FTIR SURFACE SITE ANALYSIS OF PILLARED CLAYS USING PYRIDINE PROBE SPECIES

The surface acidities of alumina-, zirconia-, and titania-pillared cla ys (montmorillonite, synthetic mica-montmorillonite, and rectorite) an d the unpillared parent clays have been studied by infrared spectrosco py using pyridine as a spectroscopic probe species under variable-temp erature desorption conditions. These semiquantitative studies of therm ally activated pillared clays suggest that the characteristics of surf ace Lewis acid sites are primarily determined by the pillar species wh ile those of the Bronsted sites are determined by both the pillar spec ies and the parent clay used. Alumina-pillared clays exhibit both Lewi s and Bronsted acidity associated with the pillars, while zirconia- an d titania-pillared clays exhibit only Lewis acidity on the pillars wit h Bronsted activity being associated with the exposed clay surfaces an d pillar-to-clay layer bonding sites. Relative acid site strengths are estimated by using the extent of retention of pyridine under desorpti on conditions and by determining the magnitude of adsorption-induced w avenumber shifts for pyridine vibrational bands. The overall acidity o f alumina-pillared rectorite was found to be the strongest of the pill ared clays studied, while the acidity of zirconia-pillared montmorillo nite was the weakest.