SBA-15 as Support for MoS2 and Co-MoS2 Catalysts Derived from Thiomolybdate Complexes in the Reaction of HDS of DBT

Abstract

Molybdenum sulfide and cobalt-molybdenum sulfide catalysts supported on mesoporous SBA-15 were prepared by thermal decomposition of ammonium thiomolybdate (ATM). SBA-15 was synthesized at 353 K and 413 K to obtain pore diameters of about 6 and 9 nm, respectively. The (Co)-MoS 2 /SBA-15 catalysts were characterized with X-ray diffraction (XRD), N 2 -physisorption and high-resolution transmission electron microscopy (HRTEM). HRTEM images give evidence for the presence of a poorly dispersed MoS 2 phase with long MoS 2 slabs and a pronounced MoS 2 stacking. The catalytic performance in the hydrodesulfurization (HDS) reaction of dibenzothiophene (DBT) was examined at T = 623 K and P = 3.4 MPa. The Co-MoS 2 /SBA-15 materials show a relatively high catalytic activity with a strong preference for the direct desulfurization (DDS) pathway. This is an interesting result in view of the significant stacking of MoS 2 particles and the size of the slabs. The generation of the catalytically active CoMoS phase and a large number of coordinately unsaturated sites (CUS) may explain the high performance of Co promoted MoS 2 /SBA-15 catalysts in the HDS reaction.A confinement effect of the mesoporous channels of SBA-15 is observed for the unpromoted MoS 2 /SBA-15 catalysts. SBA-15 with 9 nm channel diameter with 11 wt.% Mo loading shows a higher selectivity for the hydrogenation pathway than SBA-15 with 6 nm channel and 16 wt.% Mo loading.

Preparation and Characterization of SBA-15 Supported Cobalt–Molybdenum Sulfide Catalysts for HDS Reaction: An All Sulfide Route to Hydrodesulfurization Catalysts

“…In addition, all catalysts, regardless of the type of the thiomolybdate source, show a high selectivity at DBT conversions of ca. 30% (HYD/ DDS * 0.2), being in good agreement with the results published in a previous study [12]. The total DBT conversions after 5 h reaction time for all catalysts are displayed in Fig.…”

“…The reduction of the intensity can be explained by the strong absorption of X-rays by Mo(Co) and/or a partial loss of the high order of the mesostructure. The same phenomenon was observed in previous studies [9,12,19].…”

“…3c, Co(1.5)Mo(11)/SBA-15(B)] caused by small Co-Mo sulfide particles settling within the mesopores. The mean pore diameter is shifted marginally toward higher values after introduction of Mo and Co in SBA-15 suggesting minor changes occurring after the introduction of Mo and Co. A similar phenomenon was described in previous reports [8,12]. The specific surface areas of SBA-15 and the Co-MoS 2 /SBA-15 catalysts are summarized in Table 1.…”

“…For all catalysts typical diffraction patterns of poorly crystalline 2H-MoS 2 with the characteristic reflections at 14.4, 33, 40 and 58°2h are observed. The asymmetric shape on the low angle side of the reflections at 33°, 40°and 58°2h is a typical feature of layered materials with a partial turbostratic disorder [12,20]. The average MoS 2 particle size can be determined from the peak width (full width at half maximum, FWHM) and the reflection position using the Scherrer formula, d = 0.941k/B cosh B , where d is the mean diameter of the particle, k is the wavelength of the Cu K a1 line, h B is the angle between the incident beam and the reflecting lattice plane and B is the width of the diffraction peak.…”

“…However, the calcination step can cause a loss of active metals on the support and a complete sulfidation of the active phase is difficult to achieve [11]. Recently, we reported the synthesis and catalytic performance of SBA-15 supported Co-Mo sulfide catalysts derived from ammonium thiomolybdate (ATM) [12]. The catalysts activated by a gas mixture H 2 /N 2 (H 2 = 10%) showed a higher HDS activity compared to a commercial CoMo/c-Al 2 O 3 material, despite the pronounced MoS 2 stacking and the presence of long MoS 2 slabs.…”