Catalytic nitroxidation of toluene into benzonitrile on chromia-alumina aerogel catalyst

The Cr2O3-Al2O3 catalyst aerogel with atomic percentage in chromium equals 5% presents a high selectivity in the reaction between toluene and nitrogen monoxide to benzonitrile in the high temperature range 400-460 degrees C. Kinetic and EPR studies show that alumina stabilizes the chromium species w hich produce benzonitrile and the catalyst becomes more stable at the stead y state. At the lower temperature range 250-350 degrees C, conditions under which partial oxidation of toluene to benzaldehyde predominates, the Cr2O3 -Al2O3 catalyst is inactive in the toluene nitroxidation. This result seeme d to indicate that nitrogen monoxide dissociation requires higher energy th an dioxygen. The mechanistic study shows that the reaction proceeds by a redox process i n which the chromium species swing between two types Cr3+ and Cr5+ and thes e ions are interconverted by oxidizing and reducing atmosphere. (C) 2000 El sevier Science B.V. All rights reserved.