New low-temperature preparations of some simple and mixed Co and Ni dispersed sulfides and their chemical behavior in reducing atmosphere

Article abstract of DOI:10.1021/ic026024j

A series of simple (CoS₂, Co₉S₈, NiS₂, NiS, Ni₃S₂) and mixed sulfides (NiCo₂S₄, Ni_0.33Co_0.67S₂, Ni₃Co₆S₈, CuCo₂S₄, Cu_0.33Co_0.67S₂) was prepared using low-temperature procedures. To obtain the mixed sulfides, the mixtures of the solutions of the corresponding salts were precipitated by Na₂S and then heated in a sulfiding atmosphere at 300 °C. It has been found that the product phase composition depends on the sulfiding atmosphere. Using a H₂S/Ar mixture leads to pyrite type sulfides, whereas treatment in H₂S/H₂ flow allowed the preparation of Ni-Co and Cu-Co thiospinels. The as prepared highly dispersed single-phase materials were characterized by X-ray powder diffraction, scanning electron microscopy, temperature-programmed reduction (TPR), elemental analysis, and BET surface area measurements.

Full text of DOI:10.1021/ic026024j

Inorg. Chem. 2003, 42, 1764−1768
New Low-Temperature Preparations of Some Simple and Mixed Co and
Ni Dispersed Sulfides and Their Chemical Behavior in Reducing
Atmosphere
I. Bezverkhyy,* M. Danot, and P. Afanasiev§
,
†
†,‡
Institut des Mat e´ riaux Jean Rouxel, 2 rue de la Houssini e` re, B.P. 32229, 44322 Nantes Cedex 3,
France, and Institut de Recherches sur la Catalyse, 2 aV Albert Einstein, 69626 Villeurbanne
Cedex, France
Received September 11, 2002
A series of simple (CoS
) was prepared using low-temperature procedures. To obtain the mixed sulfides, the mixtures of the
solutions of the corresponding salts were precipitated by Na S and then heated in a sulfiding atmosphere at 300
C. It has been found that the product phase composition depends on the sulfiding atmosphere. Using a H S/Ar
mixture leads to pyrite type sulfides, whereas treatment in H S/H flow allowed the preparation of Ni−Co and
2 9 8 2 3 2 2 4 2 3 6 8 2 4
, Co S , NiS , NiS, Ni S ) and mixed sulfides (NiCo S , Ni0.33Co0.67S , Ni Co S , CuCo S ,
Cu0.33Co0.67S
2
2
°
2
2
2
Cu−Co thiospinels. The as prepared highly dispersed single-phase materials were characterized by X-ray powder
diffraction, scanning electron microscopy, temperature-programmed reduction (TPR), elemental analysis, and BET
surface area measurements.
Introduction
methods allowed the preparation of the simple Co and Ni
sulfides in a highly dispersed form. On the contrary, little
attention was paid to the preparation of highly dispersed
mixed sulfides. With exception of the work of Bouchard8
The sulfides of cobalt and nickel attract significant atten-
tion due to their importance for catalysis. Mixed Ni(Co)-
Mo(W) sulfides are used as the hydrotreating catalysts;
individual Ni and Co sulfides are active in the carbon
reporting on the preparation of poorly crystalline Co
x 2
Ni1-xS ,
1
Fe and Cu solid solutions, no information
x
Co1-x
S
2
x 2
Ni1-xS
liquefaction reaction. High-temperature synthesis of Ni and
is available in the literature. As the most efficient catalysts
Co sulfides from the metals and sulfur gives large crystals
with low specific surface area, which are not suitable for
catalytic applications. Therefore, many soft procedures were
developed in order to increase the sulfides’ dispersity, in-
cluding “homogeneous precipitation”, solvothermal reaction
between the corresponding salts and thiourea, decomposition
1
are always mixed-metal sulfides, development of methods
allowing the preparation of highly dispersed ternary sulfides
is of considerable interest.
Another important question related to the applications of
the mixed sulfides as catalysts concerns their stability under
2
3
4
5
2 2
different reaction conditions, in the presence of H S and H .
of dithiooxamate or diethyldithiocarbamate complexes, or
sulfidation of the hexamine chlorides or sulfates. These
If for the binary sulfides the data are available,9 the be-
havior of mixed sulfides in these conditions was not studied.
In the present work we describe low-temperature prepara-
tion procedures which allow one to obtain dispersions of
different mixed and simple Co- and Ni-containing sulfides.
