Electrocatalytic Oxidation of Methanol - American Chemical Society

Chapter 10 Electrocatalytic Oxidation of Methanol

Downloaded by STANFORD UNIV GREEN LIBR on August 6, 2012 | http://pubs.acs.org Publication Date: January 12, 2006 | doi: 10.1021/bk-2006-0921.ch010

Corey R. Anthony and Lisa McElwee-White Department of Chemistry and Center for Catalysis, University of Florida, Gainesville, F L 32611-7200

The electrochemical oxidation of methanol to dimethoxymethane ( D M M ) and methyl formate (MF) is catalyzed by several RuPt, RuPd and RuSn heterobimetallic complexes. The product ratios and current efficiencies depend on the catalyst, solvent, potential and presence of water. Complete selectivity for D M M and high current efficiency can be obtained by electrolysis of CpRu(TPPMS) (SnCl ) in methanol. 2

3

Introduction Fuel cells have been postulated as the power generation system of the immediate future, possibly replacing not only fossil fuel based engines (1,2) but also advanced alkali batteries (2,3). Due to their simplicity, high energy efficiency and low pollution, direct methanol fuel cells (DMFCs) are especially suited for portable electronic devices (2,3). The electrooxidation of methanol to C 0 is a mechanistically complex reaction (Scheme 1) with stable intermediates causing a large overpotential. Through the use of catalysts the overpotential associated with the overall process can be lowered. Although there has been moderate success with platinum anodes for D M F C , the presence of a second metal can decrease the overpotential and increase the lifetime of the anode. The beneficial effects of an additional metal have been 2

130

© 2006 American Chemical Society

In Feedstocks for the Future; Bozell, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2006.

131 - 2e", - 2 H

- 2e% - 2 H

+

CH OH

H CO

3

2

H 0

+

^

- 2e, - 2 H

+

HCOOH

co

2

2

+ CH3OH

+ 2 CH3OH

H C(OCH ) + H 0 Downloaded by STANFORD UNIV GREEN LIBR on August 6, 2012 | http://pubs.acs.org Publication Date: January 12, 2006 | doi: 10.1021/bk-2006-0921.ch010

2

3

2

2

HCOOCH3 + H 0 2

Scheme 1. Electrooxidation of methanol

observed with several combinations, including PtSn (4), PtRe (5), PtNi (6), PtRu (7-111 PtRuOs (72), PtRuMoW (73), and PtRuOsIr (14,15). The role of the non-Pt metal in these anodes has been a topic of interest. Although electronic effects have been invoked (6,16,17), the major effect of an additional metal has generally been ascribed to a bifunctional oxidation mechanism (18,19). For the PtRu anodes (the most effective combination), the postulate is that Pt sites engage in methanol binding and dehydrogenation, while the Ru serves as a source of "active oxygen" for the formation of C 0 (20). Our work on the electrooxidation of alcohols with homogeneous heterobimetallic catalysts was initially motivated by the advances in D M F C anodes (8,21-23). The strategy initially employed for this project was to utilize the bifunctional oxidation mechanism observed in D M F C anodes to design discrete bimetallic complexes as catalysts for the electrooxidation of renewable fuels. These complexes can be viewed as utilizing all of the metal as opposed to bulk metal anodes, where the reaction occurs only at active surface sites. Although bimetallic complexes are not accurate models of the proposed surface binding site on bulk metal anodes, our investigations address the question of whether it is possible to reproduce the essential functions of the proposed electrooxidation mechanism in discrete heterobinuclear complexes (24-26). 2

Experimental Section Electrochemistry. Electrochemistry was performed at ambient temperature in a glove box under N using an E G & G P A R model 263A potentiostat/galvanostat. Cyclic voltammetry (CV) was performed with a threeelectrode configuration consisting of a glassy carbon working electrode (3 mm 2


