid.

[0072] In this invention, the ion exchanger is used to obtain Pd. 0 CuO. Preferably, the ion exchanger is potassium bromide.

[0073] The present invention has a wide range of choices for the molybdenum precursor, as long as it can provide H x MoO 3-y Mo can be used, and preferably, the molybdenum precursor is selected from at least one of molybdenum trioxide, ammonium molybdate, and sodium molybdate.

[0074] Preferably, the Pd precursor is selected from at least one of sodium chloropalladate, palladium chloride, and palladium nitrate;

[0075] Preferably, the Cu precursor is selected from at least one of copper chloride, copper nitrate, copper acetate, and copper sulfate.

[0076] According to a preferred embodiment of the present invention, the molar ratio of Pd precursor to Cu precursor, based on metal elements, is 0.5-12:1, preferably 1-10:1, for example, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1. The present invention controls the performance of the resulting catalyst material by adjusting the feed ratio of copper and palladium metal sources, achieving a synergistic effect of plasma resonance and PdCu alloying to promote ammonia synthesis.

[0077] Preferably, the amounts of Pd precursor, Cu precursor, and molybdenum precursor are such that, based on the total amount of photocatalyst, the total molar content of Pd and Cu elements in the prepared photocatalyst is 10-13%, preferably 11-12%. Based on this disclosure, those skilled in the art will know how to adjust the amounts of Pd precursor, Cu precursor, and molybdenum precursor.

[0078] In this invention, the dosage range of the structure-directing agent, reducing agent and ion exchanger is relatively wide, as long as their respective purposes can be achieved.

[0079] In this invention, preferably, the amount of the structure-directing agent is 100-300 mg relative to the total amount of 0.4 mmol of Pd precursor and Cu precursor, for example, 100 mg, 150 mg, 200 mg, 250 mg, or 300 mg.

[0080] In this invention, preferably, the amount of reducing agent used is 100-300 mg relative to the total amount of 0.4 mmol of Pd precursor and Cu precursor, for example, 100 mg, 150 mg, 200 mg, 250 mg, or 300 mg.

[0081] In this invention, preferably, the amount of ion exchanger used is 500-700 mg relative to the total amount of 0.4 mmol of Pd precursor and Cu precursor, for example, 500 mg, 550 mg, 600 mg, 650 mg, or 700 mg.

[0082] Using the above-mentioned preferred dosage of additives is more conducive to promoting the formation of PdCu alloy.

[0083] According to a preferred embodiment of the present invention, the method further includes removing the structure-directing agent, reducing agent, and ion exchanger from the mixture in step (1) before step (2), and then allowing it to stand (preferably for 1-5 hours) to obtain the precursor material. Specifically, in this invention, the structure-directing agent, reducing agent, and ion exchanger can be removed by centrifugation (e.g., centrifugation with ultrapure water).

[0084] The present invention does not have any particular limitation on the specific operation of washing in step (2), the purpose of which is to remove unreacted materials and / or impurities that are present on the surface of the obtained precursor material.

[0085] According to a preferred embodiment of the present invention, in step (2), the washing agent used is an organic solvent. The washing agent can be a conventional choice in the art, and ethanol is preferred.

[0086] Preferably, the method further includes drying after washing, followed by calcination. The drying conditions preferably include: a drying temperature of 50-80°C, a vacuum degree of -3000 to -1000 kPa, and a drying time of 4-10 hours.

[0087] According to the present invention, preferably, the calcination conditions in step (2) include: a temperature of 200-400℃ and a calcination time of 0.5-2h.

[0088] According to the present invention, preferably, the hydrogen-containing atmosphere is provided by hydrogen and optionally an inert gas. The present invention does not particularly limit the hydrogen content in the hydrogen-containing atmosphere, but preferably not less than 50% by volume, and more preferably 80-100% by volume. The inert gas can be selected by conventional means, including but not limited to nitrogen, argon, helium, and neon.

[0089] The preparation method of this invention is simple and feasible, with low energy consumption. The resulting catalyst material has strong stability and adaptability, and can be used to treat flue gas containing different concentrations of nitric oxide. It is beneficial for the prevention and control of air pollution and the efficient production of high-value-added product ammonia, and has good prospects for practical application.

[0090] The third aspect of the present invention provides a photocatalyst prepared by the method described in the second aspect.

