REACTION PATHWAY OF BENZONITRILE FORMATION DURING TOLUENE AMMOXIDATION ON VANADIUM PHOSPHATE CATALYSTS

The reaction pathway of the ammoxidation of toluene on (VO)(2)P2O7 use d as catalyst and the interaction of potential intermediates with the pyrophosphate were studied by spectroscopic techniques (FTIR, EPR), te mperature-programmed chemisorptions/reactions (TPD, TPRS) and transien t studies such as the temporal analysis of products (TAP) technique. N H3 is chemisorbed on the catalyst surface, forming three different spe cies, i.e., NH4+ ions located on Bronsted sites, coordinatively bound NH3 on Lewis sites and NH2- groups, presumably P-NH2. Toluene that is probably adsorbed on Lewis sites reacts in a first step to a benzyl ra dical. A subsequent partial oxidation by interaction of V-IV=O groups generates a V ... O=CH-C6H5 surface structure. This benzaldehyde-like surface species reacts with adsorbed NH3 according to a Langmuir-Hinsh elwood mechanism. TAP experiments on ammonium-containing vanadium phos phates revealed that NH4+ ions could act as potential N-insertion spec ies. No formation of benzylamine as well as the generation of V=NH sur face groups as possible intermediates or N-insertion sites were observ ed.