Research in Engineering and Aviation
TAP reactor studies of hydrocarbon oxidation over surface modified VPO catalysts
226th ACS National Meeting, September 7-11, 2003, New York, New York.
This talk presents the results of new studies using a TAP-2 reactor system in conjunction with an atomic beam deposition technique to determine how changes in the surface composition of VPO catalysts influences the catalytic kinetics. Atomic beam deposition is used to add transition metal atoms to the surface of catalyst particles in a precise stepwise manner. “Reactor-equilibrated” catalysts prepared by non-aqueous procedures, and formed under steady-state reaction conditions were used as substrates. The initial catalysts, and surface modified catalysts were tested over a variety of kinetic regimes at vacuum and atmospheric pressures. The oxidation of butane, propane, propene and furan at different temperatures over a range of oxidation/reduction states of initial and surface modified catalyst was studied. TAP single pulse and multi-pulse transient response experiments were used to determine the instantaneous and integral characteristics of different catalyst states. Based on these characteristics, information about the number, the primary (chemical) structure and kinetic properties of active centers and the detailed kinetic mechanism was obtained. Information was also obtained on the exchange between surface and bulk oxygen in VPO and the role of different oxygen species in hydrocarbon oxidation. Other results of this study will show how the activity and selectivity of VPO catalysts change when the transition metal surface composition is modified. Comparison of kinetic parameters for n-butane oxidation obtained in non-steady-state experiments under vacuum conditions at different VPO catalyst oxidation states is made with kinetic parameters obtained in steady-state experiments at atmospheric pressures. The changes in activity and selectivity are correlated with changes in other kinetic parameters, and with structural information. This information is compared with current theoretical models of the VPO catalyst system.