Direct decomposition of NO into N 2 and O 2 over La(Ba)Mn(In)O 3 perovskite oxide

Abstract

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 dopants and compositions, the highest N 2 yield was achieved with La 0.7Ba 0.3Mn 0.8In 0.2O 3. On this catalyst, NO conversion increased with increasing reaction temperature, 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 12 h. Coexistence of oxygen decreased the N 2 yield with P O 2 −0.53; however, a N 2 yield of 15% could be sustained even at 10% coexisting O 2 at 1073 K. The NO decomposition rate increased with increasing NO partial pressure and obeyed with P NO 1.31. O 2 temperature-programmed desorption measurements showed that oxygen desorption was greatly enhanced by In doping at the Mn site. NO TPD also showed that the amount of NO adsorbed 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 0.7Ba 0.3Mn 0.8In 0.2O 3 was further studied. It was found that La 0.7Ba 0.3Mn 0.8In 0.2O 3 is highly active in the direct decomposition of N 2O even under the coexistence of O 2. Therefore, decomposition of NO on La 0.7Ba 0.3Mn 0.8In 0.2O 3 may proceed via N 2O as the intermediate species.