New aspects for heterogeneous cobalt-catalyzed hydroamination of ethanol

Article abstract of DOI:10.1016/j.jcat.2007.10.013

Gas-phase hydroamination of ethanol and ammonia over supported cobalt on silica catalysts was investigated at 103 kPa. Besides the desired products, mono-, di- and triethylamine, acetonitrile, diethylimine, and hydrocarbons (methane, ethene, ethane, propane, and propene) were identified as byproducts. The formation of hydrocarbons was found to depend on the cobalt loading of the catalyst and on the pretreatment of the catalyst. Guaranteeing a sufficient reduction of the cobalt catalyst allows a reduction in the selectivity of hydrocarbons from 25 to 10 mol% at a constant conversion of 90%. In addition, rapid deactivation of the catalyst was observed in the absence of hydrogen. The deactivation was ascribed to the interaction of ammonia with the catalyst and is largely reversible. Carbonaceous species are present on the spent catalyst, as shown by temperature-programmed reduction. These species are thought to be responsible for a slow deactivation in the presence of hydrogen.

Full text of DOI:10.1016/j.jcat.2007.10.013

Journal of Catalysis 253 (2008) 111–118
www.elsevier.com/locate/jcat
New aspects for heterogeneous cobalt-catalyzed hydroamination of ethanol
A.K. Rausch a, E. van Steen b, F. Roessner a,∗
a
Industrial Chemistry 2, University of Oldenburg, 26111 Oldenburg, Germany
b
Catalysis Research Centre, Department of Chemical Engineering, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa
Received 4 May 2007; revised 6 October 2007; accepted 21 October 2007
Available online 26 November 2007
Abstract
Gas-phase hydroamination of ethanol and ammonia over supported cobalt on silica catalysts was investigated at 103 kPa. Besides the desired
products, mono-, di- and triethylamine, acetonitrile, diethylimine, and hydrocarbons (methane, ethene, ethane, propane, and propene) were iden-
tified as byproducts. The formation of hydrocarbons was found to depend on the cobalt loading of the catalyst and on the pretreatment of the
catalyst. Guaranteeing a sufficient reduction of the cobalt catalyst allows a reduction in the selectivity of hydrocarbons from 25 to 10 mol% at a
constant conversion of 90%. In addition, rapid deactivation of the catalyst was observed in the absence of hydrogen. The deactivation was ascribed
to the interaction of ammonia with the catalyst and is largely reversible. Carbonaceous species are present on the spent catalyst, as shown by
temperature-programmed reduction. These species are thought to be responsible for a slow deactivation in the presence of hydrogen.
© 2007 Elsevier Inc. All rights reserved.
Keywords: Ethanol amination; Cobalt; Catalyst deactivation
1. Introduction
not demonstrated a single consistent mechanism, because they
were achieved for a range of catalysts and educts under different
reaction conditions. Two mechanisms are primarily discussed
for the hydroamination of ethanol [3,5–7], both of which as-
sume that the abstraction of the α-H-atom of the alcohol is the
rate-determining step in amination. These mechanisms differ
with respect to the nitrogen-containing intermediates adsorbed
on the catalysts surface. Baiker et al. [7] investigated the ki-
netics of the amination of long-chain aliphatic alcohols with
methylamines and proposed a reaction pathway with nitrogen-
containing intermediates with a hydroxyl group (see Scheme 1).
The intermediate amino alcohol is converted through elimina-
tion of the hydroxyl group and subsequent addition of hydrogen
to amines. Jones et al. [5] and Jackson et al. [6] proposed a
mechanism for the amination of ethanol with ammonia based
on their experiments with nickel catalysts suggesting the for-
mation of surface ethylidene [5] or ethyl [6] intermediates. The
C–N bond is formed in a reaction between the chemisorbed
amine or ammonia and an oxygen-free surface derivative of the
alcohol (see Scheme 2). This mechanism yielded a better de-
scription for hydroamination of isotopic-labeled ethanol with
ammonia. However, DFT calculations performed by Cheng et
al. [8] showed that the mechanism proposed by Baiker et al. [7]
Short-chain aliphatic amines (C2–C6) are important inter-
mediates for the chemical and pharmaceutical industries. Nu-
merous drugs, dyes, herbicides, and other compounds contain
amino groups that are introduced by reaction with an amine [1].
