The Mechanism Of Methanol Oxidation Catalyzed By Zirconia: A First-principles Study

Volatile organic compounds?VOCs?not only seriously pollute the environment but also cause great harm to human health.Catalytic oxidation combustion is one of the most effective methods to eliminate volatile organic compounds.Designing a cheap and efficient catalyst is the key to the development of this process.It can save costs and improve efficiency.It is significate to research it.Methanol as a kind of VOCs,its dissociation and oxidation attract the people's great attention.Due to its chemical stability and acid-alkali features of surface,zirconia has a widespread attention on the support and catalyst.Results show that there are different forms of hydroxyl on the surface of zirconia and the surface hydroxyls have a great influence on reaction.Due to the complexity of surface catalytic reactions and the limitation of experiment methods,reaction path can't be given in detail.Studying from the perspective of theoretical calculation can improve the efficiency of predicting the reaction mechanism.The first-principles calculation based on density functional theory has been widely used.This work studied the dissociation and oxidation of methanol on zirconia as well as the silver clusters'adsorption and growth mechanism in different crystalline phases of zirconia based on periodic supercell model and the first-principles calculation,the specific content and the corresponding conclusions are as follows:?1?the oxidation of CH₃OH on H-m-ZrO₂?-1 1 1?surface:The presence of hydroxyl groups on the surface of zirconia may have different reaction paths due to the influence of surface hydroxyl groups.The dissociation and oxidation of methanol on H-m-ZrO₂?-1 1 1?surface was studied based on density functional theory and periodic supercell model.Methanol prefers to adsorb on top-site of H-m-ZrO₂?-1 1 1?surface.For the dissociation of methanol,O-H bond is easier to breakage compared with C-O and C-H bonds.Two types of mechanism,“terminal”and“bridge”,were considered.The route?CH₃OH?CH₃O?CH₂O?H₂COO?HCOO?CO?is the most feasible and the rate-determining step is transformation of H₂COO into HCOO and H₂O,the calculated energy barrier is 1.42 eV.?2?the adsorption and growth of Ag_n clusters on zirconia:The catalyst of Ag/Zr O₂ has a wide range of applications.Activity and product selectivity of reaction are different by different crystalline phase of zirconia.There is a catalyst sintering phenomenon in practical applications.The exploration of the interaction between the active component and the support can be understood from a microscopic perspective.The adsorption and growth of Ag_n?n=1⁴?clusters on zirconia were studied based on the first-principles calculation and periodic supercell model.The trend of Ag_n?n=1⁴?clusters adsorbed on zirconia:t-ZrO₂?1 0 1?>m-ZrO₂?-11 1?>c-ZrO₂?1 1 1?.Growth of Ag_n?n=2⁴?clusters on zirconia are feasible thermodynamicly and the trend is different on different surface of zirconia.The Bader charge analysis was conducted on the most stable adsorption structure of zirconia for a single silver atom.It was found that the electrons were transferred from the silver atom to the surface of zirconia.The projection state density analysis shows that there is a strong interaction between the d orbital of Ag and the p orbitals of Zr and O.