Comparison between alumina supported catalytic precursors and their application in thiophene hydrodesulfurization: (NH 4 ) 4 [NiMo 6 O 24 H 6 ]·5H 2 O/γ-Al 2 O 3 and NiMoOx/γ-Al 2 O 3 conventional systems

• Published in: RSC advances 2015, Vol.5 (124), p.102652-102662
• Main Authors: Ayala-G, Mónica, Puello P, Esneyder, Quintana, Patricia, González-García, Gerardo, Diaz, Carlos
• Format: Article
• Language: English
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/C5RA17695F

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 γ-Al 2 O 3 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 27 Al 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 ∼ 7). The specific surface area and pore volume of NiMo-AP/γ-Al 2 O 3 precursors were greater than those of the NiMo-COP/γ-Al 2 O 3 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 Å. XRD and XPS analysis confirmed the presence of (NH 4 ) 4 [NiMo 6 O 24 H 6 ]·5H 2 O and Mo 5+ /Mo 6+ for solids obtained by Anderson-type precursors, whereas NiMo-COP/γ-Al 2 O 3 precursors exhibited Mo 6+ from NiMoO 4 and MoO 3 . 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. 27 Al solid-state MAS NMR showed higher tetrahedrally coordinated aluminium for the NiMo-COP/γ-Al 2 O 3 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 ( 27 Al 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.