[0091] A fourth aspect of this invention provides the application of the above-described photocatalyst in the photocatalytic reduction of NO to ammonia. Using the photocatalyst provided by this invention for the photocatalytic reduction of NO to ammonia can improve photocatalytic activity and ammonia selectivity.

[0092] The fifth aspect of the present invention provides a method for photocatalytic reduction of NO to ammonia, the method comprising: reacting a photocatalyst with a gas containing NO under light irradiation conditions, wherein the photocatalyst is the photocatalyst described in the first or third aspect above.

[0093] This invention offers a wide range of specific operations and conditions for the photocatalytic reduction of NO to ammonia. Preferably, the photocatalyst is provided in the form of a mixture, wherein the ratio of photocatalyst to solvent is 4-6 mg: 40-60 mL.

[0094] The present invention allows for a wide range of solvent choices, including water and / or organic solvents (preferably ethylene glycol). Preferably, the volume ratio of water to ethylene glycol in the solvent is 30-55:4-6.

[0095] The method provided by the present invention can process NO-containing gases of different concentrations. Preferably, the volume concentration of NO in the NO-containing gas is 1-100%, for example, 1%, 10%, 20%, 50%, 70%, 90%, and 100%.

[0096] There are no specific restrictions on the types of components other than NO in NO-containing gases; the type should be determined based on the actual gas to be treated.

[0097] Preferably, the contact reaction conditions include: photocatalytic reaction under 180-320W light irradiation for 0.5-2 hours.

[0098] The light source includes, but is not limited to, a 300W Xe full-spectrum illumination lamp and a cutoff filter.

[0099] According to a preferred embodiment of the present invention, the method for photocatalytic reduction of NO to ammonia comprises: placing the photocatalyst in the form of a mixture in a reactor, introducing NO-containing gas to induce bubbling, removing air and sealing the reactor; and placing the reactor under a light source for irradiation to carry out the reaction. Preferably, the flow rate of the NO-containing gas is 10-30 sccm, and the bubbling time is 10-50 min.

[0100] The present invention will be described in detail below through embodiments.

[0101] In the following examples, TEM and EDS characterization were performed on a JEOL JEM 2100 microscope with an accelerating voltage of 200 kV.

[0102] XRD characterization was performed using a BRUKER D8 / Advance X-ray diffractometer (Cu Kα x-rays: λ = 0.1545 nm).

[0103] XPS characterization was performed using a Thermo Fisher Scientific ESCALab250XI photoelectron spectrometer.

[0104] UV / Vis-NIR characterization was performed using a PerkinElmer Lambda 900 spectrometer.

[0105] ESR characterization was performed using a Bruker A300-10 / 12 electron spin resonance spectrometer from Germany.

[0106] Example 1

[0107] This example illustrates the preparation of a photocatalyst.

[0108] (a) 400 mg MoO3 was dispersed in 20 mL of water, stirred and heated in a water bath at 80 °C for 30 min to obtain a MoO3 dispersion; 98.06 mg Na2PdCl4 and 11.36 mg CuCl2·2H2O powder (molar ratio of Na2PdCl4 to CuCl2·2H2O was 5:1) were added to the MoO3 dispersion, stirred and then allowed to stand for 1 hour;

[0109] (b) Add 210 mg of polyvinylpyrrolidone K-30 (PVP), 240 mg of L-ascorbic acid and 600 mg of potassium bromide (KBr) to the solution in step (a) and stir magnetically for 3 h; then remove PVP, L-ascorbic acid and KBr by centrifugation with ultrapure water, and let the precursor solution stand for 2 h.

[0110] (c) The precursor material obtained in step (b) was washed with ethanol, centrifuged at 10000 r / min, and then dried in a vacuum chamber at 60℃ (vacuum degree of -3000 kPa) for 6 h to obtain Pd. 0 CuO / MoO3 powder;

[0111] (d) Take the Pd obtained in step (c) 0 CuO / MoO3 powder is placed in a tube furnace and calcined at 320℃ under a H2 atmosphere for 1 hour to obtain PdCu / H2O. x MoO 3-y Hybrid photocatalysts.

