Zhang Xiaohong, Savara Aditya, Getman Rachel B
Department of Chemical and Biomolecular Engineering, Clemson University, Clemson, South Carolina 29634-0909, United States.
Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States.
J Chem Theory Comput. 2020 Apr 14;16(4):2680-2691. doi: 10.1021/acs.jctc.9b01249. Epub 2020 Mar 20.
Adsorption is an important step in heterogeneous catalysis as it predetermines how many reactant molecules can participate in a surface reaction per unit time. While the rate of adsorption processes is well studied in gas-solid adsorption in both theory and experiment, such rates are still not well studied for liquid-solid adsorption. This is partly because the ever-changing configurations of liquid-phase solvent molecules impede the ability to study a molecule approaching a surface from a liquid phase by either experiment or theory. In this work, we develop a method using molecular dynamics (MD) simulations to study the rate of adsorption in liquid-solid adsorption processes. Specifically, we use MD to model the diffusion of a methanol molecule in aqueous solvent and its adsorption to a Pt(111) surface. We find that by approximating the solute motion as following the same displacement rates as a random walk model, the adsorbed and non-adsorbed states of the methanol molecule near the Pt(111) surface can be discerned and quantified. In particular, this methodology enables extracting a sticking coefficient and a macroscopically relatable adsorption rate. This method can be applied to arbitrary types of reactants and surfaces, as well as different liquid environments, thus providing a general tool for predicting quantitative adsorption rates of liquid-solid adsorption systems.
吸附是多相催化中的一个重要步骤，因为它预先决定了每单位时间有多少反应物分子能够参与表面反应。虽然吸附过程的速率在气固吸附的理论和实验方面都得到了充分研究，但在液固吸附中，这些速率仍未得到充分研究。部分原因在于，液相溶剂分子不断变化的构型阻碍了通过实验或理论研究分子从液相接近表面的能力。在这项工作中，我们开发了一种使用分子动力学（MD）模拟来研究液固吸附过程中吸附速率的方法。具体而言，我们使用MD来模拟甲醇分子在水性溶剂中的扩散及其在Pt(111)表面的吸附。我们发现，通过将溶质运动近似为遵循与随机游走模型相同的位移速率，可以辨别和量化Pt(111)表面附近甲醇分子的吸附态和未吸附态。特别是，这种方法能够提取附着系数和宏观相关的吸附速率。该方法可应用于任意类型的反应物和表面，以及不同的液体环境，从而为预测液固吸附系统的定量吸附速率提供了一个通用工具。
