Indium, as an efficient co-catalyst of Cu/Al2O3 in the selective hydrogenation of biomass derived fatty acids to alcohols

Article abstract of DOI:10.1016/j.catcom.2012.04.023

Octanoic acid (OA) as model reactant of medium chain length, and its reduced products, octanal and octanol were hydroconverted over different components of a CuIn/Al₂O₃ composite catalyst. A fixed-bed flow through reactor was used at 21 bar total pressure in the temperature range of 240-360 °C. Fatty acid hydroconversion activity of alumina supported Cu catalyst and mainly the yield of selectively produced octanol can be greatly increased by In₂O₃ doping, suppressing the dehydration side reactions. Appearance of metallic indium on alumina supported reduced copper catalyst can arrest the consecutive catalytic reaction at the alcohol formation step prior to further dehydration to ether or alkenes. An industrial, conventionally used Adkins catalyst (72 wt.% CuCr₂O₄ and 28 wt.% CuO) and the novel bimetallic composite (CuIn/Al₂O ₃) were compared: both produce octanol with high selectivity, but the new chromium-free fatty acid hydrogenation catalyst is more active, nearly as active as earlier investigated NiIn/Al₂O₃.

Full text of DOI:10.1016/j.catcom.2012.04.023

Catalysis Communications 26 (2012) 19–24
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Catalysis Communications
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Short Communication
Indium, as an efficient co‐catalyst of Cu/Al2O3 in the selective hydrogenation of
biomass derived fatty acids to alcohols
⁎
György Onyestyák, Szabolcs Harnos , Dénes Kalló
Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Pusztaszeri u. 59‐67, Budapest, H‐1025, Hungary
a r t i c l e i n f o
a b s t r a c t
Article history:
Octanoic acid (OA) as model reactant of medium chain length, and its reduced products, octanal and octanol
were hydroconverted over different components of a CuIn/Al2O3 composite catalyst. A fixed‐bed flow through
reactor was used at 21 bar total pressure in the temperature range of 240–360 °C. Fatty acid hydroconversion
activity of alumina supported Cu catalyst and mainly the yield of selectively produced octanol can be greatly
increased by In2O3 doping, suppressing the dehydration side reactions. Appearance of metallic indium on
alumina supported reduced copper catalyst can arrest the consecutive catalytic reaction at the alcohol formation
step prior to further dehydration to ether or alkenes. An industrial, conventionally used Adkins catalyst (72 wt.%
CuCr2O4 and 28 wt.% CuO) and the novel bimetallic composite (CuIn/Al2O3) were compared: both produce
octanol with high selectivity, but the new chromium‐free fatty acid hydrogenation catalyst is more active, nearly
as active as earlier investigated NiIn/Al2O3.
Received 29 February 2012
Received in revised form 17 April 2012
Accepted 20 April 2012
Available online 27 April 2012
Keywords:
Biomass
Fatty acids
Hydroconversion
Alcohols
Cu/alumina
In2O3 doping
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
been found to be a suitable catalyst for the de‐NOx reactions [5],
for dehydrogenation of propane to propylene with carbon dioxide
The actual significence of the catalytic reduction of carboxylic
acids to alcohols has been surveyed in the previous paper [1] wherein
the applicability of Ni/Al2O3 with co‐catalyst In2O3 was discussed.
Indium doped Ni/Al2O3 catalyst proved to be highly efficient for
directing the hydrogenation of fatty acids to aliphatic alcohols
opening a novel route for catalyst development. Copper catalysts
enable the selective addition of hydrogen to carbon–oxygen bonds
but are relatively inactive in the hydrogenolysis of the carbon–carbon
bonds unlike nickel catalysts [2]. From the early 1930s it is recognised
that the chromium promoted copper catalysts show much higher
activity and selectivity for alcohol formation than unpromoted ones
[3]. Due to what happened the promotion effect of indium for copper
catalyst can be also similarly efficient as for nickel and may substitute
the chromium promoter applied in copper catalysts.
