Ni?Cu Hydrotalcite-Derived Mixed Oxides as Highly Selective and Stable Catalysts for the Synthesis of β-Branched Bioalcohols by the Guerbet Reaction

Article abstract of DOI:10.1002/cssc.201601042

A series of Ni?Cu hydrotalcite-derived mixed oxides have been synthesized and evaluated as heterogeneous catalysts for the dimerization of linear aliphatic alcohols to afford β-branched Guerbet alcohols. The use of the hydrotalcite-structured catalyst precursor highly favors the catalyst stability. This Cu/Ni catalyst has an enhanced reducibility of Ni²⁺ species under reaction conditions, favoring the hydrogen transfer and hydrogenation capacity of the catalyst system. Catalytic results are reported for C₈, mixed C₈/C₁₀, and C₁₈ alcohol feeds, with full conversions and Guerbet product purities of 72.5–96 %.

Full text of DOI:10.1002/cssc.201601042

DOI: 10.1002/cssc.201601042
Full Papers
NiꢀCu Hydrotalcite-Derived Mixed Oxides as Highly
Selective and Stable Catalysts for the Synthesis of b-
Branched Bioalcohols by the Guerbet Reaction
Willinton Y. Hernꢀndez,[a] Kevin De Vlieger,[a, b] Pascal Van Der Voort,*[a] and
An Verberckmoes*[b]
A series of NiꢀCu hydrotalcite-derived mixed oxides have been
synthesized and evaluated as heterogeneous catalysts for the
dimerization of linear aliphatic alcohols to afford b-branched
Guerbet alcohols. The use of the hydrotalcite-structured
catalyst precursor highly favors the catalyst stability. This Cu/Ni
catalyst has an enhanced reducibility of Ni2+ species under re-
action conditions, favoring the hydrogen transfer and hydroge-
nation capacity of the catalyst system. Catalytic results
are reported for C8, mixed C8/C10, and C18 alcohol feeds, with
full conversions and Guerbet product purities of 72.5–96%.
Introduction
In recent years, much attention and research effort has been
focused on the utilization of biomass and biomass-derived
products as renewable energy sources and future feedstocks
for the chemical industry. Bioalcohols, such as ethanol and bu-
tanol, are produced in increasing amounts, for use mainly as
biofuels and/or fuel blenders.[1] Nevertheless, the upgrading of
these types of biomolecules to more complex and functional
ones is highly desirable with a view to increasing chemical
complexity and producing commodities from renewable sour-
ces. One interesting way to valorize linear aliphatic alcohols is
by converting them into the branched dimers, the so-called
Guerbet alcohols.[2] These branched alcohols can be used in
the production of highly value-added solvents, surfactants, and
lubricants.[3]
time, acidic, basic, and dehydrogenation/hydrogenation
properties.
Most of the reported studies on upgrading bioalcohols by
the Guerbet reaction have described the self and cross con-
densations of short-chain alcohols, such as methanol, ethanol,
propanol and butanol.[2b,5] Nevertheless, fatty alcohols (C8–C18)
obtained directly from natural fats and oils or from fatty acids
and esters, can also be upgraded to their respective Guerbet
dimers. The condensation of fatty alcohols has not been com-
monly reported in the literature; however, the importance of
the Guerbet reaction in converting these types of substrates is
reflected the number of patents that concern such reactions.[6]
The higher molecular weight b-branched primary alcohols
(C16+) formed in this way have great practical value for the
production of detergents, lubricants, and personal care
products.[3]
The Guerbet reaction involves condensation of two alcohols
forming a b-branched dimer alcohol, with the concomitant re-
lease of water. The Guerbet reaction is generally agreed to pro-
ceed by four main sequential steps: 1) dehydrogenation of the
starting alcohols to give the corresponding aldehydes; 2) aldol
condensation of the resulting aldehydes; 3) dehydration and
4) hydrogenation of the unsaturated condensation products to
give the higher Guerbet alcohols.[4] Therefore, the reaction re-
quires the use of a catalyst system that exhibits, at the same
Typically, the Guerbet reaction of these types of fatty alcohol
substrates can be carried out by using a base (e.g., KOH) and
a catalyst to accelerate the overall reaction rate and to favor
the selectivity of the process to the target molecule. Because
the dehydrogenation is considered to be the rate-determining
step in liquid-phase Guerbet reactions, most of the catalyst
systems described in the patent literature have concerned the
use of transition or noble metals in the homogeneous phase
as catalysts.[7] Although high conversions and selectivities can
be obtained with these types of homogeneous systems (base
and homogeneous catalyst), issues related to the product pu-
rification, recovery, and cost of the catalyst and waste treat-
ment are important for the industrial production of Guerbet al-
cohols. The use of heterogeneous systems (base and heteroge-
neous catalyst) has been reported as an alternative way to
deal with the aforementioned problems, as reviewed exten-
sively in ref. [7]. Dehydrogenation catalysts based on Cu, Ni,
Rh, Ru, Pd, and Ir are the most commonly used. Nevertheless,
from an industrial point of view, the utilization of noble metal-
based catalysts gives rise to a significant increase in the final
[a] Dr. W. Y. Hernꢀndez, K. De Vlieger, Prof. P. Van Der Voort
Center for Ordered Materials, Organometallics and Catalysis (COMOC)
Department of Inorganic and Physical Chemistry, Ghent University
Krijgslaan 281-S3, 9000 Ghent (Belgium)
E-mail: Pascal.VanDerVoort@Ugent.be
[b] K. De Vlieger, Prof. A. Verberckmoes
Industrial Catalysis and Adsorption Technology (INCAT), Department of
Chemical Engineering and Technical Chemistry, Ghent University
Valentin Vaerwyckweg 1, 9000 Ghent (Belgium)
E-mail: An.Verberckmoes@Ugent.be
Supporting information and the ORCID identification number(s) for the
author(s) of this article can be found under http://dx.doi.org/10.1002/
cssc.201601042.
