Catalytic properties of the thermoactivated schungite rock

Article abstract of DOI:10.1007/s11172-005-0005-1

A high catalytic activity of the thermoactivated schungite rock was demonstrated for reactions of CO oxidation, neutralization of CO + NO _x mixtures (model exhaust gas), oxidation of o-xylene, and oxidative dehydrogenation of ethylbenzene to st

Full text of DOI:10.1007/s11172-005-0005-1

Russian Chemical Bulletin, International Edition, Vol. 53, No. 8, pp. 1615—1620, August, 2004
1615
Catalytic properties of the thermoactivated schungite rock
a
b
c
I. G. Lugovskaya,a S. I. Anufrieva, N. V. Golubtsov, and A. V. Krylova
ꢀ
aN. M. Fedorovsky AllꢀRussia Institute of Mineral Resources,
31 Staromonetnyi per., 119017 Moscow, Russian Federation.
Fax: +7 (095) 959 3447. Eꢀmail: vims@df.ru
bPublic Corporation "Tsentrenergokomplex,"
office 4133ꢀ413, building 32, 8 Leningradskii prosp., 125040 Moscow, Russian Federation.
Eꢀmail: ng@ru.ru
cD. I. Mendeleev Russian University of Chemical Technology,
9 Miusskaya pl., 125047 Moscow, Russian Federation.
Fax: +7 (095) 978 9542. Eꢀmail: sark@mhti.msk.su
A high catalytic activity of the thermoactivated schungite rock was demonstrated for
reactions of CO oxidation, neutralization of СО + NOх mixtures (model exhaust gas), oxidaꢀ
tion of oꢀxylene, and oxidative dehydrogenation of ethylbenzene to styrene.
Key words: schungite rocks, thermoactivation, catalytic activity, carbon monoxide,
ethylbenzene.
has an exotherm corresponding to a rapid loss in weight due to
carbon burnꢀoff.4 The same temperature was used for SR activaꢀ
tion in a hydrogen atmosphere.
Thermooxidative and thermoreductive activations of the
samples were carried out in a flow of air (3 or 6 h) or hydrogen
(6 h), respectively. The thermooxidativeꢀreductive activation
was performed by the successive treatments in a flow of air and
hydrogen (6 h each). The activated SR exhibited catalytic activꢀ
ity in all reactions studied. An increase in the activation proceꢀ
dure beyond 6 h did not affect the activity.
Except for carbon, the content of the main chemical comꢀ
ponents in the samples recalculated to oxides was determined at
the Analytical Certification Testing Center of the AllꢀRussia
Institute of Mineral Resources using chemical and elemental
analyses.5
The specific surface area of the samples (Ssp) was measured
by the Brunauer—Emmett—Teller method using the thermal
desorption of argon adsorbed at a low temperature.6 The pore
volume (Vp) was determined by mercury porosimetry.7
To prepare Pt catalysts, H2PtCl6 was used. The successive
treatments of the samples impregnated with an acid were carried
out in a flow of air and then hydrogen. The catalysts containing
0.1 and 0.4 wt.% Pt on SR were studied.
The catalytic activity has been studied by methods described
earlier.8,9 The oxidation of CO on the SR was studied in a flowꢀ
type unit. The volume of the SR samples was 1 cm3, the flow
rate was 900 h–1, and the reaction mixture contained 5—6% CO
and 94—96% air. The compositions of the reaction mixture and
reaction products were examined by GC on an LKhMꢀ72 chroꢀ
matograph (katharometer as the detector, helium as the carrier
gas, columns were packed with molecular sieves 5 Å to deterꢀ
mine CO and with Polysorb to determine СО2).
The reaction of neutralization of СО + NOx mixtures (model
exhaust gas) was also studied in a flowꢀtype unit with a flow rate
of 2000 h–1. The reaction products were analyzed by chromaꢀ
tography on a column packed with Polysorb.
One of the promising routes to simplify preparation,
reduce the cost of catalyst manufacture, and decrease the
level of technogenic contamination during their producꢀ
tion and utilization is the replacement of synthetic cataꢀ
lytic systems by naturally occuring, usually multicompoꢀ
nent, materials.
Schungite rocks of Karelia represent a poorly studied
(with respect to the catalytic properties) and rare in comꢀ
position natural material formed mainly by quartz and
schungite carbon. Carbonates (calcite, siderite, dolomite),
laminated aluminosilicates (kaolinite, hydromica), and
iron sulfides and hydroxides (pyrite, goethite, hydroꢀ
goethite) are present in the rocks as minor components.
