Hydrophobic surface modification of Zr-based metal–organic frameworks with silane for oxidative desulfurization

Abstract

Oxidative desulfurization (ODS) is an effective technology to eliminate sulfur compounds from fuels. Zr-based MOFs are frequently employed as ODS catalyst support. In this paper, a Zr-based MOF (NNU-28) catalyst was synthesized by a hydrothermal method, and three hydrophobic catalysts (OTES-NNU-28, DTS-NNU-28, HDTMS-NNU-28) were synthesized by surface modification with organosilanes of different alkane chains. Then the hydrophobic OTES-NNU-28, DTS-NNU-28, and HDTMS-NNU-28 were used as ODS catalysts directly without the loading of active components. The catalysts before and after hydrophobic modification were characterized by FT-IR, XPS, XRD, FE-SEM, TEM, Contact angle test, UV–Vis DRS, Mott-Schottky and N₂ adsorption–desorption. Under appropriate reaction circumstances, OTES-NNU-28 can completely remove DBT in 50 min and has a good removal efficiency for BT, 4,6-DMDBT, and DBT. The removal efficiency for DBT could reach 85% after 12 cycles. We found that the electronic structure of NNU-28 is more favorable for charge migration due to its anthracene-based ligand structure with a narrow band gap and higher electron density than other typical Zr-based MOFs, and the surface hydrophobicity modification greatly improves the ODS reaction rate and the stability of the catalyst, which also verifies that the degree of hydrophobicity modification needs to be in an appropriate range. Finally, the oxidation mechanism of the catalyst in the ODS process was examined.