Zeolites nomenclature

Figure 1 Binuclear iron core inserted over a) Z" and b) Z"0h clusters used to represent the 5MR portion of the ZSM-5 zeolite framework. T site numbers follow the ZSM-5 nomenclature. Pink balls are Al, grey balls are Si, blue balls are Fe, red balls are O and white balls are H.

The nomenclature for the catalysts is as follows XAGaZB, where letter X refers to the treatments to which the sample was submitted, letter T referring specifically to the case where the sample was submitted to the two reduction-oxidation cycles described above letter A refers to the wt. % impregnated gallium amount letter B indicates the SAR of the zeolite. In this way, for example, the catalyst named T3GaZ38 is a ZSM-5 zeolite with SAR 38 impregnated with 3 wt. % gallium submitted to two reduction-oxidation cycles. 

The nomenclature of zeolites is rather arbitrary and follows no obvious rules because every producer of synthetic zeolites uses his/her own acronyms for the materials. However, as mentioned before, at least the structure types of the different zeolites have a unique code. For example, FAU represents Faujasite-type zeolites, LTA Linde Type A zeolites, MFI Mobile Five, and BEA Zeolite Beta. The structure commission of the International Zeolite Association (IZA) is the committee granting the respective three-letter codes [4], Some typical zeolites, which are of importance as catalysts in petrochemistry, will be described in the following sections. 

Barrer, R.M. (1979) Chemical nomenclature and formulation of compositions of synthetic and natural zeolites. Pure Appl. Chem., 51 (5), 1091-1100. 

Materials 2M2B 2-methyl-2-butene HZSM-5 zeolite with MFI framework (lUPAC nomenclature) NaCaA zeolite with LTA framework (lUPAC nomenclature) NaX zeolites with FAU framework (lUPAC nomenclature) Pd/A Os alumina supported palladium catalyst TAME tert-amyl methyl ether or 2-methoxy-2-methylbutane TAOH tert-amyl alcohol or 2-methyl-butan-2-ol... 

The three-letter framework-type codes, recognized by the IUPAC Commission on Zeolite Nomenclature, have been used to organize the entries in this publication. The powder diffraction data and simulated patterns for the reference structures are listed alphabetically according to the respective framework type code. An index of material names, and associated three-letter codes, is included in the companion volume, the Atlas of Zeolite Framework Types (Baerlocher, McCusker and Olson (2007)). 

Using the Si( Al) nomenclature, these are designated Si(OAl), Si(lAl), Si(2Al), Si(3Al), and Si(4Al), respectively, and each has a characteristic chemical shift. This has been very well documented for a number of zeolite types 49,51-57 Although there has been some duplication of effort the conclusions are important, and are essentially summarized by Melchior et al.57 and Klinowski et al.5 who state that in addition to identification of the Si(wAl) species, the framework Si/Al ratios can be determined from signal intensities, thereby providing an attractive alternative method to X-ray diffrac-... 

The reversible Type I isotherm (Type I isotherms are sometimes referred to as Langmuir isotherms, but this nomenclature is not recommended) is concave to the p/pa axis and na approaches a limiting value as p/p° — 1. Type I isotherms are given by microporous solids having relatively small external surfaces (e.g. activated carbons, molecular sieve zeolites and certain porous oxides), the limiting uptake being governed by the accessible microporc volume rather than by the internal surface area. 

In the context of microporous and mesoporous materials, lUPAC has provided a variety of recommendations for nomenclature and characterization of porous materals, that can be found in the literature. Microporosity should not be based on structural data but on adsorption data. Sorption by materials that show Type 1 isotherms is an indication of a microporous material. Pore size distributions less than 20 A are related to microporous materials like zeolites. Materials having pores between 20 A and 500 A are refered to as mesoporous materials. Materials that have pores larger than 500 A are refered to as macroporous. 

Other nomenclature is associated with these channels. Narrow points in a channel are called windows or, less definitively, rings. These further limit the movements of ions and molecules. Wider areas between windows and/or at channel intersections are called cavities or cages, and these may be the primary source of the intrazeolitic volume which is available for ions and molecules. This volume can be as large as half of the total volume of a zeolite crystal. Cavities accessible from only one side may be called side-pockets. A zeolite whose channels are of relatively uniform diameter may be viewed as having neither windows nor cages. 

