Engineering Pt-loaded shape-selective ZSM-5 via atomic layer deposition for stable Para-xylene Production

Alkylation of toluene with methanol using ZSM-5 zeolite represents a key shape-selective route to para-xylene, an essential monomer for polyester production. However, rapid catalyst deactivation due to coke deposition remains a major challenge. In this work, we demonstrate that atomic layer deposition (ALD) offers a superior strategy for constructing Pt-loaded, SiO₂-P₂O₅-modified ZSM-5 (Pt/SPZ) catalysts with enhanced stability and selectivity. By systematically comparing ALD with conventional impregnation (IM) method, it is revealed that ALD method facilitates precise, external-surface-enriched Pt deposition with high dispersion and minimal acid site loss, whereas IM method leads to broader Pt distribution, pore blockage, and significant acid site loss. Additionally, coke formation patterns differed: ALD catalysts accumulated coke mainly inside zeolite channels, whereas IM catalysts showed more coke at pore mouths and external surfaces, influencing catalyst deactivation. Consequently, ALD-derived catalysts exhibit higher toluene conversion, superior para-xylene selectivity (> 95%), and markedly prolonged stability. This study highlights the importance of Pt loading amount and Pt spatial distribution in balancing acid catalysis and hydrogenation, providing guidance for designing efficient, stable metal/zeolite bifunctional catalysts for shape-selective alkylation.