Rational design of ionic V-MOF with confined Mo species for highly efficient oxidative desulfurization

Abstract

The ionic metal-organic frameworks (MOFs) can be efficiently obtained by regulating the valence state of the metal units. Herein, phosphomolybdic acid (PMA) is introduced in the well-defined vanadium-MOF (V-MOF) structure to modify the valence state of V. By varying the ratio of PMA to V-MOF, tetrahedrally coordinated MoO42- confined in the ionic V-MOF structure or octahedrally coordinated MoO3 phase dispersed on the surface of ionic V-MOF can be selectively formed, thus influencing the oxidative desulfurization (ODS) activity. The difference in confining effects of ionic V-MOF on MoO42- or MoO3 active species are clearly interpreted including spatial confining effect, electronic confining effect and kinetic confining effect by various characterizations. Oxygen vacancies and V4+ with abundant electrons are observed in the PMA/V-MOF composites, which are beneficial to ODS activity. Furthermore, according to DFT calculations, tetrahedrally coordinated MoO42- species confined in the ionic V-MOF with V4+ state is the most active among the Mo-O-V species. The clear structure-activity relationship obtained in this work is thus critical for designing new efficient ionic MOFs rationally, integrating the advantages of encapsulated active components and MOFs.