Toward an Understanding of Selective Alkyne Hydrogenation on Ceria: On the Impact of O Vacancies on H 2 Interaction with CeO 2 (111)

WENG, XUEFEI; KROPP, THOMAS; WILDE, MARKUS; FREUND, HANS-JOACHIM; CALAZA, FLORENCIA; PAIER, JOACHIM; FUKUTANI, KATSUYUKI; WERNER, KRISTIN; STERRER, MARTIN; SAUER, JOACHIM; SHAIKHUTDINOV, SHAMIL

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY

AMER CHEMICAL SOC

Lugar: Washington; Año: 2017 vol. 139 p. 17608 - 17616

0002-7863

Ceria (CeO2) has recently been found to be a promising catalyst in theselective hydrogenation of alkynes to alkenes. This reaction occurs primarily on highlydispersed metal catalysts, but rarely on oxide surfaces. The origin of the outstandingactivity and selectivity observed on CeO2 remains unclear. In this work, we show thatone key aspect of the hydrogenation reactionthe interaction of hydrogen with theoxidedepends strongly on the presence of O vacancies within CeO2. Through infraredreflection absorption spectroscopy on well-ordered CeO2(111) thin films and densityfunctional theory (DFT) calculations, we show that the preferred heterolyticdissociation of molecular hydrogen on CeO2(111) requires H2 pressures in the mbarregime. Hydrogen depth profiling with nuclear reaction analysis indicates that H speciesstay on the surface of stoichiometric CeO2(111) films, whereas H incorporates as avolatile species into the volume of partially reduced CeO2−x(111) thin films (x ∼ 1.8−1.9). Complementary DFT calculations demonstrate that oxygen vacancies facilitate H incorporation below the surface and that they are the key to the stabilization of hydridicH species in the volume of reduced ceria.