A pd-loaded photothermal catalyst, a preparation method and application thereof

Abstract

This invention relates to the fields of environmental protection and new energy technologies, specifically disclosing a Pd-supported photothermal catalyst, its preparation method, and its application. The Pd-supported photothermal catalyst comprises a rare earth hexaboride support and Pd nanoparticles. The preparation method of the Pd-supported photothermal catalyst includes: weighing anhydrous rare earth chloride and magnesium boride powder, grinding and mixing them evenly, calcining them under vacuum, and after cooling to room temperature, immersing them in a dilute sulfuric acid solution and stirring, followed by centrifugation, washing, and drying to obtain the rare earth hexaboride support; adding PdCl2 solution and the rare earth hexaboride support to water, stirring until the solution is completely evaporated, calcining, and then reducing with a H2-Ar mixed gas to obtain the Pd-supported photothermal catalyst. This photothermal catalyst enhances the performance of the transition metal Pd in ​​the catalytic reaction of NO hydrogenation to ammonia synthesis through photothermal synergy by loading Pd nanoparticles onto the surface of the rare earth hexaboride support.

Description

Technical Field

[0001] This invention relates to the fields of environmental protection and new energy technologies, specifically to a Pd-supported photothermal catalyst, its preparation method, and its application. Background Technology

[0002] Ammonia (NH3) is an important raw material for the production of fertilizers, pharmaceuticals, and fine chemicals, and is also an ideal zero-carbon energy carrier. NO has received widespread attention and research in recent years as a potential nitrogen source for ammonia synthesis. One pathway to ammonia production is the catalytic reduction of NO using H2 at low temperature and ambient pressure (2NO + 5H2 → 2NH3 + 2H2O). This method not only reduces the use of NH3 as a reducing agent and lowers the reaction temperature in traditional NH3-SCR denitrification reactions, but also enables the resource utilization of harmful nitrogen oxides into high-value-added ammonia. Therefore, it has significant implications for both theoretical research and practical application.

[0003] For the catalytic reduction of NO to NH3 by H2, the reaction generally follows the hydrogen-assisted activation mechanism of NO on the catalyst surface. That is, in commonly used catalysts supported on transition metal nanoparticles, NO adsorbed on the surface of metals such as Pd, Pt, and Rh first dissociates to produce nitrogen and oxygen atoms (NO→N). * +O * Subsequently, nitrogen atoms and highly reactive hydrogen atoms (H*) gradually combine to form NH3 (N). * +3H * →NH3). The dissociation of NO is considered the rate-determining step of this reaction, and the highly reactive hydrogen atoms, by rapidly removing the reactive oxygen species generated during NO dissociation, thus avoiding poisoning oxidation by the transition metal catalyst, also contribute to the continued activation of NO. The outer electronic structure of the NO molecule is (σ... g 2 ) (σ u 2 ) (σ g , π u ) (π g 1 NO has unpaired electrons in its 2π* orbitals, which, when interacting with transition metals, can form 5σ-d bonds similar to those formed by CO adsorption on metal surfaces. It is generally believed that the richer the electrons on the metal surface where NO is adsorbed, the more electrons can be provided to NO's 2π* antibonding orbitals, resulting in a stronger activation and dissociation effect on NO.

[0004] Due to the work function difference between semiconductors and metals, in recent years, the photoexcitation of semiconductor carriers with high Fermi levels to promote the transfer of photogenerated electrons to loaded low Fermi-level nanomaterials has attracted widespread research and attention, and some results have been achieved. However, limited by the matching of the Fermi levels of metals and semiconductors, when a space charge layer is formed at the contact between the semiconductor and the metal, the energy band of the semiconductor bends upward, forming a Schottky barrier at the interface. This barrier typically has a high contact resistance, restricting the free flow of charge carriers at the interface, resulting in a decrease in the utilization rate of photogenerated electrons, which may lead to a decrease in the long-term stability of the catalyst. Therefore, in order to regulate the adsorption and dissociation behavior of NO on the surface of transition metals and the process of hydrogenation to ammonia, it is worthwhile to find other ways or promoters that can continuously and effectively provide electrons to the active metal. Summary of the Invention

[0005] To address the aforementioned problems, the first objective of this invention is to provide a Pd-supported photothermal catalyst that enhances the performance of transition metal Pd in ​​the NO hydrogenation to ammonia synthesis reaction through photothermal synergy by loading Pd nanoparticles onto the surface of a rare earth hexaboride support.

[0006] The second objective of this invention is to provide a method for preparing a Pd-supported photothermal catalyst, which is simple and easy to implement and conducive to widespread application.

