J. Chem. SOC., Faraday Trans. 1, 1985, 81, 1297-1302 Crystallization Field of Zeolite T at 100 "C for a SiO,/A1,0, Ratio of 28 and Crystallization Sequences in the Na,O-K,O-SO,-Al,O,-H,O System BY ANDRZEJ CICHOCKI Institute of Chemistry, Jagiellonian University, Karasia 3, 30-060 Krakow, Poland Received 16th August, 1983 A crystallization field of zeolite T has been found at n = 28 which differs in area and shape from those with lower values of n. Crystallization has been found to be very sensitive to changes in the ratio of OH to SiO, in the reaction mixture. Crystallization sequences of zeolite phases, depending on the composition of the reaction mixture, have been plotted and the disproportionation phenomenon has been observed. Crystallization fields of zeolite T (the erionite-offretite type) at 100 "C in the system Na,0-K20-Si02-A1203-H20 at n = Si0,/A1203 = 20.2 and 26.5 have been reported previously.' However, zeolite T can be crystallized ' relatively free from zeolites of similar crystalline structure' in the initial n range from ca.20 to ca. 2K2 Several successful attempts to synthesize zeolite T at n = 27.8 and 28.0 have been made.3 The purpose of this work was to define the limits of the zeolite T crystallization field at n = 28 and compare them with the limits at lower values of n ; other synthesis conditions were unchanged. Another purpose was to study the crystallization sequences of zeolite phases obtained from reaction mixtures (r.m.) of different compositions. EXPERIMENTAL Starting materials were, as before,l? 3, silica sol, sodium aluminate, KOH, NaOH and water, which were manufactured in Poland or at this laboratory.Syntheses were by the standard methods described previously;3* 100 g of silica sol was used in all cases. Hydrogels were always aged for 24 h at room temperature before crystallization, which was carried out in identical, sealed glass ampoules (Termisil, the Polish analogue of Pyrex) in an air oven at 100 "C for 168 h. The solid products were filtrated and washed with water to pH 9-10. In all experiments n had the value 28 and the content of water was 92 mol % . Two series of experiments were performed. In the first series (A-1 to A-9) the percentages of K,O and of the hypothetical compound A1,03. 28Si0, were changed while the Na,O content in the anhydrous raction mixture was kept constant.In the second series (A-10 to A-22) the percentages of Na,O and K,O were changed while A1,O3-28Si0, was kept constant. In experiment A-23 the percentages of Na,O and A1,0, - 28Si0, were changed. The samples were examined as before,l i.e. by X-ray powder diffraction, B.E.T. sorption of nitrogen and optical and scanning electron microscopy (s.e.m.). The ratios of the sums of the intensities of the chosen diffraction lines of the sample and of the standard were used to measure the zeolite contents in the sample (wt %). 12971298 CRYSTALLIZATION OF ZEOLITE T Table 1. Changes in chemical composition of the reaction mixture, 'concentration' of components in both series (mol per 1000 mol H20) and changes of the mole ratios OH/Si02 and Na/(Na + K) order of changes : series 1 series 2 experiments : A-1 A-9 A-10 A-22 A-23 wt% in anhydrous r.m.Na,O 20.0 20.0 25.0 10.0 18.0 K2O 14.0 6.00 5.50 20.5 14.0 A1203. 28 SiO, 66.0 74.00 69.5 69.5 68.0 'concentration ' change Na,O 18.1 17.7 22.0 9.30 16.4 K2O 8.40 3.50 3.20 12.5 8.37 2.10 2.30 2.10 2.20 2.14 SiO, 58.3 63.7 59.6 62.8 60.1 OH/SiO, Na/(Na + K) 0.91 0.67 0.85 0.70 0.82 0.68 0.83 0.87 0.43 0.66 outer scale: OH-/Si02 inner scale: Na+/(Na++ K+) 0.65 0.75 0.85 0.95 I I I I 0.87 1.00 "* 16 0 0.57 0.67 0.77 0.87 0.97 OI.89 0.'87 0.?7 0.bl 0.'65 I inner scale: OH-/Si02 outer scale: Na+/(Na++ K+) Fig. 1. Nitrogen sorption capacity (77 K, p / p o = 0.2) in cm3 liquid per 100 g against OH/Si02 and Na/(Na + K) in the r.m. : (a) series 1 and (b) series 2.A.CICHOCKI 1299 RESULTS AND DISCUSSION Table 1 shows changes in the composition of the r.m. of both series. Despite the constant water content in the system, the concentrations of all the components varied (mol per 1000 mol H,O), though to a different degree. A review of literature data regarding various zeolites showed that the result of a synthesis depends on both the absolute values of component concentration (i.e. the r.m. dilution) and the ratios of their concentration^.^-^ In bi-alkaline systems, besides the absolute OH- ion concentration (equal to approximately twice the concentration of Na,O + K,O) and the relative OH/SiO, concentration, an important part is played by the molar ratio Na+/(Na+ + K+). At constant n the OH/SiO, ratio characterizes the relative changes in the concentrations of skeleton-modifying (Na,O and K,O) and skeleton-forming (SiO, and Al,O,) components in the r.m.On the other hand, the Na/(Na + K) ratio characterizes the specific templating action of cations during the formation of structure of a given type. Therefore both ratios were chosen to characterize the composition changes of the r.m. (fig. 1-3). In both series changes in the r.m. composition caused strong changes in the sorption capacities (fig. 1) and phase compositions of the products (fig. 2 and 3). The sorption capacities of the materials for nitrogen correlate well with the phase composition after consideration of the decrease of the sorption capacities of zeolites with increasing occupation of sites by K+ ions (as Eberly has shown for erionite*).Generally, at n = 28 no completely pure