Prediction of morphological changes of catalyst materials under reaction conditions by combined: Ab initio thermodynamics and microkinetic modelling

In this article, we couple microkinetic modelling, ab initio thermodynamics and Wulff-Kaishew construction to describe the structural variation of catalyst materials as a function of the chemical potential in the reactor. We focus specifically on experiments of catalytic partial oxidation (CPO) of methane on Rh/α-Al2O3. We employ a detailed structureless microkinetic model to calculate the profiles of the gaseous species molar fractions along the reactor coordinate and to select the most abundant reaction intermediates (MARIs) populating the catalyst surfaces in different zones of the reactor. Then, we calculate the most stable bulk and surface structures of the catalyst under different conditions of the reaction environment with density functional theory (DFT) calculations and ab initio thermodynamics, considering the presence of the MARIs on the catalyst surface in thermodynamic equilibrium with the partial pressures of their reservoirs in the gas phase surrounding the catalyst. Finally, we exploit the Wulff-Kaishew construction method to estimate the three-dimensional shape of the catalyst nanoparticles and the distribution of the active sites along the reactor coordinate. We find that the catalyst drastically modifies its morphology during CPO reaction by undergoing phase transition, in agreement with spectroscopy studies reported in the literature. The framework is also successfully applied for the analysis and interpretation of chemisorption experiments for catalyst characterization. These results demonstrate the crucial importance of rigorously accounting for the structural effect in microkinetic modeling simulations and pave the way towards the development of structure-dependent microkinetic analysis of catalytic processes

Quo vadis multiscale modeling in reaction engineering? A perspective

This work reports the results of a perspective workshop held in summer 2021 discussing the current status and future needs for multiscale modeling in reaction engineering. This research topic is one of the most challenging and likewise most interdisciplinary in the chemical engineering community, today. Although it is progressing fast in terms of methods development, it is only slowly applied by most reaction engineers. Therefore, this perspective is aimed to promote this field and facilitate research and a common understanding. It involves the following areas: (1) reactors and cells with surface changes focusing on Density Functional Theory and Monte-Carlo simulations; (2) hierarchically-based microkinetic analysis of heterogeneous catalytic processes including structure sensitivity, microkinetic mechanism development, and parameter estimation; (3) coupling first-principles kinetic models and CFD simulations of catalytic reactors covering chemistry acceleration strategies and surrogate models; and finally (4) catalyst-reactor-plant systems with details on linking CFD with plant simulations, respectively. It therefore highlights recent achievements, challenges, and future needs for fueling this urgent research topic in reaction engineering