Mechanism of the acetonitrile hydrogenation to amines over a platinum catalyst investigated by in situ infrared spectroscopy and DFT modeling

Abstract

The mechanism of the hydrogenation of acetonitrile (CH3CN and CD3CN) to amines over a platinum filmand Pt/Al2O3 catalyst was investigated by in situ infrared spectroscopy. The reaction was studied under realisticconditions -liquid phase with toluene as solvent- using a flow-through cell-microreactor in attenuated total reflection(ATR) mode developed in our research group. Reaction intermediates were identified combining infrared spectra withtheoretical modeling by DFT. A sequential hydrogenation mechanism is proposed. Acetonitrile linearly and 2-foldchemisorbed on platinum sites is hydrogenated to form an imine surface intermediate (CH3CH=NH), which ishydrogenated to ethylamine. In turn, this imine intermediate can condense producing diethylamine and triethylamineand ammonia as a by-product. The time-evolution of the IR signals were modeled using a proposed microkineticmechanism and intrinsic kinetic constants were obtained under chemical control.