Monday, February 27, at 12:10 p.m. in CUE 419
The Gene and Linda Voiland School of Chemical Engineering and Bioengineering is hosting a seminar presented by Steven Buratto, Department of Chemistry and Biochemistry, University of California.
Dr. Buratto obtained his B.S. in 1987 from the University of Puget Sound with a double major in Chemistry and Mathematics, and his Ph.D. in 1992 from the California Institute of Technology in Chemical Physics. He was a postdoctoral member of the technical staff at AT&T Bell Laboratories from 1992-1994 before joining the UCSB faculty in the 1994-95 academic year. Since coming to UCSB, Dr. Buratto has received a Camille and Henry Dreyfus New Faculty Award, an NSF Early Career Development Award, a David and Lucile Packard Foundation Fellowship and an Alfred P. Sloan Foundation Fellowship. Dr. Buratto has served as the chair of the Department of Chemistry and Biochemistry at UCSB since 2015.
The Reactivity and Structure of Size Selected VxOy Nanocluster Catalysts on TiO2 (110)
The selective oxidative dehydrogenation (ODH) of methanol to formaldehyde by vanadium oxide/TiO2 model systems has received a great deal of interest in the surface science community. Previous studies using temperature programmed desorption and reaction (TPD/TPR) to probe the oxidation of methanol to formaldehyde by vanadia/TiO2 model catalysts have shown that the activity of these systems varies considerably with the preparation conditions. The formaldehyde formation temperature observed ranges anywhere from room temperature to 660 K. The principle reason for this variation is that the preparation of sub-monolayer films of vanadia on TiO2 produces clusters with a multitude of VxOy structures and a mixture of vanadium oxidation states. As a result the stoichiometry of the active vanadium oxide catalyst as well as the oxidation state of vanadium in the active catalyst remain unknown. To better understand this system, our group has probed the reactivity and structure of size-selected Vx, VOy and VxOy clusters on a reduced TiO2 (110) support in ultrahigh vacuum (UHV) via TPD/TPR and scanning tunneling microscopy (STM). Ex situ preparation of these clusters in the gas phase prior to deposition has allowed us to systematically vary the stoichiometry of the vanadia clusters; a layer of control not available via the usual routes to vanadium oxide. The most active catalysts are shown to have (VO3)n stoichiometry in agreement with the theoretical models. We have shown that both the activity and selectivity of V2O6 and V3O9 cluster catalysts depend sensitively on the oxidation state of the TiO2 (110) support. For example, V2O6 on a reduced surface is selective for the oxidation of methanol to formaldehyde while the selectivity shifts to favor methyl formate as the surface becomes increasingly oxidized. STM studies show that the structure of size-selected V2O6 clusters, upon adsorption to the surface, varies considerably with the oxidation state of the support, in good agreement with our reactivity studies. V3O9 was shown to catalyze the oxidation of methanol to both formaldehyde and methyl formate on a reduced surface while STM suggests that, unlike V2O6, these clusters exhibit several different equilibrium structures when adsorbed to the surface. Finally, TPD/TPR of size selected V2O5 and V2O7 on TiO2 suggests that altering the stoichiometry of the (VO3)n clusters by a single oxygen atom significantly inhibits the activity of these catalysts.
