Catalytic Wet Hydrogen Peroxide Oxidation of 4-Chlorophenol Over Iron-Exchanged Clays

Abstract

Chlorophenols were selected for this study because most of them are toxic and difficult to biodegrade. They represent a particular group of priority toxic pollutants listed by the US EPA in the Clean Water Act and by the European Decision 2455/2001/EC. The efficiency of advanced oxidation processes for degradation of chlorophenols has been extensively documented. The catalytic wet hydrogen peroxide oxidation process, involving oxidation with H 2 O 2 and solid catalysts in mild reaction conditions, was found to be very attractive for different pollutants; however, data regarding the degradation of chlorophenols are very scarce. The aims of this paper were: (i) to prepare and characterize a series of iron-exchanged montmorillonites and (ii) to assess their catalytic performances in a Fenton-like process for the oxidation of para-chlorophenol. DR-UV-VIS spectroscopy was tentatively used to elucidate the structure of the iron oxo sites intervening in the reaction. This approach has been used previously for ion-exchanged zeolites and was able to distinguish between isolated Fe(III) species and Fe x O y clusters of different nuclearity. The catalytic tests, performed at room temperature, showed that all iron-containing clays were very active, leading to the complete oxidation of parachlorophenol and a significant reduction of TOC values. 4-chlorocatechol was the major reaction intermediate found in the CWHPO of 4-CP, followed by hydroquinone and traces of benzoquinone, 5-chloro-1,2,4-benzenetriol, 1,2,4-benzenetriol and 3-chloro-muconic acid. The leaching test indicates that the catalytic activity is mainly due to leached iron ions, at least in the second part of the process.

Development of Pillared Clays for Wet Hydrogen Peroxide Oxidation of Phenol and Its Application in the Posttreatment of Coffee Wastewater

“…However, the interest for pillared clays has increased substantially in the last decade, given their use in different oxidation processes such as WHPCO and photocatalytic oxidation [118]. The properties of pillared clays-based catalysts have been mainly studied in the wet hydrogen peroxide oxidation of phenolic compounds as model molecules, among them are phenol [44,45,48,57,58,62,65,68], 4-nitrophenol [122,123], tyrosol [70], and p-coumaric and p-hydroxybenzoic acids [69].…”