Selective conversion of aqueous sorbitol to sorbitan by amorphous Silica-Alumina catalysts

Biomass-derived chemicals are key enablers of a circular bioeconomy, offering renewable solutions to mitigate climate change. Notably, 1,4-sorbitan is a versatile platform chemical for food, chemical, and pharmaceutical industries. We can obtain 1,4-sorbitan from solid acid-catalyzed dehydration of biomass-derived sorbitol. However, the instability and poor selectivity of most solid acid catalysts in aqueous sorbitol significantly hinder the efficient production of 1,4-sorbitan, limiting their industrial viability. Here, we show that the hydrothermal stability and optimal Brønsted acid strength of commercial amorphous silica-alumina with 40 wt% silica enabled high selectivity of 1,4-sorbitan (65 %) derived from aqueous sorbitol. The silica in amorphous silica-alumina catalysts provided optimal Brønsted acidity that minimized the degradation of the desired 1,4-sorbitan product by preventing further dehydration to isosorbide and polymerization to coke. Moreover, the silica content in amorphous silica-alumina catalysts improved the hydrothermal stability and prevented the phase transformation of the γ-alumina matrix. Our findings demonstrate that amorphous silica-alumina is a highly selective catalyst for 1,4-sorbitan production from aqueous sorbitol, and amorphous silica-alumina offers enhanced stability. These findings pave the way for designing improved solid acid catalysts for other sustainable, aqueous biomass conversions.