Highly dispersed copper particles were generated on special
aluminosilicate supports formed by destructive hydrogen reduction/
dehydration of Cu zeolites. These samples have the lowest Si/Al ratios
and consequently the highest cation content of quite homogeneous
distribution. They show high activity and selectivity in the catalytic
hydroconversion of carboxylic acids [4]. The activity and the selec-
tivity to alcohols over these specially supported Cu catalysts can be
effectively increased by In2O3 doping [4] similarly to Ni/Al2O3
catalyst [1]. Indium (III) oxide supported on zeolite or alumina has
[6,7]. However such supported In2O3 based materials have received
limited attention as hydrogenation catalysts, where indium can be
present in metal phase.
Cu or Cu2In catalysts supported on destructed zeolites (zeolite
structures collapsed in consequence of unstable H‐form formation,
during reduction of charge compensating cations) having less than
30 m2/g specific surface area, depending on the type of zeolite
precursors [4]. Alumina support has more than six times higher
surface area and its structure is well definied compared with the
collapsed zeolite structures becoming X‐ray amorphous and con-
taining small islands of unknown different phases. Indium doping to
Ni/Al2O3 catalyst cannot give reliable information on indium doping
to copper oxide since these two metals differ, e.g., the nickel oxide
is partly reduced in hydrogen at the usual pretreatment temperature
450 °C whereas copper oxide is fully reduced to metal (see later). The
aim of present research is to learn more about influences of indium
metal for the different active metals in the selective hydrogenation
of carboxylic acid to alcohols.
2. Experimental
The catalytic reduction of octanoic acid (OA) (Aldrich) as a model
reactant with medium chain length, octanal (C8AL) (Fluka) as inter-
mediate compound, and catalytic conversions of octanol (C8OL)
(Fluka) as product are also investigated under similar conditions as
in ref. [1] (in general at 20 bar hydrogen, 1 bar octanoic acid
partial pressures in the temperature range of 240–360 °C. Catalyst
⁎
Corresponding author.
E-mail address: harnos.szabolcs@ttk.mta.hu (S. Harnos).
1566-7367/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2012.04.023

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G. Onyestyák et al. / Catalysis Communications 26 (2012) 19–24
Al2O3. Composite catalysts were prepared by adding indium (III)
oxide powder to the Cu/alumina samples and grinding the mixture in
agate mortar. 159 m2/g was the specific surface area of the composite
which is equal to 203 m2/galumina
.
X–ray patterns were recorded and evaluated as in ref. [1].
3. Results and discussion
NiIn/Al2O3 catalyst is more active in octanoic acid hydroconversion
than CuIn/Al2O3 since the conversion and octanol yield curves are
shifted by 20–30 °C to higher temperatures for Cu,In/Al2O3 (Fig. 1).
However, the product distributions are the same on the two bimetallic
catalysts. Hence similarity of catalytically active phases seems probable.
For 9Ni/Al2O3 catalyst at the routine pretreatment temperature, at
450 °C only a small part of NiO is reduced and a complete reduction
can be attained only at 650 °C [1]. Contrarily, in 9Cu/Al2O3 catalyst
Fig. 1. Comparison of the conversion (●■) and the target product evolution (○□) over
9Cu/Al2O3 +10% In2O3 (circles) and 9Ni/Al2O3 +10% In2O3 (squares) catalysts in the
hydroconversion of octanoic acid as a function of reaction temperature at 21 bar total
pressure. WHSV of OA was 2.0 h−1
.
pretreatment was carried out in hydrogen flow in situ in the reactor
at 450 °C, 21 bar for 1 h). Product analysis as well as representation
of results in stacked area graphs is similar as in ref. [1], i.e. the
distance between two neighboring curves represents the concentra-
tion of a given product at a given temperature in weight percent.
γ‐Al2O3 (Ketjen CK 300, Akzo‐Chemie, BET: 199 m2/g) activated at
550 °C was impregnated with NH4OH solution (Reanal Finechemical
Co.) of Cu (acetate)2 (Merck) applying incipient wetness method,
dried, and calcined at 550 °C. After impregnation the specific surface
area changed to 180 m2/g, corresponding to 207 m2/galumina. The
samples contained 3, 9 and 20 wt.% copper designated as 3‐, 9‐, 20Cu/
Fig. 2. HT‐XRD patterns of 9Cu/Al2O3 (a) and 3Cu/Al2O3 +10% In2O3 (b) catalysts treat-
ed step by step up to 450 °C in H2 flow for half an hour.
