Alumina and Alumina–Baria Supported Cobalt Catalysts for DeNO _x : Influence of the Support and Cobalt Content on the Catalytic Performance

Abstract

Co/Al₂O₃ and Co/Al₂O₃–BaO catalysts with low cobalt loading (0.1, 0.3 and 1 wt%) for the selective catalytic reduction (SCR) of NO _x by C₃H₆ were prepared. The distribution of cobalt species was investigated by UV–vis diffuse reflectance spectroscopy and by H₂-TPR in order to identify the active cobalt species in hydrocarbons (HC)-selective catalytic reduction (SCR). It was found that the nature of cobalt species strongly depends on the cobalt loading as well as on the properties of the support. The barium addition to the alumina slows down solid state diffusion processes, improving the thermal stability of the support and preventing diffusion of cobalt into the bulk. Highly dispersed surface Co²⁺ species over alumina were identified as active sites in the NO-SCR process. Accordingly, a high concentration of surface Co²⁺ sites in Co 1 wt%/Al₂O₃ improves the catalytic performance in NO-SCR, the long term stability as well as the water tolerance. On the contrary, the formation of Co₃O₄ particles in Co 1 wt%/Al₂O₃–BaO promotes the propylene oxidation by oxygen, decreasing the activity and selectivity of the catalyst in NO reduction.