According to the available data, the schungite rock
(SR) manifests catalytic activity in the dehydration of
alcohols1 (acidꢀbase type reactions) and decomposition
of hydrogen peroxide2 and oxidation of CO 3 (redox type
reactions).
The purpose of this work is to study the catalytic activꢀ
ity of the thermoactivated SR in reactions of oxidation of
CO, neutralization of model exhaust gases (СО + NOx
mixtures), oxidation of oꢀxylene, and oxidative dehydroꢀ
genation of ethylbenzene.
Experimental
Samples of the SR from the Zazhoginskoe deposit with a
carbon content of ~30 wt.% and a grain size of 1.0—2.5 mm were
studied. The SR samples without thermal treatment manifested
no measurable activity in the reactions chosen for the study.
The SR were thermally activated at 500 °С. This temperaꢀ
ture was chosen from the results of thermogravimetric analyses
of the SR in air, which showed that near 500 °С the thermogram
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1555—1560, August, 2004.
1066ꢀ5285/04/5308ꢀ1615 © 2004 Springer Science+Business Media, Inc.

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Russ.Chem.Bull., Int.Ed., Vol. 53, No. 8, August, 2004
Lugovskaya et al.
Table 1. Content of the main chemical components in the starting and thermoactivated SR samples
Sample
Composition (wt.%)
C
SiO2
Al2O3
Fe2O3
CaO
MgO
MnO
K2O
TiO2
Starting SR
SR thermoꢀ
31.00
10.08
54.50
74.63
4.62
5.76
2.04
1.58
1.50
0.77
0.66
0.71
0.02
0.90
1.15
2.43
0.22
0.28
activated in an air
flow at 500 °C
An SR sample 2 cm3 in volume was used for oꢀxylene oxidaꢀ
tion, the oꢀxylene concentration in vapor being 0.1 mol cm–3
and the flow rate of an oꢀxylene—air reaction mixture was
1800 h–1
Table 2. Influence of thermooxidative activation on the paramꢀ
eters of the SR texture: specific surface (Ssp), pore volume (Vp),
and average pore radius (r)
,
.
Oxidative dehydrogenation of ethylbenzene was studied in a
flowꢀtype reactor of a KLꢀ1 design (Special Design Bureau of
the N. D. Zelinsky Institute of Organic Chemistry, Russian
Academy of Sciences). The concentration of ethylbenzene in a
Sample
Ssp/m2 g–1 Vp/cm3 g–1 r/nm
Starting SR
SR thermoactivated
in an air flow
9.0
12.0
0.025
0.192
13
211
mixture with air or (for comparison) nitrogen was 0.1 mol cm–3
,
the volume of the SR sample being 2 cm3, and the flow rate of
the reaction mixture was 1060 h–1. The reaction products were
analyzed on columns packed with Polysorb.
for 6 h at 500 °C
SR thermoactivated
in air for 8 h at 411 °C*
SR thermoactivated
in air for 1 h at 528 °C*
28.0
29.3
0.289
0.175
596
106
IR spectroscopic analysis was performed on a Specord Mꢀ80
spectrophotometer. Samples of the SR were compacted into
pellets with КBr. The spectra were recorded in air at 20 °С.
* According to the data in Ref. 4.
Results and Discussion
ironꢀcontaining phase on the surface of the thermoꢀ
activated SR are higher than their average content in
the rock.
Following the thermooxidative activation, the specific
surface and total pore volume (Table 2) increase by 1.3
and 8 times, respectively. This is caused by the developꢀ
ment of the porous structure when a portion of carbon
was "burnt off." The Ssp values correspond to usual values
for catalysts based on individual and mixed oxides of tranꢀ
sition metals, including iron oxides.
Varying the conditions of oxidative activation, one
can control the average content of carbon in the samples,
the content of carbon and the ironꢀcontaining phase on
the surface, and the characteristics of the texture (see
Table 2). As shown by the study of benzene vapor adsorpꢀ
tion, this activation renders the samples microporous.12
The IR spectra of the starting SR and the sample subꢀ
jected to thermooxidative activation are shown in Fig. 1.
