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).