22541-53-3Relevant articles and documents
Nucleation, growth, and repair of a cobalt-based oxygen evolving catalyst
Surendranath, Yogesh,Lutterman, Daniel A.,Liu, Yi,Nocera, Daniel G.
, p. 6326 - 6336 (2012)
The mechanism of nucleation, steady-state growth, and repair is investigated for an oxygen evolving catalyst prepared by electrodeposition from Co2+ solutions in weakly basic electrolytes (Co-OEC). Potential step chronoamperometry and atomic force microscopy reveal that nucleation of Co-OEC is progressive and reaches a saturation surface coverage of ca. 70% on highly oriented pyrolytic graphite substrates. Steady-state electrodeposition of Co-OEC exhibits a Tafel slope approximately equal to 2.3 × RT/F. The electrochemical rate law exhibits a first order dependence on Co2+ and inverse orders on proton (third order) and proton acceptor, methylphosphonate (first order for 1.8 mM ≤ [MePi] ≤ 18 mM and second order dependence for 32 mM ≤ [MePi] ≤ 180 mM). These electrokinetic studies, combined with recent XAS studies of catalyst structure, suggest a mechanism for steady state growth at intermediate MePi concentration (1.8-18 mM) involving a rapid solution equilibrium between aquo Co(II) and Co(III) hydroxo species accompanied with a rapid surface equilibrium involving electrolyte dissociation and deprotonation of surface bound water. These equilibria are followed by a chemical rate-limiting step for incorporation of Co(III) into the growing cobaltate clusters comprising Co-OEC. At higher concentrations of MePi ([MePi] ≥ 32 mM), MePO 32- equilibrium binding to Co(II) in solution is suggested by the kinetic data. Consistent with the disparate pH profiles for oxygen evolution electrocatalysis and catalyst formation, NMR-based quantification of catalyst dissolution as a function of pH demonstrates functional stability and repair at pH values >6 whereas catalyst corrosion prevails at lower pH values. These kinetic insights provide a basis for developing and operating functional water oxidation (photo)anodes under benign pH conditions.
Baxendale, J. H.,Wells, C. F.
, p. 800 - 812 (1957)
Bawn, C. E. H.,White, A. G.
, (1951)
Kinetics of the Iron(II) Reduction of Glycinatobis(malonato)-, trans-Bis(malonato)bis(pyridine)-, Nitrilotriacetato(malonato)-, and Nitrilotriacetato(oxalato)cobaltates(III)
Viswanathan, Ramakrishnan,Vijayaraghavan, Venkatapuram Raman.
, p. 3243 - 3246 (1986)
The kinetics of the iron(II) reduction of glycinatobis(malonato)-, trans-bis(malonato)bis(pyridine), nitrilotriacetato(malonato)-, and nitrilotriacetato(oxalato)cobaltates(III) have been studied in aqueous perchlorate medium at I=1.0 mol dm-3 (LiClO4) and 30 deg C in the +> range 0.01-0.90 mol dm-3.The reductions are found to be second order.The reduction of 2- and - is accelerated by H+, while the reduction of 2- and 2- is independent of +> in the range 0.1+>-3.The reduction of 2- is, however, faster at +>-3.The activation parameters for the reduction of 2-, -, 2-, and 2- are respectively as follows: ΔH=49.8+/-4.8, 51.2+/-2.6, 41.1+/-3.2, and 41.4+3.6 kJ mol-1, ΔS=-98.3+/-8.3, -93.7+/-7.2, -119.2+/-9.7, and -114.6+/-9.6 J K-1 mol-1.The proposed mechanism invokes (L-py2 or gly) formed in a H+-assisted step as the reactive species for the bis(malonato) complexes. 2- is proposed to be present as - while 2- remains unaffected by H+.
