A review on reaction mechanisms of metal-catalyzed deoxygenation process in bio-oil model compounds

Bio-oil is a potential liquid fuel source which can be produced through the pyrolysis of biomass. Catalytic deoxygenation is an instrumental step for the defunctionalization of bio-oil which will result in liquid fuel which is of lower oxygen content and higher heating value. Numerous studies were done to investigate the deoxygenation mechanisms and the kinetics of various bio-oil model compounds. In this review, heterogeneous metal-catalyzed deoxygenation mechanisms of oxygenated model compounds with functional groups such as phenolics, furans, ethers, carboxylic acids, aldehydes, ketones and alcohols were compared and discussed. The limitations, benefits and feasibilities of such mechanisms were also presented in this article. The discussions on the classes of model compounds and the bonding configurations of oxygenated compounds have also shown that there is a strong correlation between these parameters and the reaction pathways. Hence, this review presented a summary of the model compound based approach researches which would be useful in correlating such knowledge with the actual bio-oil deoxygenation process. Several outlooks on the deoxygenation reactivity of model compounds were also presented in this article based on the studies on the literatures.