PREPARATION AND PROPERTIES OF NEW ACID CATALYSTS OBTAINED BY GRAFTINGALKOXIDES AND DERIVATIVES ON THE MOST COMMON SUPPORTS - PART II - GRAFTING ZIRCONIUM AND SILICON ALKOXIDES ON GAMMA-ALUMINA

In this work, the preparation and properties of the acid catalysts obt ained by grafting zirconium and silicon alkoxides and zirconium-sulfat ed alkoxide on gamma-alumina were studied. The catalysts prepared were examined with electrochemical techniques to evaluate the hydroxyl den sity, the ZPC (zero point charge) and the intrinsic surface ionization constants. The catalysts were also submitted to TPD (temperature-prog rammed desorption) analysis using different organic bases to determine the distribution of acid sites. Some samples were also submitted to m icrocalorimetric analysis using pyridine as probe molecule, and to XPS measurements. Finally, the catalysts prepared were tested in three di fferent reactions: methanol dehydration, n-hexane isomerization and cr acking and skeletal isomerization of I-butene to isobutene. The most r elevant results obtained were: (i) grafted zirconia strongly promoted methanol dehydration up to an upper limit of grafting; (ii) grafted zi rconium sulfated alkoxide showed a moderate activity, but good selecti vity in n-hexane isomerization; (iii) silicated aluminas (prepared in the absence of solvents) showed high activity, selectivity and stabili ty in the l-butene skeletal isomerization reaction. (C) 1998 Elsevier Science B.V. All rights reserved.