Effects of metal promotion on the performance of CuZnAl catalysts for alcohol synthesis

Article abstract of DOI:10.1002/cctc.201402037

A series of CuZnAl catalysts modified with different promoters (Fe, Co, Ru, Zr, Mo, Mg, Mn, and Cr) have been prepared through co-precipitation, characterised by applying a combination of techniques, and tested for carbon monoxide hydrogenation. Cu reducibility in CuZnAl catalysts was affected by the addition of promoters. The ease of Cu reduction in the promoted catalysts leads to more active catalysts for the hydrogenation of carbon monoxide and the production of C₂₊ alcohols, whereas lower catalytic activity was observed over less reducible catalysts. The promotion of CuZnAl catalysts even with small amounts of Cr, Mn, and Fe resulted in a significant modification in the reaction selectivity. The Fe-containing catalyst demonstrated a dramatic increase in carbon monoxide conversion and C₂₊ alcohol productivity (30 mg g^-1_cath^-1). Choose your alcohol wisely: The ease of Cu reduction in CuZnAl methanol synthesis catalysts promoted with metals leads to more active catalysts for the hydrogenation of carbon monoxide and the production of C₂₊ alcohols. The promotion of CuZnAl catalysts even with small amounts of Cr, Mn, and Fe results in a significant modification in the selectivity patterns.

Full text of DOI:10.1002/cctc.201402037

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DOI: 10.1002/cctc.201402037
Effects of Metal Promotion on the Performance of CuZnAl
Catalysts for Alcohol Synthesis
Jorge M. Beiramar, Anne Griboval-Constant, and Andrei Y. Khodakov*[a]
A series of CuZnAl catalysts modified with different promoters
(Fe, Co, Ru, Zr, Mo, Mg, Mn, and Cr) have been prepared
through co-precipitation, characterised by applying a combina-
tion of techniques, and tested for carbon monoxide hydroge-
nation. Cu reducibility in CuZnAl catalysts was affected by the
addition of promoters. The ease of Cu reduction in the pro-
moted catalysts leads to more active catalysts for the hydroge-
nation of carbon monoxide and the production of C2+ alco-
hols, whereas lower catalytic activity was observed over less re-
ducible catalysts. The promotion of CuZnAl catalysts even with
small amounts of Cr, Mn, and Fe resulted in a significant modi-
fication in the reaction selectivity. The Fe-containing catalyst
demonstrated a dramatic increase in carbon monoxide conver-
sion and C2+ alcohol productivity (30 mggÀca1t hÀ1).
Methanol synthesis in the industry involves Cu-based cata-
lysts containing zinc oxide and aluminium oxide (CuZnAl) op-
erating at 250–3008C. Numerous studies have been performed
with CuZnAl methanol synthesis catalysts. Although the active
sites for methanol synthesis have usually been associated with
Cu, the presence of Zn is important for obtaining good catalyt-
ic performance. Syngas conversion in these catalysts occurs on
Cu sites,[1,9] whereas ZnO is important for catalyst stabilisation
and maintaining good dispersion of Cu.[10–12] Several reports
suggest that Cu can be decorated with Zn[13–15] and the Cu–
ZnOx interface[16] plays a crucial role in the reaction. A Cu–Zn
surface alloy forms during the reaction[17,18] but bulk reduction
of zinc oxide does not usually occur. In addition, zinc oxide de-
creases the catalyst acidity and the rate of dehydration of
methanol to dimethyl ether.[17]
Introduction
The demand for clean energy generated from alternative and
renewable sources has been steadily growing around the
world. The renewable energy sources (such as biomass) ac-
count for approximately 19% of total energy use and have the
capacity to supply 50% of world energy demand in the next
century. The catalytic conversion of syngas (mixtures of carbon
monoxide and hydrogen) leads to hydrocarbons, methanol,
and higher alcohols.[1–5] Higher alcohols can be used as fuels,
chemicals, or chemical intermediates. Several catalytic systems
have been tested for the synthesis of higher alcohols.[1,6]
Among them are Rh catalysts, MoS2 catalysts, modified Co or
Fe Fischer–Tropsch synthesis catalysts and modified CuZn
methanol synthesis catalysts.
