Tailored Synthesis of ZSM-5 Nanosheets with Controllable <i>b</i>-Axis Thickness and Aspect Ratio: Strategy and Growth Mechanism
Jiaxing Zhang, Limin Ren, Ajuan Zhou, Wenhui Li, Shujie Shang, Yi Liu, Zhenghao Jia, Wei Liu, Anfeng Zhang, Xinwen Guo, Chunshan Song
Abstract
The b-axis-oriented ZSM-5 zeolite is regarded as a highly desired material for catalytic reactions and membrane separation. Here, the tailored synthesis of ultrathin ZSM-5 nanosheets with controllable b-axis thickness and aspect ratio is achieved by adjusting the amount and aging time of silicalite-1 seed suspension in the fluoride medium for crystallization in a short time. On the basis of synthesis and scanning electron microscopy (SEM), transmission electron microscopy (TEM), and 19F MAS NMR analysis, the seed suspension overcomes the difficulty of nucleation in a near-neutral solution, and its [010] crystal facet facilitates the adsorption of fluoride, which promotes the b-axis-oriented growth of nanosheets. This work highlights the important role of seed suspension and fluoride in the growth process. The thinner nanosheets exhibit better catalytic performance (conversion, lifetime, and resistance to deactivation) in the cracking of n-heptane, which can be attributed to their larger surface area and shorter straight channel length. It is anticipated that ZSM-5 nanosheets can be widely used in catalytic reactions that are more sensitive to diffusion limitation.