Structure and redox properties of Co promoted Ni/Al2O3 catalysts for oxidative steam reforming of ethanol

Abstract

The effect of the Co addition on the structure and redox properties of Ni/γ-Al2O3 catalyst for oxidative steam reforming of ethanol (OSRE) was studied as a function of the CoO content (1–6wt%). Systematically investigations during reduction process of the oxide samples under H2 atmosphere and the oxi-reduction behaviour of the reduced catalysts under reaction conditions of OSRE were performed via in situ temperature resolved X-ray absorption near structure (XANES) spectroscopy. The composition-dependent and temperature-dependent structural changes were analyzed by means of N2 adsorption–desorption isotherms, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and H2-temperature programmed reduction (TPR). The TPR and in situ XANES-TPR analysis of the samples clearly indicated that the Co addition into the Ni/Al2O3 system has a considerable effect on the metal–support interaction, by assisting the formation of NiO and Co3O4 species weakly interacting with the alumina surface and decreasing the reduction temperature compared to that of the monometallic system. It was found that the reducibility of the metallic oxide species in bimetallic CoNi/Al2O3 catalysts increases with increasing the Co content. The bimetallic CoNi/Al2O3 catalysts exhibited a higher resistance to oxidation compared to that of the monometallic system in the reaction of OSRE by hindering the oxidation of the metallic Ni and Co particles on the surface. It was suggested that the synergetic effect between the Ni and Co components reflects to a significant extent on the stability and ethanol conversion of the bimetallic CoNi/Al2O3 catalysts toward higher H2 yields in the OSRE with time on stream.