Synergistic effect of Zn species and ZSM-5 in bifunctional Zn-ZSM-5 for efficient conversion of n-butane

Given the goals of reducing carbon emissions and overcoming the challenge of energy shortages, the efficient conversion of industrially abundant and cheap n-butane to high value-added light olefins and aromatics is of particular significance. In this study, Zn-ZSM-5 catalysts with highly dispersed Zn species were successfully prepared via a dual-bed method using commercial ZnSiO$_3$ and ZSM-5. At 500°C, the optimized catalyst with a Zn content of 0.41 wt% exhibits an outstanding n-butane conversion rate (0.39 mmol·g$^{−1}$·min$^{−1}$) which is approximately 4 and 30 times as high as that over a conventionally prepared Zn/ZSM-5 catalyst and pristine ZSM-5, respectively. The achieved performance is also remarkable in comparison with representative Pt-, or Ga-containing catalysts. In-situ DRIFTS analysis revealed that the high dispersion of Zn-containing species was achieved through the strong interplay between the Zn atoms formed during the preparation of Zn-ZSM-5 catalysts at 600°C in H$_2$ and acidic hydroxyl groups in ZSM-5. Furthermore, the relationships between Zn species and butenes formation rates were identified, corroborating that the isolated [Zn(OH)]$^+$ and binuclear ZnO$_x$ species synergistically interact resulting in high activity in n-butane dehydrogenation, and the former species contributes more. ... mehrAccording to the selectivity-conversion relationship and kinetic analysis, the unique structure of Zn species in ZSM-5 matrix affects catalytic performance towards n-butane dehydrogenation, thus promoting the cleavage of C–H bonds, which is instrumental in the efficient utilization of n-butane. The obtained fundamentals provide hints for designing highly efficient Zn-containing catalysts for heterogeneous reactions beyond n-butane conversion.