A study of the acidic and catalytic properties of pure and sulfated zirconia-titania and zirconia-silica mixed oxides

Protonated pyridine (PyH+) was not found on ZrO2 (Z) or ZrO2-TiO2 (ZT), but was detected on sulfated oxides (Z-S, ZT-S) by IR spectroscopy. In contrast, ZrO2-SiO2 samples containing about 30-80 mol% ZrO2 showed Bronsted acidity both in non-sulfated (ZS) and sulfated (ZS-S) forms. The total acidity was determined by NH3-TPD. Introduction of sulfate ions increased the site-specific catalytic activity (TOF) in the conversion of cyclopropane or n-hexane. The effect of sulfate ions was more significant on samples rich in zirconia. Results suggest that Zr is homogeneously distributed in ZS samples rich in silica. Zirconia-bound dimeric sulfate, generating strong acidity, could not be formed in these preparations due to the absence of fairly large ZrO2 domains.