New Aspects on the Mechanism of C_3H_6 Selective Catalytic Reduction of NO in the Presence of O_2 over LaFe_(1-x)(Cu, Pd)_xO_(3-δ) Perovskites

摘要

A series of LaFe_(1-x)(Cu, Pd)_xO_(3-δ) perovskites was fully characterized and tested for the selective catalytic reduction (SCR) of NO by C_3H_6 in the presence of O_2. The adsorbed species and surface reactions were investigated for mechanistic study by means of NO- temperature-programmed desorption (TPD), C_3H_6/O_2-TPD, and in situ diffuse reflectance Fourier transform spectroscopy, in order to discriminate the effects of copper and palladium partial substitutions. With respect to LaFeO_3, Cu~(2+) incorporation obviously improved SCR performance, due to its properties for C_3H_6 activation with an easy generation of partially oxidized active surface C_xH_yO_z species. The excellent catalytic activity at the low temperatures over La- F_(0.94)Pd_(0.06)O_3 was attributed to the formation of reactive nitrites/ nitrates, leading to a rapid reaction between adNO_x and C_xH_yO_z species, as well as a decreased occupation of the active sites by the inactive ionic nitrates. A mechanism was herein proposed with the formation of nitriteitrate and C_xH_yO_z surface species and the further organo nitrogen compounds (ONCs)/-CN/-NCO as important intermediates. Moreover, the acceleration of both formation of inactive ionic nitrate and deep oxidation of C_3H_6 contributed to a negative effect of O_2 excess for NO reduction, while Pd substitution significantly increased the O_2 tolerance ability.