110
K, TSUTSUMI AND H. TAXAHASHI
A Study of the Nature of Active Sites on Zeolites by the Measurement of Heat of Immersion. 11. Effects of Silica/Alumina Ratio to Electrostatic-Field Strength of Calcium-Exchanged Zeolites
by Kazuo Tsutsumi* and Hiroshi Takahashi Institute of Industrial Science, The University of Tokyo, Roppongi, Minato-ku, Tokyo, J a p a n
(Received M a y 21, 1970)
Publication costs borne completely by T h e Journal of Physical Chemistry
The electrostatic-field strengths of Na- and Ca-exchanged zeolites were determined by measurements of the heats of immersion into various organic liquids. The correlation between the silica/alumina ratio and the electrostatic-field strength of zeolites was studied. The electrostatic-field strength of Na-form zeolites is not much affected by the silica/alumina ratio. I n the case of Ca-exchanged zeolites, however, the more the silica/alumina ratio increases, the stronger the electrostatic field becomes. It was noted that the cumene cracking activity of Ca-form zeolites follows in magnitude the change in the electrostatic-field strength. The electrostatic-field strength of decationated zeolite was also investigated.
Introduction
was discussed by Rabo, et a1.,2118819 and by Boudart, et al. *O The electrostatic-field strength was calculated Crystalline zeolites show a very characteristic adsorpon the model of the ionic crystal. tion behavior with a molecular sieve character. Our fundamental knowledge of the structure, properties, (1) For example, R. -M.Barrer, Proc. Roy. Sac., Ser. A , 167, 392 and synthesis of several zeolites is due largely to Barrer, (1938); R. M . Barrer, J. Sac. Chem. Ind., 44, 130 (1945); R . M. et al.' Ever since Barrer first reported the results of Barrer and L. Belchetz, ibid., 44, 131 (1945); R. M. Barrer, Trans. Faraday Soc., 45, 358 (1949); R. M. Barrer and A. B. Robins, ibid., the measurement of the peculiar adsorptive character of 49, 807, 929 (1953); R. M. Barrer and B. E. F. Fender, J. P h y s . zeolites, various practical methods of utilization have Chem. Solids, 21, 1, 12 (1961); R. &I. Barrer, Endeavour, 23, No. 90, 122 (1964). been developed; certain species have, for example, been (2) J. A . Rabo, P. E. Pickert, D. N. Stamires, and J. E. Boyle, used for the drying, separation, and purification of Actes 2nd Congr. I n t . Catalyse, Paris, Sec. 11, N o . 104 (1960). solvents. Besides, their ion-exchange property is also (3) P. B. Weisa and V . J. Frilette, J. P h y s . Chem., 64, 382 (1960). widely helpful in water softening. (4) A. E. Hirschler, J. Catal., 2, 428 (1963). I n 1960, Rabo, et U Z . , ~ and Weisz and Frilettea found ( 5 ) M. Ikemoto, K. Tsutsumi, and H. Takahashi, Seisan K e n k y u , 21, 453 (1969). a high catalytic activity of X and Y zeolites for the (6) H. Otouma, Y. Arai, and H. Ukihashi, Bull. Chem. Sac. J a p . , cracking of paraffins, olefins, and alkyl aromatics and 42, 2449 (1969). for isomerization, etc. Thereafter, the application of (7) D. N. Stamires and J. Turkevich, J. A m e r . Chem. Soc., 86, 749 (1964). zeolites as catalysts was rapidly developed, and the (8) J. T. Richardson, J. Catal., 9, 172 (1967). zeolite catalyst became the subject of intensive inves(9) F. R. Dollish and W.K. Hall, J.P h y s . Chem., 71, 1005 (1967). tigation. Though the catalytic character has been (10) W. K. Hall and F. R. Dollish, J. Colloid Interface Sci., 26, 261 discussed in connection with various kinds of zeolites, in (1968). order for zeolite to be of practical use, its pore size must (11) J . B. Uytterhoeven, L. G. Christner, and W. K. Hall, J. P h y s . Chem., 69, 2117 (1965). be large enough to adsorb reactants. Therefore, interest (12) T. R. Hughes and H. M. White, ibid., 71, 2192 (1967). is focused on faujasite-type synthetic zeolites, X and Y, (13) J. W. Ward, J. Catal., 9, 225, 396 (1967); 10, 34 (1968); 11, and mordenite. 238. 251 (1968); 13, 321 (1969). It is considered that the activity of zeolite catalysts (14) P. E. Eberly, Jr., J . P h y s . Chem., 72, 1042 (1968). stems from one of the following three factors: (1) (15) F. R. Cannings, ibid.,72, 4691 (1968). the molecular sieve character, ( 2 ) solid acid, as ob(16) J. A. Rabo, C. L. Angell, and V. Schomaker, Proc. 4th I n t . Congr. Catalysis, Moscow, No. 54 (1968). served in the case of the silica-alumina catalyst, and (17) J. B. Uytterhoeven and R. Schoonheydt, J. Catal., 13, 425 ( 3 ) the electrostatic-field strength on the surface, which (1969). may promote carboniogenic reaction. The solid acids (18) P. E. Pickert, J. A . Rabo, E. Dempsey, and V. Schomaker, Proc. Srd I n t . Congr. Catalysis, Amsterdam, 714 (1964). mentioned in 2 including both Brgnsted and Lewis acid (19) J. A. Rabo, C. L. Angell, P. H. Kasai, and V. Schomaker, sites have been investigated by amine t i t r a t i ~ n , ~ - ~Discuss. Faraday Soc., 41, 328 (1966). electron spin resonance spectro~copy,~-'~ infrared (20) Y.-Y. Huang, J. E. Benson, and M.Boudart, I n d . Eng. Chem., spe~troscopy,11-~7 etc. The effect of electrostatic field Fundam., 8, 346 (1969). T h e Journal of Physical Chemistry, Vol. 76, N o . 2 , 1972
A STUDY OF
THE
NATUREOF ACTIVESITESON ZEOLITES
In a previous paper,21we measured the heat of the immersion of cation-exchanged zeolites using an organic adsorbate and establishcd quantitativrly that, when Na of Na-Y zeolite is replaced with Ca, the electrostatic-field strength increases. When the Ca exchange is low, Ca ions mainly occupy the SI sitr, which i,s linked to the large cavity through pores about 2 A in diametrr. ,4s the pore is not large enough for the organic liquid to pass through, the cation exchange does not influenctl t h r heat of immersion. With increasing cxchangc, thc Ca ions saturate the SI site and then occupy sites in the large cavity. K i t h Ca ions at the later sites, the electrostatic-field strength, as calculated from the heat of immcrsion, increases remarkably. This paper will report a study on the effect of changing silica/alumina ratio on the electrostatic-field strength, using five differcnt faujasite-type zeolites. The correlation of the silica/alumina ratio with the catalytic activity for cumrne cracking will also be discussed.
Experimental Section The zeolites used for the experiment were Ka-X, . 6 , Na-Y5.0, Ya-Y3.26,Ka--Y3.85, and Na-1-4.6; the first two are Linde molecular sieve 13X and SI