Fig. 3. HT‐XRD patterns of 9Cu/Al2O3 catalysts with 3% (a), 10% (b) and 20% (c) In2O3
loading treated step by step up to 450 °C in H2 flow for half an hour.

G. Onyestyák et al. / Catalysis Communications 26 (2012) 19–24
21
a
c
b
d
Fig. 4. Octanoic acid hydroconversion over commercial Adkins (a), 14CuP+10% In2O3 (b), 9Cu/Al2O3 (c) and 9Cu/Al2O3 +10% In2O3 (d) catalysts characterised by distributions of
main products between 240 and 360 °C at 21 bar total pressure using stacked area graphs. WHSV of OA was 2.0 h–1. (symbols: C8−: octane, C8=: octenes, C8OL: octanol, C8AL:
octanal, (C8)2O: dioctyl ether, H2O:water, OA: octanoic acid, OP: other products).
copper oxide is already fully reduced at 200 °C forming small copper
particles of ~20 nm average diameter (∇ in Fig. 2a). These particles do
not change up to 650 °C (and not only up to 450 °C as shown in
Fig. 2a). Reduction of admixed In2O3 can be observed at much higher
temperature, i.e., between 350 and 450 °C (see Figs. 2b and 3a, b, c)
detected by disappearence of In2O3 diffraction lines (*). This process
is completed up to 450 °C on all 9Cu/Al2O3 samples (see Fig. 3) but
not on 3Cu/Al2O3 sample mixed with 10 wt.% In2O3 (see Fig. 2b),
where trace indium (III) oxide can be alone detected. This sample of
the lowest copper content can already form copper–indium alloy
directly with the generated indium metal atoms (•) above 350 °C. In
the case of this composition copper particles cannot be detected
below the reduction temperature of In2O3 indicating either the
formation of too small Cu0 nanoparticles not detectable by XRD
method. More probably, the alloying of the low concentration Cu0
with small amount of reduced In2O3 as shown by the appearance of
a new phase (marked with • in Figs. 2 and 3) which can be assigned
to some kind of CuIn alloy. Mainly Cu2In phase, but Cu4In and
Cu9In4 phases may also be present in lower concentration. These
phases were determined based on ICDD database [8], the
corresponding ICDD numbers are Cu2In: 42–1475, Cu4In: 42–1477
and Cu9In4: 42–1476.
After treatment at 450 °C for half an hour the 3Cu/Al2O3 sample
mixed with 10 wt.% In2O3 and cooling down the composite sample
to R.T. the presence of excess solid metallic indium phase (+) can
be also detected (see Fig. 2b) similarly to diffractograms of 9Cu/
Al2O3 sample admixed with 20 wt.% In2O3 containing also excess
indium beyond the amount needed to alloy formation (Fig. 3c).
Frozen indium particles with average sizes of ~130 nm are larger
than copper particles indicating higher mobility of indium atoms
above the melting point (156.4 °C) than that of copper atoms. The
9Cu/Al2O3 +10 wt.% In2O3 composite contains Cu and In nearly in
2:1 atomic ratio, so all amounts of two metals are consumed in forma-
tion of the alloy phase (Cu2In) having average sizes of ~10 nm
Fig. 5. Comparison of the conversion (●■▲▼) and the target product evolution
(○□△▽) over 10% In2O3/Al2O3 catalysts with different Cu loadings in the
hydroconversion of octanoic acid as a function of reaction temperature at 21 bar total
Fig. 6. Comparison of the conversion (●■▲▼) and the target product evolution
(○□△▽) as a function of reaction temperature over 9Cu/Al2O3 catalysts with various
amounts of In2O3 admission in the hydroconversion of octanoic acid at 21 bar total
pressure. WHSV of OA was 2.0 h−1
.
pressure. WHSV of OA was 2.0 h−1
.

