The Theoretical Study Of CO₂ Reduction Facet-dependent Catalytic Performance On Anatase TiO₂

Because carbon dioxide is one of the main contributors to greenhouse effect,the recycling of CO₂ has become an important topic in recent years.TiO₂ is a promising catalyst.Utilizing density functional theory,this thesis is aimed at researching the facet-dependent catalytic activity of TiO₂ for CO₂ reduction.A new explanation for exposing?001?facets: The traditional explanation believed that the adsorbed fluorine atoms could cause an exceptional stabilization of the?001?facets that can increase the exposed?001?facets.But some experiment phenomena,that the exposure ratio of?001?facets largely depends on the concentration of hydrofluoric acid,appeared gradually that cannot be explained well with the tranditional explanation.This thesis proposed a new explanation that the HF molecule may play a key role in exposing?001?facets.Comparison of catalytic activities for?101?and?001?facets: The facet-dependent photocatalytic activity of Ti O₂ has been found in CO₂ photoreduction.However,which facet is more reactive and the nature of its dramatically different activity are still in the great debate.Two key photocatalytic steps?photon-generated electrons transfer and photoreaction?are investigated on anatase TiO₂?001?and?101?facets to unravel such puzzles.The facts that the higher conduction band can generate more strongly reductive electrons,the lower reaction barrier can lead to the faster reaction rate and the product adsorption can have more suitable properties give rise to a higher activity on?101?facets than that on?001?facets.Separation of photo-generated carriers between?101?and?001?facets: For the photocatalytic reactions,fabrication of junction structure has been proven to be an effective method to increase the photo-generated carriers?excited electrons and photo-generated holes?separation efficiency,but the carrier separation mechanism has not been studied in detail.In this thesis,density functional theory method was employed to study the separation of photo-generated carriers based on an interfacial model consisting of TiO₂?101?and?001?facets.Both the excited electrons and photo-generated holes preferentially locate on the?001?facets rather than?101?facets.However,the high conduction band energy level of interface inhibits the interfacial electron migration.In contrast to the migration process of excited electrons,the suitable valence band energy of interface permits the migration of the interfacial holes from?101?to?001?facets.Elucidation of the high CO₂ reduction selectivity by isolated Rh supported on TiO₂:The co-adsorbed CO₂ and H2 on Rh atom can reacts with each other to form CO.The inhibition of further H2 adsorption on the CO pre-adsorbed Rh atom stops the following sequential hydrogenations of CO which can explain the experimentally observed high selectivity of CO₂ to CO on Rh1/TiO₂.