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Although hexagonal boron nitride (h‐BN) has recently been identified as a highly efficient catalyst for the oxidative dehydrogenation of propane (ODHP) reaction, the reaction mechanisms, especially regarding radical chemistry of this system, remain elusive. Now, the first direct experimental evidence of gas‐phase methyl radicals (CH3.) in the ODHP reaction over boron‐based catalysts is achieved by using online synchrotron vacuum ultraviolet photoionization mass spectroscopy (SVUV‐PIMS), which uncovers the existence of gas‐phase radical pathways. Combined with density functional theory (DFT) calculations, the results demonstrate that propene is mainly generated on the catalyst surface from the C−H activation of propane, while C2 and C1 products can be formed via both surface‐mediated and gas‐phase pathways. These observations provide new insights towards understanding the ODHP reaction mechanisms over boron‐based catalysts. [ABSTRACT FROM AUTHOR]

A series of NbO x /CeO 2 -rod catalysts were synthesized and employed as catalysts for oxidative dehydrogenation of propane (ODHP) reaction. Nb–CeO 2 interaction and reaction mechanisms were studied with synchrotron-radiation-based techniques. Synchrotron radiation photoemission spectroscopy and resonant photoemission spectroscopy results demonstrate that the Nb 5+ precursor preferentially interact with surface oxygen vacancies on CeO 2 rods. Surface redox reactions occur between Nb 5+ and Ce 3+ (surface oxygen vacancy) to produce Nb 4+ and Ce 4+ , resulting in decreased surface oxygen vacancy concentrations on CeO 2 rods. CeO 2 rods are active in catalyzing propane combustion at low temperatures (below 400 °C) via the MvK mechanism. The loading of NbO x suppresses the surface reducibility of CeO 2 rods, leading to decreased activity but greatly enhanced propene selectivity. The ODHP reaction catalyzed by CeO 2 rods and NbO x /CeO 2 -rods catalysts at high temperatures (above 450 °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 CeO 2 -based catalysts for ODHP reaction. [ABSTRACT FROM AUTHOR]

Titelbild: Radical Chemistry and Reaction Mechanisms of Propane Oxidative Dehydrogenation over Hexagonal Boron Nitride Catalysts (Angew. Keywords: hexagonal boron nitride; mass spectrometry; methyl radicals; oxidative dehydrogenation; reaction pathways EN hexagonal boron nitride mass spectrometry methyl radicals oxidative dehydrogenation reaction pathways 8045 8045 1 05/13/20 20200518 NES 200518 B Hexagonales Bornitrid b ist ein vielversprechender Katalysator für die oxidative Dehydrierung (ODH) von Alkanen zu Olefinen mit hoher Selektivität und Aktivität. Hexagonal boron nitride, mass spectrometry, methyl radicals, oxidative dehydrogenation, reaction pathways. [Extracted from the article]