200
KASUMOVA
region be associated with the stretching vibrations of both
Co–O and Al–O in γ-Al2O3. A characteristic feature of
the spent sample is that its absorption spectrum contains
bands at 280 and 240 cm–1, suggestive of the presence
of cobalt sulfide.
spent cobalt–alumina catalyst samples are in good agree-
ment with the corresponding DTA and IR-spectroscopic
findings (Table 3). In other words, the X-ray patterns
recorded after the appropriate treatment procedures were
performed are indicative of formation of new, in particu-
lar, cobalt sulfide, sulfate, and oxide, phases.
The absorption bands observed in the spectrum of
the spent sample at 1080, 1100, and 1260 cm–1 can be
assigned with high reliability to vibrations of the sulfate
ion. It must be added that vibrations of the carbonate ion
can also be manifested in this region, but the presence
of the carbonate-carboxy moieties in the system is out
of question because of the lack of comparatively high-
frequency absorption bands at 1200–1700 cm–1.
Thus, the results of the physicochemical examina-
tions suggest that new phases (in particular, sulfide and
sulfate) are generated on the surface of the cobalt–alu-
mina catalyst during formation of the contacts. To iden-
tify the most active phase, experiments with individual
CoS·Al2O3, CoSO4·Al2O3, and Co3O4·Al2O3 as catalysts
were carried out.
The absorption band of sulfates may occur at ν =
1070 cm–1, and those of Al2O and CoO, at 970 and
930 cm–1, respectively. However, these bands cannot be
differentiated because of a strong overlap with absorption
of alumina proper (1000–1100 cm–1).
Acharacteristic band of aluminum sulfate at 1300 cm–1
is lacking in the spectrum recorded. This fact, coupled
with the results of comparing the spectra of the catalyst
with those of cobalt sulfate, allows the bands observed
to be tentatively assigned to cobalt sulfates in the cata-
lyst, whose absorption bands occur at 1100, 1030, and
970 cm–1.
The optimum conditions for these experiments,
as established earlier, were as follows: temperature
350°C, space velocity 1000 h–1, (CO + H2) : SO2 =
2.1 (vol/vol), and SO2 concentration in the initial gas
20 vol %. The results are shown in Fig. 4, which sug-
gest that the most active compound among those tested
is γ-Al2O3-supported Co3O4; its maximum activity is
stabilized after 2 h in reaction medium.
Obviously, the most active ratio of the components
(CoS, CoSO4, CoO) is achieved faster in the case of cobalt
oxide. Thus, in the spent catalyst sample cobalt occurs in
three different forms: sulfide, sulfate, and oxide.
Along with the above-mentioned surface reac-
tions leading to formation of sulfates and sulfides, the
catalytic process can involve chemisorption of SO2 via
coordination with the metal ions by the donor-acceptor
mechanism. This interaction may result in a shift of the
absorption band of S=O to lower (1280 cm–1) frequen-
cies, as actually observed in the spectrum recorded (in
the gaseous state νS=O = 1361 cm–1).
The absorption bands at 3680 and 3550 cm–1 are
characteristic for bound hydroxy groups of alumina.
These bands suggest that reduction of sulfur dioxide with
converted gas involves partial chemisorption of the water
molecules, thereby leading to formation of bound hydroxy
groups which are subsequently involved in adsorption of
other components of the reaction.
CONCLUSIONS
(1) The products of steam conversion of natural gas,
characterized by the CO : H2 ratio of 1 : 4, were found to
be the most active reducing agents for SO2.
(2) The cobalt–alumina catalyst displays high catalytic
activity at 300–350°C, with the sulfur yield after the stage
I reactor being 64–90% depending on space velocity
(250–2000 h–1).
(3) In spent cobalt–alumina catalyst sample, cobalt
is represented by a mixture of cobalt oxide, sulfide, and
sulfate.
REFERENCES
Therefore, the spectrum recording technique that was
employed in this study allows accurate differentiation
of the bands of sulfates, but the fact of proceeding on
the surface of these catalysts of reactions giving sulfates
(which concerns predominantly supported cobalt cata-
lysts) is beyond any reasonable doubt.
1. Eremin, O.G., Research and Development of an Efficient
Technology for Sulfur Recovery from Autogenous Smelting
Off-Gases for Metallurgical Raw Materials, Doctoral Dis-
sertation, Moscow, 2005.
2. Ilyukhin, I.V., Platonov, O.I., Ryabko, A.G., and Tseme-
khman, L.Sh., Tsvet. Met., 2005, no. 5, spec. issue, pp. 62–
The X-ray diffraction data for both the initial and
66.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 85 No. 2 2012