The production of aliphatic amines is often performed by hy-
droamination, the conversion of an alcohol with ammonia or
a primary or secondary amine in the presence of hydrogen.
A typical heterogeneous catalyst for hydroamination contains
metallic cobalt, nickel or copper supported on silica or alumina.
The conversion of alcohol is believed to be metal-catalyzed,
with activity for the conversion of the alcohol proportional to
the metal surface area [2].
Due to the manifold applications of amines, hydroamination
has been investigated using a variety of alcohols and amines
or ammonia [3]. The hydroamination of ethanol with ammo-
nia, the topic of the present study, was investigated by Sewell
et al. [4] on cobalt catalysts and by Jones et al. [5] and Jackson
et al. [6] on nickel catalysts. The results reported to date have
*
Corresponding author. Fax: +49 0441 798 3360.
E-mail address: frank.roessner@uni-oldenburg.de (F. Roessner).
0021-9517/$ – see front matter © 2007 Elsevier Inc. All rights reserved.
doi:10.1016/j.jcat.2007.10.013

112
A.K. Rausch et al. / Journal of Catalysis 253 (2008) 111–118
Scheme 1. Reaction pathway for amination of an aliphatic alcohol by a primary or secondary amine via hydroxygroup containing intermediates (∗, active site).
Adapted from [5].
Scheme 2. Reaction pathway for amination of ethanol by ammonia via ethylidene intermediate. Adapted from [3].
is energetically slightly favored on nickel and cobalt catalysts,
but both mechanisms may be operative at the same time under
typical hydroamination conditions.
During hydroamination, various byproducts can be ob-
served, including hydrocarbons [9–11], nitriles [10], imines
[10] and enamines [7]. The formation of hydrocarbons, which is
ascribed to the hydrogenolysis of amines [10,11], is particularly
undesirable. The formation of other products might be the result
of successive dehydrogenation of the product amines. Selectiv-
ity of amines and byproducts strongly depends on such reaction
parameters as feed composition, temperature, and hydrogen
partial pressure. The affect of feed composition, temperature
(between 140 and 200 ◦C), and hydrogen partial pressure on
the amination of ethanol has been investigated [4]; however,
a detailed analysis of the byproducts has not been conducted.
Copper, nickel, and cobalt catalysts may deactivate in alco-
hol hydroamination. Mechanisms have been proposed for the
deactivation of these catalysts via formation of metal nitrides,
metal carbides, and carbonaceous deposits during the dispro-
portionation of methylamines [11]. In addition, the influence

A.K. Rausch et al. / Journal of Catalysis 253 (2008) 111–118
113
of hydrogen on catalyst deactivation and conversion of long-
chain alcohols in liquid phase has been investigated for copper
catalysts. However, the influence of hydrogen on the product
selectivity has not been discussed [12].
In the present study, the hydroamination of ethanol was
investigated on silica-supported cobalt catalysts as a model
catalyst known to have catalytic activity in this reaction [4].
The investigation focused on the formation of hydrocarbons as
byproducts and on deactivation of the catalysts.
a six-port valve. A 30 m × 0.32 mm i.d. capillary column with
a 1 µm phenylsiloxan/methylsiloxan film was used for separa-
tion. Due to the complexity of the product mixture, two sets of
gas chromatography programs, adapted for proper separation of
nitrogen-containing products and hydrocarbons, were used for
complete analysis. The product identification was confirmed by
a HP 6890 gas chromatograph with a mass-sensitive detector.
2.4. TPR as a postreaction treatment
Postsynthesis characterization of some catalysts was per-
formed by TPR. For this purpose, the catalysts were cooled
after the reaction to 100 ◦C, and the reaction apparatus and the
reactor were flushed with hydrogen for at least 20 min. Then the
temperature was increased to 700 ◦C at a rate of 10 ◦C/min, and
the compounds desorbed in hydrogen flow during the TPR were
analyzed by mass spectrometry using an Omnistar GSD 300O
(Pfeiffer Vacuum) equipped with a Prisma QMS 200 quadrupol
mass spectrometer.
