The Role of O Vacancies and Presence of Hydridic H in the Alkyne Semi-Hydrogenation Reaction on CeO2(111)

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

Orlando

Conferencia; 257th ACS National Meeting, Orlando, FL; 2019

AMERICAN CHEMICAL SOCIETY

Ceria (CeO2) was recently identified as a promising catalyst in the selective hydrogenation of alkynes to alkenes. This reaction occurs primarily on highly dispersed metal catalysts, such as Pd, but rarely onoxide surfaces. The origin of the outstanding activity and selectivity observed on CeO 2 remains unclear. In this work, we show that one key aspect of the hydrogenation reaction ? the interaction of H2 with theoxide ? depends strongly on the presence of O vacancies within CeO2. By infrared reflection absorption spectroscopy (IRAS) on well-ordered CeO 2 (111) thin films and density functional theory (DFT)calculations, we show that the preferred heterolytic dissociation of molecular hydrogen on CeO2(111) requires H2 pressures in the mbar regime. Hydrogen depth profiling with nuclear reaction analysis (NRA) indicates that H species stay on the surface of stoichiometric CeO 2 (111) films, whereas H incorporates as a volatile species into the volume of partially reduced CeO 2-x (111) thin films. Complementary DFT calculations suggest that oxygen vacancies facilitate H incorporation below the surface and that they are the key to the stabilization of hydridic H species in the volume of reduced ceria. Finally, results for activation of molecules are presented, showing the effect of O vacancies and the presence of H in thesubsurface/bulk region.