[0007] A third objective of this invention is to provide an application of a Pd-supported photothermal catalyst.

[0008] The first technical solution adopted in this invention is: a Pd-supported photothermal catalyst, comprising a rare earth hexaboride support and Pd nanoparticles, wherein the content of Pd nanoparticles in the Pd-supported photothermal catalyst is 0.5-2.5 wt%.

[0009] Preferably, the rare earth hexaboride support has a size of 50-200 nm; the rare earth element contained in the rare earth hexaboride support includes one of La, Ce, Pr, Nd, Sm and Eu.

[0010] The second technical solution adopted in this invention is: a method for preparing a Pd-supported photothermal catalyst as described in the first technical solution, comprising the following steps:

[0011] S1: Weigh anhydrous rare earth chloride and magnesium boride powder, grind and mix the anhydrous rare earth chloride and magnesium boride powder evenly, calcine under vacuum, and after cooling to room temperature, soak in dilute sulfuric acid solution and stir, then centrifuge, wash and dry to obtain the rare earth hexaboride carrier.

[0012] S2: Add PdCl2 solution and the rare earth hexaboride support to water, stir until the solution is completely evaporated, calcine, and then reduce with H2-Ar mixed gas to obtain the Pd-supported photothermal catalyst.

[0013] Preferably, the mass ratio of anhydrous rare earth chloride to magnesium boride powder in step S1 is 16:9 to 4:3.

[0014] Preferably, step S1 includes:

[0015] Anhydrous rare earth chloride and magnesium boride powder were weighed and added to a mortar. After grinding and mixing evenly under an infrared lamp, the mixture was transferred to a glass flask. The glass flask was sealed under a vacuum of 10 Pa using a vacuum sealing machine and an oxyhydrogen flame. The sealed glass flask was then transferred to the center of a muffle furnace and calcined at 850 °C for 10 h at a heating rate of 2 °C / min. After naturally cooling to room temperature, the sample was removed from the glass flask and immersed in 0.5 M dilute sulfuric acid solution with stirring for 6 h. The sample was then centrifuged, washed with deionized water, and vacuum dried at 60-80 °C to obtain the rare earth hexaboride support.

[0016] Preferably, the concentration of the PdCl2 solution in step S2 is 3.0 mg / mL; the mass ratio of Pd to the rare earth hexaboride support is 0.5%-2%.

[0017] Preferably, step S2 includes:

[0018] PdCl2 solution and the rare earth hexaboride support were added to 10 mL of water and mixed and stirred at 80 °C until the solution was completely evaporated. The mixture was then transferred to a muffle furnace and calcined at 400 °C for 2 h at a heating rate of 2 °C / min. Finally, the mixture was reduced at 300 °C for 2 h in a microtubular reactor using a H2-Ar mixed gas to obtain the photothermal catalyst supported on Pd.

[0019] Preferably, the concentration of H2 in the H2-Ar mixture is 5-10%, and the flow rate of the H2-Ar mixture is 100 mL / min. -1 .

[0020] The third technical solution adopted in this invention is: an application of a Pd-loaded photothermal catalyst as described in the first technical solution, comprising: placing the Pd-loaded photothermal catalyst and a focusing lens in a catalytic converter.

[0021] Preferably, the reaction pressure in the catalytic converter is 0.1 MPa, the temperature is 120-220 °C, and the light intensity is 2.0-3.0 W / cm². 2 .

[0022] The beneficial effects of the above technical solution are as follows:

[0023] (1) The photothermal catalyst for Pd supported in this invention is obtained by loading Pd nanoparticles onto the surface of a rare earth hexaboride support. The rare earth hexaboride support fully utilizes the metal-like LSPR effect, low work function, high conductivity, high carrier concentration, and high chemical stability of rare earth hexaborides. When Pd nanoparticles are loaded onto a rare earth hexaboride support, the interfacial barrier formed when loaded onto a traditional oxide semiconductor can be eliminated. The high-energy hot electrons generated by photoexcitation of the rare earth hexaboride support (e.g., LaB6) are more easily transferred to the surface of the active component Pd nanoparticles, thereby increasing the surface electron density of the active metal Pd and promoting the adsorption and activation of NO on its surface and the hydrogenation to ammonia reaction. The performance of the transition metal Pd in ​​catalyzing the hydrogenation to ammonia reaction of NO is improved through photothermal synergy.

