Scaling-relation based kinetic Monte Carlo modeling of higher alcohol synthesis

在过去的几年里，基于第一性原理的微动力学建模已经发展成为对多相催化过程的机理理解和识别新的、改进的催化剂的宝贵贡献者。这一发展主要沿着两条互补的方向进行。动力学蒙特卡罗（kMC）模拟基于明确的第一性原理数据，旨在对单个系统进行全面和最准确的描述。计算筛选研究转而采用简化的平均场动力学和近似趋势能量学，这是由标度、br - nsted- evans - polanyi和其他关系推导出来的。在复杂反应网络的应用中，这两种方法都受到了挑战。全面的kMC模拟需要大量原则上可能的基本步骤的高能数据。简化的平均场动力学表达式可能依赖于对主要反应机理或速率决定步骤的错误假设，并且在处理活性表面的微观非均质性和发生在不同活性位点的反应步骤之间可能存在的敏感相互作用时显示出固有的缺陷。这项工作的目标是通过结合迄今为止大部分共存的链来克服这些限制，并普遍探索在kMC模拟中使用基于比例关系的能量学。作为一个示范系统，研究将侧重于从合成气中选择性合成高级醇，作为一种有吸引力的能源解决过程，它将大量产生这些可持续的燃料替代品，从而减少对石油的依赖和温室气体的排放。从机制上讲，这些研究将确定决定铑迄今为止独特选择性的重要因素，并针对氧化促进在阻断和改变台阶位点方面的作用。所产生的见解将直接用于精确的筛选方案，以确定替代金属化合物，促进或掺杂策略，以取代昂贵的铑。

Over the past years first-principles based microkinetic modeling has evolved into an invaluable contributor to mechanistic understanding of heterogeneously catalyzed processes and the identification of new, improved catalysts. This development proceeded largely along two complementary strands. Kinetic Monte Carlo (kMC) simulations based on explicit first-principles data aimed at a comprehensive and most accurate description of individual systems. Computational screening studies resorted instead to simplified mean-field kinetics and approximate trend energetics derived from scaling, Brønsted-Evans-Polanyi and other relations. In the application to complex reaction networks both strands are challenged. Comprehensive kMC simulations require energetic data for an exceeding number of in principle possible elementary steps. Simplified mean-field kinetic expressions might rely on erroneous assumptions regarding the dominant reaction mechanism or rate-determining steps, as well as reveal intrinsic shortcomings when dealing with microscopic heterogeneity of the active surface and a possibly sensitive interplay between reaction steps taking place at different active sites. The objective of the work is to overcome these limitations by combining the hitherto largely coexisting strands - and generally explore the use of scaling-relation based energetics in kMC simulations. As a showcase system the investigations will focus on the selective synthesis of higher alcohols from synthesis gas, as an attractive energy solution process that would yield these sustainable fuel substitutes in larger quantities and thereby reduce oil dependency and greenhouse gas emissions. Mechanistically, the studies will establish the important factors that determine rhodiums hitherto unique selectivity and target the alleged role of oxide promotion in terms of blocking and alteration of step sites. The generated insight will directly be exploited in refined screening protocols to identify alternative metal compounds, promotion or doping strategies to replace the prohibitively expensive rhodium.