Cu- and Fe-ZSM-5 as catalysts for phenol hydroxylation

Abstract

Cu- and Fe-ZSM-5 catalysts were hydrothermally synthesized and characterized by XRD, BET, FT-IR and UV–vis. The catalytic activity of several samples was tested for the aqueous hydroxylation of phenol with hydrogen peroxide. Two different mineralizing agents were used to prepare Cu-ZSM-5 catalysts: methylamine (Cu-Z-o) and sodium hydroxide (Cu-Z-B). Fe-ZSM-5 catalysts were synthesized either without mineralizing agent (Fe-Z-s) or with ammonium fluoride (Fe-Z-f). The metallic content of the synthesized materials varied between 0 and 1.8 wt.% and the Si/Al ratio varied from 32 to infinity. The type of mineralizing agent has a strong influence on the Cu or Fe species incorporated into ZSM-5. Cu I and Cu II predominated in Cu-ZSM-5 prepared with methylamine whereas Cu° clusters besides Cu I and Cu II were detected on Cu-Z-B. When copper and Al contents decreased in Cu-ZSM-5 catalysts catechol production was favored. Cathecol was also preferably obtained over low iron loaded ZSM-5 prepared with NH 4-F as mineralizing agent. Fe-Z-f samples contained both framework and extraframework iron species. The best reaction conditions found in this work to obtain high yields of catechol and hydroquinone are 1 mmol phenol, molar ratio phenol/H 2O 2 = 3, catalyst = 20 mg, T = 80 °C, water = 5 g, reaction time = 4 h.