[0024] (2) In this invention, Pd nanoparticles are combined with rare earth hexaborides with light absorption to prepare a Pd-supported photothermal catalyst. By introducing a focusing lens into a catalytic converter containing the Pd-supported photothermal catalyst, the removal of NO and the generation of NH3 can be achieved simultaneously at low temperature by utilizing photothermal coupling.

[0025] (3) By utilizing the LSPR effect of rare earth hexaboride supports (e.g., LaB6), this invention can not only promote the generation of high-energy hot electrons under photoexcitation conditions, but also significantly reduce the external heat source temperature required for the NO hydrogenation to ammonia synthesis reaction, thus effectively reducing the energy consumption of traditional thermocatalysis. Therefore, compared with the current conventional thermocatalytic reaction, this invention can not only effectively reduce the temperature of catalytic reduction of NO through photothermal coupling, but also significantly reduce the energy consumption required for traditional ammonia synthesis. It shows great promise in the development of a catalytic system for the removal of polluting nitrogen oxides and synergistic ammonia synthesis.

[0026] (4) The supported catalyst disclosed in this invention can not only improve the removal efficiency of nitrogen oxides through photothermal synergistic catalysis, but also significantly promote the generation of ammonia, a high industrial value-added product.

[0027] (5) The preparation method of the Pd-supported photothermal catalyst disclosed in this invention is simple and easy to operate. It is expected to achieve the efficient conversion of polluting nitrogen oxides into high-value-added chemical NH3 by adding a concentrating device around the photothermal reactor, and is suitable for widespread application. Attached Figure Description

[0028] Figure 1 A scanning electron microscope image of Pd / LaB6 with a Pd content of approximately 1.0 wt% provided for an embodiment of the present invention;

[0029] Figure 2An XRD pattern of Pd / LaB6 with a Pd content of approximately 1.0 wt% provided for one embodiment of the present invention;

[0030] Figure 3 The UV-Vis diffuse reflectance spectrum of Pd / LaB6 with a Pd content of approximately 1.0 wt% is provided for one embodiment of the present invention.

[0031] Figure 4 This is a schematic diagram of an atmospheric pressure flow reaction apparatus provided in one embodiment of the present invention. Detailed Implementation

[0032] To make the contents of this invention easier to understand, the invention will be further described below through specific embodiments. It should be noted that those skilled in the art can make several modifications and improvements without departing from the principle of this invention, and these should also be considered to fall within the protection scope of this invention.

[0033] The contents not described in detail in this specification are common knowledge to those skilled in the art.

[0034] This invention discloses a Pd-supported photothermal catalyst, comprising a rare earth hexaboride support and Pd nanoparticles, wherein the rare earth hexaboride support has a size of 50-200 nm; the content of Pd nanoparticles in the Pd-supported photothermal catalyst is 0.5-2.5 wt%, preferably 1.0 wt%; that is, the Pd-supported photothermal catalyst is a highly dispersed supported catalyst composed of a rare earth hexaboride as the support and Pd nanoparticles as the active component; wherein the rare earth elements contained in the rare earth hexaboride support (LnB6, Ln=La, Ce, Y, Sm…) include, but are not limited to, La, Ce, Pr, Nd, Sm and Eu;

[0035] The Pd-supported photothermal catalyst can achieve 100% conversion of NO and generation of NH3 under low temperature and normal pressure conditions of 120-220℃ under light irradiation.

[0036] This invention also discloses a method for preparing a Pd-supported photothermal catalyst, comprising: preparing a rare earth hexaboride support by vacuum calcination (i.e., vacuum calcination of molten salt), and loading the active component Pd onto the surface of the rare earth hexaboride support by hot impregnation reduction (i.e., hot impregnation-stirring method); wherein the rare earth elements contained in the rare earth hexaboride support include, but are not limited to, La, Ce, Pr, Nd, Sm and Eu.

[0037] The rare earth hexaboride support is LnB6 support, and the preparation method of the Pd-supported photothermal catalyst includes, for example, the following steps:

[0038] S1: Weigh anhydrous rare earth chloride (e.g., lanthanum chloride powder LaCl3) and magnesium boride powder (MgB2) in a mass ratio of 16:9 to 4:3 and add them to a mortar. Grind and mix them evenly under an infrared lamp, then transfer them to a glass flask (e.g., a single-necked flask). Seal the glass flask under a vacuum of 10 Pa using a vacuum sealing machine and an oxyhydrogen flame. Then transfer the sealed glass flask to the center of a muffle furnace and calcine it to 850 °C for 10 h at a heating rate of 2 °C / min. After it cools naturally to room temperature, take out the sample from the glass flask, immerse the sample in a 0.5 M dilute sulfuric acid solution and stir for 6 h. After centrifugation and washing with deionized water, dry it under vacuum at 60-80 °C to obtain the LnB6 support (e.g., LaB6 support).

