FTIR and Raman spectroscopic investigation of 2, 2′-bipyridine adsorption on silica, alumina, zirconia and titania
The adsorption of 2,2′-bipyridine on silica, γ-alumina, monoclinic zirconia and mixed anatase/rutile titania have been studied by infrared (IR) and Raman spectroscopic techniques. These oxides were chosen because they constitute pillars in various pillar interlayered clay (PILC) catalysts which have been the subject of a separate 2,2′-bipyridine study. Four different types of adsorbed 2,2′-bipyridine molecule have been identified depending on the specific oxide. Physisorbed neutral molecules were common to all four oxides. Hydrogen-bonded neutral species were observed on silica, γ-alumina and titania, while neutral 2,2′-bipyridine, coordinatively bound in a bidentate manner to single Lewis sites was also detected on γ-alumina, zirconia and titania. An additional Lewis-bound species was observed on γ-alumina where the adsorbate was bound to two adjacent Al3+ Lewis sites. At high temperature these adsorbed molecules were observed to dissociate into individual adsorbed pyridine molecules. Physisorbed bipyridine molecules exhibited trans symmetry, while H-bonded and chemisorbed bipyridine molecules possessed cis symmetry.