Supercritical water oxidation of 2-chlorophenol catalyzed by Cu2+ cations and copper oxide clusters

Experimentally, the selectivity to decomposition (S/D) (S/D = (amount of 2- chlorophenol (2CP) oxidized to CO2 and H2O)/(disappearance of 2CP)) ratio f or oxidation of 2CP with Cu2+ cations in supercritical water was greater th an that without any catalysts by 60%. The enhancement was due to a fast pre cipitation of copper chloride in the supercritical water oxidation (SCWO) p rocess. Formation of toxic byproducts was significantly reduced. Because of a confined environment in the channels of ZSM-5, formation of undesired he avy chlorinated phenols and PAH (polycyclic aromatic hydrocarbon) byproduct s in the SCWO of 2CP (catalyzed by CuO/ZSM-5) was also highly suppressed. O nly trace light-PAHs with a molecule size less than 6 Angstrom were found i n the SCWO of 2CP. Carcinogenic PAHs (heavy-PAHs) were not observed. The ex tended X-ray absorption fine structural (EXAFS) spectra of the catalyst sho wed 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 Angstrom, respectively . The Cu3O2 clusters were oxidized to Cu3O4 by H2O2 in the supercritical wa ter. Since the diffusion coefficients of copper oxide clusters (Cu3O4) in t he 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.