Catalytic hydrodeoxygenation of bio-oil and model compounds - Choice of catalysts, and mechanisms

In recent decades, the quest for renewable and sustainable alternatives, namely biomass/bio waste, has been prompted by rising environmental concerns, demand, and the depletion of natural fossil fuels. Further, converting biomass (wood, agricultural, and solid) residues into liquid fuels using thermochemical means, seems to be the most promising and environmentally beneficial approach. However, bio-oil produced through pyrolysis is of poor quality due to the high moisture and oxygenated compounds that reduce its heating value, chemical stability, and corrosion resistance. Hence, it cannot be used as drop-in fuel or alternative energy means. Hydrodeoxygenation (HDO) is a cutting-edge method for upgrading bio-oil into sustainable fuels that may compete with traditional fossil fuels. Furthermore, catalytic HDO improves the quality of the pyrolysis oil, which will be classified as renewable and significantly impacts the clean energy structure and industrial application. However, being the primary difficulty in catalytic HDO, producing high-performance catalysts has been the core focus of the study. Furthermore, given the intricate composition of bio-oil and the complex chemistry of its volatile compounds, there has been limited research focused on comprehending the physico-chemical aspects. Recent advances in upgrading actual pyrolysis bio-oil to gasoline will greatly assist biorefineries and need an emphasis, in detail. Hence, the present review provides a detailed HDO mechanism, biofuels, model compounds, and the suitability of the catalyst for biofuels/model compounds obtained from a wide range of feedstock.