J. Phys. Chem. 1992,96,4985-4990
for AGmI(H02)which yields HHQ= 4 X lo3M atm-' at 298 K. To obtain estimates of the Henry's law coefficients at lower temperatures, we used a value for ASmlof -23 f 3 cal K-' mol-'. This results in a change in the value of AGml from that at 298 K of -0.5 and -1.1 kcal mol-' at 275 and 249 K,respectively, assuming AHd does not change with temperature. Thus the values for HOH are 100 and 500 M atm-' and for HHol are 2 X 104 and 2 X lo5M atm-' at 275 and 249 K,respectively. The uncertainty in these estimates for the Henry's law coefficient is substantial: a f0.5 kcal mol-' uncertainty in AGml results in a factor of 2.5 uncertainty in H. Registry No. Hydroxyl radical, 3352-57-6; hydroperoxy radical, 3 170-83-0; sulfuric acid, 7664-93-9.
References and Notes (1) Utter, R. G.; Burkholder, J. B.; Howard, C. J.; Ravishankara, A. R. J. Phys. Chem., preceding paper in this issue. (2) Danckwerts, P. V. Gas-Liquid Reactions; McGraw-Hill: New York, 1970. (3) Schwartz, S.E. J. Geophys. Res. 1984,84, 11589. (4).Baldwin, A. C.; Golden, D. M. J . Geophys. Res. 1980, 85, 2888. Baldwin. A. C.: Golden. D. M. Science. 1979. 206. 562. (5) Gershenbn, Y. M.; Ivanov, A. V i Kucheryavyi, S.I.; Rozenshtein, V. B. Kinet. Karal. 1987, 27, 923. (6) Mozurkewich, M.; McMurry, P. H.; Gupta, A.; Calvert, J. G. J . Geophys. Res. 1987, 92, 4163. (7) Monchick, L.; Mason, E. A. J. Chem. Phys. 1961,35, 1676. (8) Mason, E. A.; Monchick, L. J. Chem. Phys. 1961, 36, 2746. (9) Emmert, R. E.; Pigford, R. L. Chem. Eng. Prog. 1954, 50, 87. (10) Schlichting, H. Boundary Luyer Theory; McGraw-Hill: New York, 1955. (11) DeMore, W. B.; Sanders, S. P.; Molina, M. J.; Golden, D. M.; Hampson, R.F.; Kurylo, M. J.; Howard, C. J.; Ravishankara, A. R. Chemical Kinetics and Photochemical Data for Use in Stratospheric Modeling Evaluation No. 8. NASA JPL Publication 90-1; Jet Propulsion Laboratory: Pasadena, CA, 1990. (12) Vaghjiani, G.L.; Ravishankara, A. R. J. Phys. Chem. 1990,93,7833. ~
4985
(13) Keyser, L. F. J . Phys. Chem. 1984,88, 4750. (14) Handbook of Chemistry and Physics, 60th ed.;Weast, R. C.,Ed.; CRC Press: Boca Raton, FL, 1979. (15) Gable, C. M.; Betz, H. F.; Maron, S.H. J . Am. Chem. SOC.1950, 72, 1445. (16) Perry, J. H. Chemical Engineer's Handbook; McGraw-Hill: New York, 1950. (17) Stirba, C.; Hurt, D. M. AIChE. J. 1955, 1, 178. (18) Lynn, S.;Straatemeier, J. R.; Kramers, H. Chem. Eng. Sci. 1955, 4, 49. (19) Brown, R. L. J . Res. Narl. Bur. Stand. (US.)1978, 83, 1. (20) Motz, H.; Wise, H. J . Chem. Phys. 1960, 32, 1893. (21) Murphy, D. M.; Fahey, D. W. Anal. Chem. 1987.59, 2753. (22) Schell, M.;Kapal, R. J . Chem. Phys. 1981, 75, 915. (23) Howard, C. J. J. Phys. Chem. 1979, 83, 3. (24) Schwartz, S . E. In Chemistry of Multiphase Atmospheric Systems; Jaeschke, W., Ed.; NATO AS1 Series; Springer-Verlag: Berlin, 1986; Vol. G6, p 415. (25) Danckwerts, P. V. Trans. Faraday SOC.1951, 47, 1014. (26) Worsnop, D. R.; Zahniser, M. S.;Kolb, C. E.; Gardner, J. A.; Watson, L. R.; Van Doren, J. M.; Jayne, J. T.; Davidovits, P. J. Phys. Chem. 1989, 93, 1159. (27) Golden, D. M.; Bierbaum, V. M.; Howard, C. J. J. Phys. Chem. 1990, 94, 5413. (28) Buxton, G.V.; Greenstock, C. V.; Helman, W. P.; Ross,A. B. J. Phys. Chem. Ref. Data 1988,17, 513. (29) Farhatziz; Ross, A. B. Selected specific rate of reactions of transients from water in aqueous solutions. III. Hydroxyl radical and perhydroxyl radical and their radical ions. NBS National Standards Reference Data Series NSRDS-NBS 59; National Bureau of Standards: Washington DC, 1977. (30) Fairbanks, D. F.; Wilke, C. R. Ind. Eng. Chem. 1950,42,471. (31) Marrero, T. R.; Mason, E. A. J . Phys. Chem. Ref. Data 1972, 1, 3. (32) The dipole moments for H202 and H 2 0 from: Townes, C. H.; Schawlow, A. L. Microwave Spectroscopy; Dover: New York, 1975; p 639. H 0 2 from: Saito, S.;Matsumura, C. J . Mol. Spectrosc. 