Aktive Zentren in CaNaX und NiNaX-Zeolithen / Active Sites in CaNaX and NiNaX Zeolites

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Abstract
Temperature programmed desorption of pyridine and benzene was carried out on NaX-13, CaNaX and NiNaX. This was correlated with IR investigation of pyridine adsorption according to WARD3 and with microcatalytic investigations of 2-butanol dehydration and butene isomerisation. Pyridine showed three definite desorption maxima for each of the three zeolites. While the catalytically inactive NaX-13 desorbed pyridine up to 385 °C, the comparable desorption maxima of the active CaNaX and NiNaX were situated at 490 and 470 °C, respectively. IR investigations showed zeolitic cations for these adsorption centres (bands at 1443-1444,1443-1445,1447-1448 cm-1). The lower desorption temperature of the system pyridine/NiNaX, compared with CaNaX, is incompatible with the higher acidity of Ni2+ and the higher IR band level, while the desorption temperature on NaX-13 and CaNaX is conform with the acidity of the ions and the IR band. Benzene on NiNaX behaves in the same way as on NaX-13 (highest desorption temperature 160 °C) while a desorption peak still occurs at 375 °C on CaNaX. The special case of NiNaX is explained by migration of the Ni2+ into the sodalite cave.

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