132 +

diameter), a Pt flag counter electrode and a A g / A g reference electrode. For experiments in 1,2-dichloroethane (DCE) or methanol, the reference electrode consisted of an acetonitrile or methanol solution respectively of freshly prepared 0.01 M A g N 0 and 0.1 M tetrabutylamonium triflate (TBAT) along with a silver wire. The A g solution and wire were contained in a 75 mm glass tube fitted at the bottom with a Vycor tip. Constant potential electrolysis utilized similar equipment except the working electrode was a vitreous carbon electrode. A l l potentials are reported vs. N H E and are not corrected for the junction potential of the A g / A g reference electrode. The E° values for the ferrocenium/ferròcene couple in 0.7 M T B A T / D C E and 0.1 M T B A T / M e O H were +0.50 V and +0.795 V . Electrolysis products were analyzed by gas chromatography on a Shimadzu GC-17A chromatograph containing a 15 m χ 0.32 mm column of A T - W A X (Alltech, 0.5 μπι film) on fused silica. The column was attached to the injection port with a neutral 5 m χ 0.32 mm A T - W A X deactivated guard column. The electrolysis products were quantitatively determined with the use of η-heptane as an internal standard. Products were identified by comparison to authentic samples. Ligands: triphenylphosphine (PPh ), bis(diphenylphosphino)-methane (dppm), (/w-sulfonatophenyl)diphenylphosphine (TPPMS) and 1,5cyclooctadiene (COD). 3

+


+

3

Synthesis and Electrochemistry of Heterobimetallic Catalysts Heterobimetallic catalysts have been of long-standing interest, due to the possibility of exploiting the different reactivities of the two metals in chemical transformations (27-30). It has long been recognized that two metals in close proximity may exhibit new reactivities which are different from their parent mononuclear compounds (31-33). In designing our initial catalysts two structural motifs were utilized in tandem: bridging bidentate phosphines for stability and μ-halides for electronic communication between the metal centers (Figure 1). The synthesis of our first electrocatalyst was accomplished by reacting CpRuiClXPPhsXV-dppm) with Pt(COD)Cl to afford the Ru/Pt complex CpRu(PPh )fa-Cl)^-dppm)PtCI (1) (34). Cyclic voltammetry of complex 1 exhibits three redox couples (35) (Figure 2, Table I which have been assigned to the reversible Ru(II/III), irreversible Pt(II/IV) and Ru(III/IV) oxidation processes, respectively. 2

3

2


133

Cl


«Γ . A l '

4^ A. Ru

Ru Pt Ph P ^ J ^Cl Ph P\.PPh

Ru Pt

ph p' i 3

Ph P^

3

2

2

ρΐι ρ' ^

2

3

Pt. I

I ^ci

Ph P^ ^PPh 2

2

Cl

^

AÏ

Ru Pd. *C1 Ph P" k Ph P\.PPh

Ru Pd *Cl Ph P' i 2 \^PPh

3

3

p h

P

2

2

2

5

I Ph

3 P

.Ru^° ^

.RuX

PPh,

PPh

3

Na0 S

2X = C1

3

7 X = SnCI

S0 Na

3

3

8X=C1 9 X = SnCl

3

Figure 1. Structures of heterobimetallic catalysts and mononuclear model compounds.


>i

PPh

2


134

Potential/Vvs NHE

Figure 2. Cyclic voltammograms of ! under nitrogen in 3.5 ml of DCE/0.7 M TBAT; glassy carbon working electrode; Ag/Ag reference electrode; 50 mV/s, solutions as specified. +

