(52e) Spectroscopic Signatures and Reactivity of CO Adsorbed to Atomically Dispersed Pt Atoms, Pt Oxide Clusters, and Metallic Pt Clusters on Anatase TiO2

DeRita, L. - Presenter, University of Delaware
Christopher, P., University of California, Santa Barbara
Dai, S., University of California, Irvine
Due to their broad application in industrial chemical conversion processes and low abundance in the earths crust, significant efforts have been dedicated to developing efficient approaches for utilizing Pt-group metals as catalysts. The primary approach for optimizing Pt-group metal utilization in catalysis is synthesizing metal active sites that exhibit 100% dispersion - all metal atoms exposed to catalytic environment. However, there are significant challenges associated with the controlled synthesis and structural characterization of perfectly dispersed (this could be single metal atoms on the support, or sub-nanometer metal clusters) Pt-group metal species, which has led to a variety of inconsistent conclusions about their reactivity.

In this talk we will discuss a rigorous comparison of the reactivity of single Pt atoms, sub-nanometer PtOx clusters, and sub-nanometer Pt0 clusters supported on anatase TiO2 for CO adsorption and catalytic CO oxidation. Control over the synthesized structure was achieved through the use of strong electrostatic adsorption synthesis protocols on extremely high surface area TiO2 (290 m2/g) at dilute synthesis conditions and varied Pt weight loadings (0.025-1%), combined with controlled oxidative or reductive pre-treatments. Using correlated IR spectroscopy and scanning transmission electron microscopy (STEM) we identify characteristics signatures of CO bound to cationic single Pt atoms, PtOx clusters and Pt0 clusters. Interestingly, it was identified that while single Pt atoms on TiO2 and PtOx clusters both exhibit similar electronic and local coordinative environments, they exhibit drastic variation in CO adsorption energies, with single Pt atoms adsorbing CO weakly and PtOx clusters adsorbing CO even more strongly than Pt0 clusters. Using the correlated STEM-IR characterization we compare the CO oxidation reactivity of single Pt atoms and metallic clusters under conditions of strict kinetic control where we find that both types of active sites exhibit an identical reaction mechanism, while single Pt atoms are more active on Pt mass and Pt surface area bases. We discuss the ramification of these findings in the context of designing stable catalysts with optimal Pt-group metal utilization.