CuIIlocation and adsorbate interaction in CuII-exchangedsynthetic Na-omega gallosilicate EPR and electron spin echo modulation studies
| Autor: | Suk Bong Hong, Jong-Sung Yu, Larry Kevan, Sun Jin Kim, Chul Wee Lee, Jeong Yeon Kim |
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| Rok vydání: | 1997 |
| Předmět: | |
| Zdroj: | Journal of the Chemical Society, Faraday Transactions. 93:4211-4219 |
| ISSN: | 1364-5455 0956-5000 |
| Popis: | The location of CuII and its interaction with adsorbates in CuII-exchanged synthetic Na-omega gallosilicate have been studied by EPR and electron spin echo modulation (ESEM) spectroscopies. These results are compared with those of CuII-exchanged Na-omega aluminosilicate and also those of L and offretite gallosilicates of similar channel type and size, and the differences are discussed. In general, similar results to those for CuNa-omega gallosilicate are obtained for CuNa-omega aluminosilicate. It is concluded that, in fresh hydrated omega material, CuII is in a main channel coordinating to three water molecules and to framework oxygens in the main channel wall. A minor CuII diaquo species not seen in the gallosilicate is observed in the aluminosilicate. Upon evacuation at increasing temperature, CuII moves from the main channel to a gmelinite cage. Dehydration at 410°C produces one CuII species located in a six-ring window of a gmelinite cage, based on a lack of broadening of its EPR lines by oxygen. In L and offretite gallosilicates, there is evidence for back migration of CuII from a hexagonal prism into a main channel to coordinate with adsorbates. However, in omega the back migration from a gmelinite cage to a main channel seems to be blocked, as shown by very slow changes in the EPR spectra and differing coordination numbers for methanol, ethanol and propanol to CuII when alcohols are adsorbed. CuII does not form a complex with propanol or larger adsorbates in omega gallosilicate. It is suggested that, in omega, small adsorbates must diffuse into a gmelinite cage where CuII is located, to form CuII–adsorbate complexes. The slow changes in the EPR spectra correspond to the time for adsorbate diffusion into a gmelinite cage. CuII interacts with one molecule each of ethylene and acetonitrile, based on EPR and ESEM analyses. CuII forms a square-planar complex containing four molecules of ammonia, based on resolved nitrogen superhyperfine coupling. |
| Databáze: | OpenAIRE |
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