Petrovic et al. (1993) reported seven high-silica zeolite structures (ATI, EMT, FAU, FER, MEL, MFI, and MTW, topologies in standard International Zeolite Association nomenclature) to be 5.6-14.3 kJ/mol less energetically stable than a-quartz. Navrotsky et al. (1995) reported the enthalpy of MEI was 13.9 0.4 kJ/mol higher than that of a-quartz. Piccione et al. (2000) found eleven high-silica zeolite structures (AST, BEA, CFI, CHA, IFR, ISV, ITE, MEL, MFI, MWW, and SST) to be 6.0-15.5 kJ/mol less stable in enthalpy than a-quartz. 

The natural zeolite community has followed a different path towards a systematisation of its nomenclature. An historically-determined nomenclature in which the crystal structure, the nature of the charge-compensating cation and some thermal properties were taken into account in a non-systematic manner [41] has been replaced by a nomenclature in accordance with the rules of the International Mineralogical Association (IMA) [42], in which both the structure and composition of the mineral are considered. This has led to a substantial increase... 

The blossoming of new materials has been so rapid that the nomenclature of ordered mesoporous materials is in the wild state in which zeolite nomenclature was thirty years ago. A set of rules for writing a standardized crystal chemical formula for both microporous and mesoporous materials has been established by the Physical Chemistry Division of the International Union for Pure and Applied Chemistry, through its Commission on Colloid and Surface Chemistry including Catalysis [65]. The impact of this nomenclature on the activity of the scientists dealing with mesoporous materials has still to be verified. 

The concept of natural zeolite and the connected classification underwent numerous changes in the last seventy years. The first definition, taking care not only of the physical-chemical behaviour, but also of the peculiar structure, is due to Hey in the early 1930s [22]. Further proposals on this subject were made by Smith [23] and Liebau [24], but the discovery of new minerals having only partly the structural features, the chemistry and the properties of the "traditional" zeolites, made necessary the redefinition of the term "zeolite" and the proposition of novel nomenclature rules. A Committee was constituted for this in 1993 by the International Mineralogical Association. After a capillary work lasted about five years a Report was produced on the Recommended nomenclature for zeolite minerals [25]. 

GIS). A three letter code (e.g. GIS) is assigned to confirmed framework types by the Structure Commission of the International Zeolite Association according to rules set up by an 1UPAC Commission on Zeolite Nomenclature [3,4]. The codes are normally derived from the name of the zeolite or type material , e.g. FAU from the mineral faujasite, LTA from Linde Type A, and MFI from ZSM-5 (Zeolite Socony Mobil - five). Information pertinent to these framework types is published in the Atlas of Zeolite Framework Types [5] and on the internet at http //www.iza-strncture.org/databases/. As new codes are approved, they arc announced on the IZA Structure Commission s WWW pages (http //www.iza-structure.org/) and included in the internet version of the Atlas. As of January 2005, 161 zeolite framework types had been confirmed by the Structure Commission. In this chapter, all references to materials whose framework types are known will be accompanied by the appropriate three letter code in boldface type. 

The main feature of a zeolite structure is its framework type, which describes the arrangement of the cages, the dimensionality of the channel system and the approximate size of the pore openings. A few framework types, selected for their industrial relevance and/or to illustrate some of the more common structural nomenclature, have been presented. However, there are many more, and for more information about a specific framework type, the reader is referred to the relevant references in the Atlas and the Collection. To fully understand the properties of a real zeolitic material though, not only the framework type, but also the composition and true geometry of the framework, the location and nature of the extraframework species, and the number and type of defects must be investigated. 

A statement by Hey (45) that, "the development of mineralogical nomenclature has been rather haphazard and many species and varieties have received totally different names, is applicable to the zeolite nomenclature problem that exists today. 

The differentiation of individual mineral species and mineral nomenclature is a continuing problem. In the zeolite group of minerals, the situation has been improved greatly as the result of recent structural analyses. At present, I believe the zeolite mineral group includes 34 different species. Five of these minerals have been discovered since 1950 garronite was reported in 1962 (79) (Table I). 

The designation of a synthetic zeolite by an arbitrary code is no less subjective than the historical methods for naming minerals. The characteristic properties which are the basis for designating the synthetic zeolite as a separate species first must be determined carefully. It is unlikely that any proposed system for zeolite nomenclature will meet with complete approval by all concerned. However, the following practices are generally applicable. 

Since the nomenclature problem is a matter of communication, a glossary is necessary. This leads naturally to the scheme for systematizing zeolites by structural classification. 

---