Ethanol steam reforming over cobalt catalysts: effect of a range of additives on the catalytic behaviors

In this study, we made an effort to modify the Co/Al₂O₃, a typical catalyst for various steam reforming reactions, with Na, Mg, Zr, La, Ce and the elements from K to Zn in the periodic table of elements, in order to obtain a whole picture of impacts of these commonly used additives on catalytic behaviors of cobalt-based catalyst on one basis. The results showed Na, Mg, Zr, Sc, K and Cr addition increased specific area of the catalysts by creating new mesopores or decreasing pore radius while Ca filled the pores. The additives could also react with either cobalt species or alumina. CoV₂O₆, MgAl₂O₄, MnAl₂O₄ NiAl₂O₄ and ZnAl₂O₄ and Co₇Fe₃ alloy were formed during calcination/reduction of the catalysts. Na, K, Cu, Ni or Ce addition promoted the catalytic activity, while Mg, Ca, Sc, Ti, V, Cr, Mn suppressed. As for coking, Na, K, Ca, Fe, Zn, La helped to suppress coking while Cu or Zr enhanced. The coke became more aromatic over the modified catalysts. V or La promoted formation of the coke with graphite structure, while Cu or Fe was the opposite. The additives also affected the morphology of the coke or diameter of the carbon nanotubes formed. The in-situ DRIFTS studies showed that ethanol could be dehydrated to form C=C and dehydrogenated to form acetyl species at 100 °C. The addition of Na suppressed the formation of the acetyl species, while Cu addition promoted the acetyl species, C=O and C=C formation, leading to the high tendencies of Cu–Co/Al₂O₃ towards coking.