Oxidative dehydrogenation of propane (ODHP) is a key technology for producing propene from shale gas, but conventional metal oxide catalysts are prone to overoxidation to form valueless COx. Boron-based catalysts were recently found to be selective for this reaction, and B–O–B oligomers are generally regarded as active centers. We show here that the isolated boron in a zeolite framework without such oligomers exhibits high activity and selectivity for ODHP, which also hinders full hydrolysis for boron leaching in a humid atmosphere because of the B–O–SiOx linkage, achieving superior durability in a long-period test. Furthermore, we demonstrate an isolated boron with a –B[OH…O(H)–Si]2 structure in borosilicate zeolite as the active center, which enables the activation of oxygen and a carbon–hydrogen bond to catalyze the ODHP.

Dinitrogen activation and reduction is one of the most challenging and important subjects in chemistry. Herein, we report the N 2 binding and reduction at the well-defined Ta 3 N 3 H − and Ta 3 N 3 − gas-phase clusters by using mass spectrometry (MS), anion photoelectron spectroscopy (PES), and quantum-chemical calculations. The PES and calculation results show clear evidence that N 2 can be adsorbed and completely activated by Ta 3 N 3 H − and Ta 3 N 3 − clusters, yielding to the products Ta 3 N 5 H − and Ta 3 N 5 − , but the reactivity of Ta 3 N 3 H − is five times higher than that of the dehydrogenated Ta 3 N 3 − clusters. The detailed mechanistic investigations further indicate that a dissociative mechanism dominates the N 2 activation reactions mediated by Ta 3 N 3 H − and Ta 3 N 3 − ; two and three Ta atoms are active sites and also electron donors for the N 2 reduction, respectively. Although the hydrogen atom in Ta 3 N 3 H − is not directly involved in the reaction, its very presence modifies the charge distribution and the geometry of Ta 3 N 3 H − , which is crucial to increase the reactivity. The mechanisms revealed in this gas-phase study stress the fundamental rules for N 2 activation and the important role of transition metals as active sites as well as the new significant role of metal hydride bonds in the process of N 2 reduction, which provides molecular-level insights into the rational design of tantalum nitride-based catalysts for N 2 fixation and activation or NH 3 synthesis.

Vanadium and silicon heteronuclear oxide cluster anions V x Si y O z − (x + y ≥ 2, z ≥ 4) are prepared by laser ablation and reacted with n-butane (C4H10) in a fast flow reactor. A time-of-flight mass spectrometer is used to detect the cluster distribution before and after the reactions. The observation of hydrogen-containing products (V2O5) m (SiO2) n OH− (m = 1, n = 1−4; m = 2, n = 1) strongly suggests the following reactions: (V2O5) m (SiO2) n O− + C4H10 → (V2O5) m (SiO2) n OH− + C4H9. Although V2O6 − is produced in the cluster source, no V2O6H− product is produced under the same experimental condition. It indicates that specific heteronuclear oxide clusters V2O5(SiO2)1−4O− and (V2O5)2SiO2O− are more reactive than the homonuclear oxide cluster V2O6 − (or V2O5O−). Density functional theory (DFT) calculations are performed to study reaction mechanisms of V2O5SiO2O− (or V2SiO8 −) + C4H10. The calculated results are in good agreement with the experimental observations. The structural and bonding properties of (V2O5) m (SiO2) n O− (m = 1, n = 1−4; m = 2, n = 1) are also investigated by the DFT calculations. The unpaired electron in each of the clusters is mainly distributed over one or two O atoms (2p orbitals) bonded with Si rather than V atom(s). Furthermore, the experimentally observed higher reactivity of the V−Si heteronuclear oxide cluster (V2O5) m (SiO2) n O− over the homonuclear V2O6 − in the reaction with C4H10 is interpreted based on the theoretical results.

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