[0112] TEM results of photocatalysts are as follows Figure 1 As shown, by Figure 1 It can be seen that in H x MoO 3-y PdCu alloy nanoparticles with a size (~5 nm) and a shape similar to spheres were deposited on the nanosheets;

[0113] Figure 2 PdCu / H prepared in Example 1 x MoO 3-y TEM image and corresponding energy-dispersive X-ray spectroscopy (EDS) image of the photocatalyst; in a, the yellow line represents the range of the EDS scan, corresponding to the horizontal axis in b, where b represents the elemental types and quantities of the catalyst sample within the scanned range. Figure 2 It can be seen that PdCu / H x MoO 3-y In the hybrid, Pd and Cu elements have the same spatial distribution. Figure 1 and Figure 2 This fully demonstrates the formation of the PdCu alloy.

[0114] Depend on Figure 3 It can be seen that PdCu / H x MoO 3-y The XRD patterns of the hybrids mainly point to orthogonal H. 0.34 The MoO3 phase (PDF#34-1230) shows no obvious diffraction peaks for Pd and Cu nanoparticles, indicating that PdCu in H... x MoO 3-y Highly dispersed.

[0115] Example 2

[0116] The method is the same as in Example 1, except that in step (a), 107 mg of Na2PdCl4 and 6.2 mg of CuCl2·2H2O powder (the molar ratio of Na2PdCl4 and CuCl2·2H2O is 10:1) are added to the MoO3 dispersion.

[0117] Example 3

[0118] The method is the same as in Example 1, except that in step (a), 58.9 mg of Na2PdCl4 and 34.1 mg of CuCl2·2H2O powder (the molar ratio of Na2PdCl4 and CuCl2·2H2O is 1:1) are added to the MoO3 dispersion.

[0119] Comparative Example 1

[0120] The method is the same as in Example 1, except that in step (a), the molar ratio of Na2PdCl4 and CuCl2·2H2O is 1:0, that is, 117.7 mg of Na2PdCl4 and 0 mg of CuCl2·2H2O are weighed out respectively.

[0121] Comparative Example 2

[0122] The method is the same as in Example 1, except that in step (a), the molar ratio of Na2PdCl4 and CuCl2·2H2O is 0:1, that is, 0 mg of Na2PdCl4 and 68.2 mg of CuCl2·2H2O are measured respectively.

[0123] Comparative Example 3

[0124] The method is the same as in Example 1, except that in step (a), the molar ratio of Na2PdCl4 and CuCl2·2H2O is 0:0, that is, 0 mg of Na2PdCl4 and 0 mg of CuCl2·2H2O are measured respectively.

[0125] The X-ray photoelectron spectroscopy (XPS) spectra of the photocatalysts prepared in Examples 1-3 and Comparative Examples 1-3 are shown below. Figure 4 As shown, by Figure 4 It can be seen that only Mo exists in MoO3. 6+ In contrast, the photocatalyst prepared in Comparative Example 3 also contained Mo. 6+ and Mo 5+ In the photocatalysts prepared in Examples 1-3 and Comparative Examples 1-2, the oxidation state of Mo is Mo. 6+ Mo 5+ and Mo 4+ The three forms illustrate how H overflow caused partial reduction of Mo.

[0126] Depend on Figure 5 It can be seen that the photocatalysts prepared in Examples 1-3 and Comparative Examples 1-3, as well as the O 1s XPS spectra of the MoO3 samples, all have three peaks, namely 532.4 eV and -OH2(O) coordinated to Mo atoms. H2O ) group, 531.4 eV and -OH group coordinated with Mo atom (O) -OH) and 530.85 eV lattice O atom coordinating groups (O latt Compared to MoO3, the peak intensity of the -OH component in the photocatalysts prepared in Examples 1-3 and Comparative Examples 1-3 was significantly enhanced, demonstrating the presence of Mo-OH bonds. Furthermore, (O -OH +O H2O ) / O total The proportions are in the order of MoO3 < Comparative Example 3 < Comparative Example 2 < Comparative Example 1 < Examples 1-3, further indicating that the H in the photocatalysts prepared in Examples 1-3 is... + The degree of intercalation is relatively high.

