Surface characterization of acidic ceria–zirconia prepared by direct sulfation

• Published in: Applied surface science 2010-05, Vol.256 (14), p.4570-4581
• Main Authors: Azambre, B., Zenboury, L., Weber, J.V., Burg, P.
• Format: Article
• Language: English
• Subjects: Acidity; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; DRIFTS; Exact sciences and technology; Physics; Pyridine adsorption; Sulfated ceria–zirconia; TPD
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2010.02.049

Acidic ceria–zirconia (SCZ) solid acid catalysts with a nominal surface density of ca 2 SO 4 2−/nm 2 were prepared by a simple route consisting in soaking high specific surface area Ce x Zr 1− x O 2 (with x = 0.21 and 0.69) mixed oxides solutions in 0.5 M 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 °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 Brønsted (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 Ce x Zr 1− x O 2 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 Ce x+ and Zr x+ cations). Basicity studies by CO 2 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 Ce x Zr 1− x O 2 materials.