Bielański Adam

Datka J.

Drelinkiewicz A.

Małecka A.

English

University of Szeged

f i BUTENE-1ISOMERIZATION ON ALUMINUM-DEFICIENT NaHY ZEOLITES By A. BIELANSK.I, J. DATKA, A. DRELINKIEW1CZ and A. MALECKA Department of Chemistry, Jagiellonian University, Cracow, Poland (Received 7 t h February, 1978) A series of NaHY zeolites with Si02 /Al203 molar ratio 5.34, 6.70 and 8.45 was prepared. The properties of zeolitic 3550 and 3650 c m - 1 OH groups and especially their interactions with adsorbed pyridine and butene-1 molecules were investigated using qualitative and quantitative IR spectroscopy. It was also shown that their acid strength increased both with cation exchange degree and with increasing dealumination. 3650 c m - 1 OH groups are active centres in the catalytic isomerisa-tion of butene-1. Their activity (turnover number) changes parallel to their acid strength. The aim of the present paper was to investigate the effect of dealumination of NaHY zeolites on their catalytic properties and to correlate it with the acidity of the zeolite which was studied by the infrared spectroscopy. Experimental The samples of aluminum deficient NaHY zeolites with Si02/Al203 molar ratio 6.70 and 8.45 were obtained from the Institute of Industrial Chemistry, Warsaw. The extraction of aluminum was carried out by treating normal NaY zeolite (Si02/Al203 ratio 5.34) with a boiling solution of EDTA. No distinct loss of crystallin-ity was observed. In the course of the present investigation sodium zeolites were transformed into ammonium form by treating them with NH4N03 solution at 80 °C [1]. The conditions were chosen in such a way that 3 series of NaNH4Y zeolites were obtained showing different Si02/Al203 ratios but very much similar numbers of NH^ ions in a unit cell (Table I). The hydrogen form of zeolites was obtained by vacuum decomposition of NaNH4Y zeolites at 400 °C for several hours. Such a treatment was always applied "in situ" in the infrared cell or in the catalytic reactor. The IR spectra of zeolites and molecules adsorbed on them were recorded with a UR—10 Zeiss Spectrophotometer. The detailed procedure of such measurements is given in previous papers [2, 3]. The catalytic measurements of butene-1 isomerisation were carried out in a pulse microreactor (sample of catalyst 0.02 g, hydrogen carrier gas) and the products 9 0 A. BIELAN'SKI, J. D A T K A , A. D R E L I N K I E W I C Z A N D A. M A L E C K A Table I Chemical composition of zeolites Sample* Number of N H , + ions per unit cell af ter cation exchange N a H Y (5.34) 22.4 12.2 N a H Y (6.70) 25.6 12.1 N a H Y (8.45) 31.0 11.2 N a H Y (5.34) 47.5 26.2 . N a H Y (6.70) 48.8 23.4 N a H Y (8.45) 72.7 26.4 N a H Y (5.34) 72.5 40.4 N a H Y (6.70) 81.5 39.8 N a H Y (5.34) 93.6 51.2 N a H Y (6.70) 96.0 46.1 N a H Y (8.45) 94.5 34.3 analysed gas-chromatographically. Further details of the method are given in [4, 5]. Rate constants k were calculated using first order kinetic equation l n ! = i s L j t . T x-x0 where x and x0 are molar fractions of bu-tene-1 in the products and in the equili-brium state resp. x is contact time. Results and their discussion OH groups in NaHY zeolites * The first figure after N a H Y symbol is S i 0 2 / A l 2 0 3 molar ratio, the second one the cation exchange degree (in%). Only very weak OH band at 3760 cm - 1 was present in the IR spectrum of not decationized NaY zeolites with normal Si02/Al203 ratio. The intensity of this band characteristic of silanol Si—OH groups increased somewhat with the increasing degree of dealumination. Such OH groups do not react with pyridine nor ammonia mole-cules and are inactive in the catalytic isomerisation of butene-1. In the IR spectra of NaOH zeolites two distinct OH bands at about 3550 cm - 1 (LF OH groups) and 3650 cm - 1 (HF OH groups) are present. It was stated that positions of both bands are not influenced by the dealumination of zeolites. Similar results for aluminum deficient zeolites were obtained by JACOBS