In Situ Calorimetric Study: Structural Effects on Adsorption and Catalytic Performances for CO Oxidation over Ir-in-CeO2and Ir-on-CeO2Catalysts

Abstract

In this study, the formation processes of CO2 and carbonates during CO oxidation over Ir-in-CeO2 and Ir-on-CeO2 catalysts at 40 °C were compared. An in situ pulse calorimetry, in combination with H2-TPR, Raman, DRIFTS, and adsorption microcalorimetry techniques, was used to reveal the effect of structural differences of these two catalysts on the adsorption and catalytic performances for CO oxidation. It was found that encapsulating Ir in CeO2 greatly weakened the Ce–O bond strength on Ir-in-CeO2. This led to the formation of more oxygen vacancy sites, promoting the accumulation of carbonates. Comparatively, supporting Ir on CeO2 showed a higher Ce–O bond strength and less oxygen vacancy sites on Ir-on-CeO2 but exposed more surface accessible Ir sites, which favored the CO adsorption. During CO oxidation, more oxygen vacancy sites on Ir-in-CeO2 resulted in the formation of carbonates with 0.06 monolayers coverage initially before the production of CO2, whereas surface Ir sites on Ir-on-CeO2 facilitated the adsorbed CO reacting with the oxygen species to directly produce CO2.