The concept of selectivity is usually notconsidered in heterogeneous photocatalysis. In this presentation, selectivityin photodecomposition of two adsorbates on the rutile TiO2(110)surface will be examined. For trimethyl acetate (TMA), the oxygen partialpressure controls the partitioning between the two immediate C4 reactionproducts: isobutene and isobutane. Under anaerobic conditions, thephotoreaction occurs with pseudo first order kinetics yielding a near 1:1 ratioof these C4 products, whereas in excess of O2 there ishigh selectivity toward isobutene. The varying selectivity is linked toformation of surface oxygen-containing products (from O2photoreduction) that convert t-butyl radicals preferentially into isobutene. O2shifts the reaction from pseudo first order to one occurring at the boundariesbetween hydrophilic and hydrophobic domains. Photodecomposition oftrifluoroacetone is shown to proceed by C-C bond cleavage to adsorbed acetateor trifluoroacetate, and a gas phase radical (CF3 or CH3,respectively). The selectivity of this reaction is shown to depend not on thethermodynamics of which C-C bond is weakest but on the dynamics of the bondbreaking event itself, with the ratio of these channels affected coverage.These examples of varying selectivity in a photochemistry on TiO2(110)provide motivation for learning how to predict and guide heterogeneousphotochemical reactions to desired products.

Predicting pathways in photocatalytic
reactions on TiO<sub>2</sub>

242nd National Meeting (2011)

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Predicting pathways in photocatalytic reactions on TiO2

Predicting pathways in photocatalytic reactions on TiO₂