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首页> 外文期刊>Coordination chemistry reviews >A perspective on the properties and surface reactivities of carbides and nitrides of titanium and vanadium
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A perspective on the properties and surface reactivities of carbides and nitrides of titanium and vanadium

机译：钛和钒的碳化物和氮化物的性质和表面反应性透视

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The electronic structure of the early transition metal carbides and nitrides is linked to their remarkable physical properties and their surface chemistry. In this review, we focus on experimental studies of the electronic structure and surface adsorption properties of these rock-salt structured materials. A straightforward molecular orbital framework is used to understand the surface chemical interactions of the materials, primarily the stoichiometric (001) surfaces of Tie and VC, with small molecule adsor-bates. This framework is then expanded to include more comprehensive theoretical treatments of the surface adsorption, with a particular emphasis on recent density functional theory results. The adsorbates reviewed include CO, NH_3, O_2, H_2O, SO_2, methanol, methyl formate, and ethanol. This overview reveals that the properties of these materials are heavily influenced by two factors: highly covalent bonding interactions between the metal and carbon species and the total number of electrons present, as the added electron per formula unit in either VC or TiN relative to TiC, populates low lying metal 3d levels that are formally unoccupied in TiC. This results in materials that appear to be d~0(TiC), d~1 (VC, TiN) or d~2 (VN), with actual charges on the atoms that are close to ±1. These influences are apparent in valence band photoemission data obtained on the (001) surfaces. The surface chemistry trends with probe molecules such as CO and NH_3 can be predicted based on coordination chemistry principles, with the cf-donor ammonia molecule, for example, have very similar interactions with TiC and VC, while CO adsorption is measurably stronger on the VC surface due to π-backbonding interactions. More comprehensive surface models are needed to probe surface reactions as they are heavily influenced by neighboring carbon and metal atoms on the (1 0 0) surface, with the added d-electron density on the metal in VC or TiN enabling stronger surface bonding with reaction intermediates than is found on TiC.
机译：早期过渡金属碳化物和氮化物的电子结构与其出色的物理性能和表面化学性质有关。在这篇综述中，我们专注于这些岩石盐结构材料的电子结构和表面吸附特性的实验研究。一个简单的分子轨道框架用于了解材料的表面化学相互作用，主要是Tie和VC的化学计量（001）表面与小分子吸附剂的相互作用。然后将该框架扩展为包括表面吸附的更全面的理论处理，尤其着重于近期的密度泛函理论结果。所审查的吸附物包括CO，NH_3，O_2，H_2O，SO_2，甲醇，甲酸甲酯和乙醇。此概述表明，这些材料的性能受到两个因素的严重影响：金属和碳物种之间的高度共价键相互作用以及存在的电子总数，因为相对于TiC，每分子式VC或TiN中添加的电子，填充TiC中正式没有使用的低空金属3d水平。这导致材料看起来是d〜0（TiC），d〜1（VC，TiN）或d〜2（VN），原子上的实际电荷接近±1。这些影响在（001）表面获得的价带光发射数据中很明显。可以根据配位化学原理预测探针分子（例如CO和NH_3）的表面化学趋势，例如CF供体氨分子与TiC和VC的相互作用非常相似，而VC对VC的吸附作用强得多表面由于π反向键相互作用。需要更全面的表面模型来探测表面反应，因为它们受到（1 0 0）表面上相邻的碳和金属原子的严重影响，并且VC或TiN中金属上增加的d电子密度可实现与反应更牢固的表面键合中间产物比在TiC上发现的多。

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