Mechanism of Dielectric Barrier Discharge Plasma Effect on Pt/CeO2 Catalysts

Author:Wang Bang Fen

Supervisor:ye dai qi


Degree Year:2018





The volatile organic compounds(VOCs)were important precursors for atmospheric pollution.The traditional treatment methods cannot meet current requirements of the waste gas emission standards.Therefore,the non-thermal plasma catalysis system applying for VOCs removal had attracted much attention,which were advantages of low concentration and complex composition of VOCs.With the non-thermal plasma treatment,the physicochemical properties of the catalyst would be changed,and enhcanced activity,selectivity and stability.In this work,the Pt/CeO2 catalyst was widely applied in catalytic oxidation and selected as the objects of study.The Pt/CeO2 catalyst was treated by non-thermal plasma with different discharge conditions(discharge power and discharge time),and the discharge sequence(pre-or post-discharge treatment).The activity was evaluated by catalytic oxidation of toluene,and with the characterizations of physical and chemical properties(XRD,BET,HRTEM,XPS,Raman,CO-pluse,O2-pluse,H2-TPR,O2-TPD,toluene-TPD,TGA and Gas FT-IR)and in situ reaction(in situ UV/Vis-Raman)to investigate the effect of non-thermal plasma on the activity,selectivity and stability of the catalyst,and also discuss the mechanism of DBD plasma effect on Pt/CeO2 catalyst.The results and conclusions were as following:(1)In the range of discharge power(3.39-12.10 W)and discharge time(10-240min),the relationships between catalysts’activities and discharge power or time were nonlinear.Both of their activities showed two volcanic peaks,and the values of peaks were(Pt/CeO2)-P2(4.31 W)and(Pt/CeO2)-P6(9.46 W),(Pt/CeO2)-PT3(30 min)and(Pt/CeO2)-PT6(180 min),respectively.Compared with the T90 of the untreated catalyst,their temperature decreased 57°C and 75°C,24°C and 34°C,respectively.The second peak with higher discharge power and longer discharge time were better catalytic activity.In conclusion that the DBD plasma had significantly effect on the catalytic activity of Pt/CeO2 catalyst with different discharge power and time.(2)After DBD plasma treated,Pt/CeO2–P(T)x catalysts kept their crystal structure.However,the size of CeO2 nanorods and Pt particle,the concentration of Ce3+,Pt0 and oxygen vacancies presented nonlinear changes with the increasing discharge power and time.And the improved catalytic activities of the Pt/CeO2 catalyst with DBD plasma treatment were attributed to the increase of specific surface area,the higher dispersion with the smaller size of Pt particles,the more amount of oxygen vacancies,and the stronger interaction between Pt and CeO2.In addition,the plasma treatment could also improve the properties of redox and toluene adsorption,increase the values of TOFs(TOFPt and TOFOv)and decrease the activation energy of Pt/CeO2 catalyst for toluene oxidation.It was concluded that DBD plasma treatment could increase the performance of Pt/CeO2 for toluene oxidation.(3)There was effect of DBD plasma on Pt and oxygen vacancies with different discharge power and time.In the range of 3.39-5.63 W discharge power,the relationship between catalytic activities and TOFPt and TOFOv values was a linear,and more significant effect on Pt particle.In the range of 10-60 min discharge time,the relationship between catalytic activities and TOFPt and TOFOv values was a linear,and more significant effect on oxygen vacancy;at the range of higher discharge power(7.58-12.10 W)and longer discharge time(120-240 min),the catalytic activities were nonlinear relationships with the TOFPt and TOFOv values;The effect of DBD plasma on catalyst,which was mainly due to the differenct energy density of plasma producing by different discharge powers and times.(4)By combining the experimental results with relevant theoretical analysis,and considered that the main acting particles of DBD plasma were high energy electrons,reactive ions and active radicals,especially the high energy electrons.And the mechanism of DBD plasma effect on Pt/CeO2 catalysts was speculated to change surface morphology of CeO2 mainly due to the etching,the fracture of nanorods mainly as to the thermal stress,the Pt particle recombined with the high electron temperature,and the increase of surface oxygen vacancies mainly cause by the changed distance or energy of Ce-O bond.(5)The selectivity and stability of the Pt/CeO2 catalyst after discharge treatment were investigated.It was found that the selectivity of CO2 was improved,and variety of the high toxic organic by-products(nitrogenous benzene series and cyanogens)and amount of carbon deposition on surface were reduced.During 50 h or with less than 20vol%water vapors in reaction,the toluene conversion did no significantly decrease.Hence,the treated Pt/CeO2 catalyst had better selectivity and still with the structure and good stability,and also possessed excellent water resistance.