Heterogeneous Catalytic Transfer Hydrogenation as an Effective Pathway in Biomass Upgrading

Abstract

Reducing oxygen content in biomass-derived feedstocks via hydrodeoxygenation (HDO) is a key step in their upgrading to fuels and valuable chemicals. Organic molecules, e.g., alcohols and formic acid, can donate hydrogen to reduce the substrate in a process called catalytic transfer hydrogenation (CTH). Although it is practiced far less frequently than molecular-hydrogen-based HDO processes, CTH has been proven to be an efficient and selective strategy in biomass upgrading in the last two decades. In this paper, we present a selective review of recent progress made in the upgrade of biomass-derived feedstocks through heterogeneous CTH, with a focus on the mechanistic interpretation. Hydrogenation and cleavage of C═O and C–O bonds, respectively, are the two main categories of reactions discussed, owing to their importance in the HDO of biomass-derived feedstocks. On acid–base catalysts, Lewis acid–base pair sites, rather than a single acid or base site, mediate hydrogenation of carbonyl groups with alcohols...