Interaction of NO and H 2 with Pt(100)

Abstract

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 N 2 and H 2O at ∼~ 400 K. Temperatures 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 × 1 ⇌ hex phase transition. Besides H 2O one also observes NH 3 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/H 2 mixture and then cooling into a temperature window between 410 and 450 K.