Catalytic nitroxidation of toluene into benzonitrile on chromia–alumina aerogel catalyst Original Research Article

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°C. Kinetic and EPR studies show that alumina stabilizes the chromium species which produce benzonitrile and the catalyst becomes more stable at the steady state. At the lower temperature range 250–350°C, conditions under which partial oxidation of toluene to benzaldehyde predominates, the Cr2O3–Al2O3 catalyst is inactive in the toluene nitroxidation. This result seemed to indicate that nitrogen monoxide dissociation requires higher energy than dioxygen. The mechanistic study shows that the reaction proceeds by a redox process in which the chromium species swing between two types Cr3+ and Cr5+ and these ions are interconverted by oxidizing and reducing atmosphere.