Pulsed-reactant in situ studies of ceria/CuO catalysts using simultaneous XRD, PDF and DRIFTS measurements

• Redox of ceria/CuO determined with simultaneous XRD/DRIFTS pulsed gas techniques.
• During oxidation of reduced ceria on Cu0, Ce3+ ? Ce4+ was seen before Cu0 ? Cu+.
• In situ CO DRIFTS indicates presence of Cu+ when XRD indicates that only Cu0 exists.
• Carbonate formation and decomposition was observed with DRIFTS and MS.
• In situ pair distribution function measures structural features including oxygen vacancies.

The transient reduction–oxidation (redox) response of a ceria/CuO catalyst has been studied with pulsed gas techniques. The experimental setup allowed for simultaneous measurement of X-ray diffraction (XRD) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) coupled to mass spectrometric (MS) analysis of reactants and products. The DRIFTS showed the bonding of CO to CuxO and formation of carbonates on ceria. The CO stretch signal was observed in the DRIFTS as the Cu2O phase appeared in the simultaneous XRD pattern. This signal was still observed when XRD indicated that the Cu2O phase had converted to Cu(0). This unexpected result could arise from an amorphous surface of Cu2O which could not be detected by XRD or because the surface sensitivity of the DRIFTS technique is much higher than the surface sensitivity of the XRD technique. Time-resolved pair distribution function (PDF) analysis was useful for tracking the appearance or disappearance of key structural features (CuO, CeO, CeCe, and CuCu) during the pulse experiments. The in situ PDF analysis provided new evidence that oxygen vacancies in the ceria could be detected with XRD data.