Synthesis, characterization and catalytic activities of vanadium–cryptomelane manganese oxides in low-temperature NO reduction with NH 3

Abstract

Vanadium doped cryptomelane-type manganese oxides (V-OMS-2) with V/Mn molar ratios of 0–10% were synthesized and investigated for low-temperature selective catalytic reduction of NO by NH 3 (NH 3-SCR). The characterization results of XRD patterns and Raman spectra demonstrated that V 5+ isomorphously substituted for framework Mn 4+ of the V-OMS-2. The adsorption and desorption of NH 3 and H 2-TPR results revealed that both surface defect sites (Lewis acid) and redox abilities were efficiently controlled by amounts of vanadium doping, and more vanadium dopings resulted in more Lewis acid sites and weaker bulk redox abilities. The results of catalytic tests revealed that the 2%V-OMS-2 catalyst showed the highest catalytic activities among the V-OMS-2 catalysts. In fact, the desired doping amount of V 5+ can not only provide more Lewis acid sites for adsorption of NH 3 but also maintain excellent surface redox abilities for activation of NH 3, which resulted in higher catalytic activities in the low-temperature NH 3-SCR reactions.