2. Experimental
2.1. Catalyst preparation
Co/SiO2 catalysts with different cobalt loadings were pre-
pared by incipient wetness impregnation of silica gel (Sigma–
Aldrich, SBET = 110 m2/g, Vpore = 0.3 cm3/g) using an aque-
ous solution of Co(NO3)2·6H2O (Fluka). The cobalt concen-
tration was adjusted to yield metal loadings of 1, 5, 10, 15, and
20 wt%. After impregnation, the catalysts were dried at 100 ◦C
for 16 h.
3. Results and discussion
3.1. Catalyst characterization
2.2. Catalyst characterization
Table 1 shows the cobalt content as determined by AAS for
the prepared catalysts. The measured cobalt content is in good
agreement with the amounts adjusted during the synthesis. The
cobalt recovery rate was between 90 and 98%. Fig. 1 presents
the results of the TPR of the oxidized catalysts. The profiles are
typical for supported cobalt on silica [13] containing Co3O4.
The reduction of Co3O4 is believed to proceed stepwise, be-
cause Co3O4 contains Co2+ and Co3+ ions [14]:
The metal loading of the prepared catalysts was confirmed
by atomic-absorption spectroscopy (AAS) using a Varian Spec-
traAA 300 spectroscope. The reducibility of the catalysts was
investigated by temperature-programmed reduction (TPR) in
hydrogen using a TPR apparatus (Raczek GmbH) with a ther-
mal conductivity detector (TCD). The samples were oxidized
in air at 500 ◦C before the TPR. The TPR was performed at 50
to 800 ◦C with a temperature ramp of 10 ◦C/min using 50 ml
(NTP)/min of 5 vol% H2 in argon as the reduction gas.
Co3O4 + H2 → 3CoO + H2O,
3CoO + 3H2 → 3Co + 3H2O.
(1)
(2)
2.3. Hydroamination of ethanol
Consequently, the TPR spectra show two main peaks of hy-
drogen consumption. The first peak at approximately 300 ◦C
represents the reduction step of Co3O4 to cobalt(II) oxide
[Eq. (1)]; the second peak, which extends over a wider temper-
ature range, can be assigned to the reduction of CoO to metal-
lic cobalt. All investigated catalyst samples showed these two
peaks, with the second peaks always being the largest. This is in
agreement with the fact that the second reduction step requires
a threefold greater amount of hydrogen, although it should be
noted that the measured ratio of the two peaks is always <3.
This ratio increases with increasing cobalt loading (from 1.2
The amination of ethanol was performed in fixed-bed
reactor at atmospheric pressure. For the catalytic experi-
ment, a nitrogen flow (14 ml (NTP)/min) was saturated with
ethanol at 36 ◦C, resulting in a flow rate of gaseous ethanol of
2.3 ml (NTP)/min. The ammonia flow rate was always 7 ml
(NTP)/min, resulting in a molar ratio of NH3 to EtOH of 3.
Thus, the experiments were performed in excess ammonia. The
hydrogen flow rate was varied between 0 and 80 (NTP)ml/min
with nitrogen as a balance, keeping the partial pressures of am-
monia and ethanol in the feed constant at 6.8 and 2.3 kPa,
respectively. For a hydrogen flow of 80 ml (NTP)/min, the
molar ratio of EtOH:NH3:H2 was 2:7:80. Most experiments
were performed using 165 mg of 9.2 wt% Co/SiO2. In this
case, the weight hourly space velocity (WHSV) of ethanol was
1.5 gEtOH/gcat h, corresponding to a contact time of 0.2 s for
ethanol. Before each experiment, the catalyst precursor was re-
duced in situ in pure hydrogen (60 ml (NTP)/min) at 500 ◦C
for 9 h. Deviating reaction and reduction conditions are given
where appropriate.
