Dehydrogenataion of Bicyclohexyl over Ni/Oxidized Sibunit Catalyst

Article abstract of DOI:10.1134/S0036024419040150

Abstract: The dehydrogenation of bicyclohexyl over single-component Ni-containing catalyst supported on oxidized Sibunit containing 3, 10, and 20 wt % of Ni is studied. The effect of addition of small amounts of Pt to Ni-catalysts on their activity with respect to hydrogen release is investigated. It is shown that the presence of nickel in the oxidized state facilitates electron transfer from platinum, reducing the dehydrogenation properties of two-component (Ni–Pt)-catalysts. It is established that the formation of a shell from the two metals on the surface of the material greatly slows the process of carbon support methanation.

Full text of DOI:10.1134/S0036024419040150

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2019, Vol. 93, No. 4, pp. 652–657. © Pleiades Publishing, Ltd., 2019.
Russian Text © A.N. Kalenchuk, A.V. Leonov, V.I. Bogdan, L.M. Kustov, 2019, published in Zhurnal Fizicheskoi Khimii, 2019, Vol. 93, No. 4, pp. 529–535.
CHEMICAL KINETICS
AND CATALYSIS
Dehydrogenataion of Bicyclohexyl over Ni/Oxidized Sibunit Catalyst
A. N. Kalenchuka,b,*, A. V. Leonova, V. I. Bogdana,b, and L. M. Kustova,b
a Department of Chemistry, Moscow State University, Moscow, 119991 Russia
b Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, 119991 Russia
*е-mail: akalenchuk@yandex.ru
Received July 14, 2018; revised July 14, 2018; accepted July 14, 2018
Abstract—The dehydrogenation of bicyclohexyl over single-component Ni-containing catalyst supported on
oxidized Sibunit containing 3, 10, and 20 wt % of Ni is studied. The effect of addition of small amounts of Pt
to Ni-catalysts on their activity with respect to hydrogen release is investigated. It is shown that the presence
of nickel in the oxidized state facilitates electron transfer from platinum, reducing the dehydrogenation prop-
erties of two-component (Ni–Pt)-catalysts. It is established that the formation of a shell from the two metals
on the surface of the material greatly slows the process of carbon support methanation.
Keywords: catalysis, bicyclohexyl dehydrogenation, nickel, platinum
DOI: 10.1134/S0036024419040150
INTRODUCTION
In this work, we investigated the dehydrogenation
of bicyclohexyl over a single-component Ni/С catalyst
supported on Sibunit (Sib) with Ni contents of 3, 10,
and 20 wt %, compared to two-component Ni–Pt/C
catalysts with 0.1 and 0.5 wt % Pt and the respective
Hydrogen is now considered one of the main alter-
natives to hydrocarbon-based fuel (gasoline and diesel
fuels) for environmentally friendly vehicles. The dehy-
drogenation of such cycloalkanes as cyclohexane, single-component Pt/C catalysts. The catalyst sam-
ples were characterized via XRD, XPS, TPR, electron
microscopy (TEM), and СО chemisorption.
decalin, or bicyclohexyl with high hydrogen contents
(>7 wt %) could allow the storage and supply of chem-
ically pure hydrogen without traces of СОх gases to a
fuel cell [1–6]. The main problem is developing cata-
lytic systems that combine high activity and high
selectivity towards the final product. Pt- and Ni-con-
taining catalysts are considered the ones most efficient
in the reactions of cycloalkane dehydrogenation [7, 8].
Pt-catalysts are usually more active in the dehydroge-
nation of naphthene molecules, but nickel is much less
expensive. In some cases, the content of the expensive
noble metal can be reduced by introducing a second
metal whose presence has a synergetic effect and shifts
the equilibrium toward the formation of the final
products [9–11]. An increase in the rate of hydrogen
release during the dehydrogenation of cyclohexane on
two-component Ni–Pt/C catalysts with 0.5 wt % Pt
added to 20Ni/С catalyst, compared to the respective
EXPERIMENTAL
Single-component catalysts Ni/Sibох with Ni con-
tents of 3, 10, and 20 wt % were produced by impreg-
nating carbon supports with an aqueous solution of
Ni(NO3)2 · 6H2O by incepient wetness method.
