Crystalline molecular sieves

Crystalline molecular sieve zeoHtes, and related molecular sieve materials that are not technically zeoHtes, eg, siHcaHte, AlPO s, SAPOs, etc. 

Typical pore size distributions for these adsorbents have been given (see Adsorption). Only molecular sieve carbons and crystalline molecular sieves have large pore volumes in pores smaller than 1 nm. Only the crystalline molecular sieves have monodisperse pore diameters because of the regularity of their crystalline stmctures (41). 

Moderately polar crystalline molecular sieves with low aluminum and low cation contents, siUca gel, activated alurnina, activated carbons with highly oxidh... 

Nonpolar sihcaUte, F-siUcahte, other high siUca content crystalline molecular sieves, activated carbons with reduced surfaces. 

Isotherms for H2O and / -hexane adsorption at room temperature and for O2 adsorption at Hquid oxygen temperature on 13X (NaX) zeoHte and on the crystalline Si02 molecular sieve siHcaHte are are shown in Figure 8 (43). SiHcaHte adsorbs water very weaMy. Further modification of siHcaHte by fluoride incorporation provides an extremely hydrophobic adsorbent, shown in Figure 9 (44). These examples illustrate the broad range of properties of crystalline molecular sieves. 

Ion Exchange. Crystalline molecular sieve ion exchangers do not foUow the typical rules and patterns exhibited by organic and other inorganic ion exchangers. Many provide combinations of selectivity, capacity, and stability superior to the more common cation exchangers. Their commercial utilization has been based on these unique properties (59). 

Chao, C.C., Sherman, J.D., and Barkhausen, C.H. (1989) Latex polymer bonded crystalline molecular sieves. US Patent 4,822,492. 

The acid strength of protons in the crystalline molecular sieve structure plays a key role in of MTO catalysis. The acid sites of silicoalumina-based zeolites... 

Over the past five years, we and our colleagues have undertaken an extensive study of the acid-catalyzed dehydration of the four isomeric butyl alcohols. In so doing, we compared the performance of crystalline, molecular-sieve acid catalysts (HZSM-5) in a range of crystal sizes (so as to vary diffusion path and active-site concentration) with that of amorphous aluminosilicate (AAS) gels in which the pore size is significantly larger. Our results, which permit the... 

Corma, A. and Davis, M. E. Issues in the synthesis of crystalline molecular sieves towards the crystallization of low framework-density structures, Chem Phys Chem, 2004, 5, 304—313. 

Thomas, J. M, New Microcrystalline Catalysts. Philos. Trans, R. Soc, London A, 1990, 333 173. Davis, M, E, The quest for extra-large pore, crystalline molecular sieves Chem. Eur. J. 1997, 3, 1745. Francis, R, J, O Hare, D. The kinetics and mechanisms of the crystallization of microporous materials. J. Chem. Soc., Dalton Trans, 1998, 3133. 

The 27 papers in this volume present a cross section of synthesis, characterization, and chemical studies by academic and industrial researchers. Although zeolite research activity has been predominantly industrially based, increasing effort and results are now emanating in academic laboratories. The synergism and mutual stimulation of these efforts can be expected to increase the quality and quantity of current and future research involving microporous crystalline molecular sieves. 

One of the most exciting aspects of zeolite chemistry is our increasing understanding of the functionality of framework structure, chemisorption, and mass transport as related to chemical behavior. The research in this area has resulted in numerous advances during the past 2 years, many of which are presented in this text. It is expected that the applications and interest in crystalline molecular sieves will continue to expand rapidly. 

A new family of crystalline molecular sieves, 2) having aluminophosphate frameworks was synthesized. Strict alternation of A1 and P on the tetrahedral nodes yields neutral oxygens in contrast to the aluminosilicate zeolites, and non-framework cations are not needed for charge balance. Whereas a microporous silica (silicalite, 3 ) with neutral oxygens is hydrophobic, the aluminophosphate sieves are moderatley hydrophilic. 

TS1 is a crystalline molecular sieve with the MFI structure in which titanium (IV) is isomorphously substituted for silicon in the framework. The location of Ti in the framework has been demonstrated by using several techniques XRD, UV-Visible spectroscopy, EXAFS-XANES (23). Its remarkable efficiency for selective oxidation of various functional groups with dilute aqueous hydrogen peroxide can be attributed (24) to ... 

As the shortcomings of the traditional preparative methods outlined above became apparent, it was realized that alternative procedures were required to produce uniform or tailor-made adsorbents and shape-selective catalysts. As we saw in Chapter 11, one major route was opened up by the Linde synthesis in 1956 of the crystalline molecular sieve zeolite A. The search for new microporous crystalline materials has continued unremittingly and has resulted in the synthesis of novel zeolitic structures including the aluminophosphates, which are featured in this chapter. 

Bulletin Union Carbide Molecular Sieves for Selective Absorption, The British Drug Houses Ltd. D. W. Breck, Crystalline Molecular Sieves," X Chem. Ld., 41,678 (1964)... 

A. Corma and M.E. Davis, Issues in the Synthesis of Crystalline Molecular Sieves Towards the Crystallization of Fow Framework-Density Structures. Chem. Phys. Chem., 2004, 5, 304-313. 

Corma, Davis 2004 Issues in the synthesis of crystalline molecular sieves [49]... 

The UF membrane can be pictured as a sieve on a molecular-dimensional scale. II is usually polymeric and asymmetric, dmigned for high productivity and resistance to plugging. Compared to crystalline molecular sieves, it is imprecise because pore size is not controllable within anrrow limits. Adsotplion effects are usually significant, altering both the rate and retention characteristics of UF. The UF membrane... 

Medium-pore zeolites can be generally described as crystalline molecular sieves consisting of linked silica- and alumina-tetrahedra forming 10-membered oxygen ring channels. The dimensions of these medium-size pores are 0.5 to 0.6 lun. With respect to the conversion of methanol to olefins, only ZSM-5 or its isostructural analogs and, to a much less extent, ZSM-11 and ZSM-48 have been studied. 

Aluminophosphates (denoted as ALPO s) are porous crystalline molecular sieves, consisting of AlO g Since the first synthesis of these materials,... 

Diffraction-based techniques are widely applicable to crystalline molecular sieves. For samples available as crystals ca. 10 pm or more in size. X-ray single... 

---