Hierarchical Refinement of Microkinetic Models: Assessment of the Role of the WGS and r-WGS Pathways in CH4 Partial Oxidation on Rh

In this article, we demonstrate how first-principles calculations can be effectively employed in the development of microkinetic models for practical catalysis, despite material gaps and calculation uncertainties. In particular, we develop a hierarchically refined microkinetic model for the conversion of CH4 to syngas on Rh/alumina that incorporates peculiar insights from first-principles modeling. This model is able to correctly describe the behavior of the reacting system under significantly different conditions and also exhibits consistency between the predicted catalytic cycle and the observed reaction orders. We show that consistency between the kinetic parameters of all of the elementary steps included in the microkinetic model is of utmost importance in achieving full predictivity of the model. As a consequence, the information from various levels of theory needs to be integrated in an underlying framework that accounts for coverage effects and thermodynamic and kinetic consistencies. Within this scope, we performed a detailed microkinetic analysis of kinetic experiments in an annular reactor to hierarchically modify the reaction parameters guided by first-principles analysis. Then, to further assess the capabilities of the refined microkinetic model, we performed a microkinetic analysis of spatially resolved CH4 partial oxidation experiments on foams at different conditions of H2O and CO2 cofeed. The insights derived from first-principles calculations and included in the semiempirical microkinetic model were found to be pivotal for explaining the roles of the WGS and r-WGS in catalytic partial oxidation experiments. On the whole, this contribution provides a clear demonstration of the current possibilities and potentialities of first-principles machinery in developing microkinetic models for complex catalytic processes and represents the first practical example of the full application of the first-principles hierarchical refinement of a microkinetic model.