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Evaluating the Benefits of Kinetic Monte Carlo and Microkinetic Modeling for Catalyst Design Studies in the Presence of Lateral Interactions
preprintrevised on 04.10.2020, 16:53 and posted on 05.10.2020, 12:41 by Xiao Li, Lars Grabow
Popular computational catalyst design strategies rely on the identification of reactivity descriptors, which can be used along with Brønsted−Evans−Polanyi (BEP) and scaling relations as input to a microkinetic model (MKM) to make predictions for activity or selectivity trends. The main benefit of this approach is related to the inherent dimensionality reduction of the large material space to just a few catalyst descriptors. Conversely, it is well documented that a small set of descriptors is insufficient to capture the intricacies and complexities of a real catalytic system. The inclusion of coverage effects through lateral adsorbate-adsorbate interactions can narrow the gap between simplified descriptor predictions and real systems, but mean-field MKMs cannot properly account for local coverage effects. This shortcoming of the mean-field approximation can be rectified by switching to a lattice-based kinetic Monte Carlo (kMC) method using cluster expansion representation of adsorbate−adsorbate lateral interactions.
Using the prototypical CO oxidation reaction as an example, we critically evaluate the benefits of kMC over MKM in terms of trend prediction accuracy and computational cost. After confirming that in the absence of lateral interactions the kMC and MKM approaches yield identical trends and mechanistic information, we observed substantial differences between the two kinetic models when lateral interactions were introduced. The difference, however, is mainly manifested in the absolute rates, surface coverages and the optimal descriptor values, whereas relative activity trends remain largely intact. Moreover, the nature of the rate-determining step as identified using Campbell’s degree of rate control is also consistent between both approaches. Considering that the computational cost of MKM is ca. three orders of magnitude lower than for a kMC simulation, the MKM approach does provide the best balance between accuracy and efficiency when used in the context of computational catalyst screening.