Adsorption and dehydrogenation of ammonia on Ru55, Cu55 and Ru@Cu54 nanoclusters: role of single atom alloy catalyst

Abstract

Hydrogen production by the catalytic decomposition of ammonia (NH₃) is an important process for several important applications, which include energy production and environment-related issues. The role of single Ru-atom substitution in a Cu₅₅ nanocluster (NC) has been illustrated using the NH₃ decomposition reaction as a model system. The structural stability of Ru@Cu₅₄ NC has been evaluated using Ru₅₅ and Cu₅₅ NCs for comparison. Ru@Cu₅₄ prefers an icosahedron structure (I_h), like Ru₅₅ and Cu₅₅ NCs, with almost comparable average binding energies of −5.55 eV per atom. The adsorption of NH_x (x = 0–3) on different adsorption sites of the icosahedron Ru@Cu₅₄ NC has also been studied and the corresponding adsorption energies have been estimated. The site-preference investigation suggested that NH₃ prefers to adsorb vertically to the Ru@Cu₅₄. The stable geometries of the N and H atoms on the high symmetry adsorption sites of Ru@Cu₅₄ NC have been studied. Although the N atom favours top and hollow sites, the H atom prefers to stay in the Ru–Cu bridge site along with the hollow sites. The adsorption energy of N on the Ru@Cu₅₄ NC fcc site is found to be −5.42 eV, which is very close to the optimal value (−5.81 eV) of the ammonia decomposition volcano curve. The reaction energies for stepwise H atom elimination from an adsorbed NH₃ molecule have been estimated. Finally, NH₃ adsorption and decomposition on Ru@Cu₅₄ have been illustrated in terms of electronic structure analysis. The energetics calculations for the dehydrogenation of NH₃ suggest that Ru@Cu₅₄ NC can be a suitable catalyst.