Effect Of Non-Thermal Plasma On The Pt/CeO₂ Catalysts For Toluene Oxidation

The problem of VOCs pollution is still serious in China.And the technology of catalytic destruction is the most effective mean for VOCs pollution control.Non-thermal plasma modification technology can optimize the catalyst.Therefore,it is of great significance for the development of high-performance catalysts to deeply study the reaction mechanism of plasma on catalysts.In this paper,dielectric barrier（DBD）discharge is taken to treat Pt/CeO₂ catalyst.This study has analyzed the variety of catalytic activities caused by different plasma-treated sequence in the combined treatment,and obtained an efficient method for plasma optimization;The peformances of catalysts which are modified by plasma in various atmospheres was compared,and we futher studied the effects of discharge atmoshpheres on catalyst modification;By studying the direct influence of plasma on Pt and CeO₂,the reaction mechanism of plasma on active sites of Pt/CeO₂ was explored.The main results of this paper are as follows:The single treatment（plasma or thermal reduction）and combined treatment（plasma and thermal reduction）were adopted for Pt/CeO₂ modification,the catalytic evaluation shows that plasma can improve the activity of catalyst,and the improvement of combined treatment are more prominent.The results of TOFs value prove that Pt particles and oxygen vacancy are both the active sites.Compared the effects of different plasma-treated sequences in combined treatement,plasma treatment followed by the thermal reduction as a modified method can reduce the T₁₀₀ of catalyst by 30°C,so this method has a better toluene oxidation.The plasma modifications in various atmosphere are applied to Pt/CeO₂ catalysts.And it is found that the discharge characteristics is positively correlated with the catalyst reactivity within limits.On the other hand,the redox property of discharge atmosphere has more significant influence on Pt/CeO₂,when the catalyst treated by H₂ plasma exhibited the best activity that T₁₀₀=189°C.It is probably because the active hydrogen species formed in discharge can promote the reduction of Ce⁴⁺to Ce³⁺,generate more Pt-O-Ce species,and increase the number of Ce-defects,which significantly improve the reaction activity.The performances of catalyst Pt/SiO₂ and CeO₂ before and after plasma treatment were studied by Toluene-TPD,CO-Pulse and XPS characterization,and the results show that the dispersion of Pt particles on the plasma-treated catalyst improve greatly,and the formation of low-coordinated Pt atoms is conducive to the adsorption and dissociation of toluene.What’s more,the plasma can directly affect the generation of oxygen vacancy on CeO₂ surface,which accelerate the conversion of intermediate products to CO₂.Combiend with the theoretical analysis,we speculate the the plasma treatment can affect the electron distribution of Pt/CeO₂,which might promote the interaction between Pt and CeO₂ and the formation of oxygen vacancy,and hence the the catalytic oxidation of toluene is enhanced significantly.