In Situ DRIFTS Studies of NH(3)-SCR Mechanism over V(2)O(5)-CeO(2)/TiO(2)-ZrO(2) Catalysts for Selective Catalytic Reduction of NO(x)

TiO(2)-ZrO(2) (Ti-Zr) carrier was prepared by a co-precipitation method and 1 wt. % V(2)O(5) and 0.2 CeO(2) (the Mole ratio of Ce to Ti-Zr) was impregnated to obtain the V(2)O(5)-CeO(2)/TiO(2)-ZrO(2) catalyst for the selective catalytic reduction of NO(x) by NH(3). The transient activity tests and the in situ DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) analyses were employed to explore the NH(3)-SCR (selective catalytic reduction) mechanism systematically, and by designing various conditions of single or mixing feeding gas and pre-treatment ways, a possible pathway of NO(x) reduction was proposed. It was found that NH(3) exhibited a competitive advantage over NO in its adsorption on the catalyst surface, and could form an active intermediate substance of -NH(2). More acid sites and intermediate reaction species (-NH(2)), at lower temperatures, significantly promoted the SCR activity of the V(2)O(5)-0.2CeO(2)/TiO(2)-ZrO(2) catalyst. The presence of O(2) could promote the conversion of NO to NO(2), while NO(2) was easier to reduce. The co-existence of NH(3) and O(2) resulted in the NH(3) adsorption strength being lower, as compared to tests without O(2), since O(2) could occupy a part of the active site. Due to CeO(2’)s excellent oxygen storage-release capacity, NH(3) adsorption was weakened, in comparison to the 1 wt. % V(2)O(5)-0.2CeO(2)/TiO(2)-ZrO(2) catalyst. If NO(x) were to be pre-adsorbed in the catalyst, the formation of nitrate and nitro species would be difficult to desorb, which would greatly hinder the SCR reaction. All the findings concluded that NH(3)-SCR worked mainly through the Eley-Rideal (E-R) mechanism.