Selective catalytic reduction of NO_x by methane over La_(1-x)Sr_xMnO₃ perovskites

Powder perovskite-type La_(1-x)Sr_xMnO₃(x=0, 0.2, 0.4) were synthesized by sol-gel method, and supported La_(1-x)Sr_xMnO₃(x=0.2, 0.4) were synthesized by excessive dipping method. The powders were characterized by XRD and SEM, and supported catalysts were then submitted to activity tests in the selective catalytic reduction(SCR) of NO by methane with or without O₂. The experimental results showed that the crystal structure of Sr-substituted samples was the characteristic perovskite structure, and what's more, La_0.8Sr_0.2MnO₃ possessed a porous structure. In the absence of O₂, the reduction of NO_x by CH₄ was performed over La_0.8Sr_0.2MnO₃ and La_0.6Sr_0.4MnO₃, leading to a maximum of 90% at 800-900°C. The catalytic performance of La_0.8Sr_0.2MnO₃ could reach a maximum of 80% at 800°C with 6% O₂, on the other hand, the performance of La_0.6Sr_0.4MnO₃ was suppressed by the presence of O₂. The catalytic performance was improved by both La_0.8Sr_0.2MnO₃ and La_0.6Sr_0.4MnO₃ at 500-600°C.