Ultrastable Y (USY) zeolite remains the most important component in catalysts for converting oil fractions into gasoline. Usually, USY zeolite contains a large amount of extraframework aluminum (EFAL) species responsible for enhancing catalytic activity and improving zeolite stability. Despite numerous studies, EFAL remains, somehow, the chimaera of acid catalysis involving zeolites. Herein, we attempt to understand the influence of EFAL in the activation mechanism(s) of isobutane (chosen as a model alkane) over acidic FAU zeolites, namely HY and NaHY zeolites (exempted from EFAL), HUSY (30% of Al being EFAL) and HUSYLEFAL (EFAL partially removed by complexation with EDTA). The exchange of all Brønsted sites with deuterium enabled following the formation of primary products of isobutane cracking at 200 °C by gas online mass spectrometry. In the absence of EFAL (HY and NaHY), CH 3 D (m/z 17) was the sole product detected. Conversely, HUSY zeolite yielded both HD (m/z 3) and CH 3 D (m/z 17). Our results were interpreted as the tertiary σC−H bond in isobutane selectively underwent a protolytic reaction at low temperature solely in the presence of EFAL acid sites, while the σC−C bond could be activated by Brønsted sites in the absence of EFAL and also by EFAL acid sites. A proposal of the nature of the active EFAL site was made based on quantum chemical calculations and on the catalytic data. These results shed light on the understanding of the mechanism of small alkane activation over acidic zeolites.
The use of oil refineries to convert second generation biomass (BM) into fuels is a powerful approach to reduce the carbon footprint. However, BM undergoes parallel reactions, yielding undesirable products...
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