,10
6
7
*
Corresponding author. Current address: Institut de Recherches sur la
Catalyse, 2 av Albert Einstein, 69626 Villeurbanne Cedex, France. E-mail:
bezver@catalyse.univ-lyon1.fr. Tel: +33 472 44 54 50. Fax: +33 472 44
5
3 99.
†
Institut des Mat e´ riaux Jean Rouxel.
‡
§
E-mail: Michel.Danot@cnrs-imn.fr.
(5) Cui, H.; Pike, R. D.; Kershaw, R.; Dwight, K.; Wold, A. J. Solid State
Chem. 1992, 101, 115.
Institut de Recherches sur la Catalyse. E-mail: afanas@catalyse.
univ-lyon1.fr.
(6) Passaretti, J. D.; Dwight, K.; Wold, A.; Croft, W. J.; Chianelli, R. R.
Inorg. Chem. 1981, 20, 2631.
(7) Pasquariello, D. M.; Kershaw, R.; Passaretti, J. D.; Dwight, K.; Wold,
A. Inorg. Chem. 1984, 23, 872.
(8) Bouchard, R. J. Mater. Res. Bull. 1968, 3, 563.
(9) Chianelli, R. R.; Daage, M.; Ledoux, M. J. AdV. Catal. 1994, 40, 177.
(10) Olivas, A.; Cruz-Reyes, J.; Avalos, M.; Petranovskii, V.; Fuentes, S.
Mater. Lett. 1999, 38, 141.
(
(
(
(
1) Topsøe, H.; Clausen, B. S.; Massoth F. E. Hydrotreating Catalysis;
Springer-Verlag: New York, 1996.
2) Candia R.; Clausen B. S.; Topsøe H. Bull. Soc. Chem. Belg. 1981,
9
0, 1225.
3) Meng, Z.; Peng, Y.; Yu, W.; Quian, Y. Mater. Chem. Phys. 2002, 74,
30.
4) Abboudi, M.; Mosset, A. J. Solid State Chem. 1994, 109, 70.
2
1764 Inorganic Chemistry, Vol. 42, No. 5, 2003
10.1021/ic026024j CCC: $25.00 © 2003 American Chemical Society
Published on Web 02/13/2003

Some Simple and Mixed Co and Ni Dispersed Sulfides
Table 1. Preparation Conditions, Chemical Composition, and Some
Properties of Sulfides Obtained in This Work
BET
surface
crystallite area,
%
metal
annealing
c
2
d
product
NiCo2S4
atm
size, Å
m /g metal obsd calcd
Ni 19.2 19.3
26.6
H2S/H2
243
Co 39.5 38.7
Ni 22.1 22.4
23.5
Ni3Co6S8a
H2S/H2 f H2
H2S/Ar
295
177
346
152
Co 43.9 45.0
Ni 15.3 15.8
22.8
Ni0.33Co0.67S2
CuCo2S4
Co 30.5 32.1
Cu 21.4 20.5
21.8
H2S/H2
Co 38.6 38.1
Cu 16.3 16.9
25.7
Cu0.33Co0.67S2
H2S/Ar
Co 31.4 31.7
Co9S8
CoS2
NiS (millerite)
H2S/H2
H2S/Ar
H2S/H2
259
144
489
526
520
307
49.3
48.6
5.6
2.7
7.1
64.8 67.4
45.0 47.9
63.3 64.7
63.0 64.7
72.8 73.3
46.9 47.8
b
NiS (NiAs type) H2S/H2
a
Ni3S2
NiS2
H2S/H2 f H2
H2S/Ar
Figure 1. XRD patterns of some sulfides prepared in this work: (a)
31.3
NiCo2S4, (b) Ni3Co6S8, (c) CoS2, and NiS (millerite).
a
h in H2S/H2, then 4 h in H2. Prepared at 450 °C. c 300 °C, 4 h, 15
b
4
d
vol % of H2S. Measured after desorption at 300 °C during 15 h.
metal containing solutions are X-ray amorphous. The exact
nature of these materials was not studied here, but it was
previously supposed that the composition of the Co and Ni
sulfides freshly precipitated from the aqueous solution is
2
Chemical behavior of the obtained highly dispersed solids
in H S/H and H S/Ar atmospheres was also studied.
