N-doped carbon nanotube encapsulated nZVI as a high-performance bifunctional catalyst for oxidative desulfurization

Great efforts have been made to remove sulfur from fossil fuels to protect the environment. We proposed synthesis of high efficiency oxidation desulfurization (ODS) catalysts by encapsulating nano zero valent iron (nZVI) in self-catalyzed carbon nanotubes. The synthetic strategy features facile hydrothermal and pyrolysis process. The specific surface area, pore structure, and microstructure of the catalysts were characterized by series techniques, and the catalytic ability was evaluated by the reduction of sulfur after oxidation and reflux-extration. The optimized nZVI@CNT catalyst exhibits outstanding catalytic performance (within 120 min, the oxidative removal rate of DBT reached 96%) and enhanced stability (a 80% retention of initial performance after six cycles.), revealing the effective optimization and modulation between carbon nanotubes and iron particles. This excellent ODS activity originated from the defects of N-doped nanotubes as well as excellent particle dispersion and material transport capacity, which excites highly active free radicals with the assistance of H2O2. In addition, the unique two-dimensional tube channel and mesoporous structure promoted the diffusion and transfer of reactants and electrons, leading to high density of active sites. The different experimental conditioins confirmed that the material is a bifunctional catalyst integrating adsorption and catalysis. This work provides an creative ideas for the rational design and synthesis of advanced ODS catalysts for fuel oil.