Oxidation of benzene over bimetallic Cu–Ce incorporated rice husk silica catalysts

Abstract

Oxidation of benzene to phenol with 30% H 2O 2 in liquid-phase was carried out over a series of Cu–Ce incorporated rice husk silica catalysts using acetonitrile as solvent at 343 K under atmospheric pressure. Cu and Ce incorporated rice husk silica catalysts were prepared by the sol–gel technique using cetyltrimethyl ammoniumbromide as the template. These catalysts were labeled as RHA–10Cu5Ce, RHA–10Cu20Ce, and RHA–10Cu50Ce. TG/DTG analysis of the catalysts confirmed complete removal of the template at 773 K and all catalysts were X-ray amorphous even after 50 wt% cerium incorporation. The rate for benzene oxidation increased linearly with cerium incorporation and depended directly on H 2O 2 decomposition. The high activity and phenol selectivity observed under mild reaction conditions (343 K, atmospheric pressure) could be correlated to the enhanced textural properties such as the BET surface area (403–279 m 2 g −1) and large pore volume (0.90–0.54 m 3 g −1) of the catalysts. Conversion during catalytic performance followed the order RHA–10Cu50Ce > RHA–10Cu20Ce > RHA–10Cu5Ce while phenol selectivity followed the order RHA–10Cu20Ce > RHA–10Cu5Ce > RHA–10Cu50Ce. A redox mechanism between Cu 2+/Cu + and Ce 4+/Ce 3+ active centers on the silica surface was responsible for the high catalytic activity of 84% with 96% phenol selectivity given by RHA–10Cu20Ce.