Catalytic wet hydrogen peroxide oxidation of para-chlorophenol over Al/Fe pillared clays (AlFePILCs) prepared from different host clays

In this work, three AlFePILCs prepared from different host clays were synthesized, characterized and tested in the catalytic wet hydrogen peroxide oxidation of 4-chlorophenol. Two reference clays, with widely different cation exchange capacities (1.2 meq/g for SAz-1 and 0.87 meq/g for SWy-2), and a Romanian montmorillonite (Mt) were used for the preparation of the catalysts, their structural and textural properties being determined by X-ray diffraction and nitrogen adsorption-desorption isotherms. The catalyst based on SAz-1 has a more ordered structure and a higher surface area than the other two catalysts, prepared from SWy-2 and Mt, and this was attributed to its higher layer charge. The 4-chlorophenol oxidation proceeds with the formation of 4-chlorocatechol (main reaction intermediate) and hydroquinone. Other chlorinated benzenediols and triols as well as dimerization products have been also identified by derivatization and GC-MS analysis. All the catalysts allowed the total elimination of 4-chlorophenol and significant removal efficiencies for the total organic carbon, of 60, 52 and 45%, for Mt. SWy-2 and SAz-1 based catalysts, respectively. The iron leaching was very low, but the most active catalyst produced the higher amount of dissolved iron (1 ppm), as compared with AlFePILCs based on SWy-2 and SAz-1 (0.5 ppm). To explain the differences in the catalytic properties, Mossbauer and diffuse-reflectance UV-vis spectroscopies were used to investigate the nature of the active sites. Both methods suggested the presence of two iron species: low-nuclearity ferric oxides and well-ordered hematite-like nanoparticles. The low-nuclearity ferric oxides seem to be responsible for the iron leaching and for the differences in the catalytic activity. (C) 2010 Elsevier B.V. All rights reserved.