Hydrogen-deuterium exchange of methane on nickel surface prepared by the reduction of nickel oxide

Article abstract of DOI:10.1016/j.molcata.2008.09.030

The hydrogen-deuterium exchange reactions of methane in a deuterium stream were studied by a pulse experiment over a reduced nickel catalyst. The reduced nickel (Ni1373) prepared from nickel oxide calcined at 1373 K had a higher activity than the reduced

Full text of DOI:10.1016/j.molcata.2008.09.030

Journal of Molecular Catalysis A: Chemical 298 (2009) 111–114
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Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Hydrogen–deuterium exchange of methane on nickel surface prepared by the
reduction of nickel oxide
∗
Tsutomu Osawa , Yuki Hamano, Sachiyo Saga, Osamu Takayasu
Graduate School of Science and Engineering for Research, University of Toyama, Gofuku, Toyama 930-8555, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 June 2008
Received in revised form
The hydrogen–deuterium exchange reactions of methane in a deuterium stream were studied by a pulse
experiment over a reduced nickel catalyst. The reduced nickel (Ni1373) prepared from nickel oxide cal-
cined at 1373 K had a higher activity than the reduced nickel (Ni773) prepared from the nickel oxide
calcined at 773 K. This could be due to the ratio of the Ni(1 0 0) to Ni(1 1 1). As the Ni1373 could have the
surface of a higher Ni(1 0 0)/Ni(1 1 1) ratio, Ni1373 had a higher activity than Ni773.
19 September 2008
Accepted 30 September 2008
Available online 14 October 2008
©
2008 Elsevier B.V. All rights reserved.
Keywords:
Nickel oxide
Hydrogen–deuterium exchange
Methane
Nickel
Structure-sensitive reaction
1. Introduction
that of Ni1373, but no such investigation has been carried out to
prove this point.
A tartaric acid-modified nickel catalyst is one of the most
successful enantio-selective heterogeneous catalysts. For the
hydrogenations of prochiral ␤-ketoesters, an enantioselectivity up
to 98% e.e. was attained [1]. The catalyst is simply prepared by
immersing an activated nickel catalyst in an aqueous solution of tar-
taric acid [2]. The enantioselectivity is obtained by the adsorption of
the tartaric acid on the nickel surface. The enantio-selective hydro-
genation over a tartaric acid-modified nickel catalyst is known to be
a structure-sensitive reaction [3,4]. It was reported that the modi-
fied catalyst with greater than a 40 nm nickel crystallite size gave
a high enantioselectivity [4]. A certain smooth surface area would
be necessary for tartaric acid to be adsorbed in the appropriate
conformation to interact with a substrate in order to attain a high
enantioselectivity. It was also reported that the enantioselectivity
of a modified reduced nickel catalyst depended on the prepara-
tion temperature of the nickel oxide. The reduced nickel (Ni1373)
prepared from the nickel oxide calcined at 1373 K (NiO1373) had a
higher enantioselectivity than the reduced nickel (Ni773) prepared
from the nickel oxide calcined at 773 K (NiO773) [5]. This could be
due to the difference between the surface structure of Ni773 and
The hydrogen–deuterium (H/D) exchange reaction of CH4 with
D2 over various metals [6,7] and metal oxides [8–10] has been stud-
ied for many years. Various types of methods for this exchange
reaction have been reported, that is, (i) D2 was pre-adsorbed on
the catalyst in the recirculation reactor followed by CH4 circula-
tion [11], (ii) the mixture of dilute CH4 and D2 was passed through
the catalyst bed in the flow (or circulation) reactor [10,12], and (iii)
the adsorption of CH4 on the catalyst followed by desorption as
deuterated methane in the D2 stream [13].
In this study, during the course of the studies for investi-
gating the difference between Ni773 and Ni1373, the hydrogen–
deuterium (H/D) exchange reaction of CH4 with D2 was carried
out over these reduced nickel catalysts as follows: (i) a catalyst
was placed in a fix-bed flow reactor under a flowing mixture
of He and D2 and (ii) CH4 was introduced by a pulse and the
exchanged methane by a dissociated deuterium on the catalyst
was detected by mass spectroscopy. We previously reported a new
method of corrections for the fragmentation peaks in order to pre-
cisely determine the ratio of the exchanged products by quadrupole
mass spectrometry [14]. Methane decomposition is known to
be a structure-sensitive reaction and the reactivity is reported
as Ni(1 0 0) > Ni(1 1 1) [15]. As the H/D exchange of methane
would also be a structure-sensitive reaction, the exchange activ-
ity could reveal the surface, which predominantly catalyzes the
reaction.
∗ Corresponding author.
E-mail address: osawa@sci.u-toyama.ac.jp (T. Osawa).
1381-1169/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2008.09.030