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cost of the product and, therefore, catalysts based on Ni and/
or copper are preferred. In particular, NiꢀCu-based catalysts
(e.g., NiꢀCu/Al2O3 or NiꢀCu metal powder) have been patent-
ed as highly versatile and efficient catalysts for the production
of Guerbet alcohols, affording yields up to 90% depending on
the starting alcohol and the nature of the base.[8] For example,
Matsuda and Horio (Kao Corporation) patented the effective
production of Guerbet alcohols by heating a primary alcohol in
the presence of an alkaline substance and a supported NiꢀCu
catalyst obtained by impregnation (weight ratio of copper to
nickel was in the range of 1:9 to 9:1).[8a] These authors claimed
that the amounts of the catalytic metals was not particularly
critical; it was possible to use 10–60 wt% of copper plus nickel
supported on a suitable carrier. Nevertheless, neither reutiliza-
tion nor stability of the catalysts was reported in this patent. In
a more recent patent, Dwarakanath and Shong (Chevron USA)
claimed the utilization of mixtures of different carbon chain-
length alcohols (C10–C14) for the synthesis of the respective
Guerbet alcohols.[8b] For this reaction, an 80:20 Cu/Ni powder
catalyst was used alongside potassium hydroxide. Again, no
additional information about the catalyst stability was reported
in the patent.
Table 1. Chemical composition by XRF analysis, BET surface area (SBET),
and crystal domain size (C.S. of the obtained mixed oxides.
Sample
Molar ratio
SBET
Vp
C.S.
[m2 gꢀ1
]
[cm3 gꢀ1
]
[nm][c]
NiþCu
Ni/Cu[a]
–
[b]
ðNiþCuþMgþAlÞ
Cu(10)
Ni(2.5)Cu(7.5) 0.35
(0.33)
0.11
0.12
118
114
0.27
0.34
4
4
Ni(5.0)Cu(5.0) 1.04
(1.00)
Ni(7.5)Cu(2.5) 2.97
(3.00)
0.12
0.12
0.11
138
146
152
0.33
0.38
0.36
4
4
4
Ni(10)
–
[a] Values in parentheses refer to theoretical molar ratios; [b] theoretical
value=0.1; [c] calculated by applying the Scherrer equation.
Considering the promising results reported on the utilization
of NiꢀCu-based materials as (de)hydrogenation catalyst and
KOH as homogeneous base for the preparation of Guerbet al-
cohols, we decided to systematically analyze the catalytic per-
formances of NiꢀCu mixed oxides (with KOH as base) for the
Guerbet reaction. The studied catalysts were prepared by ther-
mal decomposition of layered double hydroxides (LDHs; also
known as hydrotalcites), as these types of structures allow an
intimate distribution of the composing cations within
a common crystalline structure, making it an excellent precur-
sor for the preparation of nonstoichiometric mixed oxides.[9]
We investigated the effect of the Ni/Cu ratio and the nature of
the Cu–Ni interaction, as well as its influence on the redox
properties of the materials, catalytic activities, and catalyst sta-
bilities, by performing the one-pot Guerbet reaction of renew-
able C8, C10, and C18 alcohols produced from coconut oil and
palm kernel oil.
Results and Discussion
Catalyst characterization
The synthesized materials were named as follows depending
on the NiꢀCu ratio used during the synthesis: Cu(10),
Ni(2.5)Cu(7.5), Ni(5.0)Cu(5.0), Ni(7.5)Cu(2.5) and Ni(10). Cu(10,
for example, corresponds to Cu0.8Mg5.2Al2O9 mixed oxide and
Ni(7.5)Cu(2.5) to Ni0.6Cu0.2Mg5.2Al2O9. The chemical composition,
given by X-ray fluorescence (XRF) spectroscopy and the BET
surface area of the mixed oxides obtained after calcination of
the synthesized hydrotalcites (HTs) are given in Table 1.
Figure 1. XRD patterns obtained for as-synthesized hydrotalcites (a) and
calcined mixed oxides (b): A) Cu(10); B) Ni(2.5)Cu(7.5); C) Ni(5.0)Cu(5.0);
D) Ni(7.5)Cu(2.5); E) Ni(10).
viously reported by Blanch-Raga et al.[10] and Tanasoi et al.[11]
for different Cuꢀ(Mg or Ni)ꢀAl mixed oxides.
The structure of the synthesized HTs and the corresponding
mixed oxides was characterized by XRD analysis (Figure 1). The
XRD patterns of the as-synthesized HTs present the diffraction
lines typical for a hydrotalcite compound, independently of
the Ni/Cu ratio used (Figure 1a; JCPDS 14-191).[12] The d-
The XRF analysis indicated that the molar ratios are very
close to the theoretical ones, indicating an efficient and homo-
geneous co-precipitation process. The BET surface area slightly
depended on the Cu2+/Ni2+ ratio used in the materials, as pre-
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spacing values calculated for the (003) diffraction peaks for all
materials were close to 7.8 ꢂ, which is consistent with an inter-
layer gallery height of 3.0 ꢂ, where carbonate species behave
as charge-balancing anions.[13] After calcination of the HTs, the
layered structure was destroyed and the corresponding mixed
oxides were formed, maintaining the distinctive periclase crys-
tal structure of the magnesium oxide (Figure 1b; JCPD 45-946).
No additional crystallographic phases can be discerned in the
process.[16] With the gradual replacement of copper by nickel
in the material compositions, a different behavior in the reduci-
bility of the samples was identified (Figure 2). For example,
Ni(2.5)Cu(7.5) clearly showed at least two major reduction
peaks; one centered at 2308C and the other at 6648C. The first
can be related to the reduction of more stable Cu2+ species re-
sulting from the incorporation of copper into the structure of
the CuꢀMgꢀAl solid solution, as Ni2+ can induce copper to
arrange in an undistorted octahedral coordination geometry
typical of the brucite structure by decreasing the Jahn–Teller
effect.[17] The second reduction peak can be attributed to the
reduction of the structural Ni2+ species, albeit at lower temper-
ature than for the Ni(10) sample.
It is clear that the combination of Cu2+ and Ni2+ in the
same oxide structure has a relevant effect on two aspects:
1) the incorporation and stabilization of the copper species
into the structure of the mixed oxide, causing a shift in the re-
duction of Cu2+ towards higher temperatures (up to 2738C)
than for the Cu(10) catalyst; 2) an improved reduction capacity
of the Ni2+ species at lower temperatures (down from 6648C),
compared to the Ni(10) catalyst. The effect of Ni2+ on the sta-
bilization of copper species is most pronounced in the
Ni(7.5)Cu(2.5) catalyst. This behavior could be related to the
maximum incorporation-stabilization of Cu2+ into the structure
of the hydrotalcite. Nevertheless, the formation of highly dis-
persed CuO species could not be avoided, leading to the ap-
pearance of a low-temperature reduction shoulder in H2-TPR of
the studied NiꢀCu catalysts (163, 173, and 1848C in
Ni(2.5)Cu(7.5), Ni(5.0)Cu(5.0), and Ni(7.5)Cu(2.5), respectively).
