Synergetic Catalysis of Copper and Iron in Oxidation of Reduced. Keggin Heteropolytungstates by Dioxygen

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Kathryn Patterson
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1 Supporting Information for: Synergetic Catalysis of Copper and Iron in Oxidation of Reduced Keggin Heteropolytungstates by Dioxygen Mooeung Kim, Masoumeh Chamack,, Yurii V. Geletii,*, Craig L. Hill*, Department of Chemistry, Emory University, Atlanta, Georgia 30322, United States Department of Chemistry, Tarbiat Modares University, Tehran, Iran AUTHOR INFORMATION Corresponding Author * *

2 Figure S1. Dependence of solution electrochemical potentials as a function of 4 ox /4 red ratio measured by Pt-redox electrode vs NHE in 0.1 M NaNO 3 at ph 1.8 adjusted by HNO 3. Figure S2. The shape of initial part of the kinetic curve of 3 red oxidation by O 2 and dependence of initial rate ( d[3 red ]/dt) on time intervals. Conditions: [3 red ] 0 ~ 0.38 mm, [Cu(II)] 0 = 10 µm, [Fe(II)] 0 = 50 µm, [O 2 ] 0 = 0.12 mm, ph 1.8, 50 mm sulfate buffer, 0.1 M NaNO 3, 25 C. Black line is experimental data. Red line is a trend line with a slope taken between 3 4 seconds. The slope measured in between seconds is (green line). The blue curve is obtained from fitting using the parameter in the Table 2.

3 Figure S3. Dependence of a solution electrochemical potential on the ratio [Fe(III)]/[Fe(II)] in 50 mm sodium sulfate buffer containing 0.1 M NaNO 3 at ph 1.8. Figure S4. Kinetics of 3 red oxidation by O 2 in (a) 50 mm phosphate buffer and (b) 50 mm sulfate buffer. Conditions: ph 1.8, 25 C. Red and blue lines represent the kinetics performed under air and saturated O 2. Solid lines indicate the experimental curves. Dotted lines are the theoretical curves.

4 Reaction Rate Constant k 8. We thought that from the kinetics of this reaction we would be able to find the range of values for the reaction rate constants k 8. We have found that 4 red oxidation by H 2 O 2 is efficiently catalyzed by Fe(II), but that the addition of Cu(II) only slightly increases the reaction rate. Since the 4 red oxidation by O 2 is very slow, only four reactions, eqs 2, 8, 9 and 13, were used to fit the experimental data. 4 ox + Fe(II) 4 red + Fe(III) (2) Fe(II) + H 2 O 2 Fe(III) + HO + HO (8) POM red + HO POM ox + HO (9) Fe(II) + HO Fe(III) + HO (13) The equilibrium constants K 2 were varied ± 0.1 units from the values obtained from the thermodynamic analysis, k 13 was taken to be M 1 s 1. The values of K 2 and k 8 were the variable parameters. The results of fitting are given in Figure S5. The equilibrium constant K 2 within experimental error is the same as estimated from the reaction thermodynamics. In the Figure S5. Absorbance change during oxidation of 0.5 mm 4 red by 0.5 mm H 2 O 2 in 50 mm phosphate (a) and sulfate (b) buffers at ph = 1.8. [Cu(II)] = 10 µm, [Fe(II)] = 0.1 (black), (red), and 0.25 (blue) mm. Solid and dotted lines are experimental data and calculated fits, respectively. The parameter: (a) k 8 = 106 M 1 s 1, k 4 = M 1 s 1, K 2 = 0.1; (b) k 8 = 350 M 1 s 1, k 4 = 140 M 1 s 1, K 2 = 17.

5 fitting of kinetics curves (Figure S5), k 2, was varied but over a narrow range of values, ( ) 10 4 M 1 s 1 in phosphate and M 1 s 1 in sulfate buffers. Solubility of FePO 4. We used the ChemEq v3.1 software package with a built-in database to calculate the speciation under our conditions. The solubility products are pk sp = 26.4 for the mineral Strengite, FePO 4 2H 2 O(s), and 21.6 for the amorphous FePO 4 (the most likely product in our system). The concentration of PO 3 4 in 50 mm phosphate buffer at ph 1.8 is < The concentration of Fe(III) is < 0.5 mm under our experimental conditions. The concentration of free Fe 3+, calculated with ChemEq v3.1 in 50 mm phosphate buffer at ph 1.8 is M. Thus, the formation of Strengite crystals is thermodynamically feasible. Importantly, however, the formation of solid FePO 4 is prohibitively slow. Under our experimental conditions, the initial rate law is d[fepo 4 ]/dt = k[fe 3+ ][PO 3 4 ]. The reaction rate constant k < M 1 s 1 (diffusion controlled), and the life-time of [Fe 3+ ] is longer than 1/k[PO 3 4 ] > 10 7 s or > 4 months. Therefore, regardless of pk sp value, our solutions are kinetically stable.

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