Silver Catalysts Supported on High Surface Area α-Alumina: Effect of Carbohydrate Template Size and Heat Treatment on Phase Purity

Abstract

α-Alumina is a non-porous metal oxide with applications in ceramics and catalysis. Introducing pores into this material to create catalytically relevant surface area is challenging due to phase transitions over a wide temperature range. Current synthesis strategies involve hard templates such as synthetic polymers, e. g. polymethylmethacrylate (PMMA). Here, we compare cellulose and carbonized glucose as low-cost and natural alternative templates for high surface area α-alumina with a two-step heating method. Quantitative XRD was used to methodically investigate alumina phase purity. Increasing the template size in the range of 220–1000 nm improved α-alumina purity from 75 to 98 %, while maintaining high surface areas (21–29 m2 g−1). Phase purity increases substantially by prolonging the calcination time. The synthesized high surface area α-alumina was studied as support for silver catalysts in the epoxidation of ethylene and allowed high silver loadings. Ethylene oxide selectivity increased with enhanced α-alumina phase purity. Our 30 wt % silver catalyst on pure high surface area α-alumina did not show loss in selectivity compared to a 15 wt % silver catalyst on commercial non-porous α-alumina. This shows the potential of carbohydrate templates, the importance of templating parameters and the benefits of pure high surface area α-alumina as support for silver catalysts.