Isothermal titration of supported platinum. Part 1.—CO–O2 titration

Abstract

The rate and extent of titrations of preadsorbed oxygen by gaseous CO and of preadsorbed CO by gaseous O₂ upon oxide-supported Pt vary with the titration temperature; results suggest that 423 K is close to the optimum and is to be preferred to previously used ambient conditions. The consumption of titrant CO and the total amount of heat liberated in the primary titration processes are directly proportional to the Pt surface area available to chemisorb CO and may thus be used to estimate Pt dispersions rapidly and reproducibly. However, they require careful calibration with traditional chemisorptive methods because of great temperature sensitivity if absolute metal surface areas are to be estimated. Importantly, the ratio of enthalpies of the two primary titration processes (Q_COTo/Q_OTco) appears to be very sensitive to the average Pt particle size, possibly as a result of the presence of different types of Pt adsorption site thereon. The thermokinetic profiles dQ/dt vs. t provide an insight into the kinetics of such titrations, which may be relevant to the catalysis of CO oxidation.