Interaction of Carbon Dioxide with the Surface of Zirconia Polymorphs

A series of zirconia powder samples with different crystallographic phases and surface areas, either prepared at the laboratory or obtained commercially, have been studied in relation to the interaction of CO 2 with their surfaces. Three complementary techniques such as infrared spectroscopy, adsorption microcalorimetry, and temperature-programmed desorption have been applied to the study of the CO 2 adsorption. It has been found that the crystallographic structure of ZrO 2 determines the number (or density) of CO 2 adsorption sites on its surface, and consequently the type and stability of adsorbed species. Upon carbon dioxide adsorption on zirconia with monoclinic structure, hydrogen carbonates and monodentate and bidentate carbonates are formed, while bidentate and polydentate carbonates are generated on tetragonal zirconia. Although the bidentate carbonates are observed on monoclinic and tetragonal zirconia, they appear at different frequencies and they have different thermal stability, confirming that the surfaces of the two zirconia phases have different geometries. The results from the three techniques applied confirm that the monoclinic structure of zirconia brings about stronger surface adsorption sites concerning CO 2 than the tetragonal structure. Moreover, for a given crystallographic structure the surface area and texture of the sample also affect the strength of the surface adsorption sites.