Nickel-Based Catalysts for Deoxygenation of Biorefinery Products to Renewable Fuels: A Mini Review

Abstract

Nickel-based catalysts have shown decent performance in deoxygenation reactions. Although palladium catalyst is very effective for this  reaction, its high cost increases the cost of production. This review concerns the deoxygenation reactions of higher fatty acids, vegetable  oils, bio-oil and its model compounds to fuels using nickel-based catalysts. The hydrodeoxygenation and decarboxylation of model fatty  acids and vegetable oils over nickel-based catalysts have been found to produce appreciable hydrocarbons that can be used directly as  fuel in diesel engines. Similarly, bio-oil and its model compounds produce hydrocarbons in the presence of various nickel-based catalysts,  but the yield is not as prominent as in vegetable oils. In general, the catalytic performance of nickel in such reactions depends  on the co-metal, support and the reaction conditions. Like palladium and platinum, the electronic properties of nickel-metal have been  shown to significantly contribute to the cleavage of the C–C or C–H bonds during the reactions. It has been reported that hydrogen  molecule is stuck in the defect sites of the nickel=metal surface resulting in a decrease in the activation energy of hydrogen dissociation.  Nickel, is, therefore, one of the most promising metals for catalyzing hydrodeoxygenation of bio-oils into hydrocarbons.