Table 1
Determination of cobalt content of Co/SiO catalysts synthesized by impreg-
2
nation
Cobalt content adjusted
in synthesis (wt%)
Cobalt content found
by AAS (wt%)
Cobalt recovery rate
(%)
1
5
10
15
20
0.9
4.9
9.2
14.3
18.6
90
98
92
95
93
The products were analyzed using an online gas chromato-
graph (HP 6890 with a flame ionization detector) equipped with

114
A.K. Rausch et al. / Journal of Catalysis 253 (2008) 111–118
for 0.9 wt% Co/SiO2 to 2.4 for 18.6 wt% Co/SiO2). This may
be attributed to the increased formation of (weakly interacting)
cobalt–silica species with decreasing cobalt concentration. The
reduction of all catalysts was not complete at temperatures be-
low 650 ◦C. Thus, at a reduction temperature of 500 ◦C, which
was the typical reduction temperature before the hydroamina-
tion, catalysts with different cobalt loadings were reduced to
different extents. A higher reduction temperature was not ap-
plied, to prevent metal sintering.
bution of hydroamination depends on the molar ratio of ethanol
and ammonia, hydrogen partial pressure, temperature, and the
cobalt loading of the catalyst. The selectivity of the hydrocar-
bons is particularly influenced by the reaction temperature and
cobalt loading on the catalyst.
3.3. Formation of hydrocarbons
Fig. 2 shows the results for the hydroamination of ethanol
with ammonia at 210 ◦C for silica-supported catalysts with a
cobalt loading of 1 to 20 wt% after 30 min time on stream.
The ethanol conversion over these catalysts ranged from 35 to
50 mol%. The observed variation in the conversion can be at-
tributed to differences in the reduced metal surface area of the
catalysts, due to the variation in the cobalt loading, reducibility,
and cobalt metal dispersion accompanying various cobalt load-
ings [2]. The amine selectivity decreased with increasing cobalt
loading, accompanied by an increase in hydrocarbon selectiv-
ity. The selectivity for acetonitrile and diethylimine was low
for all catalysts. In essence, the observed trend in the change of
selectivity of hydrocarbons correlated with the variation in con-
version; higher conversion resulted in higher selectivity for the
formation of hydrocarbons at the expense of amine selectivity.
A similar correlation of amine and hydrocarbon selectivity
was also observed with variation of the reaction temperature be-
tween 130 and 300 ◦C for the hydroamination of ethanol over
9.2 wt% Co/SiO2 using a feed comprising EtOH, NH3, H2, and
3.2. Hydroamination of ethanol
The hydroamination of ethanol yielded the amines mo-
noethylamine (MEA), diethylamine (DEA), and triethylamine
(TEA). Acetonitrile (ACN) and N-ethylideneethylamine (di-
ethylimine [DEI]) were identified as other nitrogen-containing
side products by mass spectroscopy. It might be assumed that
the latter two products are formed by dehydrogenation of mo-
noethylamine and diethylamine, respectively (see Scheme 3).
The formation of equivalent dehydrogenation products was re-
ported previously [7,10]. In addition to the nitrogen-containing
products, up to 14 mol% of hydrocarbon was formed during
hydroamination. Methane, ethane, ethane, and even propane
and propene were identified as the hydrocarbon products. The
formation of hydrocarbons was been mentioned previously
[10,11], but the high yield and the wide variety of the hydrocar-
bons was surprising. Their formation was investigated to find
ways to suppress them, because hydrocarbons can be major
byproducts of hydroamination. In general, the product distri-
◦
Fig. 2. Influence of cobalt loading on conversion and selectivity at 210 C
over silica supported cobalt. Molar ratio EtOH:NH :H :N = 2:7:80:14,
3
2
2
Fig. 1. Temperature-programmed reduction of Co O /SiO catalyst precursors
with different cobalt loadings.
WHSV = 1.5 g
/g h (for 0.9 wt% Co/SiO WHSV = 0.6 g
/g h;
cat
EtOH
cat
3
4
2
EtOH
2
other N-compounds are acetonitrile and diethylimine).
Scheme 3. Consecutive reactions for formation of ethylamines and corresponding reduction products.

A.K. Rausch et al. / Journal of Catalysis 253 (2008) 111–118
115
Fig. 4. Hydrocarbon selectivity over 9.2 wt% Co/SiO as a function of f reaction
2
Fig. 3. Effect of reaction temperature on the hydroamination of ethanol over
temperature. Contact time = 0.2 s. Molar ratio EtOH:NH :H :N = 2:7:80:14.
