Kostantinos Kourtakis

Kinetics of the reoxidation of propylene-reduced γ-bismuth molybdate: A TAP reactor study

Abstract The reoxidation of γ-bismuth molybdate following reduction by propylene at elevated temperatures was examined using a TAP reactor. Use of the TAP reactor permitted examination of the catalyst surface at the earliest stages of reaction involving less than 1/100th of the surface. Pulsing of oxygen over the reduced catalyst at high (840 torr) and low (6 × 10 −7 torr) total pressures yielded kinetic information on the reoxidation rates as functions of oxygen partial pressures, oxygen vacancies and temperature. In both pressure regimes, the reoxidation was found to be first order in both oxygen and in oxygen vacancies created during the propylene reduction. At high pressures, the reoxidation activation energy was found to be 3.4 kcal/mol while at low pressures it was measured as 5.0 to 8.7 kcal/mol.

High yield butane to maleic anhydride direct oxidation on new supported catalysts

The preparation and the characterization of VPO supported on a new SiC support are described. This catalyst provides a very significant gain in maleic anhydride yield by reacting air and butane, because of the control of the surface temperature.

Novel thermal and photo curable anti-reflective coatings using fluoroelastomer nanocomposites and self-assembly of nanoparticles

We describe novel optical coatings which require either thermal or photocuring to render them mechanically robust and abrasion resistant. These new coatings are low refractive index fluoroelastomer-nanoparticle composites that form a unique nanostructure during drying of the liquid coating. During drying, the nanoparticles in these liquid coatings migrate towards the substrate. The final, 100-nm-thick anti-reflective coatings are novel and exhibit a unique bilayer structure in which the nanoparticles are ordered and segregated towards the substrate. The coatings are rapidly cured using a new process and exhibit surprising “scratch durability” as measured by aggressively testing with steel wool. Sol gel chemistry is used which involves the reaction of the nanoparticles with an acrylic oxysilane to form nanoparticles which are functionalized with sol gel derived oligomers. The functionalized nanoparticles are combined with a fluoroelastomer containing a free radical initiator and multiolefinic crosslinker, and the composite film is rapidly cured by a thermal or UV process at low temperatures. The final product is a mechanically robust, low refractive index anti-reflective film which is useful for displays and photovoltaic devices. These are unique fluoropolymer nanocomposites which utilize nanoparticle self-assembly to enhance important properties.

Reactivity of novel metal substituted heteropolyacid catalysts using steady-state and transient response kinetics

Abstract The reactivity of molybdenum-based heteropolyacid (HPA) catalysts was investigated using both steady-state and transient response methods. Using the non-substituted catalyst H 4 PMo 11 VO 40 as the basis, other HPAs were synthesized where either Mo cations or protons were substituted with other metal cations, such as Mn, Co, Ni, Cu, Zn, Ca and Cs. It is shown that the transient reoxidation of reduced HPAs can be quantitatively described by combining a surface oxidation reaction that is first order in gas phase oxygen and second order in surface oxygen vacancies with subsurface oxygen diffusion. The rate of diffusion of oxygen in the lattice of the HPA catalysts during their reoxidation is found to correlate with the activity at steady-state. However, the rate constant for surface reoxidation does not correlate with activity at steady-state. It is suggested that the rate of reoxidation of the catalyst is not the only property that affects the activity at steady-state, but that surface acidity might also play an important role. Finally, the amount of both CO 2 and maleic anhydride formed during the transient reduction of reoxidized HPAs by n-butane increases with the oxo-capacity, whereas no correlation is observed between the oxo-capacity and the activity under steady-state conditions.