The role of lattice oxygen in CO oxidation over Ce18O2-based catalysts revealed under operando conditions

Ceria-based materials are today the most prominently used catalyst supports for CO oxidation and NOx reduction in three-way catalytic converters (TWCs) worldwide. Acting as oxygen buffer compounds, the underlying reaction mechanism and especially the distinct role of surface and lattice oxygen for catalytic reactions are still under debate. This is partially related to the complexity of the real CeO2 surface containing important amounts of water and carbonates. Combining TG-MS, Raman spectroscopic experiments and isotope labeling pulse temperature programmed oxidation reaction (ILPOR), coupled with mass spectrometric analysis of O-18-doped ceria, we explored here the oxygen uptake/release behavior under operando conditions, together with the catalytic activity related to surface and/or lattice oxygen mobility and exchange. Specific changes in the lattice dynamics induced by (18)/O-16 isotope exchange were analyzed by Raman spectroscopy, allowing the temperature-dependent onset of lattice oxygen mobility and isotope exchange behavior to be studied selectively. For Pt-supported nano-ceria, we evidenced high catalytic performance for CO oxidation, activated slightly above ambient conditions without significant lattice oxygen participation. The distinct role of surface and lattice oxygen in the catalytic reaction of ceria catalysts is discussed as a function of temperature, grain size, Gd doping and Pt impregnation.