Ammonia Dehydrogenation on Cobalt Cluster Cations Doped with Niobium

Anomalously Efficient Dehydrogenation of NH3 on Ir4+ and Ir5. J Phys Chem A 2022;126:4451-4455. [PMID: 35786880 DOI: 10.1021/acs.jpca.2c03316] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Gas-phase reactions of iridium cluster cations, Ir_n⁺ (n = 1-8), with ammonia are studied at near-thermal energies. In single collision reactions, dehydrogenation of NH₃ proceeds at n = 1-5, and in particular, Ir₄⁺ and Ir₅⁺ are found to be significantly reactive. This size dependence is quite different from those of other platinum group metal cluster cations, where usually only the dimers are able to dehydrogenate NH₃. Moreover, the sequentially dehydrogenated products, Ir_4,5(NH)_m⁺ (m = 2-5), are chiefly observed under multiple collision conditions. This observation suggests that the NH species on Ir_4,5⁺ possibly encourages, or at least does not prohibit, the adsorption of the coming NH₃ molecule and the dehydrogenation.

Preadsorption Effect of Carbon Monoxide on Reactivity of Cobalt Cluster Cations toward Hydrogen

We report gas-phase reactions of free Co_n(CO)_m⁺ (n = 3-11, m = 0-2) with H₂, expecting a catalytic reaction of coadsorbed CO and H₂ on Co_n⁺. Preadsorption of CO molecules is found to promote H₂ adsorption, in particular, on Co_n(CO)⁺ (n = 5, 8-10). Density functional theory (DFT) calculations reveal that the reactivity is governed by the molecular-orbital energy of Co_n⁺, which is tuned by preadsorbed CO molecules. Collision-induced-dissociation experiments performed on Co_nCOH₂⁺ (n = 8-10) imply that at least some of the CO and H₂ molecules are bound together on Co_n⁺.

Reactivity of Cobalt Clusters Con±/0 with Ammonia: Co3+ Cluster Catalysis for NH3 Dehydrogenation

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 Co_n^±/0 and perform a comprehensive study of their reactivity with ammonia (NH₃). The anions Co_n^- are found to be inert, the neutrals allow the adsorption of multiple NH₃ molecules, while the cationic Co_n⁺ clusters readily react with NH₃ giving rise to dehydrogenation. However, incidental dehydrogenation of NH₃ on Co_n⁺ is only observed for n ≥ 3. The dramatic charge- and size-dependent reactivities of Co_n^±/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.

Liquid-phase catalysis by single-size palladium nanoclusters supported on strontium titanate: size-specific catalysts for Suzuki–Miyaura coupling

Size-specific catalysis by single-size palladium nanoclusters.