Activation of nickel–chromium hydrogenation catalysts with hydrogen

Article abstract of DOI:10.1134/S0023158416020130

The kinetics of the reduction of nickel cations in nickel oxide and nickel–chromium catalysts whose oxide precursors have different structures has been investigated by thermal analysis. The reduction of nickel oxide with a hydrogen-containing gas takes place at 250–330°C. The apparent activation energy of this reaction is about 88 kJ/mol. The introduction of up to 30 at % chromium cations into the nickel oxide structure shifts the reduction temperature of nickel in the oxide phase to 300–450°C and increases the apparent activation energy of the reduction of nickel cations to ～108 kJ/mol. The introduction of 67 at % chromium into nickel oxide results in the formation of an oxide precursor with a spinel structure. The apparent activation energy of the reduction of nickel cations in this spinel is about 163 kJ/mol. The results of this study can be used in optimizing the composition of Ni-containing hydrogenation catalysts and their activation and operation conditions.

Full text of DOI:10.1134/S0023158416020130

ISSN 0023ꢀ1584, Kinetics and Catalysis, 2016, Vol. 57, No. 2, pp. 251–254. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © I.I. Simentsova, N.V. Shtertser, L.M. Plyasova, T.P. Minyukova, T.M. Yurieva, 2016, published in Kinetika i Kataliz, 2016, Vol. 57, No. 2, pp. 245–249.
Activation of Nickel–Chromium Hydrogenation Catalysts
with Hydrogen
I. I. Simentsovaa, *, N. V. Shtertsera, b, L. M. Plyasovaa, T. P. Minyukovaa, and T. M. Yurievaa
aBoreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
bNovosibirsk State University, Novosibirsk, 630090 Russia
*eꢀmail: sii@catalysis.ru
Received March 21, 2015
Abstract—The kinetics of the reduction of nickel cations in nickel oxide and nickel–chromium catalysts
whose oxide precursors have different structures has been investigated by thermal analysis. The reduction of
nickel oxide with a hydrogenꢀcontaining gas takes place at 250–330°C. The apparent activation energy of this
reaction is about 88 kJ/mol. The introduction of up to 30 at % chromium cations into the nickel oxide strucꢀ
ture shifts the reduction temperature of nickel in the oxide phase to 300–450°C and increases the apparent
activation energy of the reduction of nickel cations to ~108 kJ/mol. The introduction of 67 at % chromium
into nickel oxide results in the formation of an oxide precursor with a spinel structure. The apparent activaꢀ
tion energy of the reduction of nickel cations in this spinel is about 163 kJ/mol. The results of this study can
be used in optimizing the composition of Niꢀcontaining hydrogenation catalysts and their activation and
operation conditions.
Keywords: NiCr catalysts, nickel oxide, spinel, reductive activation
DOI: 10.1134/S0023158416020130
INTRODUCTION
from aqueous solutions of nitrates at
pH 7.2–7.4. The nitrates—Ni(NO3)2
grade, USSR state standard GOST 4055ꢀ78) and
Cr(NO3)3 9H2O (pure grade, GOST 4471ꢀ78)—were
received from the Ural Plant of Chemical Reagents. In
the synthesis of catalysts with Ni2+ : Cr3+ = 1 : 0 (no
chromium) and 2.3 : 1, the precipitant was sodium
carbonate; ammonium carbonate was used in the
preparation of the Ni2+ : Cr3+ = 1 : 2 sample. The preꢀ
cipitates were washed to remove sodium ions (down to
Т
= 65–68
°C and
·
6H2O (pure
Nickelꢀcontaining compounds are widely used as
catalysts in the hydrogenation of organics and carbon
oxides [1–5]. Prior to being employed in a hydrogenaꢀ
tion reaction, the catalysts are activated with a hydroꢀ
genꢀcontaining gas. The activity of such systems is
determined by the presence of ~2–10 nm nickel metal
particles [6–8]. The activity and selectivity of the catꢀ
alysts in hydrogenation reactions is known to depend
significantly on the structure of their hydroxo precurꢀ
sors and on the conditions under which the precursors
were heatꢀtreated [9]. However, it is still unclear how
the kinetics of the reduction of nickelꢀcontaining catꢀ
alysts depends on the composition and structure of
their oxide precursors.