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G. Onyestyák et al. / Catalysis Communications 26 (2012) 19–24
a
A
B
C
b
c
Fig. 7. Hydroconversion of octanoic acid (a‐A), octanal (b‐B) and octanol (c‐C) over Al2O3 (a, b, c) and over Al2O3 with 10% of In2O3 (A, B, C) as a function of reaction temperature at
21 bar total pressure, using stacked area graphs ((C8)2ALD: 2‐hexyldec‐2‐enal, other symbols as in Fig. 4).
(Fig. 3b). At lower In2O3 admission Cu and Cu2In phases are present
altogether (Fig. 3a) and in composites containing indium in excess
to the composition of Cu2In alloy phase, indium can also appear as
distinct pure metal phase (see Figs. 3c or 2b), but it can only be
detected below its melting point 156.4 °C. The admitted In2O3
contains crystals with particles of ~70 nm average diameter (*)
however it can form much bigger aggregates and the poor method
applied for admission cannot result in homogeneous distribution,
which can be true for CuO, too. A not uniform distribution can explain
the presence of In2O3 near 3Cu/Al2O3 at 450 °C in Fig. 2b and In
detected at 25 °C after admission only 3% In2O3 to 9Cu/Al2O3 (Fig. 3a).
Formation of Cu and/or Cu2In alloy nanoparticles, and appearance
of metallic indium on the support is evident on the basis of HT–XRD
results. In view of catalytic properties complete understanding of
the multiple behaviors over such a complex ensemble of active sites
requires comprehensive catalytic investigations. On adding a large
amount of In2O3 (10 wt.% In2O3 of the mass of monometallic 9Cu/
Al2O3 catalyst) as a co‐catalyst, the activity significantly increases
and the selectivity changes strikingly by suppressing of the consecu-
tive octanol dehydration side–reactions (cf. Fig. 4c and d).
selectivity in narrower temperature range than the Adkins catalyst.
The novel CuIn/Al2O3 catalyst seems, however, to be more active:
80% overall conversion of OA on 9Cu/Al2O3 catalyst doped with
10 wt.% In2O3 is attained at 310 °C while on copper chromite at
350 °C.
Dioctyl ether ((C8)2O) formation in bimolecular octanol dehydra-
tion on CuIn/Al2O3 sample becomes significant only at high octanol
yield above 310 °C (Fig. 4). Monomolecular dehydration of octanol to
octene (C8=) appears only above nearly full conversion of OA to
octanol. Both acid catalysed side reactions may be attributed to alumina.
However, these undesirable reactions can be highly mitigated on highly
active and stable 9Cu/Al2O3+10 wt.% In2O3 catalyst composite, using
lower reaction temperature and higher space velocity.
Use of indium as efficient promoter with Cu/Al2O3 catalyst turned
out also to be a success (Fig. 4) similarly to In2O3 doped Ni/Al2O3
samples [1]. However, for In2O3 doped Cu/Al2O3 samples at constant
indium content (10 wt.% in Fig. 5) the conversion and the octanol
yield (the product distribution) is hardly influenced by the Cu–
content between 3 and 20 wt.%. Similar behavior can be observed at
a fixed Cu‐loading (9 wt.%) changing the amount of added indium
oxide in 3–20 wt.% range (see in Fig. 6). Hence it seems likely to
apply in low concentration the expensive, but strongly efficient
In2O3 co‐catalyst. It can be estimated that both active metal compo-
nents can be used in about 10 wt.% to attain high carboxylic acid
conversion with high and stable octanol yield (fauling of these
catalysts was not observed).