9.2 wt% Co/SiO . All measurements after 30 min t.o.s. at the given conditions.
3
2
2
2
All measurements after 30 min t.o.s. at the given conditions.
Molar ratio EtOH:NH :H :N = 2:7:80:14.
3
2
2
the molar ratio of methane:ethane:propane was 17:4:1. In ad-
dition, ethene and propene were formed at temperatures above
210 ◦C, reaching their maximum selectivity at 250 ◦C. The for-
mation of methane and C3-hydrocarbons requires C–C-bond
fission and coupling. The high molar methane content indi-
cates a rather facile fission of the C–C bond. The absence of
methylamines in the product stream would indicate C–C fission
in a C2-hydrocarbon surface species formed on hydrogenoly-
sis of ethylamines. The surface C1 species can then recombine
to form longer-chain hydrocarbons, such as C3 hydrocarbons,
in a process similar to the Fischer–Tropsch process [15,16]. It
should be noted, however, that the observed molar ratio of C2
hydrocarbons to methane in the hydroamination of ethanol was
larger than that of C3 hydrocarbons to C2 hydrocarbons. The
opposite was observed in the Fischer–Tropsch synthesis [16].
This may be explained by a dual reaction pathway for the for-
mation of C2 hydrocarbons, that is, through desorption of C2
surface species formed directly from ethanol, as proposed by
Jones et al. [5] and Jackson et al. [6], on the hydrogenolysis of
ethylamines and through desorption of C2 surface species gen-
erated through a chain growth process.
Because hydrocarbons are undesired byproducts, efforts
were taken to decrease their selectivity while maintaining a
high level of ethanol conversion. It was found that the degree
of reduction of the cobalt catalyst is an important factor in the
production of the hydrocarbons. Fig. 5 shows the ethanol con-
version and the hydrocarbon selectivity as a function of reaction
temperature for a 0.9 wt% Co/SiO2 catalyst reduced before the
reaction in 60 ml (NTP)/min hydrogen at different reduction
conditions: 1 h at 300 ◦C, 14 h at 350 ◦C, 14 h at 500 ◦C, and
14 h at 600 ◦C. The four samples had different degrees of reduc-
tion (cf. TPR spectra of the 0.9 wt% Co/SiO2 catalyst in Fig. 1);
however, similar levels of ethanol conversion were obtained
for samples reduced at temperatures below 500 ◦C (Fig. 5).
The sample reduced at 600 ◦C showed a lower ethanol con-
version, which might be explained by sintering of the cobalt
metal and the simultaneous decrease in the active metal sur-
face [2]. The selectivity of the hydrocarbons decreased with
increasing applied reduction temperature. At a reaction temper-
ature of 250 ◦C, the selectivity of hydrocarbons was 10 mol%
N2 at a molar ratio of 2:7:80:14. The effect of reaction tempera-
ture was investigated at different space velocities ranging from
0.38 to 8 gEtOH/gcat h by varying the catalyst mass, resulting in
contact times between 0.8 and 0.05 s. These experiments started
at 130 ◦C, and the temperature was increased by 10 ◦C every
30 min, with each sample obtained immediately before the next
temperature increase. Taking into account the contact time of
<1 s, the chosen time range of 30 min should be sufficiently
long to obtain steady-state conditions at the next temperature
level. Identical results were obtained by decreasing the tem-
perature stepwise from 300 ◦C. Thus, catalyst deactivation did
not falsify these results, legitimating the use of a single catalyst
sample for the entire temperature range.
Fig. 3 shows the yields of amines and hydrocarbons as a
function of temperature at the three different contact times.
Contact time strongly affected the amount of amines formed
relative to the amount of hydrocarbons formed. An increase
in the contact time (and thus a decrease in the space veloc-
ity) at a particular temperature was accompanied by an increase
in the hydrocarbon yield. The influence of contact time on
the distribution of amines and hydrocarbons shows that this
distribution is kinetically controlled. At higher reaction tem-
peratures, the amount of hydrocarbons formed relative to the
amount of amines formed increases. The reaction temperature,
at which exclusively the formation of hydrocarbons is observed,
decreases with increasing contact time. For instance, at a con-
tact time of 0.05 s, a temperature above 300 ◦C is required to
observe the exclusive formation of hydrocarbons, whereas at a
contact time of 0.8 s, this occurs at temperatures above 250 ◦C.
