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Comparison of Mo/MgO and Mo/γ-Al2O3 catalysts: impact of support on the structure and dibenzothiophene hydrodesulfurization reaction pathways
Heidarinasab, A.; Soltanieh, M.; Ardjmand, M.; Ahmadpanahi, H. & Bahmani, M.
Abstract
The MgO and P2O5-promoted γ-Al2O3 supports
with alkaline and acidic natures, respectively, were
prepared, impregnated with Mo atoms, and compared for
dibenzothiophene (DBT) hydrodesulfurization (HDS)
reaction. Ultraviolet spectroscopy and the principal component
analysis were used to identify the impact of the
supports on the reaction pathways. The catalysts were
characterized by BET surface analysis, X-ray diffraction,
temperature-programmed reduction, Fourier transform
infrared, and X-ray photoelectron spectroscopy. The γ-Al2O3-supported catalyst favors the hydrogenation pathway
relative to the MgO-supported catalyst, which facilitates
the direct desulfurization route. The different
performance was attributed to the dissimilar Mo phases
that emerged during the activation procedure. The activation
under sulfo-reductive condition changed the Mo atoms
on γ-Al2O3 support into the sulfide phase while extra
oxidation took place for the MgO-supported catalyst. The
migration and consumption of loosely bonded bulk oxygen
atoms with under-coordinated Mo atoms on the MgO
support were introduced as a possible reason for such extra
oxidation. DFT calculations predicted an interaction
between the Mo/MgO catalyst and DBT via the electron
donation from the catalyst oxygen atoms to the aromatic
rings, resulting in weakening and breaking of the C–S
bonds. In spite of the higher resistance of the MgO-supported
catalyst toward coking and its superior activity, its
lower hydrogenation capability suggested using a dualfunction
catalyst. Accordingly, two catalysts were mixed
and the synergism was observed in the HDS reaction of
thiophene.
Keywords
DFT; Predominance diagram; Principal component analysis; Reaction mechanism; Synergism; Thiophene
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