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 pre ssures (3.1 MPa) and liquid-phase conditions. It was shown that the reactio n occurred mainly through a p-elimination mechanism for all catalysts and t hat the product distribution was similar for all carbides and sulfide catal ysts. Temperature-programmed desorption (TPD) of ethylamine was used to inv estigate the acid properties of the catalytic surfaces, and a good agreemen t between the specific rate of reaction and the number of Bronsted acid-sit es was obtained. Infrared spectroscopy was used to ascertain that the amine s interacted with the acid centers to form adsorbed quartenary ammonium spe cies, It is proposed that the deamination reaction over the carbide and sul fide catalysts occurs by a common mechanism involving a push-pull process b y 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.