Catalytic Hydrodechlorination of 4-Chlorophenol in an Aqueous

Apr 16, 2010 - Catalytic Hydrodechlorination of 4-Chlorophenol in an Aqueous Solution with Pd/Ni Catalyst and Formic Acid ... Electrocatalytic dechlor...
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Ind. Eng. Chem. Res. 2010, 49, 4561–4565

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Catalytic Hydrodechlorination of 4-Chlorophenol in an Aqueous Solution with Pd/Ni Catalyst and Formic Acid Shu Wang,† Bo Yang,†,‡ Tingting Zhang,† Gang Yu,*,† Shubo Deng,† and Jun Huang† Department of EnVironmental Science and Engineering, POPs Research Center, Tsinghua UniVersity, Beijing 100084, China, and Department of EnVironmental Science and Engineering, College of Chemistry and Chemical Engineering, Shenzhen UniVersity, Shenzhen 518060, China

Palladized foam nickel (Pd/Ni) catalyst was prepared by replacement deposition and employed to hydrodechlorinate 4-chlorophenol (4-CP) with formic acid (FA). 4-CP was rapidly transformed to phenol by means of hydrogenolysis. Major factors that may influence the 4-CP conversion rate, including the Pd loading amount, FA dosage, and solution pH value, were investigated. A moderate Pd loading amount (1.0 wt %), an excess of FA dosage (FA/4-CP ratio of 51.4:1), and a relatively low pH (4.0) were found to be the optimal operational conditions under which 4-CP was degraded up to 96.2% within 2 h and the catalytic activity of Pd/Ni reduced negligibly after three recycles. The dechlorination pathway is postulated as follows: (1) HCOOH (or HCOO-) decomposed on Pd particles with atomic hydrogen ([H]) generated; (2) [H] served as the direct reducing agent in the hydrodechlorination of 4-CP adsorbed on both Pd particles and Ni substrate, through the radical mechanism. Pd/Ni is found to be a promising catalyst in the elimination of organochlorines. Introduction Organochlorines (OCs) are ubiquitous in multienvironmental matrixes because of their wide usage in industrial processes and daily life. These compounds, especially chloroaromatics, are toxic, biorefractory, and bioaccumulative. With most OCs listed as priority pollutants by the U.S. Environmental Protection Agency,1 there is urgent need to develop efficient and costeffective methods to detoxify and destroy them. Recently, numerous methods have been developed to eliminate OCs, such as thermochemical,2,3 photochemical,4,5 electrochemical,6,7 sonochemical,8,9 and mechanochemical methods.10,11 Among them, catalytic hydrodechlorination (HDC), which involves the reductive cleavage of a C-Cl bond by highly reactive atomic hydrogen ([H]), is a green and cost-effective technology. HDC can realize in situ detoxification at mild/ ambient conditions and recover some valuable raw materials without the production of more hazardous byproducts. So far as, the effective degradation of various OCs, including chlorobenzenes,12,13 chlorophenols,14,15 chlorofluorocarbons,16,17 polychlorinated biphenyls (PCBs),18,19 and polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans20,21 has been successfully achieved. In HDC, the catalyst is of the most importance, and the zerovalent iron-based bimetallic catalyst (Pd/Fe, Ni/Fe, Ru/Fe, or Ag/Fe)22–29 is mostly focused on. In those bimetallic particles, iron acts as the reducing agent, whereas the other metal serves as the catalyst to collect hydrogen gas and dissociate it to active [H], which is found to be the real reducing agent.27,28 However, their further use is restrained because of the gradual deactivation of catalyst, resulting from iron dissolution, catalyst loss, extensive dihydrogen (H2) formation, and iron hydroxide precipitation.23,24 Some researchers have veered to inert bimetallic catalysts such as Pd/Au,30 which showed high catalytic activity as well as desirable stability. Obviously, with no metal acting as the reducing agent, the deactivation of the catalyst * To whom correspondence should be addressed. Tel.: +86 10 62787137. Fax: +86 10 62794006. E-mail: [email protected]. † Tsinghua University. ‡ Shenzhen University.

