(491c) Numerical Investigation of the Kinetics of Methane Dry Reforming at Low Temperature

Dry reforming of methane (DRM) over Ni-based supported catalysts at relatively low temperature (500°C-700°C) has been widely studied owing to the low cost and abundant of Ni. To increase the activity and stability of the catalysts, many groups have focused on modifying Ni-based catalysts with small amount of noble metals. Recent studies reported the effect of morphology on the activity of the yolk-shell structured catalysts under DRM, suggesting the possible solution to maintaining high catalysts performance under low temperature by tuning the catalyst structure. However, the reaction mechanisms of the DRM over the yolk-shell catalyst remain unclear. Here, we studied the reaction kinetics by proposing detailed elementary reaction mechanisms of DRM over NiCe@SiO₂ multi-yolk-shell nanotube catalyst. We investigated the formation of 12 surface species, and simulated the kinetics of 17 elementary steps of DRM, reverse water-gas shift, methane decomposition, and carbon gasification in a fixed-bed reactor using COMSOL Multiphysics®. The result shows CO₂ and CH₄ conversion of 14% and 8.1%, respectively, and the CO yield of 10% at the initial stage of the reaction. This matches well with the experiments. The model also shows that the adsorption of CO₂ and CH₄ can be determined as the rate limiting steps, which is consistent with the widely accepted Langmuir-Hinshelwood mechanism. The surface dissociation of CH₃*, CH₂*, and CH* are fast, compared with the adsorption of CH₄, which improve the production of H₂ by pushing the equilibrium of CH₄ decomposition to the forward direction. The dissociative adsorption of CO₂ and the production of CO* have a significant effect on CO production. Our model suggests O* is the primary deactivating surface species in the process, likely by occupying oxygen vacancies in the catalyst structure. Insights drawn from this work can lead to the design of high-performance DRM catalysts.