Rh catalysts have so far demonstrated the highest selectivity
towards higher alcohols; however, the higher cost of Rh and
its limited reserves restrict the use of Rh catalysts.[1,6] MoS2 cat-
alysts[7] operate at higher pressure and require continuous ad-
dition of several parts per million of H2S to the reactor feed. In
addition, these catalysts demonstrate a long start-up period. A
significant selectivity towards relatively cheap light hydrocar-
bons (e.g., methane) is usually observed over modified Co or
Fe Fischer–Tropsch synthesis catalysts, which undermines the
economic efficiency of carbon monoxide conversion. Carbon
monoxide hydrogenation with CuZnAl catalysts usually leads
to higher selectivity towards methanol. The performance of
these catalysts could be improved, provided the reaction selec-
tivity is transferred from methanol to longer chain mixed
alcohols.[8]
Mixed higher alcohols are major by-products during carbon
monoxide hydrogenation with methanol synthesis catalysts. It
has been shown previously that promotion with alkali ions
(e.g., Na, K, and Cs) could increase, to some extent, the selec-
tivity of these catalysts towards higher alcohols.[19–23] Alkali pro-
moters could provide basic sites for the aldol-type condensa-
tion and thus increase higher alcohol selectivity.[19,23] Some in-
crease in higher alcohol productivity was also observed upon
the promotion of the CuCo/Al2O3 catalyst[24] as well as CuMnZn
and CuMnZr catalysts[25–27] with Fe.
Herein, we address a systematic comparative investigation
on the effect of the addition of small amounts (1 mol% for all
elements) of different promoters (Fe, Co, Ru, Zr, Mo, Mg, Cr,
and Mn) on the structure and catalytic performance of the
modified CuZnAl methanol synthesis catalysts for the hydroge-
nation of carbon monoxide to C2+ alcohols.
[a] J. M. Beiramar, Dr. A. Griboval-Constant, Dr. A. Y. Khodakov
Unitꢀ de catalyse et de chimie du solide (UMR8181 CNRS)
Universitꢀ Lille1-ENSCL-EC Lille, BꢁT. C3
Results and Discussion
Catalyst characterisation
Citꢀ scientifique, 59655 Villeneuve d’Ascq (France)
Fax: (+33)3-20-43-65-61
The textural properties of the calcined catalysts are listed in
Table 1. The promotion with Ru and Mo does not lead to any
notable change in the BET surface area. For other promoters,
E-mail: andrei.khodakov@univ-lille1.fr
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201402037.
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XRD peaks was relatively low,
which made it difficult to esti-
mate the ZnO crystallite size
from XRD profiles.
Table 1. Characterisation of promoted CuZnAl catalysts.
Catalyst
Chemical composition [mol%]
BET surface area
Pore volume
[m2 gÀ1
]
Pore diameter
[nm]
Promoter
Cu
Zn
Al
[m2 gÀ1
]
The hydrogen temperature-
programmed reduction (H2-TPR)
profiles (Figure 2) of unpromot-
ed or promoted CuZnAl catalysts
demonstrate at least two reduc-
tion peaks. The profiles show
that these peaks shift to lower
temperatures compared with
those of pure bulk CuO.[23,30] The
peak integration suggests that in
CuZnAl
–
62.8
61.9
62.6
62.3
62.4
62.3
61.9
62.0
62.0
28.4
28.2
27.9
28.4
28.3
28.4
28.3
28.4
28.1
8.9
8.9
8.5
8.9
8.8
8.8
8.9
8.8
8.8
79.2
61.8
56.7
76.7
56.5
71.9
63.5
75.5
68.5
0.36
0.35
0.31
0.35
0.31
0.37
0.35
0.51
0.39
14.2
18.2
15.2
12.4
14.6
14.8
17.4
18.6
20.0
Fe–CuZnAl
Co–CuZnAl
Ru–CuZnAl
Zr–CuZnAl
Mo–CuZnAl
Mg–CuZnAl
Mn–CuZnAl
Cr–CuZnAl
1.0
1.0
0.8
0.5
0.4
1.0
0.9
0.9
a significant decrease in the BET surface area was observed.
