Grant Johnson - Cluster reactivity experiments: Employing mass spectrometry to investigate the molecular level details of catalytic oxidation reactions

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      Publication Details (including relevant citation   information):

    PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA

      Volume:   105

        Issue: 47

        Pages: 18108-18113

    DOI:10.1073/pnas.0801539105

    Published: NOV 25 2008

      Abstract:

        Mass spectrometry is the most widely used tool in the study of   the properties and reactivity of clusters in the gas phase. in   this article, we demonstrate its use in investigating the   molecular-level details of oxidation reactions occurring on the   surfaces of heterogeneous catalysts via cluster reactivity   experiments. Guided ion beam mass spectrometry (GIB-MS) employing   a quadrupole-octopole-quadrupole (Q-O-Q) configuration enables   mass-selected cluster ions to be reacted with various chemicals,   providing insight into the effect of size, stoichiometry, and   ionic charge state on the reactivity of catalyst materials. For   positively charged tungsten oxide clusters, it is shown that   species having the same stoichiometry as the bulk, WO(3)(+),   W(2)O(6)(+), and W(3)O(9)(+), exhibit enhanced activity and   selectivity for the transfer of a single oxygen atom to propylene   (C(3)H(6)), suggesting the formation of propylene oxide   (C(3)H(6)O), an important monomer used, for example, in the   industrial production of plastics. Furthermore, the same   stoichiometric clusters are demonstrated to be active for the   oxidation of CO to CO(2), a reaction of significance to   environmental pollution abatement. The findings reported herein   suggest that the enhanced oxidation reactivity of these   stoichiometric clusters may be due to the presence of radical   oxygen centers (W-O circle) with elongated metal-oxygen bonds.   The unique insights gained into bulk-phase oxidation catalysis   through the application of mass spectrometry to cluster   reactivity experiments are discussed.

      Address (URL): http://www.pnas.org/content/105/47/18108