One-pot ethanol-mediated synthesis of surface Si-zoned ZSM-5 zeolites

Abstract

Passivation of external surface acid sites in zeolites is a widely used strategy to enhance catalytic stability and to mitigate undesired non-shape-selective reactions. However, the synthesis of zeolites with a uniform and thickness-controllable Si-zoned shell in a true one-pot process remains a significant challenge. Here, we develop an ethanol-mediated one-pot route to synthesize surface Si-zoned ZSM-5 zeolites. Ethanol creates a favorable synthesis environment that promotes a classical, layer-by-layer crystallization pathway, enabling the near-quantitative utilization of aluminosilicate species during the initial crystallization stage. This complete consumption of framework-forming species allows soluble silicate species to be subsequently added directly into the mother liquor, where they are selectively incorporated onto the preformed ZSM-5 crystals to build a thickness-tunable silica-rich shell. Notably, bulk and surface analyses together with probe reactions using bulky molecules confirm that the silica-rich shell is structurally continuous and effectively inert toward bulky reactants. This ethanol-mediated strategy offers a facile, high-yield, and scalable one-pot platform for engineering surface compositions in zeolites. The resulting surface Si-zoned ZSM-5 offers a versatile basis for the design of catalysts with improved stability and shape-selectivity.