NbOx/CeO2-rods catalysts for oxidative dehydrogenation of propane: Nb-CeO2 interaction and reaction mechanism

A series of NbOx/CeO2-rod catalysts were synthesized and employed as catalysts for oxidative dehydrogenation of propane (ODHP) reaction. Nb-CeO2 interaction and reaction mechanisms were studied with synchrotron-radiation-based techniques. Synchrotron radiation photoemission spectroscopy and resonant photoemission spectroscopy results demonstrate that the Nb5+ precursor preferentially interact with surface oxygen vacancies on CeO2 rods. Surface redox reactions occur between Nb5+ and Ce3+ (surface oxygen vacancy) to produce Nb4+ and Ce4+, resulting in decreased surface oxygen vacancy concentrations on CeO2 rods. CeO2 rods are active in catalyzing propane combustion at low temperatures (below 400 degrees C) via the MvK mechanism. The loading of NbOx suppresses the surface reducibility of CeO2 rods, leading to decreased activity but greatly enhanced propene selectivity. The ODHP reaction catalyzed by CeO2 rods and NbOx/CeO2-rods catalysts at high temperatures (above 450 degrees C) involves the radical mechanism, in which the gas-phase propyl radical was observed with synchrotron radiation VUV photoionization time-of-flight mass spectroscopy. These results greatly deepen the fundamental understanding of CeO2-based catalysts for ODHP reaction. (C) 2016 Elsevier Inc. All rights reserved.