Shape selectivity of trace by-products for supercritical water oxidation of 2-chlorophenol effected by CuO/ZSM-48

Shape selectivity of trace by-products in supercritical water oxidation (SCWO) of 2-chlorophenol (2CP) catalyzed by CuO/ZSM-48 has been investigated. Experimentally, destruction efficiency of 2CP in the SCWO process is effectively enhanced by CuO/zeolite catalysts. In the two-dimensional (2D) channels of ZSM-48, formation of undesired by-products such as polycyclic aromatic hydrocarbons (PAHs) and higher chlorinated phenols (via the Cl-reinsertion) is extremely suppressed in the SCWO of 2CP compared to those observed for zeolites ZSM-5 and Y with three-dimensional (3D) channel structure and larger pore sizes, respectively. The main oxidation active species on CuO/ZSM-48 surfaces were CuO and Cu2O determined by X-ray photoelectron spectroscopy (XPS). Ratios of the surface species CuO/Cu2O are between 13.4 and 14.1 in the SCWO process. However, the existence of the Cu-O and Cu-Cu species with a Cu-O/Cu-Cu ratio of 3.5 in the copper catalyst is also observed by extended X-ray absorption fine structure (EXAFS) spectroscopy. Furthermore, since the absence of Cu-Cl species in the XPS and EXAFS spectra, one would suggest that copper in the channels of ZSM-48 is unlikely involved in the abstraction of Cl species from 2CP in the SCWO process. (C) 1999 Elsevier Science B.V. All rights reserved.