[0039] The MgB2 raw material used in the rare earth hexaboride carrier preparation method disclosed in this invention is readily available, and the uniformly ground and mixed precursor only needs to be calcined after vacuuming once, without the need for continuous gas protection. The preparation method is simple and low in cost.

[0040] S2: Add an appropriate amount of PdCl2 solution and the LnB6 support (e.g., LaB6 support) to 10 mL of water, mix and stir at 80 °C until the solution is completely evaporated (e.g., slowly evaporated in an oil bath), then transfer to a muffle furnace. The muffle furnace is heated to 400 °C at a rate of 2 °C / min and calcined for 2 h. Finally, it is reduced in a microtubular reactor at 300 °C for 2 h using an H2-Ar mixed gas to obtain the Pd-supported photothermal catalyst. The concentration of the PdCl2 solution is 3.0 mg / mL, and the mass ratio of metallic Pd to the LnB6 support (e.g., LaB6 support) is 0.5%-2%. The concentration of H2 in the H2-Ar mixed gas is 5-10%, and the flow rate of the H2-Ar mixed gas is 100 mL / min. -1 .

[0041] This invention also discloses an application of a Pd-supported photothermal catalyst, comprising placing the Pd-supported photothermal catalyst and a focusing lens in a catalytic converter, and adjusting the focal length of the focusing lens to achieve the temperature and light intensity required for the photothermal reaction process, thereby achieving NO removal and NH3 generation at low temperatures through photothermal synergy; wherein the actual reaction pressure in the catalytic converter is 0.1 MPa, the temperature is 120-220 °C, and the light intensity is 2.0-3.0 W / cm². 2 .

[0042] The Pd-supported photothermal catalyst disclosed in this invention can realize the conversion of nitrogen oxides (NO) into high-value-added product NH3. Its application method is to introduce a focusing lens around the photothermal converter, thereby achieving the removal of NO and the generation of NH3 at low temperature and normal pressure through photothermal synergy. For planar reactors, the focusing lens is introduced by arranging it in the planar layer of the catalytic reactor; for annular reactors, the focusing lens can be arranged around the catalytic reactor.

[0043] To address the high energy consumption and poor low-temperature selectivity issues of traditional thermocatalytic NO hydrogenation to ammonia synthesis, this invention selects LnB6, which has good photoresponse and photothermal conversion effects, as a support to prepare a Pd-supported catalyst. This improves the performance of Pd / LnB6 in catalytic NO hydrogenation to ammonia synthesis by utilizing photothermal coupling. The catalyst preparation method is simple and easy to implement, which is conducive to its widespread application.

[0044] Rare-earth hexaboride carriers, as important hot electron emission source materials, possess a cubic CsCl-type crystal structure. In this structure, rare-earth atoms (Ln) occupy the eight vertices of the unit cell, while six boron atoms form an octahedral structure at the cell center via boron-bearing covalent bonds. One valence electron in each boron atom is not involved in bonding, resulting in free electrons within LnB6. This unique octahedral structure, combined with the special 4f orbitals of rare-earth elements and the 2s electron distribution in the outer shell of boron, contributes to the presence of free electrons in LnB6. 2 2p 1 The electron-deficient nature of LnB6 gives it a host of excellent physicochemical properties, including metallicity, low work function, high conductivity, high carrier concentration, and high chemical stability. Furthermore, when the particle size of rare-earth LnB6 is reduced to the nanoscale, its surface rich in free electrons exhibits a metal-like LSPR effect, demonstrating strong light absorption in the visible and even infrared regions, making it an excellent photoresponse and photothermal conversion material. Therefore, for the catalytic reduction of NO, given that transition metals typically have high work functions (low Fermi levels), this invention utilizes the metallicity, low work function, excellent photoresponse, and high carrier concentration of rare-earth hexaborides to construct an efficient heterojunction interface in conjunction with transition metal nanoparticles. This effectively guides the hot electrons generated by the LSPR effect of the LaB6 carrier to transfer directionally to the surface of the transition metal Pd, increasing the electron density on the Pd nanoparticle surface, and thus regulating the NO adsorption-dissociation-reduction process through photothermal synergy.

