The promotion effect of Mn over Co/ZnO catalysts in the steam reforming of ethanol (ESR) and water gas shift (WGS) has been studied in samples prepared by impregnation or co-precipitation with Mn(at)/Co(at) =0.05-0.35. Alloy particles in Co-Mn/ZnO catalysts prepared by impregnation are smaller as deduced from high resolution transmission electron microscopy (HRTEM) and exhibit a rapid and higher degree of redox exchange between reduced and oxidized Co as deduced from temperature programmed reduction (TPR) and oxidation pulse experiments with respect to Co-Mn catalysts prepared by co-precipitation, which show a stronger Mn segregation on the surface, as deduced from X-ray photoelectron spectroscopy (XPS). Honeycomb catalysts have been prepared with the best catalytic formulation, a sample prepared by impregnation with Mn(at)/Co(at) similar to 0.1 and 10wt.% Co, and tested in ESR and WGS as well. Honeycombs show good adherence of catalyst coatings and are significantly more active and selective than Co/ZnO honeycomb samples in both reactions.
