Reactivity of small transition-metal clusters with CO

Mats T. Andersson; H. Gronbeck; L. Holmgren; Arne Rosen

doi:10.1117/12.220843

18 September 1995 Reactivity of small transition-metal clusters with CO

Mats T. Andersson, H. Gronbeck, L. Holmgren, Arne Rosen

Proceedings Volume 2548, Laser Techniques for State-Selected and State-to-State Chemistry III; (1995) https://doi.org/10.1117/12.220843
Event: SPIE's 1995 International Symposium on Optical Science, Engineering, and Instrumentation, 1995, San Diego, CA, United States

Abstract

The size-dependent reactivity of several transition-metal clusters: Co_n, Nb_n, Rh_n, and W_n with CO has been investigated in a cluster beam experiment. The reactions occur at single-collision-like conditions and the results are evaluated in terms of the reaction probability (S) in a collision. For all the four metals, clusters with more than 10 - 15 atoms show a high reaction probability, S >= 0.4, rather independent of size. For smaller Nb_n and W_n, the reaction probability is lower, and for Nb_n, large variations in the CO reactivity are observed in the n equals 8 - 13 range with a distinct minimum at Nb₁₀. Using an LCAO approach within the local spin density approximation (LSDA) the adsorption of molecular CO on Nb_n has also been investigated theoretically. The geometries of the bare clusters were optimized and two different sites for CO were investigated. The discussion is based on a detailed analysis of Nb₄. The calculations show that compact structures with high coordination numbers are the most stable ones for the bare Nb clusters and hollow sites, also maximizing the coordination, are preferred for CO adsorption. The calculations indicate that a high CO-Nb_n bond strength is obtained for clusters with a high density of states close to the Fermi level and for which the HOMO level has a symmetry that allows for an efficient back-donation of electrons to the 2(pi) ^*-orbital of CO. A particularly low chemisorption energy was calculated for the Nb₁₀ cluster.

Citation Download Citation

Mats T. Andersson, H. Gronbeck, L. Holmgren, and Arne Rosen "Reactivity of small transition-metal clusters with CO", Proc. SPIE 2548, Laser Techniques for State-Selected and State-to-State Chemistry III, (18 September 1995); https://doi.org/10.1117/12.220843

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