Wu Xiao-Nan, Li Jilai, Schlangen Maria, Zhou Shaodong, González-Navarrete Patricio, Schwarz Helmut
Institut für Chemie, Technische Universität Berlin, Straße des 17. Juni 135, 10623, Berlin, Germany.
Department of Chemistry, Fudan University, Shanghai, 200433, P. R. China.
Chemistry. 2017 Jan 18;23(4):788-792. doi: 10.1002/chem.201605226. Epub 2016 Dec 13.
The thermal reactivity of the heteronuclear metal-oxide cluster cations [XAlO ] (X=V, Nb, and Ta) towards methane has been studied by using mass spectrometry in conjunction with quantum mechanical calculations. Experimentally, a hydrogen-atom transfer (HAT) from methane is mediated by all the three oxide clusters at ambient conditions. However, [VAlO ] is unique in that this cluster directly transforms methane into formaldehyde. The absence of this reaction for the Nb and Ta analogues demonstrates a striking doping effect on the chemoselectivity in the conversion of methane. Mechanistic aspects of the two reactions have been elucidated by quantum-chemical calculations. The HAT reactivity can be attributed to the significant spin density localized at the terminal oxygen atom (O ) of the cluster ions, while the ionic/covalent character of the Lewis acid-base unit [X-O ] plays a crucial role for the generation of formaldehyde. The mechanistic insight derived from this combined experimental/computational investigation may provide guidance for a more rational design of catalysts.
通过质谱联用量子力学计算，研究了异核金属氧化物簇阳离子[XAlO ]（X = V、Nb和Ta）对甲烷的热反应活性。实验表明，在环境条件下，所有这三种氧化物簇都能介导甲烷发生氢原子转移（HAT）。然而，[VAlO ]的独特之处在于，该簇能直接将甲烷转化为甲醛。Nb和Ta类似物不存在这种反应，这表明在甲烷转化过程中，掺杂对化学选择性有显著影响。通过量子化学计算阐明了这两个反应的机理。HAT反应活性可归因于簇离子末端氧原子（O ）上显著的自旋密度，而路易斯酸碱单元[X-O ]的离子/共价特性对甲醛的生成起着关键作用。这种结合实验/计算研究得出的机理见解可为更合理的催化剂设计提供指导。
