Atomistic Picture of the Catalytic Activity of Platinum Nanoparticles through Coherent Diffraction Imaging and Reactive Molecular Dynamics Simulations

Abstract

Platinum nanoparticles are among the most widely used catalysts due to their high chemical stability, surface reactivity and electron transfer rate. They find applications in chemical and bio-sensing, fuel cells, photocatalysis and methanol formation. Elucidating the catalytic mechanism under in-situ conditions is vital to the structural and chemical design of more efficient catalysts that are urgently needed to meet the energy needs of today. Coherent X-ray diffraction imaging (CDI) is a powerful technique for operando characterization with the ability to provide evolving snapshots of defect structure, lattice dynamics and structural evolution at ~10 nm resolution, while reactive molecular dynamics (MD) simulations provide atomistic details of lattice dynamics, bond breakage and formation as well as reaction kinetics at experimentally inaccessible length and time scales. We present results from combined CDI experiments and reactive MD simulations on the atomistic processes underlying methanol formation from methane on Pt nanoparticles. We observe the preferential oxidation of edge and corner sites on the Pt nanoparticle in an O2 rich atmosphere, which when followed by the introduction of methane, leads to the binding of CH4 to disassociated O atoms. Fig. 1 a) shows the partially oxidized Pt particle in a methane atmosphere. O2 on surface sites is not seen to disassociate while oxygen at corner and edge sites disassociates due to the higher site reactivity at edges and corners. Fig 1. b)-c) shows a close-up of the surface during the binding of CH4 to the disassociated oxygen. Finally, the mechanism predicted by the reactive MD simulations is validated through CDI experiments, with the observation of local lattice strains at edge and corner sites, which arise due to the binding of O2 and CH4 molecules. Figure 1