Hinuma Yoyo, Mine Shinya, Toyao Takashi, Maeno Zen, Shimizu Ken-Ichi
Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8502, Japan.
Phys Chem Chem Phys. 2021 Aug 12;23(31):16577-16593. doi: 10.1039/d1cp02068d.
Metal/oxide support perimeter sites are known to provide unique properties because the nearby metal changes the local environment on the support surface. In particular, the electron scavenger effect reduces the energy necessary for surface anion desorption, and thereby contributes to activation of the (reverse) Mars-van Krevelen mechanism. This study investigated the possibility of such activation in hydrides, carbides, nitrides, and sulfides. The work functions (WFs) of known hydrides, carbides, nitrides, oxides, and sulfides with group 3, 4, or 5 cations (Sc, Y, La, Ti, Zr, Hf, V, Nb, and Ta) were calculated. The WFs of most hydrides, carbides, and nitrides are smaller than the WF of Ag, implying that the electron scavenger effect may occur when late transition metal nanoparticles are adsorbed on the surface. The WF of oxides and sulfides decreases when reduced. The surface anion vacancy formation energy correlates well with the bulk formation energy in carbides and nitrides, while almost no correlation is found in hydrides because of the small range of surface hydrogen vacancy formation energy values. The electron scavenger effect is explicitly observed in nanorods adsorbed on TiH2 and Ti2O3; the surface vacancy formation energy decreases at anion sites near the nanorod, and charge transfer to the nanorod happens when an anion is removed at such sites. Activation of hydrides, carbides, and nitrides by nanorod adsorption and screening support materials through WF calculation are expected to open up a new category of supported catalysts.
已知金属/氧化物载体周边位点具有独特性质，因为附近的金属会改变载体表面的局部环境。特别是，电子清除剂效应降低了表面阴离子脱附所需的能量，从而有助于（反向）Mars-van Krevelen机理的活化。本研究调查了在氢化物、碳化物、氮化物和硫化物中发生这种活化的可能性。计算了含有第3、4或5族阳离子（Sc、Y、La、Ti、Zr、Hf、V、Nb和Ta）的已知氢化物、碳化物、氮化物、氧化物和硫化物的功函数（WFs）。大多数氢化物、碳化物和氮化物的功函数小于Ag的功函数，这意味着当后期过渡金属纳米颗粒吸附在表面时，可能会发生电子清除剂效应。氧化物和硫化物在还原时功函数会降低。在碳化物和氮化物中，表面阴离子空位形成能与体相形成能有很好的相关性，而在氢化物中几乎没有相关性，因为表面氢空位形成能的值范围较小。在吸附在TiH₂和Ti₂O₃上的纳米棒中明确观察到了电子清除剂效应；纳米棒附近阴离子位点的表面空位形成能降低，并且当在此类位点去除阴离子时会发生电荷转移到纳米棒上。通过纳米棒吸附活化氢化物、碳化物和氮化物以及通过功函数计算筛选载体材料有望开辟一类新的负载型催化剂。
