Gan Wen, Geng Lijun, Huang Benben, Hansen Klavs, Luo Zhixun
Beijing National Laboratory for Molecular Science, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China.
School of Chemical Science, University of Chinese Academy of Sciences, Beijing 100049, China.
Phys Chem Chem Phys. 2024 Mar 20;26(12):9586-9592. doi: 10.1039/d3cp06135c.
The reactivity of Nb (1 ≤ ≤ 21) clusters with BH is studied by using a self-developed multiple-ion laminar flow tube reactor combined with a triple quadrupole mass spectrometer (MIFT-TQMS). The Nb clusters were generated by a magnetron sputtering source and reacted with the BH gas under fully thermalized conditions in the downstream flow tube where the reaction time was accurately controlled and adjustable. The complete and partial dehydrogenation products NbB and NbBH were detected, indicative of the removal of H and likely BH moieties. Interestingly, these NbB and NbBH products are limited to 3 ≤ ≤ 6, suggesting that the small Nb clusters are relatively more reactive than the larger Nb clusters under the same conditions. By varying the BH gas concentrations and the reactant doses introduced into the flow tube, and by changing the reaction time, we performed a detailed analysis of the reaction dynamics in combination with the DFT-calculated thermodynamics. It is demonstrated that the lack of cooperative active sites on the Nb cations accounts for the weakened dehydrogenation efficiency. Nb forms partial dehydrogenation products at a faster rate. In contrast, the Nb clusters are subject to more flexible vibrational relaxation which disperse the energy gain of BH-adsorption and thus are unable to overcome the energy barriers for subsequent hydrogen atom transfer and H release.
采用自行研制的多离子层流管反应器与三重四极杆质谱仪（MIFT-TQMS）联用，研究了Nb（1≤n≤21）团簇与BH的反应活性。Nb团簇由磁控溅射源产生，并在下游流管中完全热化条件下与BH气体反应，反应时间可精确控制和调节。检测到了完全脱氢产物NbB和部分脱氢产物NbBH，表明H和可能的BH部分被去除。有趣的是，这些NbB和NbBH产物仅限于3≤n≤6，这表明在相同条件下，小尺寸的Nb团簇比大尺寸的Nb团簇反应活性相对更高。通过改变引入流管中的BH气体浓度和反应物剂量，并改变反应时间，我们结合密度泛函理论（DFT）计算的热力学对反应动力学进行了详细分析。结果表明，Nb阳离子上缺乏协同活性位点导致脱氢效率降低。Nb能更快地形成部分脱氢产物。相比之下，Nb团簇经历更灵活的振动弛豫，这分散了BH吸附的能量增益，因此无法克服随后氢原子转移和H释放的能量障碍。
