(689a) Characterization of Isolated Pt Atoms on Anatase TiO2

Supported single atom catalysts (SACs) have gained substantial interest in heterogeneous catalytic reactions. Synthesis of SACs has been challenging due to the aggregation of metals upon initial deposition on a support when subjected to subsequent thermal treatment or reaction. The strong electrostatic adsorption method is one of the most promising techniques to synthesize isolated single atoms on supports. Unfortunately, it only works well when the amount of metal loading is reduced to an extremely low level, making characterization of isolated single atoms challenging.

In this study, we have employed comprehensive characterization methods to compare isolated Pt atoms and nanoparticles anchored on anatase TiO₂. Aberration-corrected HAADF-STEM images clearly reveal isolated Pt single atoms dispersed on the TiO₂ surface. We used FTIR to monitor the changes in vibrational frequency of the CO adsorbed on Pt SACs and Pt nanoparticles. Our in situ EXAFS results also provide evidence of SACs by monitoring the Pt-Pt coordination to determine the spatial location of isolated Pt atoms and Pt nanoparticles. We further conducted in situ near ambient pressure XPS that demonstrated that the Pt single atoms are stable at 250 °C upon exposure to 1.5 Torr H₂ due to the full coordination of Pt with O on TiO₂; in contrast, Pt nanoparticles were progressively reduced under the same condition. We provide computational insights into the stability of the catalyst.