Regarding the improved reduction capacity of the Ni2+ spe-
cies induced by the presence of Cu2+ in the materials, it is
clear that a higher content of copper provoked an enhanced
reduction of the structural nickel species. Thus, on
Ni(2.5)Cu(7.5), the reduction of the Ni2+ species was observed
diffractograms, suggesting the incorporation of the Al3+, Cu2+
,
and/or Ni2+ cations in the structure of the MgO and/or the
generation of highly dispersed oxidized species.
The crystal domain size of the obtained mixed oxides, calcu-
lated by using the Scherrer equation with the XRD pattern cen-
tered at 2q=43.28, is rather small (4 nm in all the materials),
owing the effect of the ultrasound during the co-precipitation
process.[14]
The reducibilities of the calcined materials were analyzed by
temperature-programmed reduction with H2 (H2-TPR). Figure 2
displays the TPR profiles as a function of the temperature ob-
tained for the different samples. In the case of the materials
composed only by one reducible cation, that is, Cu(10) and
Ni(10), there is a big difference in the temperature at which
the reduction of the sample was observed.
at 6648C,
a lower temperature than that observed for
Ni(5.0)Cu(5.0) (6878C) and the Ni(7.5)Cu(2.5) (7198C). The posi-
tive effect of copper on the reducibility of Ni2+ has been previ-
ously reported for hydrotalcite-derived catalysts.[16b,18] During
the H2-TPR analysis, the reduced copper gives rise to spillover
hydrogen, which can considerably accelerate the reduction of
the NiꢀO bonds.
Figure 2. H2-TPR profiles obtained for the calcined materials: a) Cu(10);
b) Ni(2.5)Cu(7.5); c) Ni(5.0)Cu(5.0); d) Ni(7.5)Cu(2.5); e) Ni(10).
Catalytic evaluation: Self-condensation of 1-octanol
Ni(10) gave rise to a broad reduction peak at a relatively
high temperature (centered at 7338C) associated with the re-
duction of Ni2+ species from the NiꢀMgꢀAl solid solution.[15] In
contrast, Cu(10) gave rise to a more defined reduction peak
between 100 and 3008C, which can be correlated to the reduc-
tion of the different Cu2+ species present in the structure of
the catalyst.[11] The highest hydrogen consumption rate, cen-
tered at 1808C, can be attributed to the reduction of the
highly reducible copper coming from well-dispersed CuO spe-
cies present on the surface of the MgꢀAl mixed oxide (not de-
tected by XRD analysis). The formation of these CuO species is
due to the strong Jahn–Teller effect of Cu2+, which provokes
a weak interaction of the copper with the host hydrotalcite
structure and its segregation as CuO during the calcination
The self-condensation of 1-octanol (denoted here as “octanol”)
was performed by using the synthesized NiꢀCuꢀMgꢀAl mixed
oxides as (de)hydrogenation catalysts, whereas the basic condi-
tions for the aldol condensation were ensured by using KOH
as a homogeneous base (1.5 wt% with respect to the initial
weight of octanol). The octanol conversions and yields of the
C16 products (2-hexyl-1-decanol and C16 aldehydes; Scheme 1)
as a function of the reaction time are presented in Figure 3.
The octanol conversion and selectivity of the process to the
C16 Guerbet alcohol are clearly influenced by the Ni2+/Cu2+
ratio in the catalysts. During the first hour of the reaction, the
partial replacement of 50% and 75% of Cu2+ by Ni2+ in the
structure of the mixed oxide has a negative effect on the
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Scheme 1. Schematic representation of the Guerbet reaction pathway expected for the self-condensation of octanol.
kinetics of the process. However, after 2 h, for all catalyst com-
positions exception for Ni(10), the octanol conversion was very
high (ca. 90%; Figure 3a).
However, the presence of Ni has a positive influence on the
selectivity of the reaction, notably when the NiꢀCu ratio is ꢁ1
[i.e., Ni(5.0)Cu(5.0) and Ni(7.5)Cu(2.5) catalysts]. Thus, whereas
the Cu(10) catalyst showed a maximum yield of the C16 Guer-
bet alcohol of roughly 42% after 6 h reaction, the catalyst
Ni(7.5)Cu(2.5) afforded a 62% yield of the targeted alcohol
after the same reaction time. This value corresponds to the
highest yield achieved among the analyzed catalysts. Although
Ni(7.5)Cu(2.5) is highly selective to the hydrogenated C16 con-
densation product 2-hexyl-1-decanol, a loss in the mass bal-
ance of the reaction (>15%) was observed due to the forma-
tion of carboxylic products (solids) and octanol evaporation.
The solid carboxylic products were analyzed and were found
to consist solely of C8 carboxylic salts (i.e., potassium C8 soap)
generated through disproportionation of the aldehyde in the
presence of KOH and/or the direct oxidation of the aldehyde
or alcohol.[7] Although the NiꢀCu catalysts synthesized in this
work can be considered as basic materials (mainly Lewis-type
basicity after thermal decomposition of the LDH structure), the
presence of an homogeneous base in the reaction medium
was found to be very important in speeding up the in situ re-
duction of the catalyst and enhancing the kinetics of the reac-
tion. In fact, the blank reaction performed in the absence of
KOH gave a conversion of only 6% after 6 h, with negligible
production of the C16 Guerbet alcohol (see the Supporting In-
formation, Figure S1), indicating that the basicity of the mixed
oxide is not sufficient for the reaction under the used
conditions.
Figure 3. Catalyst screening as a function of the Ni/Cu ratio: a) Octanol con-
version [%]; b) yield [%] of C16 products [continuous lines represent the yield
of 2-hexyl-1-decanol (C16 Guerbet alcohol), whereas dotted lines represent
those of C16 aldehydes (2-hexyl-2decenal, 2-hexyldecanal)].
