Thermolysis of Coprecipitated Copper(II)-Nickel(II) Hydroxides

Article abstract of DOI:10.1023/A:1012711025614

Coprecipitated copper(II)-nickel(II) hydroxides and mechanical mixtures of these were obtained at varied metal ion ratio and time of mother liquor aging and studied by potentiometric titration, chemical and differential thermal analyses, IR spectroscopy,

Full text of DOI:10.1023/A:1012711025614

Russian Journal of Applied Chemistry, Vol. 74, No. 1, 2001, pp. 12 17. Translated from Zhurnal Prikladnoi Khimii, Vol. 74, No. 1,
2001, pp. 12 18.
Original Russian Text Copyright
2001 by Kopylovich, Kirillov, Baev.
INORGANIC SYNTHESIS
AND INDUSTRIAL INORGANIC CHEMISTRY
Thermolysis of Coprecipitated Copper(II) Nickel(II) Hydroxides
M. N. Kopylovich, A. M. Kirillov, and A. K. Baev
Lisbon Technical University, Lisbon, Portugal
Belarussian State Technological University, Minsk, Belarus
Received May 4, 2000
Abstract Coprecipitated copper(II) nickel(II) hydroxides and mechanical mixtures of these were obtained
at varied metal ion ratio and time of mother liquor aging and studied by potentiometric titration, chemical and
differential thermal analyses, IR spectroscopy, and X-ray phase analysis.
Hydroxide oxide compounds are widely used as
materials in various fields of science and technology,
in particular, as rather inexpensive and stable catalysts
[1]. For example, it has been shown that systems con-
taining aqua and hydroxo complexes of copper(II) and
nickel(II) are promising catalysts for selective oxida-
tion of alkanes [2 5]. It is also known that some in-
dustrial processes of basic organic and petrochemical
syntheses are performed with copper- and nickel-con-
taining catalysts, including those of the oxide hydrox-
ide type [6 8]. Catalysts of this kind are mainly
obtained by mixing of the appropriate oxides followed
by thermal treatment [9, 10]. However, this method
fails to always yield complex materials with sufficient
reproducibility. Moreover, the ceramic synthesis tech-
nology employs high temperatures, which leads to
energy losses and frequently impairs the catalytic
activity of the synthesized materials. Therefore, co-
precipitation of hydroxides is in some cases a more
promising route to mixed copper nickel systems con-
taining hydroxo and oxo groups [9].
Potentiometric titration was performed with tem-
perature control ( 0.1 C) on a pH-150 pH-meter-
millivoltmeter. Glass electrode of the ESL-15-11 type
and silver chloride electrode of the EVL-1M4 type
served as measuring and reference electrodes, respec-
tively; the pH measurement error was 0.02 pH units.
The titration was done as follows: 1 M NaOH solution
was added from a burette with scale division value of
0.02 ml to the starting mixture of 1 M Cu(II) and
Ni(II) nitrates. To obtained comparable results and
simplify the interpretation of the titration curves, the
added NaOH volume was converted to the molar ratio
2+
[OH
]/[M ].
With account of the potentiometric titration data,
solid phases were isolated by gradually adding to the
starting mixture of 1 M Cu(II) and Ni(II) nitrates, with
continuous stirring, 1 M NaOH solution in a stoi-
chiometric ratio of 1 : 2, respectively. The obtained
solid phases were homogenized for 5 min and filtered
off under a vacuum, washed 3 or 4 times with water
and then i-C H OH to negative reaction for NO ions
3
7
3
[14], dried at 30 40 C in an oven, and analyzed. For
comparison purposes, mechanical mixtures of Cu(II)
and Ni(II) hydroxides (MMHs) were obtained under
identical conditions at the same Cu(II) : Ni(II) ratios
and studied in a similar way. To reveal the effect of
the time of aging of the hydroxide precipitates on
their properties, samples were also synthesized at
Cu : Ni ratio of 1 : 1 and aging time of 24 and 72 h.
