Solid acid catalysts from clays - Evaluation of surface acidity of mono- and bi-pillared smectites by FT-LR spectroscopy measurements, NH3-TPD and catalytic tests

Alumina-pillared and double-pillared montmorillonite and saponite samples have been prepared and characterised from the point of view of their thermal stability, porosity and structure. Surface acidity was studied by ammonia TPD, iso-propanol conversion and n-butene skeletal isomerisation catalysis, and by FT-IR spectroscopy of the surface hydroxy-groups, and of adsorbed acetonitrile and pivalonitrile. The data show that the alumina pillars of pillared montmorillonite carry stronger Lewis sites than those of pillared saponite. Additionally, stronger Bronsted sites are carried by the montmorillonite layers with respect to those of saponite. Finally, pillared montmorillonite is more active in converting iso-propanol. However, it is also too active in converting n-butene, so giving rise to faster coking and more extensive cracking, So, pillared saponite has a more selective behavior in converting n-butene into iso-butene. (C) 2000 Elsevier Science B.V. All rights reserved.