Studies of hydrogen held by solids. Part 11.—Interaction of simple olefins and pyridine with decationated zeolites

Abstract

Three OH stretching bands, with maxima at about 3745, 3650 and 3545 cm^–1, are present in infrared spectra of decationated X- and Y-type zeolites. Pyridine reacted with the 3650 cm^–1 species to form pyridinium ion. This band underwent a hydrogen-bonding shift when ethylene was adsorbed at room temperature, indicating a strong physical adsorption which was quantitatively and rapidly reversible on raising or lowering the pressure. No exchange occurred between C₂H₄ and the OD groups of an exhaustively deuterated zeolite. The hydrogen-bonding shift from 3650 to 3300 cm^–1 was identical when C₂D₄ was substituted for C₂H₄. The 3745 and 3545 cm^–1 bands were not noticeably altered by the adsorption, at least in the pressure region where the 3650 cm^–1 band was affected. Adsorption isotherms, calculated from the spectra, could be superimposed on those determined by volumetric techniques. Both were close to Langmuir-type but showed evidence of a superimposed non-selective adsorption at higher pressures. Ethylene may also adsorb, via a charge-transfer interaction, on the residual Na⁺ ions of the zeolite. At about 500 torr, the total adsorption of C₂H₄ was about 30 % greater than the available zeolite hydroxyl groups. It was inferred that the strongest interaction was with the acidic hydroxyl groups and that, at low pressures, most of the adsorbed C₂H₄ was hydrogen-bonded to these. In the CH bending and stretching regions, only the Q-branch of the spectra of the gaseous molecules appeared, indicating that molecular rotation was hindered in the adsorbed state. Qualitatively similar results were obtained with C₃H₆. The hydrogen-bonding shift was greater by about 100 cm^–1, however, and the adsorption was not entirely reversible. Moreover, the irreversible portion increased with time, and products stemming from polymerized olefin could be recovered; also, C₃D₆ exchanged with the OH groups of the 3650 and 3545 cm^–1 bands, but not with those of the 3745 cm^–1 band. Preliminary results for these substrates adsorbed on dehydroxylated, decationated zeolites are given.