Oxidation of CO, ethanol and toluene over TiO2 supported noble metal catalysts

The oxidation of CO, ethanol and toluene was investigated on noble metal catalysts (Pt, Pd, Ir, Rh and Au) supported on TiO2. The catalysts were prepared by liquid phase reduction deposition (LPRD) and by incipient wetness impregnation (IMP). It was observed that the preparation method can have a significant effect on the dispersion of the metallic phase, and subsequently on the performance of the catalysts towards total oxidation of CO or VOC.For CO oxidation, Au IMP was the worst catalyst, while Au LPRD was the most active. This can be explained in terms of different Au particle sizes, well known to be related with catalytic activity. For all the other metals, LPRD also produces better results, although the differences are not so marked as with gold. Iridium seems to be the only exception since results were very similar.In VOC oxidation, the following performance trend was observed: Pt/TiO2 > Pd/TiO2 ≫ Rh/TiO2 ≈ Ir/TiO2 ≫ Au/TiO2, for both preparation methods. Ethanol and toluene oxidation over Pt and Pd catalysts were found to be structure sensitive reactions.Some experiments with ethanol/toluene mixtures were performed using the best catalyst (Pt/TiO2). It was observed that toluene inhibits the combustion of ethanol, namely by slowing down the partial oxidation of ethanol towards acetaldehyde. Ethanol also has a slight inhibition effect on the total oxidation of toluene.

Specific activity at 285 °C in VOC oxidation as a function of oxygen dissociative chemisorption energies on metals.Figure optionsDownload as PowerPoint slideResearch highlights▶ The Au/TiO2 catalyst prepared by LPRD is very active for the oxidation of CO. ▶ This is related with the high dispersion of the metallic phase attained by LPRD. ▶ Pt catalysts are the most active in VOC oxidation. Specific activities depend on O2 adsorption strengths on metals (volcano plots). ▶ VOC oxidation on titania supported Pt and Pd catalysts is structure sensitive.