Design And Construction Of Highly Active Catalysts And Their Photocatalytic Methane And Plastic Oxidation Performance

This thesis focuses on design and construction of the photocatalysts with highlyefficiency active sites and their application in the field of CH4/plastic oxidation to alleviate the greenhouse effect caused by CH4 and the white pollution caused by plastics.Initially,the synthesized conditions of photocatalysts are regulated to precisely construct the highly-efficiency active sites on their surface,achieving the adjustment of the reactive active sites.Moreover,by the multidimensional in situ characterizations and theoretical calculation,the microcosmic mechanism of CH4/plastic photooxidation is disclosed in molecular/atomic level,which reveal the intrinsic interaction between active sites and the property of CH4/plastic photooxidation,finally reaching the high active and selective CH4/plastic photooxidation.The main contents of this dissertation are as follows:Ⅰ.The mechanism of CH4 activation by charge-localized active sites1.Based on the conductor charge transfer mechanism,the idea of metal sites with partial positive charge serve as active sites is designed,and the charge-accumulated carbon atoms are constructed to promote the polarization and activation of inert C-H bond.In addition,the microcosmic mechanism of CH4 photooxidation is revealed by in situ EPR spectra and in situ FTIR,and thus achieving the selective CH4 photooxidation into CH3OOH.2.Based on the charge transfer pathway on the Z-scheme heterojunction,the idea of metal sites with highly localized electric field as active sites is proposed,and a methodology of analyzing heterojunction types is developed,which directly confirms the type of Fe2O3/ZnO heterojunction.Moreover,in situ characterizations and theoretical calculation uncover the charge-accumulated Fe sites enable to boost the adsorption and activation of CH4.Furthermore,the charge-accumulated Fe sites can strengthen the O-H bond in CH3OH,and hence achieving the highest active of CH4 photooxidation into CH3OH than that of previous reported literatures under room temperature,ambient pressure and oxygen-free system.Ⅱ.Mechanism of CH4 coupling reaction intermediates anchored on dual-active species1.Based on the active site regulation of reaction intermediates mechanism,the idea of dual-active species anchoring the reactive intermediates is designed,and the Auδ-and O-dual-active species are built to improving the performance of CH4 coupling.Besides,in situ characterizations unveil the Auδ-and O-dual-active species anchor the reactive intermediates for the generation of[Auδ-··CH4··O-]and[Auδ-··CH3··O-]structure,which can boost the polarization of CH4 and suppress the overoxidation of CH4,and therefore Au/ZnO porous nanosheets achieve the highest yield of CH4 coupling into C2H6 than that of previous reports under oxygen-free system.Ⅲ.The novel approach of plastic photooxidation1.Based on the study of the C-H bond in CH4 molecules,the idea of charge asymmetric dual-active sites system is proposed and the application in the high stability of plastic photooxidation.Here,the asymmetric charges at adjacent Zr and Fe sites are constructed to promote the oxidation of reactive intermediates.Moreover,in situ characterizations and theoretical calculation demonstrate the asymmetric charge of dual-active sites can assist the polarization of plastic and subsequent stepwise oxidation to form the C2 products,reaching the plastic oxidation into CH3COOH.2.Based on the research of CH4 photooxidation and CO2 photoreduction,the idea of plastic-CO2-fuels system is designed,and the photocatalysts with the Nb5+-O2polarized sites are synthesized to achieve the total oxidation into CO2.Subsequently,the generated CO2 can be reduced into carbonaceous fuels by the Nb5+-O2-polarized sites,and building the system of two-step redox process for plastics to carbonaceous fuels.