Directing Polyol Dehydration via Modification of Acid Catalysts with Metals

Abstract

Metal–acid bifunctional catalysts consisting of an acidic silica-alumina support and a hydrogenating metal (nickel, copper, platinum, palladium, or ruthenium), were tested for their ability to modify the selectivity of the 1,2,6-hexanetriol dehydration reaction in the gas phase. The selectivity was found to be controlled by metal type and loading, with the highest observed selectivity to linear α,ω-dioxygenates occurring with a low loading of platinum or copper on silica-alumina and with the highest selectivity to pyrans observed over a nickel on silica-alumina catalyst. The observed selectivity changes were found to be due to parallel reactions leading to the formation of either linear α,ω-dioxygenates or pyran rings and not ring-opening of pyrans to α,ω-dioxygenates suggesting that the metals influenced the interaction of the polyol with the catalyst surface. The introduction of metals also enhanced activity and diminished catalyst deactivation. These results demonstrate that addition of metals to acid catalysts can have significant impact on the dehydration reaction both in terms of selectivity and activity.