We employed a new experimental technique known as spatially resolved capillary-inlet mass spectrometry (SpaciMS) to observe the evolution of multiple species inside the channels of a monolithic NOx storage-reduction (NSR) catalyst. The NSR material consisted of a Pt/K/ Al2O3 washcoat deposited inside cordierite monolith channels. Spatially and temporally resolved measurements were made over the monolith length in a bench flow reactor during fast cycling between synthetic lean and rich environments at 200 and 300 degrees C. Regeneration was found to be very efficient at 300 degrees C regardless of whether pure H-2, pure CO, or mixtures of H-2 and CO were employed. At 200 degrees C, CO was noticeably less effective than H-2. We conjecture that at 200 degrees C CO may be inhibiting the regeneration process through its strong adsorption on Pt. Generation of H-2 by water-gas shift was seen at 300 degrees C but not at 200 degrees C. Published by Elsevier B.V.