Catalysis of Organic..

Singh and Chuang 9913. Reaction Pathways forPropylene Partial Oxidation on Au/TiO 2Rahul Singh and Steven S. C. ChuangDepartment of Chemical and Biomolecular Engineering, the University of Akron,Akron, OH, 44325Abstractschuang@uakron.eduThe surface OH (i.e., hydroxyl) group plays an important role in the formation of C 3oxygenates. Propionaldehyde and acetone are proposed to be formed via a commonintermediate because they have the same maximum formation rates at 160 °C onAu/TiO 2 -SiO 2 and 140 °C on Au/TiO x -SiO 2 . The propylene oxide formation occursat higher temperature than that of propionaldehyde and acetone, suggesting itsunique formation pathway which may involve different form of adsorbed oxygen andthe active site.IntroductionThe activity and selectivity of propylene partial oxidation is very sensitive to thecatalyst composition and reaction conditions (1, 2). Extensive studies have shownthat Au supported on TiO 2 is one of the most active and selective catalysts for COoxidation in the presence of H 2 and propylene epoxidation producing propyleneoxide (i.e., PO) from propylene and oxygen in presence of hydrogen (3-8).Propionaldehyde,*O partial oxidation route Acetone, *OPO,CO2 ,C 3 H 6 Intermediates2-Propanol H 2 OAcrolein*O = adsorbed oxygentotal oxidation routeFigure 1. General reaction scheme for propylene partial oxidation.Fig. 1 shows the general reaction scheme for propylene partial oxidation.Depending on the surface and structure of catalysts, adsorbed propylene species canreact with various forms of adsorbed oxygen, producing a wide range of C 3oxygenated products including propanal (propionaldehyde), acetone, 2-propanol, PO,and acrolein. A general catalyst requirement for catalytic partial oxidation includes(i) the capability of the catalyst to activate adsorbed olefin and adsorbed oxygen and(ii) the low activity for oxidation of desired reaction product.