Sunlight-driven toluene photo-elimination using CeO2-TiO2 composite systems: A kinetic study

Abstract

A kinetic study of the behavior observed in the photocatalytic degradation of toluene under sunlight-type excitation and using composite CeO2-TiO2 catalysts is presented. The study focuses on analyzing kinetic differences within a series of composite catalysts with varying CeO2:TiO2 molar ratios. To this end, intrinsic expressions to represent the kinetics of toluene photo-degradation were derived from a proposed reaction scheme. These expressions explicitly included the effect of photon absorption on the reaction rate and lead to a mathematical expression of the reaction rate including two adjustable parameters. The modeling of the radiation field in the reactor was accomplished by numerically solving the radiative transfer equation. The radiation field and kinetic schemes were jointly used into a partial differential equation corresponding to the mass balance of toluene. The mathematical model was solved with an algorithmic based in the method of lines to deal with the partial differential equation, coupled with a nonlinear least-squares fitting algorithm to obtain kinetic parameter value estimations. Experimental runs for single oxide and composite CeO2-TiO2 catalysts were used for the fitting process. Good agreement was obtained between model predictions and experimental data, with a root mean square error below 0.65%. The kinetic behavior of composite samples with respect to the titania reference seems intimately related with the hole handling steps of the mechanism.