Catalytic Hydrothermal Decarboxylation and Cracking of Fatty Acids and Lipids over Ru/C

Here, we report on the catalytic hydrothermal conversion of fatty acids and lipids to a range of hydrocarbons using Ru/C without the need for addition of external H2 supplies. Catalyst screening experiments showed the following trend with respect to conversion of stearic acid: Pt/C > Ru/C > Pd/C > Rh/C (nominal 5 wt % metal loadings). Reactions with Ru/C were then examined further due to its high activity and comparatively low cost. Fatty acid decarboxylation and alkane cracking reactions yield a mixture of liquid n-alkanes of varying chain lengths (mainly as C7–C17) and gaseous products (mainly as CO2, CH4, and H2), with the product distribution dependent on reaction time and initial headspace gas composition. Conversion of an intact lipid (1,2-distearoyl-3-palmitoyl-sn-glycerol) occurs faster than that of stearic acid due to in situ generation of H2 by aqueous phase reforming of glycerol, a coproduct of the initial triacylglyceride hydrolysis reaction, which, in turn, accelerates fatty acid decarboxylation. Almost complete deactivation of Ru/C was observed after repeated use, but partial recovery of activity was achieved by heat treatment. These findings demonstrate that low-cost Ru catalysts can be applied to produce a mixture of alkanes that can be tailored to match the properties of existing petroleum hydrocarbon fuel blends (e.g., diesel, jet fuel).