112
T. Osawa et al. / Journal of Molecular Catalysis A: Chemical 298 (2009) 111–114
2. Experimental
2.1. Materials
CH4 (99.99%), D2 (99.995%), and He (99.995%) were supplied
from the Takachiho Trading Co., Ltd., Japan.
2.2. Preparation of nickel oxide
Nickel oxides were prepared by the decomposition and cal-
cination of nickel hydroxide (Wako Pure Chemical Ind., Ltd., Lot
3
−1
3
−1
ACJ6158) in a mixture of N (40 cm min ) and O (10 cm min ).
2
2
The nickel oxides prepared at 773 K and 1373 K were designated
NiO773 and NiO1373, respectively.
Fig. 1. H/D exchange activity over the reduced Ni catalysts.
2.3. Catalytic test
S(CH D ) of its corrected intrinsic parent ion (Eq. (1))
i
4−i
A continuous gas-flow fixed bed glass reactor (14 mm i.d.) was
used for the catalytic test. The measurement without an exchange
P(CH4) = 100 × S(CH4)/Ssum
P(CH3D) = 100 × S(CH3D)/Ssum
P(CH2D2) = 100 × S(CH2D2)/Ssum
P(CHD3) = 100 × S(CHD3)/Ssum
P(CD4) = 100 × S(CD4)/Ssum
3
reaction was first carried out by a CH pulse (0.6 cm ) without a
4
3
−1
catalyst in a He (50 cm min ) stream. The NiO773 or NiO1373
(1)
(
(
0.127 g) was placed in the reactor and treated with a D stream
mixture of D2 (3 cm min ) and He (50 cm min )) at an atmo-
2
3
−1
3
−1
spheric pressure for 1 h at 623 K. The reduction of NiO773 and
NiO1373 was confirmed by XRD (Shimadzu XD-3A) experiments.
The resulting reduced nickel catalysts were designated Ni773 and
Ni1373, respectively. The H/D exchange reaction was carried out
Ssum = S(CH4) + S(CH3D) + S(CH2D2) + S(CHD3) + S(CD4)
3
. Results and discussion
3
in the same reactor by a CH4 pulse (0.6 cm ) under a continuous
3
.1. The H/D exchange activity and the composition of the
exchanged species over the reduced nickel catalyst
3
−1
3
−1
gas flow of a mixture of D2 (3 cm min ) and He (50 cm min )
at 573 K or 613 K. A small amount of the outlet flow was leaked
continuously through a silica capillary tube (0.05 mm i.d. × 2.5 m)
into a Q-mass spectrometer (PFEIFFER Vacuum Prisma QMS 200)
for isotopic analysis. The data set of the ion current (m/z = 12–20)
was collected every 0.7 s. Background corrections to the observed
Fig.
and Ni1373 at 573 K and 613 K. The exchange activity
P(CH D) + P(CH D ) + P(CHD ) + P(CD )) of Ni1373 was much
1
shows the H/D exchange activity over Ni773
(
3
2
2
3
4
higher than that of Ni773. Considering the surface areas of Ni773
spectra were made (H O at m/z = 18). The second exchange reaction
2
−1 −1
2
2
(
5.8 m g ) and Ni1373 (4.0 m g ), the activity per Ni surface
was carried out at a 45 min interval for checking the stability of the
catalyst. From the beginning of the first run to the end of the second
area of Ni1373 was 11.0 times that of Ni773 at 573 K, and 6.6
times at 613 K. Fig. 2 shows the percentage of each exchanged
species in all the exchanged species over Ni773 and Ni1373 at
run, the gas flow of D and He was maintained. As the results of the
2
first run and the second run were almost the same, the catalysts
were stable during the experiment and the results of the first run
are shown in this paper.
573 K and 613K. For the reaction over Ni773, the percentage of
CH D was small compared to the other isotopologues. At 613 K,
2
2
the percentage of CH D and CD4 decreased and that of CH D2 and
3
2
CHD3 increased compared to the results at 573 K. On the other
hand, for the reaction over Ni1373, the composition of CH D2
2
2
.4. Determination of BET surface area
was much greater than the reaction over Ni773. The composition
of each methane isotopologue was almost not changed by the
increase in the reaction temperature from 573 K to 613 K.
The BET surface area of the reduced nickel catalysts was mea-
sured using a Micromeritics Gemini 2375 by N2 adsorption at 77 K.
2.5. Determination of the exchanged species by the correction of
the methane isotopologues
When the determination of the isotopologues of methane
was carried out by quadrupole mass spectroscopy, the methane
isotopologues CH D
(i = 4–0) have their own characteristic frag-
i
4−i
mentation patterns, which overlap each other. Therefore, to obtain
the pure molecular ion peaks of the methane isotopologues, cor-
rections have to be made for the observed ion peaks. In this study,
to determine each of the isotopologues in the pulse experiment,
the pulse areas of the ion current were calculated by our newly
proposed method. The detailed correction method is described
elsewhere [14].
The composition of the isotopologue P(CH D ) (i = 4–0) after
i
4−i
the exchange reaction was calculated using the peak area
Fig. 2. Composition of the exchanged species over the reduced Ni catalysts.