Electrochemical oxidation of complex 1 in the presence of methanol leads to considerable enhancement of the oxidative currents (Figure 2), consistent with an electrocatalytic oxidation process. The onset of this catalytic current coincides with the irreversible Pt(II/IV) oxidative wave at 1.70 V . The bulk electrolysis of 1 and dry methanol were performed at 1.70 V (onset of catalytic current) in 0.7 M T B A T / D C E . Gas chromatographic analysis of the solution indicated that dimethoxymethane ( D M M , formaldehyde dimethyl acetal) and methyl formate (MF) are formed (Scheme 1). This result is consistent with the electrooxidation of dry methanol on PtRu anodes, which yields D M M after acidcatalyzed condensation of the formaldehyde product with excess methanol (36). Bulk electrolysis of methanol in the presence of heterobimetallic complex 1 resulted in higher current efficiencies than those obtained from the mononuclear model compound CpRu(PPh ) Cl (2) (Table II). No oxidation products were found when the electrolysis was performed at 1.70 V in the absence of a Ru complex or in the presence of the Pt model compound (r| -dppm)PtCl2. These results suggest that Pt enhances the catalytic activity of the Ru metal center. 3

2

2


135


Table I. Formal Potentials for Complexes 1-9' Complex

Couple

F h

(V)

(V)

1

Ru(II/III)

1.25

1.21

2

Ru(II/HI)

0.93

0.87

3

Ru(II/III)

1.29

1.25

4

Ru(Il/Ul)

1.10

Couple

Em

(V)

1.54

1.47

Ru(III/IV)

Pt(II/IV)

1.49

1.43

Ru(HI/IV)

1.98

Ru(III/IV)

1.92

Ru(III/IV)

1.98

Ru(II/III)

1.30

Pd(II/IV)

1.49

1.29

Pd(II/IV)

1.55

Ru(II/III)

1.48

1.44

Ru(II/III)

0.79

0.73

r

Ru(II/UI)

1.29

1.90

Pt(H/IV)

Ru(II/III)

C

Ru(III/lV)

1.69

6 7

Epa

(V) 1.91

Pt(II/IV)

5

8

Couple

b

(V)

1.50

"All potentials obtained in 0.7 M TBAT/DCE unless otherwise specified and reported vs. NHE. reported for reversible waves. Potential obtained in 0.1 M TBAT/MeQH and reported vs. NHE.

b

Ey

Based on the electrocatalytic activity of the RuPt complex 1, we decided to prepare additional Ru-containing heterobimetallic complexes (Figure 1). Modifications were made in the identity of the second metal, the ligands on the second metal and the bridging moiety. These changes were designed to provide variation in 1) the oxidation potential of the metal centers; 2) the degree of electronic communication between the metals and 3) the distance between the metal centers. Figure 1 summarizes the additional catalysts that were prepared by reacting CpRu(PPh )(V-Ph P(CH2)PPh2)X [X = CI, or I] with the appropriate Pd or Pt complex (19). Cyclic voltammograms of the heterobimetallic complexes 3-6 generally exhibit three redox waves (Table I) within the solvent window. In the presence of methanol, the Ru/Pd and Ru/Pt complexes all display a current increase at the Pd(II/IV) and Pt(II/IV) waves, indicating a catalytic methanol oxidation process similar to what was observed for complex 1 (Figure 2). Bulk electrolyses of methanol with complexes 3-6 were carried out for product identification and quantification. For comparison purposes, bulk electrolyses of methanol were performed at the same potential (1.70 V vs. N H E ) as compound 1 (25). Therefore, the electrocatalysis with these complexes was performed at potentials positive of both the Ru(II/III) couple and the first oxidative wave of the second metal but before the Ru(III/IV) wave. 3

2


2

136 Table II. Product Ratios and Current Efficiencies for Dry Methanol Oxidation 8


Product ratios (DMM/MF) Charge (C)

Ru/Pt

Ru/Pt

Ru/Pt

Ru/Pd

Ru/Pd

(3)

(4)

(5)

(6)

CpRu(PPh ) Cl + Pd(COD)Cl

CpRu(PPh ) Cl

(1)

25

2.45

2.27

2.23

3.18

1.85

3.85

4.20

50

2.35

1.68

1.66

2.41

1.56

2.95

4.00

75

1.51

1.24

1.40

1.54

1.21

2.58

3.73

100 Current Efficiency

1.23

0.98

1.26

0.94

0.91

1.97

2.87

186

43

39

24.6

42

18

12

3 2

3 2

(2)

