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

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 506,61, as shown by inultitechnique characterization: IR (diagnostic v(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 center dot center dot center dot(OC)Mo interaction with the framework open Ni(II) site, which causes the markedly blue-shifted stretching band observed at v(CO) = 1797 cm(-1). Upon decomposition in dihydrogen-hydrogen sulfide at 350 degrees C (to 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 NiMoO4 (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 MoS2 nanopartides (average sheet thickness 25 A, corresponding to about 4 stacked layers of MoS2 sheets, the MoS2 (011) interlayer distance being 6.15 angstrom). The presence of Ni in the MoS2 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.