Chain Length Effects of Linear Alkanes in Zeolite Ferrierite. 1. Sorption and ¹³C NMR Experiments

Abstract

Temperature-programmed desorption, heat of adsorption, adsorption isotherm, and 13 C NMR measurements are used to study the sorption properties of linear alkanes in ferrierite. Some remarkable chain length effects are found in these properties. While propane, n-butane, and n-pentane fill the ferrierite pore structure completely, n-hexane and n-heptane can only access a part of the pore structure. It is shown by 13 C NMR that n-hexane adsorbs only in the 10-ring channels of ferrierite and not in the ferrierite 8-ring cages. Adsorption of n-pentane in this cage is possible but only at relatively high pressures. At low pressures, only the 10-ring channels are filled by n-pentane. This remarkable sorption behavior is caused by the much lower heat of adsorption of n-pentane in the ferrierite 8-ring cage compared to the 10-ring channels and results in a twostage desorption profile. In contrast to n-pentane, propane and n-butane adsorb easily into the complete pore structure, which is reflected in the normal single-stage desorption profile. The 13 C NMR measurements show furthermore that propane is preferentially adsorbed in the ferrierite 8-ring cage, while no clear preference is found for n-butane.

Molecular simulations of adsorption isotherms of small alkanes in FER-, TON-, MTW- and DON-type zeolites

“…At high pressure propane adsorbs in both the cages and the 10-ring channels. This observation compares nicely to the results of NMR experiments performed by Van Well et al [32,33]. Similar results were obtained in the computational part of their study [15,32] using a slightly different forcefield from the one used in this study.…”

Biochemical evolution III: Polymerization on organophilic silica-rich surfaces, crystal–chemical modeling, formation of first cells, and geological clues

“…Y crystal chemistry of high-silica materials: Fourier TransformRaman studies of single-component and binary adsorption in silicalite-1 (3); vapor adsorption in thin silicalite-1 films studied by spectroscopic ellipsometry (4); adsorption͞de-sorption of n-alkanes on silicalite crystals (5); adsorption equilibria of C1 to C4 alkanes, CO 2 , and SF 6 on silicalite (6); adsorption of linear and branched alkanes in zeolite silicalite-1 (7); combined quantum mechanical͞molecular mechanics ab initio modeling, demonstrating that the most stable Brønsted sites occur in high-silica zeolites (8); simulation of adsorption and diffusion of hydrocarbons in silicalite, demonstrating that a linear hydrocarbon moves more freely than a branched one, whose CH group becomes locked at a channel intersection (9); adsorption isotherms of linear alkanes in ferrierite-smaller ones, C1-C5, fill the entire pore system, whereas C6 and C7 fit only in a 10-ring channel unless forced into an eight-ring channel by pressure (10,11); nuclear magnetic resonance of 1 H in water adsorbed on silicalite (12); heterogeneity of Brønsted acid sites in Al-substituted faujasites (13); nuclear magnetic resonance of 17 O in silica, albite glasses, and stilbite (14,15); simulation of alkane adsorption in aluminophosphate-5, and calorimetry of alkane absorption in high-silica zeolites (16,17); hydrophobic properties of all-silica beta zeolite (18); structural location of sorbed p-nitroaniline in silicalite͞MFI molecular sieves from x-ray powder diffraction and 29 Upper illustrate the results of packing simulations based on Monte Carlo techniques for glycine and histidine molecules encapsulated within the 10-ring channels of silicalite. It is possible at low pressure to pack 28 glycine molecules per unit cell or eight histidine.…”

Molecular Competition Effects in Liquid‐Phase Adsorption of Long‐Chain n‐Alkane Mixtures in ZSM‐5 Zeolite Pores

“…For example, ferrierite behaves as a 1D pore system for long-chain n-alkane molecules (> C 5 ), whereas only shorter molecules can exploit its full 2D pore system. [1][2][3][4] With ferrierite and ZSM-22, the siting of dibranched alkane seems to depend subtly on their size. At low coverage the dibranched alkanes adsorb in parallel to the outer surface of the zeolite and as coverage increases, additional molecules adsorb in such a manner that propyl and butyl groups point into the pores.…”