Photoactive Single-Site Tin(IV) Catalyst for 5-Hydroxymethylfurfural Production from Sugars

The conversion of biomass into value-added platform chemicals represents one of the most accessible and sought-after routes toward resource-efficient chemical synthesis. In this report, visible light activation of a simple heterogeneous catalyst system that comprises Lewis acidic Sn(IV) cations immobilized on an alumina solid support (γ-Al2O3) is employed to efficiently convert C6 sugars into 5-hydroxymethylfurfural (HMF). Under photoirradiation, the reaction rate of HMF formation is 167 times higher than the equivalent thermal reaction (without light). The turnover number (TON) of the d-glucose molecule per Sn(IV) single site can reach as high as 1867 during the photocatalytic process. X-ray absorption spectroscopy (XAS) characterization indicates that Sn(IV) cations are dispersed at the single-cation level over the γ-Al2O3 support. These Sn(IV) single sites exhibit stronger Lewis acidity and increased interactions with reactant sugar molecules. The results clearly demonstrate the successful development of an original photocatalyst for biomass conversion at moderate temperatures using visible light. The catalyst system can be recycled up to 6 times, delivering >45% HMF yields each time.