In situ Generated Ru(0)-HRO@Na-β From Hydrous Ruthenium Oxide (HRO)/Na-β: An Energy-Efficient Catalyst for Selective Hydrogenation of Sugars

摘要

A green process for the hydrogenation of sugars to sugar alcohols was attempted using hydrous ruthenium oxide (HRO) as pre-catalyst supported on Na-β zeolite in aqueous medium. At optimised reaction conditions, the sugars such as xylose, glucose, and mannose converted completely to the corresponding sugar alcohols xylitol, sorbitol, and mannitol with 100% selectivity. The pre-catalyst (HRO) is converted in situ to active Ru(0) species during the reaction under H2, which is responsible for the hydrogenation. The catalyst was recyclable up to five cycles with no loss in activity. The reduction of HRO to the active Ru(0) species is dependent on the reaction temperature and H2 pressure wherein Ru(0) formation increased and consequently an increased hydrogenation of sugars was observed with an increase in reaction temperature and hydrogen pressure. Further, the reduction behaviour (in situ generation of Ru(0) from HRO) was assessed in different solvents such as water, methanol, and tetrahydrofuran, among which aqueous medium was found to be the most efficient in reducing HRO. This work further demonstrates the use of supported HRO as an efficient catalyst for biomass-based hydrogenation reactions.