Krack, I.,Braun, P.,Eldik, R. van
, (1986)
Kinetics and Mechanism of Oxidation of S2O32? by a Co-Bound μ-Amido-μ-Superoxo Complex
Singh, Bula,Das, Ranendu Sekhar,Banerjee, Rupendranath,Mukhopadhyay, Subrata
, p. 88 - 97 (2016)
In acetate buffer media (pH 4.5–5.4) thiosulfate ion (S2O32?) reduces the bridged superoxo complex, [(NH3)4CoIII(μ-NH2,μ-O2)CoIII(NH3)4]4+ (1) to its corresponding μ-peroxo product, [(NH3)4CoIII(μ-NH2,μ-O2)CoIII(NH3)4]3+ (2) and along a parallel reaction path, simultaneously S2O32? reacts with 1 to produce the substituted μ-thiosulfato-μ-superoxo complex, [(NH3)4CoIII(μ-S2O3,μ-O2)CoIII(NH3)4]3+ (3). The formation of μ-thiosulfato-μ-superoxo complex (3) appears as a precipitate which on being subjected to FTIR shows absorption peaks that support the presence of Co(III)-bound S-coordinated S2O32? group. In reaction media, 3 readily dissolves to further react with S2O32? to produce μ-thiosulfato-μ-peroxo product, [(NH3)4CoIII(μ-S2O3,μ-O2)CoIII(NH3)4]2+ (4). The observed rate (k0) increases with an increase in [TThio] ([TThio] is the analytical concentration of S2O32?) and temperature (T), but it decreases with an increase in [H+] and the ionic strength (I). Analysis of the log At versus time data (A is the absorbance of 1 at time t) reveals that overall the reaction follows a biphasic consecutive reaction path with rate constants k1 and k2 and the change of absorbance is equal to {a1 exp(–k1t) + a2 exp(–k2t)), where k1 > k2.
Measurement of solvent dynamics effects on the electron transfer reaction of Co(NH3)4ox+ in mixed solvents: A quantitative approach
Anbalagan,Geethalakshmi,Poonkodi
, p. 1918 - 1927 (2003)
For reactions involving electron transfer or nucleophilic attack on the transition state/excited state of metal complex in aquo-organic solvent mixtures, a linear relationship between logarithms of rate constant and solvent empirical parameters can be derived. Fe(CN)64- reduction of Co(NH3)4ox+ and ligand to metal charge transfer (LMCT) excited-state redox reaction of Co(NH3)4ox+ were studied in varying compositions of aqueous mixtures of methanol (MeOH) and 1,4-dioxane (Diox). A quantitative estimation of relative importance of the components was attempted. A number of empirical solvent parameters were used in the multiple regression equations. The correlation analysis showed significant information on the effect of solvent-solvent and solvent-solute interactions on reactivities. The addition of MeOH or Diox to the medium brings about marked structural changes in the prevailing water structure by making progressive desolvation between partners of the transition state/geminate radical pair which in all probability is highly solvated in the water medium. The positive sign of multiparametric coefficients suggested that the solvent mixture strongly solvates the transition state, and the negative sign of the coefficients shows the specific solvation of incipient reactants.
The solid-state electrochemistry of metal octacyanomolybdates, octacyanotungstates, and hexacyanoferrates explained on the basis of dissolution and reprecipitation reactions, lattice structures, and crystallinities
Schr?der, Uwe,Scholz, Fritz
, p. 1006 - 1015 (2000)
The electrochemical behavior of solid microparticles of metal (Ag+, Cd2+, Co2+, Cr2+, Cu2+, Fe2+, Mn2+, Ni2+, Pb2+, and Zn2+) octacyanomolybdates, octacyanotungstates, and hexacyanoferrates has been studied by voltammetry, electrochemical quartz crystal microbalance, and microscopic diffuse reflectance spectroelectrochemical measurements. The solid microparticles have been immobilized on the surface of graphite electrodes prior to the electrochemical measurements. A comparative study of the cyclic oxidation and reduction of these compounds in the presence of potassium ions revealed that any interpretation of the electrochemistry requires the solubility equilibria of the reduced compounds to be taken into account, such as in the case of the silver salts {Ag3K[X]} and {Ag4[X]} (with X = Fe(II)(CN)6/4-, M(IV)(CN)8/4- (M = Mo, W)). Because {Ag4[X]} has a lower solubility than {Ag3K[X]}, the electrochemistry is accompanied by a conversion of solid {Ag3K[X]} into solid {Ag4[X]}. Two distinct voltammetric signal systems are generated by these two compounds according to {Ag3K[X]} ? {Ag3-[X]} + K+ + e- and {Ag4[X]} ? {Ag3[X]} + Ag+ + e-. When silver ions are present in the solution adjacent to the microparticles, the silver octacyanometalates and silver hexacyanoferrate show a chemically reversible and very stable voltammetric behavior. Despite the fact that the electrochemistry is based upon a single-electron/single-ion transfer reaction ({Ag4[X]} ? {Ag3[X]} + Ag+ + e-), more than one electrochemical signal is observed because of the simultaneous presence of amorphous and crystalline particles. This study shows that the interplay of solubility equilibria and electrochemical equilibria is generally observed for the other metal octacyanomolybdates, octacyanotungstates, and hexacyanoferrates as well.