[0045] Example 1

[0046] (1) Add 1.6 g of anhydrous LaCl3 and 1.2 g of MgB2 powder to a mortar, grind evenly under an infrared lamp, and then transfer to a 50 mL glass flask. Use a vacuum sealing machine to evacuate the glass flask to 10 Pa and seal it with a hydrogen-oxygen flame. Then transfer it to the center of a muffle furnace and heat it at 2...o Heating rate increased to 850 °C / min o Calcination at C for 10 h. After naturally cooling to room temperature, the sample was removed from the glass flask and immersed in 0.5 M dilute sulfuric acid solution with stirring for 6 h. After centrifugation and washing with deionized water until the ion concentration was below 10 ppm, the sample was vacuum dried at 60-80 °C to obtain the LaB6 support.

[0047] (2) Add 2 mL of 3.0 mg / mL LPdCl2 solution and 0.36 g of LaB6 carrier to 10 mL of water, mix and stir, 80 o After being slowly dried in an oil bath, it is first transferred to the center of a muffle furnace at 2°C. o The heating rate was increased to 400 °C / min. o After calcining at C for 2 hours and cooling to room temperature, the mixture was transferred again to a microtubular reactor and heated at 300 °C with an H2-Ar mixture containing 5% H2. o A Pd-supported photothermal catalyst, namely Pd / LaB6 photothermal catalyst, was prepared by reduction at C for 2 h.

[0048] The prepared Pd / LaB6 photothermal catalyst was subjected to SEM testing, and the test results are as follows: Figure 1 As shown, from Figure 1 It can be seen that the Pd-supported photothermal catalyst exhibits an irregular and rough surface morphology of scattered particles, which helps the mass transfer of reactants and has a certain promoting effect on the adsorption of reactant molecules.

[0049] The Pd / LaB6 photothermal catalyst prepared on the LaB6 support was subjected to XRD testing, and the test results are as follows: Figure 2 As shown, by Figure 2 It can be seen that the diffraction intensity of LaB6 support and Pd / LaB6 photothermal catalyst is different at different diffraction angles (2 Theta). Compared with LaB6 support, the diffraction peak of Pd / LaB6 photothermal catalyst (i.e. Pd-supported photothermal catalyst) does not change significantly, and no characteristic diffraction peak of Pd is observed in the Pd-supported photothermal catalyst, which also indicates that Pd nanoparticles are uniformly dispersed on the LaB6 surface.

[0050] The Pd / LaB6 photothermal catalyst prepared on the LaB6 support was subjected to UV-Vis diffuse reflectance spectroscopy. The test results are as follows: Figure 3 As shown, by Figure 3It can be seen that the absorbance of LaB6 support and Pd / LaB6 photothermal catalyst at different wavelengths is as follows: The prepared LaB6 support itself has excellent light absorption capacity, which is further enhanced after loading metal Pd nanoparticles. This indicates that the prepared rare earth hexaboride as support for Pd photothermal catalyst can better utilize visible light and exert its photocatalytic effect.

[0051] Example 2

[0052] (1) Add 1.6 g of anhydrous CeCl3 and 1.0 g of MgB2 powder to a mortar, grind evenly under an infrared lamp, and then transfer to a 50 mL glass flask. Use a vacuum sealing machine to evacuate the glass flask to 10 Pa and seal it with a hydrogen-oxygen flame. Then transfer it to the center of a muffle furnace and heat it at 2... o Heating rate increased to 850 °C / min o Calcination was performed at C for 10 h. After the sample was allowed to cool naturally to room temperature, it was removed from the glass flask and immersed in 0.5 M dilute sulfuric acid solution with stirring for 6 h. The sample was then centrifuged, washed with deionized water until the ion concentration was below 10 ppm, and vacuum dried at 60-80 °C to obtain the CeB6 support.

[0053] (2) Add 1 mL of 3.0 mg / mL LPdCl2 solution and 0.36 g of CeB6 carrier to 10 mL of water, mix and stir, 80 o After being slowly dried in an oil bath, it is first transferred to the center of a muffle furnace at 2°C. o The heating rate was increased to 400 °C / min. o After calcining at C for 2 hours and cooling to room temperature, the mixture was transferred again to a microtubular reactor and heated at 300 °C with an H2-Ar mixture containing 5% H2. o A Pd-supported photothermal catalyst, namely Pd / CeB6 photothermal catalyst, was prepared by reduction at C for 2 h.

[0054] Example 3

[0055] (1) Add 1.6 g of anhydrous NdCl3 and 0.9 g of MgB2 powder to a mortar, grind evenly under an infrared lamp, and then transfer to a 50 mL glass flask. Use a vacuum sealing machine to evacuate the glass flask to 10 Pa and seal it with a hydrogen-oxygen flame. Then transfer it to the center of a muffle furnace and heat it at 2... o Heating rate increased to 850 °C / min oCalcination at C for 10 h. After naturally cooling to room temperature, the sample was removed from the glass flask and immersed in 0.5 M dilute sulfuric acid solution with stirring for 6 h. After centrifugation and washing with deionized water until the ion concentration was below 10 ppm, the sample was vacuum dried at 60-80 °C to obtain the NdB6 support.

