Sorption-enhanced hydrogen production by steam reforming of ethanol over mesoporous Co/CaO[sbnd]Al2O3 xerogel catalysts: Effect of Ca/Al molar ratio

Abstract

A series of multifunctional Co/CaOAl2O3 catalysts (Co/XCA, X = 0, 0.25, 0.5, 0.75, and 1.0) with different Ca/Al molar ratio (X) were prepared for use in the sorption-enhanced hydrogen production by steam reforming of ethanol. Mesoporous structure was successfully formed in all the calcined catalysts, and surface area of the catalysts decreased with increasing Ca/Al molar ratio. Co3O4, CaCO3, and γ-Al2O3 phases were dominantly formed in the calcined catalysts. It was revealed that addition of Ca neutralized support acidity, resulting in a decrease of C2H4 selectivity. Addition of Ca also increased strong base sites which were related to sorption-enhanced hydrogen production at the initial reaction stage. In the XRD and H2-TPD analyses, Co/0.5CA catalyst retained the smallest crystallite size of metallic cobalt and the highest cobalt surface area among the catalysts. Catalytic activity in the steam reforming of ethanol exhibited a volcano-shaped trend with respect to Ca/Al molar ratio. Hydrogen yield increased with increasing cobalt surface area. Among the catalysts tested, Co/0.5CA catalyst with the highest cobalt surface area showed the best catalytic performance. Thus, cobalt surface area served as a crucial factor determining the catalytic activity for ethanol steam reforming. Low acidity and high surface area were also responsible for stable catalytic activity of Co/0.5CA catalyst in the steam reforming of ethanol.