Heteroatomic Zn-MWW Zeolite Developed for Catalytic Dehydrogenation Reactions: A Combined Experimental and DFT Study

摘要

To incorporate divalent transition metals into molecular sieve frameworks remains a great challenge in zeolite chemistry. In this study, Zn was successfully incorporated inside the MWW zeolite framework, namely Zn-MWW (Zn-Si), through hydrothermal synthesis. A combined DFT and X-ray absorption near edge structure (XANES) simulation was applied to unravel the location of Zn inside the structure, indicating that the most plausible Zn position is T5 with two sodium cations close to the neighboring oxygen to neutralize the charge of the zeolite. The as-synthesized material exhibits superior catalytic performance for 1-butene oxidative dehydrogenation with CO2 compared with MCM-22 and ITQ-1 supported ZnO. The 1,3-butadiene (BD) selectivity is doubled at similar 1-butene conversions. On the other hand, more than 51% acetaldehyde is produced during ethanol conversion on the Zn-MWW zeolite, whereas MCM-22 mainly gives ethylene. The remarkable performance is associated with the efficient combination of acidity and redox properties owing to the successful insertion of atomic Zn inside the MWW framework, as demonstrated by XRD, FTIR, Si-29 MAS NMR, XANES analysis, and DFT simulations.