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

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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.