Vapour-phase nitration of fluorobenzene with N2O4 over aluminosilicates. Effects of structure and acidity of the catalyst Original Research Article

The vapour-phase nitration of fluorobenzene with dinitrogen tetroxide has been investigated over amorphous silica-alumina and zeolites with various structures and aluminium contents. The activity of the catalysts increases with the number and the strength of the acid sites, but is also very dependent on the accessibility controlled by the pore structure and the size of the crystals. Except, the zeolite BEA which is the most active and the most stable, the deactivation of the catalysts is fast since the activity is high. The addition of water to the feed increases the activity and the stability of all the zeolites, but decreases the activity of amorphous silica-alumina. A large part of deactivation is attributed to the marginal formation of 2,4-dinitrofluorobenzene which stays on the surface of the catalyst, but can be eliminated by ‘steam distillation’. No evidence of shape selectivity was obtained. Zeolite BEA proved to be a remarkably efficient catalyst.