AND UYTTERHOEVEN [6] who investigated the samples prepared — as in our case — by the dealumination of NaY zeolite. On the other hand BEAUMONT ET AL. [7] who dealuminated NH4NaY zeolite observed the IR bands at 3555, 3630 c m - 1 and a shoulder between 3670 and 3695 c m - 1 . The procedure of dealumination seems therefore to influence the properties of OH groups in zeolites. The HF OH groups react with adsor-bed pyridine molecules forming pyridinium ions. In the case of non-dealuminated NaHY zeolites LF OH groups do not pro-tonate pyridine molecules (some dimini-shing of the corresponding IR band intensity is explained [8,9] as the result of hydrogen bond formation). The LF OH groups in aluminum deficient zeolites may protonate pyridine at 150°C. The extent of this reaction increases with the O— Si0a/Al203=5.34 Si0i/Al203=a70 •--Si02/Al203=a45 20 30 NHj per unit cell Fig.l. The concentration of 3650 c m - 1 OH groups as the function of the number of sodium cations substituted by protons (or N H i ions) in a unit cell. Particular curves represent the results obtained for the series of zeolites diffe-ring by the Si0 2 /Al 20 3 ratio BUTENE-1 ISOMERIZATION .91 Si02/Al203 ratio [1]. These facts may be interpreted as indicating an increased accessibility of LF OH groups for pyridine molecules or increased mobility of protons bonded in these OH groups. The intensity of 1545 cm - 1 band of pyridinium ion increased linearly with the increasing amount of adsorbed pyridine. From the slope of such linear plot the integrated extinction coefficient of this band was calculated (0.82±0.08/|iinole). The amount of pyridine molecules necessary to the neutralization of all HF OH groups was also determined and their concentration calculated [1, 3]. The results obtained for zeolites with Si02/Al203 ratio 5.34, 6.70 and 8.45 are given in Fig. 1. It is seen that irrespectively of the dealumination degree the curves are very much similar in their shape. They increase at first almost linearly with the cation exchange degree and then reach a constant value of about 15—16 HF OH groups per unit cell. An analogous result was obtained for NaHY zeolite with Si02/Al203 ratio equal to 5.22 [3]. It is interesting to notice that this highest concentration of HF OH groups observed by us is very close to the number of hexagonal prisms in the zeolite lattice (16 per unit cell). It means that the highest concentration of HF OH groups corresponds to the situation in which there is an average one such group per one hexagonal prism. Similar value was also obtained by JACOBS ET AL. [10] for a zeolite with 70% of cations exchan-ged. The acid strength of HF OH groups was estima-ted by studying thermodesorption of pyridine. This method was based on the assumption that the mole-cules of pyridine adsorbed on the stronger acid sites are desorbed at higher temperature than those adsorbed on the weaker ones. The B500/B350 ratio was assumed as the measure of the acid strength (B350 is the intensity of 1545 cm - 1 pyridinium ion band after adsorption and evacuation at 350 °C, B500 the same value measured after subsequent desorption at 500 °C. In both cases spectra were registered at 150 °C). B500/B330 ratio expresses the fraction of pyridinium ions remaining after desorption at 500 °C. The results given in Fig. 2a show that at the constant concentration of HF OH groups their acid strength increases with the Si02/Al203 ratio. On the other hand at the con-stant Si02/Al203 ratio the strength of HF OH groups increases with the cation exchange degree [11]. This latter conclusion was also reached by us in a previous study of a series of normal NaHY zeolites. The simultaneous increase in the acid strength of NaOH zeolites with increasing Fig. 2. a. The values of B5oo/B350 ra-tio characterizing the acid strength of H F OH groups b. The activation energy of butene-1 catalytic isomerization c. The turnover number of H F OH groups in the catalytic isomerization of butene-1 at 110°C. All three va-lues are presented as the function of Si02 /Al203 ratio. The lines are joi-ning the points corresponding to the different values of Si02/Al203 ratio but containing nearly the same number of protons introduced into a unit cell. The exact content of protons in unit cell is given by the numbers at each point. 