Abstract Monolithic reactors are an attractive alternative to conventional multi-phase reactors. Advantages are the low pressure drop, the absence of a need for a catalyst separation, and the large geometrical surface area. The main disadvantage is, however, the lack of practical experience with monolithic reactors. A pilot-scale study has been carried out to evaluate the performance of a monolithic reactor on a larger scale. The results of this study have demonstrated that a higher productivity can be obtained for a monolithic reactor compared to a trickle-bed reactor for a solid catalysed gas–liquid reaction that is mass transfer limited in the gas-phase reactant. A higher selectivity has been demonstrated for the selective hydrogenation of benzaldehyde towards benzylalcohol when a monolithic reactor is used instead of a trickle-bed reactor as a result of the narrower residence-time distribution.