Zeolite ultra-small

While it is true that high population densities of these ultra-small QD s can be assembled in zeolite cavities, the QD may lose the properties of bulk crystallinity with respect to the parent bulk semiconductor. Furthermore the extent of lattice periodicity within a QD is likely to be too small for the EMA to be valid. Indeed a pivotal, and still unanswered question, concerns precisely the... 

Coker, E. N. and Jansen, J. C. (1998) Approaches for the synthesis of ultra-large and ultra-small zeolite crystals. In Molecular Sieves. (H. G. Karge and J. Weitkamp, eds.). Springer, Berlin Germany and New York, N.Y. pp. 121-155. 

Approaches for the Synthesis of Ultra-Large and Ultra-Small Zeolite Crystals... 

Naturally-produced zeolites often far surpass those made in the laboratory in terms of their large size and sheer beauty. However, the time-frame of nature s synthesis procedure is measured in millennia - clearly not an option for even the most patient scientist. Hence it is up to the scientist to use his ingenuity in creating methods to prepare ultra-large or ultra-small crystals in the laboratory. 

Table 1. Parameters which influence the growth of ultra-large and ultra-small zeolite crystals ...

Excellent studies have been performed on the synthesis of ultra-small crystals of MFI-type zeolite [59,60]. In particular the preparation of suspensions of colloidal silicalite-1 crystals (less than 100 nm) with a narrow particle-size distribution have been extensively studied. 

Apart from the pore width and pore architecture, the crystal size of a zeolite is often very important. In Chapter 5, E.N. Coker and /. C. Jansen present a systematic evaluation of the attempts to synthesize either ultra-small (i.e.,... 

Coker EN, Jansen JC (1998) Approaches for the Synthesis of Ultra-Large and Ultra-Small Zeolite Crystals. 1 121-155... 

In 2012, Mintova and coworkers captured ultra-small EMT zeolite of 6-15 nm from the organic-template-free system at low temperature [30]. Traditionally, pure EMT could only be synthesized with an expensive organic template (18-crown-6 ether) [31]. The novel organic-template-free synthesis of EMT zeolite is from Na-rich precursor suspensions. 

Gel composition, nucleation temperature and time, and heating method are the key for the formation of ultra-small EMT zeolite, avoiding the conversion of zeolite EMT into zeolite FAU or SOD. The synthesis proceeded at near ambient temperature (30°C) with a very high yield. The successful synthesis of EMT zeolite provides a good example of zeolite synthesis by an energy-efficient and green route. 

There are three different kinds of octane catalysts in current use. Some are based in part on an active non-zeolite matrix composed of a porous silica/alumina component. Others are based on low cell size (2.425-2.428 nm) ultra stable faujasite (USY), a catalyst composition developed in 1975 (2) for the purpose of octane enhancement. A third catalyst system makes use of a small amount (1-2%) of ZSM-5 as an additive. While the net effect in all cases is an increase in the measured octane number, each of the three catalytic systems have different characteristic effects on the composition and yield of the gasoline. The effects of the ZSM-5 component on cracking is described in other papers of this symposium and will not be discussed here. 

Zeolites are conveniently divided into groups on the basis of their pore sizes - small, medium, large and ultra large - which are determined by the ring size... 

The earliest applications of zeolites utilized the molecular sieving properties of small pore zeolites, e.g. zeolite A, in separation and purification processes such as drying and linear/branched alkane separation [33]. In 1962 Mobil Oil introduced the use of synthetic zeolite X, an FCC (fluid catalytic cracking) catalyst in oil refining. In the late sixties the W. R. Grace company introduced the "ultra-... 

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