zeolite T was obtained, as impurities such as zeolite L and chabazite (Ch) tended to crystallize. This can be linked to the change in n and the different absolute concentrations of Al,O, in the r.m.; at lower values of n a series of practically pure samples of zeolite T were obtained, but for n = 26.5 zeolite L impurities tended to form. Note that, almost independent of n, the highest amounts of zeolite T were obtained in the range OH/SiO, = 0.80-0.82.l Therefore this parameter should be included among the critical parameters for the synthesis of zeolite T. The plots in fig. 2 and 3 can be regarded as the so-called crystallization sequences, i.e. they illustrate the order of crystallization of the individual zeolite phases, depending on kinetic parameters of the synthesis.They are analogous to the plots given by Sandg and Dwyer et for ZSM-5 and ZSM-4 zeolites, with the exception that the time of crystallization was marked on the abscissa at constant temperature and composition of the r.m. Here the role of the kinetic parameter is played by the chosen composition parameters. The curves in fig. 2 and 3 show the existence and characteristic order of crystallization for zeolites T, L and Ch, which are superimposed partially or completely, depending on the composition of the r.m. However, obtaining pure zeolite T or another zeolite phase may only be a question of a careful choice of other factors which affect the kinetics of the crystallization. This can be shown specifically by the lack of zeolite Ph (Phillipsite type) as an impurity in the small-scale tests, carried out in glass ampoules, when the heat transport took place by air and the ampoule glass.On the other hand, zeolite T impurities existed at the same r.m. composition, time and crystallization temperature when the heat transport was more effective, i.e. in steel autoclavesll or glass vessels heated in oil or glycerol baths.12 The crystallization sequences agree with the order of stability of the zeolite phases, as devised ear1ier:ll L < T < Ch < Ph. In series 1 the phenomenon of disproportionation is observed. Instead of zeolite T the more stable zeolite Ch and less stable zeolite L are formed. Series 2, however,1300 CRYSTALLIZATION OF ZEOLITE T 40 c a 20 0 0.57 0.67 0.77 0.87 0.97 I I I I 1 J 0.89 0.83 0.77 0.71 0.65 inner scale: OH-/SiO, outer scale: Na+/(Na'+ K') Fig. 2.Crystallization sequences for series 1 (wt% zeolite) with simultaneous increase of OH/SiO, and decrease of Na/(Na+ K) in the r.m. : 0, zeolite T; x , zeolite L; 0, zeolite Ch. 100. 80 T c 60 .d 0 $ 8 24 40 c a 20 0 0.55 0.65 0.75 0.85 0.95 t 1 L I 1 I 0.06 0.33 0.60 0.87 1.00 inner scale: OH-/SiO, outer scale: Na"/(Na++ K') Fig. 3. Crystallization sequences for series 2 (wt% zeolite) with simultaneous increases of OH/SiO, and Na/(Na+K) in the r.m.: 0, zeolite T; x , zeolite L; 0, zeolite Ch.A. CICHOCKI 1301 Fig. 4. Crystallization fields of zeolite T plotted against n in the r.m. (compositions in wt%): (-)n = 28,(---*-.- ) n = 26.5 and (----) n = 20.2; 0, positive result; a, ‘limit’ result (on the limit of the crystallization field); x , negative result; transition (‘limit’) area is shaded.conforms with the Ostwald rule: as the speed of crystallization increases, more stable phases appear. The effect of glass corrosion on zeolite T synthesis has been discussed elsewhere.12 It was not investigated in this work and is treated only as a constant. This is corroborated by the correlation between crystallization sequences and stability series based on the results of crystallization in steel autoclaves.ll Results of X-ray, sorption and microscopic investigations were used to plot the crystallization-field borders of zeolite T on a triangular diagram of the r.m. compo- sitions (fig. 4).The criteria used to judge the results were as before.’ For comparison, the previously found crystallization-field borders for lower values of n were also plotted (other parameters remaining the same). For n = 28 the field is larger, has an elongated shape and diffusion of the field border into the border area occurs. Similar broadening of the crystallization field was observed by Robson et aZ.13 However, the elongation and its direction point to less sensitivity of the system to changes in Na/(Na+K) than in OH/SiO,. Knowledge of the crystallization fields, crystallization sequences and stability of zeolites, as well as the kinetic factors and their effect on the crystallization of zeolite, are important for the production of pure zeolites and for understanding the processes which take place. ’ A. Cichocki, Zesz. Nauk. Uniw. Jagiellon., Pr. Chem., 1977, 22, 259. D. W. Breck and N. A. Acara, U.S. Patent, 2950952, 1960. A. Cichocki, Zesz. Nauk. Uniw. Jagiellon., Pr. Chem., 1976, 21, 377. A. Cichocki, Zesz. Nauk. Uniw. Jagiellon., Pr. Chem., 1975, 20, 215. S. P. Zhdanov and E. N. Egorova, Chemistry of Zeolites (Nauka, Leningrad, 1968). D. W. Breck, Zeolite Molecular Sieves: Structure, Chemistry and Use (Wiley, New York, 1974). ’ R. M. Barrer, Hydrothermal Chemistry of Zeolites (Academic Press, London, 1982). P. E. Eberly, Am. Mineral., 1964, 49, 30.1302 CRYSTALLIZATION OF ZEOLITE T A. Erdem and L. B. Sand, J. Catal., 1979,60, 241. lo F. G. Dwyer and P. Chu, J. Catal., 1979, 50, 263. A. Cichocki, J. Grochowski and t. Lebioda, Krist. Tech., 1979, 14/1, 9. l2 A. Cichocki, Zeolites, in press. l3 H. E. Robson, G. P. Hamner and W. F. Arey Jr, Adv. Chem. Ser., 1971, 102, 417. (PAPER 3/1452)