Enhancement of the photocatalytic activity of pelletized TiO2 for the oxidation of propene at low concentration

In a previous study we have shown that the pelletization of titanium dioxide, a convenient step for gas phase applications, causes an important activity lost. Such activity lost can be partially recovered pelletizing in presence of carbon materials. Porosity, as well as carbon conductivity of the selected carbon material, is important. Based on these previous results, we analyze the pelletization of TiO2 in presence of white additives, such as MCM-41, zeolites, metal-organic framework, SiO2, Al2O3, glass wool and quartz wool. Our results show that the activities of these composite photocatalytic pellets are higher than that of 100% TiO2-pellets. Pellets containing MCM-41, precipitated SiO2, glass wool and quartz wool present the highest propene conversions. Attention has been paid to the effect of porosity and UV-absorbance on the resulting photocatalytic activity. Although it is difficult to find a correlation between the porosity of these white additives and the photocatalytic activity of the TiO2-based materials, additives with no porosity or with some mesoporous contribution seem to be desired to maximize the activity. The different catalytic activities for the studied photocatalysts could not be explained on basis of their UV-absorption and further research is currently being performed trying to deep into the reasons for such behaviour. Comparison of the photocatalytic activities for pellets containing the above-mentioned white additives with those of a TiO2/carbon photocatalyst having the highest porosity and conductivity among all those studied highlights the superior performance of the samples containing white additives. (C) 2007 Elsevier B.V. All rights reserved.