Sustainable Generation of a Homogeneous Ni(I) Catalyst in the

Research Article pubs.acs.org/journal/ascecg

Sustainable Generation of a Homogeneous Ni(I) Catalyst in the Cathodic Compartment of a Divided Flow Electrolytic Cell for the Degradation of Gaseous Carbon Tetrachloride by Electroscrubbing G. Muthuraman and I. S. Moon* Department of Chemical Engineering, Sunchon National University, 315 Maegok Dong, Suncheon 540-742, Chonnam, South Korea S Supporting Information *

ABSTRACT: A mediated electrochemical reduction reaction using a divided electrolytic flow cell with a scrubber column in a closed loop process was successfully devised for the practical electrolytic degradation of gaseous chloro-organics. The authors describe the generation of a low valent homogeneous Ni(I) catalyst and its application for the degradation of gaseous carbon tetrachloride (CCl4) at room temperature. The electrochemical generation of Ni(I) was identified using oxidation reduction potential (ORP) changes during electrolysis and its formation at KOH concentrations of >5 M demonstrated Ni(I) stabilization at higher KOH concentrations. Of the three different cathode materials (Ag, Cu, Ti) employed, Cu produced higher yield of Ni(I) (0.0042 M at 30 mA cm−2). An online FTIR analyzer showed almost 99% of gaseous CCl4 fed continuously at 50 ppm was removed by the electrochemically generated Ni(I) catalyst. A reaction pathway is proposed based on the results of GC/MS analysis of reaction products formed in solution; this analysis also confirmed the complete removal of chlorine from gaseous CCl4. Three consecutive experimental runs showed that Ni(I) generation and CCl4 removal rates were reproducible, which suggests the developed mediated electrochemical reduction (MER) process is sustainable and offers a promising means for treating chloro-organics in the gas phase. KEYWORDS: Divided electrolytic cell, Electroscrubber, Ni(I) homogeneous mediator, Gaseous CCl4 reduction, Air pollutants, MER

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favorable for CVOC degradation,15−18 and to enhance this process, researchers have utilized a packed bed multiphase iron oxide column,19 a concentric 3D copper column,20 and a granular graphite reactor.21 Furthermore, the DER process has been carried out in several aprotic media, such as, acetonitrile (AN) and dimethylformamide (DMF) and in ethanol/water mixtures using different Zn, Ag, and carbon cathodes to synthesize useful compounds from CCl4.9,10,22 On the other hand, it has been proposed that secondary products generated by reduction directly on an electrode’s surface by hydrogen adsorption23 or water splitting13 could be utilized to degrade target organic pollutants, considered as indirect reduction processes, as shown below:

INTRODUCTION Industrialization involves the use of many “chlorinated volatile organic compounds” (CVOCs) as solvents, which harm both man and the environment.1−4 The US Environment Protection Agency has included dichloromethane (DCM), trichloroethane (TCA), trichloroethylene (TCE), perchloroethylene (PCE), and CCl4 on a list of 17 dangerous chemicals that should have permissible industrial emission levels reduced.5 In addition, to upgrade existing degradation techniques, the electrochemical degradation of CVOCs has received considerable attention because it uses environmentally clean electrons.6 CVOC release into the environment occurs via gaseous release to atmospheric air or as liquid release to the ground or water. The majority of electrochemical degradation studies on CVOCs have targeted liquid CVOC removal due to groundwater contamination.7−10 Two electrocatalytic processes have been devised for this purpose; that is, direct electrocatalytic oxidation (DEO) using an undivided electrolytic cell and boron doped diamond (BDD) and PbO2 electrodes, which achieved complete mineralization of CVOCs,11,12 and direct electrocatalytic reduction (DER) using a similar undivided electrolytic cell with Ni or Ag cathodes, which achieved good degradation efficiencies for CVOCs present in surface and groundwater aquifers.13,14 Several studies have shown cathodic DER is more © 2016 American Chemical Society

H 2O → H + OH• − e−

(1)

H• + H• → H 2

(2)

2H• + RCl → RH + H+ + Cl−

(3)

Scialdone et al. adopted both DEO and DER processes in a single divided electrolytic cell for cathodic reduction of 1,2Received: October 27, 2015 Revised: December 24, 2015 Published: January 21, 2016 1364

