Modification of Brønsted acidity of zeolites by Ga+, GaO+ and AlO+: comparison for alkane activation

Modification of Bronsted acid sites in zeolites by Ga(+), GaO(+) and AlO(+) ions profoundly changes the way of alkane activation. Over Bronsted acid protons propane is activated via a carbonium ion mechanism resulting in propylene, methane and ethylene as hydrocarbon products. Over Ga(+) ions, heterolytic dissociation of propane takes place over the Lewis acid-base pair formed by the Ga(+) ion and the zeolite oxygen anion. Propylene is now the main product. Similarly, propane gives propylene over the acid-base pair of GaO(+), however, via a lower energy barrier. Regeneration of the GaO(+) cation is difficult and instead Ga(+) cations are generated. Finally, our work indicates that non-reducible AlO(+) ions enhance the activity of the Bronsted protons for protolytic cracking.