Abstract
Positron annihilation (PA) data are presented for various zeolites, collected by lifetime spectroscopy (LS) and by recording the full energy distributions of the annihilation radiation. Long-lived PA components were found, corresponding to positronium (Ps) formation in different types of free volume within the zeolite structure. These Ps states are influenced by various factors, such as the synthesis, the presence of adsorbates, impurities, water content, etc. Our studies were aimed therefore to correlate the PA parameters (lifetime, intensity, 2γ/3γ annihilation ratio) with the variety of “free volumes” in zeolites and examine their changes upon ion sorption and filling-up. Silicalite-1 and Na-Y are favourable matrices for high Ps formation. The filling-up of cages was investigated by LS measurements on PdFe-X, PdFe- ZSM-5 and PtFe-Y systems and a correlation of PA data with the cage-filling due to formation of metallic particles was found. Mössbauer measurements have shown that these particles are bimetallic. Water removal in Na-Y and La,Na-Y was also studied by both methods.
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