The nature of thermal hysteresis during CO oxidation over Pt catalysts

Abstract The origins of activity hysteresis during heating and cooling stage in CO oxidation are still in heavy debate. Pt-CeO2 and Pt-Al2O3 were observed to display completely different hysteresis phenomena; Pt-Al2O3 exhibited normal behavior while Pt-CeO2 showed inverse hysteresis. The affecting issues of initial Pt nanoparticle size, mass and heat transfer limitations, and local overheating were all excluded for both catalysts. By using operando and in situ characterization technologies, kinetics analyses, density functional theory (DFT) calculations as well as ab initio molecular dynamics (AIMD) simulations, the nature of thermal hysteresis was revealed. The different interactions between the metal and supports induced the different dynamic oxidation behaviors and morphology evolutions of Pt during the heating and cooling reactions are the root causes. Pt in Pt-CeO2 suffered irreversible oxidation mainly raised by reverse oxygen spillover and formed PtxOy ensemble which displays poorer activity. In contrast, Pt in Pt-Al2O3 underwent structural collapse and dispersion on Al2O3 surface at high temperature, and oxygen spillover to support preserved the initial chemical state of Pt.