Stability Improvement of FAU Zeolites Ion-Exchanged with Copper–Ammonia Solution for the Removal of Thiophene and Benzothiophene from Model Fuel

Faujasite (FAU) zeolites with low Si/Al ratios (e.g., X-type zeolites) have much more exchangeable cation sites than those with high Si/Al ratios (Y-type zeolites) for Cu(I), which could improve the adsorption performance via π-complexation. However, the structure of Cu-exchanged X-type zeolites was unstable during autoreduction at high temperatures as reported [Takahashi; et. al., Ind. Eng. Chem. Res., 2002, 41, 2487−2496]. Here, we proposed a scheme of Cu-exchanged X-type zeolites in copper–ammonia solution to improve the stability of the zeolite structure during autoreduction. Therefore, it makes us be able to study the adsorption properties of thiophenic compounds in Cu(I)-exchanged FAU zeolites from low to high Si/Al ratios. The modified zeolites were characterized by X-ray diffraction, high-resolution transmission electron microscopy, inductively coupled plasma spectroscopy, X-ray fluorescence, and Brunauer–Emmett–Teller analysis and tested by adsorption desulfurization experiments in model fuels. The results indicate that the modified zeolites with various Si/Al ratios show different adsorption properties for thiophene and benzothiophene. The adsorption capacity for thiophene decreased in the order Cu(I)Y-5.30 > Cu(I)X-1.23 > Cu(I)Y-2.30. For benzothiophene, the adsorption capacity decreased in the order Cu(I)Y-2.30 > Cu(I)Y-5.30 > Cu(I)X-1.23.