Constructing Dual-Function TiO₂/MWCNTs-NH₂-HPW Composites as Both Catalysts and Adsorbents for Highly Efficient Oxidative Adsorption Desulfurization in Fuel Oil

Abstract

The rational design of efficient polar heterogeneous catalysts for catalytic oxidative–adsorptive desulfurization (OADS) in fuel oil is of paramount significance in the field of environmental remediation. Herein, we fabricate a polar heterogeneous catalyst (titanium dioxide-assisted phosphotungstic acid supported aminated multiwalled carbon nanotubes (TiO2/MWCNTs-NH2-HPW)) with highly effective oxidative–adsorptive desulfurization (OADS) performance, which was prepared by depositing titanium dioxide and immobilizing phosphotungstic acid (HPW) on aminated multiwalled carbon nanotubes (NH2-MWCNTs). HPW, as a catalytic center, is immobilized on MWCNTs-NH2 via the positive charge of −NH3+ by electrostatic attraction. More importantly, amorphous titanium dioxides that contain Ti–OH, as adsorption centers, are well coated on MWCNTs-NH2-HPW, and the polarity of the catalysts can be easily tuned by loading different amounts of polar TiO2 (with abundant −OH), which can affect their catalytic performance and improve their adsorption capacity. The 15% TiO2/MWCNTs-NH2-HPW catalyst exhibits the highest desulfurization performance, and its dibenzothiophene (DBT) removal efficiency can reach 99% in 30 min at 60 °C without using an extractant. Its equilibrium adsorption capacity of the S element is approximately 63.36 mg/g because polar groups, such as −OH from TiO2 and −NH2, can effectively adsorb oxidation products (sulfoxide or sulfones) by hydrogen bonding. Furthermore, a possible OADS mechanism of TiO2/MWCNTs-NH2-HPW is proposed by monitoring the desulfurization process via gas chromatography (GC) and Fourier transform infrared (FTIR). This work provides a rational design strategy for constructing dual-function composites as both catalysts and adsorbents for oxidative–adsorptive desulfurization in fuel oil.