Observation of Plasma-Catalyst Interactions: Determining the Role of Plasma Conditions and Catalyst Support

When working with both thermal and non-thermal plasma stimulated systems, it is important to note that catalytic materials are dynamic in nature and require careful selection. In this study, hydrogen plasma was utilized to induce strong metal support interaction (SMSI) on a Pt/Nb₂O₅ catalyst, causing a reduced phase of Nb₂O₅ to diffuse onto Pt nanoparticles (NPs) forming an overlayer on the NPs surfaces. Additionally, Nb was able to diffuse into the Pt lattice causing the lattice to expand increasing the d-spacing of Pt facets. This resulted in reduced accessibility of CO to the Pt sites, and loss of accessibility to bridged CO Pt sites. Several techniques, including HRTEM imaging, EDX mapping, in-situ IR spectroscopy with CO probe molecule, and CO titration, confirmed the presence of SMSI. XRD analysis confirmed Nb diffusion into the Pt lattice, which was also supported by EDX mapping. The average Pt particle size was not significantly affected by hydrogen plasma treatment but increased slightly by thermal treatment. From in-situ IR studies it was found that bridged Pt sites were completely removed via hydrogen plasma treatment and were not recovered by subsequent oxygen plasma treatment whereas linear sites were partially recovered. The potential for site selectivity presents a powerful tool for reaction systems with structure sensitive pathways.