SURFACE CHARACTERIZATION OF YTTRIA-STABILIZED TETRAGONAL ZRO2 .2. ADSORPTION OF CO

Two preparations of tetragonal zirconia (t-ZrO2) stabilized with 3 mol % Y2O3 have been characterized, and their features compared with those of a 2 mol% t-ZrO2 preparation and of a monoclinic zirconia (m-ZrO2) preparation. At ambient temperature, CO adsorption occurs only on surf ace cationic Lewis acid sites located in crystallographically defectiv e configurations. The various t-ZrO2 preparations present several type s of such defective sites, depending on the temperature of the sinteri ng stage. The spectral features of the ambient-temperature interaction of t-ZrO2 with CO are complemented, on quantitative grounds, by gas-v olumetric and microcalorimetric data. At high firing temperatures, amo rphous phases start segregating from the t-ZrO2 crystallites, causing the ambient-temperature adsorptive capacity towards CO to decline. Upo n CO adsorption at low temperature (ca. 77 K), weaker adspecies form p revalently. These are ascribed to CO adsorption on cationic Lewis acid sites located in regular patches of low-index crystal planes, and to CO H-bonded to surface OH groups. Different t-ZrO2 preparations and di fferently sintered samples exhibit different particle sizes and Variou s proportions of crystal surface defect sites vs. regular-face termina tions: these differences are reliably monitored by CO adsorption patte rns observed via IR spectroscopy, both at 300 and ca. 77 K.