Tsuji Yuta, Yoshida Masataka, Kamachi Takashi, Yoshizawa Kazunari
Faculty of Engineering Sciences, Kyushu University, Kasuga, Fukuoka, 816-8580, Japan.
Laboratory for Chemistry and Life Science, Tokyo Institute of Technology, Midori-ku, Yokohama 226-8503, Japan.
J Am Chem Soc. 2022 Oct 12;144(40):18650-18671. doi: 10.1021/jacs.2c08787. Epub 2022 Sep 25.
Oxidative addition of CH to the catalyst surface produces CH and H. If the CH species generated on the surface couple with each other, reductive elimination of CH may be achieved. Similarly, H's could couple to form H. This is the outline of nonoxidative coupling of methane (NOCM). It is difficult to achieve this reaction on a typical Pt catalyst surface. This is because methane is overoxidized and coking occurs. In this study, the authors approach this problem from a molecular aspect, relying on organometallic or complex chemistry concepts. Diagrams obtained by extending the concepts of the Walsh diagram to surface reactions are used extensively. C-H bond activation, i.e., oxidative addition, and C-C and H-H bond formation, i.e., reductive elimination, on metal catalyst surfaces are thoroughly discussed from the point of view of orbital theory. The density functional theory method for structural optimization and accurate energy calculations and the extended Hückel method for detailed analysis of crystal orbital changes and interactions play complementary roles. Limitations of monometallic catalysts are noted. Therefore, a rational design of single atom alloy (SAA) catalysts is attempted. As a result, the effectiveness of the Pt/Au(111) SAA catalyst for NOCM is theoretically proposed. On such an SAA surface, one would expect to find a single Pt monatomic site in a sea of inert Au atoms. This is desirable for both inhibiting overoxidation and promoting reductive elimination.
CH 向催化剂表面的氧化加成产生 CH 和 H。如果表面生成的 CH 物种相互偶联，则可实现 CH 的还原消除。同样，H 可以偶联形成 H。这就是甲烷非氧化偶联（NOCM）的概述。在典型的 Pt 催化剂表面上很难实现这种反应。这是因为甲烷会过度氧化并发生结焦。在本研究中，作者从分子层面入手，依靠有机金属或络合物化学概念。通过将沃尔什图的概念扩展到表面反应而获得的图表被广泛使用。从轨道理论的角度对金属催化剂表面上的 C-H 键活化（即氧化加成）以及 C-C 和 H-H 键形成（即还原消除）进行了深入讨论。用于结构优化和精确能量计算的密度泛函理论方法以及用于详细分析晶体轨道变化和相互作用的扩展休克尔方法起到了互补作用。指出了单金属催化剂的局限性。因此，尝试对单原子合金（SAA）催化剂进行合理设计。结果，从理论上提出了 Pt/Au(111) SAA 催化剂对 NOCM 的有效性。在这样的 SAA 表面上，预计会在惰性 Au 原子的海洋中找到单个 Pt 单原子位点。这对于抑制过度氧化和促进还原消除都是有利的。
