前期遷移金属ヒドリド化合物触媒の開拓と機構解明

已知早期3d过渡金属，例如Ti、V、Nb或Cr，由于它们的强M-N键，对于哈伯-博施工艺是无活性的。我将研究扩展到其他早期过渡金属，即，V和Nb。这些金属除了具有相对较低的M-N键强度之外，还受益于增强氢化物扩散的体心立方（bcc）相关结构。氢化钒的活性最有可能具有VH0.44N0.16的活性成分，其活性上级优于先前报道的TiH 2和BaTiO 2.5H0.5，并且与Cs-Ru/MgO相当。这些结果表明，在不牺牲活性的前提下，开发新的单相氢化物催化剂具有更大的潜力。拓扑化学反应在发现具有新的化学和物理性质的新亚稳化合物方面取得了很大进展，使其成为合成新氢化物材料的有效方法。我报道了一种新的六方晶系氮化物氢化物h-Ca 3CrN 3 H的拓扑化学合成，通过加热正交氮化物o-Ca 3CrN 3，在氢气下在673 K，伴随着旋转结构转变。氢的插入使o-Ca 3CrN 3中的Ca-N类岩盐原子堆积转变为h-Ca 3CrN 3 H中的八面体共面链。令人印象深刻的是，h-Ca 3CrN 3 H在用作催化剂时显示出稳定的氨合成活性，尽管前过渡金属Cr不是氨合成的活性元素。密度泛函理论计算表明，氮的还原可以有效地实现通过缔合机制。

Early 3d transition metals, such as Ti, V, Nb or Cr are known to be inactive for the Haber-Bosch process, due to their strong M-N bonds. I expanded the study to hydrides of other early transition metals, i.e., V and Nb. These metals benefit from body-centered cubic (bcc) related structures which enhance hydride diffusion, in addition to having relatively lower M-N bond strengths. The activity of vanadium hydride, most likely with an active composition of VH0.44N0.16, is superior to the previously reported TiH2 and BaTiO2.5H0.5, and comparable to Cs-Ru/MgO. These results show that there is more potential for developing new single-phase hydride catalysts of previously overlooked elements without sacrificing activity.Topochemical reactions have led to great progress in the discovery of new metastable compounds with novel chemical and physical properties, making it an effective method of synthesizing new hydride materials. I reported a topochemical synthesis of a new hexagonal nitride hydride, h-Ca3CrN3H, by heating an orthorhombic nitride, o-Ca3CrN3, under hydrogen at 673 K, accompanied by a rotational structural transformation. The hydrogen intercalation modifies the Ca-N rock-salt-like atomic packing in o-Ca3CrN3 to a face-sharing octahedral chain in h-Ca3CrN3H. Impressively, the h-Ca3CrN3H exhibited stable ammonia synthesis activity when used as a catalyst, even though the early transition metal Cr is not an active element for ammonia synthesis. DFT calculations reveal that nitrogen reduction could be effectively achieved through an associative mechanism.