Studies of the hydrogen held by solids. Part 15.—Cation exchanged zeolites

Abstract

Dehydration of multivalent ion-exchanged zeolites produced structural hydroxyl groups of varying thermal stability as evidenced by differences in the retention of their L-r. bands on heating in uacuo. The retention increased with the electron af6nity of the base-exchange cation. Although the i.-r. bands in the 3650 and 3545 cm-l regions appeared to have the same chemical identity as those formed by heating the NHZ-zeolite, these hydroxyl groups were less reactive with pyridine (Py). Temperatures of 85-150" were required to react a substantial fraction of them to PyH+, whereas with the decationated zeolites, both bands were removed by Py interaction at room temperature although the 3545 cm-' band could be restored to its original intensity by evacuation at 150".Py also co-ordinated with the base-exchange cations (became Lewis bonded). The strength of this interaction (retention of PyL at elevated temperatures) increased with the electron affinity of the cation and the frequency of the corresponding i.-r. band increased concomitantly from 1443 cm-' (Na+) to 1455 cm-l (Zn2+). Addition of H20, or H20+C02, effected conversion of PyL to PyH+, and again the extent of these reactions paralleled the electron affinity of the cation.

Modification of commercial NaY zeolite to give high water diffusivity and adsorb a large amount of water

“…6, a new peak of 3638 cm À1 appeared for Y-Mg. The peak was assigned to Mg(OH) + and acidic Si-OH [15][16][17] showed in Fig. 7, which contributed to the increased amount of water adsorbed.…”

Raman spectra of pyridine adsorbed on a series of ion-exchanged forms of zeolite Y

“…Infrared studies show that the surface concentrations of O H groups is very snlall for the alkali-metal Y-zeolites after heating above 450 "C (5,6,16,17 observed with HY (18). Nonacidic hydroxyl groups are also present and are assigned to MOHf species.…”

“…6) implies the presence of a variety of surface species. The changes of spectra with time may be associated with activated diffusion of pyridine from initial sites to more stable ones (17), e.g. in supercages, or possibly with the movement of Ce3+ ions from inaccessible to accessible sites in the presence of pyridine as has been observed for Cu3 and Ni2+ iolis (25).…”

“…CeY is an intermediate case in that infrared studies show that the same type of OH groups are present as on decationated HY (17) but that adsorption to Ce3+, rather than the formation of pyridinium ions, occurs at room temperature. ~nfrared work also suggests that pyridiniun~ ions are only forliled after heating to 70 "C (17) or after co-adsorption of water at room temperature.…”

“…Infrared studies show that there are two main types of O H groups with frequencies near 3650 and 3545 cm-l, of which the former is more acidic and forms pyridinium ions (17,21,22), while the latter hydrogen-bonds to adsorbed pyridine. The observed Raman spectra from pyridine on H Y (Fig.…”