Authors:Viorel Chihaia, Karl Sohlberg, Viorel Sasca, Nicolae Doca, Alexandru Popa, and Nils Jaeger
The reduction kinetics with CO of the 12-molybdophosphoric—HPMo, 1-vanado-11-molybdophosphoric—HPVMo acids and their salts with NH4+, K+ and Cs+ cations were studied for reduction/reoxidation cycles with mixtures of CO:Ar and O2: Ar, by means of “in situ” UV–Vis–DRS measurements. The reflectivity versus time curves registered during the reduction/reoxidation processes for the HPMo and HPVMo and its salts with NH4+, K+ and Cs+ cations, at the constant wavelength of 620 nm and different reaction temperatures between 523 and 623 K, were processed as the Kubelka–Munk function versus time. The linear shape of Kubelka–Munk function versus time curves for the reduction process suggests apparent zeroth order kinetics and it was used for the calculation of apparent activation energy. The kinetic compensation effect between the apparent activation energy and the pre-exponential factor was observed. The Kubelka–Munk function versus time curves for the reoxidation process consist of two steps, the first with a very fast reaction rate and the second with a slow reaction rate. An explanation for their shape is proposed. The heteropoly oxomolybdates reach a degree of reoxidation higher than heteropoly compounds containing vanadium together with molybdenum.
Authors:Sankaran Anuradha and Venkatapuram Vijayaraghavan
The kinetics of the oxidation of hydroquinone (H2Q), catechol (H2cat) and substituted catechols with nickel(III) macrocycle [NiL1]3+ (L1 = 1,8-bis(2-hydroxyethyl)-1,3,6,8,10,13-hexaazacyclotetradecane) has been studied spectrophotometrically in aqueous perchloric
acid in the presence of sulfate. Over the pH range 1–2.6, and at higher sulfate concentration 0.05 < [SO42−] < 0.2 mol dm−3, the decomposition of [NiIIIL1] in the oxidation of benzenediols via [NiIIIL1(OH)(H2O)] is small. With hydroquinone, the rate constant is almost independent of the hydrogen ion concentration and with catechols,
the involvement of catechol anion (Hcat−) has been considered. The rate constants for cross reactions are discussed in terms of the Marcus relationship.