Arunachalam, M. K.,Balasubramanian, P. N.,Vijayaraghavan, V. R.
, p. 753 - 756 (1981)
Zwickel, A.,Taube, H.
, p. 793 - 796 (1961)
Eldik, R. Van,Kelm, H.
, p. 91 - 94 (1983)
Kinetics and Mechanism of Ce(IV) Oxidation of Free and Coordinated Glyoxylic Acid
Mohanty, Nirod Kumar,Nanda, Rabindra Kumar
, p. 3597 - 3601 (1985)
The kinetics and mechanism of Ce(IV) oxidation of glyoxylic acid and pentaammineglyoxalatocobalt(III) perchlorate have been investigated in acidic sulfate media in the temperature range 35 to 50 deg C and at ionic strength 0.95 M.The rate of decrease of was found to be first order in and .The observed second order rate constant, kobsd, for the disappearance of is satisfactorily given by, kobsd = 1 + k2K34->/+>>/34->/+>> (for glyoxylato complex) and kobsd = k1/34->/+>> (for glyoxylic acid).Both Ce(SO4)2 and 4)3)2- appear to be the oxidant species for coordinated glyoxylate while for free glyoxilic acid Ce(SO4)2 seems to be the only oxidant species.The values of k1 and k2 and the associated activation parameters have been computed.A suitable mechanism has been suggested for the reaction.
Kinetic studies on the oxidation of trimeric aquomolybdenum(IV)
Harmer, Mark A.,Richens, David T.,Soares, Allan B.,Thornton, Andrew T.,Sykes, A. Geoffrey
, p. 4155 - 4158 (1981)
Oxidations of the Mo(IV) aquo trimer, Mo3O44+, with IrCl62- and Fe(phen)33+ have been studied under the conditions [H+] = 0.6-2.0 M and I = 2.0 M (LiClO4). With MoIV3 in large excess, the IrCl62- reaction can be expressed as 2MoIV3 + 6IrIV → 3MoV2 + 6IrIII, and the initial step MoIV3 + IrCl62- is rate determining. Second-order rate constants kIr are dependent on [H+]: kIr = k-1[H+]-1, where at 25°C k-1 = 1.36 s-1, ΔH? = 14.1 kcal mol-1, and ΔS? = -9.6 cal K-1 mol-1. An alternative stoichiometry MoIV3 + 4IrIV → MoV2 + MoVI + 4IrIII cannot be entirely ruled out, and at nearly equivalent amounts of reactants the slower oxidation of MoV2 to MoVI contributes. With Fe(phen)33+ a different reactivity pattern is observed in that oxidation of MoV2 is more rapid than that of MoIV3, and the equation MoIV3 + 6Fe(phen)33+ → 3MoVI + 6Fe(phen)32+ applies. This different behavior is accounted for by the reaction of Fe(phen)33+ occurring exclusively by an outer-sphere mechanism, whereas IrCl62- can react inner sphere. The initial step, MoIV3 + Fe(phen)33+, is again rate determining and at 25°C k-1 for the [H+]-1-dependent path is 0.53 s-1, I = 2.0 M. No evidence was obtained for stable trimeric mixed-oxidation-state species as product(s) of the oxidation of MoIV3. The complex Co(C2O4)33- does not oxidize MoIV3, whereas (as reported elsewhere) oxidation of aquo MoIII and MoIII2 through to MoV2 is rapid. It is concluded that oxidation of monomeric and/or dimeric Mo(IV) occurs more readily than that of the trimer. No oxidation of MoIV3 by the two-electron oxidant PtCl62- is observed.
