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MoS2 HDS catalysts promoted with Ni supported on SBA-15 were synthesized from sulfur containing Mo (ammonium thiomolybdate, ATM, and tetramethylammonium thiomolybdate, TMATM) and a Ni complex (Nickel diethylthiocarbamate, NiDETC). The catalysts have been characterized by X-ray diffraction (XRD), N2-physisorption and High-resolution transmission electron microscopy (HRTEM). The catalytic performance in the hydrodesulfurization (HDS) reaction of dibenzothiophene (DBT) was examined at T = 623 K and P H2 = 3.4 Mpa. In comparison with the impregnation mode, the nature of the employed thiomolybdate complex shows a stronger influence on the MoS2 morphology and consequently on the HDS activity of DBT. A similar high HDS activity to a commercial NiMo/γ–Al2O3 catalyst despite the pronounced stacking number is shown for a Ni–MoS2/SBA-15 catalyst derived from ATM. The catalysts derived from TMATM showed lower HDS activities compared to the catalysts obtained from ATM precursors due to probably the presence of closed shell structures (nano-onions) of MoS2 which offer significantly smaller amount of HDS active sites (edge sites). Moreover, the HYD/DDS ratios are interestingly higher with respect to the HYD/DDS ratio of the commercial NiMo/γ–Al2O3 catalyst which could be ascribed to the generation of multilayered MoS2 active phase. Nickel promoted molybdenum sulfide catalysts supported on mesoporous SBA-15 were prepared by an all sulfide route using Mo and Ni thiosalts. Similar high catalytic activity to a NiMo/γ–Al2O3 catalyst at high Mo loading is observed for Ni–MoS2/SBA-15 catalysts derived from ammonium thiomolybdate despite a pronounced stacking of MoS2 slabs. The catalysts prepared with tetramethylammonium thiomolybdate show lower HDS activities probably due to the generation of nano-onions composed of bent MoS2 with a low crystalline perfection. The enhancement of the Ni content by post-impregnation leads to the formation of segregated Ni3S2 particles, which can cover the surface of the Ni–Mo–S phase resulting in a decrease of the HDS activity. The multilayered nature of the Ni–MoS2 phase may be responsible for the higher HYD/DDS ratios (0.79–1.01).[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

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)-MoS2/SBA-15 catalysts were characterized with X-ray diffraction (XRD), N2-physisorption and high-resolution transmission electron microscopy (HRTEM). HRTEM images give evidence for the presence of a poorly dispersed MoS2 phase with long MoS2 slabs and a pronounced MoS2 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-MoS2/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 MoS2 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 MoS2/SBA-15 catalysts in the HDS reaction. A confinement effect of the mesoporous channels of SBA-15 is observed for the unpromoted MoS2/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. [ABSTRACT FROM AUTHOR]

An efficient method for improving the catalytic properties of unsupported Ni/MoS2 catalysts is mixing thiometalate precursors applying the appropriate precursors and thermal conditions. High active catalysts for the hydrodesulfurization (HDS) of dibenzothiophene (DBT) are prepared by the controlled decomposition of physical mixtures of Ni(diethylentriamine)2MoS4 (NDTA-TM) and [(Propyl)4N)]2MoS4 (TPA-TM). The catalysts with a higher content of NDTA-TM are very active with a high selectivity for the direct desulfurization pathway (DDS) due to the synergistic effect of nickel. In addition the presence of a large amount of carbon may produce single-slabs of nickel promoted carbon containing molybdenum sulfides. The activity enhancement is attributed to an increased number of NiMoS active sites originated by the chemical interaction between the precursors NDTA-TM and TPA-TM during the mixing procedure. Furthermore, the carbon content in the final products is related to the enhancement of the activity and the preference of the DDS pathway. The controlled decomposition of mixtures of NDTA-TM + TPA-TM yields catalysts which are about twofold more active than an industrial NiMo/Al2O3 catalyst. This improvement may be attributed to an intense interaction of the precursors during the synthesis causing a re-dispersion of nickel atoms from NDTA-TM over the surface of carbon containing molybdenum sulfide provided by the precursor TPA-TM, increasing the amount of active sites. The catalysts from mixtures of (NH4)2MoS4 (A-TM) and NDTA-TM behave similarly to the pure precursors. [ABSTRACT FROM AUTHOR]