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It is worth noting that the improvement in selectivity owing
to the presence of Ni was accompanied by a diminished con-
centration of C16 aldehydes (Figure 3b, dashed lines). The
Cu(10) catalyst still produced a 13% yield of the less desirable
C16 aldehydes, whereas Ni(7.5)Cu(2.5) produced them in less
than 2.5% yield. Therefore, increasing the Ni2+/Cu2+ ratio in
the catalysts slows down the initial conversion rate, but im-
proves the selectivity towards the targeted Guerbet alcohol.
These catalytic results indicate the different roles played by
the Ni and Cu species present in the catalyst during the Guer-
bet reaction. The presence of copper is important in order to
ensure good reaction kinetics, whereas nickel favors produc-
tion of the totally hydrogenated C16 product (2-hexyl-1-dec-
anol). Dehydrogenation of the starting alcohol is often identi-
fied as the rate-limiting step of the Guerbet reaction,[7] and
copper would be mostly involved in this step, whereas nickel
would favor the hydrogenation of the final dehydrated aldol-
condensation product.
Supported Cu catalysts for dehydrogenation of alcohols and
hydrogen transfer processes have been reported as promising
and effective systems to replace the commonly used noble-
metal based catalysts.[19] Nonetheless, most such reports have
pointed to the importance of having Cu0 and/or Cu+ species
as actives sites for the hydrogen transfer reaction and a previ-
ous reduction of the catalyst is generally required.[19a,20,21] In
the case of the catalysts screened in this work, the self-conden-
sation reaction of octanol was performed without any prior re-
duction of the catalysts. However, during the first 30 min (i.e.,
after the octanol reached its boiling point), the catalyst’s color
turned from green to reddish brown, indicating the generation
of reduced copper species[22] (see the Supporting Information,
Figure S2a). Only Ni(10) did not show any observable color
change during the course of the reaction.
Figure 4. Product distribution of C16 aldehydes generated as a function of
time on the different catalysts evaluated in this work (different Ni/Cu ratios):
a) 2-hexyl-2-decenal; b) 2-hexyldecanal.
When performing the reaction with catalysts containing
both Ni2+ and Cu2+, we expect the reduction or partial reduc-
tion of both copper and nickel species. As Ni-based catalysts
show high activity and selectivity in C=C bond hydrogena-
tion,[23] the selectivity of the process to the totally hydrogenat-
ed products can be highly favored. This can be confirmed by
analyzing the distribution of the C16 aldehydes produced as
a function of the used catalyst presented in Figure 4, where it
is quite clear that the presence of Ni in the catalysts formula-
tion strongly reduces the concentration of the a-b unsaturated
C16 aldehyde (2-hexyl-2-decenal) (see Scheme 1). Moreover, the
mixed oxide with higher Ni/Cu ratio shows an enhanced hy-
drogenation capacity of the aldehyde towards the alcohol as
shown by the reduced amount of 2-hexyldecanal in Figure 4.
In order to corroborate the positive effect of the Ni–Cu inter-
actions on the selectivity of the catalytic process, a physical
mixture of Ni(10) and Cu(10) catalysts (maintaining a Ni:Cu
molar ratio=3:1) was also evaluated under the same reaction
conditions. The conversion of octanol and yield of C16 products
as a function of time are presented in Figure 5.
Figure 5. Reaction conversion and yields obtained with physical mixture of
Cu(10) and Ni(10) catalysts (Ni/Cu molar ratio=3:1).
for Cu(10) and 62% for Ni(7.5)Cu(2.5)], demonstrating the
lower Guerbet alcohol selectivity for the physical mixture. In
addition, the utilization of the this physical mixture was also
not as effective as the Ni(7.5)Cu(2.5) catalyst in decreasing the
concentration of the less desirable C16 aldehydes. Whereas the
utilization of the Ni(10)/Cu(10) physical mixture produced over
10% yield to C16 aldehydes, the implementation of the
The catalytic results obtained for this system are very similar
to those presented in Figure 3 for Cu(10). Thus, although the
reaction is rather fast (almost 80% conversion after 1 h), the
highest yield of the C16 Guerbet alcohol was around 50% [42%
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Ni(7.5)Cu(2.5) catalyst allowed a yield below 2.5% of those side
products. These results highlight the importance of having
copper and nickel in the same catalyst structure as an effective
way to provide a good catalytic efficiency for the Guerbet
reaction of octanol.
Finally, as the catalyst stability is a very important feature for
the further implementation of these materials on an industrial
scale, the final reaction mixtures were analyzed by ICP-AES
technique in order to determine the amount of metals leached
out during the reaction (Table 2).
Table 2. Leaching analysis of the final reaction mixtures obtained by ICP-
AES.
Sample
Ni [ppm]
Cu [ppm]
Cu(10)
–
134
6.01
6.85
5.43
–
Ni(2.5)Cu(7.5)
Ni(5.0)Cu(5.0)
Ni(7.5)Cu(2.5)
Ni(10)
0.24
0.21
0.46
0.45
It is clear that the presence of Ni in the NiꢀCu catalysts also
has a strong influence on the stability of the copper species
during the reaction. Whereas for the pure Cu(10) catalyst,
134 ppm of Cu leached out during the Guerbet reaction (pro-
voking a light-blue coloration of the final reaction mixture), the
amount of copper leached from the NiꢀCu catalysts is sup-
pressed by up to 95%. This further evidences the aforemen-
tioned stabilization of Cu2+ by Ni2+, as established by H2-TPR.
The interaction between the copper and nickel species pres-
ent in the catalyst structure is very important for three main
reasons: 1) To favor the reducibility of the catalyst during the
course of the reaction, which is important to generate the
“real” active sites on the catalyst; 2) to improve the hydrogen
transfer (fast hydrogen spillover coming from the copper to
the nickel) and hydrogenation capacity of the system; 3) to sta-
bilize the Cu2+ species in the structure of the catalysts. As a hy-
drotalcite was used as catalyst precursor, one can expect
a very good distribution of the copper and nickel species, as
was concluded from the XRD and H2-TPR analyses performed
on the calcined materials.