DOI: 10.1021/acssuschemeng.5b01383 ACS Sustainable Chem. Eng. 2016, 4, 1364−1372

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ACS Sustainable Chemistry & Engineering

electrolytic cell to generate a low valency Ni(I) complex ion. The electrolytic reduction of [Ni(II)(CN)4]2− (Ni(II)) was conducted at different KOH concentrations and reduction yields were calculated. Changes ORP values during electrolysis were viewed as evidence of Ni(I) complex formation. Preliminary cyclic voltammetric (CV) investigations of Ni(II) in solutions containing different concentrations of KOH were also carried out to investigate the redox behavior of Ni(II). Applied current densities were varied to optimize the generation of Ni(I) complex. A gaseous CCl4 (as model gas) was fed into the electroscrubber, containing cathodically generated Ni(I) continuously at a controlled rate and system parameters were optimized. CCl4 removal efficiencies were monitored using an online FTIR gas analyzer. In addition, liquid phase samples were extracted with benzene and analyzed by GC/MS to identify intermediates formed and to elucidate the reduction mechanism.

dichloroethane using an Ag cathode and the simultaneous anodic oxidation of 1,1,2,2-tetrachloroethane using a BDD anode.24 A similar divided electrolytic cell approach was developed for PCE degradation using PbO2 for both electrodes.12 In this previous study, it was shown undivided electrolytic cells are more efficient at degrading PCE in ground wastewater. However, to date, no indirect reduction method based on the use of homogeneous metal ion catalysts or metal complexes has been devised for the aqueous phase removal of CVOCs, presumably largely because of practical difficulties associated with mediator separation from waste streams. On the other hand, no such mediator contamination problem exists for closed-loop gaseous pollutant removal processes, because the mediator electrolyte is well contained in a reactor. Based on this concept, we previously removed air pollutants using a mediated electrochemical oxidation (MEO) process, and have been working in this field for more than a decade to remove gaseous pollutants, such as, odorous gases, benzene and flue gases (SOx and NOx), using electrochemically generated free metal ions, such as, Ce(III), Ag(II), and Co(III).25−28 Our studies have shown that no metal ions or acids or bases used as electrolytes are released from electroscrubbing systems, which convinces us of the suitability of the proposed MER process for the removal of air pollutants.29 To progress these studies, we devised a MER process in aqueous media suitable for decontaminating gaseous pollutants. No previous report has been published on the degradation of gaseous CVOCs stream using an indirect or homogeneous catalyst mediated reduction process based on the use of metal ion complex in the cathodic compartment of a divided electrolytic cell. The role of the metal complex in this process (rather than metal ions) is to stabilize the low valent active states, such as, Co(I) and Ni(I), during electrolytic cathodic reduction.30,31 Although, many metal complexes are used as homogeneous catalysts for water reduction,32−36 their low solubilities in aqueous medium, costs, and complexities (related to electrochemical stability) restrict the use of such complexes to fundamental studies aimed at improving understanding. Cyano metal complexes have high solubilities and stabilities in both acidic and basic solutions.37 In fact, the “electro-winning” of several precious metals is still conducted using cyanide complexation based processes.37−39 Furthermore, some organic conversions have been carried out using these cyano complexes. For example, chemically (NaBH4) reduced [Ni(II)(CN)4]2− complex was used for the hydrogenations of dienes and monoenes at the batch level.40 Hanaya et al. reported aromatic nitro compounds were reduced by chemically prereduced [Ni(II)(CN)4]2− complex.41 Furthermore, the fundamental redox electrochemistry of [Ni(II)(CN)4]2− complex on a hanging mercury drop electrode (HMDE) was comprehensively analyzed by Galus et al. These authors found low valent [Ni(I)(CN)4]3− exists in alkaline medium.42 This finding means that [Ni(II)(CN)4]2− complexes can be considered precursors for the generation of Ni(I) complex mediator species. In the present study, we investigated homogeneous [Ni(I)(CN)4]3− (Ni(I)) mediator generation and its use for the degradation of gaseous CCl4 using a plate and frame divided electrolytic cell with the aim of developing a mediated reduction based process for the of atmospheric pollutants. Based on our previous experiences of divided electrolytic cells for MEO process,25−28 we optimized the cathodic half of the

