Synthesis of cement-containing nickel-copper catalytic systems using formic acid aqueous solutions

Article abstract of DOI:10.1023/A:1020350210508

Regular trends in the formation of phase composition, structure, and mechanical strength of nickel-copper catalysts used for treatment of process and off-gases were considered in relation to the concentration (5.0-60.0 wt %) of formic acid aqueous solutions used in their preparation. The optimal conditions of the preparation process were determined.

Full text of DOI:10.1023/A:1020350210508

Russian Journal of Applied Chemistry, Vol. 75, No. 5, 2002, pp. 745 751. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 5,
002, pp. 763 769.
Original Russian Text Copyright
2
2002 by Efremov, Tesakova, Mamaeva, Golosman.
CATALYSIS
Synthesis of Cement-Containing Nickel Copper Catalytic
Systems Using Formic Acid Aqueous Solutions
V. N. Efremov, G. M. Tesakova, I. A. Mamaeva, and E. Z. Golosman
Novomoskovsk Institute of Nitrogen Industry, Novomoskovsk, Tula oblast, Russia
Received September 25, 2001; in final form, February 2002
Abstract Regular trends in the formation of phase composition, structure, and mechanical strength of
nickel copper catalysts used for treatment of process and off-gases were considered in relation to the concen-
tration (5.0 60.0 wt %) of formic acid aqueous solutions used in their preparation. The optimal conditions
of the preparation process were determined.
In modern industrial installations, oxygen is re-
moved from process gases with platinum and palladi-
um catalysts, the use of which is limited by high cost
and short supply of these metals. A series of NKO-
type cement-containing nickel copper catalysts were
catalytic systems [7 14], and for regenerating dead
catalysts [15 18].
EXPERIMENTAL
1
developed [1] for a wide range of catalytic processes,
As the raw material we used substances applied in
the synthesis of cement-containing nickel-copper
catalytic systems: nickel(II) (NSC) and copper(II)
in which PK and APK catalysts with platinum and
palladium active components are the most active. As
opposed to these catalysts, the use of NKO-type cata-
lysts requires their preliminary reduction by a hy-
drogen-containing gas at 350 450 C. In some cases it
is difficult to provide such temperatures in the exist-
ing installations.
(
CSC) subcarbonates, and technical-grade calcium
aluminate (talum), which is a mixture of calcium
monoaluminate (CaO Al O , CA) and dialuminate
2
3
(CaO 2Al O , CA ). Samples were synthesized by
2 3 2
mixing the initial components in the presence of
formic acid aqueous solution, the concentration of
which was varied within 5.0 60.0 wt %. The mixing
The goal of this work was to develop a mechanical-
ly strong and highly active nickel copper catalyst,
which can be activated in an inert medium at low
temperatures (180 280 C).
(liquid : solid ratio from 1 : 1 to 1.5 : 1) was carried
out at 60 80 C. The catalyst mass with 15 20%
moisture content was dried at 100 C, crushed, and
pressed at 650 MPa into cylindrical pellets 6.0 mm
in diameter and 5.0 mm high.
There are various procedures for the preparation of
nickel copper catalytic systems. These procedures
mainly consist in deposition of an active component
on a support by impregnation, coprecipitation, or
fusion of catalyst components and mixing active com-
ponents with the support.
The X-ray phase analysis (XPA) of the samples
was carried out on a DRON-2 diffractometer with
CuK radiation, and the thermogravimetric analysis,
on a Q-1500 D derivatograph. The stages of phase
formation in inert media were studied in the linear
heating mode on a thermochromatographic installa-
tion. The specific surface area was measured on a
Tsvet-211 device by thermal desorption of argon.
