Operando study on wet CO oxidation over ceria and alumina supported platinum catalysts

The effect of water on carbon monoxide oxidation activity of highly dispersed Pt/ceria and Pt/alumina catalysts with narrow Pt particle size distributions at around 1-2 nm has been studied by kinetic measurements and infrared spectroscopic characterisation under in situ and operando conditions. Water promotes the low-temperature activity for both catalysts, however, by different mechanisms. For Pt/ceria, the reaction proceeds with a very weak dependence on water concentration whereas the apparent activation energy increases. It is proposed that water, on the one hand, promotes the Mars-van Krevelen mechanism through destabilisation of ceria lattice oxygen favouring its reaction with CO and/or desorption of product CO 2 and, on the other hand, turn ionic Pt clusters active for CO oxidation. For Pt/alumina, the CO oxidation proceeds via Langmuir-Hinshelwood mechanism on Pt, however, with a positive dependency on water concentration. Likely water both weakens the interaction between CO and Pt, and may enable the proposed reaction pathway between CO and OH ad-species to form surface carboxylates as part of a wet CO oxidation mechanism.