The kinetics and mechanism of CeIV oxidation of the water oxidation catalyst [(bpy)2(H2O)RuIIIORuIII(OH2)(bpy)2]4+ (1, RuIIIORuIII) have been investigated by UV−visible measurements with application of global analysis. The reaction proceeds by stepwise oxidation of RuIIIORuIII to RuVORuV with oxidation of RuIVORuIII the slow step. RuVORuV has been identified as an intermediate by the appearance of its ClO4 - salt as a black suspension in concentrated solutions at 5 °C. It is the key intermediate in water oxidation. The mechanism may involve a bimolecular step and formation of a peroxo-bridged intermediate. Catalytic water oxidation is greatly retarded after just a few catalytic cycles because of anation induced by O2 evolution.

Silica gel, under various hydration conditions, was investigated using a novel calorimetric adsorption (CalAd) method. This method combines data from calorimetric and adsorption titrations of a solid surface using a small probe molecule in a noninteractive solvent. The Cal-Ad method proved to be more sensitive than other characterization techniques (e.g. temperature-programmed desorption) and calorimetric techniques. Previously, it was believed that the silica surface consisted of one type of hydrogen-bonding site. The Cal-Ad method has elucidated three hydrogenbonding sites of different strengths using pyridine as the basic probe molecule. The equilibrium constant of binding, enthalpy of binding, and number of each of these sites have been determined.

No abstract

Ce(IV) oxidation of the ruthenium blue dimer leads to catalytic oxidation of water. Kinetic and spectroscopic studies have revealed evidence for RuVORuV as the active catalyst. Redox cycling occurs between RuIIIORuIII and RuVORuV via a complex sequence of coupled steps involving oxidations by Ce(IV) and second-order cross reactions of the dimer. The oxygen-evolving step is not rate determining in the catalytic cycle.