(669e) Site-Specific IR Spectroscopy for Analyzing Pt Structure Sensitivity from Single Atoms to Fully Coordinated Surfaces
Significant efforts have been focused on understanding the structure sensitivity of Pt catalysts from the limit of well-coordinated Pt atoms in terraces on large particles, down to single Pt atoms coordinated directly to oxide supports for the CO oxidation and water gas shift reactions. Often X-ray based spectroscopy and transmission electron microscopy provide ensemble measurements of structural features of supported Pt catalysts that are used to correlate the reactivity of various active sites on different supports. Recently, it has been demonstrated that site-specific CO probe molecule FTIR spectroscopy is a powerful approach to identify the reactivity of various Pt active site geometries on supported Pt catalysts, overcoming shortcomings of characterization techniques that rely on ensemble measurements. However, the use of FTIR to study the reactivity of various Pt active sites requires unequivocal assignment of spectral features, which can vary as a function of support composition. Here we will present results of rigorous FTIR-based analysis of molecular adsorption, temperature programmed studies, and oxidation reactions for Pt catalysts on various oxide supports prepared through conventional dry impregnation and strong electrostatic adsorption (SEA) wet impregnation techniques with weight loadings ranging from ultra-low to more typical (0.05 - 2%). Through these approaches we are able to directly differentiate the reactivity of various Pt active sites, ranging across Pt single atoms, well-coordinated Pt metal sites, and Pt oxide clusters while simultaneously exploring the role of the support in modifying the reactivity of these active sites.