(378c) Zinc Promoted Pt/ZSM-5 Catalysts for Ethane Dehydroaromatization

The recent growing production of natural gas liquids drives the chemical industry to search for on-purpose techniques converting light alkanes to other building blocks like olefins and aromatics. Ethane dehydroaromatization is one of the promising approaches that has been under exploration for decades, but so far still no report about industrial installment due to the inadequate activity and stability of existing catalysts. Pt species has demonstrated outstanding performance in C-H bond activation. However, the loading of Pt among most reported Pt-based catalysts was higher than 0.05 wt% partially prevents its industrial application on ethane dehydroaromatization because this precious metal is extremely costly. Our previous study shows that the lifetime (stability) of Pt/ZSM-5 catalyst during ethane dehydroaromatization depends highly on the loading of Pt. While the lifetime of the 0.05wt% Pt/ZSM-5 catalyst is about 15 h, the 0.01wt% Pt/ZSM-5 catalyst was completely deactivated within only 4 h. In this work, we found the presence of Zn significantly improved the aromatics selectivity and stability (lifetime) of the 0.01 wt% Pt/HZSM-5 catalyst. The zinc species was introduced through simple ion-exchange before the impregnation of Pt species. Over a typical Zn(1.4wt%)-Pt (0.01wt%)/ZSM-5 catalyst, the production rate of aromatics remains up to 50% of its initial activity, and not deactivation was observed for olefins with time-on-stream up to 15 h. The promotion effect of Zn still exists when the loading of Pt reaches 0.003wt%, whereas the effect disappears when the loading is 0.001wt%. The physical and chemical properties of the metal species have been extensively characterized by combining TEM, STEM-EDS, XAS, CO-FTIR, NH₃-/propylamine-TPD, and ICP-MS techniques. It is suggested that the formation of Zn-Pt alloy structure in the bimetallic Zn-Pt/ZSM-5 catalysts contribute to the improved aromatic selectivity as well as the enhanced stability of the catalysts.