[0056] (2) Add 5 mL of 3.0 mg / mL LpdCl2 solution and 0.35 g of NdB6 carrier to 10 mL of water, mix and stir, 80 o After being slowly dried in an oil bath, it is first transferred to the center of a muffle furnace at 2°C. o The heating rate was increased to 400 °C / min. o After calcining at C for 2 hours and cooling to room temperature, the mixture was transferred again to a microtubular reactor and heated at 300 °C with an H2-Ar mixture containing 5% H2. o A Pd-supported photothermal catalyst, namely Pd / NdB6 photothermal catalyst, was prepared by reduction at C for 2 h.

[0057] Example 4

[0058] (1) Add 1.6 g of anhydrous LaCl3 and 1.2 g of MgB2 powder to a mortar, grind evenly under an infrared lamp, and then transfer to a 50 mL glass flask. Use a vacuum sealing machine to evacuate the glass flask to 10 Pa and seal it with a hydrogen-oxygen flame. Then transfer it to the center of a muffle furnace and heat it at 2... o Heating rate increased to 850 °C / min o Calcination at C for 10 h. After naturally cooling to room temperature, the sample was removed from the glass flask and immersed in 0.5 M dilute sulfuric acid solution with stirring for 6 h. After centrifugation and washing with deionized water until the ion concentration was below 10 ppm, the sample was vacuum dried at 60-80 °C to obtain the LaB6 support.

[0059] (2) Add 2 mL of 3.0 mg / mL LPdCl2 solution and 0.18 g of LaB6 carrier to 10 mL of water, mix and stir, 80 o After being slowly dried in an oil bath, it is first transferred to the center of a muffle furnace at 2°C. o The heating rate was increased to 400 °C / min. o After calcining at C for 2 hours and cooling to room temperature, the mixture was transferred again to a microtubular reactor and heated at 300 °C with an H2-Ar mixture containing 5% H2. o A Pd-supported photothermal catalyst, namely Pd / LaB6 photothermal catalyst, was prepared by reduction at C for 2 h.

[0060] Example 5

[0061] (1) Add 1.6 g of anhydrous LaCl3 and 1.2 g of MgB2 powder to a mortar, grind evenly under an infrared lamp, and then transfer to a 50 mL glass flask. Use a vacuum sealing machine to evacuate the glass flask to 10 Pa and seal it with a hydrogen-oxygen flame. Then transfer it to the center of a muffle furnace and heat it at 2... o Heating rate increased to 850 °C / min o Calcination at C for 10 h. After naturally cooling to room temperature, the sample was removed from the glass flask and immersed in 0.5 M dilute sulfuric acid solution with stirring for 6 h. After centrifugation and washing with deionized water until the ion concentration was below 10 ppm, the sample was vacuum dried at 60-80 °C to obtain the LaB6 support.

[0062] (2) Add 2 mL of 3.0 mg / mL LPdCl2 solution and 0.72 g of LaB6 carrier to 10 mL of water, mix and stir, 80 o After being slowly dried in an oil bath, it is first transferred to the center of a muffle furnace at 2°C. o The heating rate was increased to 400 °C / min. o After calcining at C for 2 hours and cooling to room temperature, the mixture was transferred again to a microtubular reactor and heated at 300 °C with an H2-Ar mixture containing 5% H2. o A Pd-supported photothermal catalyst, namely Pd / LaB6 photothermal catalyst, was prepared by reduction at C for 2 h.

[0063] Example 6

[0064] The photothermal catalyst with Pd supported prepared in Example 1 was used to evaluate the performance of photothermal synergistic catalytic synthesis of ammonia from NO. This performance evaluation was conducted on a self-designed atmospheric pressure flow reactor; the atmospheric pressure flow reactor is as follows: Figure 4 As shown, the atmospheric pressure flow reaction device includes a gas distribution system (NO and H2 are respectively connected to a mass flow meter, and the mass flow meter is connected to a gas mixing tank), a quartz reactor, a circulating oil bath temperature control system, a light source, and a photoacoustic spectrometer; the quartz reactor is connected to the gas distribution system, the circulating oil bath temperature control system, and the photoacoustic spectrometer.