2

" Electrolyses were performed at 1.70 V vs. NHE. A catalyst concentration of 10 mM was used. Methanol concentration was 0.35 M. Determined by GC with respect to κ-heptane as an internal standard. Each ratio is reported as an average of 2-5 experiments. Average current efficiencies after 75-100 C of charge passed. h

c

The oxidation products formed during the bulk electrolysis of methanol with complexes 3-6 are D M M and M F , just as were observed for complex 1. Product distribution and current efficiencies for the formation of D M M and M F are shown in Table II. Initially, all the Ru complexes yield higher proportions of D M M . However, as the reaction progresses, this ratio shifts toward the more highly oxidized product, M F . Differences in the catalytic activity of the heterobimetallic and monometallic complexes can also be observed in Table II. A l l the heterobimetallic complexes favor the formation of M F and have higher current efficiencies than the Ru model compound CpRu(PPh ) Cl. The C l bridged complexes 1 and 5 gave lower current efficiencies (24.6 and 18.6% respectively) (24) compared to the I-bridged complexes 3, 4 and 6 (approximately 43%). This significant increase in current efficiency has been attributed to the higher stability of the I-bridges that maintain the close proximity of the metal centers. The stability is also reflected in the Pd(II/IV) and Pt(II/IV) oxidation waves (Table I), which are irreversible in 1 and 5, but reversible in 3 and 6, implying greater stabilities for the oxidized I-bridged species (35). 3

2

In order to probe whether the reaction involves both metal centers in close proximity, a mixture of CpRu(PPh ) Cl and Pd(COD)Cl was used as a model for the Ru/Pd catalysts (Table II). The product distribution and current efficiency for the mixture was similar to that of complex 5 and the Ru model compound CpRu(PPh ) Cl. A higher current efficiency was afforded by complex 6 (stable halide bridge). The differences in product distribution and current efficiency between the mixture and complex 6 indicate that the bimetallic structure is significant to the catalytic activity of the complexes. 3

3

2

2

2


137 The condensation of H C O and H C O O H with C H O H (Scheme 1) produces I mole of water for each mole of D M M and M F formed. The effect of additional water on the electrocatalytic reaction was then probed by introducing 5 μΐ, of water before starting the electrolysis. The C V s of complexes 1, 3 - 6 all display a slight increase in current when water is introduced. The presence of water, as predicted in Scheme 1 favors the formation of M F (Table III). A similar effect was previously described for heterogeneous catalysts (37). The effect of water on the ratio of D M M to M F can also be observed during the electrolysis of dry methanol since as the reaction progresses the amount of water formed increases while the ratio of D M M to M F decreases. Downloaded by STANFORD UNIV GREEN LIBR on August 6, 2012 | http://pubs.acs.org Publication Date: January 12, 2006 | doi: 10.1021/bk-2006-0921.ch010

2

3

Table III. Product Ratios and Current Efficiencies for Wet Methanol Oxidation with Complexes 1,4,5 and 6 a

Product ratios (DMM/MF) Charge 25

Ru/Pt (1) 1.68

Ru/Pt (4) 2.23

Ru/Pd (5) 1.38

Ru/Pt (6) 1.26

50

1.34

1.66

0.98

1.06

75

1.17

1.40

0.84

0.72

100 Current Efficiency (%f

0.67

1.26

0.70

0.58

19.5

39

20.6

41

" Electrolyses were performed at 1.70 V vs. NHE. A catalyst concentration of 10 mM was used. Methanol concentration was 0.35 M . Determined by GC with respect to w-heptane as an internal standard. Each ratio is reported as an average of 2-5 experiments. Average current efficiencies after 75-100 C of charge passed. h

