Boron‐containing materials, and in particular boron nitride, have recently been identified as highly selective catalysts for the oxidative dehydrogenation of alkanes such as propane. To date, no mechanism exists that can explain both the unprecedented selectivity, the observed surface oxyfunctionalization, and the peculiar kinetic features of this reaction. We combine catalytic activity measurements with quantum chemical calculations to put forward a bold new hypothesis. We argue that the remarkable product distribution can be rationalized by a combination of surface‐mediated formation of radicals over metastable sites, and their sequential propagation in the gas phase. Based on known radical propagation steps, we quantitatively describe the oxygen pressure‐dependent relative formation of the main product propylene and by‐product ethylene. Free radical intermediates most likely differentiate this catalytic system from less selective vanadium‐based catalysts.

In this contribution we report on the oxidative dehydrogenation (ODH) activity of silica-supported boron oxide prepared via incipient wetness impregnation. Characterization of pristine and spent catalysts with infrared, Raman, and solid-state NMR spectroscopy reveals the presence of both isolated and aggregated oxidized boron sites. The results of these investigations, in combination with our earlier work on bulk boron-containing ODH catalysts (e.g., h-BN, metal borides, and elemental boron), bolster the hypothesis that oxidized boron species in situ formed on the surface of these materials are responsible for the exceptional catalytic behavior. We anticipate that investigation of supported boron materials can provide insight into the structural characteristics required for selective boron-containing ODH catalysts. Disciplines DisciplinesPhysical Chemistry Comments CommentsAbstract. In this contribution we report on the oxidative dehydrogenation (ODH) activity of silica-supported boron oxide prepared via incipient wetness impregnation. Characterization of pristine and spent catalysts with infrared, Raman, and solid-state NMR spectroscopy reveals the presence of both isolated and aggregated oxidized boron sites. The results of these investigations, in combination with our earlier work on bulk boron-containing ODH catalysts (e.g., h-BN, metal borides, and elemental boron), give direct evidence that oxidized boron species formed in situ on the surface of these materials are responsible for the exceptional catalytic behavior. We anticipate that investigation of supported boron materials can provide insight into the structural characteristics required for selective boron-containing ODH catalysts.

Bulk boron materials, such as hexagonal boron nitride (h‐BN), are highly selective catalysts for the oxidative dehydrogenation of propane (ODHP). Previous attempts to improve the productivity of these systems involved the immobilization of boron on silica and resulted in less selective catalysts. Here, we report that acid‐treated, activated carbon‐supported boron prepared via incipient wetness impregnation with boric acid (B/OAC) exhibits equal propylene selectivity and improved productivity (kgpropylene kgcat−1 hr−1) as compared to h‐BN. Characterization of the fresh and spent catalysts with infrared, Raman, X‐ray photoelectron, and solid‐state NMR spectroscopies reveals the presence of oxidized/hydrolyzed boron that is clustered on the surface of the support.

Boron‐containing materials, and in particular boron nitride, have recently been identified as highly selective catalysts for the oxidative dehydrogenation of alkanes such as propane. To date, no mechanism exists that can explain both the unprecedented selectivity, the observed surface oxyfunctionalization, and the peculiar kinetic features of this reaction. We combine catalytic activity measurements with quantum chemical calculations to put forward a bold new hypothesis. We argue that the remarkable product distribution can be rationalized by a combination of surface‐mediated formation of radicals over metastable sites, and their sequential propagation in the gas phase. Based on known radical propagation steps, we quantitatively describe the oxygen pressure‐dependent relative formation of the main product propylene and by‐product ethylene. Free radical intermediates most likely differentiate this catalytic system from less selective vanadium‐based catalysts.

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The Cover Feature shows “The Catalyst Store” that contains a variety of catalysts used in important chemical transformations. In the foreground is the shelf housing oxidative dehydrogenation catalysts, featuring the exciting new boron‐based catalysts as well as traditional vanadium oxide‐based catalysts. Top‐shelf options are the highly‐selective h‐BN and the newly described B/C – an equally selective, higher performing, and less expensive ODH catalyst that h‐BN. In their Full Paper, L. O. Mark, R. W. Dorn et al. show that oxidized activated carbon‐supported boron (B/OAC) exhibits higher performance for the oxidative dehydrogenation (ODH) of propane than the benchmark hexagonal boron nitride. XPS, IR, Raman and solid‐state NMR spectroscopies revealed the presence of clustered oxidized/hydrolyzed boron on the surface of the support. The high performance of B/OAC opens the door for investigation of other surface modified supports for next generation ODH catalysis. More information can be found in the Full Paper by L. O. Mark, R. W. Dorn et al.