The spectrum of the starting sample (see Fig. 1, curve 1)
contains several bands at 1200—400 cm–1 attributed to
stretching vibrations of Si—O. The highꢀfrequency region
exhibits a broad band at 3500 cm–1 caused by the presꢀ
ence of water of hydroxyl groups linked with the surface
by a hydrogen bond. The thermooxidative treatment of
the SR (see Fig. 1, curve 2) increases the intensity of the
bands due to the partial removal of carbon and improves
their resolution, which usually indicates a decrease in the
degree of imperfection of the lattice.9
Influence of thermoactivation on the composition and
texture of the samples. The changes in the content of the
main chemical components due to the thermooxidative
activation of the SR sample are shown in Table 1.
The carbon content in the samples upon their activaꢀ
tion in an air flow decreases due to partial burnꢀoff from
31 to 10 wt.%, and the content of silica and alumina, as
well as that of several other oxides, increases. According
to the published data,10,11 iron oxides predominate
(1.5—2 wt.%) among the transition metal oxides occurꢀ
ring in the rock.
According to Xꢀray diffraction data, the main phases
in the starting rock and in the sample subjected to
thermooxidative activation are lowꢀtemperature quartz
and schungite carbon. The latter is a carbonaceous subꢀ
stance represented by an amorphous to Xꢀrays phase.
Mineralogical and Xꢀray computational microtomoꢀ
graphic (XCMT) analyses showed that in the starting
rock the siliceous matrix is uniformly saturated with finely
dispersed schungite carbon. After the thermooxidative
treatment, the fraction of the carbonaceous component
decreases and the component migrates to enrich the exꢀ
ternal peripheral zone of pellets and zones of internal
breaks.
A similar surface enrichment is also observed in the
peripheral zone of grains of the ironꢀcontaining mineral
phase (minerals of the goethite group: goethite, hydroꢀ
goethite).12,13 Thus, the concentrations of carbon and the
The spectra of the SR after thermoreductive and
thermooxidativeꢀreductive activations are presented in

Thermoactivated schungite rocks as catalysts
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 8, August, 2004
1617
1150
Thus, the thermooxidative activation of the SR favors
a decrease in the carbon content and an increase in the
content of other components. Moreover, it heals imperꢀ
fections in the crystal structure renders the samples
microporous with an increase in Ssp, and enriches the
nearꢀsurface grain layers in carbon and the ironꢀcontainꢀ
ing mineral phase. For the thermoreductive activation of
the SR, the main effect is the partial reduction of foreign
metal oxides. For the thermooxidativeꢀreductive activaꢀ
tion, the effects caused by the thermooxidative and
thermoreductive treatments are combined.
1100
500
1200
3450
3450
710
780
520
1100
2
1
400
370
Oxidation of CO, neutralization of СО + NOх mixꢀ
tures, and oxidation of oꢀxylene. The main catalysts for
exhaust gas neutralization are known to be multicompoꢀ
nent systems based on noble metals (Pd, Pt, Rh). Intenꢀ
sive search for alternative catalysts using, in particular,
transition metal oxides, is under study.
470
790
690
500
690
2
390
1
3600
3200
1500
1100
700
ν/cm–1
The influence of the thermoactivation method on the
catalytic activity of SR, as characterized by the temperaꢀ
ture dependence of the CO conversion (α), is shown in
Fig. 3. Curve 1 indicates a low activity of the SR after the
thermoreductive activation for 6 h: the CO conversion
at 400 °С is ~20%. The thermooxidative activation
for 3 or 6 h makes it possible to achieve the 100% converꢀ
sion of CO at temperatures about 500 and 400 °С, respecꢀ
tively. The thermooxidativeꢀreductive activation increases
the activity of the SR more strongly: the 100% conversion
is achieved at 370—380 °С (see Fig. 3, curve 4).
Fig. 1. IR spectra of the starting SR (1) and SR thermoactivated
for 6 h at 500 °C in an air flow (2).
Fig. 2. Unlike the thermooxidative treatment, the thermoꢀ
reductive treatment does not virtually change the shape of
the spectrum in a region of stretching Si—O vibrations
(see Fig. 2, curve 1) but increases the intensity of the band
at 3450—3500 cm–1 and induces the appearance of a band
at 1630—1640 cm–1 (cf. curve 1 in Fig. 1) corresponding
to bending vibrations of H—O—H. This indicates the
formation of water, probably, due to the partial reduction
of metal oxides, which are present in the SR as impurities.