Figure 6. Reuse of Ni(7.5)Cu(2.5) catalyst: a) Octanol conversion; b) yield of
2-hexyl-1-decanol (C16 Guerbet alcohol).
ing around 90% conversion after 3 h reaction. Moreover, after
8 h reaction, the first reuse of the catalyst had a positive effect
on the yield of the C16 Guerbet alcohol, going from 62.5% on
the fresh catalyst, to 67.6% (Figure 6b). Furthermore, by using
the catalyst for a second time, an additional improvement on
the C16 Guebert yield was also observed, attaining a yield of
72% after 8 h reaction. This value remains almost the same
after the third reuse. Because the catalyst was separated from
the reaction medium by centrifugation and was immediately
reused in the next catalytic cycle, the accumulation of carbox-
ylic side-products was qualitatively evidenced by the clear
weight and volume increase of the catalyst after every reuse
(see the Supporting Information, Figure S2b). Nonetheless,
given the efficiency of the catalyst system, even after the
fourth catalytic cycle, the presence of carboxylic products does
not present a major obstacle to the technological application
of this catalyst. These carboxylates can be separated relatively
easy from the catalyst by washing with, for example, hot
water, after which they can be further valorized or post-
treated.
Catalyst reusability
Considering the excellent selectivity and stability obtained
with the Ni(7.5)Cu(2.5) catalyst in the self-condensation reac-
tion of octanol, the reusability of this material was evaluated.
The spent catalyst was separated from the liquid phase by
simple centrifugation without any washing treatment or drying
step and was added to a new reaction mixture containing
fresh feed octanol and KOH. The conversion of octanol and the
yield of 2-hexyl-1-decanol (the C16 Guerbet alcohol) as a func-
tion of time after each catalyst use (up to 4 times) is presented
in Figure 6.
So far, Ni(7.5)Cu(2.5) catalyst derived from a hydrotalcite
structure has been presented as a highly selective, robust, and
reusable catalyst for the Guerbet reaction. Moreover, to prove
and highlight the advantages of using the hydrotalcite as cata-
lyst precursor for this reaction, we compared the efficiency and
reusability of the Ni(7.5)Cu(2.5) catalyst with two different ma-
terials synthesized by wet impregnation method. Catalysts con-
The octanol conversions did not show any significant differ-
ence for any of the catalytic runs performed (Figure 6a), reach-
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sisting of NiꢀCu supported on g-Al2O3 or MgO were prepared,
keeping the same loading and Ni/Cu ratio as in the
Ni(7.5)Cu(2.5) catalyst (experimental details are described in
the Supporting Information).
The octanol conversion and selectivity to the C16 Guerbet al-
cohol after 6 h reaction were compared for the three different
NiꢀCu catalysts. The reusability of these materials was com-
pared up to the third catalytic run (second reuse). Figure 7
shows the conversions and selectivities obtained for the evalu-
ated catalysts. Independently of the support used as a carrier
for Ni and Cu species, the catalytic performances observed on
the three different catalysts were very similar during the first
and the second catalytic runs. Nonetheless, when the catalysts
were used for a third time, a strong decrease in the conversion
and selectivity was observed for the g-Al2O3- and MgO- sup-
ported NiꢀCu catalysts, which was not evident at all for
Ni(7.5)Cu(2.5) (catalyst A in Figure 7).
Figure 8. Use of Ni(7.5)Cu(2.5) catalyst in the self-/cross-condensation of
a mixed octanol/decanol feed (50:50 w/w).
tion conditions used in this work, Ni(7.5)Cu(2.5) has
the same catalytic activity for the dehydrogenation
of both octanol and decanol. The main side products
generated in this reaction were the respective C16,
C18, and C20 aldehydes (total concentration was
<3 wt%), as the final hydrogenation of the C=O
bond to obtain the Guerbet alcohol is the most diffi-
cult step.
To compare the quality of the Guerbet alcohols
synthesized by the catalyst system described herein,
the compositions of the final reaction mixtures were
analyzed by GC after centrifugation and separation of
the solid phase (catalyst plus carboxylic salts). The
obtained results are presented in Table 3 for the two
different alcohol feeds used, under similar reaction
conditions (fresh catalyst, 8 h reaction, Tmax =2258C,
catalyst/KOH weight ratio=0.67 and using 1.0 wt%
catalyst with respect to the initial mass of alcohol).
A very high purity of the final Guerbet alcohols
was achieved with the Ni(7.5)Cu(2.5) catalyst for both
pure and mixed feeds. In addition, the purity of the
synthesized Guerbet alcohols could be improved by
Figure 7. Catalytic efficiency and reusability of Ni(7.5)Cu(2.5) hydrotalcite-derived catalyst
vs. supported NiꢀCu catalysts: A=Ni(7.5)Cu(2.5); B=NiꢀCu/g-Al2O3; C=NiꢀCu/MgO.
Cross-condensation of C8–C10 aliphatic alcohols
reusing the catalyst. The purity of the C16 Guerbet alcohol ob-
tained by self-condensation of octanol was improved up to
89% after the first and second reuses. In addition, we found
A wide variety of biomass-derived alcohols and mixtures could
be upgraded by converting them into the respective Guerbet
alcohols. We therefore tested a 50:50 w/w mixture of octanol
and decanol as a probe for an actual biomass feed. We used
the Ni(7.5)Cu(2.5) catalyst under the same conditions as for the
octanol condensation. The evolution of the concentration of
the starting alcohols and the produced C16, C18, and C20 Guer-
bet alcohols is plotted in Figure 8 as a function of time (the
structures of the produced Guerbet alcohols were confirmed
by GC-MS).
Table 3. Product quality of centrifuged non purified product.
Product [%]
Alcohol feed
C8/C10 (50:50 w/w)
C8
6.0
–
–
83.4
5.3
–
–
–
–
5.3
83.4
octanol
decanol
decanal
1.3
1.0
<1.0
23.8
1.2
44.9
2.2
20.7
1.0
C16 Guerbet
C16 aldehyde
C18 Guerbet
C18 aldehyde
C20 Guerbet
C20 aldehyde
trimers
The catalytic performance of Ni(7.5)Cu(2.5) for this mixed
feed was just as good as for the pure octanol. The conversion
rate of the two different alcohols towards the respective self-
condensation products (C16 and C20 Guerbet alcohols) was
practically the same during the whole process, generating
a 1:2:1 mixture of C16, C18, and C20 products, as can be statisti-
cally predicted. This result also suggests that, under the reac-
3.8
89.4
total Guerbet
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that the purity of the C16 Guerbet alcohol obtained during first
use of the Ni(7.5)Cu(2.5) catalyst could be enhanced by in-
creasing the KOH concentration in the reaction medium; in-
creasing the base concentration from 1.5 wt% to 5.0 wt% re-
sulted in an increase in the final purity of the C16 Guerbet alco-
hol from 83.4 to 96% (see the Supporting Information,
Table S1). Burk et al.[4b,c] reported this type of synergistic inter-
action between the metal and the basic component for the
self-condensation of n-butanol to 2-ethyl-1-hexanol at low
temperatures in the presence of Rh/C catalyst and sodium but-
oxide as base. They concluded that the initial dehydrogenation
step required the presence of both the transition metal cata-
lyst and the base, whereas the a,b-unsaturated aldehyde de-
rived from aldol condensation might be reduced to the Guer-
bet alcohol through two pathways; one that is promoted only
by the base and the other characterized by the successive
assistance of both catalytic components.
