This study investigates transition metal ion-exchanged Y zeolites as effective adsorbents for the deep desulfur- ization of diesel fuel. Among the prepared materials, NiY exhibited the highest adsorptive activity, followed by CuY, ZrY, and NaY, highlighting the superior performance of nickel-based zeolites. Under optimal conditions, the NiY adsorbent removed approximately 97% of the total sulfur from diesel fuel (initial concentration: 2000 ppm), reducing it to about 48 ppm. More than 94% of the total adsorption capacity was achieved within the first 15 min, confirming the high efficiency and industrial applicability of these materials due to their rapid kinetics. Density Functional Theory (DFT) calculations, which incorporated the effect of an n-hexane solvent via a COSMO model, revealed that adsorption stability is governed by charge transfer between sulfur molecules and the exchanged metal centers. Projected Density of States, HOMO–LUMO, and Fukui function analyses further defined the strengthened interaction between active sites and aromatic sulfur species. Collectively, these findings provide fundamental insights into the structure–activity relationship of metal-exchanged zeolites and underscore their significant potential as highly active adsorbents for ultra-deep desulfurization processes in the petroleum industry

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