Co(Ni)/MoS2 nanostructured catalysts for the hydrodesulphurization of dibenzothiophene.

In this study Co(Ni)/MoS2 unsupported nanocatalysts (nanorods and nanoribbons) were synthesized with Co(Ni)/(Co(Ni) + Mo) = 0.3, 0.5 molar ratios for Co and Ni respectively. First the alpha-MoO3 nanostructures were impregnated with an aqueous solution of Co(Ni)Cl2 x 6H2O or Co(Ni)(NO3)2 x 6H2O, then were treated for 2 h at 473 K, and finally the precursors were activated under a H2S/H2 mixture (15% v/v H2S) by ramping the temperature from room temperature to 773 K and keeping it at that value for 2 h. The resulting materials were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, X-ray diffraction, specific surface area and X-ray photoelectron spectroscopy, and tested as catalysts for the hydrodesulfurization (HDS) of dibenzothiophene (DBT). It was found that these materials presented specific surface areas below 25 m2/g. The catalytic test showed that only when Co is added a promoter effect is observed compared with MoS2 unpromoted catalysts. Among the materials prepared, the Co/MoS2 catalyst made from cobalt chloride presented the highest catalytic activity (6.95 mol s(-1) g(-1)catalyst) for the HDS of DBT. The selectivity for the latter indicated a clear preference for the direct desulphurization over the hydrogenating pathway.

Optimization of the synthesis of alpha-MoO3 nanoribbons and hydrodesulfurization (HDS) catalyst test.

An optimized process for synthesis of alpha-MoO3 nanoribbons characterized by uniform morphology and composition was carried out. The optimized process turned out to be the aging of a precursor of an aqueous solution of ammonium heptamolybdate for a week under constant stirring at 333 K; followed by hydrothermal treatment for 36 h up to 48 h at 473 K. The dimensions of the nanoribbons were between 5 and 10 microm in length and a width between 100 and 600 nm. The thickness was between 60 and 200 nm. This material was tested for hydrodesulfurization (HDS) of dibenzothiophene (DBT) by in situ activation and showed its catalytic activities to be similar to those of unsupported MoS2 catalysts. The structure and morphology of these materials was characterized by analytical transmission electron microscopy, scanning electron microscopy, and X-ray diffraction using the Rietveld method to determine the quantitative crystallographic phases. A chemical semiquantitative analysis was carried out by energy dispersive spectroscopy and a qualitative analysis was carried out by electron energy loss spectroscopy.

Synthesis of MoS(2) nanorods and their catalytic test in the HDS of dibenzothiophene.

Partially sulfided nanostructures were synthesized by direct sulfurization of alpha-MoO(3) nanorods using a mixture of H(2)S/H(2), 15 vol%, at several temperatures (400, 500, 600, 700, and 800 degrees C). These materials were tested as catalysts in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and characterized by specific surface areas using the expression developed by Brunauer, Emmett, and Teller (BET equation), x-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The TEM images show a gradual evolution from a smooth surface to a rough material, presenting some type of holes all over the particles, but keeping their rod-like structure throughout sulfidation. The results of evaluating the catalysts in the HDS of DBT showed that the best temperature for sulfidation is 500 degrees C. In all samples, a higher selectivity for hydrogenation over sulfur removal was observed.