Upgrading the oxidative desulfurization performance of metal-organic frameworks with proton stimulation

Abstract

The modification of metal-organic frameworks (MOFs) to achieve desirable performance is attracting extensive investigation in heterogeneous catalysis, however, exploring the potential peculiarity of pristine MOFs for targeted applications is often overlooked. In this work, we developed an efficient approach for upgrading the oxidative desulfurization (ODS) performance of Zr-MOFs with proton stimulation. The ODS performance of pristine Zr-MOFs prepared under solvothermal conditions was commonly very poor at ambient temperature but could be activated when protons were introduced. Moreover, the upgradation of ODS efficiency by protons exhibited a sharply increasing trend (from 0.05 to 17.5 mmol g−1 h−1) with the increased density of defects in Zr-MOFs. The most defective UiO-66(Zr) showed ultrahigh activity in model oil which removed 1000 ppm sulfur after 25 min at 30 °C or after 4 min at 50 °C upon proton stimulation that is better than the sample pre-treated with 1 M HCl, and in multicomponent model oil which removed 972 ppm sulfur after 20 min at 50 °C in the present of proton. The turnover frequency (TOF) could reach 211.6 h−1 at 50 °C, surpassing the most investigated ODS catalysts. Quenching experiments and EPR tests demonstrated that the reaction pathway of UiO-66(Zr) could be altered by protons from free radical (OH• and O2•-) into non-free-radical (Zr–OOH) that manipulate the sulfur removal efficiency. Experimental results indicated that the terminal Zr–OH/OH2 sites could decompose H2O2 with assistance of H+ to form Zr–OOH, which probably accounts for the enhancement of ODS activity. Our work reveals a facile and efficient strategy for upgrading the ODS performance of pristine MOFs.