PHOTOCATALYTIC REACTIONS INVOLVING HYDROXYL RADICAL ATTACK - I - REACTION-KINETICS FORMULATION WITH EXPLICIT PHOTON-ABSORPTION EFFECTS

A kinetic model to represent the time evolution of a photocatalytic re action is presented. It can be applied for reacting systems having the following characteristics: (i) the catalyst is a suspension (in water ) of fine particles of titanium dioxide, (ii) the substrate is a hydro carbon compound amenable to hydroxyl radical attack for the initiation of an oxidative reaction, (iii) the catalyst activation is produced b y radiation energy in the near ultraviolet range (300 nm less than or equal to lambda less than or equal to 400 nm), (iv) oxygen is always p resent in the reacting medium, and (v) there are no mass transport lim itations. The model is based on Turchi and Ollis (J. Catal. 122, 178 ( 1990)) proposed reaction sequence. The described formulation incorpora tes a precise and detailed evaluation of the radiation energy absorpti on effects. With this purpose the kinetic model is used in conjunction with a specially developed experimental device (Cabrera et al., Ind. Eng. Chem. Res. 33, 3031 (1994); Alfano et al., Ind. Eng. Chem. Res. 3 3, 488 (1995)) for which a one-dimensional-one-directional radiation a nd reactor model has been derived and validated. The model provides an explicit formulation for the radiation-absorbed effects that comprise s in a single equation the cases of low and high irradiating condition s. The whole kinetic model development has been applied to the photode gradation of trichloroethylene in water, and it is the subject of a co mpanion paper. Using this approach, reliable intrinsic kinetic data ca n be obtained. (C) 1997 Academic Press.