was not evident. Our group has also found palladized foam nickel (Pd/Ni) to be a promising HDC catalyst.31–33 It has successfully destroyed PCBs in the electrocatalytic process and is stable. Moreover, from the practical and engineering point of view, electroless technology is much more feasible and available in various environmental remediation cases. In the electroless dechlorination process, H2 is the most frequently used the H donor. However, because of its low solubility (SH152 °C ) 0.84 mM at pH2 ) 100 kPa), H2 may not be sufficient to treat highly contaminated water. Formic acid (FA), however, has been reported to be as active as H2, and its high miscibility and in situ buffering effect make the in situ treatment of wastewaters with a high concentration of OCs possible.34–36 Therefore, the goal of this work is to evaluate the performance of the Pd/Ni catalyst in HDC of OCs using FA as the reducing agent. 4-Chlorophenol (4-CP) was selected as the objective contaminant. The effects of the Pd loading amount, FA dosage, and initial pH on the 4-CP conversion efficiency were investigated, and the dechlorination pathway was primarily postulated. Experimental Section Chemicals and Materials. 4-Chlorophenol (4-CP, 99.9%) and phenol (P, 99.9%) were supplied by Sigma-Aldrich (Natick, MA). NaOH (96.0%), HCOOH (FA, 88.0%), CH3COOH (99.5%), and H2SO4 (98.0%) were purchased from Beijing Modern Eastern Fine Chemical Co. (Beijing, China). Foam Ni (99.9%; SBET ) 1.2217 ( 0.1296 m2 g-1; PPI ) 130) was obtained from Changsha Lyuan Material Co. (Changsha, China). Palladium chloride (PdCl2; 99.5%) was from Changsha Asia Light Co. (Changsha, China). Methanol and acetone (HPLCgrade) were provided by Fisher Chemical Co. (Waltham, MA). All compounds were used as received without further purification. Preparation of Pd/Ni Bimetallic Catalyst. The Pd/Ni catalyst was prepared by replacement deposition. PdCl2 and NaCl were dissolved in deionized water (DI) with a molar ratio of 1:3, with production of [PdCl6]4-. Foam Ni substrates (1 mm × 2 mm × 2 mm) were degreased and cleaned in acetone for 40 min under ultrasonic vibration and then etched in a diluted H2SO4 (80 g L-1) solution for 90 s to remove any possible

10.1021/ie9005194  2010 American Chemical Society Published on Web 04/16/2010

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surface oxides. After being rinsed with DI, they were put into a vial with the previously made [PdCl6]4- solution. The vial was placed in an incubator shaker at a constant vibration of 150 rpm and a temperature of 25 °C. The replacement was carried out until the yellow solution turned colorless. Pd deposited on the surface of the Ni substrate by the following reaction: [Pd Cl6]4- + Ni ) Ni2+ + Pd + 6Cl-

(1)

The deposition procedure was performed exactly at the same conditions. After deposition, the catalyst was washed by DI water several times and then stocked in methanol for later use. For more details, refer to our previous work.32 Experimental Procedure Batch dechlorination was carried out in a 100 mL glass vessel with an aliquot of a 50 mL solution containing 4-CP (0.389 mmol L-1). The catalyst (3.0 g L-1) and FA were then injected into the solution. Diluted NaOH and CH3COOH solutions (0.1 and 0.01 mol L-1) were used to adjust the solution pH. The dechlorination system was stirred by a magnetic stirrer at 400 rpm. All experiments were performed at room temperature (25 ( 3 °C) and ambient pressure. Sample Analyses. At different reaction times, an aliquot of a 1 mL solution was withdrawn using a 5 mL syringe and filtered through a 0.45 µm membrane for analysis. The concentrations of the parent 4-CP and the organic product were measured using a high-performance liquid chromatography (HPLC) system equipped with a C18 column (Sunfire, 150 × 4.6 mm i.d., 5 µm particle size) and a Waters 2487 Dual λ absorbance detector. A mobile phase of 60% methanol and 40% water was employed at a flow rate of 1.0 mL min-1 at 40 °C, and the detector wavelength was set at 225 nm. The concentrations of Cl- and FA were determined by ion chromatography. Quantification of the products and remaining reactants was revealed by standard curves, respectively. The dechlorination efficiency of 4-CP was calculated by the 4-CP conversion rate. Results and Discussion Products of 4-CP Dechlorination. First of all, the control experiments were conducted in the absence of Pd/Ni or FA. The 4-CP concentration slightly changed in 24 h regardless of the pH (2.0-10.9). However, when both Pd/Ni and FA were present, transformation of 4-CP was immediately commenced. An example of 4-CP dechlorination with Pd/Ni and FA is depicted in Figure 1. Phenol (P) was the only detected organic product, and the mass balance was well above 99%. It was reported in some publications that cyclohexanone, the further hydrogenation product of P during HDC of 4-CP (or 2-CP) by FA and Pd/activated carbon (or Pd/chitosan), was detected in the long run.35,37 However, in the present study, no further hydrogenation of P took place, even in the extended reaction, which was in accordance with those using Pd/ZVI.22,24 In order to further verify whether P could be hydrogenated to cyclohexanone by Pd/Ni and FA, an experiment was conducted that was identical with that in Figure 1, except that P was spiked as the objective chemical rather than 4-CP. As expected, the concentration of P remained constant throughout 20 h of contact, whereas FA disappeared by approximately 40%. The reason for the product profile difference is unclear but may be due to the absorption characteristics of the support. In conclusion, 4-CP