Sibunit oxidized with nitric acid [12] with a specific
surface area of 240 m2/g and an average pore size of
4 nm was used as the support. Following impregna-
tion, the catalysts were dried in air at room tempera-
ture for 24 h and then calcined in a N2 flow (99.9%,
50 mL/min) at 500°C for 2 h. Prior to reaction, the
Ni-catalysts were activated in a Н2 flow (99.99%,
50 mL/min) at 500°C for 2 h.
Single-component Pt/Sibох catalysts with Pt con-
single-component catalysts, was reported in [9]. tents of 3, 0.5, 0.3, and 0.1 wt % were produced by
impregnating the oxidized Sibunit with an aqueous
solution of H2PtCl6 · 6H2O by incepient wetness
method. The catalysts were then dried in air at room
temperature for 24 h with subsequent calcination in a
N2 flow (99.9%, 50 mL/min) at 350°C for 2 h. Prior to
reaction, the Pt-catalysts were activated in a Н2 flow
(99.99%, 30 mL/min) at 350°C for 2 h. The same pro-
cedure was used for the preparation of 0.5 and
Despite an increase in activity, the selectivity with
respect to the side process of methane formation was
0.3%, which is rather high for systems of reversible
hydrogen storage. It was shown in [12] that the effi-
ciency of Pt/С (Sibunit) catalyst with respect to
hydrogen release during the dehydrogenation of bicy-
clohexyl could be increased through surface hydro-
philization.
652

DEHYDROGENATAION OF BICYCLOHEXYL OVER Ni/OXIDIZED SIBUNIT CATALYST
653
0.1 wt % Pt/Sib catalysts on non-oxidized Sibunit
used later for comparison.
The dehydrogenation of bicyclohexyl over Ni- and
Ni–Pt-catalysts was conducted in a flow reactor [6,
12]. The duration of the reaction for all catalysts was
4 h at 320°С, atmospheric pressure, and a cata-
lyst/substrate ratio of 1.85 g/6 mL h−1. Reaction prod-
ucts were analyzed on a Kristalyuks-4000M chro-
matograph (Russia) using a ZB-5 capillary column
(Zebron, United States) equipped with a flame ion-
ization detector from a FOCUS DSQ II chromato-
mass-spectrometer (Thermo Fisher Scientific, United
States) with a TR-5ms capillary column. Analysis was
performed in the temperature-programmed mode at
70–220°C with a heating rate of 6 K/min. The purity
of the released hydrogen was evaluated via gas chro-
matography using a thermal conductivity detector and
packed Porаpak Q column.
Two-component (Ni–Pt)-catalysts were produced
in two ways. With 0.1Pt/3Ni/Sibох, 0.1Pt/10Ni/Sibох,
and 0.5Pt/3Ni/Sibох catalysts, platinum was intro-
duced by applying aqueous H2PtCl6 · 6H2O solutions
onto calcined single-component catalysts of 3 and
10 wt % Ni/Sibох, respectively. The catalysts were
dried in air at room temperature for 24 h with subse-
quent calcination in a N2 flow (99.9%, 50 mL/min) at
350°C (catalysts with a platinum content of 0.1 wt %)
and at 150°С (catalyst with a platinum content of
0.5 wt %) for 2 h. Catalysts (0.1Pt–3Ni)/Sibох and
(0.1Pt–10Ni)/Sibох were produced via simultaneous
impregnation with calculated amounts of an aqueous
solution of H2PtCl6 ⋅ 6H2O and Ni(NO3)2 · 6H2O.
Following impregnation with the mixture of solutions,
the catalysts were first dried in air at room temperature
for 24 h and then calcined in a N2 flow (99.9%,
50 mL/min) at 150°C for 2 h. Prior to reaction, all
two-component (Ni–Pt)-catalysts were activated in a
Н2 flow (99.99%, 30 mL/min) at 500°C for 2 h.
Particle size and Pt dispersity were determined on
an ASAP 2020 instrument (United States) through
irreversible CO chemisorption at a temperature of
35°С [13]. Surface composition and the nature of the
surface functional groups were determined via X-ray
photoelectron spectroscopy (XPS) using a Kratos Axis
Ultra DLD instrument (United Kingdom) with
monochromatic AlKα-radiation (1486.6 eV, 150 W)
[14]. The microstructure of the catalyst samples was
examined by means of transmission electron micros-
copy (TEM) with a Hitachi HT7700 electron micro-
scope. Images were acquired in the bright-field mode
with an accelerating voltage of 100 kV [15].
