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 CH 4 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 CH 4 partial oxidation experiments on foams at different conditions of H 2 O and CO 2 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.

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This paper extends a previous investigation on the thermal behavior of CH 4 -CPO reformers with honeycomb catalysts. Modeling and experimental studies on the short contact time catalytic partial oxidation (CPO) of CH 4 to syngas from our and from other groups have shown that Rh-catalysts rapidly deactivate at the very high temperatures, close to 1000°C, that establish in the inlet zone of the reactor. We have previously shown that a significant reduction of the surface hot-spot temperature can be obtained by properly designing the catalyst: beneficial effects are observed at increasing opening of the honeycomb channels, which decreases the rate of O 2 inter-phase mass transfer, and at increasing catalyst activity, which promotes the rate of the endothermic reactions. In this work, we explore the effect of the reactor configuration, namely the effect of heat dispersion from the glowing front face of the monolith. Three reactor configurations were compared in CH 4 -CPO experiments: (i) a configuration with perfect continuity between the front heat shield (FHS) and the catalytic module, which behaved close to an ideal adiabatic reactor, (ii) a configuration where the FHS was separated from the catalytic monolith and (iii) a configuration where the FHS was at large distance from the catalytic module. State of the art experimental tools, including the spatially resolved measurement of temperature and concentration profiles were used to characterize the thermal behavior of the various configurations. Detailed kinetic modeling supported the analysis of data. The results showed that, at the expense of a small loss of thermal efficiency, a very moderate loss of performance in terms of conversion and selectivity, but, remarkably, an important reduction of the surface inlet temperatures were achieved. Preliminary experiments with propane/air mixtures suggest that the adoption of a moderately dispersive reactor can represent a promising solution for the stable operation of catalytic units treating heavier fuels than methane.

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