Byproduct shape selectivity in supercritical water oxidation of 2-chlorophenol effected by CuO/ZSM-5

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 angstrom 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 angstrom, respectively. The Cu₃O₂ clusters were oxidized to Cu₃O₄ by H₂O₂ in supercritical water.