Experimental microkinetic approach of the photocatalytic oxidation of isopropyl alcohol on TiO2. Part 2. from the surface elementary steps to the rates of oxidation of the C3H(x)O species.

The present study concerns an experimental microkinetic approach of the photocatalytic oxidation (PCO) of isopropyl alcohol (IPA) into acetone on a pure anatase TiO2 solid according to a procedure previously developed. Mainly, the kinetic parameters of each surface elementary step of a plausible kinetic model of the PCO of IPA are experimentally determined: natures and amounts of the adsorbed species and rate constants (preexponential factors and activation energies). These kinetic parameters are used to evaluate a priori the catalytic activity (turnover frequency, TOF, in s(-1)) of the solid that is compared to the experimental value. The kinetics parameters are obtained by using experiments in the transient regime with either a FTIR or a mass spectrometer as a detector. The microkinetic study shows that only strongly adsorbed IPA species (two species denoted nd-IPA(sads) and d-IPA(sads) due to non- and dissociative chemisorption of IPA respectively) are involved in the PCO of IPA. A strong competitive chemisorption between IPA(sads) and a strongly adsorbed acetone species controls the high selectivity in acetone of the PCO at a high coverage of the surface by IPA(sads). The apparent rate constant (1.4 10(-3) s(-1)) of the Langmuir-Hinshelwood elementary step between IPA(sads) and the active oxygen containing species generated by the UV irradiation provides the TOF of the PCO for IPA/O2 gas mixtures. The kinetic parameters of the elementary steps determined by the experimental microkinetic approach allow us to provide a reasonable simulation of the experimental data (coverages of the adsorbed species and partial pressures of the gases of interest) recorded during a static PCO of IPA(sads) species.