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 (C 2 H 5 OH) over a TiO 2 -coated optical microfiber catalyst and two other TiO 2 -based catalysts. Adsorption of ethanol on the surface of the TiO 2 /optical microfiber catalyst formed a strongly hydrogen-bonded species and a Ti ethoxide species. In situ UV irradiation experiments under 13 C magic angle spinning (MAS) conditions reveal the formation of two main reaction intermediates, 1,1-diethoxyethane (CH 3 CH(OC 2 H 5 ) 2 ) and acetic acid, under dry conditions. The catalyst was shown to be highly effective for the degradation of ethanol as complete photooxidation of ethanol was observed to form acetic acid and CO 2 . These results were compared to those using a monolayer catalyst supported on porous Vycor glass and powdered TiO 2 . Solid-state NMR investigations on TiO 2 powder modeled after temperature-programmed desorption experiments confirm the identities of the hydrogen-bonded and Ti ethoxide species and show that the strongly bound ethoxide species has a number of adsorption sites. Kinetic experiments indicate this latter species reacts much more rapidly. Studies of the effect of surface hydration show that the presence of water decreases the rate of ethanol photodegradation. Water and ethanol compete for the same adsorption sites on the surface of the TiO 2 catalysts.