INTERACTION OF NO AND H2 WITH PT(100)

The catalytic reduction of NO by H-2 on Pt(100) exhibits sustained kinetic oscillations at low feed-gas pressures (total pressures less than 10(-3) Pa) and isothermal conditions. As part of a study of these phenomena work function change, low energy electron diffraction (LEED) and thermal-desorption spectroscopy (TDS) measurements have been made of the interaction of NO and H-2, separately and together, with the Pt(100) surface. Coadsorption of H-2 and NO at 170 K leads to the appearance of extremely narrow TDS product peaks of N2 and H2O at approximately 400K. Temperature cycles under conditions of constant H-2 and NO partial pressures revealed the existence of a hysteresis in the reaction rate that is associated with the 1 x 1 reversible hex phase transition. Besides H2O one also observes NH3 as a reaction product with the product ratios depending on the temperature and on the surface structure. A specific procedure is required for the initiation of kinetic oscillations. This involves first heating the sample to 550 K in an appropriate NO/H2 mixture and then cooling into a temperature window between 410 and 450 K.