Preparation,Characterization And Mechanism Of Ceria-Based Pt Catalysts For Formaldehyde Purification At Low Temperatures

Formaldehyde released from interior decoration materials and car accessories is a carcinogen,which seriously endangers human health.Studies have shown that catalytic oxidation is the most environmentally friendly and clean method,and it is more efficient as a supported Pt catalyst.Among them,ceria is a carrier that has received more attention due to its excellent redox performance.In this thesis,we prepared CeO₂nanocrystal,Pt/CeO₂ nanorod and Pt/CeO₂ nanocube catalysts to systematically study the performance and mechanism of formaldehyde purification at low temperature.The main conclusions are as follows:1.Ceria nanocrystals with the size of 2.5 nm were synthesized by hydrothermal method,which showed good formaldehyde purification performance in low temperature formaldehyde oxidation reaction,and formaldehyde can be completely oxidized at 553 K under dry and wet conditions.The physical and chemical properties of nanocrystals show that the small size of nanocrystals makes them produce abundant oxygen vacancies,showing high oxygen activation ability and lattice oxygen oxidation activity,which significantly improves the performance and stability of formaldehyde oxidation reaction.Mechanism analysis shows that formaldehyde is oxidized under the action of ceria lattice oxygen to produce intermediate products DOM（dioxymethylene）and formate,which are then further oxidized to carbon dioxide and water by adsorbed oxygen.2.Pt/CeO₂ nanorod catalysts with the same morphology but different Ceria nanocrystals were prepared,and they have extremely high formaldehyde purification performance at room temperature.The catalyst physical characterization and formaldehyde oxidation reaction performance results show that the formaldehyde oxidation performance of the Pt/CeO₂ nanorod catalysts are highly dependent on the ceria nanocrystals size.Compared with 0.2Pt/CeO₂-B and 0.2Pt/CeO₂-C nanorod catalysts with larger ceria nanocrystals size,0.2Pt/CeO₂-A nanorod catalyst with the smallest nanocrystals size has the highest oxidation performance and good stability in high wet conditions.Mechanism analysis shows that formaldehyde is first activated by the lattice oxygen on the ceria surface to generate intermediate products DOM,formate and CO,and then it is oxidized to the final product CO₂ by active lattice oxygen on the surface of CeO₂and atomic oxygen on the surface of Pt.3.Pt/CeO₂-R and Pt/CeO₂-C catalysts supported on CeO₂ nanorods and nanocubes were synthesized,and the influence of the morphology of the support on the oxidation performance of formaldehyde at room temperature was investigated.The results show that Pt/CeO₂-R catalyst has smaller nanocrystalline size,stronger redox performance,more abundant oxygen vacancies and higher surface lattice oxygen activity than Pt/CeO₂-C catalyst,which shows better formaldehyde oxidation performance and can completely eliminate formaldehyde at room temperature.Mechanism analysis shows that formaldehyde is activated by lattice oxygen on CeO₂ surface to form intermediate products DOM,formate and CO.Then,the adsorbed CO is further oxidized to CO₂ by the oxygen species activated by Pt particles and separated from the catalyst surface.By comparison,it is found that the morphology of CeO₂ affects the formate decomposition rate and CO₂ release rate of Pt/CeO₂-R on the Pt-CeO₂ interface.