Catalysis of Organic..

Miller and Chuang 14718. In situ Infrared Study of CatalyticOxidation over Au/TiO 2 CatalystsAbstractDuane D. Miller and Steven S.C. ChuangDept. of Chemical and Biomolecular Engineering, University of Akron,Akron, OH, 44325-3906duane1@uakron.edu, schuang@uakron.eduIn situ infrared study of catalytic CO oxidation over Au/TiO 2 shows that the catalystprepared from AuCl 3 exhibits higher activity than those prepared from HAuCl 4 . Thehigh activity of Au appears to be related to the presence of reduced and oxidized Ausites as well as carbonate/carboxylate intermediates during CO oxidation. Additionof H 2 O 2 further promotes the oxidation reaction on Au/TiO 2 catalysts.IntroductionSupported Au catalysts have been extensively studied because of their uniqueactivities for the low temperature oxidation of CO and epoxidation of propylene (1-5). The activity and selectivity of Au catalysts have been found to be very sensitiveto the methods of catalyst preparation (i.e., choice of precursors and supportmaterials, impregnation versus precipitation, calcination temperature, and reductionconditions) as well as reaction conditions (temperature, reactant concentration,pressure). (6-8) High CO oxidation activity was observed on Au crystallites with 2-4nm in diameter supported on oxides prepared from precipitation-deposition. (9) Anumber of studies have revealed that Au 0 and Au +3 play an important role in the lowtemperature CO oxidation. (3, 10) While Au 0 is essential for the catalyst activity, theAu 0 alone is not active for the reaction. The mechanism of CO oxidation onsupported Au continues to be a subject of extensive interest to the catalysiscommunity.The reaction pathway, reactivity of the active sites, and the nature of adsorbedintermediates constitute the catalytic reaction mechanism. Our study has beenfocused on the investigation of the nature of adsorbed intermediates under reactionconditions. We report the results of in situ infrared study of CO and ethanoloxidation on Au/TiO 2 catalysts. This study revealed the high activity of Au/TiO 2 isrelated to the presence of reduced Au and oxidized Au sites which may promote theformation of carbonate/carboxylate intermediates during CO oxidation.Experimental SectionTwo 1% Au/TiO 2 catalysts, designated as HAuCl 4 and AuCl 3 were prepared bydeposition-precipitation of HAuCl 4 (Aldrich) and AuCl 3 (Alfa Asar) onto Degussa-