Extensive
efforts have been devoted to developing desulfurization catalysts
to effectively remove sulfur from fuel. Active phase metals including
cobalt, nickel, molybdenum, and tungsten have been extensively used
in industry for hydrotreating/hydrodesulfurization catalysts for over
50 years. However, while it is desirable to use inexpensive materials
to do the same job, it is a grand challenge. Herein, we report a Fe-based
sulfide catalyst that is tuned by zinc with high activity for HDS,
which shows an industrial application potential to replace industrial
Mo-based catalysts. With an optimal configuration that has a Fe:Zn
ratio close to 1:1, the reaction rate constants of the dibenzothiophene
(DBT) and 4,6-dimethydibenzothiophene (4,6-DMDBT) HDS are increased
by 9.2 and 17.4 times, respectively, in comparison with the sums of
those on the monoiron and zinc sulfides. HDS activity for the sterically
hindered 4,6-DMDBT on the FeZn sulfide catalyst is even close to that
of Co-MoS2. The experimental results indicate that the
addition of Zn greatly modifies the electronic properties of iron
sulfide by transferring electrons from Zn to Fe, which tunes the d
band center to modulate the adsorption behavior of DBT and 4,6-DMDBT.
In combination with theoretical calculations, our experiments show
that the addition of Zn dramatically tunes the formation of sulfur
vacancies. We propose that the formation of sulfur vacancies is the
critical factor for designing highly efficient Fe-based sulfide catalysts.
This study provides the design principle of low-cost desulfurization
catalysts for industrial refinery applications.
Appropriate
electronic structure is vital to promote the catalytic
performance of active species. In this work, TiO2–x
was employed to regulate active Fe species to the
electron-rich state, causing remarkable synergetic effects in which
the sulfur removal rates of Fe-based catalysts were increased by 10–40%
and reaction rate constants were also increased by around 100% (pure
Fe-based catalysts) and 30% (Fe-Zn bimetallic catalysts). The results
of characterization and DFT calculations show that the strong electron-donating
effect of TiO2–x
on Fe species
can promote the dispersion of Fe species and weaken the Fe–O
and Fe–S/FeZn–S bonds, resulting in the increases in
sulfidation degrees by around 3.5% and enrichments of coordinatively
unsaturated sites or sulfur vacancies. In addition, weaker Al–OH
peaks caused by TiO2 can also facilitate the increase in
sulfidation degrees of Fe-based catalysts. Furthermore, hydrodesulfurization/direct
desulfurization ratios are decreased by adding TiO2–x
, attributed to the electron-rich Fe species that
makes C–S bonds and α/β-H more vulnerable to attacks.
Slight changes in acidity caused by TiO2–x
have little effect on the catalytic performances of Fe-based
catalysts. This work lays a solid foundation for industrial application
of eco-friendly and economical Fe-based catalysts in the HDS field.
A novel organic template-free strategy for generating mesoporosity in Y zeolites is reported. It is revealed that Fe(3+) functioned as unstable sites in the Fe-NaY zeolite, which promotes deferrization-dealumination, leading to enhanced formation of intra-crystalline mesopores as well as desirable interconnectivity. The mesopore-enriched zeolite exhibits a remarkable ability in conversion of the bulky substrate.
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