The highest yield of the C36 Guerbet alcohol (72.5%) was
achieved after 12 h reaction, together with the formation of
trimers and tetramers as side products. The other C36 products
formed during the reaction were mainly the C36 saturated alde-
hyde and the analogue a,b-unsaturated aldehyde. After 24 h,
although the conversion of the C18 alcohol was almost com-
plete, an increase in the concentration of side products was
also observed.
This test with a longer aliphatic alcohol clearly indicates the
potential of the Ni(7.5)Cu(2.5) catalyst for the Guerbet reaction
of a wide range of aliphatic alcohols (C8–C18). Althoug the use
of C18ꢀOH also led to an increase in the formation of less desir-
able condensation products, such as the C36 aldehyde, trimers,
and tetramers, a further optimization of the reaction condi-
tions (e.g., temperature, catalyst/base ratio) and/or catalyst
composition (e.g., higher nickel content to improve the hydro-
genation capacity of the system) can be addressed in order to
enhance the selectivity to the desired C36 Guerbet alcohol.
Taking into account that the industrial production of these
types of alcohols would also include the recovery (by distilla-
tion) of the monomeric species present in the final reaction
mixture (octanol and decanol), theoretical purities of 88.7 and
91.5% could be achieved for the total Guerbet products
coming from the self-condensation of octanol and cross-
condensation of octanol/decanol, respectively.
Conclusions
A series of NiꢀCu hydrotalcite-derived catalysts were synthe-
sized and evaluated in the Guerbet reaction of aliphatic bioal-
cohols in the liquid phase under atmospheric pressure (self-
condensation of 1-octanol and stearyl alcohol and cross-con-
densation of 1-octanol/1-decanol). The bimetallic catalysts dis-
played remarkable activity and selectivity to the totally hydro-
genated b-branched alcohols (Guerbet alcohol). The nickel-rich
material Ni(7.5)Cu(2.5) was the most selective catalyst, enabling
production of C16, C18, C20, and C36 b-branched alcohols with
purities of 72.5–96%. The structure of the hydrotalcite is able
to provide a good dispersion of the NiꢀCu active phases after
thermal decomposition of the LDH structure at 5008C.
The utilization of NiꢀCu mixed oxides derived from a hydro-
talcite structure represents an easy and cheap way to obtain
highly active, selective, stable, and reusable catalysts for the
Guerbet reaction. The combination of nickel and copper was
ideal for catalyzing the different processes involved in this type
of reaction. The catalysts have very low leaching and are
reusable without any regeneration steps.
Self-condensation of stearyl alcohol
Finally, Ni(7.5)Cu(2.5) catalyst was also used for the self-con-
densation reaction of stearyl alcohol, a much longer-chain ali-
phatic alcohol (C18) characterized by a melting point of 57.8–
58.38C. For this reaction, the amount of catalyst and base were
decreased (0.25 and 0.75 wt% with respect to the initial
amount of alcohol, respectively). The reaction mixture was ana-
lyzed after 12 and 24 h (additional details of the reaction con-
ditions and catalytic set-up are described in the Experimental
Section). The concentration of the different reaction compo-
nents is presented in Figure 9.
Experimental Section
Catalyst synthesis
Hydrotalcites were prepared by co-precipitation under high satura-
tion conditions, as reported elsewhere.[15] Typically, the desired
amounts of 1m solutions of metal nitrates [Ni and/or Cu, Mg and
Al, where the MII/Al molar ratio was 3.0 and the (Cu+Ni)/(Cu+Ni+
Mg+Al) ratio was 0.1] were mixed thoroughly to make a homoge-
neous solution (A; the following NiꢀCu ratios were analyzed: 0:1;
0.25:0.75; 0.5:0.5; 0.75:0.25; 1:0). Then, solution A was added drop-
wise to a solution (B) containing the precipitating agents (i.e.,
NaOH and Na2CO3; 2.2m NaOH and 0.15m Na2CO3). During the ad-
dition, solution B was kept in an ultrasonic bath, at room tempera-
ture. The obtained solids were washed by centrifugation (until ni-
trates and sodium were totally absent in the washing liquids), and
dried in an air oven at 1008C for at least 12 h. All materials were
calcined at 5008C (with a heating rate of 28Cminꢀ1) for 4 h in air
Figure 9. Use of Ni(7.5)Cu(2.5) catalyst in the self-condensation of stearyl
alcohol. Reaction conditions: Stearyl alcohol (40 g), catalyst (0.25 wt%), KOH
(0.75 wt%), T=2408C.
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to give the respective mixed oxides. The obtained materials were
named as follows, depending on the NiꢀCu ratio used during the
synthesis: Cu(10), Ni(2.5)Cu(7.5), Ni(5.0)Cu(5.0), Ni(7.5)Cu(2.5) and
Ni(10). Cu(10), for example, corresponds to Cu0.8Mg5.2Al2O9 mixed
oxide and Ni(7.5)Cu(2.5) to Ni0.6Cu0.2Mg5.2Al2O9.
The supported copper–nickel catalysts were synthesized by a wet
impregnation method, ensuring a copper/nickel molar ratio of
2.5:7.5 and a total loading of copper and nickel in the whole cata-
lyst of 12 wt%. In a typical procedure, the appropriate amounts of
Ni(NO3)2·6H2O and Cu(NO3)2·3H2O salts were dissolved in distilled
water (150 mL), in order to impregnate 4 g of support. Then, the
desired support (g-Al2O3 or MgO) was added to the cationic solu-
tion and stirred vigorously for 2 h at room temperature. After-
wards, the excess solvent was removed under reduced pressure at
508C to give a totally dried solid. Finally, the materials were
calcined in the presence of air at 5008C for 4 h.