The results of previous studies established the for-
mation of unstable heteronuclear hydroxo complexes
of copper nickel in aqueous solutions [11, 12]. It has
been proposed to rely upon this fact in developing a
new synthesis method based on formation in solution
of unstable hydroxo complexes involving metal ions,
passing subsequently into a solid phase which acts as
a precursor for the target materials [13].
In making chemical analysis, a weighed portion of
Apparently, to implement this idea, it is necessary
to study in detail the conditions under which hydrox-
ide precipitates can be obtained, the processes of their
thermal decomposition, and products formed in these
a hydroxide was dissolved in concentrated HNO and
3
analyzed. The total content of copper(II) and nickel(II)
was found complexometrically with murexide; that of
processes by various analytical methods, and just this nickel(II), by direct titration with Na EDTA in am-
2
2+
was the purpose of the present study.
monia buffer with murexide after masking Cu with
1070-4272/01/7401-0012$25.00 2001 MAIK Nauka/Interperiodica

THERMOLYSIS OF COPRECIPITATED COPPER(II) NICKEL(II) HYDROXIDES
thiosulfate ions [15, 16]; and that of copper(II), as the
13
difference of the first two quantities. Differential ther-
mal analysis was done on an MOM derivatograph
1
(Hungary) at a heating rate of 10 deg min and sen-
sitivity of DTA and DTG galvanometers of 1/10;
0.500-g samples were heated from room temperature
to 1000 C, with calcined aluminum oxide used as
reference. The IR spectra (KBr pellets) were taken
on a Specord 75-IR spectrophotometer in the range
1
4000 400 cm . X-ray diffraction patterns of the
samples were taken on a DRON-3 diffractometer with
CuK radiation and Ni filter at a scanning rate of
2 deg min .
Fig. 1. Potentiometric titration curves of aqueous solutions
1
of nitrates of (1) copper(II), (2) nickel(II), and (3 5) mix-
tures of these with varied content of Cu(II). Content of
copper(II) (wt %): (3) 30, (4) 50, and (5) 70.
Figure 1 shows the curves of titration with NaOH
solution of aqueous Cu(II), Ni(II), and Cu(II) Ni(II)
nitrate solutions with varied ratio of metal ions. The
titration curve of a nitrate solution of copper(II) shows
two equivalence points (curve 1). The jump in the
T
2+
pH range 4.3 4.9 at [OH ]/[M ] = 1.5 1.8, with the
2+
equivalence point at pH 7.0, [OH ]/[M ] = 1.7, cor-
responds to complete precipitation of polynuclear
hydroxo complexes of copper(II) [17]. Addition of
2+
alkali to the system at pH 9.45 and [OH ]/[M ] =
1.8 2.3 does not lead to any increase in pH and corre-
sponds to conversion of polynuclear hydroxo com-
plexes into mononuclear hydroxides. On further in-
troduction of OH groups into the system, the hydrox-
ide suffers no changes, and the steep increase in pH
(second jump) is presumably associated with coordi-
nation saturation of metal ions with hydroxide ligands
and appearance of an excess of free OH groups in
solution. In potentiometric titration of nickel nitrate
1
, cm
Fig. 2. IR spectra of hydroxides. (T) Transmission and
( ) wave number. Hydroxide (wt %): (1) 100 Cu; (2) 100
Ni; (3, 4) 30 Cu, 70 Ni; (5, 6) 50 Cu, 50 Ni; and (7, 8) 70
Cu, 30 Ni. (3, 4, 5) CPH and (4, 6, 8) MMH.
two fractions of homopolymers, of a certain amount
of a heteropolynuclear hydroxide precipitate [11, 12].
