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.