Catalytic fast pyrolysis of cellulose to oxygenates: Roles of homogeneous and heterogeneous catalysts

Abstract

Catalytic fast pyrolysis (CFP) of biomass is an efficient approach that can overcome the structural recalcitrance of solid biomass (e.g. crystalline cellulose) to produce sugar monomers and their derivatives in several seconds. The composition of the product mixture, accumulated in a liquid called bio-oil, is highly tuneable by the use of in-situ/ex-situ catalysts for downstream production of sustainable fuels and fine chemicals. This minireview summarises the recent advances in homogeneous and heterogeneous catalysts in CFP production of versatile oxygenates as fuel precursors or bulk chemicals. First, a brief overview of primary CFP pathways including cellulose-to-levoglucosan (LGA) conversion and production of three important derivative anhydrosugars is provided. Particular attention is paid to the role of homogeneous and heterogeneous catalysts in promoting secondary reforming of LGA by dehydration, and alternative pathways via C3–C6 cyclisation or benzylic rearrangement over versatile catalysts (e.g. aqueous acids, zeolites, metal oxides) with Brønsted/Lewis acidity to produce a variety of oxygenates in bio-oil. This minireview may provoke more CFP technologies by clarifying opportunities and challenges behind the selective production of different reformed oxygenates, serving a complementary section for CFP-based production of aromatics from biomass.