This evolution of the BET surface area is accompanied by
a slight increase in pore sizes of the catalyst. The decrease in
pore volume with the increase in pore diameter could be at-
tributed to preferential plugging of narrow catalyst pores by
the promoting oxide.[28] The promoter content measured by
using inductively coupled plasma atomic emission spectrosco-
py was 1 mol% for most of the catalysts except for Ru-, Mo-,
and Zr-promoted catalysts. With Ru- and Mo-containing cata-
lysts, the decrease in the promoter content can be attributed
to the loss of these promoters owing to the formation of vola-
tile MoO3 and RuO4 species during calcination. Lower than the
expected Mo content can be attributed to the precipitation pH
at which some of Mo species are soluble and washed out from
the catalyst.
the temperature range from room temperature to 4008C, hy-
drogen consumption corresponds to the reduction of CuO to
Cu. Notably, the position of the peaks is strongly affected by
the promoting element. Promotion with Co, Zr, and Mg shifts
hydrogen consumption peaks to higher temperatures, whereas
promotion with Cr and Mn lowers the reduction temperature
of Cu. Promotion with Fe, Mo, and Ru results in a small effect
on Cu reducibility. Because of their low content in the cata-
lysts, the degree of reduction of the promoting metals cannot
be estimated from H2-TPR profiles. However, Mg and Zr remain
The X-ray absorption spectra were measured at Cu K absorp-
tion edges for unpromoted and promoted calcined CuZnAl
catalysts. The X-ray absorption near-edge structure (XANES)
spectra (Figure 1a) are identical; they are characteristic of CuO.
The extended X-ray absorption fine structure (EXAFS) Fourier
transform modulus also indicated the presence of the CuO
phase (Figure 1b). In agreement with previous reports,[29] the
peak in the EXAFS Fourier transform modulus (without phase
correction) at 1.5 ꢁ corresponds to the CuÀO bond whereas
the peaks at 2.5 and 3.31 ꢁ could be assigned to CuÀCu coor-
dination in CuO. The changes in bond lengths were observed
with the addition of promoters. These changes were more pro-
nounced for the CuÀO bond than for the CuÀCu bond; this
observation suggests that electronic density changes, which
could be due to the promoting metal.
The XRD patterns of the catalysts are shown in Figure S1.
Only CuO and ZnO diffraction peaks are detected by using
XRD. No diffraction peaks, which could be assigned to metal
promoters, were observed, which could be due to their low
content in the catalysts (1 mol%). We also did not detect any
diffraction peaks of the Al2O3 phase even at an Al content
close to 10 mol%. This result suggests that aluminium oxide is
probably present in an amorphous form. The XRD peaks at
32.5, 35.5, 38.7, 48.7, 58.3, 61.5, and 67.98 were assigned to
CuO tenorite phase, whereas the peaks at 31.8, 36.3, 47.7, and
62.98 were assigned to ZnO zincite phase. The identical width
of the peaks related to the CuO phase in promoted CuZnAl
catalysts indicates similar Cu dispersion. The intensity of ZnO
Figure 1. a) Cu K edge XANES spectra and corresponding b) EXAFS Fourier
transform modulus of reference compounds (Cu2O and CuO) and calcined
catalysts.
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Figure 2. H2-TPR profiles of unpromoted and promoted CuZnAl catalysts.
TCD=Thermal conductivity detector.
oxidised whereas Fe, Co, Ru, Mn, Mo, and Cr could be at least
partially reduced during catalyst activation.
