Vegetable oil-based feeds are regarded as an alternative source for the production of fuels and chemicals. Paraffins and olefins can be produced from these feeds through catalytic deoxygenation. The fundamentals of this process are mostly studied by using model compounds such as fatty acids, fatty acid esters, and specific triglycerides because of their structural similarity to vegetable oils. In this Review we discuss the impact of feedstock, reaction conditions, and nature of the catalyst on the reaction pathways of the deoxygenation of vegetable oils and its derivatives. As such, we conclude on the suitability of model compounds for this reaction. It is shown that the type of catalyst has a significant effect on the deoxygenation pathway, that is, group 10 metal catalysts are active in decarbonylation/decarboxylation whereas metal sulfide catalysts are more selective to hydrodeoxygenation. Deoxygenation studies performed under H2 showed similar pathways for fatty acids, fatty acid esters, triglycerides, and vegetable oils, as mostly deoxygenation occurs indirectly via the formation of fatty acids. Deoxygenation in the absence of H2 results in significant differences in reaction pathways and selectivities depending on the feedstock. Additionally, using unsaturated feedstocks under inert gas results in a high selectivity to undesired reactions such as cracking and the formation of heavies. Therefore, addition of H2 is proposed to be essential for the catalytic deoxygenation of vegetable oil feeds.

Group 6 (W, Mo) metal carbide catalysts are promising alternatives to hydrodesulfurization (NiMo, CoMo) catalysts and group 10 (Pd) type catalysts in the deoxygenation of vegetable fats/oils. Herein, we report a comparison of carbon nanofiber-supported W 2 C and Mo 2 C catalysts on activity, selectivity, and stability for the hydrodeoxygenation of oleic acid to evaluate the catalytic potential for the upgrading of fat/oil feeds. W 2 C/CNF was more selective toward olefins, whereas Mo 2 C/ CNF was more selective toward paraffins. This was related to the hydrogenation activities of the respective metal carbides. Mo 2 C/CNF showed higher activity and stability compared with W 2 C/CNF.

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A one-pot catalytic hydrolysis-deoxygenation reaction for the conversion of unsaturated triglycerides and free fatty acids to linear paraffins and olefins is reported. The hydrothermal deoxygenation reactions are performed in hot compressed water at 250 °C over a Pd/C catalyst in the absence of external H2 . We show that aqueous-phase reforming (APR) of glycerol and subsequent water-gas-shift reaction result in the in situ formation of H2 . While this has a significant positive effect on the deoxygenation activity, the product selectivity towards high-value, long-chain olefins remains high.

Catalytic deoxygenation of unsaturated fatty acids in the absence of H2 is known to suffer from significant catalyst inhibition. Thus far, no conclusive results have been reported on the cause of deactivation. Here we show that CC double bonds present in the feed or the products dramatically reduce the deoxygenation activity of supported palladium catalysts. In the case of stearic acid deoxygenation the addition of 0.1 equivalents of a mono‐unsaturated fatty acid or olefin already reduces the catalytic deoxygenation activity by 60 %. This effect becomes more pronounced with an increasing number of double bonds. The inhibition is shown to be reversible in H2 atmosphere, indicating no significant contribution from irreversibly deposited hard coke. Furthermore, the type of support material has no apparent effect on catalyst inhibition. Hence we propose that initial catalyst inhibition proceeds through reversible adsorption of CC double bonds on the palladium active sites.