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CN-121972161-A - Preparation and doping modification of rare earth oxide loaded transition metal nano particles for low-pressure synthesis of ammonia

CN121972161ACN 121972161 ACN121972161 ACN 121972161ACN-121972161-A

Abstract

The invention belongs to the technical field of new materials, and particularly relates to preparation and doping modification of rare earth oxide loaded transition metal nano particles for low-pressure synthesis ammonia. The supported synthetic ammonia catalyst provided by the invention comprises a ceria carrier (CeO 2 ) with characteristic morphology and rich oxygen vacancies, a lanthanum doped modified ceria carrier (La-CeO 2 ), and a metal nano material which is supported on the rare earth metal oxide carrier and is generated by high-temperature gas phase reduction, wherein rare earth metal nitrate and an organic ligand are dissolved in N-N dimethylformamide, then an initiator and a stabilizer are added, the obtained mixed solution is placed in a hydrothermal kettle and subjected to solvothermal reaction at high temperature, a metal organic framework precursor obtained by the solvothermal reaction is subjected to centrifugation, washing, drying and calcination to obtain the rare earth metal oxide carrier, and a transition metal chloride is supported on the rare earth metal oxide carrier by using acetone as a solvent through a rotary evaporation method, and the rare earth metal oxide synthetic ammonia catalyst loaded with transition metal nano particles is prepared through high-temperature treatment in a reducing atmosphere. The supported synthetic ammonia catalyst has strong nitrogen activating capability and high low-pressure synthetic ammonia performance.

Inventors

  • HUANG YICHAO
  • WANG YANFEI
  • WU WENRUI
  • CHEN JIANGWEI

Assignees

  • 中国石油大学(华东)

Dates

Publication Date
20260505
Application Date
20260311

Claims (6)

  1. 1. The preparation and doping modification of rare earth oxide loaded transition metal nano particles for low-pressure synthesis ammonia are characterized in that the loaded synthesis ammonia catalyst comprises a cerium oxide carrier (CeO 2 ) with characteristic morphology and rich oxygen vacancies, a lanthanum doped modified cerium oxide carrier (La-CeO 2 ) and a transition metal nano material which is loaded on the rare earth oxide carrier and is prepared by high-temperature gas phase reduction.
  2. 2. The supported ammonia synthesis catalyst according to claim 1, wherein the rare earth metal oxide support is cerium oxide (CeO 2 ) and lanthanum doped cerium oxide (La-CeO 2 ), is prepared from cerium based metal organic frameworks Ce-UIO-66 and La-Ce-UIO-66 by muffle calcination, wherein Ce-UIO-66 is prepared from ammonium cerium nitrate ((NH 4 ) 2 Ce(NO 3 ) 6 ) and terephthalic acid (H 2 BDC) by solvothermal reaction, la-Ce-UIO-66 is prepared from ammonium cerium nitrate ((NH 4 ) 2 Ce(NO 3 ) 6 ), lanthanum nitrate hexahydrate (La (NO 3 ) 3 ·6H 2 O) and terephthalic acid (H 2 BDC) by solvothermal reaction, and/or the transition metal nanomaterial is ruthenium, is prepared from ruthenium trichloride (RuCl 3 ) by high temperature reducing atmosphere treatment.
  3. 3. A method for preparing and modifying the supported ammonia synthesis catalyst according to claim 1 or 2, comprising the steps of: Step 1: Ce-UIO-66 synthesis by dissolving terephthalic acid in N, N-Dimethylformamide (DMF) and stirring until complete dissolution. And (3) dropwise adding an aqueous solution of ammonium cerium nitrate into the solution. The initiator and stabilizer were then added and vigorously stirred for 30 minutes, forming a uniformly mixed solution. The mixture was then transferred to a polytetrafluoroethylene-lined stainless steel reactor and reacted at 120 ℃ for 24 hours. The white precipitate was collected by centrifugation. The mixture was washed with DMF and acetone by centrifugation and dried overnight under vacuum at 60℃to give Ce-UIO-66 powder. La-Ce-UIO-66 was synthesized in the same manner as described above, except that the same molar amount of ammonium cerium nitrate was replaced with a molar amount of lanthanum nitrate hexahydrate. And 2, pyrolyzing the Ce-UIO-66 and La-Ce-UIO-66 precursors in a muffle furnace for 4 hours to obtain CeO 2 and La-CeO 2 . And 3, dissolving a certain amount of ruthenium trichloride (ruthenium: 37.22%) in acetone, continuously stirring, dispersing the prepared rare earth metal oxide carrier in the solution, evaporating to dryness by using a rotary evaporator, and then placing the solution in a 500 ℃ reducing atmosphere for reduction for 2 hours to obtain the synthetic ammonia catalyst of the transition metal nano-particle Ru material loaded by the rare earth metal oxide carrier.
  4. 4. A method for preparing and modifying an ammonia catalyst for synthesizing a rare earth metal oxide-supported transition metal nanoparticle Ru material according to claim 3, wherein a ruthenium-containing compound including, but not limited to, ruthenium trichloride is used as the ruthenium source.
  5. 5. The method of claim 3, wherein the molar ratio of cerium ammonium nitrate to lanthanum nitrate hexahydrate in the rare earth nitrate precursor is 4:1, the molar ratio of metal ions (Ce 4+ 、La 3+ ) in the rare earth nitrate precursor to terephthalic acid H 2 BDC in the organic ligand solution is 1:1.2, the solvent DMF for the solvothermal reaction is 50 ml, the initiator and stabilizer for the solvothermal reaction is glacial acetic acid, the initiator and stabilizer glacial acetic acid are 8.5 ml, the pyrolysis temperature of the precursor in the muffle furnace is 500 ℃, the reducing atmosphere is a mixture of hydrogen and argon (H 2 : 8%), and the theoretical loading of the transition metal nanoparticles Ru is controlled at 5 wt%.
  6. 6. Use of a supported catalyst of rare earth metal oxide supported transition metal nanoparticle material according to claim 1 or 2 as a catalyst for ammonia synthesis in the preparation of ammonia gas.

