The Preparation And Properties Study Of Two-dimensional Cerium Oxide Nanosheets Supported Gold Nanoparticle Catalyst

CO oxidation has a wide range of applications in the treatment of environmental pollution,especially in the purification of automobile exhaust and industrial waste gas.Therefore,the design and preparation of catalysts with high-efficiency catalytic CO oxidation performance has been a hot research topic in recent years.Because of its unique electronic structure and oxygen storage and release capability,CeO₂ is often used as a support to load metal and applied to catalyze CO oxidation reactions.Many studies have shown that the performance of CeO₂-based catalysts in the CO oxidation reaction is closely related to the morphology of CeO₂nanomaterials,specific surface area,surface defects and other factors,especially directly related to the surface oxygen vacancies concentration of CeO₂.Therefore,how to achieve the controllable adjustment of the surface oxygen vacancies concentration of CeO₂ through physical and chemical methods,and to improve the intrinsic activity of the catalyst,is the key to the wide application of CeO₂-based catalysts in the field of thermal catalysis.The CeO₂nanosheets were designed and synthesized in this thesis by the liquid nitrogen rapid freezing method.Furthermore,Au nanoparticles were loaded on the as-prepared two-dimensional CeO₂nanosheets,and the catalyst had high surface oxygen vacancy concentration;and the traditional three-dimensional CeO₂ materials including nanopolyhedrons,nanoparticles,and nanocubes were compared to study the effect of the concentration of oxygen vacancies on the surface of AuNP/CeO₂ catalysts on the performance of CO oxidation reaction.The results showed that the performance of AuNP/CeO₂ nanosheets catalysts is significantly better than other catalysts.At the same time,we also studied the active center composition and structure of the catalyst in the CO oxidation process,and put forward reasonable assumptions about its reaction mechanism.The specific content were as follows:(1)Preparation of AuNP/CeO₂ nanosheets catalysts.Using graphene oxide(GO)as a template,the precursor was synthesized by the liquid nitrogen rapid freezing method.By optimizing the calcination experimental conditions,it was found that calcination at 400? for4 h can successfully prepare ultra-thin CeO₂ nanosheets.The CeO₂ with other three-dimensional morphologies was synthesized by hydrothermal method,and then 1%AuNP/CeO₂catalysts with different morphologies like nanopolyhedrons,nanoparticles,nanocubes were prepared by colloidal deposition.The test results of BET,XPS,and Raman showed that 1%AuNP/CeO₂ nanosheets catalysts have the high specific surface area and high concentration of Ce³⁺.1%AuNP/CeO₂ nanosheets catalysts show excellent catalytic activity and stability in the CO oxidation reaction.At 94?C,the CO conversion rate can reach 90%.(2)Study on catalytic performance of AuNP/CeO₂ nanosheets catalysts for CO oxidation.We tracked the evolution of the gold species on the surface of the 1%AuNP/CeO₂ nanosheets catalysts by in situ DRIFTS.After being activated by air at 300?,the gold species Au⁰ were transformed into Au⁺,possibly because the gold particles were redispersed into smaller particles and cluster structures,and the gold species Au⁺played a major role as active sites in the CO oxidation.The gold species Au⁰ and Au⁺can be reversibly transformed,and the catalytically active species Au⁺were a dynamic formation process.We also discussed its reaction mechanism,and believe that the catalyst catalyzed the CO oxidation reaction to follow the Mars-van Krevelen(M-v K)mechanism.