The mechanical strength was determined by crushing
granules with application of load on their faces. The
catalytic activity in oxygen hydrogenation was studied
under atmospheric pressure on a laboratory flow-
through installation with a four-channel reactor. The
Published data on the use of salts of carboxylic
acids and of carboxylic acids themselves as liquid
reagents in catalyst production suggest the possibility
of obtaining supports and also high-performance
catalysts that are activated at low temperatures (150
2
50 C) in a stream of inert gases.
There are three main directions of using carboxylic
acids in catalyst production: for preparing high-per-
formance catalyst supports [2 6], for synthesizing
input gas mixture contained 2.0 vol % O , 6.0 vol %
2
H , and remainder argon. The tests of the catalytic
2
1
Developed at the Novomoskovsk Institute of Nitrogen Industry.
activity were carried out at the space velocity of
1
070-4272/02/7505-0745$27.00 2002 MAIK Nauka/Interperiodica

746
EFREMOV et al.
position of nickel formate, which passes at a high rate,
as shown by the intensity of the second peak. The fur-
ther heating of the sample in the oxidizing atmosphere
results in oxidation of the formed nickel (370 C).
Copper formate (Fig. 1, curve 1) decomposes in one
stage (180 C). The resulting metallic copper is oxi-
dized first to Cu O (220 C) and then to CuO (355 C).
2
It is known [19] that salts of carboxylic acids and,
in particular, nickel and copper formates decompose
in oxidant-free media to give metals. The decomposi-
tion of these salts is exothermic and occurs with a
high rate at relatively low temperatures.
T, C
The decomposition temperature of formates can be
considerably lowered [20] by adding a formate with a
lower decomposition temperature. The decomposition
of a mixture of Ni(II) and Cu(II) formates (Fig. 1,
curve 3) is characterized by two intensive exothermic
peaks. The exothermic effect at Tmax = 180 C is due
to decomposition of Cu(HCOO) and dehydration of
2
max
Ni(HCOO) 2H O, and that at T
= 215 C, to de-
2
2
composition of Ni(HCOO) . Thus, the presence of
2
copper formate in a sample decreases the decomposi-
tion temperature of nickel formate from 290 to 215 C.
At the same time, it cannot be ruled out that a double
Cu(II) and Ni(II) salt such as CuNi(HCOO) 2H O
can form under the experimental conditions of pro-
cessing the NSC and CSC mixture [21]. This salt can
also decompose in two stages.
T, C
2
2
Fig. 1. DTG curves of samples treated with 40% aqueous
solution of formic acid: (1) CSC, (2) NSC, (3) 50 wt %
CSC + 50 wt % NSC, (4) CaCO , (5) -Al O , and (6) tal-
3
2 3
um. (T) Temperature; the same for Fig. 2.
To understand phase formation processes occurring
in the course of the synthesis of cement-containing
nickel copper catalytic systems, we studied samples
obtained by treatment of active aluminum oxide,
1
6
000 h . The degree of oxygen conversion was taken
as a measure of the catalytic activity.
The characteristic decomposition temperature of
the initial NSC NiCO 2Ni(OH) 4H O is 320 C.
The specific surface area of NiO obtained by NSC
CaCO , and calcium aluminate with a 40% aqueous
3
3
2
2
solution of formic acid. The DTG curves of these
samples are shown in Fig. 1. The experimental data
indicate that treatment of aluminum oxide and CaCO3
with HCOOH yields anhydrous aluminum and calci-
um formates (Fig. 1, curves 4, 5). In the case of treated
talum (curve 6), the peak at 300 C corresponding to
the decomposition of aluminum formate prevails.
Furthermore, two exothermic peaks were recorded at
2
1
calcination does not exceed 40 m g . The com-
pound CuCO Cu(OH)2 (CSC) decomposes at
Tmax = 280 C to CuO, which has disordered crystal
lattice and specific surface area of no more than 10
3
2
1
2
0 m g .
According to the XPA data, treatment of the
initial NSC with formic acid gives nickel formate
Ni(HCOO) 2H O, and treatment of CSC, anhydrous
3
50 and 420 C, which are characteristic of the calci-
um formate decomposition. The endothermic peak at
2
2
7
90 C corresponds to the decomposition of CaCO3
copper formate Cu(HCOO) .
