Photocatalytic treatment of automotive exhaust emissions

In the present work, the photocatalytic treatment of simulated automotive exhaust emissions was studied in an annular reactor operating in CSTR mode. Three feeds with different compositions were created, rich (λ = 0.98), stoic (λ = 1), and lean (λ = 1.02) and five photocatalysts were tested: TiO2 isopropoxide, TiO2 P25 and TiO2-P25 with addition of 1% of Pt, Fe or Ce. Pt-TiO2 P25 showed the highest activity for NO and hydrocarbons (C3H6, C3H8) removal, with hydrocarbons oxidation being promoted in lean conditions of feed and NO reduction in rich condition of feed, behavior similar to commercial three-way catalysts. Additional work was carried out in order to study separately the main reactions that take place on the catalytic surface. For NO decomposition/oxidation reaction in the presence of water there was no NO2 formation observed and also no deactivation of the catalyst which indicates that decomposition reaction is the main reaction with good selectivity to N2 formation for these conditions. In C3H6 oxidation the increase of O2 inlet concentration leads to the increase of the reaction rate and in redox reaction of NO with C3H6 the results showed that a secondary reaction for C3H6 is required to explain the conversion values. The kinetic study of the reactions showed that Langmuir-Hinshelwood expression can interpret the experimental data assuming that NO and C3H6 are co-adsorbed on the same active sites, with dissociatively adsorption of C3H6 and O2 adsorption on different active sites.