Cobalt catalyst for steam reforming of ethanol–Insights into the promotional role of potassium

Abstract

The promotional effect of potassium doping on the ESR performance of the CoZn|α-Al2O3 catalyst was thoroughly investigated in the context of its impact on the selectivity and stability of the catalyst, and discussed in terms of cobalt dispersion, oxidation state, cobalt-alumina interactions, catalyst acidity, and the deactivation resistance of the catalyst. The potassium slightly inhibited the cobalt reducibility (XPS, TPR, STEM/EELS), significantly increased the surface concentration and the strength of Lewis sites (FT-IR), enhancing the selectivity to hydrogen. The surface state of potassium at various stages of the catalyst evolution was examined with a species resolved thermal alkali desorption (SR-TAD) method. These studies revealed a pronounced migration of K from the cobalt nanograins towards the alumina support upon the activation and during the ESR processes. Potassium stabilizes the high dispersion of cobalt crystallites and prevents their detachment from the surface and subsequent encapsulation by the growing carbon deposit.