2
formed by calcium formate thermolysis. The effect of
heat treatment on the specific surface area of talum
Ssp (m g ) treated by aqueous solution of formic
acid is given below.
Figure 1 shows the rates of the weight loss by
samples of NSC, CSC, and their mixture (50 wt %
NSC 50 wt % CSC) treated with 40% aqueous solu-
tion of formic acid under conditions similar to the
conditions of the synthesis. Nickel formate decom-
poses in two stages (Fig. 1, curve 2). The first stage
2
1
This dependence passes through a maximum
2
1
(140 m g ) at 280 C. When preparing cement-
containing nickel copper catalytic systems (25 wt %
NiO 10 wt % CuO 65 wt % talum), we found that, at
(
230 C) corresponds to the loss of water of crystalli-
zation, and the second (290 C), to exhaustive decom-
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 5 2002

SYNTHESIS OF CEMENT-CONTAINING NICKEL COPPER CATALYTIC SYSTEMS
747
2
S , m g
sp
1
T,
C
1
50
5.0
10.0
25.0
2
2
2
2
3
3
4
00
20
50
80
00
50
00
70.0
140.0
135.0
80.0
45.0
room temperature, the reaction of a mixture of the ini-
tial components (NSC + CSC + talum) with an aque-
ous solution of formic acid occurs at a relatively low
rate, which reaches a maximum at 70 75 C. This
temperature is optimal for the reaction of the mixture
of components and also of each component separately
with an aqueous solution of formic acid. For compari-
son, we prepared a catalyst sample (no. 1) using dis-
tilled water. The experimental data obtained by deriva-
tography (Fig. 2) and by X-ray phase analysis allowed
us to subdivide the samples under study in three
groups depending on the concentration (%) of formic
acid aqueous solution used in the stage of mixing:
T, C
Fig. 2. DTG curves of catalyst samples prepared using
aqueous solutions of formic acid. HCOOH concentra-
tion (%): (1) 0, (2) 5, (3) 20, and (4) 30.
Metal subaluminates can contain various anions
2
replacing their OH groups [22], e.g., CO , NO ,
3
3
etc. The formula of SA-I in the general form can be
written as MAl (OH) (M = Ni, Cu, Zn, Mg, etc.),
2
8
and the formula of SA-II, as MAl (OH)8 x(HCOO)x,
2
i.e., as a metal subaluminate formate.
A number of well pronounced effects due to the
decomposition of SA-II-type compounds and also of
Ni(II) and Cu(II) formates were detected in the range
no. 1, H O, no. 2, 5.0, and no. 3, 10.0 (first group);
2
no. 4, 15.0, no. 5, 20.0, no. 6, 25.0, and no. 7, 30.0
(
second group); and no. 8, 40.0, no. 9, 50.0, and
1
20 280 C for sample no. 5 (Fig. 2, curve 3).
no. 10, 60.0 (third group).
The further increase in the acid concentration to
0% (Fig. 2, curve 4) results in preferential formation
of compounds such as SA-II, i.e., of Ni(II) and Cu(II)
subaluminoformates. Furthermore, in this sample the
amount of the formed Ni(II), Cu(II), Al(III), and
Ca(II) formates increased, and a certain amount of
The study of thermal transformations of the sam-
ples (Fig. 3) allowed us to establish the sign of ther-
mal effects, determine a mode of heat treatment, and,
using also the XPA data, identify phases formed in
the course of the preparation. Thermal transformations
of all the samples under study involve weight loss, its
value increasing as the concentration of HCOOH is
increased. The XPA data show that sample no. 2 is
almost identical to sample no. 1. The phase composi-
tion of these samples includes NSC and CSC, mixed
nickel and copper subaluminate, CuO, CaO Al O ,
3
NSC, CA, CA , CuO, and CaCO was present.
2
3
The phase composition of sample no. 8 contains
mainly Ni(II), Cu(II), Al(III), and Ca(II) formates;
only small amounts of Ni(II) and Cu(II) subaluminate
formates were detected. The use of a 50% aqueous
solution of the acid (sample no. 9) promotes the for-
mation of Ni(II), Cu(II), Al(III), and Ca(II) formates.