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EXPERIMENTAL SECTION

Chemicals. CCl4 and K3[Fe(III)(CN)6] were purchased from Aldrich and used without further purification. KOH (99.8%), CoSO4, and KMnO4 were obtained from Junsei Chemical Co., Ltd. (Japan). Sulfuric acid (95%) was supplied by Samchun Chemical Co., Ltd. (South Korea). Silver and copper mesh electrodes were purchased from 4scientific, USA. Ti mesh and Pt coated Ti mesh electrodes were purchased from Wesco Electrodes and Systems (South Korea). All solutions were prepared using reverse osmosis purified water (Human Power III plus, South Korea) of resistivity 18 MΩ-cm. Ni(II)(CN)42− Preparation. K2[Ni(II)(CN)4] was synthesized as reported previously.43 Briefly, 53.77 g potassium cyanide (KCN) dissolved in 50 mL water was added to a 60 mL of a cooled solution containing 40 g of nickel(II) nitrate under nitrogen (cyanide: Ni ratio ∼ 4:1) and then an equal volume of chilled alcohol was added. The resulting mixture was slowly cooled until a mass of thin orange platelets appeared. The obtained complex was rapidly filtered, washed with cold alcohol, recrystalysed using alcohol, dried in a vacuum desiccator, and stored in an airtight brown bottle. Ni(I) Electrocatalyst Generation and Degradation Setup. The electrolytic cell employed had a flow-through divided cell configuration, as shown in Figure 1. To optimize Ni(I) formation experiments were conducted in a small electrochemical cell with a catholyte volume of 200 mL containing 10 M KOH and 0.01 to 0.1 M Ni(II) in a 250 mL glass tank and an anolyte volume of 200 mL containing 5 M H2SO4 in another 250 mL glass tank, both connected

Figure 1. Schematic representation of the divided plate and frame electrolytic cell along and other processing equipment. 1365


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split ratio of 6:1 at 100 °C. Samples and standards were injected (injected volume 1 μL) three times. Cyclic Voltammetry Studies. A potentiostat (Princeton Applied Research, versaSTAT3, USA) was used for the cyclic voltammetry (CV) and linear sweep voltammetry (LSV) analyses and was interfaced with a personal computer running VersaStudio software. For these CV and LSV studies a three electrode cell configuration was used with Pt and Ag/AgCl as counter and reference electrodes respectively, and the working electrodes used were electrochemically cleaned (See Ni(I) Electrocatalyst Generation and Degradation Setup), Ag (0.525 cm2), glassy carbon electrode (GCE) (0.785 cm2), Cu (0.132 cm2), and Ti (0.105 cm2).

to a flow through electrolytic divided (by Nafion 324 from DuPont, USA) cell membrane. Anolyte and catholyte were continuously circulated using peristaltic pumps (Masterflex-7524-45, Cole-Parmer Instrument Company, USA) through anode and cathode compartments, respectively, at a rate of ∼70 mL min−1. The electrolysis experiments were conducted using constant current mode by different applied current densities between 10 to 50 mA cm−2 (by a dc power supply from Korea Switching Instruments). An electrode area of 4 cm2 was used for small scale electrolysis experiments. During pollutant removal, a scrubber column (40 cm high and 5.5 cm (i.d.)) packed with 1 cm2 of Teflon tubes was attached to top of the catholyte tank, which is already attached with the flow through electrolytic divided cell, as shown in Figure 1. The cell had cathode and anode areas of 50 cm2 and an electrolyte volume of 500 mL. The scrubbing system was composed of an air supply system, a scrubbing solution (Ni(II)/Ni(I) in KOH solution), a scrubbing reactor column, and an FTIR gas analyzer system (MIDAC Corporation, USA) equipped with a data logger. Anolyte and catholyte solutions were continuously circulated to flow through electrolytic cell at different flow rates (1 to 2 L min−1) using magnetic pumps (Pan World Co., Ltd., Taiwan). Catholyte solution separately pumped into the scrubber column at flow rate of 3 L min−1. CCl4 gas (from RIGAS (1000 ppm), Korea) and air mixtures, obtained by controlled mixing of air and CCl4 gas using mass flow controllers (MFCs; Line Tech., model M11113953-2, M050927-136-1, Korea) were introduced at the bottom of the scrubber at a set gas flow rate. The catholyte scrubbing solution was introduced at the top of the scrubber counter to the gas flow at a constant liquid flow rate (3 L min−1). CCl4 gas to air ratios obtained using MFCs were confirmed prior to experiments. The scrubbing solution was recirculated through the electrochemical cell to regenerate Ni(I). Before starting the CCl4 removal experiment, the electrochemical cell was first operated until Ni(II) to Ni(I) conversion attained a steady state, and then the scrubbing solution was pumped into the scrubber column. An electrochemical cleaning of each electrodes (Ag, Cu, and Ti) was carried out in 0.1 M KNO3 at a constant current of 1 A for 5 min (using as cathode and Pt as anode) to activate and remove impurities adsorbed on their surfaces before each electrolysis. All the experiments are done at room temperature 20 ± 2 °C. Ni(I) Analysis. Ni(I) concentrations were determined by redox titration against standard KMnO4 or Fe(III)(CN)6 (0.001 M) solution using an ORP electrode (EMC 133, 6 mm Pt sensor electrode and Ag/ AgCl reference electrode containing a gel electrolyte, iSTEK, USA) connected to an iSTEK multimeter (pH-240L, USA). The initial reduction potential of Ni(II) was around −170 mV and this then decreased as electrolysis progressed at constant current density to reach approximately −800 mV. Reduction efficiency was defined by the equation:

