The variety of Brønsted acid sites in amorphous aluminosilicates and zeolites

•The nature of the Brønsted acidity of several types of aluminosilicates is evaluated.•Amorphous aluminosilicates (ASA) made by cogelation display zeolitic Brønsted sites.•The surface and acidity of a commercial ASA are similar to those of grafted Si/Al2O3.•In general, the Brønsted acidity of an ASA is related to its preparation technique.•The stretching frequencies of the Brønsted acid sites of grafted ASAs are found.

Brønsted acid sites of similar strength to those in zeolites are found in ASAs prepared by cogelation, as shown by thermogravimetric study of the dehydration of ethanol to ethylene. ASAs prepared by grafting and a commercial ASA (Siralox 30) show Brønsted acid sites that differ from those of zeolites. CO respectively ethanol adsorption followed by infrared spectroscopy identified the OH stretching frequency of the Brønsted acid sites specific to Si/Al2O3 and Al/SiO2 materials obtained by grafting to be ca. 3600 cm−1 and 3640 cm−1, respectively, although the intensity of the corresponding band is weak. These sites, contrary to those of a H-USY zeolite with very few extra-framework aluminum, are highly sensitive to the surface hydration state: Their number decreases with increasing temperature. The surface structure of Siralox 30 resembles that of Si/Al2O3 prepared in anhydrous conditions, showing similar isosurface acidic properties and distribution of silicon species.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (175 K)Download as PowerPoint slide