Abstract
Catalytic hydrodeoxygenation (HDO) is a fundamental and promising route for bio-oil upgrading to produce petroleum-like hydrocarbon fuels or chemical building blocks. One of the main challenges of this technology is the demand of high-pressure H2, which poses high costs and safety concerns. Accordingly, developing cost-effective routes for biomass or bio-oil upgrading without the supply of commercial H2 is essential to implement the HDO at commercial scale. This paper critically reviewed the very recent studies relating to the novel strategies for upgrading the bio-feedstocks with ‘green’ H2 generated from renewable sources. More precisely, catalytic transfer hydrogenation/hydrogenolysis (CTH), combined reforming and HDO, combined metal hydrolysis and HDO, water-assisted in-situ HDO and non-thermal plasma (NTP) technology and self-supported hydrogenolysis (SSH) are reviewed herein. Current challenges and research trends of each strategy are also proposed aiming to motivate further improvement of these novel routes to become competitive alternatives to conventional HDO technology.