The Effect Of Rare Earth Doped Pd/Al₂O₃ Catalyst On The Oxidation Performance Of C₃H₈

Vehicle emission regulations China Phase?is landing,and China Phase?will come,the cleaning of emission pollutants such as hydrocarbons?HC?,nitrogen oxides?NOx?in automobile exhaust is a great challenge to the development of automobile catalyst.Pd/Al₂O₃catalyst is considered to be the most ideal HC oxidation catalyst,because it,s good catalytic activity,however,there are still problems such as low temperature activity and high temperature sintering in practical applications,still need to study in depth.The rare earth additives have been used to improve the catalytic activity and stability of automotive,it is important to thoroughly study the influence of Pd-rare earth interaction on the HC oxidation.This paper is based on the precious metals-rare earth interactions improve catalyst activity,researched the oxidation performance Pd/M-Al₂O₃ catalyst that were doped with different rare earth elements,prepared with different La precursors and surfactants,discussed Pd-rare earth catalytic mechanism simultaneously.?1?Pd/M-Al₂O₃?M=La,Ce,Pr,Nd and Y?catalysts were prepared by impregnation method.The catalysts samples were characterized by N₂-absorption and desorption,XRD,XPS,H₂-TPR characterization methods,and so on,the performance of catalysts C₃H₈oxidation was evaluated by multifunctional powder sample evaluation devices.The best catalytic performance of catalysts C₃H₈ oxidation is Pd/La-Al₂O₃,Pd/Pr-Al₂O₃?Pd/Nd-Al₂O₃ and Pd/Y-Al₂O₃ are the second,Pd/Ce-Al₂O₃ is the worst,This is because the Pd-La interaction in Pd/La-Al₂O₃ catalysts is the strongest,the content of oxidation state PdO is the most abundant.Doped with La,Ce,Pr,Nd and Y five different rare earth elements can produce Pd-rare earth interaction,increasing the content of PdO and improving the activity of catalyst C₃H₈ oxidation.?2?Prepared Pd/La-Al₂O₃ catalysts were impregnated with different rare earth La precursors?lanthanum nitrate,lanthanum acetate,anthanum oxide?,and the C₃H₈ oxidation performance of the catalysts was studied in different reaction atmospheres,found that the catalytic performance of catalyzed C₃H₈ oxidation were promoted modified with rare earth lanthanum.Through XRD,XPS,H₂-TPR and other characterization analysis,it shows that La can promote the dispersion of noble metal palladium,produce Pd-La interaction,stabilize high state of Pd²⁺species,increase the ratio of Pd²⁺/Pd,and improve the performance of C₃H₈ oxidation.The catalysts doped with lanthanum nitrate have the best catalytic performance because the Pd-La-doped catalyst has the strongest Pd-La interaction,the highest PdO content,and the best Pd dispersibility.?3?The Pd/La-Al₂O₃ catalysts were prepared with different surfactants?PVP,PEG,CTAB and CA?,studied the oxidation of C₃H₈ under the different reaction conditions.In O₂condition,PVP,PEG and CA modified Pd/La-Al₂O₃ catalysts have lower initial conversion temperature T_s,however,having poor performance under the condition of nitric oxide,the reason is knowable by XRD,H₂-TPR and other analysize the characterization,smaller palladium particles and weaker Pd-La interaction favors the dissociation of O₂,but it is not conducive to NO dissociation,which promotes and inhibits the reaction.