In Fig. 4 the catalytic properties of a commercial, conventionally
used Adkins catalyst (consisting of 72 wt.% CuCr2O4 and 28 wt.%
CuO, Fig. 4a) and our composites (mono‐ (Cu/Al2O3, Fig. 4c) or
bimetallic alumina supported catalysts (CuIn/Al2O3, Fig. 4d)), and an
In dopped destructed CuP zeolite (Fig. 4b) are compared along with
the increasing reaction temperature under identical conditions. All
the samples are able to produce alcohol from fatty acid with high
selectivity, but the chromium free samples are able to give good
The weak influence of the concentration changes of both active
metals in a wide range can be explained by supposing the most

G. Onyestyák et al. / Catalysis Communications 26 (2012) 19–24
23
a
b
Fig. 10. Yields and selectivities of OA conversion on 9Cu/Al2O3 +10% In2O3 catalyst as
function of OA partial pressure at 21 bar total pressure and 300 °C. The WHSV of OA
was 2.0 h–1. The partial pressure of H2 was 17.6 bar. The OA partial pressure was
changed by changing the OA/He ratio. (symbols as in Fig. 4).
producing mainly octanal and less octanol. The intermedier octanal is
extremely reactive in aldol type condensation leading to formation of
2‐hexyldec‐2‐enal /(C8)2ALD/ in high concentration mainly on alumina
(Fig. 7b). Furthermore aliphatic octyl aldehyde can easily be reduced to
octyl alcohol in presence of indium, as reflected in Fig. 7B. Octanol then
can be dehydrated to octenes over the naked alumina support, as con-
firmed in Fig. 7c using octanol as reactant. At lower reaction tempera-
ture, the dominant reaction route of octanol transformation is the
bimolecular dehydration which forms dioctyl ether. Increasing the tem-
perature, monomolecular dehydration becomes the main reaction
pathway resulting in olefin formation. Probably this change of dehydra-
tion pathway is essentially affected by the decreasing alcohol coverage
on the surface controlled by the increasing temperature. Using octanal
as reactant, dioctyl ether yield is very low because the alcohol formation
is suppressed by competing aldol condensation on the alumina surface
(Fig. 7b). Comparison of the two sides of Fig. 7 gives some insight to the
role of indium: i., OA can be reduced although with much lower rate on
indium (Fig. 7A) than on copper particles (squares in Fig. 6); ii., aldol
condensation of octanal and octanol dehydration are greatly suppressed
by indium (Fig. 7b–B) and iii., the secondary reactions of octanol are
suppressed as well by indium suggesting that indium can cover at
least partly the surface of the alumina support (Fig. 7c–C). However
the low, but significant production of ether and alkenes from octanol in-
dicates that the missing components: copper or octanoic acid should
have some influence on suppressing the dehydration of alcohol.
Fig. 8b proves that the presence of fatty acid plays an important role
to poison the active centers of dehydration together with indium, be-
cause octanol can be highly dehydrated over CuIn/Al2O3 catalyst, i.e.,
in presence of copper and indium on alumina, but in absence of the or-
ganic acid reactant. Fig. 8a shows that copper and indium can promote
the reduction of the aldehyde with hydrogen at a much lower temper-
ature than indium alone (Fig. 7B).
Fig. 8. Octanal (a) and octanol (b) hydroconversion over 9Cu/Al2O3 +10% In2O3
catalyst characterised by distributions of main products between 200 and 360 °C at
21 bar total pressure using stacked area graphs. WHSV of octanal and octanol was
2.0 h−1 similarly to octanoic acid reactant (symbols as in Fig. 4).
efficient active sites on the surface of the Cu2In alloy. This phase
surpasses the activity of copper or mainly indium metal surfaces
while the composition and the mass of bulk phase inside the
metal particles does not affect significantly the surface reactions
(Figs. 5 and 6).
