Design of ru-zeolites for hydrogen-free production of conjugated linoleic acids

Article abstract of DOI:10.1002/cssc.201100015

While conjugated vegetable oils are currently used as additives in the drying agents of oils and paints, they are also attractive molecules for making bio-plastics. Moreover, conjugated oils will soon be accepted as nutritional additives for "functional food" products. While current manufacture of conjugated vegetable oils or conjugated linoleic acids (CLAs) uses a homogeneous base as isomerisation catalyst, a heterogeneous alternative is not available today. This contribution presents the direct production of CLAs over Ru supported on different zeolites, varying in topology (ZSM-5, BETA, Y), Si/Al ratio and countercation (H⁺, Na⁺, Cs⁺). Ru/Cs-USY, with a Si/Al ratio of 40, was identified as the most active and selective catalyst for isomerisation of methyl linoleate (cis-9,cis-12 (C18:2)) to CLA at 165 °C. Interestingly, no hydrogen pre-treatment of the catalyst or addition of hydrogen donors is required to achieve industrially relevant isomerisation productivities, namely, 0.7 g of CLA per litre of solvent per minute. Moreover, the biologically most active CLA isomers, namely, cis-9,trans-11, trans-10,cis-12 and trans-9,trans-11, were the main products, especially at low catalyst concentrations. Ex situ physicochemical characterisation with CO chemisorption, extended X-ray absorption fine structure measurements, transmission electron microscopy analysis, and temperature-programmed oxidation reveals the presence of highly dispersed RuO₂ species in Ru/Cs-USY(40). Copyright

Full text of DOI:10.1002/cssc.201100015

DOI: 10.1002/cssc.201100015
Design of Ru–Zeolites for Hydrogen-Free Production of
Conjugated Linoleic Acids
An Philippaerts,[a] Steven Goossens,[a] Walter Vermandel,[a] Moniek Tromp,[b] Stuart Turner,[c]
Jan Geboers,[a] Gustaaf Van Tendeloo,[c] Pierre A. Jacobs,[a] and Bert F. Sels*[a]
While conjugated vegetable oils are currently used as additives
in the drying agents of oils and paints, they are also attractive
molecules for making bio-plastics. Moreover, conjugated oils
will soon be accepted as nutritional additives for “functional
food” products. While current manufacture of conjugated veg-
etable oils or conjugated linoleic acids (CLAs) uses a homoge-
neous base as isomerisation catalyst, a heterogeneous alterna-
tive is not available today. This contribution presents the direct
production of CLAs over Ru supported on different zeolites,
varying in topology (ZSM-5, BETA, Y), Si/Al ratio and counter-
cation (H+, Na+, Cs+). Ru/Cs-USY, with a Si/Al ratio of 40, was
identified as the most active and selective catalyst for isomeri-
sation of methyl linoleate (cis-9,cis-12 (C18:2)) to CLA at 1658C.
Interestingly, no hydrogen pre-treatment of the catalyst or ad-
dition of hydrogen donors is required to achieve industrially
relevant isomerisation productivities, namely, 0.7 g of CLA per
litre of solvent per minute. Moreover, the biologically most
active CLA isomers, namely, cis-9,trans-11, trans-10,cis-12 and
trans-9,trans-11, were the main products, especially at low cata-
lyst concentrations. Ex situ physicochemical characterisation
with CO chemisorption, extended X-ray absorption fine struc-
ture measurements, transmission electron microscopy analysis,
and temperature-programmed oxidation reveals the presence
of highly dispersed RuO2 species in Ru/Cs-USY(40).
Introduction
The term conjugated linoleic acids (CLAs) encompasses all po-
sitional and geometric isomers of conjugated linoleic acid. This
acid is a major component in vegetable oils. Soya bean and
safflower oil typically contain linoleic acid levels up to 53.7 and
77.7%, respectively.[1] Linoleic acid has two double bonds, both
in the cis configuration, located at positions 9 and 12, whereas
CLAs have two conjugated double bonds, with either cis or
trans configurations, located at various positions. Traditionally,
adding CLAs to coatings and paints improves the drying prop-
erties.[2] Because conjugated double bonds are more reactive
than unconjugated ones, CLAs are also used as co-monomers
in the production of bio-plastics by cationic and free-radical
copolymerisation.[3] Highly productive and sustainable process-
es are key challenges for industrial CLA usage.
advantageous effects in humans requires daily uptake levels of
about 3 g.[8] Therefore, enhanced CLA uptake, leading to bene-
ficial effects on human health, would require the addition of
CLA to functional food products.
