Potassium-Modified Hierarchical MFI Zeolite Nanosheets for Producing Light Olefins and Aromatics by Catalytically Cracking Oleic Acid

The incorporation of mesopores into zeolite catalysts improves both reactant diffusion and the catalyst lifespan. In this study, a bolaform surfactant, C 6 H 13 –N + (CH 3 ) 2 –C 6 H 12 –N + (CH 3 ) 2 –C 6 H 12 –O–C 6 H 4 –O–C 6 H 12 –N + (CH 3 ) 2 –C 6 H 12 –N + (CH 3 ) 2 –C 6 H 13 (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 K 2 SO 4 -derived K + and Al sources in the initial gel. The X-ray diffraction, Fourier transform infrared spectroscopy, scanning electronic microscopy, and N 2 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 m 2 g –1, indicating that the BAM –6–6–6 formed lamellar micelles based on π–π stacking. Temperature-programmed NH 3 desorption and 27 Al 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%).