INTERACTION OF CARBON-DIOXIDE WITH THE SURFACE OF ZIRCONIA POLYMORPHS

A series of zirconia powder samples with different crystallographic ph ases and surface areas, either prepared at the laboratory or obtained commercially, have been studied in relation to the interaction of CO2 with their surfaces. Three complementary techniques such as infrared s pectroscopy, adsorption microcalorimetry, and temperature-programmed d esorption have been applied to the study of the CO2 adsorption. It has been found that the crystallographic structure of ZrO2 determines the number (or density) of CO2 adsorption sites on its surface, and conse quently the type and stability of adsorbed species. Upon carbon dioxid e adsorption on zirconia with monoclinic structure, hydrogen carbonate s and monodentate and bidentate carbonates are formed, while bidentate and polydentate carbonates are generated on tetragonal zirconia. Alth ough the bidentate carbonates are observed on monoclinic and tetragona l zirconia, they appear at different frequencies and they have differe nt thermal stability, confirming that the surfaces of the two zirconia phases have different geometries. The results from the three techniqu es applied confirm that the monoclinic structure of zirconia brings ab out stronger surface adsorption sites concerning CO2 than the tetragon al structure. Moreover, for a given crystallographic structure the sur face area and texture of the sample also affect the strength of the su rface adsorption sites.