期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2008
卷号：105
期号：47
页码：18108-18113
DOI：10.1073/pnas.0801539105
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：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[IMG]f1.gif" ALT="Formula" BORDER="0">, W2O[IMG]f2.gif" ALT="Formula" BORDER="0">, and W3O[IMG]f3.gif" ALT="Formula" BORDER="0">, exhibit enhanced activity and selectivity for the transfer of a single oxygen atom to propylene (C3H6), suggesting the formation of propylene oxide (C3H6O), 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 CO2, 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[bullet]) 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.
