TAP studies of ammonia decomposition over Ru and Ir catalysts

The Temporal Analysis of Products (TAP) technique has been used to investigate the mechanism involved in the catalytic decomposition of NH3 over a series of catalysts consisting of activated carbon supported Ru (promoted and non-promoted with Na) and over an activated carbon supported Ir. An extensive study of the role played by both the support and the promoter in the "side reactions" and in the stability and surface lifetime of the NHx species has been performed. It was suggested that the N-2 produced during the first steps of the reaction over the activated carbon supported Ru catalysts promoted with Na forms a Na-N-Ru complex at the promoter-transition metal crystallite interface. This study also suggests that the Na promoter prevents the diffusion of hydrogen from the metal to the support via spill-over. A similar effect was observed after the thermal treatment at high temperature of the carbon catalyst support. Finally large differences in multi-pulse TAP results have been detected between Ru and Ir catalysts implying that the NH3 decomposition reaction mechanism must be different on both metals.