Bicyclohexyl conversion (X) was calculated as the
ratio of the difference between the amount of bicyclo-
hexyl before and after a reaction to the initial amount
of bicyclohexyl. Selectivity (S) towards biphenyl was
determined as the ratio of the amount of produced
biphenyl to the total amount of the reaction products.
Activity of catalysts (TOF, mmol (H2)/gМе min) with
respect to hydrogen release was calculated as the ratio
of the number of moles of hydrogen released over the
period of bicyclohexyl dehydrogenation to the amount
(g) of Pt and divided by the reaction time.
RESULTS AND DISCUSSION
Cyclohexylbenzene (C12H16), biphenyl (C12H10),
and hydrogen were identified as products formed on
all of the catalysts used in this work. No other products
were detected in the reactions on these siongle-metal
Pt-catalysts.
We first compared the hydrogen release activity of
the single-component Pt-catalysts with declining
platinum content. The experimental data produced
with the catalysts based on oxidized and non-oxidized
carbon supports are presented in Table 1. A compari-
son shows that the conversion of bicyclohexyl dehy-
drogenation fell along with the platinum content in
single-component Pt-catalysts. However, the effi-
ciency of catalysts with respect to hydrogen release
grew. Conversion and the selectivity toward the final
biphenyl and the TOF are higher for the catalysts
based on the oxidized Sibunit than for the ones based
on non-oxidized supports, which agrees with the
dependence established in [12].
Curves of the temperature-programmed reduction
(TPR) of the catalysts were recorded on an original
setup consisting of a system for gas preparation, a reac-
tor with a tube-like oven, and a thermal conductivity
detector. Prior to TPR, the catalysts were thermally
pre-treated in an inert atmosphere to degrade the
residual metal salts. The samples were heated in a
nitrogen flow (30 mL/min) to 400°С at a rate of
10 K/min, followed by slow cooling (3 K/min) to
room temperature. The samples were then reduced in
a flow of a 5% H2/Ar gas mixture (23 mL/min). The
rate of the linear heating of the sample was 12 K/min.
The phase composition of the samples and size of
the primary crystals of the supported metals were
The experimental data on the dehydrogenation of
determined via XRD analysis on a DRON-3 instru- bicyclohexyl over single-component Ni-containing
ment with Ni-filtered CuKα-radiation (λ
=
catalysts are presented in Table 2. A comparison shows
there was virtually no bicyclohexyl dehydrogenation
over the single-component 3 wt % Ni/Sibох catalyst.
0.1542 nm) using stepwise scanning mode (0.02°
steps) in the range of 2θ = 10°–60°. Phase composi-
tion was identified by comparing the positions and The increase in nickel content to 10 wt % results in the
intensities of lines on the resulting X-ray diffraction increase in conversion to 25%, and selectivity to the
patterns and the ICDD (International Center for Dif- level displayed by the Pt-catalysts with low platinum
fraction Data) database.
content on the non-oxidized support (Table 1). Rais-
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KALENCHUK et al.
Table 1. Conversion and selectivity of Pt/С (Sibох) catalysts in the reaction of bicyclohexyl dehydrogenation (Т = 320°С,
Р = 1 atm)
Selectivity, S, %
TOF, mmol
(H2)/gМе min
Conversion, Х, %
No.
Catalyst
( 5%)
С12Н16
С12Н22
1
2
3
4
5
6
3.0Pt/Sibох
0.5Pt/Sib
0.5Pt/Sibох
0.3Pt/Sibох
0.1Pt/Sib
84
63
73
64
26
55
29
39
16
21
42
32
71
61
84
79
58
68
47
184
238
359
855
1012
0.1Pt/Sibох
Table 2. Conversion and selectivity of Ni/С (Sibох) catalysts in the reaction of bicyclohexyl dehydrogenation (Т = 320°С,
Р = 1 atm)
S, %
TOF, mmol
(H2)/gМе min
No.