The increased hydrocarbon selectivity with increasing contact
time indicates a consecutive pathway, that is, formation from
the primary products of hydroamination. This conclusion is in
accordance with previous proposals for the formation of hydro-
carbons via hydrogenolyses of amines [10,11].
Fig. 4 shows the selectivity of the individual hydrocarbon
compounds as a function of reaction temperature at a contact
time of 0.2 s over 9.2 wt% Co/SiO2 using a feed comprising
EtOH, NH3, H2, and N2 at a molar ratio of 2:7:80:14. The
saturated hydrocarbons methane, ethane, and propane were the
main representatives of this group of products, and at 300 ◦C,

116
A.K. Rausch et al. / Journal of Catalysis 253 (2008) 111–118
Fig. 5. Ethanol conversion and selectivity of hydrocarbons as a func-
Fig. 6. Long-duration experiment with switchover from hydrogen to nitro-
◦
tion of reaction temperature on 0.9 wt% Co/SiO reduced at different
gen on 9.2 wt% Co/SiO at 210 C. WHSV = 0.75 g
/g h; molar ratio
cat
EtOH
2
2
conditions. All measurements after 30 min t.o.s. at the given conditions:
EtOH:NH :H :N = 2:7:80:14, 2:7:0:94, respectively.
3
2
2
WHSV = 0.75 g
/g h; molar ratio EtOH:NH :H :N = 2:7:80:14.
cat
EtOH
3
2
2
when the catalyst was reduced at 500 ◦C and 25 mol% after re-
duction at 350 ◦C at similar levels of ethanol conversion. Thus,
it may be concluded that the secondary formation of hydrocar-
bons is correlated with the amount of nonreduced cobalt sites
in the catalyst. The enhanced hydrocarbon formation might be
directly or indirectly related to the number of sites comprising
of nonreduced cobalt present in the catalyst. A direct corre-
lation would have been be obtained had these sites catalyzed
amine hydrogenolysis. Sewell et al. [2] proposed that acidic
sites in the catalysts, present as, for example, an unreduced
Co2+ support compound, are responsible for disproportionation
reactions, particularly those yielding monoethylamine, which
may exhibit higher reactivity for hydrogenolysis. This would
lead to an indirect correlation with the number of nonreduced
cobalt sites.
Fig. 7. Yields of all products in a long-duration experiment with switchover
from hydrogen to nitrogen. Conditions like in Fig. 6. Hydrocarbons include
ethane and ethene.
on stream restored the original activity within 30 min. This ac-
tivity remained nearly constant for another 20 h on stream.
Two main deactivation phenomena were observed: (i) deac-
tivation in the presence of hydrogen in the first few hours, which
can be explained by deactivation of the most active catalytic
sites by irreversible adsorption of educts or products and their
decomposition to carbonaceous species or carbon deposits, and
(ii) collapse of the catalyst activity when hydrogen was elimi-
nated from the feed. This rapid drop in catalyst activity and its
reversibility were previously ascribed to the formation of cobalt
nitrides, which can be formed by ammonia in the absence of hy-
drogen [11,12].
A postsynthesis characterization was performed in 9.2 wt%
Co/SiO2 samples that had been used in the hydroamination of
ethanol at 210 ◦C in hydrogen and nitrogen atmosphere, respec-
tively. Before the temperature ramp, hydrogen was flushed for
at least 20 min at 100 ◦C through the reactor. Methane was the
only product that evolved during TPR (see Fig. 8), indicating
gasification of carbonaceous species on the catalyst surface.
Methane evolution was seen in two temperature ranges. A first
peak of methane was observed at approximately 260 ◦C, which
is slightly higher than the reaction temperature. This peak can
be ascribed to reaction intermediates that remained at reaction
3.4. Deactivation of the cobalt catalyst
A long-duration experiment at 210 ◦C was performed with a
switchover from hydrogen to nitrogen (see Figs. 6 and 7) to gain
more insight in the effect of catalyst deactivation and the effect
of hydrogen on product selectivity. Under the reaction condi-
tions used (with a reduced space velocity of 0.75 gEtOH/gcat h),
formation of the amines MEA, DEA, and TEA, along with hy-
drocarbons and diethylimine, was observed. Acetonitrile as a
product could not be detected in the presence of hydrogen.
