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Cu-Enhanced Surface Defects and Lattice Mobility of Pr-CeO2 Mixed Oxides

D’Angelo, Anita M., Wu, Zili, Overbury, Steven H., Chaffee, Alan L.
The Journal of Physical Chemistry C 2016 v.120 no.49 pp. 27996-28008
adsorption, carbon dioxide, carbon monoxide, cations, ceric oxide, cupric oxide, dehydrogenation, desorption, energy-dispersive X-ray analysis, formates, hydrogen, methanol, oxidation, oxygen, scanning electron microscopy, spectroscopy, temperature
The surface properties of CeO₂, Pr-CeO₂, and 5% and 15% Cu-doped Pr-CeO₂ were investigated using methanol as a probe molecule through adsorption and desorption studies carried out using in situ DRIFTS. It was revealed that the surfaces of the 5% and 15% Cu materials were dominated by reduced cations/vacancies and that the 15% Cu material contained the highest concentration of these active species. The high oxygen storage capacity (OSC) of the 15% Cu material, as determined using TGA, reflects the available vacant sites for oxygen adsorption. Formates were formed on all materials, with those formed on the Cu-doped materials present at temperatures as low as 25 °C, hence showing their superior reactivity toward methoxy oxidation. During formate dehydrogenation, H₂, CO, CO₂, and H₂O evolved as the surface cations were simultaneously reduced. It was also observed that, for the Cu-containing materials, H₂ was not formed and the high surface mobility determined through isotopic exchange simultaneously generated CO and CO₂. The exhibited high surface mobility, surface vacancies, and OSC of the 15% Cu material can be attributed to the formation of a secondary copper oxide phase observed using SEM-EDX spectroscopy. These results highlight the importance of surface defects in contrast to bulk defects.