Mordenite, large port

Structural characteristics. Both natural and synthetic mordenite have an orthorhombic structure that consists of parallel, 12-membered ring channels in the c-direction, having an eliptical cross-section with dimensions of 6,7 x 7.0 A (Figure 9). Smaller 8-membered ring channels with dimensions of 2.9 x 5.7 A, which are perpendicular to the main channels, are too small to allow the movement of molecules from one main channel to another. Mordenite has been synthesized in a "large -port" and "small-port" form that have different sorption properties. A typical unit cell content is Na0[(A10o)o(Si0o)/rJ. 24 HO. 8 28 2 40... 

Raatz, F., Marcilly, C., and Freund, E. (1985) Comparison between small port and large port mordenites. Zeolites, 5 (5), 329-333. 

Van der Velden, G.P.M., and Veeman, W.S. (1988) Smdy of the transformation of small-port into large-port mordenite by magic-angle spinning NMR and infrared spectroscopy. J. Pkys. Chem., 92 (6), 1585-1589. 

Moreno, S and Poncelet, G. (1997) Dealumination of small- and large-port mordenites a comparative smdy. Microporous Mat., 12 (4/5), 191-222. 

Sand, L.B. (1968) Synthesis of large-port and small-port mordenites. Mol. Sieves, Pap. Conf, 1967, 71-77. 

X-ray powder patterns determined in the present studies and from the literature are summarized in Table III. The observed patterns for Zeolon 100 Na and Zeolon 100 H (synthetic sodium and hydrogen large port mordenites) arc in excellent agreement with the calculated patterns for the Cmcm structure. 

The main channels of each of the framework structures described above should be comparable in cross section. However, the size of the main channels in mordenite depends upon the cation form (21). Since cation locations in the various framework structures are expected to differ, the size of the main channels of the structures (in the same cation form) may differ. Thus the various structures may exhibit different degrees of large-port or small-port behavior although in the decationized form all should have equal sized main channels, as observed (21). Future studies may reveal correlations between the sorption properties and the presence of the other framework structures. 

Mordenite minerals vary in the ease with which they may be converted to the large port type by chemical treatment (20). The presence of Cmmm as in the Rome, Ore., mordenite should enhance the ease of the chemical conversion by providing greater access to the internal regions of the crystals. Sand (22, 28) reported that mordenite from Rome, Ore., can be easily converted to the large port variety by chemical treatment. Thus the... 

We should remember that low temperature zeolite synthesis started with Milton s gel synthesis of A and X in the early 1950 s(l). Large pore zeolites were substantially unavailable at that time. Natural faujasite was rare as it still is. Large port mordenite was still ten years in the future as were zeolites L and Omega. Zeolites were regarded as ion exchangers or as selective sorbents, not as catalysts. 

Offretite OFF 6.7 3 Ca-Q Zeolon Large port mordenite Linde-T... 

Mordenite zeolites are widely used as commercial acid catalysts. Two types of mordenites can be synthesized small port or large port. The channel system for the large port mordenite is two dimensional with a large channel with dimensions of 0.67 x 0.70 nm and a perpendicular small pore with dimensions of 0.29 x 0.57 nm separated by 0.28 nm restrictions (162). The channel system for the small-port mordenite is one dimensional for the diffusion of large molecules owing to diffusion blocks produced by crystal stacking faults or the presence of amorphous material or cations in the channels. 

Summing up, there does seem to be a small measure of agreement about cation sites in small and large port mordenites, but until more data become available, there must be doubt about the positions of sites in the much more catalytically interesting large-port mordenite. 

Hydrogen Mordenite. Very interesting results were obtained by Barrer and Klinowski" who prepared hydronium large-port mordenites by acid exchanging sodium mordenite at 25 °C, and by decomposing 1S1H4 mordenite at... 

L.B. Sand, Synthesis of Large-port and Small-port Mordenites. Mol. Sieves, 1968, 71-77. 

M.J. Eapen, K.S.N. Reddy, P.N. Joshi, and V.P. Shiralkar, Synthesis of a Gallosilicate Analogue of High Silica, Large Port Mordenite. J. Inclusion Phenom. Mol. Recognit. Chem., 1992, 14, 119-129. 

Electron diffraction patterns indicate that heavily and weakly faulted mordenite crystals were obtained weakly faulted mordenites patterns resemble those of commercially-available large port mordenites. The absence of odd order spots or streaks in the hOO rows of the ZSM-11 diffraction pattern has been taken as evidence of the presence of ZSM-11 crystals essentially free from ZSM-5 intergrowths. The (Na,K,T0A)ZSM-5 crystal morphology is different from that of typical (Na,TPA)ZSM-5 the relative lengths of straight and tortuous channels are interchanged (J ). 

Properties of Aluminum-Deficient Large-Port Mordenites... 

In the present study, by use of a combination of thermal and acid treatments, a series of large-port mordenites has been prepared down to a material with essentially no residual aluminum but which retains the mordenite crystal structure as determined by x-ray powder diffraction... 

Mordenite is a second 12-ring zeolite whose sorptive properties do not always correspond to expectations based on structure. Two synthetic types of mordenite have been reported by Sand, large-port and small-port mordenite (18). The former, synthesized from only a narrow range of reaction mixture compositions, exhibits the sorptive properties expected of a 12-ring channel (having a diameter of 6-8 A). The latter has an adsorption diameter of only about 4 A. It is indistinguishable from large-port mordenite by x-ray diffraction and may co-exist with dense structures such as analcite. 

Materials. Zeolites A, X, Y, and L were from Union Carbide Corporation, and Zeolite Z was a synthetic large port mordenite from Norton Company. Chabasite was a crystallographically very pure natural zeolite from an Hungarian deposit. Zeolite Y is an aluminum-deficient Y zeolite prepared by H4EDTA treatment. The hexammine complex of was from Strem Chemicals. The ruthenium-on-alumina catalyst was from Ventron. 

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