Metal NPs @ Organic Polymer; a Bifunctional Catalyst for the Valorization of Biomass-derived Substrates

The depletion of fossil resources has compelled the scientific community to search alternative raw materials for the production of platform and high-added value molecules. The non-edible portion of lignocellulosic biomass is attracting considerable interest in recent years, to this regard optimization of the usually complex methodologies to process this feedstock may rely in the use of bifunctional catalysts, in which a single catalytic body comprising both acidic and metallic functions works under the same reaction conditions. Herein we describe the one-pot, one-stage conversion of C5 and C6 sugars to expensive and/or rare anhydro sugar alcohols in high yields, using a heterogeneous single catalytic body comprising immobilized metal sites for hydrogenation and acid sites for dehydration onto the same support. The developed resin-supported bifunctional ruthenium catalyst Ru@Dowex-H has shown to be truly bifunctional since it catalyzes both steps in the conversion of glucose into Isosorbide; the first metal-catalyzed hydrogenation and the subsequent acid-catalyzed dehydration of sorbitol to obtain the desired product. The bifunctional system found also application in the one-stage catalytic conversion of xylose to 1,4-anhydro-D-xylitol following a homologous hydrogenation/dehydration pathway. Anhydroxylitol and isosorbide were selectively obtained with no need for organic solvents, high metal loadings, strong soluble acid additives or purification steps, from xylose and glucose, respectively. The solid catalyst could be easily and quantitatively recovered, showing no significant metal leaching in solution. We have shown that a very simple catalyst design using commercial materials allows for the conversion of sugars selectively and in a flexible way, without intermediate processing stages.