Intramolecular Charge-transfer Decomposition of the μ-Peroxo-bis- Complex in Acidic Solutions. Stabilization by Protonation and the Effect of Chloride and Sulphate
Ferrer, Miguel,Hand, Timothy D.,Sykes, A. Geoffrey
, p. 14 - 18 (1980)
The kinetics of the decomposition of the μ-peroxo-bis complex, (4+) -> 2Co(2+) + O2 + NH4(1+), generated by fast one-electron reduction of the μ-superoxo-complex, (5+), have been studied using the stopped-flow technique at =0.005-0.100M, l=0.10M (LiClO4).The dependence of first-order rate constants, kobs=kK/( + K), is consistent with the formation of a protonated non-reactive form.At 25 deg C the rate constant for decomposition of the unprotonated (brown) form is k=84 s-1, and ΔH(excit.)=17.5+/-1.0 kcalmol-1, ΔS(excit.)= 8.7+/-3.7 cal K -1mol-1, in excellent agreement with previous data for solutions =4.3-15.0M, l = 2.0M (NH4NO3).The acid dissociation constant K of the protonated (red) complex (25 deg C) is 0.084M, with ΔH=6.0+/-2.5 kcalmol-1, ΔS=15.2+/-9.0 calK-1mol-1.Chloride > 0.6M the effect of and on the rate of decomposition was studied by conventional spectrophotometry, l=2.3M (Cl(1-)/ClO4).Solid samples of the brown and red complexes interconvert rapidly in solution to give identical spectra.The protonated red complex does not react with iodide during the ca. 30 min period required for decomposition.Implications regarding the structure of the protonated complex are considered.
Highly efficient polyoxometalate-based catalysts for clean-gasoline synthesis
Wang, Chunling,Liu, Cheng,Hu, Yunhang,Bu, Xianni,Zhao, Tiejun,Chou, Kuochih,Li, Qian
, p. 21424 - 21427 (2015/11/10)
Poor selectivity for gasoline products is a critical issue for the Fischer-Tropsch synthesis (FTS). Herein, we report that the introduction of a polyoxometalate Cs2.5H0.5PW12O40 (CsPW) into a conventional FTS catalyst (Co/Al2O3) can create a highly efficient bifunctional catalyst, leading to 118% increase in the selectivity of gasoline. Furthermore, it was found that such a significant improvement is due to the effective hydrocracking of heavier hydrocarbon products at CsPW sites.
Kinetics of oxidation of nitrosodisulfonate anion radical with a metallo-superoxide
Mandal, Kaustab,Banerjee, Rupendranath
, p. 2714 - 2719 (2012/04/04)
The metal bound superoxide in μ-superoxo-bis[pentaamminecobalt(iii)] 5+ (1) oxidizes the nitrosodisulfonate anion radical (NDS 2-) by two electrons. Oxidized NDS2- quickly decomposes to SO42- and NO. 1 is itself reduced to the corresponding hydroperoxo complex which also decomposes fast to Co(ii), NH4 + ions and oxygen. 1.5 moles of volatile products formed per mole of 1 mixed with excess NDS2-. In the absence of superoxide in a bridged complex, e.g. the μ-amido-bis[pentaamminecobalt(iii)]5+ complex fails to oxidize the nitroxyl radicals, NDS2-, TEMPO and 4-oxo TEMPO. With excess NDS2- over 1, the reaction is first-order with respect to [1], [NDS2-] and inverse first order in [H+]. The activation entropy, ΔS≠, is largely negative, increased ionic strength decreased the rate and a Bronsted plot is fairly linear with a negative slope. Oxidant μ-superoxo-bis[(ethylenediamine) (diethylenetriamine)cobalt(iii)]5+ has ligands sterically more crowded though more basic than ammonia in 1. It oxidizes NDS2- much more slowly. No solvent kinetic isotope effect (kH2O/D2O ≈ 1) could be seen; a spin-adduct formation by the conjugate base of 1 followed by electron transfer is postulated. The Royal Society of Chemistry 2012.
