Push-pull mechanism of hydrodenitrogenation over carbide and sulfide catalysts

Comparison of the hydrodenitrogenation rate of a series of isomeric amines was performed over Mo2C, NbC, NbMo2-O-C and MoS2/SiO2 catalysts at high pressures (3.1 MPa) and liquid-phase conditions. It was shown that the reaction occurred mainly through a p-elimination mechanism for all catalysts and that the product distribution was similar for all carbides and sulfide catalysts. Temperature-programmed desorption (TPD) of ethylamine was used to investigate the acid properties of the catalytic surfaces, and a good agreement between the specific rate of reaction and the number of Bronsted acid-sites was obtained. Infrared spectroscopy was used to ascertain that the amines interacted with the acid centers to form adsorbed quartenary ammonium species, It is proposed that the deamination reaction over the carbide and sulfide catalysts occurs by a common mechanism involving a push-pull process by basic nucleophilic sulfur species and electrophilic Bronsted acid centers. The similarity between the carbide and sulfide catalysts suggests that a similar surface composition, a carbosulfide, is attained during reaction. (C) 2000 Elsevier Science B.V. All rights reserved.