Electrocatalytic Dehydrochlorination of Pentachlorophenol to Phenol or Cyclohexanol

Abstract

The electrocatalytic hydrogenolysis of pentachlorophenol (PCP) was carried out under galvanostatic control, in an aqueous 1 M NaOH solution in which PCP is fully soluble, and on particles of palladium or rhodium supported on alumina (Pd(5%)/Al2O3 or Rh(5%)/Al2O3) and entrapped in a reticulated vitreous carbon (RVC) electrode. On Pd/Al2O3 and at 75 °C, the conversion was complete (>99%) after 16 mol of electrons per mol of substrate (16 F mol-1) were consumed, and phenol was the sole product formed in 98% yield (61% current efficiency). On Rh/Al2O3 and 25 °C, 100% conversion was reached after 24 F mol-1, and cyclohexanol was obtained in 98% yield with some 2% of cyclohexanone (62% current efficiency). The ease of electrocatalytic hyrogenolysis was found to increase in the following order: PCP < 2,6-dichlorophenol < 4-chlorophenol.

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

“…Inorganic chloride was determined by a standard method using ion chromatography [17]. For identification and quantification 13 C-labelled standards of chlorophenol isomers (2-chloro-; 2,4-dichloro-; 2,4,5-trichloro-; 2,3,4,5-tetrachloro-; 2,3,4,5,6-pentachlorophenol) purchased from Wellington Laboratories (Guelph, Canada) were used.…”

“…Rearrangement of chlorides during the reaction seems quite unlikely, too. Figure 2 shows the distribution of chlorophenols within each substitution degree after 6 h, found on weight% by GC-MS with 13 Cstandards.…”

“…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.…”

“…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.…”

Comparable Study of 4-chlorophenol Removal from Petrochemical Wastewater Using Mesoporous and Microporous Carbons: Equilibrium and Kinetics Investigations

“…Various physical and chemical treatment techniques such as catalytic oxidation, photocatalytic, membrane separation, biodegradation, solvent extraction and adsorption have been used for the reduce of organic pollutants from water [3,[5][6][7][8][9].…”