Acidic-base properties of silica-magnesia sol-gel mixed oxides:: use of 2 butanol as test reaction

2-butanol dehydration was performed as a test reaction for acid-base characterization of a series of unsulfated and sulfated silica-magnesia sol-gel mixed oxides covering the 1.3-6.7% MgO composition range. The dehydration of 2-butanol over non-sulfated silica-magnesia yields a mixture of butenes in which the fraction of 2-butene (Saytzeff orientation) is 33%. High selectivity for l-butene (Hofmann orientation) is indicative of the E1cB mechanism over sulfated silica-magnesia oxides. The acid-base properties were also investigated by ammonia and carbon dioxide TPD and FTIR spectroscopy of adsorbed pyridine. Acid-base properties are discussed as a function of magnesium content (nature, strength and amount of sites). A very good correlation between the results of test reactions and acid-base characterization methods is observed. (C) 1999 Elsevier Science B.V. Ail rights reserved.