Beyond the metal phase which is active in hydrogenation, the
support applied and its interactions with the In2O3 co‐catalyst may be
of importance to ensure the advantageous catalytic properties. Fig. 7
demonstrates the catalytic effects observed for alumina support and
the copper free composite interacting with the reactant OA (Fig. 7a,
A), with the intermediate product aldehyde (Fig. 7b, B) and with the de-
sired final product alcohol (Fig. 7c, C). The support has no activity con-
trary to the presumably well dispersed indium metal (working highly
above its melting point), which shows some hydrogenating activity
The octanoic acid conversion to octanol over the 9Cu/Al2O3
catalyst doped with 10 wt.% In2O3 similarly increases roughly linearly
with increasing hydrogen partial pressure between 4 and 18 bar
(Fig. 9) and inversely with octanoic acid partial pressure (Fig. 10),
i.e., to the coverage of active sites by adsorbed fatty acid seems to
suppress hydrogen as in the case of Ni,In/Al2O3 [1]. Both observations
are in accordance with the Langmuir–Hinshelwood kinetics. Unlike
indium doped Ni/Al2O3 catalyst [1] the lower activity of CuIn/alumina
composite is reflected in the dependence on octanoic acid partial
pressure, too. At lower coverage of the carboxylic acid, where
hydrogen coverage may be higher resulting in higher OA conversion,
the yield of octanol is lower, but the less reduced intermedier, the
octanal is higher. This finding opens a way of aldehyde production
instead of alcohol broadened the list of available products.
Fig. 9. Yields and selectivities of OA conversion on 9Cu/Al2O3 +10% In2O3 catalyst as
function of hydrogen partial pressure at 21 bar total pressure and 300 °C. The WHSV
of OA was 2.0 h−1. The partial pressure of OA was 1.7 bar. H2 partial pressure was
changed by changing the H2/He ratio (symbols as in Fig. 4).

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G. Onyestyák et al. / Catalysis Communications 26 (2012) 19–24
4. Conclusions
The activity dependence on the reactant partial pressures reveals
Langmuir–Hinshelwood kinetics with rate controlling surface
Indium doping has been discovered to be highly efficient in reduc-
tion of fatty acids with hydrogen, opening a novel route for catalyst
development. Hydrogenation of carboxylic acid of medium chain
length resulting selectively in alcohol production can be increased
by In2O3 doping similarly over both Cu or Ni/Al2O3 catalysts. Presence
of metallic indium or rather alloying copper particles supported on
alumina can effectively stop the step by step catalytic hydrogenation
of fatty acids after alcohol formation inhibiting the following mono‐
or bimolecular dehydrations. High conversion with high level of
octanol selectivity can be attained in a wide loading range of Cu
and In on alumina support. Copper oxide can be more easily reduced
to metallic nanoparticles at lower temperature than indium (III)
oxide, but equally below the pretreatment temperature (450 °C).
This difference is not reflected by any change of catalytic behaviour
in a wide range of Cu and In content.
reaction over a CuIn/Al2O3 composite catalyst.
Acknowledgements
The authors wish to express their appreciation to Mrs. Ágnes
Farkas Wellisch for her technical assistance.
References
[1] Gy. Onyestyák, Sz. Harnos, D. Kalló, Catalysis Communications 16 (2011) 184.
[2] D.S. Brands, E.K. Poels, A. Bliek, Appl. Catal. A 184 (1999) 279.
[3] J.D. Stroupe, Journal of the American Chemical Society 71 (1949) 569.
[4] Sz. Harnos, Gy. Onyestyák, J. Valyon, M. Hegedűs, Z. Károly, Selective reduction of
caprylic acid to octanol over Cu and InCu/aluminosilicate catalysts, in: M.
Derewinski, et al., (Eds.), Proc.10th Pannonian Int. Symp. Catal. Krakow, 2010,
pp. 334–341.
[5] J.A. Perdigon–Melon, A. Gervasini, A. Auroux, Journal of Catalysis 234 (2005) 421.
[6] M. Chen, J. Xu, Y. Liu, Y. Cao, H. He, J. Zhuang, Applied Catalysis A: General 377
(2010) 35.
Appearance of Cu2In alloy phase on the surface of metal particles
results in significant increase of hydrogenation activity, beyond this,
the presence of well‐dispersed indium atoms or clusters in liquid
state on the surface of alumina support seems to be decisive in
selective poisoning the alcohol dehydration capability of the support.
[7] M. Chen, J. Xu, Y. Liu, Y. Cao, H. He, K. Fan, J. Zhuang, Journal of Catalysis 272 (2010) 101.
[8] B.D. Cullity, Elements of X–ray Diffraction, 2nd Addison–Wesley Publ Co. Reading,
MA, USA, 1978.