Methane activation on stepped Ni(511) surfaces involves the rearrangement of surface atoms as the chemical reaction proceeds. This process is particularly sensitive to temperature. Using machine-learned interatomic potentials (MLIPs) coupled with enhanced sampling techniques, we investigate the activation of methane under realistic operando conditions. Our analysis reveals that methane dissociation occurs predominantly at step-edge nickel atoms. As CHx (where x = 3 or 4) species bind to additional surface nickel atoms, their reduced mobility leads to entropic penalties that suppress certain configurations and transition states. This is reflected in the underlying free energy surfaces, where configurations such as methyl binding to hollow sites and activation routes involving two nickel atoms become unfavorable as temperature increases. At elevated temperatures, methane activation extends from step-edge sites to terrace regions because of reduced free-energy barriers and enhanced surface dynamics. By decomposing the free energy into enthalpic and entropic contributions, we uncover temperature-dependent shifts in the preferences of methane for the relevant active sites and arrive at a detailed molecular picture of methane activation.

中文翻译：

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通过机器学习和增强采样分析 Ni（511） 上甲烷活化中的自由能景观和表面动力学


阶梯式 Ni（511） 表面上的甲烷活化涉及随着化学反应的进行，表面原子的重排。这个过程对温度特别敏感。使用机器学习的原子间电位 （MLIP） 与增强的采样技术相结合，我们研究了真实操作条件下甲烷的活化。我们的分析表明，甲烷解离主要发生在阶梯边缘镍原子处。由于 CHx（其中 x = 3 或 4）物质与其他表面镍原子结合，它们的迁移率降低导致熵惩罚，从而抑制某些构型和过渡态。这反映在底层自由能表面中，其中甲基与空心位点的结合和涉及两个镍原子的活化途径等构型随着温度的升高而变得不利。在高温下，由于自由能屏障的减少和表面动力学的增强，甲烷活化从阶梯边缘站点延伸到阶地区域。通过将自由能分解为焓和熵贡献，我们揭示了甲烷对相关活性位点的偏好与温度相关的变化，并得出了甲烷活化的详细分子图。