Aluminum-deficient mordenite catalytic properties

These are some of the more important factors that should be considered in order to explain the catalytic activity of aluminum-deficient mordenite zeolites. In general, the same factors will affect the catalytic properties of aluminum-deficient Y zeolites, although fewer data are available with regard to the catalytic properties of these materials. 

The preparation methods of aluminum-deficient zeolites are reviewed. These methods are divided in three categories (a) thermal or hydrothermal dealumination (b) chemical dea-lumination and (c) combination of thermal and chemical dealumination. The preparation of aluminum-deficient Y and mordenite zeolites is discussed. The structure and physico-chemical characteristics of aluminum-deficient zeolites are reviewed. Results obtained with some of the more modern methods of investigation are presented. The structure, stability, sorption properties, infrared spectra, acid strength distribution and catalytic properties of these zeolites are discussed. 

Kerr, Plank, and Rosinski reported the preparation and catalytic properties of aluminum-deficient zeolite Y materials 35). Topchieva and co-workers studied the catalytic properties of cationic forms of aluminum-deficient Y zeolites, the aluminum deficiency being effected by the H4EDTA method 36-40). They found that up to 50% aluminum removal increased both stability and cumene cracking activity maximum activity was observed at the 50% removal level. Increased catalytic cracking activity was observed by Eberly and Kimberlin for mordenites from which about 80% aluminum had been removed (. 1). Weiss et al. removed over 99% of the aluminum from a hydrogen mordenite and found the zeolite retained catalytic activity of the type induced by Bronsted acids 42). Although the initial activity of this material was lower than that of more aluminum-rich mordenites, the aging rate was markedly reduced, and in a relatively short time the aluminum-deficient catalyst was the most active. 

Other workers (4, 5, 6, 7) have made Al-deficient sieves by leaching aluminum from the lattice structure with EDTA or HC1. These zeolites have high thermal stability (4). Extraction of Al removes selectively the aluminic sites that are catalytically inactive. The number of sites of weak or medium acid strength drops to zero (6). Eberly and Kimberlin (7) investigated the catalytic properties of Al-deficient mordenite and found it to be considerably more active than conventional mordenite for cumene cracking. 

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