Ethanol photocatalysis on TiO2-coated optical microfiber, supported monolayer, and powdered catalysts: An in situ NMR study

In situ solid-state NMR methodologies have been employed to investigate the photocatalytic oxidation of ethanol (C2H5OH) over a TiO2-coated optical mi crofiber catalyst and two other TiO2-based catalysts, Adsorption of ethanol on the surface of the TiO2/optical microfiber catalyst formed a strongly h ydrogen-bonded species acid a Ti ethoxide species. In situ UV irradiation e xperiments under C-13 magic angle spinning (MAS) conditions reveal the form ation of two main reaction intermediates, 1,1-diethoxyethane (CH3CH(OC2H5)( 2)) and acetic acid, under dry conditions. The catalyst was shown to be hig hly effective for the degradation of ethanol as complete photooxidation of ethanol was observed to form acetic acid and CO2. These results were compar ed to those using a monolayer catalyst supported on porous;Vycor glass and powdered TiO2. Solid-state NMR investigations on TiO2 powder modeled after temperature-programmed desorption experiments confirm the identities of the hydrogen-bonded and Ti ethoxide species and show that the strongly bound e thoxide species has a number of adsorption sites. Kinetic experiments indic ate this latter species reacts much more rapidly. Studies of the effect of surface hydration show that the presence of water decreases the rate of eth anol photodegradation. Water and ethanol compete for the same adsorption si tes on the surface of the TiO2 catalysts.