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.
Achieving the desired selective transformations of the very stable CO 2 into useful chemicals is quite important for the development of economically and environmentally sustainable synthetic methods. Herein, mass spectrometric experiments and quantum-chemical calculations have identified that ScNH + reacts quite efficiently with CO 2 under thermal collision conditions to exclusively yield ScO + and isocyanic acid (HNCO). This is a novel reaction type in CO 2 activation reactions mediated by gas-phase ions. In this reaction, the CN double bond has also been formed for the first time in the gas phase. The mechanism of "migratory insertion" is proposed. Coupled with the previously reported reaction of Sc + with NH 3 , HNCO can be synthesized under mild conditions from NH 3 and CO 2 in quite simple reactions. The mechanistic information gained in this gas-phase model reaction can offer fundamental insights relevant to corresponding processes and further guide on how to design brand new catalysts.
The mass-selected Fe O cation mediated propane oxidation by O was investigated by mass spectrometry and density functional theory calculations. In the reaction of Fe O with C H , H was liberated by C-H bond activation to give Fe OC H . Interestingly, when a mixture of C H /O was introduced into the reactor, an intense signal that corresponded to the Fe O cation was present; the experiments indicated that O was activated in its reaction with Fe O(C H ) to give Fe O and C H O (acetone or propanal). A Langmuir-Hinshelwood-like mechanism was adopted in the propane oxidation reaction by O on gas-phase Fe O cations. In comparison with the absence of Fe O in the reaction of Fe O with O , the ligand effect of C H on Fe OC H is important in the oxygen activation reaction. The theoretical results are consistent with the experimental observations. The propane oxidation by O in the presence of Fe O might be applied as a model for alkane and O activations over iron oxide catalysts, and the mechanisms and kinetic data are useful for understanding corresponding heterogeneous reactions.
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