2+
The results of IR spectral studies of coprecipitated
hydroxides (CPHs) and MMHs (Fig. 2) indicate the
presence in them of various kinds of water. The pres-
ence of a broad band of stretching vibrations of H O
at 3650 3100 cm points to stronger hydrogen bonds
between OH groups. These bands are more intense
and shifted to longer wavelengths in the case of CPHs
(spectra 3, 5, 7), which indicates an additional stabil-
ity of CPHs ensured by the formation of intramolecu-
lar hydrogen bonds between aqua and hydroxo ligands
[18]. Bending (1630 1625 cm ) and rocking (845
830 cm ) vibrations of H O indicate the presence of
coordination-bound water in the compound. As shown
by the IR spectra of nickel(II) and copper(II) hydrox-
ides (Fig. 2, spectra 1, 2), and also by published data
[19, 20], the bands peaked at 1387 1350 cm can be
attributed to bending vibrations of OH groups bonded
to copper(II) and nickel(II) atoms. The absorption
peaks at 1060 1035 and 700 500 cm may belong
to bending vibrations of the bridging M O M bonds
(M = Cu or Ni), and the bands at 400 500 cm cor-
(curve 2) in the pH range 6.1 7.6 at [OH ]/[M ] =
0.0 1.5, mononuclear hydroxides are formed with
minor precipitation. Intense precipitation of Ni(II)
ions coincides with the onset of the jump at pH 7.6,
2
1
2+
with the equivalence point (pH 9.6, [OH ]/[M ]
2.0) corresponding to complete precipitation of nick-
el(II) in the form of polynuclear compounds [12, 15].
The titration curves of a mixture of Cu(II) and
Ni(II) nitrate solutions (Fig. 1, curves 3 5) show three
jumps. The first of these corresponds to precipitation
of polynuclear copper(II) compounds, which is con-
firmed by the close pH values of the equivalence
points of binary solutions and a Cu(II) nitrate solu-
tion. The second jump corresponds to precipitation of
polynuclear nickel(II) compounds, and the third, pre-
sumably, to precipitation of a heteronuclear hydroxide.
It can be seen that despite the similarity of the titra-
tion curves for individual and binary systems, the
latter cannot be considered additive. This fact also
confirms the possibility of formation, together with
1
1
2
1
1
1
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 1 2001

14
KOPYLOVICH et al.
(b)
m, mol H2O
(a)
DTA
DTG
DTA
DTG
TG
TG
T, C
T, C
Fig. 3. Thermogravigrams of (a) CPH and (b) MMH of composition 30% Cu(II) + 70% Ni(II). ( m) Weight loss and
(T) temperature.
respond to stretching vibrations of M O bonds. It
should be noted that the IR spectra of MMHs are
more complex than those of CPHs because of the
splitting of the (H OH) and (H OH) bands into
doublets and triplets (spectra 4, 6, 8). In addition, in
CPHs with the Cu(II) content of 30 and 50% (spec-
1
tra 3, 5), bands of some characteristic vibrations are
1
shifted by 10 30 cm to smaller wave numbers,
which may be due to formation of heteronuclear struc-
tures in the hydroxide precipitate [12].
Table 1. XPA data for products formed in decomposition
of hydroxides of composition 30% Cu(II) + 70% Ni(II)
at 1000 C
To confirm this assumption and determine the con-
tent of water, the obtained CPH and MMH were sub-
jected to thermal analysis. The weight loss curve
dexp
I/I0, %
dref
hkl
Phase
(Fig. 3) was recalculated to moles of H O, which fur-
2
nishes an opportunity to directly analyze the obtained
thermogravigrams of decomposition of the hydroxide
precipitate in terms of stoichiometry. The DTA curve
of CPH of the composition 30% Cu(II) + 70% Ni(II)
(Fig. 3a) shows three endothermic peaks in the in-
tervals 40 240, 240 360, and 360 480 C. The first
endothermic effect corresponds to deaquation with
the loss of 7.23 mol of crystallization water, and the
second and third, to liberation of 3.33 mol of bound
water, equivalent to loss of 6.66 mol of OH groups,
with a mixed oxide formed. An X-ray phase analysis
of this oxide (Table 1) demonstrated the presence of
approximately equal amounts of two complex oxide
phases: Ni CuO (orthorhombic crystal system, a =
Coprecipitated hydroxides
2.426
2.181
2.098
1.482
1.453
1.284
1.262
1.198
100
3
68
42
3
2
11
17
2.426
2.168
2.093
1.479
1.463
1.296
1.262
1.212
101, 031 Ni2CuO3
002
200
220
Cu0.2Ni0.8
O
O
200, 060 Ni2CuO3
103
311
Cu0.2Ni0.8
202, 062 Ni2CuO3
Mechanical mixture of hydroxides
2.755
2.531
2.422
2.332
2.099
1.855
1.483
1.400
1.379
1.315
1.262
1.209
2
9
87
9
100
3
54
2
2
1
18
16
2.751
2.530
2.416
2.323
2.093
1.866
1.479
1.410
1.375
1.304
1.262
1.208
110
002
111
111
200
202
220
311
220
311
311
222
CuO
Cu0.2Ni0.8
CuO
Cu0.2Ni0.8
CuO
Cu0.2Ni0.8
CuO
O
O
O
2
3
2.925, b = 8.775, c = 4.336 ) and Cu Ni
(cubic crystal system, a = 4.217 ).
