Dietze Elisabeth M, Chen Lin, Grönbeck Henrik
Department of Physics and Competence Centre for Catalysis, Chalmers University of Technology, Göteborg, Sweden.
J Chem Phys. 2022 Feb 14;156(6):064701. doi: 10.1063/5.0078918.
Water formation is relevant in many technological processes and is also an important model reaction. Although water formation over Pd surfaces is widely studied, questions regarding the active site and the main reaction path (OH* + OH*) or (OH* + H*) are still open. Combining first-principles density functional theory calculations and kinetic Monte Carlo simulations, we find that the reaction rate is dominated by surface steps and point defects over a wide range of conditions. The main reaction path is found to be temperature dependent where the OH* + OH* path dominates at low temperatures, whereas the OH* + H* path is the main path at high temperatures. Steps facilitate the OH* formation, which is the rate limiting step under all conditions. OH* is formed via O* + H* association or OOH* splitting at low temperatures, whereas OH* is exclusively formed via O* + H* association at high temperatures. The results of the first-principles-based kinetic model are in excellent agreement with experimental observations at high and low temperatures as well as different gas-phase compositions.
水的形成在许多技术过程中都具有重要意义，同时也是一个重要的模型反应。尽管在钯表面上水的形成已得到广泛研究，但关于活性位点以及主要反应路径（OH* + OH*）或（OH* + H*）的问题仍然没有定论。结合第一性原理密度泛函理论计算和动力学蒙特卡罗模拟，我们发现，在很宽的条件范围内，反应速率由表面台阶和点缺陷主导。主要反应路径被发现与温度有关，其中OH* + OH路径在低温下占主导，而OH + H路径在高温下是主要路径。台阶促进了OH的形成，这是所有条件下的速率限制步骤。OH在低温下通过O + H缔合或OOH分解形成，而在高温下OH仅通过O + H*缔合形成。基于第一性原理的动力学模型的结果与高温和低温以及不同气相组成下的实验观测结果高度吻合。
