Investigation of the Acidic Properties of ZrO2 Modified by SO2−4 Anions

Zirconium dioxide modified by sulfate anions was investigated using diffuse reflectance IR spectroscopy. It was found that this modification enhanced the strength of bath Brønsted acid sites (terminal or bridging ZrOH groups) and Lewis acid sites (low-coordinate Zr ions). However, Brønsted acid sites with enhanced strength appeared to be weaker than bridging OH groups in zeolites. Modification also created protons with a new environment. These protons were assumed to form multicenter bonds with oxygen atoms of SO2−4 anions or with neighboring basic oxygen and to possess acidic properties comparable to those of protons in zeolites. Low-temperature ethylene and cyclopropane oligomerization and H-D exchange were shown to proceed on sulfated zirconia, presumably with participation of such sites.