The in situ XRD patterns (Figure 3) in hydrogen flow have
provided additional information about the reducibility of differ-
ent phases in CuZnAl catalysts and about Cu and Zn species
present in the activated catalysts. The in situ XRD patterns
were measured for the Fe-promoted catalyst and compared
with those of the unpromoted CuZnAl catalyst. The reduction
of mixed oxide catalysts proceeded in two distinct stages (Fig-
ure 3a). At approximately 2508C, the intensity of XRD peaks re-
lated to CuO decreases and the XRD patterns related to Cu
can be observed. The intensity of Cu XRD peaks increases at
higher reduction temperatures. This observation corresponds
to the reduction of CuO to Cu. Between 350 and 8008C, the
zinc oxide phase starts to reduce. Cu reduction proceeds simi-
larly in the Fe-promoted catalyst with the reduction of CuO di-
rectly to Cu, followed by Zn reduction and CoZn alloy forma-
tion at higher temperatures (Figure 3b). The CuZn alloy was
identified from the in situ XRD patterns of the reduced cata-
lysts, which were cooled to room temperature after their re-
duction (Figure S2). The patterns show a clear shift of XRD
peaks compared with that of the reference Cu, which indicates
the presence of CuZn alloy (JCPDS card no. 25-0322; mostly
a brass phase with a small fraction of the b brass phase[31]).
Figure 3. In situ XRD profiles of a) CuZnAl and b) Fe–CuZnAl catalysts mea-
sured in 5%H2/Ar at different temperatures.
with the increase in hydrocarbon and carbon dioxide selectivi-
ties. Carbon monoxide conversion does not increase signifi-
cantly with temperature, which could be due to the thermody-
namic limitations of methanol synthesis.[19] We did not observe
any significant catalyst deactivation under the used reaction
conditions. After performing a catalytic test at high tempera-
ture, the temperature was decreased to 2808C and conversion
was measured again. The conversion value was similar to the
activity of the freshly reduced catalyst at 2808C, which indi-
cates the insignificance of catalyst deactivation during catalyst
exposure to syngas at higher temperature.
The promotion of the CuZnAl catalyst with small amounts of
different metals significantly changes carbon monoxide hydro-
genation rate and methanol selectivity at 2808C (Table 2). An
increase in carbon monoxide conversion and mixed alcohol
productivity was observed over Cr- and Mn-promoted cata-
lysts, whereas a decrease in catalytic activity (5–10 times) was
observed over Co- and Ru-promoted catalysts. For the Mg-con-
taining catalyst, the carbon monoxide hydrogenation rate was
not affected much by promotion.
Catalytic performance
The catalytic performance data of unpromoted and promoted
catalysts obtained in a fixed-bed reactor at a total pressure of
2 MPa, H2/CO=2, and at 280 and 3208C are presented in
Table 2. Methanol, carbon dioxide, hydrocarbons, and mixed
C2+ alcohols were the major reaction products of the hydroge-
nation of carbon monoxide with CuZnAl catalysts at both 280
and 3208C. The methanol selectivity was higher than 70% at
2808C but decreased to 30.9% at higher reaction temperature
The catalytic behaviour of the promoted catalysts was much
different at 3208C than that at 2808C. Because the conversion
of carbon monoxide to methanol is limited by thermodynam-
ics at 3208C, when methanol was the major reaction product,
carbon monoxide conversion does not increase much under
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Effect of promoters on the cat-
alytic performance of CuZnAl
catalysts
Table 2. Catalytic performance data.[a]
Catalyst
T
XCO
Selectivity [mol%C]
C2+ alcohol productivity
[mggÀca1t hÀ1
]
[8C]
[%]
Hydrocarbon
CH3OH
C2+ alcohol
CO2
The catalytic results reveal a sig-
nificant effect of the catalyst
promotion on the performance
of promoted CuZnAl catalysts
for carbon monoxide hydrogena-
tion. The effect on the promo-
tion of the catalytic performance
cannot be attributed, however,
to a major change in Cu disper-
sion. The XRD results indicate
similar Cu dispersion in the pro-
moted catalysts. The XANES/
EXAFS results suggest the pres-
ence of similar CuO species in
the calcined catalysts.
