In situ thermal-assisted photocatalytic decarboxylation of high-concentration biomass-derived fatty acids to alkanes

Abstract

Heating is a straightforward method to increase reaction rates to meet industrial production, yet photocatalysis seldom incorporates it because their intrinsic driving force depends on the separation of photogenerated carriers, which is rarely affected by temperature. Here, we report a temperature-dependent photocatalytic decarboxylation strategy for producing long-chain n-alkanes from biomass-derived fatty acids using only the photothermal effect of the SnS catalyst. Under concentrated light irradiation without any external heating, and by employing high boiling-point solvents to reach optimal reaction temperatures (∼254 °C), Cn-1 n-alkane allows a very high concentration output (∼0.5 M for stearic acid to n-heptadecane) in a single operation, which is far beyond the capacity limit of conventional photocatalysis, typically no more than the mM levels. Mechanistic studies suggest that the in-situ heat brings the standing C-chain at low temperature down onto the SnS surface, increasing strain on the C-COO- bonds and facilitating reaction with photo-induced hole-electron pairs. We demonstrate that the majority of the incident light energy, when converted to heat, accelerates the photocatalytic decarboxylation.