Acidity of aluminophosphate structures. Part 1.—Incorporation of sillicon into chabazite-like structure 44

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 Brønsted 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.