Ethyl Acetate Catalytic Oxidation Via MnO_x-CeO₂ Mixed Oxides Synthesized Using Template Method And The Evolution Of Oxygen Vacancies

Volatile organic compounds?VOCs?are primary precursors of ozone?O₃?and fine particles(PM_2.5).They not only affect human health,but also do harm to ecological environment.Catalytic oxidation technologies are widely applied in VOCs end-pipe control because of low secondary pollution,high removal efficiency and high area economy.The core of catalytic oxidation technologies are catalysts,cerium dioxide?CeO₂?are excellent in oxygen storage capacity and gaseous oxygen activation ability,thus can effectively improve the performance of catalysts.Therein,oxygen vacancy is the key factor deciding its gaseous oxygen activation ability,so the study of oxygen vacancy and its evolution are important to enrich the relative theories,thereby directing the development of high-performance catalysts.In this article,MnO_x-CeO₂-s mixed oxide synthesized by template method was used on ethyl acetate catalytic oxidation,the effect of oxygen vacancy,the evolution rule of its concentration and the influence to activity are examined employing in-situ Raman and other characterization methods.In chapter 2,the effect of template method and Mn-loading were characterized,the results showed that both can remarkably improve the activity of ethyl acetate oxidation.On one hand,catalysts synthesized using template method had small crystalline size,unique micro-mesoporous structure and significantly higher specific surface area,which were benefit for reactants to enter into the interior of catalysts.On the other hand,Mn-loading was effective on amending the surface chemical properties of CeO₂,leading to the elevation of Ce³⁺ratio.In the mass,the contribution of template method and Mn-loading was contact efficiency and Ce³⁺ratio,respectively.In chapter 3,the surface oxygen vacancy concentration of MnO_x-CeO₂-s was characterized,the results showed that the concentration had positive correlation with ethyl acetate catalytic oxidation.In-situ characterization showed that the declining of oxygen vacancy concentration and the elevation of active oxygen species were simultaneously,one can affect another.Therefore,crystalline oxygen and oxygen vacancy were assigned to a same site,representing two different status of O^2-stored or not.Oxygen vacancy was also the key site of gaseous oxygen activation process,its concentration could have a great influence on catalysts performance.In chapter 4,the relationship between reaction activity and oxygen evolution was studied.Oxygen vacancy concentration was found to decline when temperature arise,displaying thermal declining effect.Furthermore,MnO_x-CeO₂-s was found to have resistance against it,thus reach completely ethyl acetate conversion faster.Based on these results,oxygen vacancy evolution model was proposed to explain the thermal declining effect combining Mars-van Krevelen mechanism and chemical equilibrium theory.The primary reason of oxygen vacancy declining was the reversibility of gaseous oxygen activation process,higher internal diffusion performance could promote the process and resist the counterreaction,reducing the effect of thermal declining eventually.In this article,MnO_x-CeO₂ mixed oxides synthesized using template method was employed for ethyl acetate catalytic oxidation,which focused on oxygen vacancy.The influence of template method and Mn-loading on catalyst properties and the effect as well as evolution of oxygen vacancy were characterized.The mechanism of oxygen vacancy thermal declining,the effect on reaction activity and the offset strategy were clarified.This research was positive in improving the high temperature activity of congeneric catalysts and enrich the theories of oxygen vacancy.