Mordenite crystals

Sr mordenite synthesized by Barrer and Marshall (16) gave the Cmcm x-ray pattern and was C-centered orthorhombic by electron diffraction. However, other electron diffraction studies, also by Kerr (12), revealed some synthetic Sr mordenite crystals of the Immm structure prepared at similar synthesis conditions. Future work should examine synthetic Sr and Ca mordenite specimens further for the possible presence of other framework structures, and correlation of structures with Sr2+/Ca2+ ion exchange selectivity. 

Figure 5. Acicular mordenite crystals grown at 200°C and 16 hours using the single-crystal seeds shown in Figure 2. (scanning electron micrographs courtesy of AMR Corp. Burlington, Mass.)...

In Linde A and sodalite syntheses the signal grew to about 20 times its initial intensity. In other systems, such as faujasite, the increase was somewhat smaller. The increase seemed to depend upon the Si/Al ratio of the resultant zeolite crystals—i.e., the smallest increase occurred for mordenite crystallizations having an Si/Al ratio of 5 (for Linde A and sodalite Si/Al = 1). No Fe3+ phosphorescence was observed in the liquid phase of the gel. In three experiments carried out under identical conditions Fe3+ phosphorescence studies of the growth kinetics gave identical results (induction periods equal within 5%, Fe3+ intensity increase on crystallization equal within 10%). 

H. A. Benesi (Shell Development Co., Oakland, Calif. 94608) With regard to the hydrogenation of olefins and aromatics over mordenite catalysts, wouldn t you agree that it is the noble metal rather than the mordenite support that is the active catalyst component In this connection, what is the degree of dispersion of the noble metal What proportion of the metal is on the outside surfaces of the mordenite crystals ... 

This study was performed in the Petroleum Processing Laboratories, Chemical Engineering Department, Louisiana State University. The project was sponsored by Esso Research and Engineering Co. The catalyst used was prepared by the Esso Research Laboratories, Humble Oil and Refining Co., Baton Rouge, La., from mordenite crystals obtained from the Norton Co. Ammonium mordenite was impregnated with 0.5% of palladium, pilled, crushed, sized, and heated to 1000 °F in the presence of air to give Pd on H-mordenite catalyst. The properties of this catalyst are shown in Table I. 

Electron diffraction patterns of heavily and weakly faulted mordenite crystals were obtained with a JEOL 100 CX transmission electron microscope fitted with a top entry two-axis tilting stage and a UHR objective pol piece (C = 0.7 mm). In this situation, electron diffraction patterns cansbe obtained from crystals tilted by about 35° from the horizontal. Experimental details have been discussed elsewhere (2). 

Figure 1. Electron diffraction patterns of several mordenite crystals. (A) Natural mordenite from Hicknoi, New Zealand,...

Figure 2. Electron micrographs of several mordenite crystals. (A) Natural mordenite from Hicknoi, New Zealand, (B) Sample 3, (C) Sample 6, (D) Sample 2. In (A) and (B), the main channels are parallel to the length of the crystals, the c axis. In (C), the channels are normal to the plates, which are shown looking down the c axis. The magnifications vary slightly between the micrographs, but are about that shown by the micron scale in (C).

Thus, the position of the T-0 bending band near or below 440 cm correlates well with the presence of faults in these synthetic and natural mordenite crystals, see Table II. 

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 ). 

In the majority of investigations on zeolite synthesis, particular attention was paid to the effect of temperatures on crystallization. Recent works on mordenite crystallization (20, 32) indicate that temperature... 

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... 

The shape and size of the crystals of mordenite, as well the Si/Al ratio, have implications on industrial applications in hydrocarbon conversion and separation. The ratio between the incorporation yields of silicon and aluminium is inversely proportional to the alkalinity level. Increased solubility of silica at higher pH accounts for the decrease of incorporation of silicon. The source of silica and the ageing of the synthesis gel also influence the final Si/Al ratio. The alkalinity of the synthesis system is also the main factor affecting the morphology of the mordenite crystals, flatter crystals being formed at low alkalinity. 

The cylinder shaped H-mordenite crystals ate characterized by average diar meten and lengths of 4.2 and 4.6 pm respectively, and the cubic crystals of H-Y possess average edge lengths of 1.35 pm. 

Isotiierms for water uptake by pure H-moidenite and H-mordenite-polymer-conqiosites with 20.7 and 9.7 wt.% of x>ly ethyl vin>d ether and pWater uptake in the pol3mm is expected to be small and so the uptake of water within the mordenite crystals is little affected by the polymer. This implies that the amount of pol3mner formed and retained within the mordenite crystals must be small, especially for poly isobutyl vinyl ether. 

The syntheses of mordenite zeolite crystals by microwave heating revealed that there is an accelerate transformation rate of mordenite crystals and also enhanced purity and surface areas of the crystals compared to conventional heating [llLl]. Highly crystalline and pure mordenite crystals were obtained after hydrothermal synthesis of 6 h at 190 °C by microwave heating, whereas prrre mordenite crystals could not be obtained even after hydrothermal treatment of 72 h at the same temperature and conventional heating. 

Fig. 14. Mordenite crystals prepared from mixtures of composition 100 Si02 5.26Al203 22.74 Na20 1545 H2O at 175 °C. Pre-treatment of the silicic acid (silica source) in air for 20 h at a un-treated b 300 °C c 550 °C d 850 °C. Reprinted with permission from Zeolites, vol. 16, Warzywoda J, Dixon AG, Thompson RW, Sacco A, Suib L, The role of the dissolution of silicic acid powders in aluminosilicate synthesis mixtures in the crystallization of large mordenite crystals, (1996),pp. 125-37, Elsevier Science Inc.

Warzywoda et al. [43, 44] recently introduced a method of controlling mordenite crystal size by heat-treating porous silica reagents in air at different... 

---