Structure–selectivity relationships for polyol hydrogenolysis over Ru catalysts

Abstract

The conversion of C6 sugar alcohols (hexitols) and other polyols over Ru catalysts was investigated regarding structure–activity and structure–selectivity relationships by testing various structurally different polyol reactants. In line with earlier studies, we find that hydrogenolysis reactions over supported Ru lead to CH₄ at 160 to 220 °C and 150 bar H₂. The main reaction is metal-catalyzed and preferably cleaves terminal –C–C– bonds, following a decarbonylation mechanism. While the preferential degradation pathway causes CO formation, no CO has been observed experimentally. Only CO₂ and CH₄ were found which suggests that CO is rapidly hydrogenated to CH₄ and/or converted to CO₂ by the water gas shift reaction (WGS).As a side reaction, the cleavage of terminal OH-groups (–C–O– hydrogenolysis) has been identified. Consecutive –C–O– cleavage reactions lead to reaction products that have thus far not been identified (e.g. 2,3,4,5-hexanetetrol or 2,3-butanediol). While terminal –C–OH groups are readily converted due to fast decarbonylation, intermediates without terminal OH groups are converted via a ketone intermediate which is a rather slow reaction.