The further increase in the acid concentration to 60%
does not affect the phase composition. The phase of
2
3
CaO 2Al O , and a minor amount of nickel, copper,
2
3
aluminum, and calcium formates (for sample no. 2).
The increase in the HCOOH concentration to 10%
(
sample no. 3) results in increased conversion of the
initial components. Sample no. 5 prepared by treat-
ment with 20% HCOOH solution considerably differs
in the phase composition from the previous samples.
In its phase composition, two types of nickel and
copper subaluminates dominate: (1) standard Ni(II)
and Cu(II) subaluminates (SA-I) having basic inter-
planar spacings d = 7.6 and d = 3.8 , respectively;
CaCO , which is a product of the exchange reaction
3
of NSC and CSC with talum in the mixing stage, was
detected in all the samples. The heat treatment of the
samples increases the content of this phase. An addi-
tional amount of CaCO is formed as a result of the
3
decomposition of Ca(II) formate.
(2) Ni(II) and Cu(II) subaluminates differing from
One of the main stages in formation of an active
standard subaluminates by the fact that their structure catalytic structure is the catalyst activation, and
contains an additional anion (HCOO) (SA-II). They
such characteristics as catalytic activity, mechanical
are characterized by the basic interplanar spacings strength, and service life depend on the conditions of
d = 11 and d = 5.5 , respectively. this stage.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 5 2002

748
EFREMOV et al.
inert gas stream. The temperature-programmed reduc-
(a)
Irel
tion data well correlate with the data of the X-ray
phase and thermal analyses.
After activation, samples were cooled in a helium
stream to room temperature and then heated in a hy-
drogen stream in a linear heating mode (Fig. 3b). For
comparison, we studied simultaneously sample no. 1
prepared with distilled water. At temperatures below
3
00 C, no effects corresponding to the reduction of
active components were detected, which suggests that
the catalysts were completely activated in the inert gas
stream. For all the sample under study, the curves of
temperature-programmed reduction in hydrogen con-
tain a single strong peak in the range 350 550 C,
which corresponds to the low-temperature catalytic
decomposition of calcium carbonate [23]. The shift of
Tmax of decomposition of this phase, as compared to
this effect in sample no. 1, results from the presence of
dispersed nickel and copper with a highly developed
surface in all the samples except for sample no. 1.
T, C
(b)
Irel
The specific surface area, mechanical strength, and
catalytic activity of samples reduced with hydrogen
are given in the table. We chose the activation tem-
peratures taking into account the data of the ther-
mogravimetric, X-ray, and thermochromatographic
analyses.
T, C
Products of the talum hydration and of its reaction
with nickel and copper subcarbonates, and partially
products of the decomposition of nickel and copper
formates make the major contribution to the surface
area development in sample no. 2, whereas in sample
nos. 4 10 these are products of the decomposition of
nickel and copper subaluminoformates (SA-II) and
subaluminates formates (SA-I). In these samples the
specific surface area, which was measured by argon
thermal desorption on a Tsvet-211 instrument, is the
total active surface area of nickel and copper. The fact
that this surface area mainly corresponds to the active
components is confirmed by the data on the surface
area of talum treated with a 40% aqueous solution of
formic acid and calcined in an inert medium at 240 C.
Fig. 3. Thermochromatograms of catalyst samples prepared
using aqueous solutions of formic acid and activated in
(
(
(
a) helium and (b) hydrogen. (I ) Relative intensity and
T) temperature. Concentration of HCOOH (%): (1) 5,
2) 30, (3) 40.
rel
We studied reduction of the samples on a ther-
mochemical installation allowing temperature-pro-
grammed reduction in various gas media and tempera-
ture modes. The curves of temperature-programmed
1
reduction at linear heating rate of 5 deg min , ob-
tained in helium and hydrogen streams, respectively,
are shown in Figs. 3a and 3b. These data show that
the thermolysis of samples in a helium stream is in
fact the stage of their activation. This process, which
occurs in the range 125 400 C, is multistage. We can
subdivide the samples under study into three groups
with respect to the nature of activation. Sample
nos. 2 and 3 comprise the first group, for which
the main activation process takes place in the range
2
1
The Ssp of this sample does not exceed 10 15 m g .