e

Catalysts with a Lewis Acidic Site One possible role of the non-Ru metal center in the RuPt and RuPd catalysts is that of a Lewis acid. A Lewis acidic site could aid the coordination of methanol before oxidation by the Ru metal center. To investigate this possibility we prepared CpRu(PPh ) (SnCl ) (7), which had previously been reported to selectively oxidize methanol to methyl acetate at elevated temperatures (38,39). In the C V of complex 7 a single reversible oxidation wave is observed at 1.44 V . A similar oxidation process has previously been assigned for CpRu(PPh ) Cl (40) (Table 1) as the one electron oxidation of the Ru metal center. Based on this assignment and the fact that S n is not redox active within the solvent window, the oxidation wave observed for complex 7 was assigned to the Ru(II/III) couple. In the presence of methanol, there is a significant increase in the current indicative of an electrocatalytic oxidation process (Figure 3). For 3

3

2

3

2

2+


138 7, the onset of catalytic current coincides with the Ru(II/III) oxidation process. This contrasts significantly with the behavior of the RuPt and RuPd complexes where the onset coincided with the oxidation of the non-Ru metal center (Figure 2). The electrolysis potential was varied to investigate what effect this would have on the reaction. Hence for complexes 2 and 7 the electrooxidation was performed at 1.55 V (onset of catalytic current for complex 7) and at 1.70 V . D M M and M F are the only products formed during the electrolysis of methanol with CpRu(PPh ) Cl and CpRu(PPh ) (SnCl ). This contrasts with the thermal reaction of methanol with CpRu(PPh ) (SnCl ) (38,39) where methyl acetate was the only product observed. Varying the oxidation potential has a significant effect on the product ratio (selectivity) of the methanol electrooxidation reaction (Table IV). Although CpRu(PPh ) (SnCl ) and CpRu(PPh ) Cl form more D M M than M F at lower potentials, this effect is more pronounced for the RuSn complex. 3

2

3

2

3


3

3

2

2

3

3

3

2

Table I V . Bulk Electrolysis Data for Complexes 2 , 7 , 8 and 9 Oxidation Potential (V)

Complex

Current Efficiency (%)

DMM (%)

b

a

MF (%)

CpRu(PPh ) Cl (2)

1.55

5.6

76.8

23.2

CpRu(PPh ) CI (2)

1.70

7.3

75.2

24.8

CpRu(PPh ) (SnCl )(7)

1.55

18.2

95.0

5.0 32.6

3 2

3 2

3 2

3

CpRu(PPh ) (SnCl )(7) 3 2

3

c

CpRu(TPPMS) Cl (8) 2

c

CpRu(TPPMS) Cl (8) 2

c

CpRu(TPPMS) (SnCI ) (9) 2

3

1.70

13.1

67.4

1.25

63.2

100

0

1.40

76.9

98.5

1.5

1.25

89.4

100

0

9.5 CpRu(TPPMS) (SnCI ) (9) 90.5 1.40 90.1 Ail electrolyses performed for five hours in 0.7 M TBAT/DCE with 1.0 mmoles methanol unless otherwise specified. Moles of product formed per mole of charge passed. Electrolyses performed in 0.1 M TBAT/MeOH u

2

3

u

b

c

The effect of methanol concentration was initially probed using complexes 3 and 6 (26). In the presence of 1.41 M methanol, current efficiencies of approximately 74% were obtained for both catalysts. This value was significantly higher than the 43% obtained at a methanol concentration of 0.35 M . This increase in current efficiency was attributed to improved electron



139

Potential / V vs NHE

Figure 3. Cyclic voltammograms of (a) CpRu(PPh ) Cl and (b) CpRu(PPh ) (SnCl ) under N in 3.5 ml ofDCE/0.7 Μ Τ ΒAT; glassy carbon working electrode; Ag/Ag+ reference electrode; 50 mV/s. (Reproducedfrom reference 41. Copyright 2004 Elsevier.) 3 2