In this study, we obtained precursors having the
cubic structure of nickel oxide and nickel–chromium
spinel and investigated the reduction of nickel cations in
nickel oxide and nickel–chromium oxide catalysts. The
activation energies of the reduction of nickel cations in
structurally different oxide precursors were estimated.
⋅
a level of
dried under an IR lamp at
at 400 and 600–650°C in flowing argon. Calcination
was performed to rule out the oxidation of Cr3+ to Cr6+
≤
0.01 wt %) and ammonium nitrate traces,
Т
≈
50–60 , and calcined
°C
.
The cationic composition of the synthesized samꢀ
ples was verified by atomic emission spectroscopy
(AES). Table 1 lists the designations and chemical
compositions of the samples synthesized.
Physicochemical Methods
of Characterization of Samples
EXPERIMENTAL
Xꢀray diffraction (XRD) patterns were obtained on
Sample Preparation
a Dꢀ500 diffractometer (Siemens, Germany) using
monochromatic CuK
mator placed in the reflected beam. The diffraction
= 10 –70° with 0.05°
α
radiation with a monochroꢀ
Oxide precursors were obtained by heat treatment
of mixed hydroxo compounds in flowing argon. The
hydroxo compounds were synthesized by the continuꢀ patterns were recorded at
2θ
°
ous coprecipitation of nickel and chromium cations increments. The counting time per data point was 5 s.
251

252
SIMENTSOVA et al.
Table 1. Designation and chemical composition of the maꢀ
terials examined
42–43 deg and the three observed reflections are
assignable to a NaCl–NiO type structure and can be
given the indexes 111, 200, and 220. The correspondꢀ
Chemical
composition
in atomic fractions
Ni2+ : Cr3+
ratio
ing unit cell parameter
slightly larger than the reference unit cell parameter
for pure NiO ( = 4.177 Å, see ICDD PCꢀWIN,
а is ~4.186 Å ( 0.003 Å),
Sample
Ni1
а
1 : 0
2.3 : 1
1 : 2
Ni1.0Cr0.0
PDFꢀ2, 00ꢀ047ꢀ1049). This is evidence that the strucꢀ
ture is disordered due to the fact that its octahedral
oxygenꢀsurrounded sites are occupied not only by Ni2+
NiCr2.3
NiCr0.5
Ni0.70Cr0.30
Ni0.33Cr0.67
cations but also by Cr3+ cations. For the NiCr0.5
sample, the strongest reflection is that occurring at
311
Differential thermogravimetric (DTG) analyses
were carried out using a Netzsch STA–409 PC Luxx
thermoanalytical system (Netzsch, Germany). The
samples were reduced in the temperatureꢀproꢀ
grammed mode in an Н2 : Ar = 50 : 50 (vol %) mixture
flowing at a rate of 80 mL/min. The temperature was
elevated at a rate of 5, 7, or 10°C/min. The samples to
be examined were preꢀheatꢀtreated at 400°C in flowꢀ
ing argon. In the preparation of Niꢀcontaining cataꢀ
lysts, the preꢀheatꢀtreatment temperature is often
chosen to be 400°C, so it was of greatest interest to
study the samples prepared at this very temperature. A
30ꢀ to 50ꢀmg catalyst sample was placed in a platinum
crucible. TGA data were processed using the standard
singleꢀpoint method ÀSTM E698 [10].
2
θ ≈ 36
°
(
≈
2.4–2.5 Å), which is characteristic of
dmax
the spinel structure. The unit cell parameter of this
spinel is ~0.05 Å larger than the reference value for
NiCr2О4 (а = 8.320 Å see ICDD PCꢀWIN, PDFꢀ2,
00ꢀ023ꢀ1271). These oxide structures are sometimes
referred to as anionꢀmodified structures [11] and, in
some works, protospinels [12]. These structures conꢀ
tain impurity anions hampering their crystallization
and are characterized by an incomplete spinelꢀtype
diffraction pattern with an increased unit cell parameꢀ
ter. Raising the heat treatment temperature leads to
the ordering of the cation distribution and to the forꢀ
mation of a normal spinel structure.
