期刊
RSC ADVANCES
卷 5, 期 124, 页码 102652-102662出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/c5ra17695f
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资金
- CINVESTAV-IPN Merida [FOMIX-Yucatan 2008-108160]
- CONACYT
The effect of the phase composition of alumina supported NiMo catalytic precursors on thiophene hydrodesulfurization (HDS) was investigated. The catalytic precursors were prepared by impregnation of the commercial gamma-Al2O3 with solutions of Anderson-type ammonium salts or co-precipitation of ammonium heptamolybdate and nickel nitrate. The precursors were characterized by XRD, BET specific surface area, pore volume and pore size, XPS, elemental analysis, TGA and Al-27 MAS NMR. The chemical analyses by ICP showed for the NiMo-AP compounds a clear agreement between experimental and theoretical values according to stoichiometric values (Mo/Ni = 6), while for NiMo-COP deviations were observed (Mo/Ni similar to 7). The specific surface area and pore volume of NiMo-AP/gamma-Al2O3 precursors were greater than those of the NiMo-COP/gamma-Al2O3 precursors, 387/325 m(2) g(-1) vs. 283/265 m(2) g(-1), and 0.34/0.27 cm(3) g(-1) vs. 0.21/0.15 cm(3) g(-1), respectively; whereas the average pore radius for all systems was 12 angstrom. XRD and XPS analysis confirmed the presence of (NH4)(4)[NiMo6O24H6]center dot 5H(2)O and Mo5+/Mo6+ for solids obtained by Anderson-type precursors, whereas NiMo-COP/gamma-Al2O3 precursors exhibited Mo6+ from NiMoO4 and MoO3. The NiMo precursor obtained from conventional methods showed a higher amount of sulfur than those synthesized from the Anderson-type phase (6.9 to 4.9 wt%), although this does not mean a highly active sample or optimum sulfided active phase. 27Al solid-state MAS NMR showed higher tetrahedrally coordinated aluminium for the NiMo-COP/gamma-Al2O3 catalytic precursors. The catalytic activity was strongly influenced by the type of catalytic precursor and metallic wt%. The activity of the catalysts obtained by the sulfided Anderson-type ammonium salts was greater than the sulfided solids obtained by the conventional method, suggesting that these precursors result in a better active phase with a molar ratio (Ni + Mo)/S = 1.01 (likely Ni-Mo-S species), due to lower loss of the Ni promoter into the alumina support (27Al NMR) and the lowest metal-support interaction (TGA). The catalysts obtained the HDS products, butane and cis-butene independent of the precursor type. Furthermore, the catalysts with 15 wt% Mo were more efficient than those obtained with 8 wt% Mo.
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