纳米材料催化硼氢化物肼合物放氢反应的原位研究

Borohydride hydrazinates are a series of new compounds, which are formed through the coordination of hydrazine, a kind of bidentate ligand, with metal cations in borohydrides. For this kind of materials, Hδ+ and Hδ– co-exist in a single phase, expectedly facilitating the dehydrogenation of borohydride hydrazinates.This study aims at solving the crystal structures of borohydride hydrazinates and investigating the mechanism of the catalytic dehydrogenation of borohydride hydrazinates on transition metal nanomaterials. Synchrotron radiation powder X-ray diffraction (XRD) measurements, in-situ X-ray absorption fine structure (XAFS) and in-stiu XRD at Shanghai Facility (SSRF) are the effective experimental methods to get the necessary information. Combining first-principles calculations with experimental results, we could have an insight into the interaction between borohydride and hydrazine, transitional states of reactions on the surface of catalysts,intermediates, reaction paths and products during the catalytic dehydrogenation of borohydride hydrazinates. Through this research, it could be expected that thermodynamic and kinetic data of the catalytic dehydrogenation of borohydride hydrazinates could be obtained and that effects of shapes, compositions, contents, synthesis methods and microstructures of catalysts on catalytic activities could be well understood, which will be the basis for the application of borohydride hydrazinates as hydrogen storage materials.

金属硼氢化物肼合物是金属硼氢化物与肼复合形成的一类新的化合物。在此类化合物中，Hδ+和Hδ-共存，有利于氢气的释放。本申请拟利用上海同步辐射光源装置X射线衍射线站和X射线吸收线站对这些新化合物进行结构测定和通过原位反应实验研究纳米材料催化放氢反应机理。通过理论计算与实验结果相结合的方式，进一步了解金属氨硼烷和肼的相互作用以及催化反应中过渡态、中间体、反应路径和反应产物，旨在获得反应过程的热力学和动力学数据。全面了解催化剂形貌、成分、含量、制备条件和结构对催化反应活性的影响,为金属硼氢化物肼合物成为实用的储氢材料提供理论依据。

本项目通过上海同步辐射光源X射线衍射和X射线吸收站对金属硼氢化物肼合物进行结构测定和通过现场原位反应实验研究过渡金属纳米材料催化他们放氢反应机理。本项目合成并表征的LiBH4,NaBH4, Mg(BH4)2和Ca(BH4)2的肼合物有LiBH4•1/2N2H4、LiBH4•1/3N2H4、LiBH4•N2H4、LiBH4•2N2H4、NaBH4•N2H4、Mg(BH4)•3N2H4和Ca(BH4)•2N2H4。金属硼氢化物肼合物为金属硼氢化物与肼复合形成的新的一类化合物，Hδ+和Hδ-共存同一物相中，有利于氢气的释放。我们提出金属硼氢化物肼合物反应机理为N2H4的Hδ+和BH4-的Hδ-直接结合放氢或者N2H4分解为NH3和N2或NH2自由基再通过NHx的Hδ+和BH4-的Hδ-直接结合放氢。金属离子电负性越高，络合肼的能力越强，可导致直接结合放氢。N2H4分解可能会导致形成中间产物，我们进一步合成了可能中间产物LiBH4氨合物、LiBH4•2LiNH2BH3、肼硼烷和碱金属肼硼烷、LiNH2BH3•N2H4和Ca(NH2BH3)2•2N2H4，和不产生NH2自由基的LiBH4、Mg(BH4)和乙二胺(EDA)配合物,LiBH4•EDA、(LiBH4)2•EDA、Mg(BH4)2•3EDA和Mg(BH4)2•4EDA，研究了它们的晶体结构、放氢性能和反应机理，证实了NHx的Hδ+和BH4-的Hδ-直接结合放氢机理。在纳米FeB合金的催化下，LiBH4•N2H4在140℃可以释放大约13.0 wt%的H2。同位素标记实验证实Hδ+和Hδ-的结合是硼氢化物-肼配合物放氢反应机理。