Studies On Mechanisms Of Catalytic Reactions On Metal Oxide Surface In The View Of Energy Levels

Activity,selectivity and stability are the three main issues in catalytic chemistry.These three performance parameters are mainly determined by active site,intermediates and reaction pathway in catalytic system.So to study the active site and reaction pathway at molecular,atomic level is profound in theoretical understanding and catalyst optimizing.Due to the limitation of the current experimental characterization,the first-principle calculation plays an important part in reaction mechanism study.In this thesis,the concept of "energy level" has been applied to study the active site and reaction networks in catalytic reaction.By doing this,I aimed to offer a thought and a method in catalytic mechanism study.And based on energy level,I studied the catalytic reaction of oxidative dehydrogenation of alkanes and hydrogenation of CO,CO2.In the reaction of HCl-assisted oxidative dehydrogenation of alkanes on CeO2 catalyst,I calculated the protonic level and electronic level of every site on the solid surface and I found the molecular O2 changed into peroxide species at oxygen vacancy site on CeO2.The peroxide species oxidized HCl into Cl-radical,which is the active center for C-H activation.After calculating the energy level of gas-phased molecules or intermediates,I found C3H5Cl was the key intermediate to stop over-oxidation.So energy levels are powerful tools to study active site and reaction pathway.And my theoretical results could explain experimental data well.After the correlation analysis of protonic and electronic levels with the kinetics of H transfer,I found oxidative dehydrogenation is a process of concerted proton-electron transfer.In the reaction of ZnAl2O4-catalyzed CO,CO2 hydrogenation,I calculated the H+and H-levels of oxygen vacancy site to study the activity of H2 activation.And analysis of the energy levels of intermediates gave information of the major reaction channel,minor reaction channel and by-product channel.Finally,I offered the strategy to improve product selectivity.The application of energy level in the above two reactions of oxidative dehydrogenation and hydrogenation proved its important role in catalytic reaction mechanism study.Of course,the thought of energy level could be extend to other catalytic systems.