Abstract
SAPO-44 samples have been prepared with different silicon contents up to 34.3 mass% SiO2. Characterization of the samples by X-ray diffraction (XRD), thermal analysis, adsorption measurements, chemical analysis, microprobe analysis and IR spectroscopy reveals that the samples are highly crystalline, even those with the highest SiO2 content. The number of Bronsted acid sites determined by NH3 sorption [calorimetric and temperature-programmed desorption (TPD) measurements] is independent of the SiO2 content of the samples and amounts to about one acid centre per double-six-ring of the chabazite-like structure.Concerning the silicon ordering within the framework, it is proposed that aluminophosphate-based as well as aluminosilicate-based double-six-rings form the structure.
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