O
0.2 0.8
A chemical analysis of the obtained hydroxides,
both freshly precipitated and aged for 1 and 3 days
(Table 2), demonstrated that the molar ratios of Cu(II)
and Ni(II) ions in the starting solutions and the hy-
droxides coincide, which points to complete precipita-
Cu0.2Ni0.8
O
1
Here and hereinafter, molar percents.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 1 2001

THERMOLYSIS OF COPRECIPITATED COPPER(II) NICKEL(II) HYDROXIDES
15
Table 2. Data of thermogravimetric and chemical analyses of copper(II) nickel(II) hydroxides
Temperature of endothermic effect, C
II III IV
Weight loss, wt %
CuO: NiO: H2O
molar ratio
Composition, %
I
I
II
III
IV
30 Cu(II) 70 Ni(II):
CPH
40 240
(165)*
40 160 160 260 260 360 360 510
(140) (180) (285)
240 360 360 480
(280) (380)
27.0
(6.66)**
10.0 14.6
(2.18) (3.17) (1.48) (0.74)
11.4
(2.81) (0.89)
6.8 3.3
3.6
42.8 1 : 2.33 : 10.56
35.2 1 : 2.33 : 7.66
MMH
50 Cu(II) 50 Ni(II):
CPH
40 190 190 250 250 350 350 520
(130) (280)
40 140 140 250 250 340 340 520
(170) (280)
12.0
(1.53) (1.22) (1.05) (0.45)
7.0 14.8 7.8 3.0
(0.90) (2.25) (0.66) (0.38)
9.5
8.29
3.8
33.0 1 : 1 : 4.25
32.8 1 : 1 : 4.23
MMH
50 Cu(II) 50 Ni(II),
1 day:
CPH
40 160 160 220 220 330 330 500
(140) (180) (265)
40 160 160 250 250 350 350 500
11.0
(1.42) (1.18) (1.3) (0.35)
10.0 12.0 6.7 3.3
(1.30) (1.56) (0.87) (0.43)
9.2
10.1
2.7
33.4 1 : 1 : 4.3
32.0 1 : 1 : 4.16
MMH
(175)
(290)
(385)
50 Cu(II) 50 Ni(II),
3 days:
CPH
40 240
(140)
240 400
(290)
400 500
18.0
(2.37)
15.2
(2.09) (0.24)
1.8
35.0 1 : 1 : 4.61
70 Cu(II) 30 Ni(II):
CPH
40 155 155 235 235 380 380 500
(180) (260)
40 140 140 240 240 330 330 520
8.1
(1.72) (2.77) (1.87) (0.38)
8.0 16.2 4.4 2.8
(1.69) (3.41) (0.93) (0.59)
12.6
9.3
1.8
31.8 2.33 : 1 : 6.74
31.4 2.33 : 1 : 6.62
28.4 1 : 0 : 1.75
40.0 0 : 1 : 2.77
MMH
(110)
40 140
(155)
140 320
(160)
240 360
(275)
(260)
100 Cu(II)
100 Ni(II)
320 460
6.0
(0.37)
20.8
(1.28)
7.6
(0.47)
4.0
40 240
360 500
(385)
24.8
(1.72)
11.2
(0.75) (0.3)
* Peak temperature.
