Spaciousness index

A good example for reactant shape selectivity includes the use of catalysts with ERI framework type for selective cracking of linear alkanes, while excluding branched alkanes with relatively large kinetic diameters from the active sites within the narrow 8-MR zeolite channels [61, 62]. Here molecular sieving occurs both because of the low Henry coefficient for branched alkanes and because of the intracrystalline diffusion limitations that develop from slow diffusivities for branched alkane feed molecules. 

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The catalytic isomerization of 1-methylnaphthalene and all lation of 2-methylnaphtha-lene with methanol were studied at ambient pressure in a flow-type fixed bed reactor. Acid zeolites with a Spaciousness Index between ca. 2 and 16 were found to be excellent isomerization catalysts which completely suppress the undesired disproportionation into nwhthalene and dimethylnaphthalenes due to transition state shape selectivity. Examples are HZSM-12, H-EU-1 and H-Beta. Optimum catalysts for the shape selective methylation of 2-methylnaphthalene are HZSM-5 and HZSM-li. All experimental finding concerning this reaction can be readily accounted for by conventional product shape selectivity combined with coke selectivation, so there is no need for invoking shape selectivity effects at the external surface or "nest effects", at variance with recent pubhcations from other groups. 

In the endeavor to find good catalysts for the isomerization of 1-methylnaphthalene, the Spaciousness Index (SI) which was introduced earlier by our group [41,42] turned out to be a very useful guide. The SI values are slightly below 1 for 2XM-5 and other ten-membered ring zeolites and around 20 for very open and spacious structures such as Y or 2SM-20 [42]. In... 

Inevitably, the zeolites with a Spaciousness Index between 2 and 16 have a higher Si/Al ratio than zeolites Y or ZSM-20. To separate the effects of the Si/Al ratio and the pore width, two dealuminated samples of zeolite Y, designated YDl and YD2, were tested which resembled in their Si/Al ratios the Beta and EU-1 sample, respectively. Table 1 gives the isomerization selectivities at 40 % conversion. While dealumination of zeolite Y brings about some improvement in selectivity, H-Beta is clearly superior to HYDl, and H-EU-1 is a much better catalyst than HYD2, which indicates that the pore width in the appropriate range is of prime importance. 

Table 1. Conversion of 1-methylnaphthalene on various zeolite catalysts at 300 °C. Influence of the effective pore width, expressed by the Spaciousness Index (SI, [41, 42]), and the Si/Al ratio on the isomerization selectivity (the time on stream was chosen in such a manner that Xi-M-Np amounted to 40 %).

Zeolite ERS-10 has been characterised as acid catalyst for ethylbenzene(EB) disproportionation and benzene alkylation. In the disproportionation of EB, ERS-10 shows some similarity with ZSM-12. In the alkylation of benzene with propylene a peculiar behaviour is related to the by-production of diisopropylbenzenes (DIPBs). Like ZSM-5 and ZSM-12, the preferred isomer produced by ERS-10 is the para. A Spaciousness Index (SI) = 5.3 and the preferred formation of p-DIPB seem to indicate that the effective pore-width of ERS-10 is in the intermediate range between large and medium pore zeolites. 

Sonochemistry in synthesis Spaciousness index Sphares, silicalite Spheres, mesoporous silica Spheres, MFI, hollow Spheres, zeolite, hollow Spin echo double resonance Spinel ceramic from zeolites Spiropyrane in zeolite Y Sr exchange Sr removal Sr,K-KFl, synthesis SSZ-33 ( CON)... 

Microporous metal aluminophosphate with silicon in the framework Spaciousness index Turnover frequency Time on stream... 

Zeolites with 12-MR pore systems can be characterized with the spaciousness index (SI), which is determined from the ratio between isobutane and... 

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