The objective of the study is to investigate the effects of inlet flow pulsation on the mixing and reaction performance of a heterogeneous gaseous T-junction microreactor numerically. The idea is to have a novel modular microreactor design comprised of two microreactors (A and B), arranged in parallel, and a valve to control the flow direction. Flow pulsation can then be implemented to alternately supply reactant to microreactor A and microreactor B. Hence, by feeding the same amount of reactant and thus same pumping power/parasitic loads, the new design is able to run two microreactors and could achieve almost the same level of performance as that of a steady flow microreactor with an expense of one microreactor. The study was carried out for a case of mixing and heterogeneous catalytic reaction of methane (gaseous fuel) oxidation at the microreactor surface coated with a platinum catalyst. A detailed parametric study was performed to include the effect of frequency, amplitude, phase difference, and different waveforms on the conversion rate of gaseous fuel and pressure drop across the microreactor. The results suggest that the flow pulsation marginally affects the reaction performance, in which, the whole novel modular system produces almost double yields and energy (temperature) than that of conventional steady flow single microreactor design under the same amount of inlet reactants. This highlights the potential of this novel design in saving energy, enhancing reactants utilization, and increasing yield production for several applications.