[0127] Depend on Figure 6 It can be seen that the Pd species in the photocatalysts prepared in Examples 1-3 and Comparative Example 1 are all Pd. 0 The Cu 2p XPS spectrum of the photocatalyst prepared in Comparative Example 2 did not show any peaks, indicating that Cu is difficult to load alone on H₂O. x MoO 3-y Above. With the addition of Pd, the binding energy is 950.9 eV (2p). 1 / 2 ) and 931.6eV (2p 3 / 2 Cu can be well loaded in H in the form of PdCu alloy. x MoO 3-y Furthermore, the XPS peak of Pd 3d in the photocatalysts prepared in Examples 1-3 showed a significant shift compared to the XPS peak of Pd 3d in the photocatalyst prepared in Comparative Example 1, indicating a strong charge transfer and electronic interaction between Cu and Pd. Figures 1-6 This indicates that PdCu / H has been successfully prepared. x MoO 3-y Hybrid photocatalysts.

[0128] Depend on Figure 7 It can be seen that Example 1 has a strong LSPR absorption peak at about 540 nm in the visible light range. The intensity and position of the LSPR peak of Comparative Example 1 are similar to those of Example 1. The LSPR peaks of Comparative Example 2 and Comparative Example 3 show obvious red shifts. This indicates that PdCu alloy and Pd nanoparticles can promote the generation of oxygen vacancies in MoO3 during H overflow, thereby inducing stronger plasma absorption peaks.

[0129] Depend on Figure 8 It can be seen that at g = 2.003, the signal strength of ESR is in the order of Example 1 > Comparative Example 1 > Comparative Example 2 > Comparative Example 3, which is consistent with... Figure 7 The consistent order of light absorption performance of the photocatalysts indicates that there are more unpaired free electrons surrounding oxygen vacancies in Example 1.

[0130] Example 4

[0131] The method is the same as in Example 1, except that in step (a), 107.9 mg of Na2PdCl4 and 5.7 mg of CuCl2·2H2O powder (the molar ratio of Na2PdCl4 to CuCl2·2H2O is 11:1) are added to the MoO3 dispersion.

[0132] Example 5

[0133] The method is the same as in Example 1, except that in step (a), 39.2 mg of Na2PdCl4 and 45.5 mg of CuCl2·2H2O powder (the molar ratio of Na2PdCl4 to CuCl2·2H2O is 0.5:1) are added to the MoO3 dispersion.

[0134] The composition and structural parameters of the catalysts prepared in the above examples and comparative examples are listed in Table 1 below.

[0135] Table 1

[0136] Example 1 9.92 1.98 5:1 0.621 Example 2 11.18 1.12 10:1 0.600 Example 3 5.85 5.85 1:1 0.606 Comparative Example 1 11.6 0 1:0 0.589 Comparative Example 2 0 <0.001 0:1 0.564 Comparative Example 3 0 0 0:0 0.473 Example 4 11.37 1.03 11:1 Example 5 3.87 7.73 0.5:1

[0137] Test case

[0138] The photocatalytic NO reduction performance of the photocatalysts prepared in the above examples and comparative examples was tested.

[0139] The total volume of the photocatalytic reactor was approximately 100 mL. 5 mg of the sample catalyst powder was dispersed in a mixture of 45 mL of water and 5 mL of ethylene glycol (EG). A 300 WXe full-spectrum irradiation lamp with different cutoff filters was used as the light source and placed above the reactor. Before the reaction, NO of different volume concentrations (1%, 5%, 10%, 25%, 50%, 99.9%, with the balance being argon) was bubbled at a gas flow rate of 20 sccm for 30 min to remove air. After sealing, the reactor was subjected to a photoreaction for 1 h. Then, the possible liquid products NH3 and NH2OH were analyzed and quantified using a Nessler's reagent spectrophotometer and 1H nuclear magnetic resonance (1H-NMR) method. Possible gaseous products (N2, N2O, H2, etc.) were analyzed and quantified using gas chromatography (GC9790Plus, Agilent).

[0140] To test the photocatalytic activity of the photocatalyst in alkali metal and heavy metal solutions, relevant experiments were designed. The photocatalytic activity test in alkali metal solution was conducted as described above, except that the 45 mL water and 5 mL ethylene glycol (EG) were replaced with 45 mL of a 50 mg / L Na₂SO₄ solution and 5 mL of ethylene glycol (EG). The photocatalytic activity test in heavy metal solution was also conducted as described above, except that the 45 mL water and 5 mL ethylene glycol (EG) were replaced with 45 mL of a 50 mg / L (CH₃COO)₂Cd solution and 5 mL of ethylene glycol (EG).

