Szilard–Chalmers cation recoil studies in zeolites X and Y. Part 3.—Recoils from locked to open sites

Abstract

The Szilard–Chalmers recoil of the cations Rb⁺, Cs⁺, Ba²⁺, La³⁺, Co²⁺, Zn²⁺, Cu²⁺ and Na⁺ from the sodalite cage and hexagonal prism sites into the supercage sites of zeolites X and Y has been studied. This study is complementary to that described in Part 2. It has been found that these cations recoil from the sodalite cage sites into the supercage sites with a probability of ∼90 % whereas the corresponding probability for these cations in the hexagonal prism sites (site I) is between 40 and 50 % depending on the cation. It is thus possible to determine the preferences shown by these cations for these “locked-in” sites as a function of temperature of calcination, T_c, concentration and type of other cations contained in these sites. In these studies the cations present in the supercage sites before irradiation were usually NH⁺ ₄ but Ba²⁺, Ca²⁺ and Na⁺ have also been used. When T_c > 400°C, Rb⁺ and Cs⁺ began to populate site I. These ions populated this site in zeolite X at lower calcination temperatures than required for zeolite Y. When T_c was increased from 110 to 220°C the occupancy of site I by Ba²⁺ was greatly enhanced and when T_c > 440°C Ba²⁺ ions now occupied this site in preference to all other “locked-in” sites. Barium exhibited a higher affinity for site I in zeolite X than in zeolite Y when T_c= 110°C. If dehydrated La–Y was assumed to have 5 La³⁺ ions per u.c. in site I, the hydration of this material did not change the concentration of La³⁺ in site I. Co²⁺, Zn²⁺ and Cu²⁺ ions all exhibited similar affinities for the “locked-in” sites of zeolites X and Y. When any of these three ions had to compete with Na⁺ ions for these “locked-in” sites at T_c 500°C, the divalent ions were always found in site I as long as the concentration of these divalent ions was kept below 8 ions per u.c. When, however, there were NH⁺ ₄ or Ca²⁺ ions present in the “locked-in” sites, only about 50 % of the Co²⁺, Zn²⁺ or Cu²⁺ ions were accommodated in site I. When T_c was 110°C the sodalite cage sites were now the preferred sites for these three ions. In the final set of experiments Na⁺, either in trace quantities or at high concentration, was made to compete with numerous other cations for site I. The ability of Na⁺ to be accommodated in site I was shown to be dependent, not only on the character of the other cation competing for this site but, also, on the character of the cation contained in the supercage sites.

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