The thermooxidativeꢀreductive activation (see Fig. 2,
curve 2) increases the intensities of all bands compared to
those in spectrum 1 following to partial removal of carꢀ
bon. In this case, the intensities of the bands at 3500 and
1640 cm–1, indicating, as assumed above, the presence of
water, increase as a result of the reduction of foreign
metal oxides.
The increase in the catalytic activity due to the
thermooxidative activation of the SR can be explained by
an increase in the accessibility of active sites for reactants:
α (%)
3
100
4
2
3450
1100
50
1640
480
510
1380
790
770
680
2
3400
1100
1
1630
1380
450
500
790
760
300
400
T/°C
1
Fig. 3. Temperature dependences of the CO conversion (α) for
the samples thermoactivated by different methods: thermoꢀ
reductive activation for 6 h (1), thermooxidative activation
for 3 (2) and 6 h (3), and thermooxidativeꢀreductive activaꢀ
tion (4).
3600
3200
1500
1100
700
ν/cm–1
Fig. 2. IR spectra of the SR after thermoreductive activation for
6 h (1) and thermoactivation for 6 h in an air flow followed by
reduction with hydrogen for 6 h at 500 °C (2).

1618
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 8, August, 2004
Lugovskaya et al.
α (%)
these sites are oxides of foreign transition metals. This
occurs due to the elimination of a portion of carbon,
which screens these sites, and diffusion of iron ions and
other impurity ions (for the ironꢀcontaining mineral phase,
this was confirmed by mineralogical and XCMT analyses)
into the nearꢀsurface grain layers. The subsequent thermoꢀ
reductive treatment can further increase the activity due
to the partial reduction of the oxide sites on the rock
surface, which is confirmed by IR spectroscopic data.
The published data indicate that the SR can be used
(without activation) as a support for oxide catalysts active
in CO oxidation.3,14 In this work, we studied the activꢀ
ity of the SRꢀsupported platinum catalysts (0.1 and
0.4 wt.% Pt) in CO oxidation. Platinum was incorporated
in both the starting SR and the SR subjected to the thermoꢀ
oxidative activation for 3 and 6 h. After impregnation of
the support with H2PtCl6, the catalysts were reduced by
hydrogen or calcined in air.
The data in Fig. 4 show that after reduction with hydroꢀ
gen the activity of the catalysts supported on the starting
rock (curve 1) is lower than that on the sample thermoꢀ
activated in air (curve 2). The catalyst activity increases
when H2PtCl6 was introduced on the starting rock folꢀ
lowed by the calcination of the catalyst at 500 °C in air
(curve 3). In this case, the catalyst is formed under the
conditions of simultaneously occurring processes of
thermooxidative activation of the support and decompoꢀ
sition of H2PtCl6. The SRꢀsupported catalysts are less
active than the conventional catalytic system 0.1 wt.%
Pt/Al2O3 (curve 4). However, taking into account a subꢀ
stantially higher Ssp value for Al2O3 (80 m2 g–1) compared
to that of the SR (9—12 m2 g–1), one can conclude that
the specific catalytic activity of the 0.1 wt.% Pt/SR sysꢀ
tem is rather high, which is evidently explained by a conꢀ
tribution from the activity of the support.
100
50
4
3
2
1
100
200
300 T/°C
Fig. 5. Temperature dependences of the CO conversion (α) for
the catalysts 0.4 wt.% Pt/SR: the catalyst on the starting SR
reduced by hydrogen (1), the catalyst on the SR after thermoꢀ
oxidative activation for 3 h reduced by hydrogen (2), the catalyst
on the starting SR calcined in air for 6 h at 500 °C (3), and the
catalyst on the SR after thermooxidative activation for 6 h reꢀ
duced by hydrogen (4).
The catalysts with a high Pt content are more active
(cf. Figs 4 and 5). The thermoactivation conditions and
the method of SR treatment exert the same effects on the
activities of the catalysts with Pt concentrations of 0.1 and
0.4 wt.% in this reaction.
The catalysts supported on the starting rock and reꢀ
duced by hydrogen (see Figs 4 and 5, curves 1) are least
active. The thermooxidative activation of the SR increases
the activities of the supported catalysts, and the 6ꢀh actiꢀ
vation has a stronger effect than the 3ꢀh treatment (see
Fig. 5, curves 2 and 4).
