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

Abstract

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 1-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.