First-Principles Investigation of Ammonia Adsorption and N-H Activation on W-B Nanoclusters
Tungsten-boride nanoclusters are nanoscale systems of potential catalytic interest, but their structural stability and reactivity remain poorly understood. We combine evolutionary structure prediction with density functional theory to investigate W$_m$B$_n$ nanoclusters containing up to 43 atoms. The calculated stability descriptors reveal a strongly non-monotonic landscape, with several compositions locally favoured relative to neighbouring stoichiometries within the explored isolated-cluster model. Molecular NH$_3$ adsorption was examined at W-top and accessible B-top sites, with adsorption energies ranging from $-1.78$ to $-0.54$ eV on W sites and from $-1.54$ to $+0.62$ eV on B sites. H adsorption at W-top and B-top sites spans $-1.47$ to $+0.67$ eV, indicating pronounced composition- and site-dependence. CI-NEB calculations show that the first N-H bond-cleavage barrier is strongly pathway-dependent. These results characterize the initial activation of NH$_3$ on W-B nanoclusters and provide an atomistic basis for further investigation of the complete ammonia-decomposition mechanism.