9 2 A. BIELANSKI, J. DATKA, A. DRELINKIEWICZ A N D A. MALECKA deahimination and cation exchange degree was observed earlier by BEAUMONT AND BARTHOMEUF [12—14] who determined acidity using titrimetric methods. Catalytic Properties of Aluminum Deficient NaHY Zeolites In an earlier research [4] it has been shown by us that in the case of Y zeolites with Si02/Al203 ratio equal to 5.22 only the HF OH groups are catalytically active in the isomerisation of butene-1. Non-decationated NaY zeolites as well as dehyd-roxylated ones and containing only Lewis acid sites are non active. In addition IR studies have shown [9] that at the temperatures of the catalytic reaction only HF OH groups interacted with butene molecules which manifested by the decrease of the intensity of 3650 cm - 1 band and simultaneous vanishing of unsaturated character of the olefine. The conclusion concerning the role of HF OH groups reached also by JACOBS ET AL. [10] was verified by us also in the case of dealuminated zeolites which are losing their catalytic activity in the measure as HF OH groups are poisoned by chemisorbed pyridine molecules. The concentration of HF OH groups determined by quantitative IR spectros-copy was used for calculating the turnover numbers for butene-1 isomerisation. Their values together with the values of activation energies determined within the tempera-ture range 90—125 °C are shown in Figs. 2b and c. It is clearly seen that if the samples contain approximately the same number of protons introduced into a unit cell (and also as Fig. 1 shows the same number of HF OH groups) the turnover number increases with increasing value of Si02/Al203 ratio. From the same figure one may conclude that at the constant value of Si02/Al203 ratio the activity is increasing with increasing degree of cation exchange. The increase in the catalytic activity is accom-panied in all the cases by a decrease in the activation energy. The catalytic properties of HF OH groups in NaHY zeolites correlate very well with their acid strength illustrated by the graphs in Fig. 2a. Increased acid strength of HF OH groups seems to be the most plausible explanation of the observed effects of decationization and dealumination. References [ l j bieianski, A., J. M. Berak, J. Datka, A. Drelinkiewicz: Bull. Acad. Polon. Sci., Ser. sci. chim., 23, 455 (1975). [2] Bieianski, A., J. Datka: Bull. Acad. Polon. Sci., Ser. sci. chim., 20, 81 (1972). [3] Bieianski, A., J. Datka: Bull. Acad. Polon. Sci., Ser. sci. chim., 22, 341 (1974). [4] Bieianski, A., A. Malecka: Bull. Acad. Polon. Sci., Ser. sci. chim., in press. [5] Bieianski, A., A. Drelinkiewicz, A. Malecka: Bull. Acad. Polon. Sci., Ser. sci. chim., in press. [6] Jacobs, P., J. B. Uytterlweven: J. Catal., 22, 193 (1971). [7] Beaumont, R., P. Pichat, D. Barthomeuf, Y. Trambouze: Proc. 5th Int. Congr. Catal., Palm Beach 1972, p. 343. [8] Liengme, B. V., W. K. Hall: Trans. Farad. Soc., 62, 3229 (1966). [9] Ward, J.: J. Catal., 28, 101 (1973). [10] Jacobs, P. A., L. J. Declerck, L. J. Vandame, J. B. Uytterhoeven: J. Chem. Soc. Farad. Trans., 71, 1545 (1975). [11] Bieianski, A., J. Datka: J. Catal., 37, 383 (1975). [12] Beaumont, R., D. Barthomeuf: J. Catal., 26, 218 (1972). [13] Beaumont, R., D. Barthomeuf: J. Catal., 27, 45 (1972). [14] Beaumont, R., D. Barthomeuf: J. Catal., 30, 288 (1973). [15] Bieianski, A., J. Datka, A. Drelinkiewicz, A. Malecka: Bull. Acad. Polon. Sci., Ser. sci. chim., 23, 137 (1976). 

Butene-1 isomerization on-aluminium-deficient NaHY zeolites

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Butene-1 isomerization on-aluminium-deficient NaHY zeolites

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