Catalytic Synthesis of Nitric Monoxide at the AlN(0001) Surface: Ab Initio Analysis

Molecular nitrogen and molecular oxygen adsorption at the Al-terminated AlN(0001) surface was investigated using ab initio simulations. It was shown that both species undergo barrierless dissociation during attachment to the surface. The H3 adsorption site was identified as the most favorable for both O and N adatoms. The adsorption energies for O₂ and N₂ were found to be 14.8 and 6.0 eV, respectively. At the clean surface, separate N and O adatoms have their energies 4.37 eV lower than the NO admolecule. At normal nitrogen pressures, the AlN(0001) surface is fully covered by nitrogen adatoms. It was shown for this coverage that adsorption of oxygen leads to creation of the NO admolecule which is a necessary step for nitric monoxide synthesis. The energetics of NO molecules is related to electronic charge transfer: from the two possible configurations, it is shown that T4 and H3 are donors and acceptors, respectively. The resulting coverage is the mixture of both configurations, controlled by electron charge balance. Thus, the ab initio modeling provides indication that AlN(0001) is the powerful catalyst for high pressure-high temperature synthesis of nitric monoxide (NO), indicating that AlN may be a candidate for applications in industrial mass synthesis of nitrogen-based materials such as fertilizers or explosives.