NOPR Collection:

Electrocatalytic Oxidation of Alkaline Methanol on Some Noble Metal Coated Electrodes

1989-04-01T00:00:00Z

Title: Electrocatalytic Oxidation of Alkaline Methanol on Some Noble Metal Coated Electrodes Authors: Guha, Prabir K; Bhattacharya, Abhijit; Kundu, Kiron K Abstract: Anodic oxidation fo alkaline methanol has been studied on Pt and C electrodes coated with Pt, Pd, Rh, Ru, Ir andlor Au. Galvanostatic steady-state and linear sweep cyclic voltammetric methods in conjunction with chronopotentiometric and scanning electron microscopic techniques have been employed for such studies. The exchange current densities [(i_o)app and (i_o)_tr] and peak current densities (i_p) clearly demonstrate the superior performance of Pt-coated electrodes as compared to the electrodes coated with other noble metals. Next to Pt, Rh appears to be the second best in the case of carbon substrate and Ru for platinum substrate. The order of i_o values is Pt > Ru > Rh ≈ Ir >Pd >Au on Pt/M and Pt >Rh >Pd >Au on C/M and that of i_p: Pt > Pd » Rh ≈ Ir >Ru » Au on Pt/M and Pt $> Rh > Pd » Au > Ru ≈ Ir on C/M. C/Ru and C/r electrodes, however, undergo corrosion in alkaline medium. The Tafel slope (b) values as also the cyclic voltammograms are indicative of a similar mechanistic pathway for Pt and Pd, which is different for Rh, Ru and Ir and yet another for Au. Rationalization of these observations by correlating them to intrinsic properties, viz. % d-band character, work function, latent heat of sublimation, H_M-H of the catalyst metals (M) and extrinsic properties, viz. roughness factor, size and extent of coverage of the deposits and porosity of the base substrate of the electrodes leads to the conclusion that none of the parameters could be 'singled out' as accounting for the observed catalytic activities. Rather, the activities appear to be governed by a combination of these properties whose possible optimization in Pt results in the highest electrocatalytic activity of this metal. Page(s): 267-275

Solubility and the thermodynamics of transfer of benzoic acid in mixed solvents

1989-04-01T00:00:00Z

Title: Solubility and the thermodynamics of transfer of benzoic acid in mixed solvents Authors: Pal, A; Lahiri, S C Abstract: The solubilities of benzoic acid in ethanol + water mixtures have been determined at three different temperatures to obtain the thermodynamic parameters (Gᵒ, Sᵒ, Hᵒ) of transfer of benzoic acid from water to ethanol + water mixtures. The results have been interpreted in terms of the structural changes occurring in the solvent mixtures with the change in solvent composition. The activity coefficients of benzoic acid in water and mixed solvents have been found to be close to unity from theoretical calculations using the data from the literature. Page(s): 276-279

Redox chemistry of hyponitrite: Part III-oxidation by hexacyanoferrate(III) in aqueous alkaline solution

1989-04-01T00:00:00Z

Title: Redox chemistry of hyponitrite: Part III-oxidation by hexacyanoferrate(III) in aqueous alkaline solution Authors: Goyal, M R; Bhatnagar, Pankaj; Mittal, R K; Gupta, Y K Abstract: Oxidation of hyponitrite by hexacyanoferrate(III) in alkaline solution occurs by two paths resulting in a stoichiometry of 1.21:1(oxidant:substrate). The final products are N₂O,N₂ and NO, and the intermediates are NO and peroxonitrite. Rate has first order dependence in [Fe(CN)] and [(N₂O] and no dependence on [OH^-]. The second order rate constant is found to be (0.87 ± 0.025) dm³ mol^-1 at 35° and 1= 0.515 mol dm^-3. Rate significantly increases in the presence of alkali metal cations. Page(s): 280-283

Kinetics of cemplexation of nickel (II) with -ɑ-aminoisocaproic acid, -ɑ-amino-γ-methylthio-n-butyric acid & histidine methyl ester

1989-04-01T00:00:00Z

Title: Kinetics of cemplexation of nickel (II) with -ɑ-aminoisocaproic acid, -ɑ-amino-γ-methylthio-n-butyric acid & histidine methyl ester Authors: Malhotra, H C; Sharma, Gian Chand Abstract: The title reactions have been studied at 25-45ᵒ (±0.05°C) and at I = 0.1 mol dm^-3 KNO₃ in the pH range of 6.35-7.39 for -ɑ-aminoisocaproic acid, 6.24-7.29 for -ɑ-amino-γ-methylthio-n-buryric acid and 6.45-7.10 for histidine methyl ester. Rate constants for the formation of Ni(II) complexes with the anions and zwitterions of these three ligands have been determined by stopped flow method and activation parameters have been calculated. The values of Kos (outer sphere complex formation constant) and k_o (rate constant for water exchange have also been calculated. Page(s): 284-287