Amorphous Zr-OMS-2 Catalyst with Synergistic Lewis Acidity-Redox Sites for Efficient Ammoxidation of Benzyl Alcohol to Benzonitrile.

Abstract

The direct ammoxidation of alcohols represents a crucial synthetic pathway for nitrile production. However, achieving high nitrile selectivity while suppressing over-reaction to amides remains a significant challenge. In the present work, a Zr-doped OMS-2 catalyst that demonstrated remarkable efficiency for the selective ammoxidation of benzyl alcohol to benzonitrile is developed. Under optimized conditions, an impressive yield of 84.9% and selectivity of 89.9% are achieved, using aqueous ammonia as the nitrogen source and molecular oxygen as the oxidant. Solvent effect studies reveal that the adsorption of benzyl alcohol and benzonitrile significantly influences the activity and selectivity of the reaction. Kinetic investigations reveal that the reaction proceeded through a three-step consecutive first-order mechanism, with the high nitrile selectivity being kinetically controlled. Comprehensive characterization demonstrates that the incorporation of Zr⁴⁺ enhances the Lewis acidity of OMS-2, increases the population of active oxygen species, and effectively lowers the activation energy barrier. Controlled experiments elucidate the reaction mechanism in detail. The catalyst exhibits excellent stability and broad substrate generality, selectively converting a wide range of aromatic alcohols to their corresponding nitriles with high yields. This work provides a robust and practical alternative to conventional cyanide-based nitrile synthesis methodologies.