1980,80, 34. OH from: Peterson, K. I.; Fraser, G.T.; Klemperer, W. Can. J . Phys. 1984, 62, 1502. (33) Danon, F.; Amdur, I. J . Chem. Phys. 1%9,50,4718. (34) Weissman, S. Proceedings of rhe Fourth Symposium on Thermophysical Properties; Moszynski, J. R., Ed.; ASME: New York, 1969; p 360.
Silicaiite Characterization. 1. Structure, Adsorptive Capacity, and I R Spectroscopy of the Framework and Hydroxyl Modes A. Zecchina,* S. Bordiga, G. Spoto, L. Marchese, Dipartimento di Chimica Inorganica, Chimica Fisica e Chimica dei Materiali, Universitii degli Studi di Torino, via P. Giuria 7, IO125 Turin, Italy
G. Petrini, G. Leofanti, and M. Padovan ENICHEM ANIC Centro Ricerche di Bollate, via S. Pietro 50. 20021 Bollate, Italy (Received: August 26, 1991; In Final Form: January 22, 1992)
T h e physical properties (microcrystal morphology, crystallinity, internal perfection, adsorptive capacities toward CO and N2, and IR manifestations of the skeletal modes and of the hydroxyl groups) of a Na- and AI-free silicalite (S) prepared following a specifically designed method are investigated. Comparison is made with the silicalite containing Na and Al impurities prepared following a more conventional (classical) path (SNa). T h e experimental techniques are X-ray diffraction (XRD), high-resolution electron microscopy (HRTEM), infrared spectroscopy in reflectance mode (FTIR), and volumetric isotherms in a BET apparatus. The most relevant results are as follows: (i) S microcrystals have very regular octagonal prismatic habit, (ii) nanodefects and microcavita are more aboundant in S than in SNa, (iii) hydroxyl groups are present at the internal defects sites, and (iv) N2 and CO volumetric isotherms at 77 K differ from S and SNa.
htroduction Silicalite, a zeolite having a MFI structure,' is often considered a purely siliceous zeolite without Al heteroatoms in the framework. However, this picture is not completely true: in fact, to our best knowledge, silicalite synthesized according to the U.S.Patent of Grose and Flanigen2contains, as impurities, variable concentrations of A1 and Na. With the exception of refs 2 and 3, all the researchers reporting about silicalite do not give full details about t h e AI and Na impurity concentrations, probably because they are considered as not influencing the properties of the zeolites.
To our experience, A1 and Na impurities cannot be completely removed by treatments of the solid at the end of the synthesis, either before or after the calcination. We think that the presence of these impurities can affect in different manners the physical properties of the samplen4 We have therefore synthesized a high-purity sample, by changing the synthesis procedure (vide infra), and the physical properties of this high-purity silicalitewere then compared with those of the analogous SNa samples used as standard reference. Another important reason for studying the Na-free silicalite (S) is that only the full understanding of its
0022-3654/92/2096-4985$03.00/00 1992 A m e r i c a n C h e m i c a l Society
4986 The Journal of Physical Chemistry. Vol. 96. No. 12, 1992
Zecchina et al.
TABLE I
Na AI
SNa "as made", '% 0.80 0.08
SNa (after leaching), '% 0.02 0.09
S,
10.1Ilcfcps
Ng/g
