Li3N is a potential H-2 storage material due to its high theoretical H-2 capacity (10.4 wt %). A critical potential issue regarding this N-based storage material is the generation of NH3, which consumes some H-2 and also constitutes a poison for the downstream processes. In this Letter, by using the temperature-programmed decomposition of a two-layer material (LiNH2 and LiH), we demonstrate that NH3 produced via the decomposition of LiNH2 is completely captured by LiH even at very short contact times (25 ms) with the carrier gas. This ultrafast reaction between NH3 and LiH inhibits NH3 formation during the hydrogenation of Li3N and also prevents the NH3 generated during the dehydrogenation of the hydrogenated Li3N to escape into the H-2 stream. However, if the hydrogenated Li3N was previously exposed to the atmosphere, some NH3 could escape into the H-2 stream during the H-2 desorption, due to the partial oxidation of LiH by the water present in air.