Ammonia Decomposition with Manganese Nitride–Calcium Imide Composites as Efficient Catalysts

Abstract Ammonia has high gravimetric and volumetric hydrogen densities and is, therefore, considered a promising carrier for the production of CO x ‐free molecular H 2 for forthcoming energy systems. Alkaline earth metals are generally regarded as structural promoters of catalysts and employed in numerous catalytic processes. Here, we report that calcium imide (CaNH) has a strong synergistic effect on Mn 6 N 5 in catalyzing the decomposition of NH 3 , leading to a ca. 40 % drop in apparent activation energy. At 773 K, the H 2 formation rate over a Mn 6 N 5 ‐11CaNH composite catalyst is about an order of magnitude higher than that of Mn 6 N 5 and comparable to the highly active Ni/SBA‐15 and Ru/Al 2 O 3 catalysts. Analysis by means of temperature‐programmed decomposition (TPD), X‐ray diffraction (XRD), and X‐ray absorption near edge spectroscopy (XANES) reveal that CaNH participates in the catalysis via forming a [Ca 6 MnN 5 ]‐like intermediate, thus altering the reaction pathway and energetics. A two‐step catalytic cycle, accounting for the synergy between CaNH and Mn 6 N 5 , is proposed.