This paper provides a proof of concept for the capability of the barrier-based micro-/millichannels reactor (BMMR) to number-up gas–liquid Taylor flow under reactive flow conditions. The hydrogenation of phenylacetylene to styrene and ethylbenzene using homogeneous cationic rhodium catalysts [Rh(NBD)(PPh3)2]BF4] (NBD = norbornadiene) was used as a model reaction. First, a parametric study in a semicontinuous batch reactor was made by changing the hydrogen pressure, the catalyst concentrations, and the initial concentrations of phenylacetylene and styrene. A mechanism for this reaction system has been proposed by Esteruelas et al. ( J. Org. Chem. 1998, 49-53). This mechanism was extended here to develop a kinetic model which predicts the experimental result within an accuracy of 20%. Catalyst deactivation was observed and incorporated in the kinetic model. Second, the reaction was conducted in the BMMR. The reactant and product concentrations of a single channel were compared to those of eight parallel channels combined. For 95% of the obtained results, the difference in concentrations between the single channel and the eight channels was within ±10% and depended on the gas and liquid flow rates. As a proof of concept, the number-up concept of gas–liquid Taylor flow in the BMMR under reactive flow conditions has been successfully realized.