Catalyst
Х, % ( 5%)
С12Н16
С12Н10
1
2
3
3 Ni/Sibох
10 Ni/Sibох
20 Ni/Sibох
4
25
13
65
27
37
35
73
63
27
10
5
Table 3. Conversion and selectivity of Pt–Ni/С (Sibunit) catalysts in the reaction of bicyclhexyl dehydrogenation (Т =
320°С, Р = 1 atm)
Selectivity, S%
TOF, mmol
(H2)/gМе min
Conversion,
Х% ( 5%)
No.
Catalyst
С12Н16
С12Н22
1
2
3
4
5
0.1Pt/3Ni/Sibох
0.1Pt/10Ni/Sibох
(0.1Pt–3Ni)/Sibох
(0.1Pt–10Ni)/Sibох
0.5Pt/3Ni/Sibох
9
27
37
54
38
47
73
63
46
62
53
34
10
28
10
26
15
23
40
31
ing the nickel content to 20 wt % resulted in consider- applied simultaneously. Adding small amounts of Pt to
ably lower conversion in bicyclohexyl dehydrogena- these catalysts increased the degree of conversion and
tion over the 20 wt % Ni/Sibох catalyst. We can see that TOF, compared to the single-component Ni-cata-
lysts, but the parameters were still lower than with the
respective single-component Pt-catalysts supported
on oxidized Sibunit. Higher values of conversion and
selectivity were observed for the two-component
(0.1Pt–10Ni)/Sibох catalyst compared to the single-
the activity of the single-component Ni-catalysts with
respect to the degree of conversion and selectivity to
biphenyl are much lower than the activity of the Pt-
catalysts with an appreciably lower content of the
active metal. Along with the low degree of conversion,
the high metal content in the single-component Ni- component 0.1 wt % Pt/Sib based on non-oxidized
catalysts greatly reduced the efficiency (TOF) with Sibunit. The content of cracking products on the two-
respect to hydrogen release. Formation of trace component Ni–Pt-catalysts fell relative to the single-
amounts of cracking products was detected on the Ni- component Ni-catalysts.
catalysts with nickel contents of 10 and 20 wt %.
Diffractograms of the single-component Pt- and
Ni-catalysts are presented in Fig. 1. A comparison
reveals no fundamental differences between the dif-
fractograms of the single-component Ni-catalysts
(Table 2). The ratio of diffraction peaks correlates with
the nickel content in the catalysts with 3%Ni/Sibох,
10%Ni/Sibох, and 20%Ni/Sibох. The most intense line
Applying platinum over the single-component Ni-
catalysts resulted in substantial deterioration of the
catalytic properties of two-component Ni–Pt-cata-
lysts in bicyclohexyl dehydrogenation, compared to
the single-component Pt-catalysts (Table 3). The sit-
uation was better when nickel and platinum were
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DEHYDROGENATAION OF BICYCLOHEXYL OVER Ni/OXIDIZED SIBUNIT CATALYST
655
metallic nickel. Finally, the third peak is related to the
process of hydrogenation of the carbon support. The
shift of the third peak toward lower temperatures in
comparison to the pure support is likely due to the for-
mation of metal shells on the support’s surface or the
catalytic effect the metal had on the process of carbon
support hydrogenation. The presence of Pt changed
the pattern of the TPR curve of the two-component
catalysts 0.5Pt/3Ni/Sibох relative to the 3Ni/Sibох cat-
alyst without platinum (Fig. 3b). The first of the two
peaks in the temperature interval of 250–350°C likely
corresponds to the process of platinum reduction to
metallic state; the second one, to the formation of
nickel oxide, as in the case of single-component Ni-
catalyst. The peak intensity in the temperature range
of 450–500°С falls appreciably in the process, due
likely to the inhibition of the process of support meth-
anation caused by the mutual effect of two metals.
Sibox
Sibox
Pt(111)
Pt(200)
1
2
3
4
5
Ni(111)
Ni(200)
20
30
40
50
60
2θ, deg
The composition and charge state of the metals on
the surfaces of the Pt- and (Ni–Pt)-catalysts were
determined via X-ray photoelectron spectroscopy
(XPS). The XPS spectra of C 1s carbon are identical
for all the investigated catalyst samples and contain
two lines characteristic of sp2-carbon (more than 80%)
Fig. 1. Diffraction patterns of catalysts (1) 3% Pt/Sib ,
ох
(2) 0.1%Pt/Sib , (3) 3%Ni/Sib , (4) 10%Ni/Sib , and
ох
ох
ох
(5) 20%Ni/Sib .
