(683a) [Pt1-Znn]?+ Hybrid Cluster in HZSM-5 for Efficient Ethane Dehydroaromatization

The recent growing production of natural gas liquids drives the chemical industry to search for on-purpose techniques for converting light alkanes to other petrochemical building blocks like olefins and aromatics. Ethane dehydroaromatization (DHA) 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. Among various catalysts, the Pt/HZSM-5 has demonstrated outstanding activity in ethane DHA. However, according to our recent studies (see Fig. 1), the lifespan (stability) of Pt/ZSM-5 catalyst during ethane DHA depends highly on the loading of Pt. While the lifespan 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, which was further decreased to 1 h when decreasing the Pt loading to 0.005 wt%.

Here, we show that ultralow-loading (0.001-0.05 wt%) Pt and Zn functionalized HZSM-5 catalyst, prepared through simple ion-exchange and impregnation, is highly active and stable for ethane DHA. The specific activity of BTX is up to 8.2 mol/g_Pt/min (or 1592 min^-1) over the 0.001 wt% Pt-Zn₂/HZSM-5 catalyst during ethane DHA at 550ºC under atmospheric pressure. Additionally, such bimetallic Pt_x-Zn_y/HZSM-5 catalysts are highly stable in contrast to the monometallic Pt/HZSM-5 catalysts. The rate constant of deactivation (k_deactiv), according to the first-order generalized power-law equation model, for the bimetallic catalysts are up to 120 times lower than the monometallic counterparts depending on the Pt loading (see Fig. 1). Extensive structural and acidity characterization suggested that this breakthrough is achieved owing to the formation of [Pt₁-Zn_n]^δ+ hybrid cluster, instead of Pt⁰ clusters-proton adducts, in the micropores of ZSM-5 zeolite. We anticipate that the concept of fabricating bimetallic clusters (with isolated noble metals) in the zeolites can be extended to other catalytic systems.