Jackson Bret, Nattino Francesco, Kroes Geert-Jan
Department of Chemistry, University of Massachusetts, Amherst, Massachusetts 01003, USA.
Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands.
J Chem Phys. 2014 Aug 7;141(5):054102. doi: 10.1063/1.4891327.
The dissociative chemisorption of methane on metal surfaces is of great practical and fundamental importance. Not only is it the rate-limiting step in the steam reforming of natural gas, the reaction exhibits interesting mode-selective behavior and a strong dependence on the temperature of the metal. We present a quantum model for this reaction on Ni(100) and Ni(111) surfaces based on the reaction path Hamiltonian. The dissociative sticking probabilities computed using this model agree well with available experimental data with regard to variation with incident energy, substrate temperature, and the vibrational state of the incident molecule. We significantly expand the vibrational basis set relative to earlier studies, which allows reaction probabilities to be calculated for doubly excited initial vibrational states, though it does not lead to appreciable changes in the reaction probabilities for singly excited initial states. Sudden models used to treat the center of mass motion parallel to the surface are compared with results from ab initio molecular dynamics and found to be reasonable. Similar comparisons for molecular rotation suggest that our rotationally adiabatic model is incorrect, and that sudden behavior is closer to reality. Such a model is proposed and tested. A model for predicting mode-selective behavior is tested, with mixed results, though we find it is consistent with experimental studies of normal vs. total (kinetic) energy scaling. Models for energy transfer into lattice vibrations are also examined.
甲烷在金属表面的解离化学吸附具有重大的实际意义和基础重要性。它不仅是天然气蒸汽重整中的限速步骤，该反应还表现出有趣的模式选择性行为以及对金属温度的强烈依赖性。我们基于反应路径哈密顿量提出了一个关于此反应在Ni(100)和Ni(111)表面的量子模型。使用该模型计算出的解离吸附概率在随入射能量、衬底温度以及入射分子振动状态的变化方面与现有实验数据吻合良好。相对于早期研究，我们显著扩展了振动基组，这使得能够计算双激发初始振动状态下的反应概率，不过对于单激发初始状态，反应概率并未产生明显变化。将用于处理平行于表面的质心运动的突然模型与从头算分子动力学结果进行了比较，发现其是合理的。对分子旋转的类似比较表明，我们的旋转绝热模型是不正确的，突然行为更接近实际情况。提出并测试了这样一个模型。测试了一个用于预测模式选择性行为的模型，结果好坏参半，不过我们发现它与关于正常能量与总（动能）能量标度的实验研究是一致的。还研究了能量转移到晶格振动中的模型。