[0141] Figure 9 The yields of NH3 and NH2OH of the photocatalysts prepared in Examples 1-5 and Comparative Examples 1-3 under full-spectrum light irradiation are shown below. Figure 9 It can be seen that, through H x MoO 3-y The deposition of Pd nanoparticles and PdCu alloy significantly improved the photocatalytic performance of the NO reduction reaction (NORR) for NH3 synthesis. The NH3 yields in Examples 1-5 were significantly higher than those in Comparative Examples 1-3, indicating that the alloy structure can improve the NH3 yield.

[0142] Depend on Figure 10 It can be seen that, under various monochromatic light irradiation conditions, the PdCu / H prepared in Example 1 can be calculated... x MoO 3-y The apparent quantum efficiency (AQE) of hybrids is used to study light utilization efficiency. Figure 10 In the figure, AQE reaches a maximum of 2.8 at 540 nm, indicating that PdCu / H x MoO 3-y The improved hybrid performance is due to the oxygen vacancy-induced LSPR effect. Figure 11 It can be seen that Example 1 and Comparative Examples 1-3 exhibit similar activity under longer wavelengths of light (λ>420nm, λ>520nm, λ>800nm), which further verifies that the improvement of the photocatalytic performance is mainly due to the LSPR effect.

[0143] Figure 12 The photocatalytic activity of the photocatalyst prepared in Example 1 under different NO concentrations was determined by... Figure 12 It can be seen that as the NO concentration gradually increases from 1% to 99.9%, the PdCu / H prepared in Example 1... x MoO 3-y The amount of NH3 produced by the hybrid photocatalyst also increased almost linearly from 8.15 ppm to 92.2 ppm, while the yield of NH2OH was highly suppressed, highlighting the high selectivity of NH3 across the entire NO concentration range.

[0144] Figure 13 The photocatalytic production of NH3 by the photocatalyst prepared in Example 1 was tested in a cyclic experiment. Figure 13 It can be seen that although the NH3 production showed a slight downward trend in the 10-cycle test, it remained at a very high level, indicating that the prepared photocatalyst has excellent stability.

[0145] Figure 14 The photocatalysts prepared in Example 1 and Comparative Examples 1-3 exhibit photocatalytic activity in alkali metal solutions. Figure 15 The photocatalytic activity of the photocatalysts prepared in Example 1 and Comparative Examples 1-3 in heavy metal solutions is shown. Figure 14 and Figure 15 It can be seen that the photocatalyst prepared in Example 1 has good alkali resistance and heavy metal resistance.

[0146] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A photocatalyst for the photocatalytic reduction of NO to ammonia, characterized in that, The photocatalyst includes H x MoO 3-y The photocatalyst contains Pd and Cu elements, where 0 < x ≤ 1 and 0 ≤ y < 3. Based on the total amount of the photocatalyst, the Pd element content is 5-12 mol%, and the Cu element content is 0.9-9 mol%. The molar ratio of Pd to Cu is 1-10:

1. Based on the total amount of the photocatalyst, the total molar content of Pd and Cu is 10-13%. Among them, Pd and Cu elements exist at least partially in the form of PdCu alloy, dispersed in H x MoO 3-y On nanosheets; Dispersed in H x MoO 3-y The size of the PdCu particles on the nanosheets is 2-10 nm; Among them, as characterized by XPS, in the photocatalyst, (O -OH + O H2O ) / O total The molar ratio is 0.6-0.65; Among them, O -OH O is a -OH group that coordinates with the Mo atom. H2O O is a -OH2 group coordinated with the Mo atom. total The total oxygen-containing groups in the sample catalyst.

2. The catalyst according to claim 1, wherein, Based on the total amount of photocatalyst, the content of Pd element is 5.5-12 mol%, and the content of Cu element is 1-6 mol%.

3. The catalyst according to claim 1, wherein, Based on the total amount of photocatalyst, the total molar content of Pd and Cu elements is 11-12%.

4. The catalyst according to any one of claims 1-3, wherein, The XRD pattern of the photocatalyst does not show diffraction peaks for Pd and Cu.

5. The catalyst according to any one of claims 1-3, wherein, XPS characterization revealed that in the photocatalyst, (O) -OH + O H2O ) / O total The molar ratio is 0.6-0.

63.