2 2 2
Experimental Section
close to M(OH,SH) , which during further aging transforms
1
1
into a complex mixture of sulfides and basic salts. We have
found that such amorphous precursors can be easily trans-
formed into different sulfides using low-temperature treat-
High purity grade Co(NO
3
)
2
‚6H
2
O, Ni(NO
3
)
2 2 2
‚6H O, and Na S‚
9
H
2
O from Aldrich were used as starting materials in the syntheses
of pure and mixed Co and Ni sulfides. To prepare the Cu-Co
sulfides the Cu(NO ‚3H O and [Co(NH ]Cl were employed.
3
)
2
2
)
3 6
3
ments in H
In the case of a Cu-Co-S system the situation is less
simple. We have found that utilization of Cu(NO ‚3H
and Co(NO ‚6H O does not allow one to obtain a single
phase of mixed sulfides and that mixtures of phases form
after treatment of the precipitate both in H S/H and in H S/
Ar atmospheres. Probably, a significant difference in the
2
S-containing gaseous mixtures.
In a typical preparation, 0.01 mol of the salt or of the mixture of
the corresponding salts was dissolved in 50 mL of water. Fifty
milliliters of the solution containing the stoichiometric amount of
3
)
2
2
O
3
)
2
2
Na
2
2
S‚9H O was then added dropwise at room temperature with
vigorous stirring. The precipitate obtained was thoroughly washed
with water and dried under vacuum at room temperature during 12
h. The as prepared fresh precursors were treated in a flow of 15
2
2
2
-
20
-35
solubility products of CoS and CuS (10
and 10
correspondingly ) provokes the phase separation already
during the precipitation. Utilization of [Co(NH ]Cl as the
2 2 2
vol % H S/Ar or 15 vol % H S/H . The samples were then cooled
1
1
to room temperature in the same atmosphere, flushed with Ar, and
stored in sealed tubes under Ar atmosphere to prevent their
oxidation. The treatment conditions and some properties of the
prepared sulfides are given in Table 1.
3
)
6
3
cobalt source may have allowed the production of a
homogeneous precipitate.
X-ray powder diffraction patterns were recorded on a SIEMENS
D5000 diffractometer using Cu KR radiation (λ ) 1.5406 Å) with
The XRD data show that the prepared sulfides are single-
phase solids having diagrams corresponding to the known
a 0.03° 2Θ scan step. BET surface areas were calculated from N
2
JCPDS patterns (Figure 1). In the case of NiCo
2 4
S and
adsorption isotherm at 78 K measured on a MICROMERITICS
ASAP 2010 instrument. Scanning electron microscopy (SEM)
images were taken on a JEOL 6400 scanning electron microscope.
Temperature-programmed reduction (TPR) was carried out in a
quartz reactor. The sulfide samples (ca. 0.01 g) were linearly heated
under hydrogen flow up to 1000 °C (5 °C/min). Hydrogen sulfide
evolved during reduction was detected by an HNU photoionization
detector equipped with a 10.2 eV UV light source. The amount of
CuCo the positions of the XRD peaks give direct evidence
2 4
S
for the formation of the mixed sulfides. In the case of the
pyrite-type solid solutions the conclusion is not straightfor-
ward, because low crystallinity of these compounds makes
impossible precise determination of their cell parameters.
Thus, taking into account the closeness of the cell parameters
of the individual components (NiS , CuS , and CoS ), the
2
2
2
2
H S evolved was quantified after the detector was calibrated with
formation of mixed sulfides cannot be directly proven.
However, in this case formation of the solid solutions might
be inferred from the chemical behavior of the solids. Indeed,
a gas mixture of known H S concentration. The chemical analysis
2
of the sulfides were performed in the Central Analysis Service of
National Center for Scientific Research (Vernaison, France).
both solids Ni0.33Co0.67
S
2
and Cu0.33Co0.67
S
2
can be easily
transformed into the corresponding thiospinels after treatment
Results and Discussion
Composition, Structural and Textural Properties. The
(11) Jellinek, F. Sulphides. In Inorganic Sulphur Chemistry; Nickless, G.
precipitates obtained after addition of Na
2
S to the transition
Ed.; Elsevier: New York, 1968.
Inorganic Chemistry, Vol. 42, No. 5, 2003 1765

Bezverkhyy et al.
Figure 2. Scanning electron microscopy photographs of (a) NiS (NiAs
type), (b) NiS (millerite), and (c) Co9S8 (scale bar is 100 nm).
2 2
at 300 °C under H S/H atmosphere during 4 h (see below).
