Microkinetic modeling of spatially resolved autothermal CH4 catalytic partial oxidation experiments over Rh-coated foams

Spatially resolved autothermal experiments of CH4 catalytic partial oxidation (CPO) performed over Rhcoated foams were analyzed using a detailed reactor model and a novel, thermodynamically consistent C1 microkinetic scheme. The effect of depositing Rh (5 wt%) on an 80 ppi a-Al2O3 foam directly or after washcoating with c-Al2O3 washcoat (2 wt%) was examined. For the first time, a fully predictive approach was adopted in the numerical analysis by introducing in the model the experimentally estimated catalyst metal surface area and state of the art correlations for heat and mass transfer in foams. Characterization of the catalysts by H2 pulse chemisorption and SEM microscopy revealed that the washcoat addition increased the metal area by almost one order of magnitude, from 74 cm2/gFoam on Rh foams to 630 cm2/gFoam on washcoated foams. The numerical results showed that the model is able to quantitatively account for the axial evolution of the species and the temperature profiles of the solid and the gas phase within the catalyst volume. In line with previous results, it was confirmed that the consumption of O2 is strictly governed by mass transfer and that the co-presence of O2 and syngas in the bulk of the gas phase is exclusively due to mass transfer limitations. Reaction path analysis showed that CH4 is activated via pyrolytic decomposition and its main oxidizer is OH and not O, both in the oxidation zone and in the reforming zone of the catalyst. By application of the most up-to-date experimental and numerical tools, the present results provide a clear picture of CH4 CPO and emphasize the importance of modeling spatially resolved experiments in order to properly interpret the high density of information that these kinds of data provide.