Transformation of Levulinic Acid to Valeric Biofuels: A Review on Heterogeneous Bifunctional Catalytic Systems.

Abstract

Valerate esters (VAEs) commonly derived from levulinic acid (LA), which is deemed as one of the most promising biomass platform molecules, have been hailed as the valeric biofuels in recent years. The cascade transformation of LA to VAEs consists of a series of acid-catalyzed and metal-catalyzed processes alternately, in which the heterogeneous bifunctional catalysts are required for a better catalytic performance. The transformation pathway from LA to VAEs was presented, and the bifunctional catalytic systems for the cascade transformation of LA to valeric acid (VA) and its esters as well as the one-pot conversion processes were thoroughly reviewed. Additionally, effects of metal and acid sites on the catalytic performance were discussed in detail, respectively. Impacts and improvements of coke deposition, which was determined to be the primary inducement for the reduction of catalytic activity, were also analyzed. Finally, feasible suggestions were proposed for the enhancement of catalytic performance and the reduction of overall costs.