Structures of Commercially Significant Zeolites

Another way to modify zeolite properties is to change the nature of the nonframework cations. Some examples of how cation exchange can affect properties are noted in Section 2.6. For catalytic applications it is often desirable to create active acidic sites. This can be done by exchanging the cations with NHJ and then calcining the zeolite, removing NH3 and leaving behind protons attached to framework oxygen atoms. 

Commercially significant zeolites include the synthetic zeolites type A (LTA), X (FAU), Y (FAU), L (LTL), mordenite (MOR), ZSM-5 (MFI), beta ( BEA/BEC), MCM-22 (MTW), zeolites E (EDI) andW (MER) and the natural zeolites mordenite (MOR), chabazite (CHA), erionite (ERl) and clinoptiloUte (HEU). Details of the structures of some of these are given in this section. Tables in each section lists the type material (the common name for the material for which the three letter code was established), the chemical formula representative of the unit cell contents for the type material, the space group and lattice parameters, the pore structure and known mineral and synthetic forms. 

To provide a common basis for research on three widely used industrial zeolites, NIST has issued reference materials for zeolite Y (RM 8850), zeolite A (RM 8851) and ammonium ZSM-5 zeolite (RM 8852). Reference and information values are provided for major and trace element content, key atomic ratios, enthalpy of formation, unit cell parameters and parhcle size distributions. 

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Structures of Commercially Significant Zeolites 45 Table 2.8 Known members of the ABC-6 family of frameworks. 

The history of commercially significant molecular sieve materials from 1954 to 2001 was reviewed in detail by one of us (E.M.F., ref [1]) Highhghts from that review and the subsequent history are presented here. The reader is referred to Chapter 2 for the structures of the materials and to Chapter 3 and ref [25] for a detailed discussion on zeolite synthesis. 

Deactivation of the copper zeolites under de-NO, conditions was one of the major reasons why the catalyst was never used in a commercial application. Recent environmental legislation intensified the hunt for a water- and sulfur-stable active catalyst One of the most successful preparative methods was reported by HaU and Feng [42, 43]. They reported excellent de-NO, performance based on an iron exchanged ZSM-5 zeolite. The activity was reported to remain constant for extended times, even under high water and sulfur content conditions. The initial catalytic study initiated a whole raft of characterization studies by a number of groups. The interest was significantly increased when it became obvious that there are issues with catalyst preparation reprodudbihty [44, 45]. XAS was crucial in the discussion of the structure of active sites for de-NO, and the site responsible for the high... 

While the structure of beta was being investigated, new uses for this zeolite were being discovered. A major breakthrough came in late 1988 when workers at Chevron invented a liquid phase alkylation process using beta zeolite catalyst. Chevron patented the process in 1990. While Chevron had significant commercial experience with the use of Y (FAU) zeolite in liquid phase aromatic alkylation. Chevron quickly recognized the benefits of beta over Y as well and other... 

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