| Abstract
| - Monomolecular cracking of propane was used to investigate the activity of the Brønsted acid sites in amorphoussilica−aluminas with three different Si/Al ratios. The reaction rates increased with increasing aluminum content,but the apparent activation energies were identical. In comparison to zeolite ZSM5, the ASA catalysts showedmuch lower activity, both per weight and per total aluminum content. However, after correcting for the heatof adsorption, the intrinsic activation energies of ASA and H-ZSM5 were similar. This indicates that theability of the active Brønsted acid sites to protonate propane is similar in amorphous and crystalline structuresand that the much lower activity of ASA is due to the lower heat of adsorption and the small number ofactive sites. Few Brønsted acid sites were detected by means of pyridine adsorption followed by infraredspectroscopy; a broad band at around 3600 cm-1 was observed in the infrared region of the hydroxyl stretchvibrations. It is unclear whether this band was related to the catalytically active sites.
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