Surface characterization of acidic ceria-zirconia prepared by direct sulfation

Acidic ceria-zirconia (SCZ) solid acid catalysts with a nominal surface density of ca 2 SO42-/nm(2) were prepared by a simple route consisting in soaking high specific surface area CexZr1-xO2 (with x=0.21 and 0.69) mixed oxides solutions in 0.5M sulphuric acid. Characterizations by TPD-MS, TP-DRIFTS and FT-Raman revealed that most of surface structures generated by sulfation are stable at least up to 700 degrees C under inert atmosphere and consist mainly as isolated sulfates located on defects or crystal planes and to a lesser extent as polysulfates. Investigations by pyridine adsorption/desorption have stated that: SCZ possess both strong Bronsted ( B) and Lewis ( L) acid sites, some of them being presumably superacidic; the B/L site ratio was found to be more dependent on the temperature and hydration degree than on the composition of the ceria-zirconia. By contrast, the reactivity of the parent CexZr1-xO2 materials towards pyridine is mostly driven by redox properties resulting in the formation of Py-oxide with the participation of Lewis acid sites of moderate strength (cus Cex+ and Zrx+ cations). Basicity studies by CO2 adsorption/desorption reveal that SCZ surfaces are solely acidic whereas the number and strength of Lewis basic sites increases with the Ce content for the parent CexZr1-xO2 materials. (C) 2010 Elsevier B. V. All rights reserved.