reduction efficiency (%) =

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RESULTS AND DISCUSSION Optimization of Electrolytic Reduction of Ni(II). It is known that a change in ORP provides first evidence of

Figure 2. Changes in ORP and reduction efficiency with electrolysis time for the reduction of [Ni(II)(CN)4]2− at different electrodes (Ag, Cu, Ti) in 10 M KOH solution. Electrolysis conditions: feed concentration = 0.05 M [Ni(II)(CN)4]2−; current density = 20 mA cm−2; solution flow rate = 70 mL min−1; electrode area = 4 cm2.

[Ni(I)] × 100 [Ni(II)]

Where, Ni(I) is the concentration of the electrolytically formed Ni(I) complex and Ni(II) is the initial concentration of Ni(II) complex precursor. Aqueous reaction samples (2 mL) were withdrawn via syringe from option provided bottom of the catholyte tank (Figure 1) after CCl4 removal by benzene (5 mL) extraction and analyzed by GC/MS to identify intermediates produced using a Shimadzu Q2010 (GC/MS), Japan, equipped with an electron capture detector. The DB-5, and DB5-MS column capillary (30 m length × 250 μm diameter × 0.25 μm thickness) was used for all chromatographic separations (J&W Scientific). The MS was used in EI+ mode at an electron energy of 70 eV, and selected ion monitoring was used to monitor m/z 153.82 (the molecular weight of CCl4). The source temperature was 250 °C and the GC transfer line was held at 280 °C. The GC oven temperature was programmed as follows; 4 min at 45 °C, increase to 100 °C at 4 °C min−1, increase to 250 °C at 8 °C min−1, and then held at 250 °C (total run time: 50 min). Helium was used as carrier at a flow rate of 2 mL min−1. Extracts were automatically injected into the GC inlet at a

Figure 3. Changes in ORP and reduction efficiency with electrolysis time for the reduction of [Ni(II)(CN)4]2− at an Ag electrode at different KOH concentrations (1, 3, 5, and 10 M). Electrolysis conditions were the same as those detailed in the legend of Figure 2.

oxidation/reduction of a compound of interest during electrolysis.44 Initially, we studied the reduction of Ni(II) in 10 M KOH using different cathode materials and a flow1366


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Figure 4. CV responses of 0.05 M [Ni(II)(CN)4]2− in 10 M KOH at different electrodes. The scan rate is 5 mV s−1.

concentration of 5 M and above, ORP changed from an initial −170 to −800 mV and the yield of Ni(I) increased from 0.002 to 0.004 M, but at a concentration of 5 M.47

Figure 6. (A) Removal efficiency of gaseous CCl4 with time for different electroscrubbing processes: (a) MER using [Ni(I)(CN)4]3− in 9 M KOH; (b) DER using 9 M KOH; (c) absorption using [Ni(II)(CN)4]2− in 9 M KOH. (B) Effect of gas flow rate on the removal efficiency of CCl4 with time during electroscrubbing using electrolyzed [Ni(I)(CN)4]3− in 9 M KOH solution: (a) 0.2; (b) 0.4; (c) 0.8 L min−1. Conditions: gas flow rate = 0.2 L min−1; liquid flow rate = 3 L min−1. Electrolysis conditions were the same as those detailed in the legend of Figure 2 with a large Cu electrode (50 cm2 area) and an electrolyte flow rate of 2 L min−1.

