A. Andersson
Aug 1, 1986
Citations
0
Influential Citations
31
Citations
Journal
Journal of Catalysis
Abstract
Abstract The oxidation and ammoxidation of 3-picoline have been studied over a V 2 O 5 catalyst using temperature-programmed desorption combined with studies of the transient responses to pulses of one of the reactants. The results obtained are related to the surface structure of the catalyst, deduced on the basis of metal-oxygen bond strength values. The mechanistic features that emerge are as follows. Some 3-picoline is adsorbed at partially reduced vanadium ions via the nitrogen atom. This picoline can either desorb unconverted or it can react with weakly bonded oxygen to afford both carbon oxides and 3-pyridinecarbaldehyde. It seems that the aldehyde formed can react with NH 3 to give nicotinamide. Some 3-picoline is immediately adsorbed in the form of partial degradation products. These products are further transformed into carbon oxides upon increasing the temperature. After abstraction of a methyl hydrogen atom 3-picoline becomes attached to a vanadyl oxygen species and then reacts with NH 3 to yield nicotinonitrile, although a dealkylation to produce pyridine also can occur. There are three different sites for the formation of nitrile. Most of the nitrile is formed in a reaction between chemisorbed 3-picoline and weakly adsorbed or gaseous NH 3 . However, adsorbed NH 3 clearly takes part in the formation of nitrile at two other sites. In one case NH 3 is proposed to be adsorbed at a vanadyl oxygen vacancy. At the other site NH 3 is even more strongly adsorbed, probably in the form of either NH 2 or NH groups, and there is a deficiency of oxygen associated with this site.