New Aspects on the Mechanism of C3H6 selective catalytic reduction of NO in the presence of O2 over LaFe1-x(Cu, Pd)xO3-δ perovskites.
Résumé
A series of LaFe(1-x)(Cu, Pd)(x)O(3-δ) perovskites was fully characterized and tested for the selective catalytic reduction (SCR) of NO by C(3)H(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(3)H(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(3)H(6) activation with an easy generation of partially oxidized active surface C(x)H(y)O(z) species. The excellent catalytic activity at the low temperatures over LaFe(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(x)H(y)O(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 nitrite/nitrate and C(x)H(y)O(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(3)H(6) contributed to a negative effect of O(2) excess for NO reduction, while Pd substitution significantly increased the O(2) tolerance ability.