When developing new catalysts and improving
available catalysts, a special attention is given to their
strength properties principally determining their ser-
vice life. The greatest decrease (30 50%) in the mech-
2
00 400 C with a rather small intensity. The second
group (sample nos. 4 and 5) is characterized by oc- anical strength takes place during activation of cata-
currence of the activation in three stages (130 170,
00 300, and 300 400 C). In the third group, the
activation is more intense and involves two stages
170 190 C and 215 225 C), corresponding to the
decomposition of nickel and copper formates in an
lysts. This is due to phase transformations causing
changes in their crystalline and porous structures. Our
experimental data on the mechanical strength of both
starting samples and samples activated in an argon
stream at 180 C are given in the table.
2
(
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 5 2002

SYNTHESIS OF CEMENT-CONTAINING NICKEL COPPER CATALYTIC SYSTEMS
749
Specific surface area Ssp of samples, their mechanical strength P, and degree of oxygen conversion at various activation
temperatures Ta in argon stream
2
1
S , m g , at indicated T ,
C
P, MPa
, %, at indicated T , C
a
sp
a
Sample
no.
cHCOOH, wt %
180
240
280
380
initial
at 180 C
150
160
180
1
2
3
4
5
6
7
8
9
0
5.0
100
145
5
25
20
45
45
90
85
110
155
30
30
45
60
70
100
95
100
120
120
65
70
95
105
100
155
95
120
125
95
145
105
150
145
120
90
29
35
60
32
15
55
90
93
50
23
8
0
5
5
5
7
10
10
12
15
15
0
12
15
18
22
28
30
32
35
35
0
50
80
100
100
100
100
100
100
100
10.0
15.0
20.0
25.0
30.0
40.0
50.0
60.0
73
100
105
58
42
30
3
2
1
0
110
100
80
28
The catalytic activity in oxygen hydrogenation was
determined at a space velocity of 6500 h . The work-
composition of this sample on its heating in air and
argon flows, using a GPVT-1500 high-temperature
X-ray camera. The phase composition of the initial
catalyst sample includes Ni(II) subcarbonate, Ni(II)
and Cu(II) subaluminates, mixed Ni(II) and Cu(II)
subaluminoformate, Ni(II), Cu(II), Al(III), and Ca(II)
1
ing gas mixture contained 2.0 vol % O , 6.0 vol %
2
N , and the remainder Ar. The catalytic activity of the
2
samples was judged from the degree of oxygen con-
version (see table). Prior to the experiments, the sam-
ples were activated at 150, 160, and 180 C for 1 h in
formates, and also CuO, CA, and CA phases. The
2
1
heating to 100 C results in the decomposition of
mixed Ni(II) and Cu(II) subaluminoformate to mixed
Ni(II) and Cu(II) subaluminate. This phase transfor-
mation results in a considerable increase in the in-
tensity of reflections of mixed Ni(II) and Cu(II) sub-
aluminate in the X-ray pattern. The heating to 175 C
promotes partial decomposition of formates. At the
same temperature, Ni(II) and Cu(II) subaluminates
start to decompose with the removal of interlayer
water, as indicated by the shift of the SA-I lines to
larger angles (d = 7.2 ). The heating to 200 C in-
duces further SA-I decomposition with the shift of the
interplanar spacing to d = 6.9 . The decomposition
of Ni(II), Cu(II), and Al(III) formates is complete at
an argon stream at W = 6500 h . It is seen that, as the
concentration of formic acid increases, the catalytic
activity (after activation at 150 and 160 C) monoton-
ically increases and reaches a maximum for sample
nos. 8 10. The increase in the activation temperature
to 180 C sharply increases the catalytic activity, and
sample no. 4 ensures almost 100% oxygen conversion.
