Ammonia activation and nitride formation pathways in transition metal clusters: insights from mass spectrometry and first-principles DFT

Abstract

The interaction of ammonia (NH3) with laser-vaporized transition metal clusters (Ti, V, Fe, Co, and Ni) was systematically investigated using reflectron time-of-flight mass spectrometry and density functional theory. Metal-specific and size-dependent trends emerge: Ti clusters readily form (TiN)n (n = 1–7), indicating strong nitride formation. Neutral Vn and Fen clusters predominantly yield mononitrides, with the NH3 dehydrogenation efficiency varying with cluster size and charge. Con clusters show limited reactivity with mainly NH3 adsorptions and partial dehydrogenation, while Nin clusters exhibit extensive NH3 uptake, leading to stable nitride/imide species such as NiN(NH3)4 and Ni(NH)2(NH3)4, along with the formation of Ni+H2 via hydrogen release─likely resulting from the reaction of Nin+ clusters with NH3. These findings provide insights into ammonia activation, N–H bond cleavage, and transition metal nitride formation mechanisms in small clusters.