The intrinsic catalytic activity in photoreactors

A methodology for determining intrinsic activity in aqueous heterogeneous p hotocatalytic reactors was introduced. The most common commercial titania p owders (Degussa P25, Aldrich anatase, Aldrich anatase 325) with high BET su rface area were evaluated for the UV-induced heterogeneous degradation of p henol to test the proposed methodology. It was demonstrated that kinetic da ta obtained from commonly used photocatalytic reactors (such as liquid-phas e reactor) do not correspond to the intrinsic activity of catalysts due to strong nonuniformity of the internal radiation field. in contrast to the va st majority of the previous studies, which report scattered data for differ ent reactors, the present work offers an objective means to characterize ph otocatalysts. The data obtain ed from a variable reaction zone were found t o approach intrinsic in a differential volume (annular reaction zone of 0.1 5 cm thickness and 6 cm length). A correction factor (eta) representing the ratio of the radical generation rate in the laboratory to that in the refe rence-ideal photocatalytic reactors was introduced. This allowed for the ob taining of the intrinsic activity (k(int)) of the photocatalyst from appare nt kinetic measurements (k(app)). The proposed methodology was tested for a n annular reactor for the above reaction (first order) and showed good agre ement with the data. The intrinsic reaction rate constants k(int) were foun d to be independent of the reactor size for cylindrical geometry for the th ree light sources employed (100, 200, and 450 W) and variable catalyst conc entration. The calculated turnover frequencies (TOF) allowed for a realisti c comparison of the intrinsic activity per unit surface area of the individ ual sites. The sites of Aldrich anatase powders were found to be more activ e (2-fold) than those of Degussa P25.