Careful analysis of the Mg 1s and 2p core-level spectra, combined with the N 1s spectrum, revealed that surface Mg species are primarily nitrogen-deficient, consisting of oxides, hydroxides, and carbonates . However, probing deeper into the catalyst layer (10-12 nm) with tender X-rays demonstrated the presence of nitrogen-rich Mg nitride phases. These are represented by broad peaks at ~1305 eV (Mg 1s) and ~ 400 eV (N 1s) , likely corresponding to Mg₃N₂ and possibly another nitride phase (e.g., MgN) . The presence of nitride-related peaks suggests surface interactions between the deposited Mg and nitrogen during ammonia synthesis.