Effect of Catalyst Deactivation on Ignition and Combustion Characteristics in a Catalytic Micro-Reactor: Numerical Study with Resolved Catalyst Coating

Catalytic micro-reactors offer a promising solution for portable power generation, yet catalyst deactivation during long-term operation remains a critical challenge to reliable ignition and combustion stability. In this work, a transient numerical model is developed to conduct a sensitivity study of ignition and combustion performance to catalyst deactivation, represented as prescribed reductions in catalytic activity, for a propane-fueled straight-channel micro-combustor. The present model explicitly resolves the porous catalyst coating layer as a separate computational domain, incorporating a combined Knudsen and molecular mixed-diffusion mechanism to capture species transport resistance within the microporous structure. The results demonstrate that increasing catalyst deactivation markedly deteriorates ignition performance. As the deactivation index rises from 0.1 to 0.9, the ignition temperature increases from 488 K to 588 K in a distinctly nonlinear manner, with the greatest sensitivity observed at high deactivation levels. At inlet temperatures 10 K above the respective ignition thresholds, the ignition delay time is prolonged from 191 s to 224 s when the deactivation index increases from 0.7 to 0.9, attributed to the dominance of kinetic deterioration over sensible heat compensation. The heterogeneous reaction contribution, although decreasing with deactivation, remains above 95% across all cases, indicating that the gas-phase pathway is largely suppressed due to the inherently low temperature environment within the microchannel. Spatial distributions of temperature and CO2 mass fraction reveal that combustion is confined to the near-inlet region, with a peak temperature of approximately 1001 K at the highest deactivation level. These findings quantify the sensitivity of ignition and combustion characteristics to catalyst deactivation.