Dependence of electron transfer among α cages on the chemical compositions of zeolite LTAs including K clusters

Abstract

K atoms are loaded in diluted amount into K-form LTA zeolites whose framework compositions are Al(x)Si(24-x)O(48) (6<x<or=12) per alpha cage. The optical and electron spin resonance (ESR) properties of K clusters formed in the alpha cages of the LTAs were investigated to elucidate the influence of the LTA compositions on the transfer of a 4s electron of a loaded K atom among the cages. Optical absorption spectra showed notable absorption at approximately 1 eV originating from cationic K clusters in the alpha cages independent of the x value. The linewidths of the ESR spectra showed a minimum value at x approximately 10. A motional narrowing effect induced by the electron transfer among the alpha cages is the origin of the sharp ESR spectra at x approximately 10. The gradual narrowing of the ESR spectral linewidth that occurred from x=12 to 10 can be explained with the assistance of numerical calculations of the periodic potential for an electron introduced into the LTAs. The potential inside the alpha cage becomes monotonously shallower with decreasing x value. On the other hand, the potential of an eight-membered ring shared with the adjacent alpha cages was insensitive to the x value. The calculation results demonstrate that the electron mobility becomes larger at smaller x values. The discrepancy between the actual ESR results and the calculation results for x<10 might be due to the aggregation of K+ ions to stabilize 4s electrons in the alpha cage in actual systems.