Impact of Crystal Size on the Acidity and the Involved Interactions Studied by Conventional and Innovative Techniques

Abstract

A series of β-zeolites with different sizes have been synthesized. Their size range from 10 μm to a few nanometers. The acidity measurement (i.e number, strength and location) were carried out by so-called conventional techniques: adsorption followed by infrared spectroscopy of various basic probe molecules (CO, C 2 H 4 , pyridine) and model reaction (n-hexane cracking). The extreme crystal downsize lowers the acid strength. These results are confirmed also by using an innovative technique: the reversed-flow inverse chromatography (RF-IGC). The involvement of the external and internal zeolitic species depend on the adsorbed molecules and the operating conditions: (i) the high content of extra-framework aluminum enhance the n-hexane cracking activity owing to the exaltation of the Brønsted sites strength, and (ii) the RF-IGC technique show an important involvement of the silanol groups (mainly present on the nanosized zeolite) in lateral interactions with ethylene.