Enhanced DBT removal with eco-friendly synthesis of bimetallic UiO-66(Zr/Sn²⁺) catalyst

To address the pressing need for clean fuel oil, the development of highly active oxidative desulfurization (ODS) catalysts is essential. Metal-organic frameworks (MOFs) have been explored as potential ODS catalysts, but many lack the necessary structural defect sites to achieve high activity. Recent efforts have focused on synthesizing MOFs with these defective sites to enhance catalytic performance. This study presents the synthesis of UiO-66(Zr) containing tin sites (UiO-66(Zr/Sn²⁺)) in a solvent-free environment. Analytical techniques, including XRD, BET, SEM-EDX, FT-IR, and TGA, confirm the successful incorporation of tin species into the UiO-66(Zr) framework. The resulting UiO-66(Zr/Sn²⁺) maintains a high BET-specific surface area (951 m²/g) and pore volume (0.75 cm³/g). The presence of additional metal sites (Zr⁴⁺ and Sn²⁺) significantly enhances its catalytic efficiency in ODS by creating defects in the structure of UiO-66(Zr) and enhancing acidity of Zr sites, achieving complete sulfur removal (DBT removal∼ 100 %) with H₂O₂ oxidant in just 20 minutes at 60 °C. Density functional theory (DFT) calculations revealed that Sn²⁺ exhibits lower Lewis acidity compared to Zr⁴⁺. Moreover, DFT analysis of the reaction profile of H₂O₂ homolytic cleavage on Zr⁴⁺ and Sn²⁺ centers confirmed that Sn²⁺ does not exhibit any catalytic activity. However, the calculations highlighted Sn²⁺'s role in generating additional defects, as the optimization of the metal center with Sn²⁺ led to increased linker dissociation. Moreover, the catalyst demonstrates excellent reusability, maintaining its effectiveness across multiple cycles. These findings suggest that the introduction of tin into UiO-66(Zr) is a promising strategy for developing efficient and durable ODS catalysts.