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.