Unidimensional channels

Virginia Polytechnic Institute number 5 (VPI-5) is a family of aluminophosphate based molecular sieves (refs. 1-5) which share a common three-dimensional topology and contain 18-membered rings (refs. 1-8). The extra-large pores of the VPI-5 materials are unidimensional channels circumscribed by rings containing 18 tetrahedral atoms and possess free diameters of approximately 12-13 A. 

A1P04-31 (structure type ATO) has unidimensional channels with nominal diameter 5.4 A. To model Xe/AlP04-31 atomistically, we assume that A1P04-31 is rigid and defect free with the experimentally determined crystal structure [7]. Xe atoms are represented as spheres, and Xe-Xe and Xe-0 interactions are taken to be Lennard-Jones potentials using previously derived parameters [5,8]. 

Various SAPO-n zeolite-supported Pd catalysts were recently investigated and compared in CO hydrogenation reactions (365). Although the acidic narrow channel (chabazite type) Pd/SAPO-34 catalyst produces mainly normal Cl—Cs alkanes, the ratios of branched hydrocarbons to normal hydrocarbons are quite high (6.7 for C4 and 10.8 for C5) on less acidic Pd/ SAPO-5, which has wide, unidimensional channels of 7.3 A cross section diameter. The comparison of product distribution on Pd/SAPO-5 and Pd/SAPO-11 catalysts is particularly interesting because in TPD of NH3, these zeolites reveal similar acid profiles and their IR spectra are similar. SAPO-11 has narrower unidimensional channels (6.3 x 3.9 A) than SAPO-5, but it produces only methane and oxygenates. The lack of higher hydrocarbons with Pd/SAPO-11 in comparison to Pd/SAPO-5 has been ascribed to shape selectivity due to the smaller pore size (365). 

The pore structure of an adsorbent is characterized by the dimensionality of the pore size (unidimensional channels, three-dimensional pore system), pore size distribu-... 

Phenylphosphonate Containing Unidimensional Channels Flanked by Hydrophobic RegionsA/igcvi. Chem. Int. Ed. Engl. 1995,54, 1508 Poojary, M. Cabeza, A. Aranda, M.AG. Bruque, S. Clearfield, A, Structure Determination of a Complex Tubular Uranyl Phenylphosphonate, (U02)3(H03PC6H5)2(03PQ H5)2 H20, ftom Conventional X-Ray- Powder Diffraction Data Inorg. Chem. 1996,55, 1468. 

Aluminum Methylphosphonate with Organo-Lined Unidimensional ChannelsAngew. Chem. Int. Ed. Engl. 1995, 54, 1199 Maeda, K. Akimoto, J. Kiyozumi, Y Mizukami, E, Structure of Aluminum Methylphosphonate, Ahnepo-Beta, with Unidimensional Channels Formed from Ladder-Like Organic-Inorganic Polymer-Chains J. Chem. Soc. Chem. Commun. 1995, 1033. 

A very unusual natural microporous iron aluminophosphate which exhibits reversible adsorption properties called cacoxenite (AlFe2405(0H)i2(P04)i7. (H20)24 ca. 51 H2O) contains a unidimensional channel system with 14.2 A pore opening [16,17]. In this structure the iron exists in octahedral coordination with aluminum occupying a distorted octahedral position within the framework. This phosphate mineral was the first known example of a microporous material with a pore size larger than 7 A. It imdergoes structural collapse when heated. 

MIL-53 materials provide a convenient model for comparison with traditional sorbents with similar geometric characteristics, such as activated charcoals and zeoUtes. The specific surface area estimated for MIL-53,1100 mVg (BET method), is similar to the average value for nanocarbon materials and exceeds that for zeolites. The framework of MIL-53 comprises unidimensional channels of 8.5 A in diameter, which is similar to the pore diameter in zeolites (6-12 A) and smaller than that in the IRMOF series, including MOF-5 (12-15 A). At the same time, the hydrogen adsorption capacity of MIL-53 is somewhat higher than that of the zeolite CaX (2.19wt.%, Table 2) and activated charcoals (2.15 wt.%) [179]. It is possible that this parameter is affected by the channel geometry, because zeolites more often have a 3D channel system, as opposed to the unbranched unidimensional channels in MIL-53. However, additional experiments on the adsorption mechanism are required to draw more definitive conclusions. 

Di-isopropylnaphthalene is an important precursor for polyesters and can be produced using dealuminated mordenites with unidimensional channels (Dow Chemical, Catalytica, Monsanto) with the preferential formation of 2,6-isomer with an... 

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