Decomposition of ammonia and hydrogen on Ir surfaces: structure sensitivity and nanometer-scale size effects

The adsorption and decomposition of ammonia and hydrogen have been studied on surfaces of clean planar Ir(210) and clean nanoscale-faceted Ir(210), which are prepared from the same crystal in situ. We find evidence for structure sensitivity in recombination and desorption of H2 and in thermal decomposition of NH3 on clean planar Ir(210) versus clean faceted Ir(210). Moreover, the decomposition kinetics of NH3 on faceted Ir(210) exhibit size effects on the nanometer scale, which is the first observation of size effects in surface chemistry on an unsupported monometallic catalyst with controlled and well-defined structure and size.