PROPERTIES OF MODIFIED ZIRCONIA USED AS FRIEDEL-CRAFTS-ACYLATION CATALYSTS

Both precipitated and aerogel synthesized zirconia were modified emplo ying gaseous and solid compounds, respectively, as well as concentrate d mineral acids. The sulfur and phosphorous-containing samples were ch aracterized by nitrogen adsorption, Xray diffraction, FTIR pyridine ad sorption, ammonia TPD, and 1-butene isomerization. Modification of zir conia samples results in enhanced Bronsted acidity and catalytic activ ity. Especially ammonium sulfate and sulfite generate strong acidic ce nters at the surface in high concentrations. As was shown on the basis of XPS measurements the final calcination step in air converts the su lfite into surface sulfate, resulting finally in the same, or at least very similar, surface states of both differently treated samples. Som e few degrees enhanced catalytic activities were obtained using sulfat ed zirconia aerogels. Applied to the benzoylation of anisole, a slurry of these catalytically active zirconia samples yields similar high co nversion degrees as nonafluorobutanesulfonic acid known as an excellen t catalyst for this reaction in homogeneous solution. There is evidenc e to assume that the benzoylation reaction under the conditions used o ccurs exclusively at Bronsted acid sites but not at Lewis sites. A hyp othetical path for the action of a sulfated zirconia surface in the ca talytic step is proposed. (C) 1998 Academic Press.