Selective Aromatization of Light Paraffins on Platinum-Ion-Exchanged Gallium-Silicate Bifunctional Catalysts

Direct conversion of propane to aromatics was investigated on Ga-ion-exchanged H-ZSM-5 (Ga/ H-ZSM-5), Pt-ion-exchanged H-ZSM-5 (Pt/H-ZSM-5), gallium-silicate having the pentasil pore-opening structure (Ga-silicate), and Pt-ion-exchanged Ga-silicate (Pt/Ga-silicate). Among the catalysts, Pt/Ga-silicate exhibited the best performance; the conversion of propane and selectivity to aromatics attained 92.3% and 60.7%, respectively, at 600 °C. Although Ga/H-ZSM-5 with low Ga content was active and selective for the propane aromatization, the increase in Ga content did not improve the performance. As for Ga-silicate, various amounts of Ga were incorporated in the framework of silicate crystal, and it was therefore more active and selective than the Ga/H-ZSM-5. Although Pt/H-ZSM-5 was much more active than Ga-silicate, the former catalyst was not selective for the aromatization. The Pt/Ga-silicate was also effective for the aromatization of such light paraffins as ethane, butane, and pentane. It was also found that Pt in Pt/Ga-silicate plays an important role to reduce the catalyst decay and to regenerate the decayed catalyst with air. Bifunctional roles of Pt and Ga were proposed to understand catalytic behaviors of the Pt/Ga-silicate.