Surface interaction of CO2/H2 mixture on mesoporous ZrO2: Effect of crystalline polymorph phases

A mesoporous zirconia (ZrO₂) series was synthesized by reflux and hydrothermal methods using Pluronic (P-123) as a surfactant. Characterizations by XPD showed that the ZrO₂ prepared via reflux consisted of only tetragonal crystalline phase when compared with that obtained by hydrothermal treatment, which was formed by tetragonal and monoclinic phases. The addition of the surfactant had a positive influence on the specific surface area and mesoporous structure ordering of ZrO₂, regardless of the method of synthesis. The surface interaction of H₂/CO₂ mixture with the ZrO₂ samples exhibited some dissimilarity due to the unlike surface acidic-basic features of the tetragonal and monoclinic phases. In-situ DRIFTS experiments revealed that the species adsorbed on the zirconia prepared by the reflux method were bidentate bicarbonate, ionic bicarbonate, bidentate carbonate, and polydentate carbonate, whereas the adsorption on the zirconia prepared by refluxing method led to increased intensity of the broadband characteristic of bidentate carbonate and the appearance of two new bands typical of bidentate carbonate and bidentate bicarbonate. After subsequent switching off CO₂, it was observed that the carbonate species (1550 cm⁻¹) strongly interacted with the zirconia surface and required high energy amount to be desorbed, which was in good agreement with the CO₂-TPD profile. This suggests that these carbonates are not active species when the reaction is carried out at 200 °C.