Preparation And Functionalization Of Boron Doped Cerium-based Catalysts And Selective Catalytic Oxidation

As a typical rare earth material,nano cerium oxide（Ce O₂）has been widely used in industrial catalysis,energy storage,photocatalysis and battery due to its unique electronic structure,physical and chemical properties,small size effect and so on.However,cerium oxide’s low visible light absorption,high carrier recombination efficiency,low specific surface area,surface interface acidity and alkalinity,and active sites limit the improvement of its catalytic efficiency in the field of catalysis.How to create a new preparation method or to control the interface properties,texture properties and optical band gap of nano-Ce O₂by means of heteratomic doping is still a hot spot and difficulty in the research of nano-functional materials of cerium oxide.In this paper,based on the nucleation and crystallization isolation method assisted by the nano-bubble effect developed by the research group,the controllable preparation of B-doped Ce O₂ nanofunctional materials with high specific surface area and rich defect sites was achieved by using the nano-bubble effect of hydrogen generated by the self-hydrolysis of sodium borohydride as precipitator.The effects of B doping on the surface interface acid/alkali,oxygen defect concentration and optical band gap of Ce O₂ materials were studied.The effects of the composition,structure and surface/interface properties on the selective catalytic oxidation performance of Ce O₂ materials were systematically investigated.The main research contents are as follows:1.Based on the explosive nucleation environment and external field force strengthening（synergy between gravity,friction and shear force）provided by the rotary liquid film microreactor,a series of high specific surface areas were obtained by controlling the dosage of sodium borohydride,hydrothermal crystallization temperature and roasting temperature,etc.The effects of the composition and structure of B-Ce O₂ catalyst and the reaction conditions（temperature,time,pressure）on the catalytic performance of cyclohexene selective oxidation were systematically investigated by using B-Ce O₂ catalyst as a probe reaction.The results show that the obtained B-Ce O₂ has excellent catalytic activity and selectivity in the oxidation of cyclohexene.The 100%conversion of cyclohexene can be achieved under the atmospheric pressure reaction condition of 70℃.The selectivity of cyclohexenone is up to 71%,cyclohexenol is up to 23%,and cyclohexane is close to 6%.The selectivity of the catalyst for cyclohexenone is better than that reported so far.The experimental results and DFT theoretical calculations show that the introduction of B can significantly reduce the energy of oxygen vacancy formation in B-Ce O₂,and facilitate the construction of more surface/interface defect sites and acid-base active centers.The abundant Lewis acid centers and defective structures on the catalyst surface are favorable for the adsorption of cyclohexene on the catalyst surface and the activation of allyl sites,and the suitable surface alkaline sites can inhibit the oxidation of C=C double bonds.2.On the basis of the above work,we found that doping B can significantly affect the B-Ce O₂ optical absorption,can not only achieve its full absorption of ultraviolet light,at the same time it can significantly improve its absorption of visible light,the DFT theory calculation results show that the introduction of the B to build atomic energy level,effectively reduce the optical band gap of Ce O₂.Based on the above research results,mono-dispersed Fe₃O₄ magnetic nucleus was prepared by combining nucleation-crystallization isolation method and reduction-oxidation method,and B-Ce O₂@Fe₃O₄ composite photocatalytic material was constructed,and highly uniform composite of Au nanoparticles on the surface of the material was realized by impregnation method.Au/B-Ce O₂@Fe₃O₄ composite photocatalyst was obtained,which showed excellent catalytic selectivity,reusability stability and recyclability in the selective catalytic oxidation of benzyl alcohol to benzaldehyde.Excellent catalytic performance is mainly thanks to the introduction of B can effectively improve the utilization rate of catalysts of visible light absorption and the photon to the synergies between Au and Ce O₂ can improve the living carrier mobility of inhibiting light electrons and holes in the compound,as well as the high specific surface area and abundant defect structure for benzyl alcohol on the surface of the catalyst,adsorption and reaction.