The high activity and selectivity of ceria in selective hydrogenation of alkynes have attracted much attention. However, the high operating temperature and the high H 2 /alkyne ratios required hamper the practical application of ceria catalysts, and the complex H 2ceria interaction as well as the ambiguous role of oxygen vacancies (O v ) prevent the further reactivity optimization of ceria-based catalysts. To elucidate the role of O v sites and hydride (Ce−H) species that can easily generate on ceria in the selective hydrogenation of propyne reaction, we constructed two model surfaces: CeO 2 (111) and CeO 2−x (111)−H with H − ions preoccupied in almost all of the O v sites. From the catalytic performance measurements, both surfaces exhibit high selectivity for propene, while the CeO 2−x (111)−H surface shows a propene production three times higher than CeO 2 (111). Using in situ ambient pressure X-ray photoelectron spectroscopy, we studied the formation and evolution of O v , Ce−H, and carbon-containing species on the two surfaces during the hydrogenation reaction and correlated with their catalytic performance. Assisted by density functional theory calculations, we found that surfaceexposed O v sites are required for the formation of Ce−H species and the dissociative adsorption of propyne. Meanwhile, Ce−H species possess high hydrogenation activity and can help weaken the adsorption of CH 3 CCH 2 * to form gas-phase propene. The propene production and selectivity are optimal only in the coexistence of O v sites and Ce−H species with sufficient concentration. Our study has thus demonstrated the crucial synergetic roles of O v sites and hydride species on ceria for the selective hydrogenation reaction.

Yttrium-doped barium zirconate (BZY) has been considered as a potential electrolyte candidate for intermediate-tolow temperature protonic ceramic fuel cell applications. However, the transport properties of BZY are often limited by the formation of highly resistive space charge zones at lattice discontinuities, such as lattice defects and surfaces. Unlike lattice defects, how to reduce the space charge effects at surfaces remains less explored. In this regard, surface defect engineering can be a meaningful way to regulate the proton transport of BZY by tailoring the space charge distribution close to the surface. Here, the Ar and/or O 2 plasma was used to prepare BZY thin films with different levels of surface defects. The results of electrochemical impedance spectroscopy and detailed structural characterization suggest that the plasma treatment is effective in improving the proton conductivities and lowering the activation energy of BZY thin films through the generation of negatively charged barium vacancy defects and the enrichment of yttrium dopants on the surface.