A High-Resolution MAS NMR Study of the Structure of Fluorinated NiW/γ-Al₂O₃ Hydrotreating Catalysts

Abstract

The structures of fluorinated oxidic and sulfided W/γ-Al 2 O 3 and NiW/γ-Al 2 O 3 catalysts were studied by means of multinuclear MAS NMR and BET measurements. The quantitative 1 H and 19 F MAS NMR results show that fluorination of γ-alumina favors the formation of polymeric tungstate in the catalysts and promotes the sulfidation of tungsten. Addition of tungsten to fluorinated γ-Al 2 O 3 leads to the transformation of part of the type-S1 fluorine, bonded to one aluminum atom, to the type-S3 fluorine, bonded to three aluminum atoms. Sulfidation results in a reorganization of the hydroxyl groups on the surface of fluorinated alumina and in a partial hydrolysis of the alumina network because of the H 2 O produced during sulfidation and the inductive effect of fluorine on the alumina lattice. Nickel reduces the NMR signal intensities in the oxidic samples because of its strong paramagnetic effect on the 1 H, 19 F, and 27 Al resonances. Sulfidation decreases the paramagnetic effect of nickel because of the combination of nickel with WS 2 into the Ni-W-S structure.

Hydrodenitrogenation of Petroleum

“…They concluded that changing the type of the support resulted in different effects on HDN relative to HDS, HDO and HYD. For example, the addition of fluoride to g-Al 2 O 3 followed by impregnation with ammonium metatungstate yielded a more active catalyst than did the catalyst containing untreated g-Al 2 O 3 (285). The support properties can be modified by various pretreatments.…”

Hydrodesulfurization of sulfur refractory compounds: Effect of gallium as an additive in NiWS/γ-Al2O3 catalysts

“…One way to obtain that could be to modify the surface properties of the alumina in order to decrease the tungsten-alumina interaction, since easier sulfidable species could be synthesized. Studies by FT-IR(NO) [14], TPS, XPS [15], quick extended X-ray absorption fine structure (QEXAFS), Xray absorption near-edge structure spectroscopy (XANES) [16] and nuclear magnetic resonance (NMR) [17] have shown that fluorination of alumina modified the interaction of tungsten with the support increasing the sulfidation of this metal. Also, it has been published that, at low concentrations, gallium decreased the interaction of Ni [18] with ␥-Al 2 O 3 , due to the high affinity of Ga 3+ to the tetrahedral sites of alumina, modifying the ratio of Ni 2+ tet /Ni 2+ oct species.…”

27Al and 29Si NMR studies of alumina and amorphous silica-alumina supported NiW(Mo) HDS catalysts

“…The interpretation of the shift of tetrahedral Al needs further investigations, because to our knowledge 27 Al NMR spectra of ASA supports and/or NiW/ASA catalysts were not published in the literature until now. Sulfidation results in a partial regeneration of surface hydroxyls similar to fluorinated NiW/Al 2 O 3 catalysts [9]. …”