First-Principles Insights into Ammonia Decomposition Catalyzed by Ru Clusters Anchored on Carbon Nanotubes: Size Dependence and Interfacial Effects

Ammonia decomposition catalyzed by Ru nanoparticles supported on carbon nanotubes offers an efficient way for COx-free hydrogen generation. To understand the catalytic mechanism, the two most important elementary steps of ammonia decomposition, namely the initial cleavage of the NH2-H bond and the nitrogen recombination, have been studied using density functional theory on a carbon nanotube deposited with Ru-x (x = 1, 2, 6, and 13) clusters. The results indicate the reaction steps are catalyzed at Ru sites with barriers significantly lower than those on Ru(0001), but the barriers have a strong dependence on the size of the cluster. It is also found that Ru sites at the interface with the carbon nanotube are more active, showing a strong interfacial effect due apparently to facile charge transfer from the carbon nanotube to interfacial metal atoms.