Infrared spectroscopic study of surface species and of CO dsorption: a probe for the surface characterization of sulfated zirconia catalysts

IR spectra of surface species and of CO adsorption at ca. 77 and ca. 300 K on pure ZrO2, sulfated ZrO2, sulfated calcined ZrO2 have been obtained and related to the catalytic activity of these systems in the isomerization of n-butane. Spectral data indicated that: (i) the catalytic activity, when present, requires the presence of both Brønsted and Lewis surface acidity; (ii) a catalyst calcination step is necessary for the elimination of sulfates from crystal defects, on which strong Lewis acid sites must form; (iii) strong Lewis acid sites actually involved in the catalytic process represent a small yet strongest fraction of all Lewis sites formed on the catalyst upon thermal activation.