The effect of the chemical nature
of the oxide support on the performance
of cobalt Fischer–Tropsch catalysts is investigated. A series
of supports is synthesized via monolayer coverage of porous γ-Al2O3 with various oxides representative of a wide
range of Lewis acid–base character, as quantified by UV–vis
spectroscopy coupled to alizarin adsorption. Incorporation of cobalt
(20 wt %) results in model catalysts with identical porosities and
similar Co particle sizes (>10 nm), allowing the study of support
effects without overlap from diffusional or particle size factors.
Under realistic reaction conditions, the initial TOF scales with the
acidity of the oxide support, whereas the cobalt time yield and selectivity
to industrially relevant C13+ hydrocarbons show a volcano
dependence, with a maximum at an intermediate acid–base character.
As inferred from in situ CO-FTIR, “selective” blockage
of a few cobalt sites, though crucial for CO hydrogenation, by atoms
from basic oxides and “unselective” site blockage via
decoration of Co nanoparticles (strong metal–support interaction)
with acidic, reducible oxides cause a decrease in reaction rate for
supports with pronounced alkaline and acidic character, respectively.
The extent of secondary isomerization reactions of α-olefin
products, of relevance for chain reinsertion processes and product
selectivity, also correlates with the support acidity. For a TiO
x
/Al2O3 as support,
a remarkable C13+ productivity exceeding 0.09 molC gCo
–1 h–1 is achieved,
owing to the combination of optimal activity and selectivity. These
results provide a unifying view of the support effects over a considerably
broad study space and delineate a blueprint toward advanced Fischer–Tropsch
catalysts.
In this memory effect study, hydrotalcite-type compounds in the lamellar double hydroxide-like (LDH)/zeolite A composite material were analyzed using X-Ray Diffration XRD) in situ experiments. Three samples were analyzed: Al,Mg-LDH, Al,Mg-LDH/ZA composite, and a physical mixture (50/50 wt%) of zeolite A and Al,Mg-LDH. The Al,Mg-LDH sample was treated at 500 °C in an O2 atmosphere and subsequently rehydrated. The Al,Mg-LDH/ZA composites had three treatments: one was performed at 300 °C in a He atmosphere, and two treatments were performed with an O2 atmosphere at 300 and 500 °C. In the physical mixture, two treatments were carried out under O2 flow at 500 °C and under He flow at 300 °C. Both went through the rehydration process. All samples were also analyzed by energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). The results show that the LDH phase in the Al,Mg-LDH/ZA compounds has memory effects, and thus, the compound can be calcined and rehydrated. For the LDH in the composite, the best heat treatment system is a temperature of 300 °C in an inert atmosphere.
Burning
fossil fuels containing significant amounts of sulfur compounds
generates toxic and pollutant products, and removal of these sulfur
compounds is of substantial interest to the oil industry. New technologies,
such as oxidative desulfurization, are being developed to achieve
this, with the aim of increasing the removal of these contaminants
at lower costs. In this work, commercial clays (K-10 and KSF), a natural
clay (Poço A), and its pillarized form (Poço A PILC)
were impregnated with 1% vanadium for the oxidation and extraction
of dibenzothiophene (DBT) in commercial diesel charge. The catalysts
were characterized by XRD, textural analysis, and SEM. The products
obtained in the catalytic tests performed were analyzed by GC-FID
gas chromatography. The vanadium-impregnated K-10 and KSF clays showed
the best results regarding DBT oxidation, with yields of 33 and 58%,
respectively. However, all clays yielded good results for extraction
of the organic compound while avoiding oxidation.
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