Ionic Liquid-Based Polyoxometalate Incorporated at ZIF-8: A Sustainable Catalyst to Combine Desulfurization and Denitrogenation Processes

Abstract

An effective and sustainable process capable of simultaneously execute desulfurization and denitrogenation of fuels is in fact an actual necessity in the refinery industry. The key to achieve this goal is the parallel oxidation of sulfur and nitrogen compounds present in fuels, which is only achieved by an active and recovered catalyst. A novel heterogeneous catalyst was successfully prepared by the encapsulation of an imidazolium-based polyoxometalate (POM) into a ZIF-8 framework ([BMIM]PMo₁₂@ZIF-8). This composite material revealed exceptional catalytic efficiency to concurrently proceed with the oxidative desulfurization and denitrogenation of a multicomponent model fuel containing various sulfur and nitrogen compounds. A complete removal of all these compounds was achieved after only one hour and the catalyst system was able to be reused for ten consecutive cycles without loss of efficiency. In fact, an ionic liquid POM was incorporated in the ZIF-8 for the first time, and this composite compound was originally applied as a catalyst for simultaneous oxidative desulfurization and denitrogenation processes.

Keywords: 1-Butyl-3-methylimidazolium cation; desulfurization; hydrogen peroxide; ionic liquid; oxidative catalysis; polyoxomolybdate; zeolitic imidazolate frameworks.

Scheme 1

Representation of the preparation of the [BMIM]PMo₁₂@ZIF-8 compound by a “bottle-around-the ship” approach and using a sustainable room temperature synthetic strategy (one-pot and in situ).

Figure 1

PXRD patterns (a) and FT-IR spectra (b) recorded for the pristine ZIF-8 compound and composite [BMIM]₃PMo₁₂@ZIF-8.

Figure 2

SEM micrographs and corresponding EDS spectra obtained for ZIF-8 (a) and [BMIM]₃PMo₁₂@ZIF-8 (b).

Figure 3

Desulfurization and denitrogenation of a multicomponent model fuel (BT, DBT, MDBT, DMDBT, IND, QUI) catalysed by the heterogeneous [BMIM]₃PMo₁₂@ZIF-8 (a) and the homogeneous [BMIM]₃PMo₁₂ (b), using [BMIM]PF₆ as extraction solvent and H₂O₂ as oxidant.

Figure 4

Reutilization performance of [BMIM]₃PMo₁₂@ZIF-8 over 10 cycles combining desulfurization and denitrogenation processes to treat a multicomponent model fuel (BT, DBT, MDBT, DMDBT, IND, QUI), using [BMIM]PF₆ as extraction solvent and H₂O₂ as oxidant.

Figure 5

Powder XRD patterns of the [BMIM]₃PMo₁₂@ZIF-8 material before catalytic utilization, isolated after the 1st ([BMIM]₃PMo₁₂@ZIF-8(AC1)) and after the 10th catalytic cycle.

Figure 6

(a) SEM micrographs of [BMIM]₃PMo₁₂@ZIF-8 before catalytic utilization, isolated after the 1st ([BMIM]₃PMo₁₂@ZIF-8(AC1)) and after the 10th catalytic cycle; (b) SEM micrographs and corresponding EDS elemental mapping and spectra for the sample [BMIM]₃PMo₁₂@ZIF-8 isolated after the 10 catalytic cycles.

Figure 6

(a) SEM micrographs of [BMIM]₃PMo₁₂@ZIF-8 before catalytic utilization, isolated after the 1st ([BMIM]₃PMo₁₂@ZIF-8(AC1)) and after the 10th catalytic cycle; (b) SEM micrographs and corresponding EDS elemental mapping and spectra for the sample [BMIM]₃PMo₁₂@ZIF-8 isolated after the 10 catalytic cycles.