** Mole of H O.
2
tion of metal ions with the initial component ratio
preserved in the precipitate. In this case, the following
scheme of dehydration of the obtained CPH composed
of 30% Cu(II) + 70% Ni(II) can be proposed:
of copper(II) and nickel(II) hydroxides. No similarity
in amounts of removed water is observed between
CPH and MMH, although the endothermic effects
occur in virtually the same temperature intervals
(Fig. 3). Moreover, the total loss of water is 7.66 mol,
which is 2.9 mol less than in the case of CPH of the
same composition. Thus, the hydroxides, the proc-
esses of their thermal decomposition, and the resulting
products exhibit specific features depending on the
preparation procedure (coprecipitation or mechanical
mixing). An X-ray phase analysis of the products of
decomposition of MMH containing 30% Cu(II) and
70% Ni(II) (Table 2) demonstrated the presence of
CuNi2.33(OH)6.66 7.23H2O
CuNi2.33(OH)6.66
7.23H O
2
0.8(Ni2CuO3 + Cu0.2Ni0.8O).
3.33H O
2
Thermal decomposition of MMH composed of
30% Cu(II) + 70% Ni(II) (Fig. 3b) occurs in a dif-
ferent way. The splitting of the endothermic peak at
40 260 C in two: at 40 160 C with a peak at 140 C
and at 160 260 C with a peak at 180 C, points to
a more complicated nature of deaquation of a mixture
a Cu Ni O phase with minor CuO admixtures
0.2 0.8
(up to 10%), with the Cu Ni O phase probably
0.2 0.8
formed via sintering of CuO and NiO oxides.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 1 2001

16
KOPYLOVICH et al.
d,
d,
Fig. 4. X-ray diffraction patterns of the products of decomposition (T = 1000 C) of (1) copper(II) and (2) nickel(II) hydroxides,
(3, 5 7) copper(II) nickel(II) CPHs, and (4, 8) MMHs. (I/I ) Relative intensity and (d) interplanar spacing. Initial content of
0
copper(II) (wt %): (3 6) 50 and (7, 8) 70; aging time (days): (5) 1 and (6) 3.
Thermogravimetric analysis of CPH and MMH
in the products of its decomposition. For example, an
X-ray diffraction pattern of a product of CPH de-
composition (3 days of aging) shows only a single
containing 50% Cu(II) and 50% Ni(II) also revealed
differences in their dehydration. Despite the close
temperature intervals of the main endothermic effects,
they differ in the amount of removed water. The total
amount of water in CPH somewhat exceeds that in the
corresponding MMH, increasing on passing from an
unaged sample to a hydroxide isolated after 3 days of
aging under mother liquor. This may be due to de-
composition, in the course of precipitate aging, of a
part of heteronuclear copper(II) nickel(II) hydroxide,
accompanied by disintegration of hydroxo bridges and
subsequent aquation of metal ions. Thus, the longer
the time of CPH aging, the smaller the amount of
heteronuclear hydroxide it contains. An additional
argument in favor is the amount of double oxide in-
dicated by X-ray diffraction patterns of the products
of complete decomposition (T = 1000 C) of mixed
hydroxides (Fig. 4). The products of decomposition
of CPH containing 50% Cu(II) and 50% Ni(II) (pat-
terns 3, 5, 6) contain phases of CuO (interplanar spac-
ings 2.530, 2.323, 1.886, and 1.418 ), NiO (2.088,
NiCuO band (2.427 ) with intensity of 49% (pat-
2
tern 6). It should be noted that the X-ray diffraction
patterns of decomposition products of MMH contain-
ing 50% Cu(II) and 50% Ni(II) show no double oxide
phase, with only the CuO and NiO phases present,
which also confirms the occurrence of a chemical in-
teraction between Cu and Ni atoms in CPH formation,
just in the stage of coprecipitation, rather than in that
of thermal treatment.
An X-ray phase analysis of decomposition products
of CPH and MMH containing 30% Cu(II) and 70%
Ni(II) (Fig. 4, patterns 7, 8) demonstrated the presence
of only copper(II) and nickel(II) oxide phases. How-
ever, the thermal behavior of the given CPH and
MMH is not additive with respect to the temperature
intervals of endothermic effects and weight loss
(Table 1), and the total weight loss is practically
the same (31.8 and 31.4%, respectively). This can be
accounted for by the different physical properties
(density, porosity, specific surface area) of the hy-
droxides obtained by coprecipitation and mechanical
mixing [21].
