A strategy for the scale-up of a monolith reactor dedicated to gas-liquid catalytic reactions is worked out; focus is made on the crucial step of gas-liquid mass transfer modelling via a steady-state numerical study based on a single channel and single unit cell representation, using a frame moving with the bubble and solving the liquid phase only. The relevance of this simplified approach is assessed through a specific case (given bubble shape, channel diameter and fluid flow rates), and hydrodynamics as well as mass transfer results are successfully compared to previously published numerical, semi-analytical and experimental works. Influence of unit cell length and of catalytic surface reaction rate is thoroughly investigated. Inferred overall mass transfer coefficients are found to increase with bubble frequency, due to higher interfacial area in unit cell and intensified recirculation in slug. Film contribution to mass transfer is usually found dominant in the case of short bubbles with reactive wall, and hardly varies with reaction rate. However, this contribution is strongly linked to bubble frequency, and a reliable evaluation of local mass transfer by correlations demands accurate knowledge on the precise dimensions of bubble, slug and film entities. (C) 2016 Elsevier B.V. All rights reserved.