Figs. 6 and 7 show that the conversion of ethanol and the
selectivity of amines decreased at the beginning of the reac-
tion, reaching steady-state conditions after 5 h time on stream.
Whereas ethanol conversion decreased from 52 to 45%, amine
selectivity decreased from 75 to 72 mol% with a concomitant
increase in the hydrocarbon selectivity. The substitution of hy-
drogen by nitrogen completely changed the reaction behavior of
the cobalt catalyst; conversion dropped from 45 to 11%. Ace-
tonitrile was the only product, with amines, diethylimine, and
hydrocarbons no longer formed. During reaction in nitrogen at-
mosphere, the conversion of ethanol decreased continuously,
dropping to <1% after 20 h on stream. The deactivation is fully
reversible; switching from nitrogen again to hydrogen after 44 h

A.K. Rausch et al. / Journal of Catalysis 253 (2008) 111–118
117
Fig. 8. Methane evolution in postsynthesis temperature-programmed reduction
Fig. 9. TPR of 9.2 wt% Co/SiO after treatment with 25 vol% ammonia.
2
of 9.2 wt% Co/SiO . Molar ratio EtOH:NH :H :N = 2:7:80:14 and 2:7:0:94,
2
3
2
2
respectively.
experiment of the spent catalyst (Fig. 8) can be explained by
the immediate release of adsorbed nitrogen species during the
isothermal step at 100 ◦C in hydrogen atmosphere. This finding
demonstrates that the interaction of ammonia with the catalyst
is rather weak and can be enduring only in the absence of hy-
drogen.
conditions on the cobalt surface due to strong adsorption. A sec-
ond peak of methane evolution was detected at around 600 ◦C.
At these temperatures, carbon deposits and strongly bonded car-
bonaceous species can be hydrogenated to methane. The latter
species can accumulate with time on stream and may cause ir-
reversible catalyst deactivation.
4. Conclusion
Nitrogen-containing compounds and water were not de-
tected during these experiments, indicating the absence of
nitrogen- and oxygen-containing species in the catalyst. The ab-
sence of nitrogen-containing compounds is surprising, because
a strong surface poisoning effect was observed when the reac-
tion was performed in a nitrogen atmosphere instead of a hy-
drogen atmosphere (see Figs. 6 and 7). This effect was ascribed
to the interaction between ammonia and the cobalt surface, for
example, the formation of cobalt nitrides.
During the hydroamination of ethanol, such products as ace-
tonitrile, diethylimine, methane, ethene, ethane, propane, and
propene have been identified along with the three desired eth-
ylamines. The formation of hydrocarbons can be explained by
catalytic fragmentation of the ethylamines through the genera-
tion of ethyl and ethylidene species, followed by carbon–carbon
bond fission and coupling.
The formation of hydrocarbons depends on the pretreat-
ment of the applied catalyst. Catalysts reduced at higher tem-
peratures exhibit lower hydrocarbon production. This is indi-
rectly ascribed to the greater catalyst reduction. Oxidic cobalt
species are thought to catalyze amine disproportionation reac-
tions, yielding more monoethylamine, which has the highest
reactivity for hydrogenolysis.
Ethanol conversion and selectivity depend strongly on the
presence of hydrogen. Without hydrogen, a reversible deacti-
vation occurs that can be ascribed to a ammonia–cobalt inter-
action, such as strong chemisorption or formation of nitrides.
Carbon-containing species and carbonaceous deposits result in
decreased catalyst activity as well. They also are formed in hy-
drogen as well as in nitrogen atmosphere, as demonstrated by
TPR.
