Structure-selectivity relationships for polyol hydrogenolysis over Ru catalysts

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 CH(4)at 160 to 220 degrees C and 150 bar H-2. 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 CO(2)and CH(4)were found which suggests that CO is rapidly hydrogenated to CH(4)and/or converted to CO(2)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 convertedviaa ketone intermediate which is a rather slow reaction.