[0065] The quartz reactor is a self-designed double-layered quartz glass (inner layer: 20 mm long × 20 mm wide × 1 mm high, outer layer: 40 mm long × 40 mm wide × 4 mm high). The inner layer of the quartz reactor is filled with catalyst, and the outer layer can be circulated with colorless and transparent circulating silicone oil to control the temperature of the external heat source. A xenon lamp light source is set above the quartz reactor to excite the catalyst to generate a photoresponse. The outlet of the xenon lamp light source is equipped with an adjustable focal length focusing lens, and the focused light source can reach the catalyst surface through the glass reactor.

[0066] Reaction conditions: 0.2 g of Pd-supported photothermal catalyst was packed into a quartz reactor as described above. The catalyst particles were approximately 0.2-0.3 mm (60-80 mesh). Reaction gas entered the glass reactor containing the catalyst particles through the inlet. The reactor was supplied with the required external temperature via a circulating oil bath controlled by a programmed temperature rise, and the reactor was irradiated with visible light. The contents of H2 and NO in the reaction gas were fixed at 0.45 vol.% and 0.15 vol.%, respectively. N2 was used as a makeup gas, and the total flow rate of the reaction gas was approximately 100 mL·min. -1 The concentrations of CO, CO2, N2O, H2O, and NH3 in the atmosphere were analyzed online using a GASERA One photoacoustic spectrometer (PAS). The concentration changes of NO were analyzed online using a Testo300 flue gas analyzer (i.e., a NO analyzer). The NO conversion rate and NH3 selectivity were calculated based on the results after one hour of reaction. The formulas for calculating NO conversion and NH3 selective conversion are as follows:

[0067] ;

[0068] ;

[0069] In the formulas for calculating NO conversion and selective NH3 conversion, [NO]... in and [NO] out The NO content (V%) in the intake air and the exhaust air, respectively, and [NH3] content, are shown below. out The NH3 content (V%) in the outflow gas.

[0070] Using this method, the performance of the Pd-supported photothermal catalyst in removing NO and its selectivity for NH3 under different conditions were evaluated, and the results are shown in Table 1.

[0071] Table 1. Performance and selectivity of 1.0 wt% Pd / LaB6 catalyst for NO removal before and after illumination, and for NH3 removal.

[0072]

[0073] As shown in Table 1, the Pd-supported photothermal catalyst prepared in this invention has good performance in reducing NO with H2. It can achieve 100% NO conversion under thermal conditions alone. Under the same conditions, the selectivity of NH3 is significantly improved after the introduction of light irradiation, which proves that light irradiation has a very significant promoting effect on the performance of the catalyst.

[0074] Example 7

[0075] The photothermal catalyst with Pd supported prepared in Example 1 was used to evaluate the performance of photothermal coupled catalytic NO hydrogenation to ammonia synthesis. This performance evaluation was conducted as follows: Figure 4The reaction is carried out in an atmospheric pressure flow apparatus as shown. The quartz reactor is a self-designed single-layer quartz glass (20 mm long × 15 mm wide × 1 mm high). The inner layer of the photothermal catalytic reactor is filled with catalyst, and a xenon lamp light source is set above it to excite the catalyst to generate photoresponse and photothermal effect. The outlet of the xenon lamp light source is equipped with an adjustable focal length focusing lens, and the focused light source can reach the catalyst surface through the glass reactor.

[0076] Reaction conditions: 0.2 g of Pd-loaded photothermal catalyst was packed into a quartz reactor as described above. The catalyst particles were approximately 0.2-0.3 mm (60-80 mesh). Reaction gas entered the glass reactor containing the catalyst particles through the inlet. Without an external heating source, the reactor was directly irradiated with a xenon lamp, and the irradiation intensity was controlled by adjusting the xenon lamp current. The contents of H2 and NO in the reaction gas were fixed at 0.45 vol.% and 0.15 vol.%, respectively. N2 was used as a makeup gas, and the total flow rate of the reaction gas was approximately 100 mL·min. -1 The concentrations of CO, CO2, N2O, H2O, and NH3 in the atmosphere were analyzed online using a GASERA One photoacoustic spectrometer (PAS). The concentration changes of NO were analyzed online using a Testo300 flue gas analyzer (i.e., a NO analyzer). The NO conversion rate and NH3 selectivity were calculated based on the results after one hour of reaction. The formulas for calculating NO conversion and NH3 selective conversion are as follows:

[0077] ;

[0078] ;

[0079] In the formulas for calculating NO conversion and selective NH3 conversion, [NO]... in and [NO] out The NO content (V%) in the intake air and the exhaust air, respectively, and [NH3] content, are shown below. out The NH3 content (V%) in the outflow gas.

