THE NO + H2 AND NO + NH3 REACTIONS ON PT(100) - STEADY-STATE AND OSCILLATORY KINETICS

The reactions of NO + H2 and NO + NH3 on Pt(100) were studied in the 10(-6) mbar range under constant flow conditions between 300-750 K with mass spectrometry, work function measurements, and video LEED. Multiple steady states and kinetic oscillations were found with each of the two reaction mixtures. For the NO + H-2 system, the primary reaction products were N2, H2O and NH3, whereas for the NO + NH3 reaction, N2 and H2O were formed. Both systems were seen to exhibit a number of common features in their steady-state and oscillatory kinetics. The similarities include spike-like features in the N2 production rate which occur between 400 and 420 K, large variations in the work function signals as a function of temperature, and the occurrence of phase transitions between the 1 x 1 and hexagonal phases of Pt(100). Kinetic oscillations, as determined from variations in the N2, H2O and work function signals, were found between 420 and 445 K. The similarities in the two systems are attributed to the relatively insensitivity of NO to the nature of the reducing agent, either H-2 or NH3, and to the presence of adsorbed NH(x) (x = 1-3) species whose concentration controls the availability of adsorbed H atoms for the removal of atomic oxygen.