FTIR AND RAMAN-SPECTROSCOPIC INVESTIGATION OF 2,2'-BIPYRIDINE ADSORPTION ON SILICA, ALUMINA, ZIRCONIA AND TITANIA

The adsorption of 2,2'-bipyridine on silica, gamma-alumina, monoclinic zirconia and mixed anatase/rutile titania have been studied by infrar ed (IR) and Raman spectroscopic techniques. These oxides were chosen b ecause they constitute pillars in various pillar interlayered clay (PI LC) catalysts which have been the subject of a separate 2,2'-bipyridin e study. Four different types of adsorbed 2,2'-bipyridine molecule hav e been identified depending on the specific oxide. Physisorbed neutral molecules were common to all four oxides. Hydrogen-bonded neutral spe cies were observed on silica, gamma-alumina and titania, while neutral 2,2'-bipyridine, coordinatively bound in a bidentate manner to single Lewis sites was also detected on gamma-alumina, zirconia and titania. An additional Lewis-bound species was observed on gamma-alumina where the adsorbate was bound to two adjacent Al3+ Lewis sites. At high tem perature these adsorbed molecules were observed to dissociate into ind ividual adsorbed pyridine molecules. Physisorbed bipyridine molecules exhibited trans symmetry, while H-bonded and chemisorbed bipyridine mo lecules possessed cis symmetry.