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ABSTRACT: The interactions between small gold oxide cluster anions, Au(2,3)O-(n) (n=1-5), and CO were investigated in a fast-flow reactor mass spectrometer, and experimental results were verified with a guided ion beam mass spectrometer. Density functional calculations along with molecular dynamics simulations were also utilized to explain the experimental findings. From these studies, we show that, for the interactions between Au(m)O-(n) and CO, each atom counts. With the addition of a single gold atom, it is observed that association of CO and replacement of O(2) by CO become the dominant reaction channels as opposed to CO oxidation. We also present results that show that the oxidation of CO takes place only in the presence of a peripheral oxygen atom. However, this condition is not always sufficient. Furthermore, the association of CO onto Au(m)O-(n) follows a general qualitative rule based on the relationship between the energy of the cluster lowest unoccupied molecular orbital and the binding energy of CO.
The Journal of Chemical Physics 12/2006; 125(20):204311. · 3.33 Impact Factor
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ABSTRACT: The interactions between small gold oxide cluster anions, Au2,3On− (n = 1–5), and CO were investigated in a fast-flow reactor mass spectrometer, and experimental results were verified with a guided ion beam mass spectrometer. Density functional calculations along with molecular dynamics simulations were also utilized to explain the experimental findings. From these studies, we show that, for the interactions between AumOn− and CO, each atom counts. With the addition of a single gold atom, it is observed that association of CO and replacement of O2 by CO become the dominant reaction channels as opposed to CO oxidation. We also present results that show that the oxidation of CO takes place only in the presence of a peripheral oxygen atom. However, this condition is not always sufficient. Furthermore, the association of CO onto AumOn− follows a general qualitative rule based on the relationship between the energy of the cluster lowest unoccupied molecular orbital and the binding energy of CO.
The Journal of Chemical Physics 11/2006; 125(20):204311-204311-14. · 3.33 Impact Factor
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ABSTRACT: A systematic experimental and theoretical investigation of the influence of reactant energy on the reactivity of (V(2)O(5))(n)=1,2(+) clusters with ethylene (Justes, D. R.; Mitrić, R.; Moore, N. A.; Bonacić-Koutecký, V.; Castleman, A. W., Jr. J. Am. Chem. Soc., 2003, 125, 6289) provided evidence of the rate controlling steps in the reaction. Herein, we present further experimental and theoretical evidence for our recently proposed radical cation mechanism for oxygen atom transfer from (V(2)O(5))(n)=1,2(+) clusters to ethylene. In particular the results of ab initio molecular dynamics simulations are found to further support the radical cation mechanism. Experimental reaction cross sections at the zero pressure limit and rate coefficients show that the energy dependence of the reaction cross section is in accord with the Langevin formula. Evidence is presented that ion-molecule association is the rate determining step, whereas subsequent hydrogen transfer and formation of acetaldehyde proceed without significant barriers. We propose a kinetic model for the reaction cross section that fully accounts for the experimental findings. The model offers the prospect of elucidating the details of the general reaction mechanisms through a study of the energy dependence of the reaction cross sections.
The Journal of Physical Chemistry B 03/2006; 110(7):3015-22. · 3.70 Impact Factor
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ABSTRACT: We present joint theoretical and experimental results which provide evidence for the selectivity of V(x)O(y)(+) clusters in reactions toward ethylene due to the charge and different oxidation states of vanadium for different cluster sizes. Density functional calculations were performed on the reactions between V(x)O(y)(+) and ethylene, allowing us to identify the structure-reactivity relationship and to corroborate the experimental results obtained by Castleman and co-workers (Zemski, K. A.; Justes, D. R.; Castleman, A. W., Jr. J. Phys. Chem. A 2001, 105, 10237). The lowest-energy structures for the V(2)O(2)(-)(6)(+) and V(4)O(8)(-)(10)(+) clusters and the V(2)O(3)(-)(6)(+)-C(2)H(4) and V(4)O(10)(+)-C(2)H(4) complexes, as well as the energetics for reactions between ethylene and V(2)O(4)(-)(6)(+) and V(4)O(10)(+) are presented here. The oxygen transfer reaction pathway was determined to be the most energetically favorable one available to V(2)O(5)(+) and V(4)O(10)(+) via a radical-cation mechanism. The association and replacement reaction pathways were found to be the optimal channels for V(2)O(4)(+) and V(2)O(6)(+), respectively. These results are in agreement with the experimental results reported previously. Experiments were also conducted for the reactions between V(2)O(5)(+) and ethylene to include an energetic analysis at increasing pressures. It was found that the addition of energy depleted the production of V(2)O(4)(+), confirming that a more involved reaction rather than a collisional process is responsible for the observed phenomenon. In this contribution we show that investigation of reactions involving gas-phase cationic vanadium oxide clusters with small hydrocarbons is suitable for the identification of reactive centers responsible for selectivity in heterogeneous catalysis.
Journal of the American Chemical Society 06/2003; 125(20):6289-99. · 9.91 Impact Factor
