| The oxidation of CO is a widely studied reaction in catalytic chemistry due to its importance in areas such as odor removal, chemical sensors, and combustion chemistry, including fuel cell applications. Various metal oxide surfaces have been utilized to increase the efficiency and selectivity of the oxidation process. Within the past 20 years, gold has received increased attention for this reaction. However, due to the inert nature of bulk gold, the mechanisms that govern the CO oxidation reaction in the presence of nanoscale gold are not fully understood, and widely varying processes and surface features are reported to be responsible. Gas phase clusters are gaining acceptance as model systems for the investigation of the fundamental characteristics of gold catalysts.{09}Experiments utilizing ionic clusters can serve to unravel some of the discrepancies found from condensed phase studies and shed light on the roles that charge state, stoichiometry, and size play on the oxidation of CO in the presence of gold.; In this context, the oxidation of CO has been investigated in the presence of preoxidized gold cluster ions. A fast flow reactor mass spectrometer, coupled to a laser vaporization source, was utilized to obtain reactivity and kinetic information. Initially, the products of the reactions between the gold cluster ions with oxygen, which is added into the metal plasma formed by the ablation of the metal rod, were investigated. This produced gold oxide ions with gold in both the molecular and atomized farms. For Aun - species with n = 1--16, between 1 and 11 oxygen atoms were observed to attach to the various gold cluster anions. However, no direct relationship between cluster size and the number of bound oxygen atoms was observed.; Upon establishing the binding patterns for oxygen atoms onto the gold oxides, the oxidation of CO in the presence of the gold oxide anions was examined. From these studies, select monomer and dimer oxide anions were observed to undergo reactions with CO to produce CO2. However, beginning with the Au3On- species, association of CO onto the gold oxide anions and replacement of oxygen atoms or molecules with CO were also observed. Furthermore, through collaboration with the theoretical group of Professor V. Bonacic-Koutecky at the Humboldt University in Berlin, structural features were realized and reaction dynamics and energetic profiles were determined. Combining the theoretical and the experimental results, a reaction mechanism for the oxidation of CO was proposed. (Abstract shortened by UMI.)... |
