Bifunctional Materials for the Catalytic Conversion of Cellulose Into Soluble Renewable Biorefinery Feedstocks

The development of bifunctional nanostructured materials for the catalytic conversion of cellulose into sugar alcohols offers the potential of a sustainable source of renewable biorefinery feedstock. Supported Ru catalysts were prepared by evaporative deposition on various ordered mesoporous silicas (SBA-15) with different functionalities and characterized using multiple techniques. The catalytic performance of these materials was compared to Ru/C and the corresponding supports.  The effects of functional group loading, reaction time and temperature on the activity and selectivity of the bifunctional catalysts were studied by monitoring the cellulose conversion and the production of sugars and sugar alcohols in a high-pressure batch reactor. Sorbitol is the main product obtained by the hydrolysis of cellulose to glucose followed by the corresponding reduction. Secondary products include sugars, ethylene glycol and glycerol. The activity of mesoporous silica catalysts increases with an increase in sample acidity and the addition of Ru allows control of the selectivity towards sugar alcohols. Ruthenium supported on arenesulfonic acid-functionalized mesoporous silica (Ru/SBA-15S) displays the best catalytic performance. Ru/SBA-15S is more hydrothermally stable than SBA-15, but loses a significant fraction of its surface area, crystallinity, and acidity after prolonged exposure to water at 483K. However, even after 72h under these conditions the catalyst retains some of its acidity and the activity is still higher than fresh unfunctionalized Ru/SBA-15 and Ru supported on amorphous silica.