Catalytic decomposition of ammonia over silicon-carbide nanotube: a DFT study

Abstract

Decomposition of ammonia is important for a series of technological and environmental applications. For developing highly active catalysts for this reaction, detailed understanding of underlying mechanisms remains a challenge. In this work, density functional theory calculations are performed to investigate the adsorption and catalytic decomposition of NH₃ molecule on a pristine silicon-carbide nanotube (SiCNT) surface. The adsorption energy of a possible stable configuration and the activation energies for elementary reactions involved are obtained in the present study. It is found that ammonia experiences a chemisorption interaction with the SiCNT surface, with a significant alter in its structure with respect to the gas-phase molecule. Subsequently, the coadsorption of two ammonia molecules on the SiCNT surface is studied and the catalytic dehydrogenation reactions are considered. The catalytic activity of SiCNT surface in the decomposition reaction of NH₃ molecules is slightly altered due to locally adsorbed NH₃. The reaction energies and the activation barriers obtained suggest that for the decomposition of ammonia molecules into N₂H₂, the rate-determining step is the NH₂ → NH + H reaction. As a result, the NH₂ is the dominant surface species after the SiCNT surface is exposed to NH₃.