Today, the industrial production of CLA involves high-tem-
perature catalysed isomerisation of vegetable oils (rich in lino-
leic acid) or fatty acids, such as linoleic acid, with homogene-
ous bases, namely, potassium hydroxide or potassium alcohol-
ates, using solvents, namely, ethylene glycol.[9] Subsequent
neutralisation with an acid, namely, phosphoric acid, is neces-
sary. In this way, almost equal amounts of cis-9,trans-11- and
trans-10,cis-12-CLA isomers are formed with high productivity
and selectivity (Table 1, entries 1 and 2). Unfortunately, the
present commercial production of CLAs, requiring the use of
dissolved alkali, solvents and acid addition, does not show the
characteristics of a sustainable process. Moreover, CLA-en-
riched triacylglycerols or methyl esters cannot be obtained di-
rectly with homogeneous bases because they hydrolyse ester
In recent years, a variety of positive health effects have been
attributed to CLAs. They are claimed to be anticarcinogenic,
antidiabetic, antioxidative and antiarteriosclerotic. They de-
crease fat and increase muscle content in the body, reduce in-
flammation, show a beneficial effect on bone formation, en-
hance immune functions and reduce asthma.[4] However, from
the 56 theoretically possible CLA isomers, only specific isomers,
namely, cis-9,trans-11-CLA and trans-10,cis-12-CLA show such
properties. More recent research indicates that trans-9,trans-11-
CLA also exhibits beneficial health effects, superior to the more
abundantly present cis-9,trans-11- and trans-10,cis-12-CLA.[5] Of
all CLA isomers, cis-9,trans-11-CLA is by far the most dominant
in food products (up to 90% of the total CLA content), espe-
cially in milk and tissue fats of ruminants, where it is synthes-
ised from linoleic acid by rumen bacteria.[6] Whereas the daily
dietary uptake of CLA is only 0.10–0.43 g,[7] the occurrence of
[a] A. Philippaerts, S. Goossens, W. Vermandel, J. Geboers, Prof. P. A. Jacobs,
Prof. B. F. Sels
Department M2S, K.U. Leuven
Kasteelpark Arenberg 23
3001 Heverlee (Belgium)
Fax: (+32)16 321998
E-mail: bert.sels@biw.kuleuven.be
[b] Prof. M. Tromp
Technische Universitat Munchen
Lichtenbergstrasse 4, 85748 Garching (Germany)
[c] Dr. S. Turner, Prof. G. Van Tendeloo
EMAT, University of Antwerp
Groenenborgerlaan 171, 2020 Antwerpen (Belgium)
ChemSusChem 2011, 4, 757 – 767
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
757

B. F. Sels et al.
Table 1. Comparison of different catalysts described in the literature for the production of CLA in different reaction atmospheres (RAs).
[a]
Entry
Substrate
Catalyst
Solvent
T [8C]
RA
YCLA
P[b]
R[c]
TOF[d]
Ref.
1
2
3
4
5
6
7
8
methyl linoleate
safflower FAME
methyl linoleate
methyl linoleate
linoleic acid
KOH
KOCH3
Ru/C
Ru/C
Ru/C
ethylene glycol
methanol
cyclohexane
hexane
n-decane
/
n-decane
n-decane
n-decane
n-decane
n-decane
n-decane
n-decane
n-decane
180
111–115
230
250
120
165
120
120
120
165
165
150
165
165
N2
N2
N2
N2
97
70
34
31
53
58
28
24
36
67
33
4
0.63
6.69
–
–
[30]
[9a]
[12a]
[12a]
[12b], [12h]
[31]
[12h]
[12h]
[12h]
[12d]
[12f]
[12f]
this work
this work
–
6.4
5.3
0.9
17.2
0.5
0.4
0.6
0.7
1.4
0.021
0.019
0.004
0.90
0.002
0.002
0.003
0.021
0.002
0.0005
0.698
0.391
15.0
13.6
1.8
23
0.9
0.8
1.2
1.5
0.7
0.2
[e]
N2
N2
N2
N2
N2
H2
H2
H2
N2
N2
linoleic acid[f]
linoleic acid
Ru/C
[e]
[e]
[e]
Ru/Al2O3
Ru/H-Y
Ru/H-b
Ag/SiO2
Au/TS-1
Au/C
linoleic acid
linoleic acid
linoleic acid
linoleic acid
linoleic acid
methyl linoleate
methyl linoleate
9
10
11
12
13
14
0.1
175.5
99.8[h]
[g]
Ru/Cs-USY
Ru/Cs-USY
67
75
419
234
[a] Yield of CLA. [b] CLA productivity [g(CLA)LÀ1(solvent)minÀ1]. [c] CLA production rate [g(CLA)gÀ1(metal)hÀ1]. [d] Turnover frequency [mol(ML converted)
molÀ1(Ru)hÀ1]. [e] Pre-activation under H2. [f] Technical grade. [g] After 120 min of reaction. [h] After 240 min of reaction.
linkages.[9a,10] Homogeneous isomerisation using transition-
metal complexes has also been studied and allows almost
quantitative conversion of linoleic acid to CLAs.[11] Despite the
high CLA selectivity, separation of the catalyst from the sub-
strate remains delicate.
second step, linoleic acid was isomerised to CLA in a nitrogen
atmosphere.[12b,c] Although the selectivity for conjugation was
higher than for hydrogenation, significant quantities of hydro-
genated products, especially oleic acid, were formed. Indeed,
with a Ru/C catalyst, pre-activated under hydrogen, 53% con-
jugation and 24% hydrogenation was achieved after 6 h at
1208C. When the pre-activation step was omitted, the catalyst
activity was reduced significantly. Ru on alumina and zeolite
catalysts, prepared by incipient wetness impregnation of ruthe-
nium acetyl acetonate and RuCl3, respectively, also show rather
low rates of CLA productivity, comparable to that of Ru/C.[12g,h]
Silver- and gold-based heterogeneous catalysts were also
tested in the isomerisation of linoleic acid in presence of hy-
drogen. Because these metals have low hydrogen-binding en-
ergies, low selectivity for hydrogenated products was obtai-
ned.[12d,e]
Heterogeneous catalysis constitutes an attractive strategy
for sustainable CLA production because the catalyst can be
separated and reused easily. Although some heterogeneous
processes for isomerisation of linoleic acid or methyl linoleate
have already been described in the literature,[12] low productivi-
ty is the main drawback (Table 1, entries 3–12). Moreover, it
was concluded that low amounts of hydrogen, present as
chemisorbed hydrogen atoms on the metal surface, were re-
quired to perform the isomerisation reaction at an acceptable
rate. Too much hydrogen caused the formation of an excess of
unwanted hydrogenated products (Scheme 1). To suppress the
hydrogenation reaction, a two-step process was used in which
the ruthenium catalyst was first covered with hydrogen. In the
In view of this, the design of a heterogeneous catalyst with
high activity towards the formation of the physiologically im-
portant cis-9,trans-11-, trans-10,cis-12- and trans-9,trans-11-CLA
isomers, and with a low activity towards the formation of
other CLA isomers and hydrogenated products, remains a chal-
lenge. We describe herein a new isomerisation catalyst for the
synthesis of CLAs in the absence of hydrogen, using a Ru/USY
catalyst with high Ru dispersion. While almost no hydrogenat-
ed products are formed, high productivity of and selectivity for
beneficial CLAs is achieved.
Results and Discussion
Support influence
Different zeolite supports were loaded with ruthenium and
tested in the isomerisation of methyl linoleate (Table 2). The
zeolites tested differ in topology (MFI (ZSM-5), BEA (BETA), FAU
(Y)), Si/Al ratio (2.5–180) and countercation (H+, Na+, Cs+). The
results of a commercial Ru/C catalyst are incorporated as a ref-
erence. During the isomerisation of methyl linoleate, four
types of products are formed, namely, conjugated (CLA) and
Scheme 1. Isomerisation/hydrogenation of linoleic acid with a heterogene-
ous catalyst.
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ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemSusChem 2011, 4, 757 – 767

Hydrogen-Free Production of Conjugated Linoleic Acids
In contrast, with Ru/USY cata-
lysts with a Si/Al ratio of 40,
large quantities of CLAs were
identified in the reaction mixture
(Table 2, entries 12–14). Further-
more, the activity of these cata-
lysts was much higher than that
of the Ru/C reference catalyst,
namely, 1.29ꢁ10À5 and 0.18ꢁ
10À5 molminÀ1 for Ru/H-USY(40)
and Ru/C, respectively.
Table 2. Catalytic properties of supported ruthenium catalysts for the isomerisation of methyl linoleate (ML)[a]
.
[c]
[d]
[e]
[f]
[g]
[h]
[i]
[j]
Entry
Support
Si/Al Ai[b] ꢁ10À5
t
XML
YCLA
SCLA
Sct
Stt
SHP
SNC
SCP
[molminÀ1
]
[min] [%]
[wt%] [%]
[%]
[%]
[%]
[%]
[%]
1
2
3
4
5
6
7
8
C
/
0.18
1.54
0.32
0.16
1.74
0.57
2.27
2.27
2.27
2.27
2.27
1.29
0.95
0.86
240
15
240
240
15
60
15
15
15
15
15
30
30
58
68
74
54
77
37
20
35
27
36
46
0
0
0
0
0
63
29
48
49
47
67
0
0
0
0
0
30
3
6
11
5
13
0
0
0
0
0
24
11
19
18
17
36
0
0
0
0
0
3
0
3
2
2
2
0
0
0
0
0
12
2
1
22
17
17
25
24
21
0
0
0
0
0
13
53
32
25
27
H-ZSM-5
Na-ZSM-5 140
Cs-ZSM-5
H-BETA
Cs-BETA
H-Y
140
140
180
180
2.5
2.5
15
15
30
40
40
69
10
100
100
100
100
100
73
100
100
100
100
100
13
Na-Y
9
H-USY
Na-USY
H-USY
H-USY
Na-USY
Cs-USY
Also, zeolite topology has an
influence on the reaction charac-
teristics. A comparison of Ru/H-
ZSM-5, Ru/H-BETA and Ru/H-
USY(40) revealed that, at compa-
rable conversions, zeolite BETA
(with small crystallites) and USY
(with mesopores) show a higher
selectivity for CLA formation (29,
47, and 45%, respectively;
Table 2, entries 2, 5 and 12). It
should be stressed that the
10
11
12
13
14
33
46
67
45
62
82
4
7
10
16
23
31
30
14
9
74
82
22
9
40
30
[a] Reaction conditions: T=1658C, [ML]=7 mmolLÀ1, 0.8 g 0.5Ru/zeolite or 0.08 g 5Ru/C, Ru/ML=4 wt%, pre-
treatment of the catalysts in nitrogen at 3508C (Table 3, entry 2). [b] Initial activity (after 15 min). [c] Conversion
of ML. [d] Yield of CLA. [e] Selectivity for total CLA. [f] Selectivity for cis-9,trans-11-+trans-10,cis-12-CLA. [g] Se-
lectivity for trans-9,trans-11-+trans-10,trans-12-CLA. [h] Selectivity for hydrogenation products (C18:1+C18:0).
[i] Selectivity for non-conjugated C18:2 isomers. [j] Selectivity for catalyst-adsorbed material (coke) (deficiency
of carbon mass balance).
non-conjugated C18:2 isomers (NC), hydrogenated products
(HP) and coke (CP), which remains on the catalyst and thus is
detected as a deficiency in the carbon mass balance. An overall
reaction network for linoleic acid disappearance is shown in
Scheme 1. The formation of conjugated and non-conjugated
C18:2 isomers is equilibrium limited, whereas the formation of
hydrogenated products and coke is irreversible. The selectivity
for the different product classes, as well as for the beneficial
CLA isomers, namely, cis-9,trans-11-+trans-10,cis-12-CLA (Sct),
and trans-9,trans-11-+trans-10,trans-12-CLA (Stt), at comparable
conversions is given in Table 2 for all catalysts.
small pores of ZSM-5 show a higher reactivity for coke forma-
tion. Probably the reactive conjugated products either under-
go slow intraporous polymerisation or just block these pores.
On the three catalysts, the nature of the products is the
same, though the individual selectivities are different. Among
the BETA and USY topology, the individual CLA selectivity is
comparable, indicating that, for the more open zeolite lattices,
pore architecture is not a selectivity-dominating parameter. It
is important to note that in earlier work, dealing with the dif-
ferentiation between trans- and cis-fatty acids, a clear influence
of the same zeolite topologies for the selective removal of
trans-fatty acids from a mixture containing both cis and trans
isomers has been reported.[15]
The use of different countercations (H+, Na+, Cs+) in the
ZSM-5 support has a large influence on the activity (Table 2,
entries 2–4); the activities of Ru/Cs-ZSM-5 and Ru/Na-ZSM-5
are reduced compared with Ru/H-ZSM-5. Ru/Cs-ZSM-5 shows
the lowest activity, which is comparable with that of Ru/C. Be-
cause the presence of bulky Cs+ ions, rather than the nature of
the charge compensating cations, namely, Na+ and Cs+, affect
overall catalyst behaviour, it seems that pore blocking in ZSM-
5 with larger cations could be at the basis of reduced activity.
An effect of the nature of the charge-compensating cations is
also encountered with BETA (Table 2, entries 5 and 6) and
USY(40) samples (Table 2, entries 12–14), mainly at the level of
the CLA selectivity. More basic Cs catalysts show an enhanced
selectivity for CLA formation, whereas acid catalysts show en-
hanced activity for the formation of coke (H+ >Na+ >Cs+).
Larger monovalent cations in zeolites result in reduced electro-
negativity of the material,[16] and according to Sanderson, re-
duced acid strength of the residual Brønsted acid sites.[17] This
explains the reduced selectivity for coke and non-conjugated
isomers of ML; the latter is obtained by acid-catalysed isomeri-
sation. The enhanced CLA yield and selectivity should be at-
It seems that the type of support has a large influence on
both methyl linoleate conversion and CLA selectivity. Zeolites
Y and USY, with a Si/Al ratio of ꢀ30, do not show any CLA for-
mation, irrespective of the countercation present in the zeolite
lattice (Table 2, entries 7–11). In all cases the conversion is very
high, since after reaction for 15 min all methyl linoleate has
disappeared. The products, collectively denoted as hydrocar-
bon coke (CP), remain strongly adsorbed on the catalyst sur-
face. Reaction simulation in a thermobalance indicated that all
reactant remained adsorbed on the catalyst support. These ob-
servations can be explained by the high acid density of such
zeolites. It is known that olefins can undergo proton-catalysed
reactions on acid sites, such as isomerisation, polymerisation
and cyclisation;[13] polymerisation products are trapped in the
pore system of the support. Furthermore, it has already been
shown that CLAs can also polymerise on Ru catalysts.[12a,14] Also
Na-exchanged Y and USY zeolites with low Si/Al ratios show
coke formation (Table 2, entries 8 and 10), caused by protons
produced during the reduction of ion-exchanged RuIII–hexam-
ine. Thus, zeolites with a low Si/Al ratio (ꢀ30) are not suitable
supports for the formation of CLAs because of their high activi-
ty for coke formation.
ChemSusChem 2011, 4, 757 – 767
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759

B. F. Sels et al.
tributed to changes in the properties of the Ru metal clusters
under the influence of the enhanced basicity of the lattice. It is
expected that these changes occur at the level of the residual
electron density on the clusters. How this mechanistically af-
fects CLA formation will be discussed below. The highest CLA
selectivity is obtained with the Ru/Cs-USY(40) catalyst, namely,
82% at a conversion of 82% (Table 2, entry 14), which is much
higher than that of the Ru/C catalyst, namely, 63% at a conver-
sion of 58% (Table 2, entry 1). Ru/C shows a higher selectivity
towards cis-9,trans-11- and trans-10,cis-12-CLA isomers, where-
as Ru/Cs-USY is more selective towards the formation of trans,-
trans-CLAs. This issue will be further discussed below.
In a next step, the Ru dispersion was determined by CO
chemisorption, TEM analysis and extended X-ray absorption
fine-structure (EXAFS) measurements. Ru dispersion from CO
chemisorption was very high, namely, 87%, which indicated
the presence of highly dispersed Ru. With TEM, no Ru clusters
could be detected, whereas EDX measurements at different
points on the zeolite confirmed the presence of Ru, implying
that Ru was indeed highly dispersed throughout the zeolite
crystal.
While ML isomerisation activity of such highly dispersed Ru
was not known, its existence has been described before.[18]
From the literature, it is known that activation conditions are
crucial to arrive at such high Ru dispersions.[18a,19] As described
in the Experimental Section, [Ru(NH3)6]3+-exchanged zeolite
was first heated under N2 to 3508C. MS analysis of the decom-
position gases revealed loss of H2O (from room temperature to
1508C) and NH3 (from 220 to 3508C), corresponding to zeolite
dehydration and decomposition of the Ru complex. In a fur-
ther step, the catalyst was reduced under a flow of H2 at
4008C (58CminÀ1). Almost no hydrogen was consumed, in
agreement with previous work using a Ru/Na-Y(2.4) catalyst.[18a]
Experimentally, it was confirmed that by omitting the reduc-
tion step, high conversions were also obtained, although the
CLA yield decreased from 75 to 55 wt% (Table 3, entries 2 and
3). Hence, no hydrogen was required when highly dispersed
Ru/USY catalysts were used for the production of CLA, or in
the pre-treatment procedure of the catalyst or during the iso-
merisation reaction.
It is important to mention that Ru/Cs-USY shows very low
selectivity for hydrogenated products due to the absence of a
hydrogen donor. In the presence of molecular hydrogen[12d–f]
or after pre-activation under hydrogen,[12b] higher selectivities
for hydrogenated products have invariably been reported.
Determination of active sites
From the above experiments it follows that superior CLA pro-
duction occurred with the Ru/Cs-USY(40) catalyst. NMR spec-
troscopy measurements of the solvent, namely, n-decane, after
the reaction, revealed that the solvent was inert under the re-
action conditions. To identify the active centres responsible for
the isomerisation reaction, tests were performed by using Cs-
USY(40) devoid of Ru. After reaction for 1 h, a CLA yield of only
1 wt% and a conversion of 5 wt% was obtained, compared
with a CLA yield of 75 wt% and a conversion of 94 wt% for
added Ru (Table 3, entries 1 and 2). Hence, the ML isomerisa-
tion activity towards CLAs can be assigned to the presence of
Ru. If no Ru is present, 3 wt% of coke is formed after 1 h,
whereas 5 wt% of coke is formed with the Ru/Cs-USY catalyst.
In agreement with the literature, this indicates that not only
the support, but also Ru contributes to the formation of
coke.[12a,14] However, it cannot be excluded that the higher
amount of coke for Ru/Cs-USY might also be associated with
the higher activity of this catalyst with respect to ML isomerisa-
tion to CLA.
From a previous report it is known that highly dispersed
nano-sized metallic Ru clusters in zeolite Y, are easily oxidised
at room temperature.[18a] This was confirmed with the Ru/Cs-
USY catalyst by means of an O2 titration experiment at room
temperature, immediately after the activation procedure, with-
out making contact with air. The high uptake of O2 at room
temperature (with Ru/O= ꢁ2) proved that metallic Ru was
rapidly converted to RuO2, in agreement with the literature.
EXAFS measurements also confirm the presence of Ru4+ spe-
cies, which are structurally similar to RuO2 species.[20] The
ruthenium K-edge X-ray absorption near-edge structure
(XANES) spectrum of Ru/Cs-USY(40) is compared with anhy-
drous RuO2, as well as (hydrated) RuCl3, in Figure 1. The ruthe-
nium K-edge energies and the detailed XANES features of the
sample are very similar to that of anhydrous ruthenium oxide,
but significantly different from ruthenium chloride, indicating a
very similar local geometry and similar electronic properties
between the sample and anhydrous RuO2. This indicates that
the ruthenium metal clusters in the catalyst after reduction are
oxidised to Ru4+, due to contact with air/oxygen at room tem-
perature. Fourier transform (FT) of the EXAFS data (Figure 2)
confirms the structural similarities between the anhydrous
RuO2 and the Ru/Cs-USY(40) sample. A similar radial distribu-
tion of the same neighbours is observed, albeit at longer dis-
tances (from ꢁ3.0 ꢂ) significantly fewer contributions are ob-
served for the catalyst sample. EXAFS analysis suggests octahe-
dral coordination of O around Ru with two RuÀO bonds with
distances of 2.01 ꢂ, four RuÀO bonds with distances of 1.95 ꢂ
and one Ru···Ru bond with a RuÀRu distance of 3.16 ꢂ. Where-
Table 3. Isomerisation of ML with various USY(40) catalysts, using differ-
ent activation procedures.[a]
Entry
Catalyst
Activation
XML
YCLA
YNC
YHP
YCP
1
2
3
4
5
Cs/USY
N2/H2/air[b]
N2/H2/air[b]
N2/air
5
94
83
85
100
1
75
55
57
55
0
10
19
15
20
0
2
3
2
7
3
5
5
9
15
Ru/Cs-USY
Ru/Cs-USY
Ru/Cs-USY
Ru/Cs-USY
N2/O2/air[c]
[d]
N2/H2
[a] Reaction conditions: 1658C, [ML]=7 mmolLÀ1, 0.8 g 0.5Ru/USY(40),
60 min; abbreviations are the same as those given in Table 2. [b] Under
N2 and H2 up to 350 and 4008C, respectively, followed by room-tempera-
ture transfer from a flow to a batch reactor in air. [c] Under N2 up to
3508C, followed by room-temperature contact with
a flow of O2.
[d] Transfer of the reduced catalyst from a flow to a batch reactor under
inert conditions.
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Hydrogen-Free Production of Conjugated Linoleic Acids
genated and non-conjugated C18:2 isomers. Indeed, with this
catalyst, more hydrogen was available on the catalyst surface,
leading to enhanced consecutive isomerisation and hydroge-
nation.
If isomerisation is performed under a hydrogen atmosphere
or if the catalyst is previously pre-activated under hydrogen,
the metallic sites on the catalyst will be covered with chemi-
sorbed hydrogen. In this case, the double-bond migration re-
action can be rationalised by the generally accepted Horiuti–
Polanyi mechanism, in which a hydrogen atom derived from a
hydrogen-chemisorbed site is added to chemisorbed linoleic
acid, resulting in a chemisorbed half-hydrogenated intermedi-
ate.[22] If hydrogen is absent and RuO2 species instead of Ru0
clusters are present, the conjugation needs to be explained by
another mechanism. It has already been suggested that ruthe-
nium at its highest oxidation state favours double-bond iso-
merisation.[14b] On (basic) metal oxide a possible reaction mech-
anism consists of the occurrence of a U-form carbanion inter-
mediate and an allylic mechanism.[23] In basic conditions a
large amount of cis,cis product indicates a high degree of ste-
reospecificity, in line with the nature of the proposed inter-
mediate carbanion. Alternatively, carbenium ions can be
formed with the assistance of Brønsted acid sites,[24] requiring
initial cis/trans product ratios of around one. This is clearly not
the case because cis–cis conjugated CLA is only present in
trace amounts (see below).
Figure 1. Ruthenium K-edge XANES spectra for samples of anhydrous ruthe-
nium oxide (c), ruthenium chloride (a) and the catalyst 0.5Ru/Cs-
USY(40) (c).
Because in our system no chemisorbed hydrogen atoms are
present on the catalyst before reaction, they should originate
from the solvent or the ML substrate. Preliminary results using
a pure mixture of fatty acid esters demonstrate that no solvent
is needed to conduct the isomerisation. Hence, it can be con-
cluded that the substrate must take part in the hydride-trans-
fer reaction to generate chemisorbed hydrogen atoms on the
Ru surfaces. This has also been suggested previously.[14b]
Figure 2. Radial distribution function from the FT of the k2-weighted EXAFS
for ruthenium oxide (anhydrous) (c), ruthenium chloride (hydrate) (a)
and 0.5Ru/Cs-USY(40) (c).
as in the RuO2 references, further RuO and RuRu contributions
can be fitted at around 3.4 and 3.5 ꢂ, these cannot be deter-
mined for the Ru catalyst sample because no significant higher
contributions are present for this sample. This indicates that
significantly smaller ruthenium oxide entities are present in the
catalyst sample, which would also explain the slight decrease
in white-line features and small-edge energy shifts. Other au-
thors also observed nano-sized RuO2 species in FAU-type zeo-
lites.[21] In this research, the RuO2 clusters showed a two-dimen-
sional structure of independent chains, in which RuO6 octahe-
dra were connected through two shared oxygen atoms. This is
also a possible explanation for our EXAFS data.
