Aluminum distribution and active site locations in the structures of zeolite ZSM-5 catalysts.

Rzepka, Przemyslaw; Huthwelker, Thomas; Dedecek, Jiri; Tabor, Edyta; Bernauer, Milan; Sklenak, Stepan; Mlekodaj, Kinga; van Bokhoven, Jeroen A · Science · 2025

basic_science · Level V

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Abstract

Zeolites have exceptional catalytic performance in oil refining and chemical synthesis that can be attributed to their well-defined porous structures that host active sites. This study pinpoints the exact locations of aluminum atoms in ZSM-5 structures-a key zeolite catalyst. Aluminum siting governs catalytic efficiency in acid and redox processes. Anomalous x-ray powder diffraction (AXRPD) at the aluminum K-edge probes the long-range order of aluminum atoms within the ZSM-5 frameworks, precisely quantifying both isolated aluminum atoms and Al(-O-Si-O-)<sub><i>x</i></sub>Al sequences (aluminum pairs). Supported by nuclear magnetic resonance studies, AXRPD unambiguously determines the crystallographic organization of aluminum pairs, recognized spectroscopically as α, β, and γ sites, linking their distribution to superior catalytic activity in propene oligomerization. This combined approach provides essential insights for optimizing zeolite catalysts and enhancing their performance.