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

Bronsted 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 H3PO4 and H2SO4 generated in situ in the cellulose reaction via the reduction of the insoluble Cu salts Cu-2(OH)PO4 and Cu-3(OH)(4)SO4 by H-2. After the reaction, such in situ formed H3PO4 and H2SO4 were readily reconverted to insoluble Cu-2(OH)PO4 and Cu-3(OH)(4)SO4 salts, 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 H3PO4 and H2SO4 produced pH values as low as 1.5 in the reaction media that effectively catalyzed the conversion of microcrystalline cellulose to C-6 alcohols, 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. [GRAPHICS]

Automated summary

In this study, we developed a novel and efficient approach for hydrolyzing cellulose using recyclable H3PO4 and H2SO4 generated via the reduction of insoluble Cu salts. The in situ formed acids catalyzed the conversion of cellulose to C-6 alcohols with high yields, and the Cu salts and mineral acids were completely recycled by simple filtration. This approach provides a rationale for designing recyclable mineral acids with wide applications, contributing to the development of green chemical processes.