Such mild conditions of phase transformation suggest
homogeneous distribution of the elements in the precursor.
The crystallite sizes calculated from the peak widths
according to the Sherrer equation12 show that the degree of
crystallinity depends on the nature of the sulfide (Table 1).
Poorly crystalline materials are obtained for the simple and
mixed sulfides having the pyrite structures. Nearly the same
Figure 3. Temperature-programmed reduction (TPR) patterns of (a) Co S ,
9 8
(b) CuCo2S4, and (c) NiCo2S4.
Table 2. The Products Obtained from the Precipitates vs the Gaseous
Mixtures Used
2
crystallite size was reported previously for CoS prepared
product obtained at 300 °C
6
in a different way (150 Å after heating at 300 °C ). The
binary nickel sulfides have the largest crystallites, showing
nearly the same crystallite size regardless of the preparation
temperatures (300 °C for millerite and 450 °C for the
hexagonal NiS). The ability of nickel sulfides to form well-
crystallized materials under mild conditions was observed
previously. For example, it has been found that the reaction
precursor
15% H2S/Ar
15% H2S/H2
H2b
Co9S8
Co-S
Ni-S
CoS2
NiS2
Co9S8
NiS (millerite)
NiS (NiAs type)a
NiCo2S4
Ni3S2
Ni-Co-S
Cu-Co-S
Ni0.33Co0.67S2
Cu0.33Co0.67S2
Ni3Co6S8
Cu2S+Co9S8
CuCo2S4
a
At 450 °C. b After a sulfiding treatment (H2S/Ar or H2S/H2).
between NiCl
2
and Na
2
S
2
O
4
in aqueous solution at pH ) 6
particles already at room tem-
Thus, the excess sulfur observed in our case is due to the
surface rather than a bulk overstoichiometry. In the case of
leads to well-defined Ni
3
S
2
1
3
perature.
Co
means of reaction with hydrogen without any change in the
structure. The reaction is clearly seen in the Co TPR
9 8
S these surface species can be easily eliminated by
The developed low-temperature procedures allowed the
preparation of well-dispersed solids having high surface areas
9 8
S
(Table 1), whereas traditional preparations from elements
pattern in which the peak at ca. 270 °C corresponds to the
elimination of such species (Figure 3a).
Chemical Behavior. The chemical behavior of the dis-
persed sulfide precipitates in different atmospheres is sum-
marized in Table 2. The general feature of all the systems
studied is that the treatment of the amorphous precursors in
in sealed evacuated silica tubes do not allow one to attain
surface areas exceeding 3-5 m /g. Comparison between the
SEM images of Co S and nickel sulfides reveals clearly the
9 8
difference in the texture of these materials (Figure 2).
Regardless of the difference in the preparation temperature,
both Ni sulfides consist of large particles (about 100-200
nm) forming compact agglomerates (Figure 2a,b). The
9 8
crystallites of Co S are much smaller (ca. 10-20 nm) and
packed less tightly, thus providing the material a high
intercrystalline surface area.
2
H
2
S/Ar (15 vol %) atmosphere leads to formation of pyrite-
type structures. The Co pyrite solid solutions were
also prepared previously in H
x
Ni1-xS
2
2
S/N
metal hydrated sulfates, and CoS
Co(NH Cl under pure H
indicate that in pure H S or in H
2
≈ 1 flow from the mixed-
8
2
was shown to form from
S at 250 °C. These similarities
6
3
)
6
2
2
The chemical compositions of the sulfides correspond well
2
2
S/Ar mixture independently
to the simple stoichiometry, with the exception of Co
CoS . By contrast, all the Ni-containing sulfides show lower
metal to sulfur atomic ratios (Table 1). For Co , deviation
9 8
S and
of the nature of the precursor the most stable structure for
simple and mixed Co and Ni sulfides is pyrite.
2
9 8
S
However, in hydrogen atmosphere (with or without H
2
S)
from the stoichiometry was previously reported. For example,
after annealing at 600 °C, the composition of the Co sulfide
was found to be Co
by the presence of weakly bound surface sulfur species. Their
amount might be considerable due to the high specific surface
area of the simple cobalt sulfides and therefore high share
of superficial atoms in the total amount of matter. Such
species are often observed on the surface of highly dispersed
all the pyrite-type sulfides are unstable and easily transform
2
-
5
into sulfides containing S anions, the particular structure
depending on the metals involved.
