Bai Yunhai, Mavrikakis Manos
Department of Chemical and Biological Engineering, University of Wisconsin-Madison , Madison, Wisconsin 53706, United States.
J Phys Chem B. 2018 Jan 18;122(2):432-443. doi: 10.1021/acs.jpcb.7b01115. Epub 2017 May 8.
Periodic, self-consistent density functional theory (DFT-GGA, PW91) calculations are used to study the reaction mechanism for nitric oxide (NO) reduction by hydrogen (H) on Pt(100). Energetics of various N-O activation paths, including both direct and hydrogen-assisted N-O bond-breaking paths, and the formation of three different N-containing products (N, NO, and NH), are systematically studied. On the basis of our analysis, NO* dissociation has a lower barrier than NO* hydrogenation to HNO* or NOH*, and therefore, the direct NO dissociation path is predicted to dominate N-O activation on clean Pt(100). The reaction of atomic N* with N* and NO* is proposed as the mechanism for N and NO formation, respectively. NH formation from N* via three successive hydrogenation steps is also studied and is found to be kinetically more difficult than N and NO formation from N*. Finally, NO adsorption phase diagrams on Pt(100) are constructed, and these phase diagrams suggest that, at low temperatures (e.g., 400 K), the Pt(100) surface may be covered by half a monolayer of NO. We propose that high NO coverage might affect the NO + H reaction mechanism, and therefore, one should explicitly take the NO coverage into consideration in first-principles studies to determine the reaction mechanism on catalyst surfaces under reaction conditions. A detailed analysis of high NO coverage effects on the reaction mechanism will be presented in a separate contribution.
采用周期性自洽密度泛函理论（DFT - GGA，PW91）计算方法研究了氢气（H）在Pt(100)表面还原一氧化氮（NO）的反应机理。系统研究了各种N - O活化路径的能量变化，包括直接和氢辅助的N - O键断裂路径，以及三种不同含氮产物（N、NO和NH）的形成过程。根据我们的分析，NO解离的势垒低于NO氢化为HNO或NOH的势垒，因此，预计在清洁的Pt(100)表面上，直接NO解离路径将主导N - O活化过程。分别提出了原子N与N和NO反应生成N和NO的机理。还研究了N通过三个连续氢化步骤生成NH的过程，发现其动力学过程比由N*生成N和NO更困难。最后，构建了Pt(100)表面上的NO吸附相图，这些相图表明，在低温（例如400 K）下，Pt(100)表面可能被半单层的NO覆盖。我们认为高NO覆盖率可能会影响NO + H反应机理，因此，在第一性原理研究中确定反应条件下催化剂表面的反应机理时，应明确考虑NO覆盖率。关于高NO覆盖率对反应机理影响的详细分析将在另一篇论文中给出。