Calcination in argon at 600–650
curves ) increases the proportion of crystalline
°C (Fig. 1,
4, 5
phases in the samples. The NiCr0.5 sample, with a
cation ratio of Ni2+ : Cr3+ = 1 : 2, which is characterꢀ
istic of spinelꢀtype oxide phases, consists mainly of
the nickel–chromium spinel phase and contains
some amount of the nickel oxide phase. The NiCr2.3
sample is the nickel oxide phase containing a minor
amount of nickel–chromium spinel.
The thermoanalytical data for the oxide samples
heatꢀtreated at 400°C in flowing argon are presented
in Figs. 2–4. Figure 2 shows DTG profiles for the
reduction of chromiumꢀfree nickel oxide that were
recorded at different heating rates. This sample was
precalcined in the chamber of the thermal analyzer at
RESULTS AND DISCUSSION
The XRD patterns of the Ni–Cr samples calcined
at 400°C in flowing argon (Fig. 1, curves 1–3) show
three diffuse maxima at 2θ ≈ 36, 43, and 62 deg, which
are assignable to an fcc phase. However, as judged
from the distribution of reflection intensities, the samꢀ
ples differ in their structure. For the NiCr2.3 sample,
the strongest reflection is the one that occurs at
2
θ ≈
x
s
x
400°С in flowing argon and was then reduced in situ
x
s
s
under anaerobic conditions. The thermoanalytical
profiles for the reduction of the sample under these
conditions show no peaks assignable to the eliminaꢀ
tion of adsorbed or weakly bonded water. It can be seen
in Fig. 2 that the reduction of nickel in nickel oxide
takes place in a single step. The weight loss rate maxiꢀ
mum shifts from 275 to 293°С as the heating rate is
increased from 5 to 10°C/min. About 20% of the samꢀ
ple weight is lost here.
s
s
s s
NiCr2.3
NiCr0.5
5
4
3
NiCr2.3
NiCr0.5
Ni1
2
1
The DTG profiles for the oxide sample NiCr2.3
precalcined at 400°С in argon, recorded at three difꢀ
ferent temperature ramp rates (5, 7, and 10°C/min),
are shown in Fig. 3. It is clear that the conversion of
the NiCr2.3 sample being heatꢀtreated with the
hydrogenꢀcontaining mixture occurs in two stages.
The first stage shows itself as a slight (2–3%) weight
loss. The extremum of the corresponding peak shifts
20
30
40
50
, deg
60
70
2
θ
Fig. 1. Xꢀray diffraction patterns of the nickel–chroꢀ
mium samples calcined in flowing argon at ( ) 400 and
) 600–650°C: , NiO phase; , spinel phase (NiCr O ).
1–3
(4
,
5
x
s
from ~116 to ~136°С as the temperature ramp rate is
2
4
KINETICS AND CATALYSIS Vol. 57
No. 2 2016

ACTIVATION OF NICKEL–CHROMIUM HYDROGENATION CATALYSTS
253
1
1
2
2
116
122
3
3
136
361
275
370
381
286
293
100 150 200 250 300 350 400
Temperature,
100
200
300
Temperature, С
400
°
500
600
°
С
Fig. 2. DTG profiles for the reduction of the Ni1 sample
(400°C, argon) in the hydrogenꢀcontaining medium at a
Fig. 3. DTG profiles for the reduction of the NiCr2.3 samꢀ
ple (400°C, argon) in the hydrogenꢀcontaining medium at
heating rate of (
50 : 50 vol %.
1) 5, (2) 7, and (
3
) 10°C/min. H : Ar =
a heating rate of (
50 : 50 vol %.
1) 5, (2) 7, and (3) 10°C/min. H : Ar =
2
2
increased from 5 to 10°C/min. This conversion of the
sample involves loss of adsorbed and weakly bound
water. The second stage of the process is the reduction
of nickel cations in the nickel–chromium oxide,
which is accompanied by a weight loss of about 14%.
