Lateral interactions in the dissociation kinetics of NO on Rh(100)

Temperature programmed desorption and static secondary ion mass spectrometr y have been used to study the dissociation and desorption of NO and the for mation of N-2 On the (100) surface of rhodium. At low coverages we find an activation energy of 37 +/- 5 kJ/mol for dissociation of NO and 225 +/- 5 k J/mol for N-2 desorption. At higher coverages the dissociation is significa ntly retarded by lateral interactions with N- and O-atoms and NO molecules. At coverages close to saturation the dissociation is entirely blocked by N O due to the lack of ensembles containing empty sites. The results are comp ared with those of earlier studies on Rh(111). It appears that dissociation of NO proceeds faster on the more open Rh(100) surface, due to the higher heat of adsorption of the N-atoms. As a consequence, formation of N-2 is sl ower than on Rh(111).