IR nanospectroscopy mapping of facet-dependent sulfur poisoning and thermal regeneration on platinum nanocrystals

Abstract

Sulfur poisoning critically limits the activity and durability of Pt catalysts, yet the nanoscale structure–reactivity relationships that govern sulfate adsorption and its thermal desorption remain poorly resolved. Using infrared nanospectroscopy, we directly map the spatial distribution, adsorption geometry, and temperature-dependent evolution of sulfate species on individual Pt nanocrystals (NCs) with well-defined facets. At room temperature, SO_x species preferentially accumulate at defect-rich inter-facet regions, edges, and open Pt(100)-like facets, in which bidentate adsorption dominates. Flat Pt(111) terraces exhibit lower SO_x coverage and a larger contribution from tridentate species. Mild annealing (50–200 °C) induces selective desorption from undercoordinated sites and drives a structural transition from bidentate to tridentate coordination as species migrate toward highly coordinated terrace regions. At 300 °C, most sulfate species desorb from edges and side facets, whereas thermally robust tridentate species persist at the NC interior. These results provide a facet-resolved picture of sulfur adsorption and regeneration pathways, revealing how local surface structure dictates the stability and thermal evolution of poisoning species on Pt catalysts.