Catalytic Hydrodeoxygenation of Phenols and Cresols to Gasoline Range Biofuels

Unlike fossil fuels, biomass has oxygen amounts exceeding 10 wt%. Hydrodeoxygenation (HDO) is a crucial step in upgrading biomass to higher heating value liquid fuels. Oxygen removal has many challenges due to the complex chemistry and the high reactivity leading to irreversible catalyst deactivation. In this study, the focus is on the catalytic HDO of aromatic oxygen-containing model compounds in biomass: phenols and cresols. In the current work, literature on catalytic HDO of phenols using molecular hydrogen is reviewed, with a focus on non-nickel-based mono- and bi-metallic catalysts, as nickel-based catalysts were reviewed elsewhere. In addition, the catalytic HDO of m-cresol using molecular hydrogen is examined. This review also addresses the use of hydrogen donors for the HDO of phenols and cresols. The operating conditions, catalysts, products, and yields are summarized to find the catalyst with promising activity and high selectivity toward aromatics. A critical review of the reactions that successfully led to HDO is presented and research gaps related to the HDO of phenols and cresols are highlighted. The conclusions provide potential successful catalyst combinations that can be used for HDO of phenols, cresols, and liquid aromatic hydrocarbons.