4,4'-Bipyridine (4bipy) adsorption on the surfaces of silica, alumina, and titania and the infrared (IR) spectra obtained therefrom are reported for the first time. This paper constitutes the second part of a multi-faceted investigation into the development of a vibrational spectroscopic technique for the determination of distances between surface acid sites of three-dimensional solid acids. The afore-mentioned oxides were chosen because their surface chemistries are generally well understood and because they constitute the pillars within pillar interlayered clay (PILC) catalysts. However, there is little information in the literature regarding the surface interactions of this novel and potentially useful spectroscopic probe. The pore structures of PILC materials have been investigated through 4bipy adsorption, the results of which will be reported in a later paper. The spectra obtained for adsorption on the parent oxides are discussed with reference to earlier 4bipy and 2,2'-bipyridine (2bipy) adsorption studies and indicate that the mode of adsorption is a unidentate, "end-on" arrangement in agreement with that observed for adsorption on MgO. This mode of adsorption results in a reduction in molecular symmetry of the adsorbed 4bipy from D2h to C2v. A previously unreported observation involving the high-temperature cleavage of the inter-ring bond of 4bipy adsorbed on γ-alumina and titania Lewis acid sites is described.
Stephen A. Bagshaw and Ralph P. Cooney, "FT-IR Spectroscopic Investigation of 4,4'-Bipyridine Adsorption on Metal Oxide Surfaces," Appl. Spectrosc. 50, 310-315 (1996)