Because no evidence of nitrogen was found on the deacti-
vated catalyst, two experiments with ammonia were performed,
to evaluate whether the applied TPR experiment is feasible for
detecting nitrogen-containing cobalt species. A catalyst con-
taining 9.2 wt% Co was treated at 310 ◦C for 25 h with a
mixture of 25 vol% of ammonia in hydrogen and nitrogen, re-
spectively [20 ml (NTP)/min]. This temperature and reaction
time should have allowed the formation of cobalt–nitrogen sur-
face compounds. After this treatment, the catalyst was cooled
to 70 ◦C, and the ammonia flow was turned off. Pure hydrogen
was passed through the reactor for approximately 15 min, sim-
ulating the isothermal step at the beginning of each TPR exper-
iment. Subsequently, the temperature was increased at a rate of
10 ◦C/min (Fig. 9). After treatment of the catalyst in a NH3/H2
mixture, no products could be detected in the TPR, indicat-
ing the absence of strongly adsorbed nitrogen-containing sur-
face species and the absence of cobalt nitride if hydrogen was
present. This finding demonstrates that the ammonia–catalyst
interaction is not responsible for deactivation in the presence of
hydrogen. Ammonia was observed in the H2-TPR of the cata-
lyst treated in NH3/N2, indicating the presence of chemisorbed
ammonia or cobalt nitride on the catalyst surface and explain-
ing its deactivation. Interestingly, the release of ammonia oc-
curred immediately after the switchover to hydrogen at 70 ◦C.
Thus, the absence of nitrogen-containing species in the TPR
In summary, high selectivity of ethylamines was obtained
with silica-supported cobalt catalysts at high hydrogen partial
pressures and low temperatures using highly reduced catalysts.
Acknowledgments
The authors gratefully acknowledge financial support from
the scholarship fund of the German Chemical Industry (VCI)
and from the German Federal Ministry of Education and Re-
search (BMBF, Germany) and the National Research Founda-
tion of South Africa (Project 39.6.L2A G.C).

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References
[6] S.D. Jackson, J.R. Jones, A.P. Sharratt, L.F. Gladden, R.J. Cross, G. Webb,
Chem. Ind. 89 (2003) 453–460.
[7] A. Baiker, W. Caprez, W.L. Holstein, Ind. Eng. Chem. Prod. Res. Dev. 22
(1983) 217–225.
[1] G. Heilen, H.J. Mercker, D. Frank, R.A. Reck, R. Jäck, in: W. Gerhertz
(Ed.), Ullmanns Encyclopedia of Industrial Chemistry, vol. 2A, fifth ed.,
VCH, Weinheim, 1985, pp. 1–18.
[8] H. Cheng, J.W. Mitchell, K.S. Hayes, in: NATO Science Series II: Mathe-
matics, Physics and Chemistry, vol. 68, 2002, pp. 385–403.
[9] J.M. Pommersheim, J. Coull, AIChE J. 17 (1971) 1075–1080.
[10] J.R. Anderson, N.J. Clark, J. Catal. 5 (1966) 250–263.
[11] A. Baiker, D. Monti, Y.S. Fan, J. Catal. 88 (1984) 81–88.
[12] A. Baiker, Ind. Eng. Chem. Prod. Res. Dev. 20 (1981) 615–618.
[13] E. van Steen, G.S. Sewell, R.A. Makhote, C. Micklethwaite, H. Manstein,
M. de Lange, C.T. O’Connor, J. Catal. 162 (1996) 220–230.
[14] B. Viswanathan, R. Gopalakrishnan, J. Catal. 99 (1986) 342–348.
[15] M.E. Dry, Appl. Catal. A 138 (1996) 319–344.
[2] G.S. Sewell, C.T. O’Connor, E. van Steen, J. Catal. 167 (1997) 513–521.
[3] T. Mallat, A. Baiker, in: G. Ertl, W.L. Knözinger, J. Weitkamp (Eds.),
Handbook of Heterogeneous Catalysis, vol. 5, VCH, Weinheim, 1997,
pp. 2334–2339.
[4] G. Sewell, C. O‘Connor, E. van Steen, Appl. Catal. A 125 (1995) 99–
112.
[5] J.R. Jones, A.P. Sharratt, S.D. Jackson, L.F. Gladden, G. Webb, in: J. Allen
(Ed.), Synthesis and Applications of Isotopically Labeled Compounds,
1994, vol. 5, Wiley, New York, 1995, pp. 751–759.
[16] M. Claeys, E. van Steen, Stud. Surf. Sci. Catal. 152 (2004) 601–680.