The platinum catalysts supported on the starting SR
and calcined in air (see Figs 4 and 5, curves 3) are more
active than the hydrogenꢀreduced catalysts supported on
the rock thermoactivated for 3 h in air. This confirms that
the activation of the support and decomposition of
H2PtCl6 can occur simultaneously. However, the highest
activity is shown by the samples supported on the SR
after its thermooxidative activation for 6 h and reduced
by hydrogen (100% conversion of CO is achieved at
170—200 °С; cf. curves 3 and 4 in Fig. 5).
The fact that the specific features of the thermoꢀ
activation of the SR and the SRꢀsupported Pt catalyst
have the same effect on the activity of the latter indicates
a substantial contribution of the activity of the support to
the activity of the supported catalyst.
α (%)
100
3
2
1
4
80
60
40
20
The 0.4 wt.% Pt/SR catalyst was tested to stability.
The temperature of the catalyst was increased to a level
providing the maximum (100%) conversion of CO, then
the reactor was cooled, hereafter the activity was meaꢀ
sured in a regime in which temperature was reduced to
room temperature. Then the reactor was heated again to
the temperature corresponding to the full conversion
150
200
250
T/°C
Fig. 4. Temperature dependences of the CO conversion (α) for
the catalysts 0.1 wt.% Pt/SR: the catalyst on the starting SR
reduced by hydrogen (1), the catalyst on the SR after thermoꢀ
oxidative activation for 3 h reduced by hydrogen (2), the catalyst
on the starting SR calcined in air for 6 h at 500 °C (3), and the
catalyst 0.1 wt.% Pt/Al2O3 (4).

Thermoactivated schungite rocks as catalysts
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 8, August, 2004
1619
of CO. The experiment was carried out for 3 days, and the
complete reproducibility of CO conversion persisted
within this time, indicating a stable operation of the
catalyst.
and at 450 °C the conversion achieves almost 100% (see
below). No products of partial oxidation were observed.
T/°C
α (%)
206
0
259
1
299
3
356
12.7
408
83.2
450
99.4
The neutralization of the model exhaust gas was studꢀ
ied for the SR samples subjected to the thermooxidativeꢀ
reductive activation. Model mixtures of the exhaust gas of
two compositions were studied: (A) 3% CО, 3.5% NO,
11% O2, and 82.5% N2 (relatively low concentrations
of toxicants and oxygen excess) and (B) 16.7% CО,
21.8% NO, 23% O2, and 59.2% N2 (a high concentration
of toxicants at a restricted oxygen content).
The temperature dependences of the catalytic activity
of the thermoactivated SR related to CO oxidation and
NOх reduction are presented in Fig. 6. Mixture A showed
much higher activities: the conversions of CO and NOх
reach 55—50% at temperatures of 200—250 °С, and for
mixture B the activity was in the region of 35—30%
at ~300 °С.
Oxidative dehydrogenation of ethylbenzene to styrene.
It is known that the industrial synthesis of styrene is mainly
performed by the dehydrogenation of ethylbenzene at
550—650 °C using Fe2O3ꢀbased catalysts containing
K2CO3 and Ce and Mo oxides. Similar catalysts of the
recent generations also contain V, W, Li, Mg, Ca, Ti, Zr,
Ni, and Co oxides. To decrease the partial pressure,
ethylbenzene is diluted with water vapor15 in a ratio of
1 : (10—15). The catalysts are regenerated with oxygen,
which removes carbonaceous deposits from the surface.
In the presence of air, ethylbenzene is reversibly
adsorbed on the SR subjected to the thermooxidative acꢀ
tivation for 6 h at 100—110 °С. This adsorption process
decreases with the temperature increase and ceases comꢀ
pletely at 200 °С. Beginning from 160 °С, styrene appears
in the reaction products. At temperatures higher than
200 °С, some amount of benzaldehyde is formed along
with styrene, and traces of light hydrocarbons are present.
The temperature dependences of the overall converꢀ
sion of ethylbenzene in the presence of air oxygen (oxidaꢀ
tive dehydrogenation) and in a nitrogen flow (dehydroꢀ
genation) and the change in the selectivity of styrene
formation (S) for oxidative dehydrogenation are presented
in Fig. 7.
For both mixtures, the CO conversion exceeds the
conversion of NOх. The lower activity of the SR in mixꢀ
ture B is caused by NOх excess, which prevents the effiꢀ
cient occurrence of the reaction
2 NO + 2 CО
N2 + 2 СО2,
and by an oxygen deficiency for the oxidation of carbon
monoxide in the reaction
2 CО + О2
2 СО2.