T. Osawa et al. / Journal of Molecular Catalysis A: Chemical 298 (2009) 111–114
113
As methane decomposition is known to be a structure-sensitive
reaction and the reactivity was reported as Ni(1 0 0) > Ni(1 1 1)
15], the H/D exchange of methane would also be a structure-
[
sensitive reaction and the reactivity would be Ni(1 0 0) > Ni(1 1 1).
The present results indicate that the ratio, Ni(1 0 0)/Ni(1 1 1), on
Ni1373 would be greater than that on Ni773, if one could assume
that the surface was composed of low index planes, i.e. (1 0 0) and
(
1 1 1). As the nickel crystallite size of Ni773 was smaller than that
of Ni1373 (Ni773: 28 nm, Ni1373: 68 nm) [16], the crystallinity of
Ni773 was lower than that of Ni1373, therefore, the Ni773 would
have a greater lattice disorder than Ni1373. The studies of the effects
of lattice disorder and/or step sites necessary for the more pre-
cise evaluation of the exchange activity are currently underway.
However, if the contribution of the lattice disorder and/or step sites
for the H/D exchange reaction were significant, the activity of Ni773
seemed to be greater than that of Ni1373. In this study, as Ni1373
had a higher exchange activity than Ni773, the Ni(1 0 0)/Ni(1 1 1)
ratio rather than the step sites would mainly control the exchange
activity on Ni1373 and Ni773.
On the other hand, it was reported that NiO(1 0 0) was reduced
to Ni(1 0 0) by hydrogen at 623 K [17]. As Ni1373, which would have
a higher Ni(1 0 0)/Ni(1 1 1) ratio, was prepared by the reduction of
NiO1373 by hydrogen at 623 K, NiO1373 could also predominantly
have the NiO(1 0 0) face. As nickel oxide is a crystal like NaCl, the
Ni(1 0 0) face has the lowest surface energy density (ꢀ). Based on
the first approximation, the equilibrium form of the crystal is a
Fig. 3. Change in the ion current of each isotopologue over Ni773: (ꢀ) CH3D; (᭹)
CH2D2; (ꢀ) CHD3; and (ꢁ): CD4.
multiple exchange, more than one hydrogen atoms in methane
are exchanged in one residence. Considering the features of the
exchanged species over Ni773 as mentioned in Section 3.1 (compo-
sition of CH D was small), the exchange reaction over Ni773 would
2
2
hexahedron, which consists of (1 0 0) faces. When ␥(1 1 1) is smaller
proceed with the same mechanism as reported in the literature [9].
√
than 3 ꢀ(1 0 0), (1 1 1) appears on the surface of the crystal [18]. As
the NiO1373 was calcined at high temperature, it is reasonable to
assume that the crystal would be relatively stable and have a high
Ni(1 0 0)/Ni(1 1 1) ratio.
As CH D is obtained by a single step (stepwise exchange), the signal
3
of the ion current would first reach a peak. The CH D , CHD , and
2
2
3
CD4 would be obtained by the multiple exchange, and the desorp-
tion of these isotopologues would be delayed compared to that of
For the already reported H/D exchange reaction over the Ni
catalyst [7,19], the initial distributions of the exchanged species
were almost the same as the results obtained with Ni773 in the
CH D. On the other hand, for the exchange reaction over Ni1373,
3
CH D, CH D , CHD , and CD began to be produced at almost the
3
2
2
3