1.476, 1.259 ), and NiCuO (tetragonal crystal sys-
2
tem, a = 4.121, c = 4.355 ) with the main reflections
at 2.427, 1.500, 1.302, 1.251, and 1.213 . With in-
creasing time of aging of the initial CPH, the intensi-
ties of CuO and NiO reflections grow and the signals
Thus, a technique is proposed on the basis of the
investigation performed for obtaining copper(II)
nickel(II) CPH whose thermal treatment can yield new
inorganic materials and, in particular, catalytic sys-
tems applicable in organic and petrochemical syn-
theses. The temperature intervals in which various
kinds of water are removed were determined and dif-
ferences were revealed between the thermal properties
from NiCuO become weaker (2.427, 1.213 ); the
2
reflections at 1.500, 1.302, and 1.251
totally dis-
appear from the X-ray diffraction patterns of the de-
composition products of CPH, subjected to aging for
1 and 3 days (Fig. 4, patterns 5, 6). A correlation is
observed between the increasing time of CPH aging
and the decreasing intensity of signals from NiCuO
2
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 1 2001

THERMOLYSIS OF COPRECIPITATED COPPER(II) NICKEL(II) HYDROXIDES
17
of CPH and MMH whose dehydration occurs under
milder conditions because of the absence of Cu OH
Ni bridge bonds and is accompanied by liberation of
a lesser amount of water. The phase composition of
the products of CPH and MMH decomposition at
T = 1000 C was determined; it was shown that com-
plex oxide compounds Ni CuO , Cu Ni O, and
ticheskie reaktsii uglevodorodov (Activation and
Catalytic Reactions of Hydrocarbons), Moscow:
Nauka, 1995.
8. Berezin, N.V., Denisov, E.T., and Emanuel’, N.M.,
Okislenie tsiklogeksana (Oxidation of Cyclohexane),
Moscow: Mosk. Gos. Univ., 1962.
9. Schwarz, J.A., Chem. Rev., 1995, vol. 95, no. 3,
2
3
0.2 0.8
NiCuO are present together with the CuO and NiO
pp. 477 510.
2
phases. The optimal hydroxide composition [30%
Cu(II) + Ni(II)] was determined at which the yield of
double oxides reaches 100% (Table 1), and the effi-
ciency of preparing these compounds from unaged
CPH was confirmed.
10. Dzis’ko, V.A., Osnovy metodov prigotovleniya katali-
zatorov (Principles of Methods for Catalyst Prepara-
tion), Novosibirsk: Nauka, 1983.
11. Kopylovich, M.N., Baev, A.K., and Chernik, A.A.,
Zh. Neorg. Khim., 1996, vol. 41, no. 10, pp. 1751
1756.
CONCLUSIONS
12. Chernik, E.O., Kirillov, A.M., Kopylovich, M.N., and
Baev, A.K., Abstracts of Papers, XIX Vserossiiskoe
Chugaevskoe soveshchanie po khimii kompleksnykh
soedinenii (XIX All-Russia Tschugaeff Meet. on
Chemistry of Complex Compounds), Ivanovo, June
21 25, 1999, p. 244.
(1) A procedure was developed for synthesizing
coprecipitated copper(II) and nickel(II) hydroxides,
ensuring formation of complex oxide catalysts with
molecular distribution of the components.
13. Kopylovich, M.N. and Baev, A.K., Abstracts of Pa-
pers, Mezhdunarodnaya nauchnaya konferentsiya
Zhidkofaznye sistemy i nelineinye protsessy v khimii i
(2) The optimal composition [30% Cu(II) + 70%
Ni(II)] of hydroxide whose thermal decomposition
gives double oxides in up to 100% yields was deter-
mined.
khimicheskoi tekhnologii
(Int. Scientific Conf.
Liquid-Phase Systems and Nonlinear Processes in
Chemistry and Chemical Technology ), Ivanovo,
September 13 15, 1999, p. 31.
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