We present local spin density approximation calculations on the adsorption and dissociation of ammonia on a copper cluster which models the Cu(111) surface. Preadsorbed oxygen increases the adsorption energy of ammonia, and promotes the dissociation of ammonia. All examined dissociation reactions in the absence of oxygen are endothermic. Dissociation of ammonia to NH2 with oxygen is also found to be endothermic, but less than for systems without oxygen. Subsequent dissociation to NH is thermally neutral, whereas NH dissociation to nitrogen is exothermic. The most endothermic steps in the catalytic reaction cycle of the ammonia oxidation reaction appear to be the dissociation of ammonia and the desorption of water.
Bibliographical noteFunding Information:
This work has been supportedb y the Netherlands Foundation for Chemical Research( SON) with financial aid from the NetherlandsO rgani-zation of Pure and Scientific Research (NWO), and by DuPont. Computationalr esourcesw ere provided by the National Computing Facilities (NCF) Foundation under project SC-183.