Figure 1. Solution composition in a typical 4-CP dechlorination process (c0(4-CP) ) 0.389 mmol L-1, FPd/Ni ) 3 g L-1, Pd loading amount ) 1.0 wt %, c0(FA) ) 20 mmol L-1, pH 3.1, stirring speed ) 400 rpm).

Figure 2. Effect of the Pd loading on 4-CP conversion (c0(4-CP) ) 0.389 mmol L-1, FPd/Ni ) 3 g L-1, c0(FA) ) 20 mmol L-1, pH 4.0, stirring speed ) 400 rpm).

was transformed to P by a hydrogenolysis reaction with C-Cl bond cleavage but without further hydrogenation of P. Effect of the Pd Loading Amount. Figure 2 illustrates the effect of the Pd loading amount on 4-CP conversion. 4-CP was found to degrade with palladized Ni and FA (no transformation with pure Ni substrate and FA), and the conversion rate in 2 h increased dramatically from 6.5% to 96.2% as the Pd loading (w/w) increased from 0.1% to 1.0%. However, with a continuous increase of the Pd loading, no significant promotion in the conversion rate was obtained. The catalytic activity, defined as the intrinsic and specific rates, moles of 4-CP transformed per gram of Pd per minute, measured by the amount of 4-CP dechlorinated within the first 5 min, was employed to determine the performance of the catalyst.37 Also, it can be seen from Figure 2 that the highest catalytic activity was at the Pd loading of 1.0%. The scanning electron microscopy (SEM) images (Figure 3) of different Pd amounts of loaded Pd/Ni showed that, at a Pd loading of 1.0%, Pd particles were highly dispersed on the surface of the foam Ni substrate, although a few aggregates were also observed in the periphery of the substrate, whereas the particles tended to assemble into clusters at higher Pd loading. The clusters were otherwise not favorable because only the outside surface could serve as active sites and the particles would strip off the substrate, as a result of the loose linkage. Although the particle scattering in the reactor would to some extent help enhance the reaction rate, the leaching of Pd would gradually deactivate the catalyst, which was confirmed by the catalyst reuse. After three recycles, the catalytic activity at Pd loadings

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Figure 5. Effect of the initial pH on 4-CP conversion (c0(4-CP) ) 0.389 mmol L-1, FPd/Ni ) 3 g L-1, Pd loading ) 1.0%, c0(HCOOH) ) 20 mmol L-1, stirring speed ) 400 rpm). Figure 3. SEM image of Pd/Ni (×10 000, 20 kV). Pd loading: (a) 0%; (b) 1.0%; (c) 2.0%; (d) 3.0%.

Figure 4. Effect of the FA dosage on HDC of 4-CP (c0(4-CP) ) 0.389 mmol L-1, FPd/Ni ) 3 g L-1, Pd loading ) 1.0%, stirring speed ) 400 rpm).