3 2

3

2


140 transfer kinetics and to the higher concentration of substrate when methanol is present in greater quantities. To further investigate this effect, the electrolyses of the water soluble complexes CpRu(TPPMS) (Cl) (8) and CpRu(TPPMS) (SnCl ) (9) were performed in 0.1 M T B A T / M e O H (41). Cyclic voltammograms of complexes 8 and 9 both exhibit a single oxidation wave assigned to the Ru(II/III) oxidation process (Table 1). The electrooxidation of neat methanol with complexes 8 and 9 was performed at 1.25 V and at 1.40 V . Higher current efficiencies for the electrooxidation of methanol are obtained with the Ru/TPPMS complexes 8 and 9 than are obtained with complexes 2 and 7 (Table IV). Complex 7 has been shown to form significantly more D M M than M F at lower potentials; this effect is also observed during the electrolysis with complex 9. When the potential was decreased from 1.40 V to 1.25 V the amount of D M M in the product mixture increased from 90.5% to 100%. To our knowledge, no other examples of selective electrooxidation of methanol to D M M have been reported. 2


2

3

Conclusion The electrochemical oxidation of methanol to D M M and M F was performed with the homogeneous catalysts 1-9. The heterobimetallic complexes afforded higher current efficiencies than the corresponding mononuclear model compounds. The presence of water favors formation of the more highly oxidized product, MF. Iodide-bridged complexes 3, 4 and 6 produced significantly higher current efficiencies than 1 and 5 because of their increased stability during the electrolysis. The Ru/Sn complexes 7 and 9 favor the formation of D M M over M F . The current efficiency and selectivity for D M M are affected by the oxidation potential and the electrolysis solvent, with both maximized when the electrolysis is performed at lower potential in neat methanol. Complete selectivity for D M M was achieved when the electrocatalyst was CpRu(TPPMS) (SnCl ). 2

3

References 1. Yoshida, P. G . Fuel cell vehicles race to a new automotive future. Office of Technology Policy, U.S. Dept. of Commerce, 2003. 2. Stone, C.; Morrison, A . E. Solid State Ionics 2002, 152-153, 1-13. 3. Kim, D.; Cho, Ε. Α.; Hong, S.-A.; Oh, I.-H.; Ha, H . Y . J. Power Sources 2004, 130, 172-177.


141 4. 5. 6.


7. 8. 9. 10. 11. 12. 13. 14.

15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30.

