Supercritical Water Oxidation of 2-Chlorophenol Catalyzed by Cu2+ Cations and Copper Oxide Clusters

Abstract

Experimentally, the selectivity to decomposition (S/D) (S/D = (amount of 2-chlorophenol (2CP) oxidized to CO2 and H2O)/(disappearance of 2CP)) ratio for oxidation of 2CP with Cu2+ cations in supercritical water was greater than that without any catalysts by 60%. The enhancement was due to a fast precipitation of copper chloride in the supercritical water oxidation (SCWO) process. Formation of toxic byproducts was significantly reduced. Because of a confined environment in the channels of ZSM-5, formation of undesired heavy chlorinated phenols and PAH (polycyclic aromatic hydrocarbon) byproducts in the SCWO of 2CP (catalyzed by CuO/ZSM-5) was also highly suppressed. Only trace light-PAHs with a molecule size less than 6 Å were found in the SCWO of 2CP. Carcinogenic PAHs (heavy-PAHs) were not observed. The extended X-ray absorption fine structural (EXAFS) spectra of the catalyst showed that the copper oxides in the channels of ZSM-5 may form Cu3O2 clusters with Cu−Cu and Cu−O bond distances of 2.79 and 1.91 Å, respectively. The Cu3O2 clusters were oxidized to Cu3O4 by H2O2 in the supercritical water. Since the diffusion coefficients of copper oxide clusters (Cu3O4) in the channels of ZSM-5 was greater than that of 2CP by at least 3 orders, it is possible that these clusters are relatively mobile in ZSM-5 in the SCWO process.