ꢂ400 rpm). Once the temperature reached 2408C, the base
(0.75 wt% of KOH with respect to the alcohol), and then the cata-
lyst (0.1 g) were added. After this point, the reaction was carried
out for 12 or 24 h. Water produced during the condensation was
released through the top of the five-necked flask, where quartz
wool was placed in order to avoid loss of alcohol. The reaction
products were analyzed by high-temperature GC-FID analysis.
Acknowledgements
This work was partially funded by the IWT-Belgium. The authors
would like to thank Funda AliÅ and Danny Vandeput for the
logistic and technical support.
Keywords: alcohols
· Guerbet reaction · heterogeneous
catalyis · layered double hydroxides · mixed metal oxides
Physicochemical characterization
The chemical composition of the mixed oxides was analyzed by X-
ray fluorescence spectroscopy (XRF) on an energy-dispersive
Rigaku NexCG spectrometer. The textural properties were analyzed
by nitrogen adsorption at 77 K on a Micromeritics Tristar 2030. The
surface areas were determined by the Brunauer-Emmett-Teller
(BET) method. X-ray powder diffraction patterns (XRD analysis)
were measured on a ARL X’TRA X-ray diffractometer with CuKa radi-
ation of 0.15418 nm wavelength and a solid state detector. Leach-
ing samples (liquid phase) after the catalytic testing were analyzed
by inductively coupled plasma atomic emission spectroscopy (ICP-
AES). H2-TPR measurements were performed on an Autosorb iQ
TPX device from Quantachrome. In a typical experiment, 80 mg of
sample was pretreated at 5008C (heating rate 108Cminꢀ1) for 1 h
in a flow of He (30 mLminꢀ1). Subsequently, the sample was
cooled down to 808C under the same flow of He. The reduction
[1] a) S. M. Sarathy, P. Oßwald, N. Hansen, K. Kohse-Hçinghaus, Prog. Energy
Combust. 2014, 44, 40–102; b) J. Goldemberg, Science 2007, 315, 808–
810; c) L. Siwale, L. Kristꢃf, A. Bereczky, M. Mbarawa, A. Kolesnikov, Fuel
Process. Technol. 2014, 118, 318–326.
[2] a) M. Guerbet, Comptes Rendus 1899, 128, 511–513; b) J. T. Kozlowski,
R. J. Davis, ACS Catal. 2013, 3, 1588–1600.
[3] a) A. J. O’Lenick, J. Surfactants Deterg. 2001, 4, 311–315; b) L. D. Rhein,
M. Schlossman, A. J. O’Lenick, P. Somasundaran, Surfactants in Personal
Care Products and Decorative Cosmetics, 3rd ed., Taylor & Francis Group,
Abingdon, UK, 2007.
[4] a) R. E. Miller, G. E. Bennett, Ind. Eng. Chem. 1961, 53, 33–36; b) P. L.
Burk, R. L. Pruett, K. S. Campo, J. Mol. Catal. 1985, 33, 1–14; c) P. L. Burk,
R. L. Pruett, K. S. Campo, J. Mol. Catal. 1985, 33, 15–21.
[5] a) C. Carlini, M. Di Girolamo, A. Macinai, M. Marchionna, M. Noviello,
A. M. Raspolli Galletti, G. Sbrana, J. Mol. Catal. A 2003, 200, 137–146;
b) C. Carlini, M. D. Girolamo, M. Marchionna, M. Noviello, A. M. R. Gallet-
ti, G. Sbrana, J. Mol. Catal. A 2002, 184, 273–280; c) C. Carlini, A. Macin-
ai, M. Marchionna, M. Noviello, A. M. R. Galletti, G. Sbrana, J. Mol. Catal.
A 2003, 206, 409–418; d) C. Carlini, A. Macinai, A. M. Raspolli Galletti, G.
Sbrana, J. Mol. Catal. A 2004, 212, 65–70; e) C. Carlini, M. Marchionna,
M. Noviello, A. M. Raspolli Galletti, G. Sbrana, F. Basile, A. Vaccari, J. Mol.
Catal. A 2005, 232, 13–20; f) D. L. Carvalho, R. R. de Avillez, M. T. Rodri-
gues, L. E. P. Borges, L. G. Appel, Appl. Catal. A 2012, 415–416, 96–100.
[6] a) R. L. Poe (Continental Oil Co., Ponca City, OK), US3328470, 1967;
b) D. A. Young, J. A. Jung, M. L. McLaughlin (Exxon Chemical Patents
Inc., Linden, NJ), US5068469, 1991; c) N. L. Cull, J. K. Mertzweiller (Exxon
Research Engineering Co., Baton Rouge, LA), US2829177, 1958; d) J. E.
Yates (Continental Oil Co., Ponca City, OK),US3979466, 1976; e) J. E.
Yates (Continental Oil Co., Ponca City, OK),US3864407, 1975; f) J. E.
Yates (Continental Oil Co., Ponca City, OK), US3916015, 1975; g) G. Mu-
eller, B. Gutsche, L. Jeromin, U. Steinberner, R. Sedelies, R. Bohlander, R.
Ridinger, D. Springer, F. Buettgen, F. Bartschik (Henkel AG & Co. KGaA,
Duesseldorf, Germany), US5777183, 1998.
analysis was performed from 80 to 9008C (108Cminꢀ1
) in
a 30 mLminꢀ1 flow of 5 vol.% H2 in N2.
Catalyst evaluation: Condensation of fatty alcohols (Guerbet
reaction)
The self and cross condensation of fatty alcohols by the Guerbet
reaction was performed in a batch reaction system, under vigorous
magnetic stirring and nitrogen atmosphere. In a typical experi-
ment, a 100 mL five-necked flask equipped with a Dean–Stark
azeotrope trap, reflux condenser, and temperature probe, was
filled with the fatty alcohol (e.g., 1-octanol; 40 g), KOH flakes
(0.6 g, 1.5 wt% with respect to the alcohol), hexadecane (internal
standard; 2.0 g) and catalyst (0.4 g, 1 wt%). Then, after fixing
a flow of N2 passing through the headspace of the reaction system
(50–60 mLminꢀ1) and setting a constant and vigorous stirring rate,
the reaction mixture was heated to the reflux temperature. The
maximum temperature allowed by the heating system was 2258C.
