Reactivity of Cobalt Clusters Co<i><sub>n</sub></i><sup>±/0</sup> with Ammonia: Co<sub>3</sub><sup>+</sup> Cluster Catalysis for NH<sub>3</sub> Dehydrogenation
Lijun Geng, Chaonan Cui, Yuhan Jia, Haiming Wu, Hanyu Zhang, Baoqi Yin, Zhen-Dong Sun, Zhixun Luo
Abstract
A customized reflection time-of-flight (Re-TOF) mass spectrometer combined with a 177 nm deep-ultraviolet laser has enabled us to observe well-resolved cobalt clusters Con±/0 and perform a comprehensive study of their reactivity with ammonia (NH3). The anions Con– are found to be inert, the neutrals allow the adsorption of multiple NH3 molecules, while the cationic Con+ clusters readily react with NH3 giving rise to dehydrogenation. However, incidental dehydrogenation of NH3 on Con+ is only observed for n ≥ 3. The dramatic charge- and size-dependent reactivities of Con±/0 clusters with NH3 are studied by the density functional theory (DFT)-calculation results of energetics, density of states, orbital interactions, and reaction dynamics. We illustrate the dehydrogenation from two NH3 molecules, where a significantly reduced transition-state energy barrier is found pertaining to the dimolecular co-catalysis effect. The reactivity of Co3+ with NH3 is illustrated showing effective catalysis for N–H dissociation to produce hydrogen applicable for designing ammonia fuel cells.