(329f) Hydrodeoxygenation of Organic Esters On Pd (111) Model Surfaces

Hydrodeoxygenation (HDO) of lipid feedstocks has received substantial interest over the past years. This process has the potential to convert lipids to fuels identical to gasoline and diesel at milder reaction conditions and lower costs than currently implemented technologies such as transesterification and co-processing in a hydrodesulfurization (HDS) unit. Lipid feed-stocks contain considerable amounts of esters and a thorough understanding of the HDO reaction mechanism of esters on metal surfaces promises the rational design of new catalysts for HDO units specially designed for lipids. In this study, the HDO of methyl propionate on a Pd (111) surface has been investigated under gas phase conditions. Periodic density functional theory (DFT) calculations have been performed using VASP 5.2 to obtain free energies of reactions and activation barriers. The DFT results have then been used to develop a microkinetic model to study the effect of temperature and partial pressure of reactants on the reaction mechanism and intermediates. Finally, Campbell’s degree of rate control method has been used to identify the rate-determining steps on the surface. Methyl propionate can go through C-O and C-H bond dissociations. It is likely that methyl propionate activates through dehydrogenation steps since the direct C-O bond dissociation steps have relatively high activation barriers in comparison to the dehydrogenation steps. We propose three different pathways for the dehydrogenation of methyl propionate via alpha, beta, and methoxy-end carbons. Overall, the dehydrogenation of alpha carbon seems to be rate determining.