Determination of Metal-Oxygen Bond Strength in Oxide Catalysts

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In this project, the energies of metal-oxygen bonds involved in reduction and reoxidation of an oxide are measured by calorimetry using a heat-flow calorimeter. Heats of reduction are measured for reduction by carbon monoxide or by hydrogen; this permits calculation of heats of formation for metal- oxygen bonds using the known heats of formation of small molecules, or, if necessary, the mesured heat of reoxidation. If surface hydroxyls are formed, their heats of formation can also be determined. Laser Raman spectroscopy, performed before and after the calorimetry, is used to identify and track the particular bonds made or broken in the calorimetric reactions. Initial experiments are on the highly dispersed phases of vanadia supported or gamma-alumina and anatase (titania). Data on the energies of metal-oxygen bonds are not available. Such data should be very useful for understanding the catalysis and surface chemistry of oxides, particularly selective catalytic oxidation reactions in which the surface is the proximate source of oxygen; the effort proposed is a formidable task. Selective oxidations are major elements in the production of a variety of commodity and specialty chemicals. Although catalytic behavior is the focus of this study, the results will also contribute to understanding semiconductor surfaces and insulating layers in electronic materials, and passivation an corrosion in structrual materials.