Biofuel synthesis from sorbitol by aqueous phase hydrodeoxygenation over bifunctional catalysts: In-depth study of the Ru-Pt/SiO2-Al2O3 catalytic system

Abstract

The catalytic performances of Ru-Pt/SiO2-Al 2O3 catalysts synthetized by three methods (co-impregnation (CI), successive impregnations (SI) and redox deposition (CR)) were compared for their sorbitol transformation to hexane under hydrothermal conditions. The existence of Pt-Ru interaction was demonstrated by TEM-EDX only on SI and CR samples, with a PtRu alloy suspected by XRD and XPS. The chemical nature of the Ru species differed according to the synthesis method with the presence of Ru4+ species on SI-(Ru-Pt) and CR catalysts. The SI-(Ru-Pt)/SiO2-Al2O3 system displayed the best metal-acid function balance leading to the highest selectivity to hexane. The study of the reactivity of isosorbide and 2,5-dimethylfuran intermediates highlighted that the first one was poorly reactive compared to the second one, and the latter was selectively convertible to hexane. The synergy effect on SI-(Ru-Pt)/SiO2-Al2O3 catalyst was attributed to the presence of small-sized bimetallic particles favoring an electronic exchange from Ru to Pt, and increasing the formation of 2,5-dimethylfuran.