The NO + CO reaction on Pt(100)

Abstract

The interaction of NO with CO and with H2 on Pt(100) was studied by temperature programmed desorption (TPD), isothermal desorption mass spectrometry, and low energy electron diffraction (LEED), TPD of NO and CO coadsorbed at 120 K yields almost complete reaction with both N2 and CO2 products desorbing as sharp, simultaneous peaks at ≈ 410 K. with full widths at half maximum as narrow as 3 K. Isothermal desorption mass spectrometry yields N2 and CO2 rates that exhibit a maximum with time. Both experiments indicate that the reaction mechanism is autocatalytic. Annealing NO-CO adlayers formed at 120 K to temperatures above 300 K causes the subsequent N2 and CO2 TPD peaks to broaden.'TPD of NO coadsorbed with H2 yields sharp N2 and H2O product peaks that closely resemble the N2 and CO2 peaks observed in the NO + CO reaction. LEED experiments during TPD and isothermal desorption showed that the (1 × 1) → hex substrate phase transformation sometimes accompanies desorption of N2 and CO2. The TPD and isothermal desorption results can be fit by two simple models: chemical autocatalysis, in which an intermediate chemical species participates in a “chain propagation” reaction, and structural autocatalysis, which involves the formation of a reactive intermediate structure involving Pt atom displacements.