The Interaction of Nitric Oxide and Carbon Monoxide With Platinum
The dissertation considers several aspects of the interactions of nitric oxide and carbon monoxide with platinum, and each other. A model based on the conservation of orbital symmetry and a simplified picture of the surface's band structure is presented. The model successfully explains the plane to plane variation in the dissociation activity of platinum for nitric oxide. The model predicts that stepped surfaces with a m(100) x n(110) orientation, with m greater than n plus one, should be especially active for nitric oxide decomposition. This prediction is experimentally tested using thermal desorption spectroscopy and reflection absorption infared spectroscopy on one such surface, platinum (410). A new system was constructed for the infared work which was capable of measuring 2 nanograms of carbon monoxide at a resolution of one reciprocal centimeter. Experiments demonstrate that the (410) face of platinum dissociates both carbon monoxide and nitric oxide. Nitrogen desorption from a nitric oxide covered (410) surface is found to follow simple second order kinetics, with an activation energy of 18 kcal/mol and a preexponential of 1.5 x 10('12)/sec. The saturation coverage of nitric oxide was found to be about half that of carbon monoxide. Coadsorption of the two molecules on the (410) surface produces carbon dioxide and molecular nitrogen. Reflective infared experiments show one band at 2075-2094 reciprocal centimeters when carbon monoxide or 1634-1641 when nitric oxide is adsorbed on platinum (100). Coadsorption of the two molecules demonstrate a chemical interaction between the two species exists. Platinum (410) demonstrates one absorbance band at 2065-2082.5 reciprocal centimeters when carbon monoxide is adsorbed at room temperature, but two bands if the layer is heated. Nitric oxide adsorption on platinum (410) at room temperature shows two bands (1641 and 1770). If this layer is heated to 373 K the high frequency band disappears. The infared experiments on the (410) surface also indicate it possesses unusual activity.
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign