Direct conversion of ethanol into ethylene oxide on copper and silver nanoparticles: Effect of addition of CeOx and Li2O

Article abstract of DOI:10.1016/j.cattod.2010.03.019

The behavior of nanoparticles of copper and silver on an alumina support in the oxidation and dehydrogenation of ethanol is investigated. Pure alumina mainly acts as an acidic catalyst and produces diethyl ether and ethylene. Addition of copper and silver nanoparticles results in a direct conversion of ethanol into ethylene oxide. Addition of Li₂O influences the selectivity by suppressing the formation of diethyl ether and ethylene. Using Ag/Li₂O/Al₂O₃ and Cu/Li₂O/Al ₂O₃ catalysts it is possible to obtain high selectivity towards ethylene oxide at a temperature of 200 °C. It is suggested that at low concentrations the main role of oxygen is to prevent coke formation on the catalytic surface. Addition of CeO_x results in higher selectivities towards CO.

Full text of DOI:10.1016/j.cattod.2010.03.019

Catalysis Today 154 (2010) 127–132
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Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Direct conversion of ethanol into ethylene oxide on
copper and silver nanoparticles
Effect of addition of CeOx and Li2O
M.J. Lippits∗, B.E. Nieuwenhuys
Leids Instituut voor chemisch onderzoek, Universiteit Leiden, Einsteinweg 55, 2333 CC Leiden, The Netherlands
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 24 April 2010
The behavior of nanoparticles of copper and silver on an alumina support in the oxidation and dehydro-
genation of ethanol is investigated. Pure alumina mainly acts as an acidic catalyst and produces diethyl
ether and ethylene. Addition of copper and silver nanoparticles results in a direct conversion of ethanol
into ethylene oxide. Addition of Li2O influences the selectivity by suppressing the formation of diethyl
ether and ethylene. Using Ag/Li2O/Al2O3 and Cu/Li2O/Al2O3 catalysts it is possible to obtain high selectiv-
ity towards ethylene oxide at a temperature of 200 ◦C. It is suggested that at low concentrations the main
role of oxygen is to prevent coke formation on the catalytic surface. Addition of CeOx results in higher
selectivities towards CO.
Keywords:
Ethanol oxidation
Ethylene oxide
Alumina
Copper
Silver
© 2010 Elsevier B.V. All rights reserved.
Lithium oxide
Ceria
1. Introduction
In this study we investigated the low temperature activity of
Cu/Al2O3 and Ag/Al2O3 catalysts in the dehydrogenation, dehydra-
Selective oxidation of ethanol is increasingly receiving more
attention as ethanol can be used for the synthesis of chemical
intermediates in the manufacture of high-tonnage commodities.
Ethanol can be converted to, e.g. acetaldehyde, ethane, carbon
monoxide/hydrogen and ethylene. The ethylene can be further con-
verted over a silver based catalyst to ethylene oxide, which is one
of the most important chemical intermediates. It is an intermedi-
ate for the production of ethylene glycol and for the production
of polyester fibers and plastics such as polyethylene terephthalate
(PET). This paper will show that ethanol can be converted directly
into ethylene oxide at mild temperatures and atmospheric pres-
sure, in addition to it total oxidation products carbon dioxide and
water.
Ethanol is a simple probe molecule to study reactions on metal
[1–3] and oxide surfaces [4,5]. On most surfaces the ethanol
molecules first dissociate to ethoxy species. These ethoxy species
are further oxidized to acetaldehyde or dehydrated to ethylene.
On metal surfaces acetaldehyde either desorbs or decomposes to
CO and methane [6]. In some cases, coupling and bimolecular
hydrogenation reactions occur resulting in production of higher
hydrocarbons such as diethyl ether [7,8].
tion and oxidation reaction of ethanol. In addition, the promoting
effect of adding Li2O and CeOx has been investigated. CeOx is
an active oxide for the oxidation of CO to CO2 and for making
H2 from ethanol by partial oxidation or steam reforming [9,10].
In earlier papers we reported that (earth) alkali metals stabi-
lize gold nanoparticles and hence, act as a structural promoter
for Au/Al2O3[11,12]. More recently, we reported that Cu and Ag
nanoparticles on ␥-Al2O3 can be stabilized in the same way [13,14].
In another study of our group it was found that highly dispersed
gold on suitable metal oxides exhibits interesting behavior toward
the oxidation of ethanol and is capable of converting ethanol
directly into ethylene oxide. This motivated us to investigate the
oxidation of ethanol over ␥-Al2O3 supported copper and silver
based catalysts. It is known for quite a long time that CuO-CeO2
catalysts are very active and selective in CO (selective) oxidation
[10,16]. Ceria has a promoting effect on the activity of the Cu/Al2O3
and Ag/Al2O3 catalysts in methanol oxidation [14]. It was argued
that the active oxygen was supplied by the ceria. The size of the
ceria particles has a great influence on the activity of the catalyst
[17].
The oxidative dehydrogenation of ethanol to acetaldehyde
is known to be catalyzed by materials possessing strong base
sites such as Li2O [18]. Earlier work of our group revealed
that addition of Li2O has great effect on the acidic sites of ␥-
Al2O3 and so influences the selectivity towards products which
are not formed on these acidic sites [14,19]. In this paper we
show that Li2O promoted Ag and Cu particles supported on ␥-
∗
Corresponding author. Tel.: +31 71 527 4484; fax: +31 71 527 4451.
E-mail addresses: m.lippits@chem.leidenuniv.nl (M.J. Lippits),
b.nieuwe@chem.leidenuniv.nl (B.E. Nieuwenhuys).
0920-5861/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.cattod.2010.03.019

128
M.J. Lippits, B.E. Nieuwenhuys / Catalysis Today 154 (2010) 127–132
Al2O3 can be used for the production of ethylene oxide from
ethanol.
3. Results
3.1. Characterization
2. Experimental
For the fresh Ag and Cu particles the average size could not be
determined by XRD because the size of the particles was below
the detection limit of 3 nm. The results of the characterization of
the catalysts after the reaction are shown in Table 1. The catalysts
without additives contain small particles of 3–4 nm. With CeOx and
Li2O addedthe average particle sizeis lower than thedetection limit
(3 nm). HRTEM data of comparable catalysts have been published in
earlier papers of our group [12,21,22]. The actual metal loading was
almost equal to the intended metal loading. In addition, we have
checked the catalysts for the Li and Ce contents with ICP-OES. These
measurements showed that the appropriate amount of Li and/or
Ce was deposited on the catalysts. The used ␥-Al2O3 support was
investigated with XRF to determine which impurities are present.
Three impurities were found: Na2O (0.05 wt%), SiO2 (0.1 wt%) and
Fe2O3 (0.05 wt%).
2.1. Catalyst preparation
Mixed oxides of ceria (denoted as CeOx) and/or Li2O with
alumina were prepared by pore volume impregnation of ␥-
Al2O3(BASF) with the corresponding nitrates. After calcination at
350 ◦C these oxides were used as supports for the Cu or Ag based
catalysts. The prepared mixed oxides have an intended atomic
ratio Ce/Al and Li/Al of 1/15. The copper and silver catalysts were
prepared via homogeneous deposition precipitation using urea as
precipitating agent. An appropriate amount of Cu(NO3)2· 3aq or
AgNO3 was added to a suspension of purified water containing ␥-
Al2O3 or the mixed oxide. The intended M/Al atomic ratio was 1/75
(M = Cu or Ag). This ratio of 1:75 is equal to 0.53 at% M and resulted
in 2.5 wt% for silver and 1.5 wt% for copper. The temperature was
kept at 80 ◦C allowing urea (p.a., Acros) to decompose, ensuring a
slow increase of pH. When a pH of around 8–8.5 was reached the
slurry was filtrated and washed thoroughly with water and dried
overnight at 80 ◦C. Because urea and silver atoms can form a soluble
3.2. Activity of catalyst supports without metal particles
In Table 2 the results are presented concerning the dehydro-
genation of ethanol in the absence of oxygen, for the supports
without Cu and Ag. The most active support is the ␥-Al2O3 without
additive. The main products are the dehydration products diethyl
ether and ethylene. In addition, some trace amounts of acetalde-
hyde are found at temperatures up to 300 ◦C. Addition of ceria to the
␥-Al2O3 results in formation of CO at the expense of diethyl ether
and ethylene, at temperatures above 300 ◦C. The formed hydrogen
is converted to water. Addition of Li2O to the alumina catalysts low-
ers the ethanol conversion compared to the ␥-Al2O3-only catalyst,
Ag[NH3]+ complex, a large surplus of silver was needed to deposit
2
enough silver on the Al2O3. The catalysts were thoroughly ground
to ensure that the macroscopic particle size was around 200 ␮m
for all the catalysts used in this study. Prior to the activity mea-
surement all catalysts were reduced at 400 ◦C with hydrogen for
2 h.
2.2. Catalyst characterization
The metal loading was verified by Inductively Coupled Plasma
Optical Emission Spectroscopy (ICP-OES) using a Varian Vista-MPX.
For that purpose a small fraction of the catalyst was dissolved
in diluted aqua regia. X-ray diffraction measurements were done
using a Philips Goniometer PW 1050/25 diffractometer equipped
with a PW Cu 2103/00 X-ray tube operating at 50 kV and 40 mA.
The average particle size was estimated from XRD line broadening
after subtraction of the signal from the corresponding support by
using the Scherrer equation [20].
Table 1
Catalyst characterization by ICP and XRD.
Catalyst
Metal loading (wt%)
Average particle size (nm)
Ag/Al2O3
2.3 0.1
1.7 0.1
2.2 0.1
1.6 0.1
4.5 0.1
3.3 0.1
< 3.0
Ag/CeOx/Al2O3
Ag/Li2O/Al2O3
Ag/CeOx/Li2O/Al2O3
< 3.0
Cu/Al2O3
1.5 0.1
1.0 0.1
1.4 0.1
1.0 0.1
3.5 0.1
< 3.0
< 3.0
Cu/CeOx/Al2O3
Cu/Li2O/Al2O3
Cu/CeOx/Li2O/Al2O3
2.3. Activity measurements
< 3.0
The amount of catalyst used was 200 mg for the Ag/␥-Al2O3 and
Cu/␥-Al2O3 catalysts. For the catalysts containing CeOx and/or Li2O
the amount of catalyst was adjusted in such a way that the amount
of metal atoms (Ag or Cu) was similar for all the catalysts with and
without additives. Prior to activity experiments the catalysts were
reduced with H2 (4 vol% in Ar) at 400 ◦C for 2 h. Activity tests of the
catalysts were performed in a micro reactor system. An oxygen flow
balanced in argon was bubbled through a vessel containing abso-
lute ethanol. For the oxidation an ethanol oxygen ratio of 1:1 was
used. For the decomposition reaction a argon flow was bubbled
through the vessel. Typically, a total gas flow of 40 ml−1 (GHSV
≈ 2500 h−1) was maintained. The effluent stream was analyzed
on-line by a gas chromatograph (HP 8590) with a CTR1 column
(Alltech) containing a porous polymer mixture and an activated
molecular sieve and a Hayesep Q column (Alltech). The experiments
were carried out under atmospheric pressure. Each measurement is
composed of multiple temperature programmed cycles of heating
and cooling, with a rate of 2 ◦C/min. Mass spectrometry confirmed
that the analysis of the reaction products with GC was correct.
Unless otherwise stated the results of the first cooling stage are
depicted in the figures.
Table 2
Conversion and selectivities of ethanol dehydrogenation on the used supports.
TC = total conversion, Si = selectivity.
Catalyst
Al2O3
Temperature (◦C)
TC
38
70
100
100
Sdiethyl ether
Sethylene
SCO
200
250
300
400
92
86
30
0
8
14
70
0
0
0
0
100
CeOx/Al2O3
Li2O/Al2O3
200
250
300
400
5
30
100
100
80
13
3
20
84
69
64
0
3
28
36
0
200
250
300
350
400
0
31
72
90
100
0
84
69
67
50
0
16
31
33
50
0
0
0
0
0
Li2O/CeOx/Al2O3
200
250
300
400
10
37
100
100
80
81
45
34
20
19
50
58
0
0
5
8

M.J. Lippits, B.E. Nieuwenhuys / Catalysis Today 154 (2010) 127–132
129
Fig. 1. Ethanol conversion vs temperature. Ethanol dehydrogenation in the absence
of oxygen. First heating stage (closed symbols), cooling stage (open symbols). (ꢀ)
Cu/Al2O3, (♦) Cu/Li2O/Al2O3, (ꢀ) Cu/CeOx/Al2O3.
Fig. 2. Ethylene oxide selectivity vs temperature. First heating stage in ethanol-only
flow. (×) Cu/Al2O3, (•) Cu/Li2O/Al2O3, (ꢀ) Cu/CeOx/Al2O3, (ꢁ) Cu/Li2O/CeOx/Al2O3.
and results in a lower selectivity towards ethylene. No acetalde-
hyde is found. The catalysts which contain both Li2O and CeOx
show a behavior typical of a mixture of Li2O/Al2O3 and CeOx/Al2O3
catalysts.
Similar measurements have been performed for an ethanol/O2
mixture of 1 using the supports without Cu or Ag deposited.
For the Al2O3 and Li2O/Al2O3 catalysts there were no significant
differences in activity and selectivity detected, compared to the
measurements without oxygen. For the CeOx containing catalysts
an increase in CO formation is recorded. For the CeOx/Al2O3 catalyst
a CO selectivity up to 50% was found and for the Li2O/CeOx/Al2O3
catalyst a selectivity to CO of 21% was found.
Fig. 3. Ethanol conversion vs temperature. Ethanol/O2 mixture of 1. First heat-
ing stage(closed symbols), cooling stage (open symbols). (ꢀ) Cu/Al2O3, (♦)
Cu/Li2O/Al2O3, (ꢀ) Cu/CeOx/Al2O3.
3.3. Ethanol dehydrogenation on copper based catalysts
In the dehydrogenation of ethanol there is a significant differ-
ence between the first heating cycle and the following cycles, which
in the figures and tables are represented by the first cooling cycle.
The results of the 2nd and further heating/cooling stages resemble
that of the 1st cooling cycle. The ethanol conversion as a function
of reaction temperature of the first heating step is presented in
Fig. 1. The Cu/Al2O3 catalyst being the most active. The conversion
starts at 140 ◦C and reaches maximum conversion around 225 ◦C.
The Cu/Li2O/Al2O3 is slightly less active and the conversion on both
CeOx containing catalysts starts around 170 ◦C and reaches 100%
conversion above 300 ◦C. In Fig. 2 the selectivities towards ethy-
lene oxide are presented. Clearly, the Cu/Al2O3 and Cu/Li2O/Al2O3
are much more selective towards ethylene oxide. The selectivity
towards ethylene oxide decreases at high temperatures and then
mainly ethylene is formed. When the gas flow was bubbled through
a diluted NaOH solution glycol was produced, which is further
evidence that the output gas flow contained ethylene oxide. Also
minor quantities of acetaldehyde and diethyl ether are formed. On
the Cu/CeOx/Al2O3 catalyst mainly CO is formed next to ethylene
oxide. In the following cooling cycle the conversion of ethanol is
slightly improved for the Cu/CeOx/Al2O3 and Cu/Al2O3 catalysts.
For the Cu/Li2O/Al2O3 catalyst the conversion is about the same.
In terms of selectivity there is a big change compared to the first
heating cycle. The results are summarized in Table 3. The great-
est difference is the absence of ethylene oxide formation. It is only
formed in trace amounts. Compared to the results of the support
oxides only, the addition of copper results in more ethylene oxide
formation.
3.4. Ethanol oxidation on copper based catalysts
For an ethanol/oxygen mixture of 1 the results are shown
in Fig. 3 and the selectivities in Table 4. Contrary to the mea-
surements without oxygen in the reaction flow, all the heating
and cooling steps show the same behavior. The Cu/Al2O3 and
Cu/Li2O/Al2O3 catalysts show ethanol conversion from 140 ◦C. For
the Cu/Li2O/Al2O3 catalyst the O2 conversion starts at higher tem-
perature. Cu/CeOx/Al2O3 is the least active catalyst with ethanol
and oxygen conversion starting at 200 ◦C. The Cu/Li2O/Al2O3 and
Table 3
Selectivities for Cu based catalysts in ethanol-only flow. First cooling cycle. Si = selectivity.
Catalyst
Temperature (◦C)
Sethylene
Sacetaldehyde
Sdiethyl ether
SCO
Sethylene oxide
Cu/Al2O3
200
300
400
–
80
100
–
15
–
100
5
–
–
–
–
–
–
–
Cu/CeOx/Al2O3
Cu/Li2O/Al2O3
200
300
400
–
25
46
–
5
10
–
–
8
100
70
36
–
–
–
200
300
400
–
60
70
–
12
15
–
12
10
–
–
–
–
15
5

130
M.J. Lippits, B.E. Nieuwenhuys / Catalysis Today 154 (2010) 127–132
Table 4
Selectivities for Cu based catalysts in an ethanol/O2 mixture of 1, Si = selectivity.
Catalyst
Temperature (◦C)
Sethylene
Sacetaldehyde
Sdiethyl ether
SCO
Sethylene oxide
Cu/Al2O3
200
300
400
–
15
100
–
15
–
–
–
–
30
20
–
70
50
–
Cu/CeOx/Al2O3
Cu/Li2O/Al2O3
200
300
400
–
20
60
–
5
-
–
-
-
–
55
40
–
20
–
200
300
400
–
60
90
–
12
2
–
12
2
10
–
2
90
15
4
Fig. 5. Ethanol conversion (open symbols) and oxygen conversion (closed sym-
bols) vs temperature. The ethanol/O2 ratio = 1 (ꢀ) Ag/Al2O3, (♦) Ag/Li2O/Al2O3,
(ꢀ) Ag/CeOx/Al2O3.
Fig. 4. Ethanol conversion vs temperature. Ethanol dehydrogenation in the absence
of oxygen. First cooling stage. (•) Ag/Al2O3, (♦) Ag/Li2O/Al2O3, (ꢀ) Ag/CeOx/Al2O3.
Cu/Al2O3 catalyst show a high selectivity toward ethylene oxide at
temperatures up to 300 ◦C. The selectivity is then shifted towards
ethylene and CO. On the Cu/CeOx/Al2O3 catalyst the selectivity to
CO is higher and the selectivity to ethylene oxide is much lower. On
all catalysts some acetaldehyde and diethyl ether are formed with
selectivities under 10%. No H2 is detected but only H2O. The Li2O
containing catalyst was also checked for stability. At temperatures
of 240 ◦C no deactivation was found for 72 h.
lyst the selectivity shifts to CO as the temperature is increased.
Also increasing amounts of H2 are detected. On the Ag/Al2O3 some
diethyl ether is formed at low temperatures and some traces of
acetaldehyde are detected.
3.6. Ethanol oxidation on silver based catalysts
In Fig. 5 the results of an ethanol/O2 mixture of 1 are presented.
The Ag/Al2O3 and Ag/CeOx/Al2O3 catalyst show ethanol conver-
sion from 100 ◦C onward. The Ag/Li2O/Al2O3 catalyst is less active
and show an onset temperature of 150 ◦C for the ethanol conver-
sion. For the Ag/Al2O3 catalyst the O2 conversion is similar to the
ethanol conversion. This is not the case for the Ag/Li2O/Al2O3 cat-
alyst, where the ethanol conversion starts at 120 ◦C and the O2
conversion starts from 190 ◦C. In this temperature region mainly
ethylene oxide is formed. Compared to the ethanol-only flow the
activity is not greatly influenced by the oxygen, but the effect of
O2 on the selectivity is much greater; as shown in Table 6. For the
Ag/Al2O3 catalyst the effect of adding oxygen results in an increased
CO production at the expense of diethyl ether, but also a decrease
in ethylene. For the Ag/CeOx/␥-Al2O3 catalyst ethylene and CO
remain still the two important products, but also other products
3.5. Ethanol dehydrogenation on silver based catalysts
The silver based catalysts are already active at a temperature of
about 100 ◦C as shown in Fig. 4, which is a significantly lower tem-
perature than for the copper based catalysts. For the Ag/Li2O/Al2O3
catalyst the onset of ethanol conversion is about 50 ◦C higher than
for the Ag/Al2O3 and Ag/CeOx/Al2O3 catalysts. The selectivities are
also quite different from the copper based catalyst as can be seen
in Table 5. No differences between first heating stage and the other
stages are found. Very little ethylene oxide is produced. Instead only
ethylene and CO are formed. When Li2O is added to the Ag/Al2O3
catalyst, some improvement to the ethylene oxide selectivity is
obtained but it remains under 10%. For the Ag/CeOx/Al2O3 cata-
Table 5
Selectivities for Ag based catalysts in ethanol-only flow. First cooling cycle Si = selectivity.
Catalyst
Temperature (◦C)
Sethylene
Sacetaldehyde
Sdiethyl ether
SCO
Sethylene oxide
Ag/Al2O3
200
300
400
–
40
100
–
–
–
100
40
–
–
20
–
–
–
–
Ag/CeOx/Al2O3
Ag/Li2O/Al2O3
200
300
400
75
64
32
–
–
–
–
–
–
20
36
68
5
–
–
200
300
400
60
90
100
–
–
–
30
–
–
–
5
–
10
5
–

M.J. Lippits, B.E. Nieuwenhuys / Catalysis Today 154 (2010) 127–132
131
Table 6
Selectivities for Ag based catalysts in an ethanol/O2 mixture of 1, Si = selectivity.
Catalyst
Temperature (◦C)
Sethylene
Sacetaldehyde
Sdiethyl ether
SCO
Sethylene oxide
Ag/Al2O3
200
300
400
–
60
16
10
5
–
–
–
–
85
40
84
5
–
–
Ag/CeOx/Al2O3
Ag/Li2O/Al2O3
200
300
400
12
24
43
5
–
–
33
13
–
39
54
57
10
9
–
200
300
400
–
23
28
4
–
–
–
21
38
–
–
4
96
54
30
are formed. For the Ag/Li2O/Al2O3 catalyst there is a big shift from
ethylene production towards ethylene oxide when O2 is added, also
diethyl ether is formed at high temperatures. The Li2O containing
catalyst was also checked for stability. At temperatures of 240 ◦C
no deactivation was found for 72 h.
which is enhanced by the addition of CeOx. Addition of Li2O shifts
the selectivity towards ethylene but also introduces another prod-
uct: ethylene oxide. This is probably caused by the effect of Li2O on
the acidic sites of the alumina, and so increasing the relative weight
of the reaction pathway to ethylene oxide. This is in particular the
case with O2 present in the gas flow, where addition of Li2O results
in a great increase in selectivity towards ethylene oxide. Apparently
for the silver particles both the presence of Li2O and O2 are needed
to obtain a good selectivity to ethylene oxide. This is in contrast to
copper and gold based catalysts which can also produce ethylene
oxide in the absence of oxygen, because those metals have greater
oxidation capabilities.
4. Discussion
4.1. Activity of copper based catalysts
In agreement with literature [10,23] the Al2O3 support only
converts the ethanol into diethyl ether and ethylene and a small
amount of acetaldehyde. When copper is added to the support,
the Cu/Al2O3 catalyst also produces ethylene oxide which is not
observed on the Al2O3 support. To our knowledge production of
ethylene oxide from ethanol in an single reaction has not been
reported before in literature. Apparently, the presence of copper
nanoparticles is necessary for the formation of ethylene oxide. In
another study of our group similar results were found for gold based
catalysts. At high temperatures the selectivity resembles that of the
support only. However, the addition of copper has a positive effect
on the ethanol conversion. Clearly, the copper particles are capa-
ble of partly oxidizing the ethanol. Especially when CeOx is added
their is a great improvement in selectivity to carbon monoxide,
while much less ethylene oxide is formed. This can be attributed
to the capability of CeOx in supplying oxygen to the copper par-
ticles. When no oxygen is added to the gas flow, the formation of
ethylene oxide is only observed in the first heating cycle and not
in the following cycles. This is probably caused by carbon deposi-
tion on the active copper sites. After all the stages indeed carbon
deposition was found. Heating the catalyst in an O2 flow produced
CO2. When this was followed by a pretreatment in hydrogen the
catalyst was regenerated. When O2 was added to the gas flow no
deactivation or carbon deposition was found, hence O2 prevents
carbon deposition on the sites that are active in converting ethanol
into ethylene oxide. The addition of Li2O to the ␥-Al2O3 support
results in a great decrease of the conversion, possibly by affecting
the strong acidic sites of the alumina [10,14,19]. The addition of
lithia to the Cu/Al2O3 catalyst does not result in significant changes
in conversion and selectivity. Apparently, in the presence of cop-
per nanoparticles the reaction pathways are not dependent on the
acidic sites of alumina.
5. Conclusions
Results show that both silver and copper nanoparticles are
active in oxidation, dehydrogenation and dehydration of ethanol.
They are also capable of converting ethanol directly into ethy-
lene oxide. Indications of multiple catalytic reaction centers and
multiple pathways are found. The presence of O2 is very impor-
tant to prevent carbon deposition for copper based catalysts. For
the silver based catalysts O2 is also needed to improve the selec-
tivity towards CO. For the silver based catalysts the presence of
both Li2O and O2 is needed to obtain a good selectivity to ethylene
oxide.
Acknowledgements
The authors thank Dr. J.-P. Lange form Shell Global Solutions,
Amsterdam for the discussions concerning the results presented in
this paper.
References
[1] P.-Y. Sheng, G.A. Bowmaker, H. Idriss, Appl. Catal. A 261 (2004) 171.
[2] J.P. Camplin, E.M. McCash, J. Chem. Soc. Faraday Trans. 92 (1996) 4696.
[3] M.K. Rajumon, M.W. Roberts, F. Wang, P.B. Wells, J. Chem. Soc. Faraday Trans.
94 (1998) 3699.
[4] H. Idriss, E.G. Seebauer, J. Mol. Catal. A 152 (2000) 201.
[5] S.V. Chong, T.R. Griffiths, H. Idriss, Surf. Sci. 444 (2000) 187.
[6] J.L. Davis, M.A. Barteau, J. Am. Chem. Soc. 111 (1989) 1782.
[7] G. Avgouroupoulos, E. Oikonomopoulos, D. Kanistras, T. Ioannides, Appl. Catal.
B 65 (2006) 62.
[8] X. Liu, B. Xu, J. Haubrich, R.J. Madix, C.M. Friend, J. Am. Chem. Soc. 131 (2006)
5757.
[9] N. Laosiripojana, S. Assabumrungrat, Appl. Catal. B 66 (2006) 29.
[10] G. Avgouropoulos, H.K. Ioannides, J. Matralis, J. Batista, S. Hocevar, Catal. Lett.
73 (2001) 33.
4.2. Activity of silver based catalysts
[11] A.C. Gluhoi, S.D. Lin, B.E. Nieuwenhuys, Catal. Today 90 (2004) 175.
[12] A.C. Gluhoi, Fundamental studies focused on understanding of gold catalysis,
Ph.D. thesis, Leiden University, 2005.
[13] M.J. Lippits, A.C. Gluhoi, B.E. Nieuwenhuys, Topics Catal. 44 (2007) 159.
[14] M.J. Lippits, R.R.H. Boer Iwema, B.E. Nieuwenhuys, Catal. Today 145 (1) (2009)
27.
The addition of silver to the ␥-Al2O3 support improves the activ-
ity but does not change the selectivity to diethyl ether and ethylene
much. These products diethyl ether and ethylene are mainly the
result of the catalytic activity of ␥-Al2O3. A difference between
Ag/Al2O3 and Al2O3 catalyst is the formation of small quantities
of CO, showing some oxidation capabilities of the silver particles,
[16] G. Avgouropoulos, T. Ioannides, Ch. Papadopoulou, J. Batista, S. Hocevar, H.K.
Matralis, Catal. Today 75 (2002) 157.

132
M.J. Lippits, B.E. Nieuwenhuys / Catalysis Today 154 (2010) 127–132
[17] S. Carrettin, P. Concepcion, A. Corma, J.M. Lopez Nieto, V.F. Puntes, Angew.
Chem. Int. Ed. (2004) 2538.
[18] R.W. McCabe, P.J. Mitchell, Ind. Eng. Chem. Prod. Res. Dev. 23 (1984) 196.
[19] S.R. de Miguel, A.C. Martinez, A.A. Castro, O.A. Scelza, J. Chem. Tech. Biotechnol.
65 (1996) 131.
[20] P. Scherrer, Nachr. K. Ges Wiss (1918) 98.
[21] A.C. Gluhoi, X. Tang, P. Margineau, B.E. Nieuwenhuys, Topics Catal. 39 (2006)
101.
[22] A.C. Gluhoi, N. Bogdanchikova, B.E. Nieuwenhuys, J. Catal. 232 (2005) 96.
[23] J. Trawczynski, B. Bielak, W. Mista, Appl. Catal. B 55 (2005) 277.