Effect of TiO2–Al2O3 Sol–Gel Supports on the Superficial Ni and Mo Species in Oxidized and Sulfided NiMo/TiO2–Al2O3 Catalysts: Influence on Dibenzothiophene Hydrodesulfurization

Abstract

The present work presents a comparative study of NiMo catalysts supported on sol-gel TiO 2 -Al 2 O 3 mixed oxides with 5 and 95 mol% content of Al 2 O 3 . The DRX and N 2 physisorption results showed that the sol-gel method allows preparation of TiO 2 -Al 2 O 3 mixed oxides possessing high superficial area and an amorphous TiO 2 structure. Results of f-potential showed that the net surface pH of the supports depends on their structure and composition. According to UV-Vis and Raman spectra obtained from the solids after impregnation, catalysts with high content of Al 2 O 3 showed Mo 7 O 24 2-and Mo 8 O 26 4-species displaying Mo-O-Mo stretching vibration modes. On the other hand, catalysts with high content of TiO 2 showed Mo 7 O 24 2-and Mo 8 O 26 4-species with vibration modes corresponding to terminal Mo=O t bonds. Therefore, it appears that impregnation of catalysts with a pH 9 solution allows a polymerization process of MoO 4 2-and [Ni 2? 4O 2-] solution species to Mo 8 O 26 4-and Mo 7 O 24 2-species with a close interaction with [Ni 2? 6O 2-] species. However, these species have low interaction with the support. Thus, composition of the support appears to be more important than net surface pH in order to obtain a better distribution of superficial Mo species. XPS results suggest a higher proportion of ''NiMoS'' phase on the TiO 2 rich support. The most active catalyst in the dibenzothiophene hydrodesulfurization was NiMo/TiO 2 -Al 2 O 3 with 5 mol% Al 2 O 3 . This suggests that Mo 7 O 24 2-and Mo 8 O 26 4-in combination with [Ni 2? 6O 2-] species produce a better Ni/(Ni ? Mo) ratio and NiMoS phase.

The Conversion of Jatropha Oil into Jet Fuel on NiMo/Al‐MCM‐41 Catalyst: Intrinsic Synergic Effects between Ni and Mo

“…No characteristic peaks attributed to Ni species were observed on monometallic Ni/A precursors. In addition to similar scattering peaks as Mo/A precursors, a new peak at 955 cm −1 appeared on NiMo/A precursors, which was usually associated with the symmetric stretching of Mo═O interacting with Ni in the bridge form, and the Mo species existing in the form of 2D polymeric Mo 7 O 24 6− with octahedral symmetry (Oh) …”

“…[55] No characteristic peaks attributed to Ni species were observed on monometallic Ni/A precursors. In addition to similar [53,54,56] Figure 6b shows the Raman spectra of different catalysts after 600 C reduction. Compared with the precursors, the Raman spectra of monometallic Mo/A and Ni/A catalysts were similar to those of the precursors, whereas the scattering peak at 955 cm À1 disappeared and the peak of tetrahedral Mo at 937 cm À1 emerged over bimetallic NiMo/A catalysts.…”

“…The monometallic Mo/A precursor showed scattering peaks at 212, 279, 333, 660, 815, and 990 cm À1 attributed to MoO 3 , which agreed well with the literature. [53,54] The peak at 212 cm À1 was ascribed to Mo-O-Mo deformation mode, and those at 815 and 990 cm À1 corresponded to Mo-O-Mo linkage in orthorhombic MoO 3 and Mo═O bond in bulk phase MoO 3 , respectively. This Mo species should be octahedrally coordinated.…”

Direct Synthesis of TiO2‐Supported MoS2 Nanoparticles by Reductive Coprecipitation

“…[9] Nevertheless, practical applications of TiO 2 as as upport in HDS catalysts are limited by its maximum Mo loading, which is constrained by the lower surfacea rea compared with Al 2 O 3 . [9a, 10] Several strategies were proposed to overcome the low Mo capacityo fT iO 2 .T hese strategies include the synthesis of highsurface-area TiO 2 , [10] mixed supports of TiO 2 with other metal oxides (ZrO 2 ,A l 2 O 3 ,a nd SiO 2 ), [11] and the synthesis of TiO 2coated Al 2 O 3 . [12] Despite the higher Mo loadings accommodated by these supports, in all cases Co and Mo were added by post-impregnation.…”

Deposition of NiO onto MoO3/γ-Al2O3 extrudates by slurry impregnation method

“…As the requirements for sulfur level in transportation fuels become increasingly strict, the NiMo catalysts have been recently a subject of numerous investigations e.g. [2][3][4][5]. Research into deposition of the active metals over shaped form of c-Al 2 O 3 support, however, has been reported only scarcely.…”