Direct decomposition of NO into N_2 and O_2 over La(Ba) Mn(In)O_3 perovskite oxide

摘要

Although LaMnO_3 perovskite oxide has been reported to exhibit low activity in NO direct decomposition into N_2 and O_2,doping Ga or In at the Mn site of La(Ba)MnO_3 has been found effective of increasing the activity for NO direct decomposition into N_2 and O_2.The activity of NO decomposition increased in the order Ba>Sr>Ca for the La site dopant,and In>Ga for the Mn site.Among the investigated dopantsa nd compositions,the highest N_2 yield was achieved with La_(0.7)Ba_(0.3)Mn_(0.8)In_(0.2)O_3.On this catalyst,NO conversion increased with increasing reaction temeprature,and at 1123 K,NO conversion into N_2 and O_2 attained values of 75 and 41%,respectively.The high yield of N_2 and O_2 was maintained for 12h.Coexistence of oxygen decreased the N_2 yield with P_(O_2)~(-0.53);however,a N_2 yield of 15% couled be sustained even at 10% coexisting O_2 at 1073 K.The NO decomposition rate increasedw ith increasing NO partial pressure and obeyed with P_(NO)~(1.31).O_2 temperature-programmed desorption measurements shwoed that oxygen desorption was greatly enhanced by In doping at the Mn site.NO TPD also showed that the amount of NO adsorption greatly increased with In doping.Therefore,improved activity of NO decomposition with In substitution seems to be caused by the weakening adsorption of oxygen and the increased adsorption of NO.IR measurements of adsorbed NO also suggest that the major adsorption species at high temperature was NO_3~- and it seems likely that NO decomposition proceeds after removal of NO_3~- and/or oxygen.N_2O direct decomposition on La_(0.7)Ba_(0.3)Mn_(0.8)In_(0.2)O_3 was further studied.It was found that La_(0.7)Ba_(0.3)Mn_(0.8)In_(0.2)O_3 is highly active in the direct decomposition of N_2O event under the coexistence of O_2.Therefore,decomposition of NO on La_(0.7)Ba_(0.3)Mn_(0.8)In_(0.2)O_3 may proceed via N_2O as the intermediate species.