Under these activation conditions, however, sam-
ple no. 1 still exhibits zero catalytic activity.
We also tested the catalytic properties of sam-
ple nos. 4 7, activated under similar conditions, in
the course of carbon monoxide hydrogenation. The
experiments were carried out at a pressure of 3.0 MPa,
1
space velocity of 30000 h , and carbon monoxide
250 C and yields nickel and copper, which are con-
concentration at the reactor inlet of 0.6 0.75 vol %.
We evaluated the catalytic activity in this process by
the temperature of the 10 ppm CO breakthrough and
found that sample nos. 6 and 7 have the maximal ac-
tivity (220 and 215 C, respectively). These data in-
dicate high catalytic performance of the system under
study. Based on the experimental data, we chose for
practical applications a catalyst with the composition
verted to NiO and CuO in this oxidizing medium. The
thermolysis of aluminum formate yields -Al O .
2
3
The X-ray pattern contains only reflections of Ca(II)
formate. The decomposition of SA-I also continues,
its interplanar spacing decreases in this case to d =
6
.7 . At 300 C, calcium(II) formate starts to decom-
pose to give CaCO , whereas the decomposition of
3
SA-I approaches completion. Its interplanar spacing d
becomes equal to 6.2 . The intensity of diffraction
reflections of this phase in the X-ray pattern consider-
ably decreases. The further temperature increase by
50 C results in complete decomposition of calcium
1
0 wt % CuO 25 wt % NiO 65 wt % talum prepared
using 20% aqueous solution of formic acid in the
stage of mixing.
We have studied in detail variation of the phase
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 5 2002

750
EFREMOV et al.
formate, as indicated by an increase in the intensity of
using aqueous formic acid involves the formation of
both mixed nickel copper subaluminate and mixed
nickel copper subaluminoformate, and also of nickel,
copper, aluminum, and calcium formates. The quan-
titative ratio of these phases depends on the concen-
tration of the aqueous solution of formic acid used.
CaCO reflections. Mixed Ni(II) and Cu(II) subalumi-
3
nate also completely decomposes. Nickel subcarbo-
nate starts to decompose intensively to form finely
dispersed nickel oxide. At 400 C, its decomposition is
complete. The phase composition of the catalyst after
thermolysis at this temperature includes the following
compounds: NiO, CuO, CaO 2Al O , CaO Al O ,
(2) The mutual influence of metal formates on
their decomposition temperature was established.
2
3
2 3
and CaCO . The phase composition remains un-
3
changed on cooling to ambient temperature.
(3) The optimal concentration of formic acid aque-
The evolution of the phase composition of this
sample on heating in an argon stream is almost identi-
cal, except for the fact that the dispersed Ni and Cu
phases originating from the decomposition of Ni(II)
and Cu(II) formates are not oxidized.
ous solution was chosen, which allowed preparation
of mechanically strong and highly active catalysts.
(4) The scheme of catalyst production taking into
account basic parameters of the preparation process
was offered.
The studies of phase composition and phase trans-
formations occurring on heating in both air and inert
gas streams, of the activation stage, and also of
changes in the specific surface area and mechanical
strength allow us to make a substantiated choice of the
scheme of the catalyst preparation. According to this
scheme, the catalyst should be prepared as follows.
The initial components (NSC, CSC, and talum) are
mixed in the presence of 15 20% aqueous HCOOH
in mixers equipped with heaters. The mixing occurs
most intensively at 70 75 C. The catalyst mass with
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CONCLUSIONS
1) The evolution of the phase composition of
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(
cement-containing nickel copper catalysts synthesized
1
1
2. US Patent 4400309.
3. JPN Patent 52-48559.
2
Manufactured in Novomoskovsk Institute of Nitrogen Industry
on industrial equipment for production of catalysts.
The tests were carried out in electrolysis shop 2 of the Azot
Joint-Stock Company, Novomoskovsk.
3
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