9
S8.3. Such a deviation can be explained
Simple Co and Ni Sulfides. In the case of nickel, single
phases of all the known sulfides can be obtained from the
same amorphous sulfide precursor, depending on the condi-
tions (Table 2). The millerite phase can be prepared at 300
°C in H S/H flow. The same treatment at higher tempera-
1
4
2
2
2
sulfide catalysts prepared in H S-containing atmosphere.
tures leads to the formation of NiS with the hexagonal (NiAs-
(12) Klug, H. P.; Alexander, L. E. X-ray diffraction procedures; Wiley:
New York, 1974.
(14) Calais, C.; Matsubayashi, N.; Geantet, C.; Yoshimura, Y.; Shimada,
(13) Jeong, Y. U.; Manthiram, A. Inorg. Chem. 2001, 40, 73.
H.; Nishijima, A.; Lacroix, M.; Breysse, M. J. Catal. 1998, 174, 130.
1766 Inorganic Chemistry, Vol. 42, No. 5, 2003

Some Simple and Mixed Co and Ni Dispersed Sulfides
type) structure. Thus, after the heating at 400 °C during 4 h
ca. 70% of millerite is transformed into NiAs-type NiS,
which is obtained pure after treatment at 450 °C. Alterna-
pound was not previously described, but its stability can be
anticipated since in Ni Co the average atomic number of
the cations (27.33) is in the range 26.5-27.5 for which the
3
6 8
S
1
8
tively, the Ni
from millerite through a post-treatment in pure H
transformation is reversible: heating of Ni in H S/H
2
S
3 2
compound (hazelwoodite) can be prepared
. This
flow
pentlandite structure was found to be stable.
2
The consecutive steps of reduction of the mixed sulfides
can be easily followed by the TPR method (Figure 3b,c). In
the TPR patterns, which describe the complete reduction of
the sulfides to the metals, the first peaks correspond to the
low-temperature transformations. The areas of these peaks
S
3 2
2
at 300 °C allows the restoration of the NiS composition and
the millerite structure. Finally, above 500 °C, reduction to
metallic Ni occurs under H
ment.
2
as shown by the TPR experi-
(related to the amount of H
2
S evolved during the reaction)
) of the whole
represent 34% (NiCo ) and 45% (CuCo S
2
S
4
2 4
The experimentally observed chemical behavior of the
nickel sulfides agrees well with the corresponding thermo-
dynamical data (see Supporting Information). Whereas reduc-
surface under the curves, which corresponds well to the part
of the sulfur eliminated according to the equations (33% for
NiCo
S
2 4
and 43% for CuCo
2 4
S ):
2 2
tion of both NiS and NiS is favorable, the presence of H S
in the gaseous atmosphere allows stabilization of the
intermediate composition: NiS.
3
NiCo S + 4H f Ni Co S + 4H S
(1)
2
4
2
3
6
8
2
The treatment of the Co-S precipitate in H
sphere at 300 °C results in the formation of Co
also remains intact in pure H . Contrary to the mixed
Ni-Co and Cu-Co sulfides (see below), the thiospinel Co
did not form in our experiments. In order to clarify the
stability of this compound it was prepared from the cobalt
and sulfur in a silica sealed tube at 600 °C. It was then found
2
S/H
2
atmo-
18CuCo S + 31H f 4Co S + 9Cu S + 31H S (2)
2 4 2 9 8 2 2
9 8
S , which
We have also found that the transformation of the Ni-
Co thiospinel into the pentlandite-like phase is reversible:
2
3 4
S
heating of Ni
thiospinel:
3
Co
S
6 8
in H
2
S/H
2
flow leads to the initial
Ni Co S + 4H S f 3NiCo S + 4H
2
(3)
3
6
8
2
2
4
that Co
However, in pure hydrogen, it transforms readily into Co
According to the thermodynamical data (see Supporting
3 4 2 2
S is stable in H S/H atmosphere at 300 °C.
9 8
S .