of 1.0%, 2.0%, and 3.0% reduced by 3.02%, 18.41%, and 27.55%, respectively. Considering the corrosion of Ni, the sample was also tested using a UV-vis spectrophotometer (DR/ 4000U, Hach), and negligible Ni2+ was detected in the solution with a Pd loading of 1.0%. On the basis of consideration of the catalytic activity, dechlorination efficiency, and catalyst stability, 1.0% was the optimal Pd loading amount and was applied in the following sections. Meanwhile, it also indicates that Pd/Ni at a Pd loading of 1.0% is stable in the HDC process. In addition, it can be seen from Figure 3 that the Pd particles in Pd/Ni are in nanoscale, immobilized on the foam Ni substrate. Li et al.38 has reported that critical research needs in the application of nanomaterials in water treatment include retaining and separation technologies. Our present research may otherwise draw more attention because of the Pd/Ni catalyst’s merits in both retaining and separation (magnetic separation). Effect of the FA dosage. The effect of the FA dosage on 4-CP conversion was investigated at acidic (pH 3.1) and alkaline (pH 10.9) conditions (because the initial 4-CP concentration was the same, the FA dosage was referred to as the ratio of FA to 4-CP [FA/4-CP)], with the results shown in Figure 4. At initial pH 3.1, higher FA/4-CP resulted in higher 4-CP conversion. With FA/4-CP of 51.4:1, 95.1% of 4-CP was transformed to P in 1 h. The result was consistent with that of Vincent et al.,37 i.e., that a large excess of FA (50:1) was necessary to achieve the rapid and complete HDC of 2-CP. By contrast, at initial pH 10.9, 4-CP was slightly converted, independent of FA/4-CP.

The distinct difference of 4-CP conversion at acidic and alkaline conditions also indicated that the pH had a potential influence on HDC of 4-CP. Effect of the Initial pH. 4-CP conversion at different initial pH values is shown in Figure 5. 4-CP was quickly transformed to P at the initial pH 3.1 and 4.0. As the initial pH increased, the reaction rate decreased. After 5 h, the conversion rates of 4-CP at the initial pH 10.9 and 7.1 were only 6.6% and 28.6%, respectively. After adjustment of the pH to 3.1, the reaction rates were greatly accelerated, resulting in 76.3% and 81.1% of 4-CP transformed after an additional 1 h, respectively. At high pH, the dominant species in the solution would be the anion, like OH-, found to be highly adsorbed on the surface of the catalyst,34 resulting in coverage of the active sites and little access for 4-CP. After adjustment back to acidic conditions, the active sites of the catalyst was reexposed to 4-CP and conversion was resumed. Thus, acidic conditions are favorable for dechlorination of 4-CP. At the initial pH 2.0, a decrease in the reaction rate was observed compared with that at pH 3.1, which was also demonstrated by Vincent et al.37 However, such a phenomenon is not yet understood and further investigations are needed at this point. Though Ni2+ was not detectable in the solution as mentioned in section “Effect of the Pd Loading”, θ 2+ with φNi /Ni of -0.230 V, Ni would inevitably corrode under acidic conditions in the long run; therefore, a relatively low pH (4.0) was more practical. After dechlorination, the solution pH values changed to 2.1, 3.8, 5.2, 8.7, 8.8, and 11.1, respectively, with the initial pH 2.0, 3.1, 4.0, 5.0, 7.1, and 10.9. Although 4-CP HDC led to the formation of HCl, which would increase the acidity of the solution, the much faster decomposition of FA resulted in an increase of the pH. Dechlorination Pathway. As depicted previously, 4-CP was dechlorinated through hydrogenolysis with C-Cl bond cleavage. Kopinke et al.34 presented two different reaction mechanisms for HDC by Pd and FA: under neutral and acidic conditions, the fast radical mechanism via [H] atoms is favored, whereas under alkaline conditions, the relatively slow hydride mechanism dominates. There is no doubt that under acidic conditions the reaction was by means of a radical mechanism. However, as to alkaline conditions, there is a difference. We had found that under alkaline conditions the 4-CP conversion rate was independent of the FA/4-CP ratio. Hence, it is more likely that 4-CP was dechlorinated through the radical mechanism in the whole range of the pH value by hydrogen generated from FA decomposition.

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CP ratio, and pH value of the solution. The Pd loading amount affected the surface morphology of the catalyst, and highly dispersed Pd particles were favorable to increase the catalytic activity and stability. An excess of HCOOH and acidic conditions were necessary to achieve rapid and complete 4-CP conversion. Under optimal conditions, 96.2% of 4-CP was converted within 2 h and the catalyst was stable after several recycles. The Pd/Ni catalyst has the potential to alternate the self-depletive Pd/ZVI bimetallic catalyst. Further investigation is in progress for the practical application of Pd/Ni. Figure 6. Proposed scheme of the 4-CP dechlorination pathway by Pd/Ni and FA.

