Carbon nanotube catalysts for oxidative desulfurization of a model diesel fuel using molecular oxygen

We firstly propose the application of CNTs as novel catalysts and molecular oxygen as the oxidant for the oxidative desulfurization (ODS) of a model fuel containing benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) at atmospheric pressure and low temperature. Results showed that when three CNTs including CNT-SZ, CNT-TS, and CNT-CD were separately used as catalysts with molecular oxygen as the oxidant, the conversion of DBT to its corresponding sulfone reached 100% at 150 °C separately within 40, 120 and 180 min. The CNT-SZ exhibited a superior catalytic activity even at a high fuel-to-catalyst ratio of 7.5 kg fuel per g catalyst. The oxidation reactivity of these benzothiophenic compounds followed the order: 4,6-DMDBT > DBT > BT. The deactivated CNT can be effectively regenerated by heat treatment under an argon atmosphere at 900 °C. Raman spectroscopy analysis revealed that the graphitization degree of the CNT played a decisive role in its catalytic activity for DBT oxidation. The CNT with the higher degree of graphitization had higher catalytic activity for DBT oxidation since its higher electric conductivity benefited the transfer of electrons involved in the oxidation–reduction reaction.