[0080] Following this method, the performance of the Pd-supported photothermal catalyst in removing NO and its selectivity for NH3 under different conditions were evaluated, and the results are shown in Table 2.

[0081] Table 2. Performance and selectivity of NO removal by 1.0 wt% Pd / LaB6 catalytic catalyst under illumination for NH3 removal.

[0082]

[0083] As shown in Table 2, the Pd-supported photothermal catalyst prepared in this invention has good performance in reducing NO with H2. Without an external heating source, 100% NO conversion can be achieved by pure light irradiation alone. Moreover, the selectivity of NH3 increases with the increase of light intensity, which proves that the catalyst has both good photoresponse and photothermal conversion effect, and has a very significant photothermal coupling effect on the catalytic hydrogenation of NO to ammonia.

[0084] The present invention has been described in detail above with reference to specific embodiments and exemplary examples. These descriptions are exemplary and not exhaustive, and are not limited to the disclosed embodiments; the above descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and implementation methods of the present invention without departing from the spirit and scope of the present invention, and all such modifications and improvements fall within the scope of the present invention; the scope of protection of the present invention is determined by the appended claims.

Claims

1. The application of a Pd-supported photothermal catalyst in the catalytic hydrogenation of NO to ammonia, characterized in that, The Pd-supported photothermal catalyst comprises a rare earth hexaboride support and Pd nanoparticles, wherein the content of Pd nanoparticles in the Pd-supported photothermal catalyst is 0.5-2.5 wt%.

2. The application according to claim 1, characterized in that, The rare earth hexaboride support has a size of 50-200 nm; the rare earth elements contained in the rare earth hexaboride support include one of La, Ce, Pr, Nd, Sm and Eu.

3. The application according to any one of claims 1-2, characterized in that, The preparation method of the Pd-supported photothermal catalyst includes the following steps: S1: Weigh anhydrous rare earth chloride and magnesium boride powder, grind and mix the anhydrous rare earth chloride and magnesium boride powder evenly, calcine under vacuum, and after cooling to room temperature, soak in dilute sulfuric acid solution and stir, then centrifuge, wash and dry to obtain the rare earth hexaboride carrier. S2: Add PdCl2 solution and the rare earth hexaboride support to water, stir until the solution is completely evaporated, calcine, and then reduce with H2-Ar mixed gas to obtain the Pd-supported photothermal catalyst.

4. The application according to claim 3, characterized in that, In step S1, the mass ratio of anhydrous rare earth chloride to magnesium boride powder is 16:9 to 4:

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5. The application according to claim 3, characterized in that, Step S1 includes: Anhydrous rare earth chloride and magnesium boride powder were weighed and added to a mortar. After grinding and mixing evenly under an infrared lamp, the mixture was transferred to a glass flask. The glass flask was sealed under a vacuum of 10 Pa using a vacuum sealing machine and an oxyhydrogen flame. The sealed glass flask was then transferred to the center of a muffle furnace and calcined at 850 °C for 10 h at a heating rate of 2 °C / min. After naturally cooling to room temperature, the sample was removed from the glass flask and immersed in 0.5 M dilute sulfuric acid solution with stirring for 6 h. The sample was then centrifuged, washed with deionized water, and vacuum dried at 60-80 °C to obtain the rare earth hexaboride support.

6. The application according to claim 3, characterized in that, The concentration of the PdCl2 solution in step S2 is 3.0 mg / mL; Pd accounts for 0.5-2 wt% of the rare earth hexaboride support.

7. The application according to claim 3, characterized in that, Step S2 includes: PdCl2 solution and the rare earth hexaboride support were added to 10 mL of water and mixed and stirred at 80 °C until the solution was completely evaporated. The mixture was then transferred to a muffle furnace and calcined at 400 °C for 2 h at a heating rate of 2 °C / min. Finally, the mixture was reduced at 300 °C for 2 h in a microtubular reactor using a H2-Ar mixed gas to obtain the photothermal catalyst supported on Pd.

8. The application according to claim 7, characterized in that, The concentration of H2 in the H2-Ar mixture is 5-10%, and the flow rate of the H2-Ar mixture is 100 mL / min. -1 .

9. The application according to any one of claims 1-2, characterized in that, include: The Pd-loaded photothermal catalyst and the focusing lens are placed in the catalytic converter.

10. The application according to claim 9, characterized in that, The reaction pressure in the catalytic converter is 0.1 MPa, the temperature is 120-220 °C, and the light intensity is 2.0-3.0 W / cm². 2 .

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