[Ni(II)(CN)4 ]2 − −KOH + e− → [Ni(I)(CN)4 ]3 − −KOH (4)

We also investigated the influence of current density on Ni(I) yield under 10−50 mA cm−2 curent densities (Figure 5). It was observed Ni(I) concentration increased on increasing current density from 10 to 20 mA cm−2 and that above 20 mA cm−2 the Ni(I) concentration decreased. This may have been due to Ni(0) formation and the subsequent formation of [Ni2(CN)3]3− by water reduction.42 Thus, the reduction of Ni(II) was found to be optimum at 20 mA cm−2. Electrolytic Degradation of CCl4 in the Presence of Ni(I). Electrolytically formed Ni(I) in the cathodic compartment under optimized conditions of current density was used to degrade CCl4 in a continuous process. When the concentration of Ni(I) reached 0.0042 M, we started injecting 50 ppm of CCl4 at a gas flow rate of 0.2 L min−1 through the bottom of the scrubber at a liquid flow rate of 3 L min−1 with closed loop catholyte circulation. As shown in Figure 6A, a quick hike in the removal efficiency of CCl4 to 99.76% was observed and continues this trend up to 1 h of operation (Figure 6a). In order to confirm that the process follows MER, DER of CCl4 was checked through the electrolyzed solution of 9 M KOH (without mediator Ni(I)); the results obtained are

Ni(II) reduction. In the case of the Ti electrode, an irreversible peak at −0.8 V appeared in forward scan at KOH concentration of 1 and 5 M (Figure SI 1 and 2). All peak intensities were increased in 10 M KOH (Figure 4). Contrary to lower concentrations of KOH (1 and 5 M), the GCE electrode showed an irreversible cathodic reduction peak at −1.32 V indicates Ni(II) reduction is possible only at higher KOH concentrations (>5 M). Cu and Ti electrodes show similar redox behavior as shown in low concentrations means Ni(II) reduction occurred at all concentrations of KOH. But, an ill-defined reduction peak (−1.15 V) in near of water splitting region was observed during forward scanning and an anodic peak (−0.5 V) during reverse scanning for the Ag electrode. The anodic peak in reverse scan looks like stripping phenomena, which means the reduced Ni(II) in the forward scan, as Ni(0), stripped at this potential (−0.5 V) from the electrode. Though peak potential differences were large, that is, 615 mV for Ag and 200 mV for Cu, the Ni(II) redox process 1368


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Figure 8. (A) GC peak separation of CCl4 extracted in benzene from the electrolysis solution at 60 min. (B) MS spectra of the m/z values of 84, 74, 46, and 40 by-products. Electrolysis conditions were the same as those detailed in the legend of Figure 6A.

of the reactants at higher gas flow rates. Thus, a 0.2 L min−1 gas flow rate favored to remove up to 50 ppm of CCl4. If Ni(I) is able to be generated continuously, the pollutant removal process becomes sustainable for longer durations and here in Figure 7, we show that the present process is sustainable, where Ni(I) was able to regenerate three consecutive experiments after each batch of CCl4 removal. After the first batch CCl4 removal, the Ni(I) concentration has reached to value 0.0032 M in 1 h electrolysis and again the second batch of CCl4 feed was started for its removal and regenerated Ni(I) after CCl4 removal. Similarly, third batch removal experiments also carried out and the initial Ni(I) regenerated successfully indicating that the MER is quite promisingly sustainable process. In other words, 0.00332 g of CCl4 sustainably removed in 1 h (at 0.2 L min−1 gas flow rate with 50 ppm feed) and 0.07991 g of CCl4

shown in Figure 6b. We found a sharp increase in removal efficiency (99%) at initial timings but started coming out in 15 min and all the 50 ppm of CCl4 feed came out at the outlet without undergoing reduction. Similarly, only absorption using scrubbing solution of Ni(II) and 9 M KOH without any electrolysis also followed almost similar trend (Figure 6c), i.e., all the 50 ppm of CCl4 has come out without degradation within 1 h. The allowable limit of CCl4 for occupational health release to atmosphere is only 5 ppm,48 we have checked the presently developed process limitation in CCl4 degradation. The results found (Figure SI 4) no CCl4 has come out in all the studied concentrations (15, 30, and 50 ppm), which tells CCl4 removed almost 100%. In addition, increasing the gas flow rate from 0.2 to 0.8 L min−1 decreases the removal efficiency found from 99% to 68% (Figure 6B) due to having less contact time 1369


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Then two carbenes react with an additional carbon to form 1,2propadiene (II) and that ethanol (III), diethyl ether (IV), and cyclopentane (V) are subsequently produced by chemical and electrochemical processes.

