Anisotropic ZSM-5 nanorod assemblies: facile synthesis, epitaxial growth, and strikingly enhanced stability in benzene alkylation

The synthesis of superior-quality zeolite nanoassemblies remains a critical objective, driven by their potential to significantly enhance mass transfer and improve accessibility to active sites, ultimately leading to enhanced catalytic performance. In this study, we report the facile synthesis of a unique class of ZSM-5 nanorod assemblies, referred to as NA-ZSM-5, through a straightforward approach that combines a Silicalite-1 (Sil-1) seed-induced strategy with the assistance of cetyltrimethylammonium bromide (CTAB). Notably, each bundle-shaped zeolite crystal exhibits an abundance of inter-nano-crystal mesopores, comprising numerous loosely stacked nanorods, thereby displaying distinctive anisotropic characteristics. Moreover, the size of the nanorods can be easily adjusted by changing the amount of CTAB added. The morphological progression of the ZSM-5 nanorod assemblies was comprehensively investigated using a range of analytical techniques. Our analysis reveals that the incorporation of Sil-1 seeds into the synthesis process plays a pivotal role in establishing the primary framework structure, facilitating the attachment of precursor particles and promoting the creation of nucleation sites crucial for nanorod growth. In contrast, CTAB primarily acts as a modulating agent, influencing the c-axis-oriented growth of the nanorods. The resulting NA-ZSM-5 zeolite demonstrates a substantial surface area, contains specific mesoporous structures, and exhibits moderate acidity, all of which contribute to its outstanding catalytic performance in the alkylation of benzene with ethanol. Remarkably, this catalyst displays remarkable reaction stability, withstanding continuous operation for over 500 hours, even under conditions characterized by a low benzene/ethanol ratio of 2.