CuZnAl
280
320
280
320
280
320
280
320
280
320
280
320
280
320
280
320
280
320
11.9
12.0
6.1
69.2
0.8
2.8
2.8
3.8
6.3
4.8
6.8
5.4
11.2
7.4
17.1
17.5
15.9
15.6
10.4
27.7
26.1
35.5
91.1
15.1
3.4
11.5
5.9
25.7
11.3
21.7
8.7
70.6
30.9
13.6
1.1
6.2
7.6
6.0
2.9
0.1
11.4
1.0
1.7
3.2
4.9
3.5
7.8
4.5
9.5
6.2
8.2
3.5
7.2
12.7
34.8
54.2
60.6
3.6
5
7
6
Fe–CuZnAl
Co–CuZnAl
Ru–CuZnAl
Mo–CuZnAl
Zr–CuZnAl
Mg–CuZnAl
Mn–CuZnAl
Cr–CuZnAl
30
0.02
5
0.6
0.9
3
3
5
7
7
5.1
51.7
92.8
74.4
75.7
32.1
71.1
44.3
61.8
36.2
39.0
20.4
61.7
29.3
21.9
1.5
12.5
15.2
25.7
12.7
26.2
23.1
34.2
27.4
37.4
19.9
34.2
20.1
27.4
34.1
15.4
29.1
8
15
20
8
17
[a] P=2 MPa, H2/CO=2, gas hourly space velocity=3600 hÀ1
.
However, the addition of even
small amounts of metal promot-
these conditions.[19] All the catalysts demonstrated a decrease
in methanol selectivity (except for the Co–CuZnAl catalyst) at
3208C, which was due to the increase in carbon monoxide
conversion to hydrocarbons, carbon dioxide, and higher alco-
hols. The formation of these compounds is much less limited
by thermodynamics than the formation of methanol at higher
temperatures.
ers to CuZnAl catalysts leads to notable modification in H2-TPR
profiles (Figure 2). Promotion with Zr and Co decreases the re-
ducibility of Cu species, whereas the addition of Cr and Mn
lowers the temperature required for Cu reduction. The relation
between C2+ alcohol productivity at 3208C and the reduction
temperature for promoted CuZnAl catalysts determined from
the most intense peak in H2-TPR profiles is shown in Figure 5.
The C2+ alcohol productivities at 2808C are plotted against
catalyst reduction temperatures in Figure S4. A decrease in cat-
alyst reduction temperature leads to a higher reaction rate for
most of the catalysts. Higher C2+ alcohol productivities were
observed over Cr- and Mn-promoted catalysts. In these cata-
lysts, the promotion improves Cu reducibility and results in
a higher fraction of active sites for carbon monoxide hydroge-
nation. Lower than expected C2+ alcohol productivities were
observed over Mo- and Ru-promoted catalysts. Under different
conditions, these catalysts may form volatile Mo and Ru com-
pounds, which would lead to the loss of these promoters.
Unexpectedly, the Fe-promoted catalyst demonstrated a re-
markable increase in carbon monoxide conversion from 6.1 to
69.2% with the increase in the reaction temperature from 280
to 3208C. This increase in carbon monoxide conversion was ac-
companied by much higher hydrocarbon and slightly higher
carbon dioxide selectivities. Of all the promoted CuZnAl cata-
lysts, this Fe-promoted catalyst also demonstrated the highest
productivity of C2+ alcohols (30 mggÀca1t hÀ1). The Cr- and Mn-
promoted catalysts also demonstrated an increase in the pro-
ductivity of C2+ alcohols, which is mainly attributed to higher
selectivity towards higher alcohols. The distribution of alcohol
and hydrocarbon on promoted CuZnAl catalysts is shown in
Figures 4 and S3.
