Reduction of NO with new vanadium-carbon xerogel composites. Effect of the oxidation state of vanadium species

Abstract

Vanadium-carbon composites were successfully prepared by sol-gel methods, and their behaviour as NOx-reduction catalysts was tested. Two different synthesis approaches were employed: the distribution of VOx (i) along the carbon matrix and (ii) on the carbon spheres surface. This allows to modify the carbon-VOx interaction and thus, evaluate the role of vanadium oxidation state in the NOx abatement. The distribution of VOx along the carbon matrix favours the dispersion and reducibility of VOx nanoparticles and improves the carbon-VOx contact stabilizing vanadium low oxidation states (V2+), however part of the VOx particles were embedded on the carbon matrix becoming inactive. The distribution of those species on the carbon spheres surface improves the accessibility to the VOx active sites but at the expense of the decrease of the carbon-VOx interaction and VOx dispersion and reducibility. The oxidation state of the active phase is related with the global synthesis procedure and that reducibility depends on the interactions between phases. Catalytic results evidence that the NO reduction is strongly influenced by the oxidation state of vanadium. Commercial V2O5 and carbon-V2O5 physical mixture are poorly reactive whereas a stronger activity improvement activity was observed for C-VOx composites reaching conversion higher than 91% at 450 °C.