Recent developments in multifunctional catalysts for fatty acid hydrodeoxygenation as a route towards biofuels

Catalytic hydrodeoxygenation (HDO) provides a promising route for upgrading biomass-derived fatty acids to alkanes, which are potential biofuels (e.g. jet fuel (C8-C16) and diesel (C12-C22)) that could reduce our reliance on unsustainable fossil fuels. Currently, catalytic HDO, conducted over catalysts such as molybdenum disulfide, necessitates harsh operating conditions (>300 degrees C) which is both environmentally and economically unsustainable and promotes unwanted side reactions, e.g. cracking, which compromises product selectivity. Accordingly, the development of novel catalysts, which enable efficient and sustainable HDO, under milder operating conditions, and their translation from lab bench to large-scale production are highly desired. This review discusses the recent development of heterogeneous catalysts for HDO (including reaction pathways, mechanisms, and side reactions) and explores design strategies for the development of new multifunctional catalysts with potential to enable future development of HDO processes under mild conditions. In particular, we consider the sequential cascade transformation of fatty acids into fatty alcohols (via hydrodeoxygenation) and then hydrocarbons (via dehydration and hydrogenation), which requires the coupling of different but complementary catalytic sites, as an attractive alternative mild HDO strategy.