Pore geometry, zeolites

The bi-functional conversion of 2,2,4-trimethylpentane over Pt/DAY has been recently reported by Jacobs et al. (104). It was compared to the corresponding conversion over Pt/H-ZSM-5 and Pt/H-ZSM-11. All three zeolites had the same chemical composition. The authors found that 2,2,4-trime-thylpentane underwent 3-scission over Pt/DAY, while the formation of feed isomers was favored over the other two catalysts. The differences in reaction products were related to differences in the pore geometry of the zeolites. A similar study was carried out with n-decane. 

Recently various kinds of porous materials have been developed and their properties and structures have been gathering great concerns in science. There are two types of pores of intraparticle pores and interparticle ones[l]. The intraparticle pores are in the primary particle itself, while the interparticle pores originate from the interparticle void spaces. Zeolites are the most representative porous solids whose pores come from the structurally intrinsic intraparticle pores. The pore geometry can be evaluated by their crystallographic data. The carbon nanotube of which pore wall is composed of graphitic sheets is also the... 

The results obtained with the slit pore model are not reported since the calculated values do not agree with the experiment [97], This is an expected outcome, since the zeolite geometry can be modeled with the cylindrical pore or the spherical pore geometries, but not with the slit pore geometry. 

The results obtained with the cylindrical pore geometry (Table 9.2) are in reasonable agreement with the reported experimental data [97], However, for the H-Y zeolite, the cylindrical pore model did not provide a good result, since the pore system of the zeolite Y resembles a three-dimensional cylindrical system [115], The appropriate model for the zeolite Y is the spherical geometry pore [107] in this regard, the results reported in Table 9.3 shows that only the zeolite Y is properly described with the spherical geometry pore model [97],... 

Table 1 Pore geometry and sizes of zeolites with 12-membered ring apertures.

Fig. 8.7 Examples of pore geometry in medium pore zeolites...

A surprisingly large number of important industrial-scale separations can be accomplished with the relatively small number of zeolites that are commercially available. The discovery, characterization, and commercial availability of new zeolites and molecular sieves are likely to multiply the number of potential solutions to separation problems. A wider variety7 of pore diameters, pore geometries, and hy7drophobicity in new zeolites and molecular sieves as well as more precise control of composition and crystallinity in existing zeolites will help to broaden the applications for adsorptive separations and likely lead to improvements in separations that are currently in commercial practice. 

Normally, carbon materials are characterised using the DFT which assumes a slit-like pore geometry [12]. However, these zeolite templated carbons are best described by the DFT-Hybrid... 

Design of Zeolite Frameworks with Defined Pore Geometry through Constrained Assembly of Atoms... 

In 2003, the Jilin group developed a computational methodology for the design of open frameworks with predefined pore geometry.[37] The concept of forbidden zone is introduced. The forbidden zone corresponds to a porous pattern inside which no T-atom can be placed. Compared with previous simulation methods, this method is much more straightforward and efficient, especially for the design of zeolite frameworks with desired pore geometry. 

Y. Li, J. Yu, D. Liu, W. Yan, and R. Xu, Design of Zeolite Frameworks with Defined Pore Geometry through Constrained Assembly of Atoms. Chem. Mater, 2003, 15, 2780-2785. Y. Li, M. Guo, J. Yu, J.Y. Li, and R. Xu, Design of Zeolite Frameworks with Cross-linked Channels through Constrained Assembly of Atoms. Stud. Surf. Sci. Catal., 2004, 154, 308-316. 

P-15 - The influence of pore geometry on the alkylation of phenol with methanol over zeolites... 

JSnchen et al. [64] have reported that the heats of adsorption of acetonitrile on mesoporous (MCM-41) and microporous (FAU and MFI) molecular sieves are mainly influenced by a specific interaction with the acidic sites, while the adsorption heats of a non-polar molecule like w-hexane are determined by the pore size or density of those materials. However, a pore-size effect, affecting the heats of acetonitrile adsorption on acidic molecular sieves, has to be taken into account when employing those heats as a measurement of acidic strength. The contribution of the pore-size governed dispersion interaction in mesoporous MCM-41 is about 15 kJ mof less than that in the narrow channels of MFI. The adsorption of molecules of different sizes (toluene, xylenes, etc.), and the consecutive adsorption of these same molecules, studied by adsorption microcalorimetry together with reaction tests, can provide useful indications of the pore geometry and reactant accessibility of new zeolitic materials such as MCM-22 [65] or ZSM-11, SSZ-24, ZSM-12, H-M and CIT-1 [66]. 

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