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

We present results of ab initio density functional theory (DFT) based calculations of the geometry, electronic structure, and reactivity of subnanometer-sized (29 atom) transition metal nanoparticles (NPs) (Cu-29, Ag-29, and Au-29) 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 Cu-29 > Ag-29 > Au-29), 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 O-2 as the prototype reactions and find that there is no barrier for O-2 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 O-2 can adsorb with similar binding energy (<0.1 eV difference). Interestingly, energy barriers for both dissociation and recombination of O-2, 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 Au-29 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 Au-29 toward oxidation reaction.