Description

Preparation and doping modification of rare earth oxide loaded transition metal nano particles for low-pressure synthesis of ammonia Technical Field The invention belongs to the technical field of new materials, and particularly relates to a preparation method and a La doping modification method of a synthetic ammonia catalyst of a transition metal nano-particle Ru material loaded by rare earth metal oxide CeO 2. Background Ammonia (NH 3) is an important inorganic compound and is widely used in agriculture, industry, military and other fields. Synthetic ammonia is one of the largest chemical industries in the world and is the basis for the development of modern society. Firstly, ammonia is used as fertilizer, which fosters almost half of the world population. Secondly, because of its high hydrogen content (17.7 wt%), ammonia can also be an important hydrogen storage material, it has very high energy density (3 kWh kg -1), and modern synthetic ammonia industry systems have well-developed and complete production transport chains, so ammonia is an excellent carbon-free energy source, becoming an important candidate for energy conversion. However, most of the hydrogen in the feed gas used in the conventional ammonia synthesis industry comes from water gas conversion or methane reforming of natural gas and coal, and is accompanied by huge energy consumption and carbon dioxide emission in the process, which does not conform to the concept of carbon-free sustainable society, so it is very important to develop an environment-friendly haber-bosch ammonia synthesis process. In recent years, along with the expansion of the electric scale of renewable energy sources, the hydrogen production from green carbon-free electrolyzed water is gradually commercialized, and the Haber-Bosch ammonia synthesis process concept driven by the electrolyzed water is proposed, and aims to realize ammonia synthesis by taking green hydrogen generated by the electrolyzed water and nitrogen separated from air as raw material gases, so that the whole process has no carbon emission, and accords with the sustainable development concept of energy conservation and emission reduction. However, the reaction pressure of the existing electrolytic water hydrogen production system is 1.0-3.2 MPa, and the Haber-Bosch synthesis ammonia process with high temperature and high pressure (400-600 ℃ and 20-40 MPa) is difficult to match, so that the development of a catalyst capable of catalyzing ammonia synthesis well under mild conditions becomes a problem to be solved urgently. The ruthenium-based catalyst taking active carbon as a carrier is used as a second-generation ammonia synthesis catalyst after the iron-based iron catalyst, and the activity of the second-generation ammonia synthesis catalyst is far higher than that of the Fe-based catalyst under mild conditions. Although Ru-based catalysts have good catalytic performance, under ammonia synthesis conditions, their activation of feed gas nitrogen is inhibited by active hydrogen occupying active sites, known as hydrogen poisoning, and during long-term reaction, methanation of the activated carbon support occurs to deactivate the catalyst, resulting in poor stability. Therefore, there is a need to develop a non-carbon carrier that can effectively inhibit hydrogen poisoning and has good stability. Cerium oxide (CeO 2) is taken as a reducible oxide, has excellent hydrogen storage capacity, rich surface defects and unique electronic properties, and reversible oxidation-reduction potential between Ce 3+ and Ce 4+, and oxygen vacancies (defect sites) are easily formed on the surface of CeO 2, and when Ru nano particles are loaded on the surface of the cerium oxide, the vacancies can transfer electrons to Ru species on the surface of the cerium oxide, so that Ru is in an electron-rich state. In the synthesis ammonia reaction, the electron transfer can effectively weaken the excessively strong adsorption of Ru to active hydrogen (H), avoid the blocking of active sites, and promote the dissociation of nitrogen (N 2). However, sintering of single CeO 2 may occur under a high-temperature reducing atmosphere, and there is room for improvement in the concentration and stability of oxygen vacancies. Compared with Ce 4+, la 3+ has larger ionic radius and lower valence state, and the La 3+ is doped into CeO 2 crystal lattice to form solid solution, so that the lattice distortion can be generated, the concentration of oxygen vacancies is obviously increased, and the thermal stability of the carrier is improved. This effect is expected to further enhance the metal-support interaction, resulting in better catalytic performance. Therefore, based on the characteristics, the ammonia synthesis performance of the supported ruthenium-based catalyst can be effectively improved by reasonably regulating and controlling the physicochemical properties of the ceria carrier. Disclosure of Invention The invention aims to provide a prep