Utilizing a customized multiple-ion laminar flow tube reactor in tandem with a triple quadrupole mass spectrometer, we report a study of the gas-phase reactivity of Ag n + clusters with acetylene. Well-resolved Ag n + clusters (n = 1–20) are produced by a self-designed magnetron sputtering source (MagS); however, on their reactions with acetylene under sufficient collisional conditions, only Ag7 +[C2H2] is produced with a reasonable intensity. DFT calculations reveal that Ag n + clusters do not form strong Ag–C bonds with C2H2 and Ag7 +[C2H2] bears larger binding energy than the other Ag n +[C2H2] although within similar cluster−π interactions. Besides gas-phase reaction rate estimation, the relatively large noncovalent cluster−π interaction in Ag7 +[C2H2] is fully demonstrated via topological analysis and natural bonding orbital analysis. Also, we illustrate both thermodynamically and kinetically favored channels in producing the Ag7 +[C2H2]. This study helps in understanding metal-involved noncovalent bonds and how such weak interactions are able to tune the material function and biological activity.
Catalytic N 2 activation and reduction for ammonia synthesis has been subject of intense research interest. Cluster-modified catalysts have been proposed as promising candidates for nitrogen activation due to the featured active sites and maximized synergistic effect. However, the nature of metal clusters itself has not been fully unveiled. Herein, we report a systematic investigation of N 2 activation and reduction on three-atom metal clusters (M 3 ) of all the 20 transition metals in the third and fourth periods of elements. We evaluate the catalysis of these M 3 clusters by taking into consideration three critical processes, namely, N 2 dissociation, hydrogenation, and NH 3 desorption. The TM I series of the M 3 clusters (Group 3B−5B metals) are found to support N 2 dissociation spontaneously, in contrast to the TM II and TM III clusters (i.e., Groups 6B−8B and 1B−2B). Based on the three criteria, Y 3 , Sc 3 , Zr 3 , and Nb 3 are identified as eligible candidates for ammonia synthesis. These clusters show preferable hollowsite N 2 adsorption and strong orbital hybridization, with electronic backdonation from the metal d orbitals to both π* and π/σ orbitals of N 2 . Further studies on ammonia synthesis have been conducted by applying Y 3 and Nb 3 clusters supported on graphene (Y 3 /G and Nb 3 /G), illustrating superior activity and potential application of such M 3 clusters. This work validates the three-atom cluster catalysis and guides the design of efficient catalysts for N 2 fixation.
We have developed an integrated instrument system of a multiple-ion laminar flow tube (MIFT) reactor combined with a tandem quadrupole mass spectrometer (TQMS) and soft-landing deposition (SD) apparatus. A customized water-cooling magnetron sputtering (MagS) source is designed, by which we are able to attain a highly efficient preparation of metal clusters of 1–30 atoms with tunable size distributions. Following the MagS source, a laminar flow tube reactor is designed, allowing for sufficient gas–collision reactions of the as-prepared metal clusters, which is advantageous for probing magic clusters and minimizing wall effects when probing the reaction dynamics of such clusters. The customized TQMS analyzer involves a conical octupole, two linear octupoles, a quadruple ion deflector, and a 19 mm quadruple mass analyzer, allowing to decrease the pressure stepwise (from ∼5 to ∼10−9 Torr), thus ensuring high sensitivity and high resolution of the mass spectrometry analysis. In addition, we have designed a dual SD apparatus for the mass-selected deposition of clusters and their reaction products. For the whole system, abbreviated as MagS-MIFT-TQMS-SD, we have performed a detailed ions-fly simulation and quantitatively estimated the ions transfer efficiency under vacuum conditions determined by real experiments. Taking these advantages, well-resolved Pbn+, Agn+, and Nbn+ clusters have been produced, allowing for meticulous studies of cluster reactions under sufficient gas-phase collisions free of electric field trapping. Also, we have tested the efficiency of the dual SD.
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