Scheme 1. Proposed Reaction Pathway for the MER of CCl4

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CONCLUSIONS The present results demonstrated for first time the feasibility of using the cathodic compartment of a two compartment electrolytic cell to generate a metal-complex mediator ion in highly alkaline medium and its application for the degradation of gaseous CCl4. It was found that long-lived Ni(I) complex could be generated only at KOH concentrations >5 M, thus confirming that highly alkaline medium stabilizes the Ni(I) state. The highly quasi-reversible redox transfer of Ni(II) shown by the Cu cathode, but not by the Ti, GCE, and Ag electrodes suggests that the reduction of Ni(II) in KOH medium is dependent on the nature of the electrode material. The removal of continuously fed CCl4 by electroscrubbing process was reflected by a sudden decrease in outlet CCl4 concentration and a concomitant decrease in Ni(I) concentration. LSV results further confirmed that electrochemically generated Ni(I) can reduce CCl4 in alkaline medium. Three consecutive batch regeneration of Ni(I) concentration after each batch CCl4 removal confirming the possibility of running the MER process sustainably. Online FTIR results revealed that 99.76% of CCl4 was degraded at feed concentrations up to 50 ppm, and the pseudo-first-order rate constant of organic dehalogenation was found to be 3.397 × 10−1 min−1. Furthermore, GC/MS results revealed the absence of any chlorine containing organic intermediate, and the identification of 1,2-propadiene, ethanol, diethyl ether, and cyclopentane intermediate reaction products encouraged us to propose a possible mechanistic pathway.

can be removed in 1 day, if same rate maintained. Further, to show that Ni(I) actually acts as a mediator species for CCl4 reduction LSV measurements were carried out (Figure SI 5), where a noticeable increase in cathodic reduction peak current for CCl4 was seen in the presence of Ni(II), which confirms the removal process follow MER,44 here electrogenerated Ni(I), as shown below (eq 5).

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[Ni(I)(CN)4 ] −KOH + CCl4 → [Ni(II)(CN)4 ]2 − −KOH + product

ASSOCIATED CONTENT

S Supporting Information *

3−

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.5b01383. CV of Ni(II) reduction at different electrodes and concentration of KOH, Tafel plot for different electrodes, CV analysis for mediated reduction of CCl4, and removal efficiency effect of different gaseous CCl4 concentrations by electroscrubbing (PDF)

(5)

On the basis of the outlet CCl4 concentrations, a pseudo first order rate constant (k) of 3.397 × 10−1 min−1 was calculated, which is faster than the solution phase direct electrochemical reduction.13 During CCl4 electrodegradation in the cathodic compartment, the aqueous liquid phase reaction mixture was collected at 60 min, extracted using benzene, and analyzed by GC/MS to identify the intermediates formed (Figure 8). Four small peaks were observed at retention times of 2.150, 1.633, 1.533, and 1.390 (Figure 8A). Mass spectral analysis indicated these corresponded to cyclopentane, diethyl ether, ethanol, and 1,2-propadiene, respectively (Figure 8B). Interestingly, none of the intermediates identified contained chlorine, demonstrating the effectiveness of Ni(I) on CCl4 removal. Most of the solution phase CCl4 removal by DER process found CHCl3 in first step and CH2Cl2 formed in second step and finally CH4 is formed,9,10 but in the present study no such intermediates were found. In addition, we found unusual nonchloro compounds at very low concentrations and based on GC/MS identified intermediates we proposed the reaction pathway shown in Scheme 1. We suggest initially carbene (I) (:CH2) is formed at initial stage from CH2Cl2, which is formed already by leaving Cl2 gas from CCl4, by leaving Cl2 gas. Note worthy hear that the carbene formation has been observed in aqueous micellar solution during electrochemical removal of allyl chloride.49

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AUTHOR INFORMATION

Corresponding Author

*Tel: +82 61 750 3581. Fax: +82 61 750 3581. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the “National Research Foundation” (NRF) funded by the Ministry of Education, Science and Technology (MEST), Government of the Republic of Korea (Grant No. 2014R1A2A1A01001974). The authors thank Prof. S. Balaji, visiting professor under the brain pool program (South Korea) from SCSVMV University, India, for his suggestions during manuscript preparation. 1370


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Sustainable Generation of a Homogeneous Ni(I) Catalyst in the

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