INVESTIGATION OF THE ACIDIC PROPERTIES OF ZRO2 MODIFIED BY SO4(2-) ANIONS

Zirconium dioxide modified by sulfate anions was investigated using di ffuse reflectance IR spectroscopy. It was found that this modification enhanced the strength of bath Bronsted acid sites (terminal or bridgi ng ZrOH groups) and Lewis acid sites (low-coordinate Zr ions). However , Bronsted acid sites with enhanced strength appeared to be weaker tha n bridging OH groups in zeolites. Modification also created protons wi th a new environment. These protons were assumed to form multicenter b onds with oxygen atoms of SO42- anions or with neighboring basic oxyge n and to possess acidic properties comparable to those of protons in z eolites. Low-temperature ethylene and cyclopropane oligomerization and H-D exchange were shown to proceed on sulfated zirconia, presumably w ith participation of such sites. (C) 1994 Academic Press, Inc.