Though the catalytic properties of the thiospinels in the
hydrodesulfurization cannot be studied due to their low
Information), under hydrogen CoS
2
can be reduced to Co
to Co
3
S
S
4
stability under reduced H S pressure, the data on the chemical
behavior of the mixed sulfides can be correlated with some
2
or to Co . On the contrary, the reduction of Co
S
9 8
3
S
4
9
8
observed under hydrogen flow at 300 °C should not proceed
taking into account the very small value of the corresponding
assumptions made about the properties of Co sulfide species
present in the hydrotreatment catalysts. One of them concerns
the oxidation state of the Co cations in the Co-Mo-S phase
-
45
equilibrium constant (K
a
) 2.23 × 10
at 600 K). This
1
9
discrepancy is likely due to the fact that under hydrogen flow
the conditions cannot be considered to correspond strictly
to equilibrium.
which was supposed to be higher than II. The stability of
the thiospinels Co S , CuCo S , and NiCo S , containing
3
4
2
4
2 4
formally Co(III), in H S/H atmosphere shows that in
2
2
Mixed Ni-Co and Cu-Co Sulfides. Heating of mixed
Ni-Co and Cu-Co amorphous precursors as well as of the
principle the Co atoms could really preserve in CoMoS
catalysts an oxidation degree greater than II despite the highly
reducing character of the gaseous medium involved in the
hydrodesulfurization reaction.
It also was suggested that the ability of the Co and Ni
atoms to change reversibly their coordination sphere and
electronic configuration can play a key role in the catalytic
desulfurization of sulfur-containing molecules.20 The easy
pyrite solid solutions under H
the formation of NiCo and CuCo
established previously that these thiospinels are direct,
2
S/H
2
flow at 300 °C leads to
2
S
4
2 4
S
(Table 2). It was
1
5,16
i.e., the cobalt atoms occupy octahedral sites and Ni or Cu
tetrahedral ones in the hexagonal close packing of the sulfur
atoms. Taking into account that these compounds formally
contain Co(III), their formation under the highly reducing
2 4
transformation of the spinel NiCo S into the pentlandite
H
2
S/H
2
atmosphere could not be predicted a priori. The
Ni Co and vice versa in a reducing atmosphere is an
3
6 8
S
stability of the mixed cobalt thiospinels means therefore that
the d electronic configuration could provide a high stability
to octahedrally surrounded Co(III) not only in the low-spin
complexes with strong donor ligands but also in sulfide
environment within an extended solid phase.
example of such a phenomenon. The rearrangement of the
anionic environment of the Co cations coupled to the change
of their electronic state observed in this bulk phase trans-
formation should naturally be much easier when the same
atoms are located on the surface of the sulfide catalysts.
6
However, this stability is not sufficient to prevent the
transformation of Cu-Co and Ni-Co thiospinels in pure
Conclusions
It is shown that a simple coprecipitation reaction in
aqueous solution can be used as an efficient synthetic method
H
2
at 300 °C. CuCo
NiCo also loses sulfur, but it transforms into a new phase
Ni Co
having a pentlandite-type structure.17 This com-
2 4 9 8 2
S decomposes into Co S and Cu S;
2 4
S
S
6 8
3
(17) Knop, O.; Huang, C.-H.; Reid, K. I. G.; Carlow, J. S.; Woodhams, F.
W. D. J. Solid State Chem. 1976, 16, 97.
(
15) Knop, O.; Reid, K. I. G.; Sutarno; Nakagawa, Y. Can. J. Chem. 1968,
6, 3463.
16) Miyatani, K.; Tanaka, T.; Ishikawa, M. J. Appl. Phys. 1998, 83, 6792.
(18) Knop, O.; Ibrahim, M. A. Can. J. Chem. 1961, 39, 297.
(19) Smit, T. S.; Johnson, K. H. Catal. Lett. 1994, 28, 361.
(20) Startsev, A. N. Catal. ReV.sSci. Eng. 1995, 37, 353.
4
(
Inorganic Chemistry, Vol. 42, No. 5, 2003 1767

Bezverkhyy et al.
for the preparation of highly dispersed mixed metal sulfides.
The proper choice of the sulfiding atmosphere allows a
control over the structure and composition of the solids. In
The treatment of NiCo
into a new pentlandite-type phase Ni Co S .
3 6 8
2
S
4
in H
2
leads to its transformation
Supporting Information Available: Table containing equilib-
rium constants for the reactions of simple Co and Ni sulfides with
hydrogen at 600 K. This material is available free of charge via
the Internet at http://pubs.acs.org.
H
2
S/Ar atmosphere the pyrite structure is the most stable
for the mixed Ni-Co and Cu-Co systems as well as for
simple Co and Ni sulfides. The thiospinels NiCo and
CuCo have been synthesized for the first time in poorly
crystalline state in reducing atmosphere (H S/H , 300 °C).
2 4
S
2 4
S
2
2
IC026024J
1768 Inorganic Chemistry, Vol. 42, No. 5, 2003