Selective Hydrogenation of Propyne to Propene Promoted by Synergistic Effect of Surface Oxygen Vacancies and Hydride Species on Ceria

Thehigh activity and selectivity of ceria in selective hydrogenationof alkynes have attracted much attention. However, the high operatingtemperature and the high H-2/alkyne ratios required hamperthe practical application of ceria catalysts, and the complex H-2-ceria interaction as well as the ambiguous role of oxygenvacancies (O-v) prevent the further reactivity optimizationof ceria-based catalysts. To elucidate the role of O-v sitesand hydride (Ce-H) species that can easily generate on ceriain the selective hydrogenation of propyne reaction, we constructedtwo model surfaces: CeO2(111) and CeO2-x (111)-H with H- ions preoccupiedin almost all of the O-v sites. From the catalytic performancemeasurements, both surfaces exhibit high selectivity for propene,while the CeO2-x (111)-Hsurface shows a propene production three times higher than CeO2(111). Using in situ ambient pressure X-ray photoelectronspectroscopy, we studied the formation and evolution of O-v, Ce-H, and carbon-containing species on the two surfacesduring the hydrogenation reaction and correlated with their catalyticperformance. Assisted by density functional theory calculations, wefound that surface-exposed O-v sites are required for theformation of Ce-H species and the dissociative adsorption ofpropyne. Meanwhile, Ce-H species possess high hydrogenationactivity and can help weaken the adsorption of CH3CCH2* to form gas-phase propene. The propene production and selectivityare optimal only in the coexistence of O-v sites and Ce-Hspecies with sufficient concentration. Our study has thus demonstratedthe crucial synergetic roles of O-v sites and hydride specieson ceria for the selective hydrogenation reaction.

Automated summary

The roles of oxygenvacancies (O-v) and hydride (Ce-H) species in ceria catalysts for selective hydrogenation of alkynes have been investigated. The presence of O-v sites is necessary for the formation of Ce-H species and the dissociative adsorption of propyne. The coexistence of O-v sites and Ce-H species with sufficient concentration is crucial for optimal propene production and selectivity.