Superacidic sulfated metal oxides were prepared by impregnating different metal oxides (or hydroxides) with sulfuric acids. The superacidic strength of prepared samples were compared by temperature-programmed desorption of ammonia (NH3-TPD) and showed a trend of HS/ZrO2 > HS/MgAl2O4 > HS/Al2O3 > HS/Fe2O3. Catalytic properties of these superacidic samples towards isomerization of n-butane to isobutane were subsequently pursued. Both the activity and the isobutane selectivity increased with the superacidic strength of catalysts. Observed variation in the selectivity was interpreted with a difference in the reaction mechanism: A high selectivity was obtained from strong superacid sites that catalyze the isomerization through a revised monomolecular mechanism; while a low selectivity became dominated on weak superacid sites that favored a bimolecular mechanism. The relative importance of these two mechanisms was kinetically controlled by formation of different butyl carbenium ions (primary or secondary) while the n-butane reactant adsorbed on superacidic sites. (C) 2000 Elsevier Science B.V.
All Science Journal Classification (ASJC) codes
- Process Chemistry and Technology
- Physical and Theoretical Chemistry