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.

No abstract

Reduction of trace polycyclic aromatic hydrocarbon (PAH) byproducts in supercritical water oxidation (SCWO) of 2-chlorophenol (2CP) effected by CuO/ZSM-5 has been investigated in the present work. In the channels of ZSM-5, due to a restricted environment, formation of undesired PAH byproducts in the SCWO of 2CP was significantly suppressed. Only trace light-PAHs with a molecular size less than 6 Å were formed in the SCWO of 2CP. Carcinogenic PAHs (heavy-PAHs) were not found. Structures of CuO and Cu2O in the channels of ZSM-5 that involved in the catalytic SCWO of 2CP were studied by X-ray photoelectron spectroscopy (XPS). The Cu2O-to-CuO ratio was approximately 0.15. Existence of the Cu(I) and Cu(II) was also confirmed by the preedge X-ray absorption near edge structural (XANES) spectroscopy. The copper oxides with a square-plane structure were observed by electron paramagnetic resonance (EPR) spectra. Furthermore, the extended X-ray absorption fine structural (EXAFS) spectra suggest 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 supercritical water.

Interactions between cations and Cl species in the supercritical water oxidation (SCWO) of 2-chlorophenol (2CP) has been investigated in a high-pressure quartz-lined reactor at 673-773 K. Experimentally, we found that the S/D ratio (defined as the amount of 2CP converted to CO 2 and H 2 O/disappearance of 2CP) for SCWO of 2CP was enhanced by cations (such as Li + , Na + , K + , Ca 2+ , Fe 2+ , or Fe 3+ ). The S/D ratio increased as the charge density of cations increased (

No abstract