Combined in Situ Infrared and Kinetic Study of the Catalytic CO + NO Reaction on Pd(111) at Pressures up to 240 mbar

The CO + NO reaction on Pd(111) has been studied at pressures up to 240 mbar using in situ polarization modulation infrared reflection−absorption spectroscopy (PM-IRAS), which simultaneously provides information on the in situ adsorption behavior as well as the reaction kinetics via gas-phase infrared absorption. Under reaction conditions (>500 K) and at pressure ratios P CO / P NO ≥ 1.5, besides CO and NO, isocyanate is adsorbed on the surface as evidenced by isotope experiments. The kinetics of the CO + NO reaction to form CO 2, N 2 O, and N 2 was followed by monitoring the evolution of gas-phase CO 2 and N 2 O. Above 550 K, a substantial increase in activity was observed. Kinetic measurements between 590 and 650 K showed an increase in the N 2 O selectivity as a result of temperature-dependent changes of the ratio [NO] a /[CO] a . Within this temperature range and on the basis of the CO 2 yields, the apparent activation energy of the reaction was determined to be 54 ± 21 kJ/mol.