ох
(111) Ni corresponds to 2θ = 44.505° (JCPDS 87-712,
type Cu); the second most intense line (200), to 2θ = and sp3-carbon, indicating disruption of the order of
54.505°. The interplanar distances corresponding to the oxidized Sibunit structure. The Pt4f XPS spectra
these lines were а111 ~ 0.3528 nm and а200 ~ 0.3528 nm, of the single-component Pt-catalysts show that more
which agrees with the reference data for metallic nickel than 96% of platinum was in the Pt0 state. In the two-
(аNi = 0.3528 nm). Due to the low concentration of component 0.5Pt/3Ni/Sibох catalyst, platinum was in
three states: Pt0 (30%), Pt2+ (44%), and Pt4+ (26%). In
accordance with the Ni 2p XPS spectra, the nickel on
the surface of this catalyst was present in the oxidized
form Ni2+ and only around 2% of it was in the metallic
state Ni0, which agrees with the results from TPR
analysis.
platinum in the single-component Pt-catalysts
(Table 1), the Pt diffraction peaks overlap with the
background line of the Sibох support, complicating
evaluation of the parameters of the platinum crystal
lattice. However, the estimate of the Pt interplanar
distance (а = 0.3923 0.0002 nm) from the diffracto-
gram of reference catalyst 3% Pt/Sibох produced using
a similar technique is in full agreement with the refer-
ence value for metallic platinum (аPt = 0.3923 nm)
(JCPDS 87-646, type Cu). The diffractograms of the
two-component Ni–Pt-catalysts (Table 3) display no
fundamental differences from the diffractograms of
the respective single-component Ni-catalysts, indi-
cating the addition of Pt had no effect on the interpla-
nar distance of nickel lattice.
According to the chemisorption data, the dispersity
of CO and the size of the platinum clusters in the
0.5% Pt/Sibох catalyst were 63% and 1.8 nm. In the
two-component 0.5Pt/3Ni/Sibox catalyst, they were
76% and 1.4 nm, respectively. Dispersity fell to 24%
and the particle size grew to 4.7 nm when the platinum
content in the 0.1% Pt/Sibox catalyst was lowered. The
dispersity and particle size of the nickel clusters in the
most
active
single-component
Ni-catalyst
The curves of temperature-programmed reduction
(TPR) for the (a) 3Ni/Sibох and (b) 0.5Pt/3Ni/Sibох
catalysts are presented in Fig. 2 along with the TPR
curves for (c) pure nickel oxide (NiO) and (d) carbon
support Sibох for comparison. The TPR curve of the
3Ni/Sibох catalyst displays three absorption peaks, in
contrast to the pure NiO. The first peak in the tem-
perature range of 130 to 170°C is likely due to the pro-
cess of NiOOH reduction to nickel oxide (NiO) pro-
ceeding according to the reaction
10% Ni/Sibох were 7% and 13.8 nm, respectively. Our
determination of the dispersity using the CO
chemisorption data was found to be overestimated,
while the particle sizes of Ni of the 3% Ni/Sibох were
underestimated, due to the ease of nickel tetracarbonyl
Ni(CO)4 formation.
The histograms of particle size distribution in sin-
gle-component catalysts (a) 3% Ni/Sibох, (b)
10% Ni/Sibох, (c) 20% Ni/Sibox, and (d) two-compo-
nent catalyst 0.5Pt/3Ni/Sibох based on the TEM
images are presented in Fig. 3.
2NiOOH + H2 = 2NiO + H2O.
The second peak in the temperature range of 350–
A comparison of the histograms of the single-com-
400°C is associated with nickel oxide reduction to ponent Ni-catalysts shows that large clusters were
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KALENCHUK et al.
80
70
60
50
40
30
20
10
0
12
10
8
(b)
(a)
6
4
2
0
−10
0
100 200 300 400 500 600 700 800
0
100 200 300 400 500 600 700 800
t, °C
t, °C
1200
1000
800
(c)
800
600
400
200
(d)
600
400
200
0
200
400
600
800
1000
0
200
400
600
800
t, °C
t, °C
Fig. 2. TPR curves of catalysts (a) 3Ni/Sib , (b) 0.5Pt/3Ni/Sib , (c) NiO, (d) Sib .
