PHOTOACTIVITY OF TITANIUM-DIOXIDE SUPPORTED ON MCM41, ZEOLITE-X, AND ZEOLITE-Y

Titanium dioxide supported on microporous zeolites of type X and Y and on mesoporous molecular sieves of the MCM41 type was studied for the photocatalytic degradation of acetophenone in an aqueous medium. The p hotoactivity of the supported catalyst is strongly influenced by the m ethod of titania loading, but less affected by the temperature at whic h the sample was calcined. The highest photoactivity among the support ed catalysts is observed for a support that has a lower Si/Al ratio in the framework and relatively large pore size. The measured apparent a ctivation energies for photocatalyzed consumption of acetophenone for a commercial TiO2 (P-25) and 10 wt % TiO2-loaded samples of zeolite A, X, Y, and Al-MCM41 are 4.2-6.7, 16.9, 13.5, 32.2 and 3.6 kJ/mol, resp ectively. Selective doping by Fe, Mn, and V into the framework of MCM4 1 suppresses the photoactivity of the supported titanium dioxide. The physical state of the titanium dioxide on the supports is characterize d by XRD, adsorption and pore size analysis, IR, and Raman spectroscop y. All methods emphasize the small particle or amorphous character of the TiO2. The normal phase transition to rutile does not occur at high er temperatures on zeolite supports. In some cases, very low loadings of TiO2 appear to achieve total absorption of the light entering the r eaction vessel. For the Al-rich MCM41-supported catalysts, maximal pho toactivity can be achieved at low TiO2 loading (13%). It appears to ab sorb 100% of light entering the reaction vessel with a much lower TiO2 load than is the case with TiO2 itself. There is evidence that the cr ystallinity of the zeolite is an important factor in photocatalytic ef ficiency, but the mechanism of zeolite participation in reactions rema ins incompletely elucidated.