The reaction site for decomposition of FA was also studied. Supplementary experiments showed that nonpalladized foam Ni had no potential to decompose FA or dechlorinate 4-CP using FA as the H donor. This was in agreement with the result of Prusse et al.,39 i.e., that FA could only be adsorbed by Pd in the bimetallic system. Adsorbed FA (or HCOO-) was decomposed to [H] and carbon dioxide (CO2)(or bicarbonate (HCO3-)) (eqs 2 and 3). The [H] served as the direct reducing agent to dechlorinate 4-CP (eqs 4 and 5, M stands for the catalytic area). Some surfeit [H] can also form [H]. Pd

HCOOH 98 2H + CO2

(2)

Pd

HCOO- + H2O 98 HCO3- + 2H

(3)

2H + M f H · M · H

(4)

4-CP + H · M · H f P + Cl- + H+ + M

(5)

In the present study, it was also found that nonpalladized foam Ni could directly use H to dechlorinate 4-CP and 7.8% of 4-CP was converted to P within 1 h with 3 g L-1 Ni and a H2 flow rate of 10 mL min-1. Therefore, the uncovered Ni substrate can use H or H2 to dechlorinate 4-CP, which helps to enhance the 4-CP dechlorination rate. This hypothesis was proven by the following experiment. After initiation of the dechlorination reaction of 4-CP at the optimal conditions (3 g L-1 Pd/Ni, 1.0% Pd loading, pH 4.0, FA/4-CP 51.4:1, and room temperature), introduction of H2 did not accelerate the reaction rate at any flow rate. The Ni substrate would have been saturated by [H], diffused from Pd particles, or dissociated from adsorbed H2; otherwise, supplemental H2 would accelerate the reaction. Collectively, the reaction pathway can be summarized as follows: (1) HCOOH (or HCOO-) decomposes on Pd particles with generation of [H]; (2) [H] reacts with the adsorbed 4-CP on Pd particles; (3) [H] diffuses to the Ni substrate or yields H2; (4) H2 is adsorbed and dissociated to [H] on the Ni substrate; (5) [H] on the Ni substrate dechlorinates the adsorbed 4-CP. The produced P and Cl- meanwhile desorb to the solution. Figure 6 presents the reaction sites and pathway. Conclusions The Pd/Ni catalyst showed a good performance in the catalytic HDC of 4-CP in an aqueous solution using HCOOH as the reductant. 4-CP was rapidly transformed to P by means of hydrogenolysis. The [H] generated upon HCOOH (or HCOO-) decomposition was used by both Pd particles and the foam Ni substrate to degrade 4-CP. The 4-CP conversion rate was highly dependent on the Pd loading amount, HCOOH/4-