Figure 4. Alcohol distribution during carbon monoxide hydrogenation over
promoted CuZnAl catalysts at 3208C (XCO =5–15%, except for Fe–CuZnAl).
Figure 5. Relation between C2+ alcohol productivity at 3208C and TPR maxi-
mum over promoted CuZnAl catalysts.
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Surprisingly, the Fe-promoted catalyst does not follow the
same trend. The H2-TPR profiles (Figure 2) and in situ XRD pat-
terns (Figure 3b) suggest similar Cu reducibility in CuZnAl and
Fe–CuZnAl catalysts. In addition, promotion with Fe reduces
carbon monoxide conversion at 2808C (Table 2). At 3208C, pro-
motion with Fe leads to a significant increase in the overall re-
action rate (Table 2 and Figure 4). A remarkable increase in
carbon monoxide conversion over Fe-promoted catalysts is at-
tributed to new active sites associated with Fe. These new
active sites are absent at lower temperatures; however, they
emerge in the Fe-containing catalyst at temperatures close to
3208C. Previously performed experiments with Fe catalysts[32–35]
indicate Fe carbidisation in syngas flow at temperatures close
to 3008C. The interaction of Fe species with syngas at approxi-
mately 3008C leads to iron carbides, which demonstrate
higher activity for carbon monoxide hydrogenation. The forma-
tion of iron carbides is also consistent with higher selectivity
towards hydrocarbons observed at 3208C over the Fe–CuZnAl
catalyst (Table 2). The variation in alcohol productivity over Co-
, Mg-, Ru-, Zr-, and Mo-promoted catalysts is attributed to the
effect of the promotion on the catalytic properties of metallic
Cu. The XRD patterns demonstrated similar Cu dispersion in
the promoted catalysts. Promotion with small amounts of the
metal has a significant effect on Cu reducibility. The ease of Cu
reduction leads to higher Cu surface areas and more active
catalysts.
Fe species could contribute to carbon–carbon chain growth,
which should result in higher selectivity towards long-chain
hydrocarbons.
Conclusions
The promotion of CuZnAl catalysts with small amounts of
metals results in a modification in the structure and catalytic
performance in carbon monoxide hydrogenation. For most cat-
alysts, C2+ alcohol productivity was correlated with Cu reduci-
bility. The ease of Cu reduction in Mn- and Cr-promoted cata-
lysts leads to higher C2+ alcohol productivities, and lower ac-
tivity was observed over less reducible catalysts. The most sig-
nificant effect was observed with Fe-containing catalysts, in
which the addition of even a small amount of the promoter re-
sults in a significant increase in carbon monoxide conversion.
Higher carbon monoxide conversion and C2+ alcohol produc-
tivity over this catalyst are accompanied by an increase in the
production of carbon dioxide and light hydrocarbons. Promo-
tion with Cr, Mn, and Fe leads to a significant modification in
catalyst selectivity and increase in the C2+ alcohol productivity.
Experimental Section
Catalyst preparation
The catalysts were synthesised through co-precipitation with use
of two aqueous solutions:[43,44] a solution of copper, zinc, alumini-
um nitrates containing a promoter (in the nitrate form) and
a sodium carbonate solution. The two solutions were added simul-
taneously with a peristaltic pump into a precipitation vessel con-
taining deionised water under vigorous stirring. The pH value of
the suspension was controlled at 7 by adjusting the flow rate of
the carbonate solution and by keeping the temperature constant
at 708C. The Cu/Zn/Al molar ratio in the catalysts was 6:3:1, and
the promoter content was 1 mol% (Fe, Co, Ru, Zr, Mo, and Mg).
After precipitation, the catalyst solution was stirred at 708C for 4 h.
Furthermore, the catalyst solution was filtered, washed to remove
residual sodium ions, and dried. Finally, the catalyst powder was
calcined under air flow at 3508C for 3 h (temperature ramp:
38CminÀ1).
