Infrared study of pyridine adsorbed on unpromoted and promoted sulfated zirconia

Infrared spectra of pyridine adsorbed on zirconia and Pt-zirconia exhibited bands consistent with Lewis acid sites. Sulfated zirconia, after heating at 400 degrees C, exhibited bands indicating about equal amounts of Lewis (L) and Bronsted (B) acid sites; the B/L ratio decreased with increasing reactivation temperature to become essentially zero after reactivation at 600 degrees C. In contrast, both Pt and Fe/Mn promoted sulfated zirconia exhibited Bn ratios that increased slightly with increasing reactivation temperature. It is proposed that pyridine reacts with a Lewis acid site to produce an adsorbed "pyridone-type" surface species with the concurrent generation of a proton. The superior performance of the promoted sulfated zirconia catalyst is believed to arise from its ability to generate Bronsted acid sites. (C) 1999 Academic Press.