Reductive Degradation of Polychlorinated Phenols by Pd/C‐Formate: An Ecoefficient Remediation Method for Aqueous Chlorinated Phenols

Abstract

A new catalytic dehydrohalogenation method for chlorinated phenols is described, which can be used to break down chlorinated pollutants in wastewater. It uses a system of Pd-C as catalyst with sodium formate as reducing agent. This economic method is easy to perform with a complete degradation of the pollutant within 12 to 30 h at room temperature. The ecoefficieny of the procedure is compared with eleven alternative methods showing the special advantages of the method. IntroductionChlorophenols have been used in pesticides, disinfectants, wood preservatives, personal care formulations, and many other technical products. They are also substantial by-products of the wood pulp bleaching process with chlorine, where they are emitted by wastewaters [1]. However, increasing knowledge about toxicity and environmental fate of these compounds resulted in regulation acts for production and distribution by various governments. In most European countries pentachlorophenol (PCP) has been banned as commercial fungicide; five chlorophenols are listed by the U.S. Environmental Protection Agency as priority pollutant, including PCP and 2,4,6-trichlorophenol, which occur, according to Ramamoorthy and Ramamoorthy [1], in the environment in significant quantities.Several oxidative degradation methods exist for these classes of compounds using H2O2 as oxidant. A French group [2] reported most effective methods for oxidations in homogeneous solution; a recent method developed uses H2O2 in the presence of Fe-TAML as catalyst [3]. An alternative remediation method would be a reductive cleavage of chlorophenols yielding chloride and phenol, the latter being readily biodegradable. While there are several reductive dechlorination methods reported in the literature for aromatic chlorine compounds, most of these methods have been used for monochlorinated compounds [4 -12].It should be mentioned that there are some other procedures for hydrodechlorination of aromatic halides such as hydrodechlorination by special electrochemistry techniques [13] and treatment with iron and photolytic hydrodehalogentions [14], but these methods are not appropriate for practical remediation. PCP has been dechlorinated efficiently with a variety of metals like Ag/Fe in subcritical water at temperatures of 200 to 3508C [15], certainly not useful for remediation of wastewaters. There is an extensive review article about reductive hydrodehalogenations of organic halides [16].Here, the development of an efficient hydrodechlorination method for perchlorinated aromatic compounds in aqueous solution is described, which uses Palladium on charcoal as catalyst and sodium formate as reducing agent. The method was described recently by an Italian group, who employed it on monochlorinated arene derivatives on preparative scale [11]. We have modified the method in order to use it for chlorinated phenols and PCP at environmentally relevant levels and compared it with other existing methods according to its practical use and ecoeffiency. Materials and Methods General Survey ...

Facile synthesis of palladium nanoparticles encapsulated in amine-functionalized mesoporous metal–organic frameworks and catalytic for dehalogenation of aryl chlorides

“…Most polychlorinated benzenes are priority pollutants [2]. Interestingly, water is used as solvent, and the dichlorobenzene derivatives (1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 2,4-dichlorophenol) and trichlorobenzene derivatives (1,2,4-trichlorobenzene and 2,4,6-trichlorophenol), which are not soluble in water, can be dehalogenated completely with high activity in only 8 h (entries [17][18][19][20][21][22]. Interesting, there was no chlorobenzene or chlorobenzene derivatives.…”

“…In contrast, heterogeneous palladium catalysts have been proven to be promising alternatives for avoiding these problems [9]. Various materials, such as Al 2 O 3 [21], carbon structures [9,14,20,22,25,26], polymers [16,17], mesoporous silica [1,24], zeolites [19], magnetic materials [15], and ionic liquids [18], have been employed as supports for palladium catalysts. Compared with other heterogeneous catalysts, palladium nanoparticles encapsulated in cages are stable and cannot agglomerate to the bulk because the cages can confine metal nanoparticles and restrict their growth.…”

“…Therefore, great efforts have been devoted to developing methods for dehalogenating aryl halides, which leads to a drastic decrease in toxicity [6][7][8]. Generally, there are several methods for solving the problem [9]: the available techniques mainly include wet catalytic oxidation [10,11], photochemical treatment [12], and palladium [1,[4][5][6][7][8][9][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] catalytic hydrogenation. Recently, an operationally simple iron-catalyzed hydrodehalogenation of aryl halides has also been developed [29][30][31][32].…”

Review: Endocrine disrupting chemicals (phenol and phthalates) in the South African environment: a need for more monitoring

“…Industrially, phenols and their derivatives are used in several useful products. They are used to manufacture chemicals such as pesticides, explosives, dyes, for pulp bleaching with chlorine, in wood preservatives, insecticides, herbicides, antioxidants, adhesives, plastics and synthetic intermediates (Baldwin and Debowski, 1988;Cledera-Castro et al, 2006;Czaplicka, 2001;Hartung et al, 2007;Ozkaya, 2005;Ribeiro et al, 2002;Santana et al, 2009;Santana et al, 2005;Suliman et al, 2006).…”