Molecular-Level Insights into the Reaction Mechanisms of Reductive Etherification for the Production of Synthetic Biofuels

Reductive etherification provides a pathway for creating low-carbon-intensity distillate fuel blendstocks and chemicals from biomass-derived alcohols and ketones. In this work, we examine the reductive etherification of representative model compounds, <i>n</i>-butanol and 4-heptanone, to form 4-butoxyheptane over size-controlled Pd nanoparticles supported on NbOPO₄ through a combination of experiments and density functional theory (DFT) calculations. Reaction rate and selectivity trends from packed-bed reactions show that both the catalyst and support are needed to carry out the reaction and that reaction rates increase with increasing Pd particle size. The DFT calculations show that the reaction most likely proceeds via the formation of an enol intermediate on the support, which is subsequently hydrogenated on Pd. Furthermore, we rationalize the dependence of 4-butoxyheptane formation rates on Pd particle size by showing the energetic favorability of enol ether hydrogenation on low-index terrace sites (Pd(111) and (100)) compared to that on high-index step sites (Pd(110)).