The role of hydrogen-deficient species during alkylamine hydrotreating on platinum catalysts

The mechanism of hydrodenitrogenation (HDN) of aliphatic primary amines, which are intermediates during HDN of renewable feedstocks, was investigated. The reactions of methylamine, ethylamine and dimethylamine on Pt(111) were studied using density functional theory (DFT). The hydrogen-deficient amine species predicted by DFT were experimentally validated through dodecylamine HDN experiments using a Pt/ZrO2 catalyst and deuterium gas. The C–H bonds of the amines were found to be labile: the amines adsorb on Pt through the NH2-group, after which C–H bond dissociation can occur, even for C–H bonds far from the NH2-group, resulting in the formation of various hydrogen-deficient species. Computational results indicated that nitrogen removal (N-removal) preferentially occurs through these hydrogen-deficient species because hydrogen removal from the α-carbon favors C–N bond dissociation. Additionally, these hydrogen-deficient species can react with each other, forming heavier condensation products such as secondary amines or imines. The experimental nitrogen removal rate of hexadecylamine on Pt/ZrO2 increased with decreasing hydrogen partial pressure, consistent with a mechanism in which hydrogen-deficient species serve as key reaction intermediates.