Toluene Oxidation Mechanism Over Pt/CeO₂ Catalysts

In resent years,the regional air pollution events caused adverse impacts to our citizen's health and livings.The emission control of VOCs is the crucial way to solve the regional air pollution events,and catalytic combustion is one of the most important technologies of VOCs treatments.Pt/CeO₂ catalyst is the focus of the research for catalytic combustion of VOCs,intensive study of its reaction mechanism of VOCs is very important and significative for developing efficient catalyst and upgrading catalytic combustion technology.In this study,Pt bases catalysts with two different supports were synthesized,and their catalytic performance over toluene catalytic oxidation were tested and the essential reasons are analyzed;by researching their reation process,the toluene reaction mechanism over Pt/CeO₂ catalyst has been studied;the characteristics of CeO₂ support is changed by doping elements of the same clan,the catalytic performance over toluene oxidation of the doped catalysts has been studied.The main research contents and results are as follows:First of all,0.6 wt%Pt/CeO₂ and Pt/Al₂O₃ catalysts were synthesized via wet impregnation method.Pt/CeO₂ sample exhibited the best catalytic activity,its reaction T₅₀ and T₉₀ were 170 ^oC and 190 ^oC,where the reaction T₅₀ and T₉₀ of Pt/Al₂O₃ sample were 180 ^oC and 220 ^oC.The BET,H₂-TPR,UV-Raman and XPS results shows that Pt/Al₂O₃ catalysts owns the higher dispersion of Pt but weak redox properties;Pt/CeO₂sample exhibited the best catalytic activity due to the best reducibility and highest surface oxygen vacancies concentration.A comparative study of the two catalysts on toluene reaction process had been carried out by H₂-TPR,Toluene-TPD,CO-FTIR,GC-MS and In-situ FTIR.The results showed that the main reaction process of toluene on two catalysts was basically the same:toluene and oxygen were first activated on Pt particles and then further reaction.But the Pt nanoparticle over Pt/CeO₂ catalyst presented higher electron concentration,resulting in better performance for toluene activation,and CeO₂ support could supply more reactive oxygen species and increase the catalytic activity for toluene oxidation.Some Pt/Ce_0.8Ln_0.2O₂ catalysts?Ln:La,Nd,Sm and Gd?were synthesized via hydrothermal method and wet impregnation method.Among them,Pt/CeGdO₂ catalyst exhibited the best performance for toluene catalytic oxidation and its reation T₅₀ and T₉₀ were 155 ^oC and 168 ^oC.Raman,OSC and In-situ FTIR results showed that Pt/CeGdO₂ catalyst owned higher surface oxygen vacancies concentration and surface oxygen adsorption capacity then Pt/CeO₂.Therefore,accelerate the oxygen supply for toluene oxidation,resulting in less intermediate products and higher catalytic performance.