Intensification of oxidative desulfurization by Zr(IV)-ionic liquid-HPW composite activating H2O2 system and mechanism insight

Abstract

The carboxyl functionalized ionic liquid ([mim(CH2)3COOH]Cl) was prepared as a linker to combine phosphotungstic acid (HPW) and Zr(IV) ion. The obtained [mim(CH2)3COO]3PW-Zr composite acted as a heterogeneous catalyst for removing DBT from liquid fuel with H2O2 as an oxidant. As a result, [mim(CH2)3COO]3PW-Zr possessed high catalytic activity in extractive and catalytic oxidative desulfurization (ECODS). Moreover, the [mim(CH2)3COO]3PW-Zr was further exploited to grow on the surface of PEI/silica gel. And the fabricated large-grained Zr-PWIL@PEI/silica gel was used in the continuous ECODS process, and the removal of DBT could still reach more than 95% after running continuously for 16 h. More importantly, the synergistic catalytic mechanism between HPW and Zr(IV) in the ECODS process has been investigated in detail by experiments and DFT calculations. As a result, a plausible mechanism has been proposed and verified, which contains two parts: the Lewis acidic center activating H2O2 to form superoxide ion radicals (OOH), and the OOH oxidizing HPW to peroxotungstate (W(O2)n), which has a high oxidizability and stability. Thus, the effective combination of Zr(IV) and HPW active sites is a very effective strategy to promote desulfurization efficiency and utilization efficiency of H2O2. Besides, we also found the distance between the corresponding active sites of catalysts plays an essential role in ECODS reaction as it strongly influences the synergistic effect between different active sites.