The structure and stability of sulfated alumina and titania

• Published in: Journal of catalysis 1986-05, Vol.99 (1), p.104-110
• Main Authors: Saur, O., Bensitel, M., Saad, A.B.Mohammed, Lavalley, J.C., Tripp, Carl P., Morrow, B.A.
• Format: Article
• Language: English
• Subjects: Catalysis; Catalysts: preparations and properties; Catalytic reactions; Chemistry; Exact sciences and technology; General and physical chemistry; General. Nomenclature, chemical documentation, computer chemistry; Theory of reactions, general kinetics; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/0021-9517(86)90203-4

The oxidation of H 2S or SO 2 in excess O 2 over Al 2O 3 or TiO 2 (anatase) yields, for either catalyst under anhydrous conditions, an infrared spectrum which is characterized by an intense sharp band near 1380 cm −1 and a broad band or doublet near 1040 cm −1. The same spectrum arises from the impregnation of Al 2O 3 with either (NH 4) 2SO 4 or Al 2(SO 4) 3 · 18H 2O or of TiO 2 with (NH 4) 2SO 4 or TiOSO 4 and heating the dried mixture at 450 °C under vacuum. The sulfated surface does not exchange with 18O 2 but does with H 2 18O and only one new shifted high-wavenumber band is produced for partial or complete oxygen-18 exchange. The infrared spectrum changes in the presence of H 2O at 20 °C and resembles that of a more traditional bidentate type sulfate species and we postulate that, in the absence of OH groups or water the sulfate has a structure resembling ( M 3 O 3) S O [ M = Al or Ti], whereas in the presence of H 2O or excess surface OH groups this is converted to ▪ type groups, thus accounting for the increased Brønsted acidity. Finally, the sulfated Al 2O 3 surface is more thermally stable and more resistant to reduction in H 2 than is the TiO 2 surface and the ramifications are discussed in terms of the use of these oxides for SO x transfer catalysts or in air pollution abatement.