Insights from Modulation-Excitation Spectroscopy into the Role of Pt Geometrical Sites in the WGS Reaction

Modulation-excitation spectroscopy coupled to diffuse reflectance infrared Fourier transform spectroscopy (ME-DRIFTS) was explored in this work to obtain valuable insights into the structure-reactivity relations in nanostructured Pt catalysts for the water-gas shift (WGS) reaction. By using model Pt catalytic systems composed of colloidal Pt nanoparticles (NPs) deposited on CeO₂ (i.e., reducible) and SiO₂ (i.e., nonreducible) supports, it was possible to probe distinct Pt active sites and correlate them to the reaction intermediates and pathways. The analysis revealed that PtNPs/SiO₂ favored the participation of well-coordinated (WC) and under-coordinated (UC) Pt sites in the reaction mechanism. In contrast, on PtNPs/CeO₂/SiO₂, the additional involvement of highly under-coordinated (HUC) Pt sites was also observed. Additionally, both fast and slow formate species were identified as active intermediates on the surface of the PtNPs/CeO₂/SiO₂ catalyst by ME-DRIFTS. More importantly, the faster reaction pathway was correlated to HUC and UC Pt sites, while the slower route was associated with WC Pt sites. Carbonates, on the other hand, were spectators. ME-DRIFTS experimentally demonstrate differences in the participation of Pt active sites according to the support, the involvement of interfacial sites, and the correlation of Pt local coordination to the surface intermediates in the WGS reaction.