Confined Heteropoly Blues in Defected Zr‐MOF (Bottle Around Ship) for High‐Efficiency Oxidative Desulfurization

Abstract

The Keggin-type polyoxometalates (POMs) are effective catalysts for oxidative desulfurization (ODS) and confining these POMs in metal-organic frameworks (MOFs) is a promising strategy to improve their performances. Herein, postsynthetic modification of POMs confined in MOFs by adding thiourea creates more unsaturated metal sites as defects, promoting ODS catalytic activity. Additional modification by confining 1-butyl-3-methyl imidazolium POMs in MOFs is performed to obtain higher ODS activity, owing to the affinity between electron-rich thiophene-based compounds and electrophilic imidazolium compounds. The ODS catalytic activities of fourZr-MOF-based composites (bottle around ship) including phosphomolybdate acid (PMA)/UiO-66, [Bmim] 3 PMo 12 O 40 /UiO-66, PMA/Thiourea/UiO-66, and [Bmim] 3 PMo 12 O 40 /Thiourea/UiO-66 are therefore investigated in detail.In order to explore the catalytic mechanism of these MOF composites, their microstructures and electronic structures are probed by various techniques such as X-ray diffraction, thermogravimetric analysis, Fourier transform infrared, Raman, scanning electron microscope, transmission electron microscope, BET, X-ray photoelectron spectroscopy, EPR, UV-vis, NMR spectra, and H 2 -temperature-programmed reduction. The results reveal that phosphomolybdate blues and imidazolium phosphomolybdate blues with different Mo 5+ /Mo 6+ ratios with the Keggin structure are confined in defected UiO-66 for all four composites. This approach can be applied to design and synthesize other POMs/MOFs composites as efficient catalysts.

Solvothermal synthesis of Co-substituted phosphomolybdate acid encapsulated in the UiO-66 framework for catalytic application in olefin epoxidation

“…Notably, Wang and coauthors recently reported that weak IR and Raman signals related to PMo12 with Keggin structure were detected in the spectra of a hybrid material composed of phosphomolybdic acid and UiO-66, which was synthesized by a similar one-pot solvothermal method as adopted in this work [26,27]. Moreover, the presence of Keggin-type PMo12 clusters in the hybrid composite was further confirmed by combining the characterization results of 31 P NMR spectra, demonstrating that the basic POM structure remained intact after being incorporated into ZrMOFs using the solvothermal synthesis process [26,27].…”

“…The typical synthesis is shown in Scheme 1. According to the coordination modulation mechanism of UiO-66 synthesis revealed in literature [26,27,35], various acids such as saturated monocarboxylic acid (e.g., acetic acid), benzoic acid, and hydrochloric acid could be used as modulator. In previous work [25], it was observed that POM@UiO-66 composites with controllable morphology and crystallinity could easily be obtained when hydrochloric acid was used as modulator.…”

“…It was reported that by immobilization of polyoxometalate (POM) clusters into Zr-based MOFs, hybrid POM@ZrMOF composites with controllable acidity, redox property, and catalytic performance were obtained [23][24][25][26][27][28][29]. In general, POM, including metal-substituted POM, were incorporated into MOFs via simple impregnation [30][31][32].…”

“…Yang et al [25] solvothermally synthesized a hybrid composite of PW12@UiO-66, which exhibited high activity and reusability in the selective oxidation of cyclopentene to glutaraldehyde with H2O2 as the oxidant. Wang and co-authors [26,27] reported that hybrid composites involving phosphomolybdic acid and UiO-66 were obtained via a one-pot solvothermal method, and a synergistic effect between active Mo species and ZrMOF carriers was demonstrated contributing to a high oxidative desulfurization activity. POM@MOFs hybrid composites derived by this method showed a high dispersion of POM clusters into the matrices of the ZrMOFs support, excellent structure/chemical stability, as well as improved catalytic activity and recyclability caused by the effective interaction between POM and MOFs.…”

Synergistic Effect between Zr-MOF and Phosphomolybdic Acid with the Promotion of TiF4 Template

“… ( a ) Keggin-type structure of H 3 PMo 12 O 40 with differently coordinated oxygen. ( b ) Structure of UiO-66 with a Zr 6 O 4 (OH) 4 (CO 2 ) 12 cluster [ 29 ]. …”