Acknowledgment The authors thank the National Natural Science Foundation of China (Grants 20707011 and 50625823), the National HighTech Research and Development Program of China (863 Program; Grant 2009AA063902), and the Science and Technology Project of Beijing for the Distinguished Doctor Degree Dissertation (YB20081000304) for the financial support. Literature Cited (1) U.S. Environmental Protection Agency. National Pollutant Discharge Elimination System, Code of Federal Regulations, 40, Part 122; U.S. Government Printing Office: Washington, DC, 1988. (2) Briois, C.; Visez, N.; Baillet, C.; Sawerysyn, J. P. Experimental Study on the Thermal Oxidation of 2-Chlorophenol in Air over the Temperature Range 450-900 °C. Chemosphere 2006, 62, 1806. (3) Nicolas, V.; Jean-Pierre, S. Thermal Degradation of 2-Chlorophenol Promoted by CuCl2 or CuCl: Formation and Destruction of PCDD/Fs. Chemosphere 2007, 67, S144. (4) Abe, K.; Tanaka, K. Fe3+ and UV-Enhanced Ozonation of Chlorophenolic Compounds in Aqueous Medium. Chemosphere 1997, 35, 2837. (5) Androulaki, E.; Hiskia, A.; Dimotikali, D.; Minero, C.; Calza, P.; Pelizzetti, E.; Papaconstantinou, E. Light Induced Elimination of Monoand Polychlorinated Phenols from Aqueous Solutions by PW12O403-. The Case of 2,4,6-Trichlorophenol. EnViron. Sci. Technol. 2000, 34, 2024. (6) Wang, H.; Wang, J. L. Electrochemical Degradation of 4-Chlorophenol Using a Novel Pd/C Gas-Diffusion Electrode. Appl. Catal., B 2007, 77, 58. (7) Wang, H.; Wang, J. L. Electrochemical Degradation of 2,4Dichlorophenol on a Palladium Modified Gas-Diffusion Electrode. Electrochim. Acta 2008, 53, 6402. (8) Lai, T. L.; Lee, C. C.; Huang, G. L.; Shu, Y. Y.; Wang, C. B. Microwave-Enhanced Catalytic Degradation of 4-Chlorophenol over Nickel Oxides. Appl. Catal., B 2008, 78, 151. (9) Lim, M.; Son, Y.; Yang, J.; Khim, J. Addition of Chlorinated Compounds in the Sonochemical Degradation of 2-Chlorophenol. Jpn. J. Appl. Phys. 2008, 47, 4123. (10) Nomura, Y.; Nakai, S.; Hosomi, M. Elucidation of Degradation Mechanism of Dioxins during Mechanochemical Treatment. EnViron. Sci. Technol. 2005, 39, 3799. (11) Yan, J. H.; Peng, Z.; Lu, S. Y.; Li, X. D.; Ni, M. J.; Cen, K. F.; Dai., H. F. Degradation of PCDD/Fs by Mechanochemical Treatment of Fly Ash from Medical Waste Incineration. J. Hazard. Mater. 2007, 147, 652. (12) Aramendia, M. A.; Borau, V.; Garcia, I. M.; Jimenez, C.; Lafont, F.; Marinas, A.; Marinas, J. M.; Urbano, F. J. Influence of the Reaction Conditions and Catalytic Properties on the Liquid-Phase Hydrodechlorination of Chlorobenzene over Palladium-Supported Catalysts: Activity and Deactivation. J. Catal. 1999, 187, 392. (13) Janiak, T. Kinetics of o-Chlorotoluene Hydrogenolysis in the Presence of 3%, 5% and 10% Pd/C Catalysts. Appl. Catal., A 2008, 335, 7. (14) Yuan, G.; Keane, M. A. Liquid Phase Hydrodechlorination of Chlorophenols over Pd/C and Pd/Al2O3: A Consideration of HC1/Catalyst Interactions and Solution pH Effects. Appl. Catal., B 2004, 52, 301. (15) Calvo, L.; Gilarranz, M. A.; Casas, J. A.; Mohedano, A. F.; Rodriguez, J. J. Hydrodechlorination of 4-Chlorophenol in Aqueous Phase Using Pd/AC Catalysts Prepared with Modified Active Carbon Supports. Appl. Catal., B 2006, 67, 68. (16) Karpinski, Z.; Early, K.; d’Itri, J. L. Catalytic Hydrodechlorination of 1,1-Dichlorotetrafluoroethane by Pd/Al2O3. J. Catal. 1996, 164, 378. (17) Juszczyk, W.; Malinowski, A.; Karpinski, Z. Hydrodechlorination of CCl2F2 (CFC-12) over Gamma-Alumina Supported Palladium Catalysts. Appl. Catal., A 1998, 166, 311.

