Ir@Pt bimetallic overlayer catalysts for aqueous phase glycerol hydrodeoxygenation

Abstract

Silica-alumina supported bimetallic overlayer catalysts of platinum on Ir (Ir@Pt) were synthesized using the directed deposition technique to investigate the modification of the Pt catalytic properties. Weakened hydrogen adsorption strength was obtained for Ir@Pt overlayer catalysts compared to pure platinum using hydrogen chemisorption and an ethylene hydrogenation descriptor reaction, consistent with literature computational studies. This reduced adsorption strength is expected to increase the Pt overlayer reactivity compared to pure Pt by releasing Pt active sites from strongly adsorbed H2 or CO. The effect of multiple Pt overlayer depositions is also studied, and it is postulated that overlayer catalysts with double and triple platinum overlayer deposition would form Pt multilayer structures. Multiple overlayers displayed a smaller degree of modification in H2 adsorption strength from pure Pt, compared to Ir@Pt single deposition sample. In aqueous phase glycerol hydrodeoxygenation, Ir@Pt single deposition sample showed higher turnover frequencies of glycerol conversion and C3 hydrocarbon production than pure Pt and the bimetallic alloy sample. The activity enhancement of Ir@Pt compared to pure Pt is ascribed to the weakened hydrogen adsorption of Ir@Pt, as fewer Pt active sites were blocked by strong H2 or CO adsorption. The improved selectivity toward C3 hydrocarbons of Ir@Pt compared to pure Pt suggested a feasible approach of using overlayer catalysts to manipulate the selectivity of Pt overlayer without sacrificing the Pt overlayer reactivity.