ENHANCED PHOTOCATALYTIC PERFORMANCE OF TITANIA-BASED BINARY METAL-OXIDES - TIO2 SIO2 AND TIO2/ZRO2/

Sol-gel prepared mixtures of silica or zirconia with titania are shown to have significantly higher activities than pure titania for the com plete photocatalytic oxidation of ethylene. These higher activities ar e only apparent when the respective catalysts are stabilized by sinter ing. The differences become even more pronounced when the catalysts ar e used in a tubular reactor. Optimum mixture concentrations are found to be 12 wt % zirconia and 16 wt % silica in titania. Both catalyst ty pes exhibit activity maxima with respect to sintering temperature. It is hypothesized that the maxima arise from opposing effects of densifi cation and phase transformation versus beneficial sintering. A compari son of our catalyst compositions with literature in this area suggests that the increase in activity due to the addition of silica or zircon ia may be a result of higher surface acidity. However, isoelectric poi nt measurements employing the unsintered and sintered catalysts show n o conclusive increase in surface acidity. The effects of sintering tem perature on the surface area, porosity, and crystal structure of the c atalysts are also presented.