The conversion of ethylbenzene in the presence of
oxygen in the 250—360 °С temperature interval increases
from 18 to 47%, and the selectivity with respect to styrene
increases. The low activity of the SR for ethylbenzene
dehydrogenation in a nitrogen flow (see Fig. 7, curve 2)
indicates that styrene is formed, in the presence of oxyꢀ
gen, predominantly via oxidative dehydrogenation.
At temperatures higher than 360 °С, the reaction is
impeded by the deep oxidation of ethylbenzene and styꢀ
rene. At 406 °С, the overall conversion of ethylbenzene
achieves 89%, and only 28.5% are transformed into
styrene.
It should be noted that the temperature at which the 50%
conversion of CO is achieved in gaseous mixture A is
much lower (~200 °C) than that for CO oxidation in the
absence of NOх (~400 °С; see Fig. 3) on the same samples
of the activated SR.
The deep oxidation of oꢀxylene on the SR subjected to
the thermooxidative activation for 6 h begins to occur
with a noticeable rate at temperatures higher than 350 °С,
α (%)
60
The overall conversion of ethylbenzene on the SR is
the sum of its conversions to styrene and products of deep
oxidation. The conversion of ethylbenzene to styrene preꢀ
vails in a region of moderate temperatures, while the deep
oxidation of hydrocarbons predominates at high temperaꢀ
tures.
The conversion and selectivities achieved by the oxiꢀ
dative dehydrogenation of ethylbenzene to styrene on the
SR at a relatively low temperature (at 360 °С, the converꢀ
sion of ethylbenzene is ~50% and the selectivity with
respect to styrene is 80%) are quite comparable with the
average parameters of the industrial process.15 This indiꢀ
cates a principal possibility and advisability to develop an
SRꢀbased natural lowꢀtemperature catalysts for styrene
2
1
3
40
20
4
100
200
T/°C
Fig. 6. Temperature dependences of the conversion (α) of
CO (1, 3) and NOx (2, 4) on the SR in mixtures А (1, 2)
and B (3, 4).

1620
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 8, August, 2004
Lugovskaya et al.
α (%)
S (%)
100
The authors thank G. N. Pirogova (Institute of Physiꢀ
cal Chemistry, Russian Academy of Sciences) for assisꢀ
tance in IR spectroscopic analysis and participation in
discussion of results of the work.
100
3
References
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124 pp. (in Russian).
1
50
50
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2
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200
300
T/°C
Fig. 7. Temperature dependences of the ethylbenzene converꢀ
sion (α) in an air flow (1) and nitrogen (2) and the selectivity of
styrene formation (S) in an air flow (3) on the SR subjected to
thermooxidative activation for 6 h.
7. Eksperimental´nye metody v adsorbtsii i khromatografii [Exꢀ
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Moscow, 1973, 448 pp. (in Russian).
synthesis appropriate for oxidative dehydrogenation or a
combined process.
In addition to metal oxides and noble metals, carbonꢀ
containing materials are known to be active catalysts of
oxidative dehydrogenation (450—700 °С). In particular,
iron oxide supported on active carbon and active carbon
itself are such catalysts.16,17 The temperature of the reacꢀ
tion on carbon is only 350—400 °С. The results obtained
show that in this reaction the optimum temperature of
catalysis (360 °С) corresponds to that observed on carꢀ
bon, indicating a possible activity of the carbon compoꢀ
nent of the SR.
Thus, we demonstrated for the reactions studied that
both the carbon component and foreign oxides of the SR
can likely be responsible for the catalytic activity. The
active surface is formed during the thermoactivation of
the SR. Varying the conditions of the this treatment, one
can control the carbon content in the rock, the degree of
enrichment of the surface with carbon and oxide impuriꢀ
ties, the specific surface, and the size and structure of
pores. This provides challenges for controlling the propꢀ
erties of SRꢀbased catalytic systems.
8. G. N. Pirogova, N. M. Panich, R. I. Korosteleva, Yu. V.
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Schungite rocks can also be used as supports, for inꢀ
stance, for Pt catalysts, to obtain stable catalytic systems
with a high specific activity in CO oxidation. The high
mechanical strength and thermal stability of the SR have
been established previously.10,11 All these data confirm
the necessity of further studies to develop novel catalysts,
including lowꢀtemperature (energyꢀsaving) catalysts, usꢀ
ing the schungite rock as an active phase or support.
Received November 17, 2003;
in revised form May 14, 2004