The effects of the catalyst pore network structure on multiphase reactions in catalyst pellets are investigated by using the experimentally validated pore network model proposed in our recent work (AIChE J, 62, 451, 2016). The simulations display hysteresis loops of the effectiveness factor. The hysteresis loop area becomes significantly larger, when having small volume-averaged pore radius, wide pore-size distribution, and low pore connectivity; however, the loop area is insensitive to pellet size, even though it affects the value of the effectiveness factor. The hysteresis loop area is also strongly affected by the spatial distribution of the pore size, in particular for a bimodal pore-size distribution. The pore network structure directly influences mass transfer, capillary condensation, and pore blocking, and subsequently passes these influences on to the hysteresis loop of the effectiveness factor. Recognizing these effects is essential when designing porous catalysts for multiphase reaction processes. (c) 2016 American Institute of Chemical Engineers AIChE J, 63: 78-86, 2017