Microchannel reactors are a promising route for monetizing distributed natural gas resources. However, intensification and miniaturization represent a significant challenge for reactor control. Focusing on autothermal methane-steam reforming reactors, a novel microchannel reactor temperature control strategy based on confining a layer of phase-change material (PCM) between the reactor plates is introduced. Melting-solidification cycles, which occur with latent heat exchange at constant temperature, allow the PCM layer to act as an energy storage buffera thermal flywheelconstituting a distributed controller that mitigates temperature excursions caused by fluctuations in feedstock quality. A novel stochastic optimization algorithm for selecting the PCM layer thickness (i.e., distributed controller tuning) is introduced. Furthermore, a hierarchical control structure, whereby the PCM layer is complemented by a supervisory controller that addresses persistent disturbances, is proposed. The proposed concepts are illustrated in a comprehensive case study using a detailed two-dimensional reactor model. (c) 2013 American Institute of Chemical Engineers AIChE J, 59: 20512061, 2013