Characterization and activity of Cu/ZSM5 catalysts for the oxidation of phenol with hydrogen peroxide

The heterogeneous catalytic wet peroxide oxidation (CWPO), involving total oxidation of organic compounds to CO2 and H2O is a possible path for the treatment of toxic and bio-refractory wastewater streams. The aim of this work was to synthesize and characterize three Cu/ZSM5 catalysts prepared by direct hydrothermal synthesis. The mass ratio of the active metal component in the zeolite ranged from 1.62-3.24 wt %. These materials were tested for CWPO of aqueous phenol in a stainless steel Parr reactor, in batch operation under mild conditions (at atmospheric pressure and a temperature of 353 K). The catalyst weight was 0.1 g dm(-3) and the initial concentration of phenol and hydrogen peroxide were 0.01 mol dm(-3) and 0.1 mol dm(-3), respectively. The catalysts were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), AAS and ICP-MS. Their catalytic performance was monitored in terms of phenol and total organic carbon (TOC) conversion, hydrogen peroxide decomposition, by-product distribution and the degree of copper leached into the aqueous solution. The experimental results indicated that within 180 min, these catalysts facilitated almost complete elimination of phenol and a significant removal of chemical oxygen demand, without significant leaching of Cu ions from the zeolite. The Cu/ZSM5-DHS3 catalyst with the highest copper loading was proven to be the best candidate. The useful fraction of hydrogen peroxide that contributed to the removal of the organic compounds quantified in terms of selectivity, S, indicated that the CWPO selectivity was always less than 100 %, which meant that there was some self-degradation of oxidant. It was also shown that oxidation of phenol took place on the catalyst surface via a heterogeneous mechanism, and that the contribution of any homogeneous reaction mechanism was not significant.