Wang, K . ; Gasteiger, H . Α.; Markovic, Ν. M . ; Ross, P. N . Electrochim. Acta 1996, 47, 2587-2593. Cathro, K . J. J. Electrochem. Soc. 1969, 116, 1608-1611. Park, K . W.; Choi, J. H.; Κwοη, Β. K.; Lee, S. Α.; Sung, Y . E.; Ha, H . Y . ; Hong, S. Α.; Kim, H.; Wieckovvski, A . J. Phys. Chem. B 2002, 106, 18691877. Gasteiger, H . Α.; Markovic, N . ; Ross, P. N . ; Cairns, E. J. J. Phys. Chem. 1993, 97, 12020-12029. Wasmus, S.; Kuver, A . J. Electroanal. Chem. 1999, 461, 14-31. Leger, J. M . ; Lamy, C. Ber. Bunsen-Ges. 1990, 94, 1021-1025. Swathirajan, S.; Mikhail, Y . M . J. Electrochem. Soc. 1991, 138, 13211326. Reddington, E.; Sapienza, Α.; Gurau, B.; Visvvanathan, R.; Sarangapani, S.; Smotkin, E. S.; Mallouk, T. E. Science 1998, 280, 1735-1737. Ley, K . L . ; L i u , R. X . ; Pu, C.; Fan, Q. B.; Leyarovska, N . ; Segre, C.; Smotkin, E. S. J. Electrochem. Soc. 1997, 144, 1543-1548. Choi, W. C.; K i m , J. D.; Woo, S. I. Catal. Today 2002, 74, 235-240. Gurau, B.; Visvvanathan, R.; Liu, R. X . ; Lafrenz, T. J.; Ley, K . L . ; Smotkin, E. S.; Reddington, E.; Sapienza, Α.; Chan, B. C.; Mallouk, T. E.; Sarangapani, S. J. Phys. Chem. B 1998, 102, 9997-10003. Lei, H . W.; Suh, S.; Gurau, B.; Workie, B.; Liu, R. X . ; Smotkin, E. S. Electrochim. Acta 2002, 47, 2913-2919. Lin, W. F.; Zei, M . S.; Eisvvirth, M . ; Erti, G.; Ivvasita, T.; Vielstich, W. J. Phys. Chem. B 1999, 103, 6968-6977. Goodenough, J. B.; Manoharan, R.; Shukla, A . K.; Ramesh, Κ. V . Chem. Mater. 1989, 1, 391-398. Goodenough, J. B.; Hamnett, Α.; Kennedy, B. J.; Manoharan, R.; Weeks, S. A . J. Electroanal. Chem. Interfacial Electrochem. 1988, 240, 133-145. Hamnett, Α.; Kennedy, B. J.; Wagner, F. E. J. Catal. 1990, 124, 30-40. Kua, J.; Goddard, W. A . J. Am. Chem. Soc. 1999, 121, 10928-10941. Iwasita, T. Electrochim. Acta 2002, 47, 3663-3674. Jacoby, M . In Chemical and Engineering News, 1999, pp 31-37. Hogarth, M . P.; Hards, G . A . Platinum Met. Rev. 1996, 40, 150-159. Matare, G.; Tess, M . E.; Abboud, Κ. Α.; Yang, Y . ; McElwee-White, L . Organometallics 2002, 21, 711-716. Tess, M . E.; Hill, P. L . ; Torraca, K . E.; Kerr, M . E.; Abboud, Κ. Α.; McElwee-White, L. Inorg. Chem. 2000, 39, 3942-3944. Yang, Y . ; McElwee-White, L . Dalton Trans. 2004, 2352-2356. Shibasaki, M . ; Yoshikavva, N . Chem. Rev. 2002, 102, 2187-2209. Severin, K . Chem. Eur. J. 2002, 8, 1514-1518. Rida, M . Α.; Smith, A . K . Mod. Coord. Chem. 2002, 154-162. Wheatley, N . ; Kalck, P. Chem. Rev 1999, 99, 3379-3419.


142 31. 32. 33. 34. 35.


36. 37. 38. 39. 40. 41.

Baranger, A . M . ; Bergman, R. G. J. Am. Chem. Soc 1994, 116, 38223835. Adams, R. D.; Barnard, T. S. Organometallics 1998, 17, 2885-2890. Xiao, J.; Puddephatt, R. J. Coord. Chem. Rev. 1995, 143, 457-500. Orth, S. D.; Terry, M . R.; Abboud, Κ. Α.; Dodson, B.; McElwee-White, L. Inorg. Chem. 1996, 35, 916-922. Yang, Y . ; Abboud, Κ. Α.; McElvvee-White, L. Dalton Trans. 2003, 42884296. Wasmus, S.; Wang, J. T.; Savinell, R. F. J. Electrochem. Soc. 1995, 142, 3825-3833. Yuan, Y . ; Tsai, K.; Liu, H.; Iwasawa, Y . Top. Catal. 2003, 22, 9-15. Einaga, H.; Yamakawa, T.; Shinoda, S. J. Coord. Chem. 1994, 32, 117 119. Robles-Dutenhefner, P. Α.; Moura, E. M . ; Gama, G. J.; Siebald, H . G . L . ; Gusevskaya, E. V . J. Mol. Catal. A-Chem. 2000, 164, 39-47. Mandai, S. K.; Chakravarty, A . R. Indian J Chem A 1990, 29A, 18-21. Anthony, C. R.; McElvvee-White, L. J. Mol. Catal. A-Chem. 2004, 227, 113-117.


Electrocatalytic Oxidation of Methanol - American Chemical Society

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