Synthesis, characterization and catalytic activities of vanadium–cryptomelane manganese oxides in low-temperature NO reduction with NH3

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 NH3 (NH3-SCR). The characterization results of XRD patterns and Raman spectra demonstrated that V5+ isomorphously substituted for framework Mn4+ of the V-OMS-2. The adsorption and desorption of NH3 and H2-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 V5+ can not only provide more Lewis acid sites for adsorption of NH3 but also maintain excellent surface redox abilities for activation of NH3, which resulted in higher catalytic activities in the low-temperature NH3-SCR reactions.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (154 K)Download as PowerPoint slideResearch highlights▶ Lewis acid and surface redox property governed NH3-SCR activity of catalyst. ▶ Doping V in cryptomelane resulted in generation of Lewis acid sites. ▶ Surface redox ability of cryptomelane could be maintained with marginal V doping. ▶ Vanadium–cryptomelane with molar ratio of V/Mn = 2% showed best NH3-SCR activity.