Kinetics of NH Formation and Dissociation on Pt(111)

Abstract

The kinetics of formation and dissociation of the NH species on the Pt(111) surface has been studied experimentally with time-resolved reflection absorption infrared spectroscopy (RAIRS) and theoretically with density functional theory (DFT). An intense and narrow peak at 3321 cm-1 due to the NH stretch vibration characterizes the NH species. This RAIRS peak enables the NH coverage to be accurately measured as a function of time during the formation and dissociation reactions. The experiment is performed by first preparing a well-ordered p(2 × 2)-N layer through oxydehydrogenation of NH3, then exposing the p(2 × 2)-N layer to H2 at low temperature. It is found that NH formation follows first-order kinetics, whereas the dissociation reaction follows second-order kinetics. Because NH is more stable on the surface than N and H, the dissociation rate is limited by the recombinative desorption of H2, which accounts for the observed reaction order. The experimental rate constants were compared with the correspo...