The progress of the reaction was monitored by taking samples
from the reaction mixture (ca. 10 mg) at defined times. The reac-
tions were performed for at least 6 h. The withdrawn samples were
diluted in 1.5 mL of heptane and analyzed by GC-FID in a Thermo-
Finnigan Trace GC provided by an ultrafast column module.
[7] D. Gabriꢄls, W. Y. Hernandez, B. Sels, P. Van Der Voort, A. Verberckmoes,
Catal. Sci. Technol. 2015, 5, 3876–3902.
[8] a) M. Matsuda, M. Horio (Kao Corporation, Tokyo, Japan), US4518810,
1985; b) V. Dwarakanath, R. Shong, T. E. Weksberg (Chevron USA Inc.,
San Ramon, CA), WO/2014/149419, 2014; c) G. E. Bennett, R. E. Miller
(Monsanto Chemicals, St. Louis, MO),US2862013, 1958.
[9] a) E. E. Sileo, M. Jobbagy, C. O. Paiva-Santos, A. E. Regazzoni, J. Phys.
Chem. B 2005, 109, 10137–10141; b) G. Fan, F. Li, D. G. Evans, X. Duan,
Chem. Soc. Rev. 2014, 43, 7040–7066.
[10] N. Blanch-Raga, A. Eduardo Palomares, J. Martinez-Triguero, G. Fetter, P.
Bosch, Ind. Eng. Chem. Res. 2013, 52, 15772–15779.
The self-condensation of the stearyl alcohol was performed under
atmospheric pressure at 2408C, with N2 flow in the headspace of
the reactor (50 mLminꢀ1). In a typical experiment, the starting C18
alcohol (40 g) was melted by using a proportional integral deriva-
[11] S. Tanasoi, N. Tanchoux, A. Urda˘, D. Tichit, I. Sa˘ndulescu, F. Fajula, I.-C.
Marcu, Appl. Catal. A 2009, 363, 135–142.
[12] M. Leꢃn, E. Dꢅaz, S. Bennici, A. Vega, S. OrdꢃÇez, A. Auroux, Ind. Eng.
Chem. Res. 2010, 49, 3663–3671.
tive (PID)-controlled heating mantle, in
a five-necked flask
(100 mL), equipped with a magnetic stirring bar (stirring rate
[13] V. Rives, M. a. Angeles Ulibarri, Coord. Chem. Rev. 1999, 181, 61–120.
ChemSusChem 2016, 9, 1 – 11
www.chemsuschem.org
9
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
These are not the final page numbers! ÞÞ

Full Papers
[14] M. J. Climent, A. Corma, S. Iborra, K. Epping, A. Velty, J. Catal. 2004, 225,
316–326.
Commun. 2005, 253–255; c) F. Zaccheria, N. Ravasio, R. Psaro, A. Fusi,
Chem. Eur. J. 2006, 12, 6426–6431.
[15] a) P. V. Tuza, R. L. Manfro, N. F. P. Ribeiro, M. M. V. M. Souza, Renewable
Energy 2013, 50, 408–414; b) K. Takehira, T. Shishido, P. Wang, T. Kosaka,
K. Takaki, J. Catal. 2004, 221, 43–54.
[20] a) R. Shi, F. Wang, Tana, Y. Li, X. Huang, W. Shen, Green Chem. 2010, 12,
108–113; b) F. Wang, R. Shi, Z.-Q. Liu, P.-J. Shang, X. Pang, S. Shen, Z.
Feng, C. Li, W. Shen, ACS Catal. 2013, 3, 890–894.
[16] a) S. Kannan, A. Dubey, H. Knozinger, J. Catal. 2005, 231, 381–392;
b) X.-P. Yu, W. Chu, N. Wang, F. Ma, Catal. Lett. 2011, 141, 1228–1236;
c) Q. Li, H. Yi, X. Tang, S. Zhao, B. Zhao, D. Liu, F. Gao, Chem. Eng. J.
2016, 284, 103–111.
[21] T. Mitsudome, Y. Mikami, K. Ebata, T. Mizugaki, K. Jitsukawa, K. Kaneda,
Chem. Commun. 2008, 4804–4806.
[22] M. Dixit, M. Mishra, P. A. Joshi, D. O. Shah, J. Ind. Eng. Chem. 2013, 19,
458–468.
[17] a) D. Li, M. Koike, J. Chen, Y. Nakagawa, K. Tomishige, Int. J. Hydrogen
Energy 2014, 39, 10959–10970; b) B. Montanari, A. Vaccari, M. Gazzano,
P. Kꢆßner, H. Papp, J. Pasel, R. Dziembaj, W. Makowski, T. Lojewski, Appl.
Catal. B 1997, 13, 205–217; c) F. Cavani, F. Trifirꢇ, A. Vaccari, Catal. Today
1991, 11, 173–301.
[23] a) N. Mahata, A. F. Cunha, J. J. M. ꢈrf¼o, J. L. Figueiredo, Chem. Eng. J.
2012, 188, 155–159; b) A. Yin, C. Wen, X. Guo, W.-L. Dai, K. Fan, J. Catal.
2011, 280, 77–88.
[18] J. Ashok, M. Subrahmanyam, A. Venugopal, Int. J. Hydrogen Energy
2008, 33, 2704–2713.
Received: July 29, 2016
[19] a) R. Shi, F. Wang, X. Mu, Y. Li, X. Huang, W. Shen, Catal. Commun. 2009,
11, 306–309; b) F. Zaccheria, N. Ravasio, R. Psaro, A. Fusi, Chem.
Published online on && &&, 0000
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FULL PAPERS
Branching out: Highly selective and
recyclable heterogeneous catalysts for
the synthesis of Guerbet alcohols are
prepared by thermal decomposition of
partially substituted layered double
hydroxide structures (Mg2+ substituted
by Ni2+ and/or Cu2+). Synergistic inter-
actions are identified between the ma-
terial components and Guerbet prod-
ucts are obtained with purities of 72.5–
96%.
W. Y. Hernꢀndez, K. De Vlieger,
P. Van Der Voort,* A. Verberckmoes*
&& – &&
NiꢀCu Hydrotalcite-Derived Mixed
Oxides as Highly Selective and Stable
Catalysts for the Synthesis of b-
Branched Bioalcohols by the Guerbet
Reaction
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These are not the final page numbers! ÞÞ