Journal of Industrial and Engineering Chemistry, Vol.127, 36-61, November, 2023
Deoxygenation of vegetable oils and fatty acids: How can we steer the reaction selectivity towards diesel range hydrocarbons?
Fast pyrolysis is a prominent and versatile process that involves thermal decomposition of biomass feedstocks to produce high volumes of liquid bio-oil, which may eventually be upgraded via deoxygenation pathways (hydrodeoxygenation, decarboxylation, or decarbonylation) into high energy content green fuels like gasoline, diesel and jet fuel. The quality of the bio-oil, its thermal stability, heating value, and the efficiency of the total conversion process can be improved by deoxygenation over properly designed catalysts. Despite the success of the available catalysts to significantly improve bio-oil quality by producing useful aromatic hydrocarbons, phenolics, or alkanes, there are still opportunities for further improvements of the catalytic performance with regards to their activity, product selectivity and resistivity against deactivation. The present work provides a comprehensive analysis of the recent developments of sulfur-free monometallic and bimetallic transition metal and noble metal supported catalysts for selective deoxygenation of vegetable oils and fatty acids model compounds for biofuel production. The attention focuses on the design of active sites on these catalysts as well as the acidic nature of the integrated supports for selectively manipulating mechanistic pathways. Moreover, this review emphasizes on the role of doping in stabilizing metal oxides to tune metal-support interaction (MSI) and electron donation properties, all strategies combined for the enhancement of biofuel production. The novelty of this review lies on bridging theoretical and experimental investigations aiming at describing and interpreting deoxygenation pathways of vegetable oils and related model compounds. Current challenges and perspective are also provided.