Quantum chemical calculation of the catalytic reaction of ethane dehydrogenation on gallium oxide-hydroxide binuclear clusters in oxidized GaO/ZSM-5 zeolite

The catalytic activity of oxidized GaO/HZSM-5 in the reaction of alkane dehydrogenation can be due to hydrogenated gallium oxide clusters stabilized in the cationic positions of the zeolite. The binuclear gallium oxide clusters Ga₂O₂]²⁺ in oxidized gallium-substituted high-silica zeolite HZSM-5, which are isomeric to two gallyl ions GaO]⁺ stabilized on two spatially separated lattice aluminum ions, were considered using the DFT method within the framework of a cluster approach. It was found that, even in the case of a relatively large distance between these aluminum ions, gallium oxide particles in oxidized GaO/HZSM-5 can occur as charged planar Ga₂O₂]²⁺ four-membered rings. These cluster particles exhibited a high affinity to hydrogen, and they were readily hydrogenated with the retention of their structural integrity. It was demonstrated that this partially hydrogenated cluster could be responsible for the catalytic process of ethane dehydrogenation. In the first step, ethane dissociatively added to the Ga₂O₂H₂]²⁺ cluster. Then, the ethylene molecule was eliminated from the resulting intermediate to leave the Ga₂O₂H₄]²⁺ cluster. The cycle was closed by the elimination of a hydrogen molecule with the formation of the initial structure of Ga₂O₂H₂]²⁺.