Ind. Eng. Chem. Res., Vol. 49, No. 10, 2010 (18) Grittini, C.; Malcomson, M.; Farnando, Q.; Korte, N. Rapid Dechlorination of Polychlorinated Biphenyls on the Surface of Pd/Fe Bimetallic System. EnViron. Sci. Technol. 1995, 29, 2898. (19) Rodriguez, J. G.; Lafuente, A. Effective Elimination of PCBs Catalyzed by the Palladium/Hydrazine System as an Ecological Sustainable Process. Ind. Eng. Chem. Res. 2008, 47, 7993. (20) Ukisu, Y.; Miyadera, T. Dechlorination of Dioxins with Supported Palladium Catalysts in 2-Propanol Solution. Appl. Catal., A 2004, 271, 165. (21) Zhang, F.; Chen, J.; Zhang, H.; Ni, Y.; Zhang, Q.; Liang, X. Dechlorination of Dioxins with Pd/C in Ethanol-Water Solution under Mild Conditions. Sep. Purif. Technol. 2008, 59, 164. (22) Liu, Y.; Yang, F.; Yue, P.; Chen, G. Catalytic Dechlorination of Chlorophenols in Water by Palladium/Iron. Water Res. 2001, 35, 1887. (23) Jovanovic, G. N.; Znidarsic-Plazl, P.; Sakrittichai, P.; Al-Khaldi, K. Dechlorination of p-Chlorophenol in a Microreactor with Bimetallic Pd/ Fe Catalyst. Ind. Eng. Chem. Res. 2005, 44, 5099. (24) Zhu, B. W.; Lim, T. T. Catalytic Reduction of Chlorobenzenes with Pd/Fe Nanoparticles: Reactive Sites, Catalyst Stability, Particle Aging, and Regeneration. EnViron. Sci. Technol. 2007, 41, 7523. (25) Ghauch, A.; Tuqan, A. Reductive Destruction and Decontamination of Aqueous Solutions of Chlorinated Antimicrobial Agent Using Bimetallic Systems. J. Hazard. Mater. 2009, 164, 665. (26) Tee, Y. H.; Bachas, L.; Bhattacharyya, D. Degradation of Trichloroethylene and Dichlorobiphenyls by Iron-Based Bimetallic Nanoparticles. J. Phys. Chem. C 2009, 113, 9454. (27) Mallouk, T. E.; Schrick, B.; Blough, J. L. Hydrodechlorination of Trichloroethylene to Hydrocarbons Using Bimetallic Nickel-Iron Nanoparticles. Chem. Mater. 2002, 14, 5140. (28) Zhang, W.; Quan, X.; Wang, J. Rapid and Complete Dechlorination of PCP in Aqueous Solution Using Ni/Fe Nanoparticles under Assistance of Ultrasound. Chemosphere 2006, 65, 58. (29) Xu, Y.; Zhang, W. Subcolloidal Fe/Ag Particles for Reductive Dehalogenation of Chlorinated Benzenes. Ind. Eng. Chem. Res. 2000, 39, 2238. (30) Nutt, M. O.; Heck, K. N.; Alvarez, P.; Wong, M. S. Improved Pdon-Au Bimetallic Nanoparticle Catalysts for Aqueous-Phase Trichloroethene Hydrodechlorination. Appl. Catal., B 2006, 69, 115.

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(31) Yang, B.; Yu, G.; Huang, J. Electrocatalytic Hydrodechlorination of 2,4,5-Trichlorobiphenyl on a Palladium-Modified Nickel Foam Cathode. EnViron. Sci. Technol. 2007, 41, 7503. (32) Yang, B.; Yu, G.; Shuai, D. Electrocatalytic Hydrodechlorination of 4-Chlorobiphenyl in Aqueous Solution Using Palladized Nickel Foam Cathode. Chemosphere 2007, 67, 1361. (33) Yang, B.; Wang, S.; Yu, G.; Zhou, Y. Electrocatalytic Reduction of 2-Chlorobiphenyl in Contaminated Water Using Palladium-Modified Electrode. Sep. Purif. Technol. 2008, 63, 353. (34) Kopinke, F. D.; Machenzie, K.; Koehler, R.; Georgi, A. Alternative Sources of Hydrogen for Hydrodechlorination of Chlorinated Organic Compounds in Water on Pd Catalysts. Appl. Catal., A 2004, 271, 119. (35) Calvo, L.; Gilarranz, M. A.; Casas, J. A.; Mohedano, A. F.; Rodriguez, J. J. Hydrodechlorination of 4-Chlorophenol in Water with Formic Acid Using a Pd/Activated Carbon Catalyst. J. Hazard. Mater. 2008, 161, 842. (36) Roy, H. M.; Wai, C. M.; Yuan, T.; Kim, J. K.; Marshall, W. D. Catalytic Hydrodechlorination of Chlorophenols in Aqueous Solution under Mild Conditions. Appl. Catal., A 2004, 271, 137. (37) Vincent, T.; Spinelli, S.; Guibal, E. Chitosan-Supported Palladium Catalyst. II. Chlorophenol Dehalogenation. Ind. Eng. Chem. Res. 2003, 42, 5968. (38) Li, Q.; Mahendra, S.; Lyon, D. Y.; Brunet, L.; Liga, M. V.; Li, D.; Alvarez, P. J. J. Review: Antimicrobial Nanomaterials for Water Disinfection and Microbial Control: Potential Applications and Implications. Water Res. 2008, 42, 4591. (39) Prusse, U.; Vorlop, K. D. Supported Bimetallic Palladium Catalysts for Water-Phase Nitrate Reduction. J. Mol. Catal. A: Chem. 2001, 173, 313.

ReceiVed for reView March 31, 2009 ReVised manuscript receiVed November 16, 2009 Accepted March 8, 2010 IE9005194