Bridging the Pressure and Materials Gap in Heterogeneous Catalysis: A Combined UHV, In Situ, and Operando Study Using Infrared Spectroscopy

The interactions of gas molecules with metal oxides usedas catalystsor support materials in heterogeneous catalysis are highly intriguing.It is of great importance to gain detailed insight into the complexand often dynamic behavior of oxide particles under operando conditions.In this study, the understanding of CO interactions with cerium oxidesurfaces is advanced by bridging the so-called materials and pressuregaps. This is accomplished by studying the influence of differenttypes of materials, pressures, and temperatures by using differentinfrared spectroscopies as the primary investigation tool. Whereaslow-temperature CO adsorption (<80 K) on various well-defined CeO2 single crystal surfaces yields distinct vibrational bandsthat can be assigned to different adsorption sites on fully stoichiometricand also on reduced surfaces using validated ab initio calculations,strong gas-phase contributions turn the interpretation of resultsobtained for powders under operando conditions into a major challenge.By using a combination of UHV-IRRAS, in situ transmission infraredspectroscopy, and operando DRIFTS measurements, the reference dataobtained for single-crystal surfaces under UHV conditions could beused to assign the features observed in spectra obtained for powdermaterials. In the next step, the different CO vibrational bands wereused to monitor surface structural changes occurring at elevated pressuresand temperatures. An increase in the concentration of Ce3+ species as a result of CO-induced reduction could be directly demonstratedeven at low (300 K) temperatures. Our results demonstrate importantprogress toward the noninvasive, nondestructive characterization ofreal catalysts under operando conditions.