Isotopic transient analysis of carbon monoxide oxidation over supported gold catalysts

In this thesis, the oxidation of CO over titania- and alumina-supported gold nanoparticles was explored using isotopic transient analysis. Isotopic transient analysis allows for the determination of the average lifetime and number of adsorbed intermediates leading to product under steady-state reaction conditions.; The gold catalysts were prepared using a deposition-precipitation method employing HAuCl4 as the metal precursor, followed by thermal treatment in helium at 623 K. X-ray absorption spectroscopy was used to monitor the oxidation state of the gold throughout the preparation and pretreatment in helium. Following deposition-precipitation, the samples contained gold in a cationic state. However, the gold was reduced to a predominantly metallic state during treatment in helium at 623 K. X-ray absorption spectroscopy and electron microscopy revealed the gold to be in a highly dispersed state, with an average gold particle diameter determined by scanning transmission electron microscopy of 3.3+/-0.5 nm on titania and 2.5+/-1.1 nm on alumina.; The global kinetics of CO oxidation were measured over the Au/TiO 2 and Au/Al2O3 to explore the effect of the metal-oxide support. The apparent activation energy was 29 kJ mol-1 over the Au/TiO2 and 8 kJ mol-1 over the Au/Al2 O3, with the same global reaction rate occurring at 245 K. The order of reaction with respect to 02 was 0.25 and 0.52 over Au/TiO2 and Au/Al2O3, respectively, whereas the order with respect to CO was approximately 0.17 over both catalysts. The presence of H2O in the reactor feed significantly increased the rate of CO oxidation.; Steady-state 13C and 18O isotopic transient analyses of CO oxidation over Au/TiO2 and Au/Al2O 3 were used to determine the intrinsic turnover frequency (TOF intr) and coverage (thetaCOx) of reactive surface intermediates leading to CO2. Isotopic transient analysis of C16O oxidation with 18O2 at 293 K resulted in the formation of C16O2, C16O18O, and C18O2 in molar ratios of 3:6:1 for Au/TiO 2 and 4:5:1 for Au/Al2O3. However, no oxygen scrambling was observed in and between O2 and CO. Furthermore, O2 did not exchange with CO2 or the lattice oxygen of the metal oxide supports. Isotopic transient analysis of a switch between C16 O2 and C18O2 revealed the lattice oxygen of the supports would readily exchange with CO2. Therefore, the distribution of CO2 isotopomers observed during CO oxidation was not the direct result of the oxidation reaction. Comparison of the isotopic transients from 13C and 18O studies suggests the primary product of C16O oxidation with 18O 2 is C16O18O. (Abstract shortened by UMI.)...