The position of the weight loss rate maximum shifts
from 361 to 381°C with an increasing heating rate.
Note that the reduction of nickel cations in the
sample that contains 30 at % chromium and has a
Table 2 presents weight loss data derived for the samꢀ
ples examined from TG curves for nickel reduction
(
Δ
m
) at the three temperature ramp rates and is suppleꢀ
mented by calculated weight loss data (
Δ
mcalc) correꢀ
sponding to complete nickel reduction in the catalysts.
Clearly, the experimental weight loss data are in good
agreement with the data calculated for the reduction of
100% of the nickel cations in the catalyst samples.
nickel oxide type structure occurs at a 90°С higher
Table 2 also presents apparent activation energy
temperature than the same process in pure nickel
oxide. The singleꢀstep reduction of this material is eviꢀ
dence that it is dominated by the nickel oxide phase.
Figure 4 shows the thermoanalytical profiles charꢀ
acterizing the reduction of the NiCr0.5 sample. Along
with the elimination of adsorbed and weakly bound
(E .
a) data for the reduction of nickel cations to Ni0
The activation energies were determined using DTG
peak temperatures at different heating rates. These
water at ~118–135
events manifesting themselves as weight loss rate maxꢀ
ima in the temperature ranges from 239 to 259 and
from 416 to 432 . The positions of these maxima
depend on the temperature ramp rate, which was varꢀ
ied between 5 and 10°C/min. The weight lost by the
°С, there are two nickel reduction
1
2
3
°
С
118
°
С
239
249
259
123
135
416
sample below 300
~10% of the nickel cations. Above 350
°
С
corresponds to the reduction of
, ~90% of the
°С
nickel cations in the catalyst undergo reduction. This
reduction behavior indicates that the sample contains
two nickelꢀcontaining oxide phases. The main event
423
432
occurring above 350°С is nickel reduction in the spinel
phase. The thermal event taking place at 239–259°С is
nickel reduction in the NiOꢀtype phase.
100
200
300
Temperature,
400
°
500
600
С
Thus, the XRD and DTG data demonstrated that
the introduction of up to 30 at % chromium into the
NiCr oxide sample does not alter the NiOꢀtype strucꢀ
ture, while the introduction of 67 at % chromium
yields a material dominated by an oxide phase with a
nickel–chromium spinel structure.
Fig. 4. DTG profiles for the reduction of the NiCr0.5 samꢀ
ple (400°C, argon) in the hydrogenꢀcontaining medium at
a heating rate of (
50 : 50 vol %.
1) 5, (2) 7, and (3) 10°C/min. H : Ar =
2
KINETICS AND CATALYSIS Vol. 57
No. 2 2016

254
SIMENTSOVA et al.
Table 2. Weight loss data pertaining to nickel cation reduction for the nickelꢀcontaining catalysts*
max, °C , %
T
Δ
m
Ea
kJ/mol
,
Sample
heating rate,
7
°
C/min
heating rate,
7
°
C/min
Δ
mcalc, %
5
10
5
10
Ni1
275
361
416
286
370
423
293
381
432
20.6
14.5
6.3
20.8
14.6
6.5
20.7
14.6
6.4
21.4
14.9
7.1
88
108
163
NiCr2.3
NiCr0.5
* Gas mixture: H : Ar = 50 : 50 vol %.
2
calculations were performed using an equation of the reduction is about 163 kJ/mol. The results of this study
standard singleꢀpoint method ÀSTM E 698:
can be used in optimizing the composition and activaꢀ
tion and operation conditions for nickelꢀcontaining
hydrogenation catalysts.
βj
E
⎛
⎞
ln ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ = –ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ,
(1)
2
⎝
⎠
RTj, max
where Tj, max is the peak temperature at the heating rate βj
Figure 5 presents experimental kinetic data fitted
Tj, max
.
ACKNOWLEDGMENTS
This study was supported by the Russian Foundaꢀ
tion for Basic Research, project no. 13ꢀ03ꢀ00469.
to Eq. (1).
