Hydrodeoxygenation (HDO) of methyl palmitate over bifunctional Rh/ZrO₂ catalyst: Insights into reaction mechanism via kinetic modeling

Hydrodeoxygenation (HDO) of triglycerides into hydrocarbons is a novel catalytic process for the production of green biofuels. In this work, the HDO reaction mechanism over Rh/ZrO₂ catalyst was studied by selecting methyl palmitate as a model compound. HDO of methyl palmitate proceeded initially via the hydrogenolysis into palmitic acid intermediate, followed by sequential hydrogenation-decarbonylation reaction into pentadecane via aldehyde intermediate. Bifunctional mechanism of the Rh/ZrO₂ catalyst is advocated for the HDO process, in which both Rh sites and oxygen vacancy sites on ZrO₂ synergistically contribute to the catalysis. The interface between Rh nanoparticle and support was proposed to host the most active sites. Based on our earlier work, a surface reaction mechanism was proposed and slightly modified to develop a set of mechanistic kinetic models. The mechanistic model consisting of two distinct types of adsorption sites for oxygenated components and H₂, gave a good fitting to the kinetic data over a broad range of reaction conditions and conversion levels.