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OXYGENATION OF HYDROCARBONS USING NANOSTRUCTURED TIO2 AS A PHOTOCATALYST: A GREEN ALTERNATIVE
Citation:
SahleDemessie**, E AND M A. Gonzalez**. OXYGENATION OF HYDROCARBONS USING NANOSTRUCTURED TIO2 AS A PHOTOCATALYST: A GREEN ALTERNATIVE. Chapter 18, P. Anastas, L.G. Heine, T. C. Williamsons (ed.), Green Chemical Syntheses and Processes, ACS Symposium Series 767. American Chemical Society, Washington, DC, , 217-228, (2000).
Description:
High-value organic compounds have been synthesized successfully from linear and cyclic saturated hydrocarbons by a photocatalytic oxidation process using a semiconductor material, titanium dioxide (TiO2). Various hydrocarbons were partially oxygenated in both aqueous and gaseous phase reactors using ultraviolet light and titanium dioxide at mild conditions. The conversions and selectivities obtained for the partial oxidation of hydrocarbons are comparable to those achieved with the conventional method. Vapor phase photocatalytic oxidation of toluene with air, at 160oC and 27 mW/cm2 irradiation, showed overall conversion of 12 % to benzaldehyde and benzoic acid, with a 95% selectivity to benzaldehyde. Experiments with cyclohexane have demonstrated the major products are cyclohexanol and cyclohexanone. Cyclohexane conversions of 2 - 6% were achieved for this reaction with no detectable formation of CO2. Oxidation of n-pentane showed formation of 2-pentanol as a major product and a small quantity of 3-pentanol. The use of a gas phase reaction eliminates any separation step involved with liquid solvents and minimizes the adsorption of products to the catalyst.
Initial life-cycle analysis indicate that this technology has the potential to reduce water contaminants and eliminate the use of toxic catalysts. Light-induced catalysis expands the possibilities for the use of oxygen in partial oxidation reactions now being conducted with far more expensive and polluting oxidants. This technology promises the potential of visible light-induced chemistry for the commercially important syntheses. The high selectivity and mild conditions of a photochemical route will be especially attractive for the manufacturing of fine chemicals.