The alcohol distribution has been significantly affected by
promotion with Cr, Mn, and Fe (Figure 4). With Co, Mg, Ru, Zr,
and Mo, no significant modification in selectivity patterns was
observed. Different selectivity over Cr–CuZnAl and Mn–CuZnAl
could be attributed to the modification in the properties of
the existing catalytic sites or the formation of new sites in the
promoted catalysts. The formation of CuCr and CuMn mixed
species active in carbon monoxide hydrogenation and particu-
larly in higher alcohol synthesis has been reported previously
in the literature.[19,36–39] These mixed species have lower reduc-
tion temperature. Their presence affects both carbon monox-
ide conversion and reaction selectivity. Our work suggests that
even the presence of small amounts of the promoters Mn and
Cr could be sufficient to significantly affect the reaction selec-
tivity and to increase the productivity of C2+ alcohols. A few
mechanisms of higher alcohol synthesis over promoted
CuZnAl catalysts suggest that alcohol chain growth can pro-
ceed via aldol-type condensation or carbon monoxide inser-
tion.[19] Promotion with Cr and Mn is not likely to affect the ba-
sicity of the catalyst and the rate of aldol condensation. In ad-
dition, Mn and Cr could improve carbon monoxide insertion
and thus alcohol chain growth. Similar effect of Mn on the
chain growth during Fischer–Tropsch synthesis has been ob-
served over Co catalysts.[40,41]
Catalyst characterisation
The chemical composition of the catalysts prepared through co-
precipitation was measured by using inductively coupled plasma
mass spectrometry (Table 1). The texture of the samples was deter-
mined from nitrogen adsorption analysis. The surface area was
measured with a Micromeritics ASAP 2010 analyser at liquid nitro-
gen temperature. The samples were degassed at 1508C for 3 h
before the analysis. The specific surface area and pore volume
were calculated by using BET and BJH methods.
The ex situ X-ray absorption spectra at Cu K absorption edges
(8.979 eV) were measured at SAMBA beamline at the SOLEIL syn-
chrotron (France). The X-ray absorption measurements were per-
formed in the transmission mode; two ionisation chambers were
used for X-ray detection. The XRD patterns were measured with
a Bruker D8 Advance X-ray diffractometer using CuKa radiation. For
the in situ measurements, the catalyst was placed in a high-tem-
perature chamber on a Bruker D8 Advance X-ray diffractometer to
The remarkable improvement in the catalytic performance
of the catalysts upon promotion with Fe could be attributed
to the formation of additional active sites for carbon hydroge-
nation, which could be associated with the promoting Fe spe-
cies (e.g., iron carbide). c-Fe5C2 species were recently uncov-
ered in Cu–Fe bimetallic catalysts by applying a combination
of characterisation techniques.[42] In the Fe-promoted catalyst,
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record the evolution of XRD patterns as a function of the increas-
ing temperature until 8008C (68CminÀ1, with 2qꢀ15 s) under H2
(3 vol%) in nitrogen. The catalyst reducibility was evaluated by
using TPR. The TPR was performed with a gas mixture of H2 (5
vol.%) in argon (flow rate: 50 mLminÀ1). The reactor was heated
up to 4508C (ramp rate: 68CminÀ1). Before measurements, the
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Published online on && &&, 0000
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ChemCatChem 0000, 00, 1 – 7
&
6
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ÞÞ
These are not the final page numbers!

FULL PAPERS
Choose your alcohol wisely: The ease
of Cu reduction in CuZnAl methanol
synthesis catalysts promoted with
metals leads to more active catalysts for
the hydrogenation of carbon monoxide
and the production of C2+ alcohols. The
promotion of CuZnAl catalysts even
with small amounts of Cr, Mn, and Fe
results in a significant modification in
the selectivity patterns.
J. M. Beiramar, A. Griboval-Constant,
A. Y. Khodakov*
&& – &&
Effects of Metal Promotion on the
Performance of CuZnAl Catalysts for
Alcohol Synthesis
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 0000, 00, 1 – 7
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