The Study Of Surface Reactive Species On MnO_x-CeO₂Powder And Supported Monolithic Catalysts Towards Toluene Oxidation

A series of MnOx-CeO2mixed oxide catalysts with various Mn/(Mn+Ce) mole ratioswere prepared by redox-precipitation method and were tested for the catalytic oxidation oftoluene. The factor of prepare method and calcination temperature were investigate for thecatalysts’activity. The method of BET、XRD、H2-TPR、Raman and XPS were usd to researchthe active species on the catalysts; in-situ Raman method were usd to investigate the changerule of active species on the catalysts when the toluene were oxidation;the powder catalystswith best catalystic activity were chosen for the active component and a series of monolithiccatalysts were prepared. The factor of prepare method、calcination temperature、activecomponent amount、toluene concentration and space velocity were investged for the catalysts’activity.The results indicated that the MnOx(0.5)-CeO2catalytic prepared by redox-precipitationmethod and calcined at400℃showed90%toluene conversion at a temperature as low as190℃. The characterization demonstrated that the MnOx(0.5)-CeO2catalysts have moreoxygen vacancies and lattice oxygen species, as well as stronger surface oxygen mobilitiesafter the introduction of manganese, which may be due to manganese entering CeO2lattice toform a solid solution with fluorite structure. In addition, Mn4+was mainly and distributed onthe surface of the catalystis, Ce was enriched in the bulk of the catalyst. The highlydispersion of surface Mn4+was believed to play a crucial role in toluene oxidation，andCe4+was not involved in the reaction directly，but working as electron transfer regent.Thechange rule of active species on the catalysts when toluene was oxidation maybe as follows:Firstly, Mn4+changed to Mn3+and Mn2+;Then active oxygen species (O2(active)) wasgenerated and migrated to reacted with toluene, accompanied by the oxygen vacancies wereformed on the catalyst;Ce4+changed to Ce3+and produced some active oxygen species,Mn3+and Mn2+were oxided to Mn4+; Gas phase O2molecules adsorbed onto the oxygenvacancy and activated to active oxygen species,supplement the consumed active oxygen(mainly OlattandOsur) and Ce3+were oxided to Ce4+，ensuring the whole reaction process runsmoothly.The catalyst prepared by redox-precipitation method calcined at400℃and used with10wt%loading showed the highest catalytic activities. In the50-500ppm of tolueneconcerntion and10000-30000h-1of space velocity, the catalyst still can maintain a highcatalytic activities;What’s more, the catalysts was tested for72hours at the temperature of 200℃, toluene concerntion of100ppm and space velocity of10000h-1, the conversion oftoluene was still at90%.