Synthesis of aluminum and gallium-incorporated MFI zeotypes and their catalytic activity for ethane dehydroaromatization

Heteroatoms such as gallium (Ga) atoms can be incorporated into the zeolite framework and can influence on the catalytic properties of zeolite-based catalysts. In particularly, Ga species is active for ethane activation, so the incorporation of Ga atoms into MFI zeolite can achieve high activity for ethane dehydroaromatization. In this work, Ga and Al atoms are incorporated into the framework of MFI zeolite (Ga-Al-MFI) with various Ga/Al ratios for ethane dehydroaromatization. Interestingly, for the incorporation behavior of Ga atom, similar trend with that of Al atom is observed in Ga-Al-MFI zeotypes synthesis. That is, these atoms need tetra-n-propylammonium (TPA⁺) molecules as charge compensators when they isomorphously substitute Si atoms. For ethane dehydroaromatization, catalytic activity and stability of Ga-Al-MFI catalysts are affected by Ga/Al ratio. In the framework of Ga-Al-MFI catalysts, the increase of Ga atom fraction enhances the dehydrogenation ability but weaken the Brønsted acidity of catalysts due to the different electronegativity of Al and Ga atoms. These results imply that there is trade-off for the production of aromatic compounds, so that the optimal Ga/Al ratio for achieving high activity and stability can be suggested in the range of 1–4. Additionally, various active sites in Ga-modified MFI catalysts, including Al sites, Ga species, and dehydrogenation components, were examined via several series of reaction to elucidate their roles in ethane dehydroaromatization.