Bulk Hydrodesulfurization Catalyst Obtained by Mo(CO)₆ Grafting on the Metal–Organic Framework Ni₂(2,5-dihydroxoterephthalate)

Abstract

The Metal−Organic Framework, [Ni 2 (dhtp)] (H 4 dhtp = 2,5-dihydroxyterephthalic acid) was modified by gas-phase grafting of Mo(CO) 6 at the gram-scale via a post-synthesis modification approach. A highly dispersed well-defined bimetallic material containing the [Ni 2 (dhtp)Mo(CO) 3 ] fragment either in the staggered or in the eclipsed conformation was obtained, with a maximum coverage of 50% mol , as shown by multitechnique characterization: IR (diagnostic ν(CO) = 1996, 1972, 1926, 1885, and 1797 cm −1 ), N 2 adsorption (Brunauer−Emmett−Teller (BET) surface area = 172 m 2 g −1 , pore volume 0.1 cm 3 /g), elemental analyses (Ni = 21.6% wt , Mo = 9.6% wt ), mass balanced analyses of evolved gases (3.0 ± 0.2 mols of CO evolved/mol of grafted Mo(CO) 6 high-resolution transmission electron microscopy (HRTEM). The staggered conformer is stabilized by an intermolecular Ni•••(OC)Mo interaction with the framework open Ni(II) site, which causes the markedly blue-shifted stretching band observed at ν(CO) = 1797 cm −1 . Upon decomposition in dihydrogen−hydrogen sulfide at 350 °C (p H2 = 50 bar), the resulting bulk material is a heterogeneous catalyst for hydrodesulfurization (HDS). The HDS activity of the catalyst was based on the average measured conversion of dibenzothiophene to biphenyl (BP) or cyclohexylbenzene (CHB) by online calibrated GC-MS analyses under steady state conditions and converted to the corresponding relative pseudo first-order rate constants [k(HDS) = k(BP) + k(CHB)]. The activity of the MOF-generated material is markedly superior to the reference bulk unsupported HDS catalysts NiMoO 4 (pseudo first-order rate k(HDS) = 30 vs 14 h −1 ) while containing 4 time less molybdenum (wt % = 10 vs 44). Activities on hydrodenitrogenation (HDN) and hydrogenation (HYD) are also reported. Analysis by HRTEM and X-ray diffraction (XRD) of the spent catalyst and comparison with model systems revealed well-formed MoS 2 nanoparticles (average sheet thickness 25 Å, corresponding to about 4 stacked layers of MoS 2 sheets, the MoS 2 (011) interlayer distance being 6.15 Å). The presence of Ni in the MoS 2 particles was inferred by the lack of HDS activity of the nickel-free material obtained from analogous chemisorption of Mo(CO) 6 in isostructural Zn analogue followed by the same in situ sulfidation procedure.

Towards Understanding Structure–Activity Relationships of Ni–Mo–W Sulfide Hydrotreating Catalysts

“…It is known that the properties of supported oxide precursors influence the features of supported sulfide catalysts even though sulfidation of oxides is not a topotactic transition . For unsupported catalysts, these relations have been recently discussed . In this work, the LCF of the XANES at the Ni K‐edge during sulfidation (Figure ) indicate that the sulfidation of Ni is relatively difficult if the precursor is crystalline as in the bimetallic NiW Ox and NiMo Ox precursors.…”

“…Such sulfides have been reported to have high activity and stability in most demanding hydrotreating conditions . Although several aspects of routes to prepare unsupported catalysts, such as impact of precursor materials, sulfidation procedures, and concentration of the promoters on the activity of working catalysts have been considered, the reasons for the high activity of such materials that could be related to catalyst preparation has not been deduced.…”

Polymer-Encapsulated Metallic Nanoparticles as a Bridge Between Homogeneous and Heterogeneous Catalysis

“…Highly selective solid catalysts were prepared by encapsulating catalyticallyactive sites within well-defined frameworks, which have specific pore dimensions and topologies [14][15][16][17]. For example, it was recently demonstrated that asymmetric hetero-Diels-Alder reactions can be activated by embedding catalytically active Ti(IV) ions within NbO-type chiral metal-organic frameworks [18].…”

Metal‐Organic Frameworks: Metal‐Uptake

“…23 Similarly, the MOF [Ni 2 (dhbd)] (dhbd = 2,5-dihydroxybenzene-1,4-dicarboxylate) can be metallated through chemical vapor deposition (CVD) with sublimation of Mo(CO) 6 into the MOF pores. 24 Again infrared spectroscopy supports the formation of (dhbd)Mo(CO) 3 species on the MOF framework, and microanalysis indicates that half of the dhbd 2− ligands are metallated. This material was degraded under an atmosphere of dihydrogen-hydrogen sulfide to give a heterogeneous catalyst for hydrodesulfurization reactions.…”