Effect of Single-Layer MoS₂ on the Geometry, Electronic Structure, and Reactivity of Transition Metal Nanoparticles

We present results of <i>ab initio</i> density functional theory (DFT) based calculations of the geometry, electronic structure, and reactivity of subnanometer-sized (29-atom) transition metal nanoparticles (NPs) (Cu₂₉, Ag₂₉, and Au₂₉) supported on single-layer MoS₂. As compared to its pristine form, defect-laden MoS₂ (with a S vacancy row) has relatively larger effect on the above properties of the NPs. The NPs bind more strongly on defect-laden than on pristine MoS₂ (in the order Cu₂₉ > Ag₂₉ > Au₂₉), confirming the important role of vacancies in stabilizing the NPs on the support. The presence of vacancies also leads to an increase in charge transfer from the NPs to MoS₂ (with the same elemental trend as for their binding energy) and to a shift of the d-band center of the NPs further toward the Fermi level, in turn influencing their propensity toward chemical activity. We examine the adsorption and dissociation of O₂ as the prototype reactions and find that there is no barrier for O₂ to adsorb on top of an atom at the NP apex, where the frontier orbitals are localized, and that the dissociation channel proceeds through a chemisorbed state. The presence of the support leads to increase in the number of sites at which O₂ can adsorb with similar binding energy (<0.1 eV difference). Interestingly, energy barriers for both dissociation and recombination of O₂, when adsorbing at the NP apex, increase in the presence of the MoS₂ support. However, since the increase in the barrier for recombination is much larger than for dissociation, the latter should be more favored. In particular, for defect-laden MoS₂ supported Au₂₉ the recombination faces a barrier of 1.36 eV whereas the dissociation does 0.5 eV, implying that the defect-laden support may significantly improve the catalytic performance of Au₂₉ toward oxidation reaction