The oxidation and co reduction kinetics of a platinum surface

A thermogravimetric technique was used to study the oxidation and CO reduction kinetics of Pt as a function of temperature, T. The measurements were performed on Pt powder (particle sizes 0.8–2.5 μm) at 1 atm pressure. After exposure to 1 atm of oxygen at 600 K for 1 h, the total uptake of oxygen by the powder amounted to less than one oxygen atom per Pt surface atom and followed a logarithmic growth law. For 400 < T < 600 K, the logarithmic rate constant, K₀, could be described by an Arrhenius law with an apparent activation energy of 2.6 kcal/mole. Above 600 K, K₀ slowly decreased, an effect believed to be associated with the dissociation of the oxide between 650 and 850 K. Oxidation isotherms were calculated using the low pressure oxygen sticking coefficient data of Hopster et al. The calculated and measured oxidation isotherms were found to be in remarkable agreement. The CO reduction data were more difficult to analyze but showed that the reduction rate had a stronger temperature dependence (~11 kcal/mole) than the oxidation rate. For427 < T<487 K, the general time scale of the reduction process was 10–50 min. Typical durations of the oxidation and CO reduction processes are consistent with the periods observed in studies of the oscillatory rate of CO oxidation over a Pt catalyst.