(6f) Carbon Monoxide Oxidation Cycles on (doped)Ceria Single Atom Catalysts

Single transition metal (TM) atoms supported on reducible oxides can display emergent catalytic behavior through tuning the collective redox behavior. Carbon monoxide oxidation serves as a probe reaction to characterize the variable redox states involved in the catalytic cycle on (doped) ceria-supported single atom catalysts (SACs). Comparing Pd, Ni, and Pt single-atoms, experimental kinetic testing and density functional theory (DFT)-guided microkinetic modeling (MKM) are used to determine the different formal oxidation states experienced by the late TM during CO oxidation. Ni oscillates through Ni⁰, Ni²⁺, and Ni⁴⁺ oxidation states during CO oxidation, whereas Pt only experiences Pt⁰ and Pt²⁺ while also using ceria lattice oxygen during its CO oxidation catalytic cycle. Pd experience the full range of oxidation states and utilizes ceria lattice oxygen, leading to a unique 1.3 reaction order for CO oxidation under lean oxidation conditions. DFT and CO-DRIFT spectroscopy are used to corroborate the accessible oxidation states. Doping of the ceria with La and Zr cations is further used to manipulate the accessible oxidation states. Collectively, this work illustrates the emergent redox behavior of the TM SAC/(doped)ceria systems and using the integrated experimental kinetics-DRIFTS-DFT-MKM approaches to detail the redox cycles on these catalysts.