6. A method for preparing a photocatalyst according to any one of claims 1-5, the method comprising the following steps: (1) Provide a mixture containing molybdenum precursor, Pd precursor, Cu precursor, structure directing agent, reducing agent and ion exchanger; (2) The precursor material obtained from the mixture in step (1) is washed and then calcined in a hydrogen atmosphere; Among them, the molar ratio of Pd precursor to Cu precursor, calculated by metal element, is 1-10:1; The amounts of Pd precursor, Cu precursor and molybdenum precursor used in the prepared photocatalyst are such that, based on the total amount of photocatalyst, the total molar content of Pd and Cu elements is 10-13%.

7. The method according to claim 6, wherein, The structure guiding agent is an alloy structure guiding agent.

8. The method according to claim 7, wherein, The structure directing agent is polyvinylpyrrolidone.

9. The method according to claim 6, wherein, The reducing agent is L-ascorbic acid.

10. The method according to claim 6, wherein, The ion exchanger is potassium bromide.

11. The method according to claim 6, wherein, The molybdenum precursor is selected from at least one of molybdenum trioxide, ammonium molybdate, and sodium molybdate.

12. The method according to claim 6, wherein, The Pd precursor is selected from at least one of sodium chloropalladium, palladium chloride, and palladium nitrate.

13. The method according to claim 6, wherein, The Cu precursor is selected from at least one of copper chloride, copper nitrate, copper acetate, and copper sulfate.

14. The method according to any one of claims 6-13, wherein, The preparation of the mixture in step (1) includes: (1-1) Mix the molybdenum precursor dispersion with the Pd precursor and Cu precursor; (1-2) Mix the mixture obtained in step (1-1) with the structure directing agent, reducing agent and ion exchanger.

15. The method according to claim 14, wherein, The molybdenum precursor was mixed with water and then heated in a water bath under stirring conditions to obtain the molybdenum precursor dispersion.

16. The method according to claim 15, wherein, The concentration of molybdenum precursors in their aqueous solutions is 10-30 g / L.

17. The method according to claim 15, wherein, The conditions for water bath heating include: water bath temperature of 70-90℃ and heating time of 20-40min.

18. The method according to any one of claims 6-13, wherein, The total molar content of Pd and Cu elements is 11-12%.

19. The method according to any one of claims 6-13, wherein, Relative to the total addition of 0.4 mmol of Pd precursor and Cu precursor, the amount of the structure directing agent is 100-300 mg, the amount of the reducing agent is 100-300 mg, and the amount of the ion exchanger is 500-700 mg.

20. The method according to any one of claims 6-13, wherein, The method further includes removing the structure-directing agent, reducing agent and ion exchanger from the mixture in step (1) before step (2), and then allowing it to stand to obtain the precursor material.

21. The method according to any one of claims 6-13, wherein, The washing process uses an organic solvent as the washing agent.

22. The method according to claim 21, wherein, The washing agent used is ethanol.

23. The method according to any one of claims 6-13, wherein, The method further includes drying after washing, followed by calcination, wherein the drying conditions include a drying temperature of 50-80°C, a vacuum degree of -3000 to -1000 kPa, and a drying time of 4-10 h.

24. The method according to any one of claims 6-13, wherein, The roasting conditions in step (2) include: a temperature of 200-400℃ and a roasting time of 0.5-2h.

25. The method according to any one of claims 6-13, wherein, The hydrogen-containing atmosphere is provided by hydrogen and an optional inert gas.

26. The photocatalyst prepared by the method according to any one of claims 6-13.

27. The use of the photocatalyst according to any one of claims 1-5 and 26 in the photocatalytic reduction of NO to ammonia.

28. A method for photocatalytic reduction of NO to ammonia, the method comprising: Under light irradiation, the photocatalyst is reacted with a NO-containing gas, wherein the photocatalyst is the photocatalyst described in any one of claims 1-5 and 26.

29. The method according to claim 28, wherein, The photocatalyst is provided in the form of a mixture in which the ratio of photocatalyst to solvent is 4-6 mg: 40-60 mL.

30. The method according to claim 28, wherein, The volume concentration of NO in the NO-containing gas is 1-100%.

31. The method according to claim 28, wherein, The conditions for the contact reaction include: photocatalytic reaction under 180-320W light irradiation for 0.5-2 hours.

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