A comparative study of the syntheses of unsupported WS2 and M/WS2 (M = Co, Ni) catalysts by ex situ/in situ decomposition of ammonium thiotungstate (ATT) is herein reported. Ex situ activation was performed under a H2S (15% volume)/H2 flow, whereas in situ activation consists in the direct decomposition of ATT or Co(Ni)/ATT precursors in the presence of a hydrocarbon solvent during the hydrodesulfurization (HDS) of dibenzothiophene (DBT). Precursors were characterized by thermogravimetric analysis and final catalysts by X-ray diffraction (XRD), scanning electron microscopy (SEM) and specific surface area (BET). Catalysts activated using the in situ mode of activation present higher specific surface areas with the noticeable exception of the Ni/ATT precursor. Activity measurements showed that the in situ activated WS2 and Ni/WS2 catalysts exhibit higher activity than the ex situ activated catalysts. [ABSTRACT FROM AUTHOR]

Catalytic properties of unsupported MoS2 catalysts in the thiophene hydrodesulfurization reaction were determined in the temperature range 623–653 K. The catalysts were prepared by ex situ decomposition of ammonium thiomolybdate (ATM) crystals in a mixture of 15% H2S in H2 at 673 K. Activity of catalysts decreased very rapidly before reaching a steady state after 15 h on stream. The thiophene conversion went down from 10–12 to 3–4% in that time. The surface area of the catalysts also decreased during the catalytic reaction from 40–50 to 8–10 m2/g. Selectivity for hydrodesulfurization, hydrogenation and isomerization reactions was affected distinctly by the deactivation process. By increasing the reaction time, double bond isomerization increased, hydrogenation of butenes decreased and hydrodesulfurization remained constant. Results indicate that the main cause of activity decay was surface area loss that was due to sintering of MoS2 crystallites. Selectivity variation indicates that different active sites are involved for the three reactions. A deactivation model involving diminution of active sites located in edge and rim sites of small MoS2 particles is proposed to explain the variation of product distribution. [ABSTRACT FROM AUTHOR]

The surface area of unsupported MoS2 catalysts prepared by thiosalt decomposition is found to increase after undergoing a treatment known as chemical exfoliation. Rate measurements of dibenzothiophene hydrodesulfurization in a batch reactor show that activity decreases for the chemically modified MoS2 catalysts, along with the hydrogenation/hydrodesulfurization ratios (HYD/HDS). These results indicate that both basal and edge planes of the layered sulfides are rearranged by the exfoliation treatment, but that other processes must also be involved. Reference crystalline MoS2 is also discussed in the work. [ABSTRACT FROM AUTHOR]

The in situ decomposition of ammonium thiometallates during the hydrodesulfurization (HDS) of dibenzothiophene (DBT), to obtain molybdenum disulfide and tungsten disulfide catalysts, was investigated. It was found that very efficient catalysts for the HDS of DBT were obtained by in situ decomposition. Mechanical uniaxial pressing of the precursors (ammonium thiometallates) affected both textural and catalytic properties of the catalysts. Surface areas of molybdenum and tungsten disulfides increased as a function of uniaxial pressing, while catalytic activities went through a maximum. For MoS2, the hydrogenation selectivity was much higher for in situ catalysts than for ex situ ones. For WS2 catalysts, the hydrogenation selectivity was less sensitive to the condition of decomposition (ex situ/in situ). The surface S/M (M = Mo, W) atomic ratio from the Auger signal decreased as a function of uniaxial pressing, while the C/M ratio remained almost constant at 1.6. The best catalyst showed an experimental S/Mo ratio that is slightly higher than the stoichiometric value. The effect of in situ decomposition and mechanical deformation of thiometallate precursors is discussed. [ABSTRACT FROM AUTHOR]

Desorption and catalytic properties of 0.3 wt% Pd catalysts supported on alumina-lanthana, prepared by the sol-gel method, were studied. A large excess of consumed hydrogen was observed during TPR experiments on these catalysts due to the partial reduction of lanthana. The enhanced hydrogen adsorption (H/Pd varies from 8 to 15) detected by TPD for these catalysts is supposed to be a consequence of spillover. Spillover of hydrogen is favored by a high dispersion of palladium on the support surface and the presence of lanthana reduced species. Palladium on alumina-lanthana catalysts show a higher catalytic activity than palladium on alumina catalysts because reduced species of lanthana stabilize palladium particles. Similarity of ammonia selectivity at high temperatures allows one to suggest that reduced lanthana is involved in the reaction on pure alumina-lanthana support and palladium on alumina-lanthana catalysts at these temperatures. A synergetic effect between small palladium particles and reduced species of lanthana is suggested to be responsible for observed behavior of the lanthana-promoted palladium catalysts. [ABSTRACT FROM AUTHOR]