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Publication costs assisted by Union Carbide Corporation Proton magnetic resonance line broadening mechanisms of adsorbed species in zeolites are analyzed using hydrated NH4+-Y~as a model. The dominant mechanism originates from inhomogeneous magnetic fields inside the zeolite cavities due to bulk susceptibility effects, although this is partially narrowed by diffusion over interparticulate dimensions. Two methods for dealing with inhomogeneous broadening are shown to give practical methods for obtaining high resolution spectra of mobile species in zeolite cavities. Chemical exchange reactions among ammonium ions, water molecules, and lattice hydroxyl groups are then differentiated and discussed semiquantitatively. The lattice hydroxyl groups are shown to be strongly acidic, and apparently lead to structure degradation above ~16 per unit cell. Proton exchange between ammonium ions and water is shown to occur via deammoniation of NH4+, whose rate is measurable. In contrast to aqueous solutions, rapid quadrupole relaxation of 14N in ammonium ions occurs inside zeolite cavities. The results in general provide a powerful means of observing structural, kinetic, and dynamic information about simple chemical processes inside zeolite cavities in comparison to aqueous solutions.

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I 0 0.01 0 0 2 0 0 1 0 0 4 0 -Figure 3. Heat of adsorption of CO and N2 on alumina: open points are from low-pressure adsorption data and solid points from high-pressure data.it was confirmed that there was no change in the helium density, surface area, or X-ray structure of the alumina sample taken out of the piezometer after finishing all high-pressure measurements. 3, The full reversibility of the adsorption and the quickness with which adsorption equilibrium is established, as indicated by steady pressure within 1 hr. of changing to a new contact of the piezometer, indicate that only physical adsorption, and no chemisorption or any such slow activated process is involved in this case. The adsorption of CO on alumina at pressures below atmospheric, however, involves much stronger adsorbent-adsorbate interactions. A conventional volumetric adsorption apparatus has been used to measure the adsorption at -78, 0, and 20" for both CO and Nz on the alumina sample. The isosteric heats of adsorption as a function of surface coverage by the two gases from the 0 and 20" low-pressure isotherms and from the 0 and 25" high-pressure isotherms (AG vs. P) are plotted together in Figure 3, which shows the high heat of adsorption for the first amounts of CO adsorbed.Calculation of entropy change on adsorption of CO and Nz on alumina both at low pressures and at high pressures gives an idea of the thermodynamic behavior of the gases in the adsorbed state, in particular the mobility of the adsorbed Until the surface coverage 8 reaches about 0.003, the adsorption of CO seems to involve strong interactions with the surface with the consequence that the adsorbed molecules seem to be quite immobile and fixed to definite sites on the surface. The small dipole moment of CO, its larger quadrupole moment, and greater polarizability, as compared to N2, apparently seem to have a profound influence on the first amounts of CO adsorbed on alumina, making it a case of stronger physical adsorption. But at about 8 = 0.011, the CO adsorption conforms more to the mobile than to the fixed-site type. At high pressure it shows supermobile adsorption, just as for N7 on alumina at the same coverage and temperature. When the total number of molecules on the surface (the amount adsorbed together with the amount present in a surface layer due to the applied high gas density only) reaches about 60-65 of the v,,% value from the B.E.T. equation, restrictions on the mobility of the adsorbed CO molecules become gradually noticeable.A detailed analysis of these results and a tentative explanation for the second ascending and endothermic part of the high-pressure N? adsorption isotherms will be published separately.Acknowledgment. The author is highly indebted to Professor A. Michels for providing all the experimental facilities for carrying out this work and his constant encouragement, and to Professor J. H. de Boer for many stimulating discussions.The direct measurement of the average chemical shift f r o m the centroid of a high-resolution n.m.r. spectrum is ...