Influence of catalyst activation conditions
From the above results, it follows that a nitrogen-activated Ru/
Cs-USY catalyst is oxygen sensitive. Although a somewhat
lower activity is obtained, the formation of RuO2 species on
the catalyst has a positive influence on the CLA yield. In con-
trast, analysis of the literature leads to the conclusion that the
formation of RuO2 species during the decomposition step, by
using O2 instead of N2, greatly influences the Ru dispersion,
since upon reduction large Ru clusters are formed on the ex-
ternal surface of the zeolite.[18a,19c] Indeed, TEM images clearly
show the presence of large Ru clusters on the external crystal
surface of the O2-pretreated catalyst (up to 20–200 nm)
(Figure 3). In contrast to the N2-activated sample, these clusters
contain only metallic Ru because no oxygen was detected by
EDX measurements. The Ru dispersion, calculated from CO
chemisorption measurements, of the O2-activated sample
(after reduction) is only 4%, whereas the N2-pretreated sample
has a Ru dispersion of 87%. The performance of both catalysts
in the ML isomerisation reaction is compared at similar conver-
sions in Table 4. Not only is the N2-pretreated catalyst much
more active, but also shows a much higher selectivity for CLA
The results of the ML isomerisation reaction with a Ru/Cs-
USY(40) catalyst, which was in contact with an O2 flow
(2 mLsÀ1 gÀ1) for 60 min at room temperature (Table 3, entry 4),
shows no activity nor selectivity differences with a catalyst that
did not receive such a treatment (Table 3, entry 3). Therefore,
in both cases there should be the presence of highly dispersed
RuO2, at least at the moment the catalyst is added to the
batch reactor. If the catalyst was not in contact with air before
the reaction, and hence the Ru species were fully reduced
before reaction, high activity for ML conversion was observed
(Table 3, entry 5) with a somewhat higher selectivity for hydro-
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761

B. F. Sels et al.
to the thermodynamically more stable trans-9,trans-11- and
trans-10,trans-12-CLA isomers, whereas only minimal positional
isomerisation is observed after 6 h of reaction. With the O2-ac-
tivated catalyst, both the cis-9,trans-11-+trans-10,cis-12- and
trans-9,trans-11-+trans-10,trans-12-CLA levels decrease after
longer reaction times. Simultaneously, the concentration of
other positional CLA isomers increases.
However, it should be stressed that the physicochemically
identified highly dispersed Ru oxide species are not necessarily
present under ML isomerisation conditions (around 1658C).
Indeed, it is known that such species are easily reduced to
small metal clusters after hydrogen treatment at around
1008C.[18a] Moreover, it is conceivable that upon contact with
ML at reaction temperature, ML is oxidised by the highly reac-
tive RuO2, at the same time, probably reducing Ru to the met-
allic state. It is known that weakly bonded oxygen species exist
in RuO2. The oxygen atoms are easily transferred to CO or alco-
hol even at room temperature, thereby reducing Ru into small
clusters.[21,25]
In conclusion, it is not necessary to invoke the presence of
RuO2 clusters for CLA formation and the occurrence of a carb-
anion mechanism. The reduction to Ru metal clusters by initial
ML autoxidation reaction conditions and the occurrence of a
common Horiutu–Polanyi mechanism is straightforward. The
favourable effect of small Ru metal particle sizes for CLA selec-
tivity is clear.
Figure 3. a) A bright-field TEM image of a large cluster in the O2-activated
Ru/Cs-USY(40) catalyst. b) A high-angle annular dark-field scanning transmis-
sion electron microscopy (HAADF-STEM) image of the same large cluster
(bright white). c) A colour map showing that the large cluster is metallic
ruthenium, not ruthenium oxide. d)–g) STEM electron energy-loss spectros-
copy (EELS) elemental maps for C (d), O (e), Ru (f) and Si (g) obtained from
the region indicated in the HAADF-STEM image, e)–g) are combined into the
colour map in c).
Influence of ML concentration
formation, whereas the O2-pretreated catalyst has a higher se-
lectivity towards non-conjugated C18:2 isomers (NC) and coke
(CP). Hence, it seems clear that small Ru oxide species, ob-
tained after pre-treatment in an inert atmosphere followed by
room-temperature exposure to air, should be the active sites
for CLAs formation. Larger Ru metal clusters obtained after
oxygen activation and subsequent reduction are not sensitive
to room-temperature air contact and should lead to higher
levels of undesired non-conjugated C18:2 isomers.
The influence of ML concentration on the reaction characteris-
tics of ML isomerisation with a Ru/Cs-USY(40) catalyst was in-
vestigated. Indeed, to obtain a process with a high productivi-
ty and TOF, and hence, to make the process industrially attrac-
tive and sustainable, it is important that the catalyst is able to
convert ML into CLAs in a reaction with a low Ru/ML ratio with
a high selectivity and activity. In Table 5 the activity and differ-
ent selectivities towards the formation of CLAs, non-conjugat-
ed C18:2 isomers, hydrogenated products and cokes at maxi-
mum CLA yield are compared (entries 1–4). It is shown that
the activity rises as the ML concentration is increased from 7
to 350 mmolLÀ1. This leads to a very significant increase in pro-
ductivity and TOF; the productivity at maximum CLA yield in-
creases from 0.029 to 0.391 g(CLA)LÀ1 minÀ1 and the TOF in-
creases from 8.1 to 99.8 hÀ1. At somewhat lower CLA yields,
namely, 67 instead of 75 wt%, the productivity and TOF are
even higher, namely, 0.698 g(CLA)LÀ1 minÀ1 and 175.5 hÀ1, re-
spectively (Table 1, entry 13).
