Study of the impregnation sequence of active phase and effect of cobalt content over Co-CeO2/MgΑl2O4 catalysts in ethanol steam reforming

Abstract

Co–CeO2/MgAl2O4 catalysts were obtained by varying the impregnation order (sequential or co‒impregnation) of active phase (Co) and Ce and were evaluated in the ethanol steam reforming (ESR) reaction. Results from TPR and XPS revealed that the impregnation order influenced the metal‒metal and/or metal‒support interactions and Co0/Con+, Ce3+/Ce4+ and the Co/Ce surface molar ratio, affecting the catalyst behavior in the ESR reaction. The solids prepared by sequential impregnation, Co/Ce/S and Ce/Co/S exhibited a greater degree of reduction than the solid obtained by co‒impregnation (CoCe/S), though these systems displayed low dispersion of Co species and low content of surface Co°. The solid CoCe/S showed the highest dispersion (68.5%) and greater presence of Co0 on the surface. The effect of the cobalt content (4, 8 and 12 wt%) was also examined in catalysts prepared using the co‒impregnation method. With the increase in cobalt content, a greater loss of stability and a greater amount of carbon deposits were observed. The highest H2 yield (5.3 mol H2/mol C2H5OH) and stability were achieved over the solid obtained by co‒impregnation with 8 wt% Co, which was attributed to the high dispersion of the active phase and its high content of surface metallic cobalt.