In this study, porous membrane reactors with various characteristic length (inner diameter), controllable catalyst support thickness, active catalyst surface area and tunable wetting properties are described for heterogeneously catalyzed gas¿liquid¿solid (G¿L¿S) reactions. We developed porous ceramic membrane reactors (Al2O3) with various geometrical parameters and applied these to a model G¿L¿S reaction. Integration of a catalyst support layer (¿-Al2O3), catalyst deposition (palladium) and surface modification (hydrophobization) steps were carried out to tailor these tubular porous ceramic reactors. These reactors were tested for catalytic hydrogenation of nitrite ions () in water for different initial concentrations and flow rates. In addition, to improve the external mass transfer in the liquid phase, we integrated additional slug flow in our porous reactors, merging the advantages of both dispersed phase and membrane reactor operation. Results showed that the reaction rate per Pd-catalyst decreased with increasing thickness of the catalyst support layer, indicating internal mass transfer limitations. Reducing the inner diameter of the reactor and also integration of slug flow enhanced the performance by improving its external mass transfer.