Chlorophenol degradation using a one-pot reduction-oxidation process

Chlorophenol degradation was achieved using a combination of hydrodechlorination and heterogeneous Fenton-like oxidation. The process was conducted at ambient conditions (25 +/- 2 degrees C, atmospheric pressure) as a one-pot reaction involving formic acid as H(2) source for both hydrodechlorination of chlorophenols and H(2)O(2) formation. An alumina-supported Pd-Fe catalyst was applied, which is able to decompose formic acid at the Pd sites, forming H(2) and CO(2), and additionally H(2)O(2) in the presence of O(2). At the same time, due to presence of iron sites on the catalyst, the H(2)O(2) formed can be utilized for a Fenton-like oxidation reaction. Three different reaction protocols were tested, including: (i) consecutive reduction-oxidation with an initial oxygen-free phase adjusted by He purging (CRO-He), (ii) consecutive reduction-oxidation with initially oxygen-limited conditions (CRO) and (iii) simultaneous reduction-oxidation where O(2) flowing was started at the beginning of the reaction (SRO). 2,4-Dichlorophenol (DCP) and pentachlorophenol (PCP) were selected as representatives for the group of chlorophenols. For DCP degradation, CRO-He and SRO showed similar efficiencies with respect to the mineralization degree (up to 70%), whereas SRO achieved a better detoxification as observed in bioluminescence tests. The CRO-He reaction over the catalyst used showed only a small decrease in its activity during the oxidation stage, with no further change after the catalyst had been recovered twice. For PCP degradation, a self-inhibition effect was observed for the SRO process, indicating that PCP is hardly degradable by catalytic oxidation. In this case, the CRO-He process, which was facilitated by initial transformation of PCP into phenol and its subsequent oxidation, clearly produced a cleaner medium. This was also confirmed by the results of the toxicity measurements. The catalyst indicated a promising stability based upon the Pd and Fe leaching results measured at the end of each run. (C) 2011 Elsevier B.V. All rights reserved.