Modulation Excitation DRIFT+MS Operando Investigation of the Gas Phase Hydrogenation of Acetonitrile on Platinum/Alumina

VOGH, LAUTARO; COLLINS, SEBASTIAN; QUAINO, PAOLA

Santa Fe

Conferencia; VI San Luis School and Conference on Surfaces, Interfaces and Catalysis; 2018

INTEC-UNL-CONICET

The mechanism acetonitrile (CH3CN) hydrogenation to amines over a Pt(5% wt)/Al2O3 catalyst was investigated by operando DRIFT spectroscopy coupled with mass spectrometry. An optimized DRIFT cell/micro-reactor was employed, which ensures reactions studies under true chemical control conditions. The reaction was studied flowing an acetonitrile/H2/He reaction mixture (molar ratio: 2/20/78) at 50 cm3/min, between 298 and 523 K. Conversion and selectivity was determined from calibrated mass spectrometer signals. The results were identical to those obtained using a conventional plug-flow reactor. In order to identify and characterize the role of the surface intermediates, modulation excitation spectroscopy (MES) experiments were carried out at 343 K. The signals of adsorbed intermediates were selectively separated from those of spectators. Additionally, reaction intermediates were identified combining observed infrared bands with theoretical modeling by DFT. A sequential hydrogenation mechanism is proposed. Acetonitrile, linearly and 2-fold chemisorbed, on platinum sites is hydrogenated to form an imine surface intermediate (CH3CH=NH), which is further hydrogenated to ethylamine. In turn, imine intermediate reacts with adsorbed acetonitrile to produce diethylamine and triethylamine and ammonia as a by-product.