4
same time. These features were quite different from the results
obtained on Ni773. As Ni1373 has a high exchange activity, these
results could be due to the repetition of the stepwise exchange,
that is, readsorption and further exchange of the partly deuterated
species. For the CD4 signal, the peaks observed at about 20 s from
the injection of the pulse could be due to the contribution of the
multiple exchange. Based on the results in Figs. 3 and 4, it is sug-
gested that the exchange reaction would proceed via a different
mechanism on Ni773 and Ni1373.
present study, that is, the composition of CH D2 was low, while
2
those of CH D and CD4 were high. The nickel catalysts reported
3
in the literature were prepared by the direct reduction of nickel
salt precursors at 673 K to 923 K [9,20,21] or prepared through the
reduction of nickel oxide, which was calcined at 673 K, on SiO [12].
2
It is assumed that the nickel catalysts in the literature and Ni773
could predominantly contain Ni(1 1 1), which is the most stable
plane for the fcc crystal. The features of the exchanged species
like Ni1373 in this study were much different from the already
reported results over the Ni catalyst. The preparation of the nickel
catalyst through the nickel oxide calcined at high temperature
would result in a different nickel surface, when compared to the
preparation not through the nickel oxide. Based on the results of
the present study, the surface of the Ni catalyst, Ni(1 0 0)/Ni(1 1 1),
could be controlled by the calcination temperature of the NiO pre-
cursor.
3.2. Time course of the exchanged species in the pulse experiment
Fig. 3 shows the change in the ion current of each isotopo-
logue over Ni773. Fig. 4 shows that over Ni1373. Both results were
obtained by the reaction at 573 K. As for the reaction over Ni773,
the CH D signal first reached a peak, and those of the other isotopo-
3
logues were delayed. On the other hand, as for Ni1373, the signals of
CH D and CH D simultaneously reached peaks, while the signals
3
2
2
of CHD and CD were broad, and particularly, the signal of CD had
3
4
4
two peaks.
Two mechanisms for the H/D exchange reaction of CH4
were proposed, that is, a stepwise exchange and a multiple
exchange [9]. For the stepwise exchange, one hydrogen atom in
methane is exchanged at each residence on the surface. For the
Fig. 4. Change in the ion current of each isotopologue over Ni1373: (ꢀ) CH3D; (᭹)
CH2D2; (ꢀ) CHD3; and (ꢁ) CD4.

114
T. Osawa et al. / Journal of Molecular Catalysis A: Chemical 298 (2009) 111–114
4
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(
[
[
The H/D exchange reactions of methane in a deuterium stream
in a fixed bed flow reactor were studied over the reduced nickel cat-
alyst. The Ni1373, prepared from the nickel oxide calcined at 1373 K,
has a higher activity than the Ni773 prepared from the nickel oxide
calcined at 773 K. This could be attributed to the ratio of the Ni(1 0 0)
to Ni(1 1 1). As the Ni1373 could have a higher Ni(1 0 0)/Ni(1 1 1)
ratio, Ni1373 had a higher activity than Ni773.
[
[
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