Abstract:Hydrogen production via ammonia decomposition faces challenges due to low NHconversion, and the activity of ammonia decomposition catalysts requires improvement. Molecularsieves, with their large specific surface areas and well-developed pore structures, can serve as excellentcarriers for ammonia decomposition catalysts to enhance their activity. However, the influence ofmolecular sieve carrier properties on ammonia decomposition remains unclear. Therefore, three types ofmolecular sieve carriers widely used in ammonia decomposition, namely ZSM-5, SBA-15, and MCM-41, were selected, and a series of Co-based molecular sieve catalysts were prepared by the equal-volume impregnation method. This work investigated the effect of Co-based catalysts with differentmolecular sieve carriers (ZSM-5, SBA-15, MCM-41) on hydrogen production from ammoniadecomposition. The catalytic activity of the Co-based molecular sieve catalysts followed the order:Co/SBA-15 > Co/MCM-41 > Co/ZSM-5. Co/SBA-15 exhibited the best ammonia decompositionactivity. The physicochemical properties of the Co-based catalysts were analyzed using characterizationtechniques including BET, XRD, SEM, H-TPR, and NH-TPD to reveal the changes in the molecularsieve carriers before and after loading and their effects on ammonia decomposition performance. Thespecific surface area, pore structure, surface morphology, catalyst particle size, and acidic sites werefound to significantly influence the ammonia decomposition activity. In contrast, the redox capacity ofthe carriers and the metal grain size had a lesser impact. Based on the catalytic activity andcharacterization results, we concluded that an ideal carrier for an ammonia decomposition catalystshould possess a high specific surface area, a well-developed pore structure with an appropriate poresize, and a low density of weak acidic sites. The active sites of the ammonia decomposition reactionwere associated with the metallic cobalt state, and H reduction treatment of the catalyst prior to thereaction could increase the number of active sites, thereby effectively improving its ammoniadecomposition activity. Meanwhile, the Co/SBA-15 catalyst exhibited a lower apparent activationenergy for ammonia decomposition compared to the other two catalysts. Additionally, the Co/SBA-15catalyst exhibited excellent catalytic stability and reproducibility. Finally, in situ DRIFTS experimentson the Co/SBA-15 catalyst revealed the enrichment of —NH and —NH intermediates on its surface,indicating that the rate-limiting step in the ammonia decomposition reaction might be the recombinativedesorption of adsorbed N atoms. This study elucidates how the physicochemical properties of catalystcarriers influence ammonia decomposition performance and provides theoretical guidance for selectingcatalyst carriers for this reaction. Close-