Simple anion-modified layered double oxides use for controlling Cu valence states for low-temperature CO-SCR

The modification of transition metal catalysts for selective catalytic reduction of NO by CO has been studied extensively. However, the effect of anion on CO-SCR catalyst modification is rarely reported. In this study, four different LDHs precursors were synthesized by using urea hydrothermal method and introducing different inorganic anions into the reaction system to control the self-assembly growth during the synthesis of LDHs. It is then loaded with a mass ratio of 7.5 % copper by impregnation method. The LDO(N)/Cu7.5 catalyst using nitrate ions regulated LDH as support achieved a high NO conversion of 96 % at 150 °C, which outdistanced the LDO(S)/Cu7.5 with support regulated by sulfate ions. A series of characterizations demonstrated that CoFe-LDH modified with different anions could modulate the valence state of loaded copper species. Among them, the LDO(N)/Cu7.5 catalyst was able to produce more Cu+ as the active site for the catalytic reaction. In situ DRIFTS further revealed the reaction mechanism, following the E-R mechanism at ≤150 °C and the L-H mechanism at 200–350 °C. This work supplies a new idea for the valence modulation of copper and the modification of LDH materials for applications in CO-SCR.