ох
ох
ох
present in the catalysts with nickel contents of 3 and
20 wt %, along with small clusters. The large number
of small clusters increased the rate of conversion when
using the 20Ni/Sibох catalyst. The distribution of the
Ni cluster particle size in the 10Ni/Sibох catalyst
is more uniform, making it the most active of the three
investigated single-component Ni-catalysts. The aver-
age particle size in the two-component
0.5Pt/3Ni/Sibох (Fig. 2d) catalyst was 9 nm. Accord-
ing to the CO chemisorption data, this is larger than
the platinum clusters and was likely due to the contri-
bution of nickel. The presence of large amounts of
platinum increases the degree of conversion, but
reduces the TOF of this catalyst. The great difference
between the sizes of the active component clusters was
likely the reason for the substantial difference between
the activity of the Pt- and Ni-catalysts in the reaction
of bicyclohexyl dehydrogenation. The lower platinum
content in the Pt0 state was probably another reason
for the reduced activity of the two-component (Ni–
Pt)-catalysts, compared to the single-component Pt-
catalysts. On the other hand, the presence of nickel in
the basic, oxidized state facilitates electron transfer
from platinum and thus degrades the dehydrogenation
properties of the two-component (Ni–Pt)-catalyst.
Raising the temperature increases the yield of cracking
products.
It has been reported in the literature that adding
0.5 wt % of Pt to 20Ni/С catalysts causes a synergetic
effect for cyclohexyl dehydrogenation over Ni/C cata-
lysts with nickel contents of 10, 20, and 40 wt % [9].
No increase in catalytic activity in the reaction of bicy-
clohexyl dehydrogenation over the two-component
catalysts 0.1Pt/3Ni/Sibох and 0.1Pt/10Ni/Sibox was
observed in this work. In both cases, increased activity
was observed for both catalysts, compared to the
respective single-component Ni-catalysts. However,
the activity was notably lower than for the pure single-
component 0.1Pt/Sibох catalyst, which was found to
be the most active of the investigated catalysts. An
increase in conversion was observed only for the two-
component (0.1Pt–10Ni)/Sibох catalyst relative to
single-component catalyst 0.1 wt % Pt/Sib based on
non-oxidized Sibunit. However, the activity of the cat-
alysts based on the oxidized Sibunit was higher than
the ones based on non-oxidized Sibunit.
CONCLUSIONS
Despite their lower cost, Ni-catalysts have param-
eters inferior to those of Pt-catalysts with respect to
achieving high rates of conversion and thus high vol-
umes of released hydrogen for fuel cells. Careful
preparation and controlled functionalization of sup-
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DEHYDROGENATAION OF BICYCLOHEXYL OVER Ni/OXIDIZED SIBUNIT CATALYST
657
35
30
25
20
15
10
5
(b)
40
35
30
25
20
15
10
5
(a)
3Ni/Sibox
10Ni/Sibox
dav = 15.8 nm
dav = 12.3 nm
0
0
14 16
(c)
3032
8
12
10
8
6
14
18
12
16
10
(d)
d, nm
d, nm
50
40
30
20
10
0
0.5Pt/3Ni/Sibox
40
30
20
10
0
20Ni/Sibox
dav = 12.3 nm
dav = 8.6 nm
10
8
12 14
d, nm
20 22
16
18
14
16
2
4
6
8
10 12
d, nm
Fig. 3. Particle size distribution of catalysts (a) 3Ni/Sib , (b) 10Ni/Sib , (c) 20Ni/Sib , and (d) 0.5Pt/3Ni/Sib .
ох
ох
ох
ох
7. A. Stanislaus and B. H. Cooper, Catal. Rev.-Sci. Eng.
ports are effective ways of minimizing the content of
Pt in catalysts.
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8. N. Kariya, A. Fukuoka, and M. Ichikawa, Appl. Catal.
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ACKNOWLEDGMENTS
This work was supported by the Russian Science
Foundation, project no. 14-50-00126.
9. A. A. Shukla, P. V. Gosavi, J. V. Pande, et al., Int. J.
Hydrogen Energy 35, 4020 (2010).
10. L. Xiong and A. Manthiram, J. Electrochem. Soc. 152,
697 (2005).
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