(127d) High CO Oxidation Activity on Pt Single Atoms and Clusters Supported on MgAl2O4

The catalytic oxidation of CO on Pt catalysts has practical importance in automotive catalysis and also serves as a probe reaction for fundamental understanding of heterogeneous catalysis. In this study, Pt single-atoms and clusters supported on MgAl₂O₄ were prepared by strong electrostatic adsorption (SEA) at constant pH. The synthesis conditions and pretreatment conditions for achieving either single atoms or clusters will be presented. The catalysts were quantitatively characterized by in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) with adsorbed-CO as probe molecule to provide information on adsorption strength and geometry. At present, supported Pt nanoparticles have been well studied for CO oxidation, however the mechanism on small clusters and single atoms is still under debate. During CO oxidation, the surface of Pt nanoparticles is poisoned by a high coverage of CO and the reaction shows reaction orders of -1 in CO and 1 in O₂ (rate = k[O₂]¹[CO]^-1). Here, we report that Pt single atoms and clusters present a very different kinetic behavior from nanoparticles under the same reaction condition. On single atoms, the reaction order is 0.8 in CO but 0 in O₂ (rate = k[O₂]⁰[CO]^0.8). More surprisingly, Pt clusters show positive reaction orders in both CO and O₂ which we hypothesize a result of non-competitive adsorption of CO and O₂ on adjacent sites. Additionally, Pt single atoms show a much higher activity (~25x) and lower apparent activation energy (40 (kJ/mol)) than nanoparticles (80 (kJ/mol)). Using in-situ DRIFTS, we will compare the most stable reaction intermediates on Pt single atoms and clusters and discuss the possible reaction mechanisms leading to the observed reaction orders. The high activity and lack of poisoning by CO make Pt single atoms and clusters ideal candidates for designing low temperature oxidation catalysts.