Cu2+-Exchanged Zeolites as Catalysts for Phenol Hydroxylation with Hydrogen Peroxide

Abstract

The Cu2+-exchanged NaY, HY, USHY, Hβ, and HZSM-5 zeolites were prepared and evaluated in phenol hydroxylation with hydrogen peroxide using an atmospheric batch reactor. CuNaY, CuHY, and CuHβ catalysts were found to be more active than TS-1 or a simple homogeneous copper nitrate catalyst under similar reaction conditions. Both zeolite type and copper content in the zeolite catalyst were revealed to exert critical impact upon the catalytic activity in phenol hydroxylation. Reaction time, reaction temperature, and the molar ratio of phenol to hydrogen peroxide also remarkably influenced the reaction results. The addition of a small amount of hydrochloric acid to the reaction systems significantly enhanced the phenol conversion, hydroxylation selectivity, and reaction rate. The used catalysts can be regenerated completely by calcination at 450 °C for 4 h in air. On the basis of ESR spectroscopy, the relationship between catalytic activity and copper loading is explained and the hydroxyl radical is suggested a...