Decomposition of NO on clean Pt near atmospheric pressures: II. Adsorbate coverages

Temperature programmed desorption (TPD) and temperature programmed adsorption (TPA) have been used to characterize adsorbate coverages during and after NO decomposition on polycrystalline Pt foils at pressures between 10^?4 and 30 Torr. The densities and stoichiometries of tightly bound species were determined after reaction by TPD of NO, N₂, and O₂ following cooling and pumpdown to <10^?8 Torr. For characterization during reaction at pressures up to 10^?3 Torr the ribbon was flashed inside a 35 cm³ reaction cell, and desorption and adsorption spectra of all species were recorded. Using digital acquisition of pressures versus time, peaks as small as 10^?3 of the background pressure could be analyzed. By flashing to different fixed temperatures, adsorption isobars during reaction were determined. These measurements show that there is a tightly bound stoichiometric layer of N and O (perhaps undissociated) and that the reactive state is weakly bound and appears to be strongly inhibited by molecular oxygen. This model also agrees with reaction rate measurements at these pressures.