Recyclable Cu Salt-Derived Brønsted Acids for Hydrolytic Hydrogenation of Cellulose on Ru Catalyst

Abstract

Brønsted acid-catalyzed hydrolysis of cellulose, the most abundant source of biomass in nature, is the critical step for its depolymerization and subsequent conversion to sugar alcohols and other important chemicals. Mineral acids are highly active; however, the difficulties in recycling and disposal limit their practical applications. Herein, we have developed a novel and facile approach to efficiently hydrolyze cellulose using recyclable H3PO4and H2SO4generated in situ in the cellulose reaction via the reduction of the insoluble Cu salts Cu2(OH)PO4and Cu3(OH)4SO4by H2. After the reaction, such in situ formed H3PO4and H2SO4were readily reconverted to insoluble Cu2(OH)PO4and Cu3(OH)4SO4salts, which were then separated by simple filtration from the product solutions to completely recycle the insoluble Cu salts and mineral acids. The in situ formed H3PO4and H2SO4produced pH values as low as 1.5 in the reactionmedia that effectively catalyzed the conversion of microcrystalline cellulose to C6alcohols, including hexitols, sorbitan, and isosorbide, in combination with hydrogenation catalyst Ru/C, affording a high yield of 93.7% at 473 K. This novel approach provides a rationale for designing recyclable mineral acids with wide applications that are important for developing green chemical processes.