A particle-resolved CFD analysis of kinetic modeling based on profile reactor data using pseudo-continuum models

Profile reactors enable the acquisition of spatially resolved concentration and temperature profiles in fixed bed reactors and have developed into an important laboratory tool in heterogeneous catalysis. However, the quantitative evaluation of such data for kinetic modeling is often accompanied by input and reactor model uncertainties, particularly with respect to heat and mass transfer as well as the impact of the sampling capillary. In this work, we combine experimentally validated particle-resolved reactive CFD of a profile reactor for the CO 2 methanation reaction on a Ni/Al 2 O 3 catalyst with a systematic assessment of heterogeneous and homogeneous pseudo-continuum models. Homogeneous pseudo-continuum models proved incapable of adequately describing product selectivity, while heterogeneous models, even when considering the influence of the sampling capillary and adjusted boundary conditions at the reactor walls, still cannot describe heat transport within the reactor correctly, leading to erroneous kinetic parameters. Neglecting the evaluation of the energy balance and inserting the measured average temperature profile directly into computationally efficient one-dimensional models can yield improved results by circumventing these model uncertainties. However, this procedure is only viable when the reaction rate can be linearized with sufficient accuracy over the radial temperature range. To verify this prerequisite, we derive a condition that can be easily evaluated numerically a posteriori, based on measured quantities in the profile reactor and the obtained reaction kinetics, ultimately enhancing the efficient utilization of profile reactors in kinetic research.