Shape Selectivity in Adsorption of n‐ and Iso‐alkanes on a Zeotile‐2 Microporous/Mesoporous Hybrid and Mesoporous MCM‐48

Abstract

The adsorption of linear and branched C5–C9 alkanes in the temperature range 50–250 °C on mesoporous MCM‐48 material and its microporous/mesoporous variant Zeotile‐2 at low surface coverage is investigated using the pulse chromatographic technique. On MCM‐48, the differences in adsorption between linear and branched alkanes are merely a result of differences in volatility, indicating that the MCM‐48 material does not present shape‐selective adsorption sites. On Zeotile‐2, there is a preferential adsorption of linear over branched alkanes. The difference arises from a difference in adsorption entropy rather than enthalpy. Upon their adsorption on Zeotile‐2 branched alkanes lose relatively more entropy than their linear isomers do. Zeolitic molecular pockets embedded in the walls of the mesoporous Zeotile‐2 impose steric constraints on the bulky isoalkanes. Zeotile‐2 combines adsorption properties from microporous and mesoporous materials. Compared to the nitrogen molecule, linear and branched C5–C9 alkanes are superior probes for investigating micropores and micropockets in hierarchical materials.

Synthesis and hydrophobic adsorption properties of microporous/mesoporous hybrid materials

“…Unfortunately, SBA-15 materials with the amorphous silica wall exhibit low mechanical and hydrothermal stability compared to zeolitic materials (such as silicalite-1) [11,12]. Hence, attempts to combine the advantages of mesoporous material (large pore diameters and good accessibility) with zeolite (many active sites, hydrothermal stability and hydrophobic property) have attracted wide attentions and industrial interests [3].…”

“…Their intricate channels and pores contribute to the development of the intracrystalline surface area at which a large number of catalytic and adsorptive sites can be generated [3]. Especially, the MFI type silicalite-1 (Sil-1) zeolite without cations and silanol defects exhibits high hydrophobic property during the adsorption of volatile organic compounds (VOCs) under wet conditions [4,5].…”

“…In current approaches to obtain hybrid materials, prefabricated zeolite seeds are assembled into mesoporous materials upon addition of surfactant and heating [3,[15][16][17][18] or pore walls of ordered mesoporous material restructured with the help of temples and recrystallization processes [19,20], and much attention has also been focused on the nanocasting method using various forms of carbon (CMKs) as template to replicate mesopore-containing zeolites [14,[21][22][23][24]. Recently, Navascués et al [5] mesoporous silica spheres seeded with silicalite-1 nanocrystals and used as an adsorbent for water, n-hexane, triisopropylbenzene and 2,2-dimethylbutane molecules to evaluate its hydrophobicity and pore accessibility.…”

An in situ growth approach to the fabrication of zeolite imidazolate framework-90 bonded capillary column for gas chromatography separation

“…Zeolite imidazolate framework-90 (ZIF-90) was used as a model MOF. 23,24 2. 21 It is also easy to synthesize at room temperature.…”

Direct Measurement of Raman Scattering Tensor of Orientation‐Fixed Single Iodine Molecules

“…In this article, we will show it is feasible to control the orientations of iodine single molecules inside the array of uniform 1D parallel nano‐channels of AlPO 4 ‐ n crystals, which are suitable to accommodate small guest molecules . The optical analysis of the embedded molecules can be easily conducted on these crystals due to their transparency from ultraviolet to near‐infrared .…”