The apparent activation energies of the reduction
of nickel cations in nickel oxide and NiCr2.3 are ~88
and ~108 kJ/mol, respectively (Fig. 5). For NiCr0.5,
the calculated Еа value is considerably higher and is
~163 kJ/mol. Therefore, the reduction of nickel catꢀ
ions in the NiOꢀtype oxide phase is characterized by a
much lower activation energy than the same process in
the spinelꢀtype oxide phase.
REFERENCES
1. Rodrigo, M.T., Daza, L., and Mendioroz, S., Appl.
Catal., A, 1992, vol. 88, p. 101.
2. Enger, B.Ch. and Holmen, A., Catal. Rev. Sci. Eng.
2012, vol. 54, p. 437.
,
3. Veldsink, J.W., Bouma, M.J., Schoon, NꢀH., and
Beenackers, A.A.C.M., Catal. Rev. Sci. Eng., 1997,
vol. 39, p. 253.
Thus, the nickel–chromium oxide catalysts with
Ni2+ : Cr3+ = 1 : 0, 2.3 : 1, and 1 : 2 differ in how their
nickel cations are reduced. It was demonstrated that
nickel oxide reduction in the hydrogenꢀcontaining gas
4. Louloudi, A., Michalopoulos, J., Gangas, N.ꢀH., and
Papayannakos, N., Appl. Catal. A, 2003, vol. 242, p. 41.
occurs at 250–330°С with an Ea of about 88 kJ/mol.
5. Minyukova, T.P., Itenberg, I.Sh., Khassin, A.A., Sipaꢀ
trov, A.G., Dokuchits, E.V., Terentiev, V.Ya., Khristolyuꢀ
bov, A.P., Brizitskii, O.F., and Yurieva, T.M., J. Chem.
Eng., 2007, vol. 134, p. 235.
The introduction of up to 30 at % chromium cations
into the nickel oxide structure increases the temperaꢀ
ture of nickel reduction in the nickel oxide phase to
300–450°C and raises the apparent Ea of nickel cation
6. Bitter, J.H., Lee, M.K., Slotboom, A.G.T., Dileen, A.J.,
reduction to ~108 kJ/mol. At a higher chromium conꢀ
tent of 67 at %, a spinelꢀtype oxide precursor forms, for
which the apparent activation energy of nickel cation
and Jong, K.P., Catal. Lett., 2003, vol. 89, p. 139.
7. Molina, R. and Poncelet, G., J. Catal., 2001, vol. 199,
p. 162.
8. Boudart, M. and Conica, C.M.M., J. Catal., 1989,
vol. 117, p. 33.
3
–10.4
9. Simentsova, I.I., Minyukova, T.P., Khassin, A.A.,
Dokuchits, E.V., Davydova, L.P., Molina, I.Yu., Plyaꢀ
sova, L.M., Kustova, G.N., and Yurieva, T.M., Russ.
Chem. Bull., 2010, vol. 59, No 11, p. 2055.
–10.6
2
1
–10.8
–11.0
–11.2
–11.4
10. Kissinger, H.E., J. Res. Nat. Bur. Stand., 1956, vol. 57,
p. 217.
11. Litvak, G.S., Minyukova, T.P., Demeshkina, M.P.,
Plyasova, L.M., and Yurieva, T.M., React. Kin. Cat.
Lett., 1986, vol. 31, p. 403.
–11.6
0.165 0.175 0.185 0.195 0.205 0.215 0.225 0.235
1000/RT
12. Erenburg, B.G., Fateeva, V.P., Likhovid, L.I., and
Min’kov, A.I., Izv. Sib. Otd. Akad. Nauk SSSR, 1981,
no. 2, p. 51.
Fig. 5. Experimental kinetic data represented in the coorꢀ
dinates of Eq. (1) for nickel reduction in the (1) NiCr0.5,
(2
) NiCr2.3, and (
3
) Ni1 catalysts.
Translated by D. Zvukov
KINETICS AND CATALYSIS Vol. 57
No. 2 2016