Characterization, oxidative desulfurization performance evaluation and the catalytic reaction mechanism of polyoxometalate-coated, semi-encapsulated heart-shaped metal organic frameworks

Abstract

The oxidative desulfurisation (ODS) process is a subject of considerable interest at present due to the mild reaction conditions, good selectivity, and significant removal efficiency for aromatic sulphides and the promise of ultra-deep desulfurisation. A large number of possible combinations between polyoxometalate (POM) and Metal Organic Frameworks (MOFs) can be realised to tailor the physicochemical properties of novel POMOF (POM@MOF) composites. In this study, a novel semi-encapsulation strategy was proposed to achieve the outer wrapping of a heart-shaped MOF (H-MOF) with a POM chocolate-style outer coating. This was achieved by regulating the stirring time, stirring temperature and sonication time of the POM and H-MOF. To the best of our knowledge, this study represents the first investigation into the semi-encapsulation of a MOF with a POM outer coating. This study demonstrates the successful preparation of H-POMOF (POM@H-MOF) composites comprising a POM chocolate-coated semi-encapsulated heart-shaped MOF (H-MOF). Furthermore, the intrinsic reaction mechanism of oxidative desulfurisation is characterised and elucidated, providing insight into the underlying chemical processes. Density functional theory calculations demonstrate that the catalyst reacts with the oxidant in the transition state, resulting in a change in the potential energy barrier and the generation of the reactive peroxo intermediate, H-POMOF-OH. The oxidation of DBT to DBTO₂ is reconstructed into nine basic steps, which clearly demonstrate the intrinsic reaction mechanism of ODS. The present work demonstrates that the newly prepared H-POMOF semi-encapsulated composites have a broad range of potential applications in the field of oxidative desulfurisation. Furthermore, it establishes a robust theoretical foundation for subsequent ODS research and industrial applications.