Site isolated Ru clusters and sulfoacids in a yolk-shell nanoreactor towards cellulose valorization to 1,2-propylene glycol

Abstract

Direct conversion of cellulose to high yield 1,2-propylene glycol (1,2-PG) is amazing in the biomass valorization to diols, since this process is atom-economic, carbon neutral, and the produced 1,2-PG has a large market demand. However, it is very challenging to control cellulose hydrogenolysis owing to high reactivity of intermediates (like glucose) and metal-acid repelling, leading to decreased selectivity of metal-acid multi-functional catalysts. Aimed at this, we herein developed a highly selective metal-acid catalyst (Ru/NC@void@MC-SO3H) with site isolated Ru clusters (1.4 nm) on the core and sulfoacids on the shell in a yolk-shell nanoreactor by a layer-by-layer assembly before chemical transformation. The spatial isolation of metal and acid sites integrated in a mesoporous yolk-shell nanoreactor not only facilitates the metal-acid synergism in hydrolysis, isomerization/hydrogenolysis and hydrogenation cascade reactions, but also provides a designated diffusion pathway that is favorable for reaction species. As expected, the elaborately fabricated Ru/NC@void@MC-SO3H proves to be highly selective to 1,2- PG (38 % yield), delivering a productivity of 342.86 mol h−1 gRu–1 and an extremely high turnover number of 173264, outperforming the state-of-art metal-acid catalysts for cellulose hydrogenolysis to 1,2-PG. Our characterization and performance test suggest that sulfoacids are mainly responsible for cellulose hydrolysis, while N-stabilized Ru centers contribute to the glucose isomerization to fructose and its further hydrogenolysis to dihydroxyacetone, followed by hydrogenation to 1,2-PG on metallic Ru species. The acidity and basicity optimized for site isolated Ru/NC@void@MC-SO3H is beneficial to balance intermediate reactions, rendering a higher selectivity to target 1,2-PG. The concept illustrated in this study will provide a guide for the development of other site isolated multi- functional catalysts towards cellulosic biomass conversion and other cascade reactions.