Potassium-ModifiedHierarchical MFI Zeolite Nanosheetsfor Producing Light Olefins and Aromatics by Catalytically CrackingOleic Acid

The incorporation of mesopores into zeolite catalysts improves both reactant diffusion and the catalyst lifespan. In this study, a bolaform surfactant, C₆H₁₃–N⁺(CH₃)₂–C₆H₁₂–N⁺(CH₃)₂–C₆H₁₂–O–C₆H₄–O–C₆H₁₂–N⁺(CH₃)₂–C₆H₁₂–N⁺(CH₃)₂–C₆H₁₃ (BAM_–6–6–6), was used to guide the synthesis of hierarchical MFI zeolite nanosheets (HMNs). The HMN pore structure and acidic sites were altered by varying the ratio of the K₂SO₄-derived K⁺ and Al sources in the initial gel. The X-ray diffraction, Fourier transform infrared spectroscopy, scanning electronic microscopy, and N₂ adsorption/desorption were used to characterize these materials. The HMNs each had an interconnected hierarchical pore structure which consisted of MFI and mesoporous structures and mesopore-specific surface areas as high as 353.8 m² g^–1, indicating that the BAM_–6–6–6 formed lamellar micelles based on π–π stacking. Temperature-programmed NH₃ desorption and ²⁷Al magic angle spinning nuclear magnetic resonance spectroscopy revealed that the intersection cavity of the HMN structure was enriched with acidic sites. Because of the layered HMN structure, which promoted diffusion and increased resistance to carbon deposition and buildup, the catalysts possessed good catalytic activity in cracking oleic acid. For the HMN zeolite, the light-olefin yield reached 50.02% at 500 °C, outweighing that of conventional ZSM-5 (39.80%), and the initial catalytic activity was retained for up to 50 h. Furthermore, for HMN, the hard coke loss (3.8%) was less than that for CZSM-5 (9.7%).