Interestingly, the Ru cluster size also has an influence on the
CLA isomer distribution. Smaller Ru(oxide) clusters (decomposi-
tion under N2) show an enhanced selectivity for the formation
of cis-9,trans-11- and trans-10,cis-12-CLA isomers compared
with the larger Ru clusters (decomposition under O2). With the
N2-activated catalyst, the cis-9,trans-11 and trans-10,cis-12 iso-
mers are initially the dominantly formed CLA isomers. After
longer reaction times, the latter isomers are mainly converted
These values are much higher
than those of other heterogene-
Table 4. Performance of a N2- and O2-pretreated Ru/Cs-USY(40) catalyst in the isomerisation of ML.[a]
ous processes found in the liter-
ature and are comparable to the
homogeneous process used in-
dustrially today (Table 1). Only
Ru/C shows a slightly higher pro-
ductivity when using technical-
grade linoleic acid in undiluted
conditions (Table 1, entry 6).
[b]
Activation
DRu
Ai[c] ꢁ10À5
t
XML
[%]
YCLA
[wt%]
SCLA
[%]
Sct
[%]
Stt
[%]
SNC
[%]
SHP
[%]
SCP
[%]
[%]
[molminÀ1
]
[min]
N2/H2/air[d]
O2/H2/air
87
4
19.24
3.40
120
480
82
83
67
19
82
23
44
3
30
11
6
35
1
2
11
39
[a] Reaction conditions: T=1658C, [ML]=350 mmolLÀ1, 0.8 g 0.5Ru/Cs-USY(40), abbreviations see Table 1.
[b] Ru metal dispersion from CO measurements for in situ pretreated samples. [c] Activity after reaction for
15 min. [d] Same conditions as Table 3, entry 2.
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Hydrogen-Free Production of Conjugated Linoleic Acids
with the respective reactions
with a low ML concentration
(7 mmolLÀ1). Comparison of the
Table 5. Influence of the ML concentration on the performance of the Ru/USY(40) catalyst in the isomerisation
of ML.[a] Results are given for maximal CLA yield.
Entry
Counter cation
[ML]
[mmolLÀ1
Ai ꢁ10À5
[molminÀ1
XML
[%]
t
YCLA
[wt%]
P
TOF[b]
[hÀ1
three
catalysts
at
[ML]=
]
]
[min]
[g(CLA)LÀ1 minÀ1
]
]
350 mmolLÀ1, shows that the
Ru/Cs-USY catalyst gives the
highest CLA yield, and hence,
also the highest productivity and
TOF (Table 5, entries 4, 6 and 8).
The obtained TOFs are consider-
ably higher than those calculat-
ed from the literature (Table 1).
1
2
3
4
5
6
7
8
Cs
Cs
Cs
Cs
H
H
Na
Na
7
21
70
350
7
350
7
0.86
2.85
12.25
19.24
1.29
14.72
0.95
11.32
94
92
92
93
73
81
93
81
60
60
60
240
30
360
60
69
74
77
75
33
40
47
68
0.029
0.093
0.289
0.391
0.028
0.139
0.020
0.236
8.1
23.7
78.9
99.8
12.5
57.9
8.0
350
360
57.9
[a] Reaction conditions: 1658C, 0.8 g 0.5Ru/USY(40). [b] mol(ML converted)molÀ1(Ru)hÀ1
.
However, much more Ru is required to obtain such high pro-
ductivity. The TOF for Ru/Cs-USY is indeed one order of magni-
tude larger than that of Ru/C.
The selectivity for the different products (CLA, non-conjugat-
ed CLA, hydrogenated products and coke) remains rather unaf-
fected by ML concentration. In contrast, the CLA isomer distri-
bution as a function of the conversion is largely influenced by
the Ru/ML ratio (Figure 4). Initially, the contribution of the cis-
9,trans-11 and trans-10,cis-12 isomers is high and at high ML
conversion levels off at around 10%. The contribution of these
beneficial isomers among all CLAs increases with higher ML
levels. Also, the fraction of the trans-9,trans-11- and trans-
10,trans-12-CLA isomers shows the same behaviour when plot-
ted against conversion. Its contribution indicates values
around 35% for higher ML levels. It is clear, at least for the
high ML concentrations, that cis,trans (trans,cis) isomers are the
primary CLA product isomers, followed by consecutive forma-
tion of trans,trans and unconjugated CLAs. For lower initial ML
concentrations, the equilibrium is reached at lower ML conver-
sion. The data allow the 9,11- and 10,12-CLA product distribu-
tion to be determined at equilibrium: cis,trans 27.5, trans,trans
65.5 and cis,cis 7%. The level of other positional CLA isomers
increases with conversion and is higher for lower ML concen-
trations. At equilibrium around 45% of the total CLA isomers
are present as CLAs with double bonds on positions different
from 9,11 and 10,12.
From these observations it can be concluded that the initial-
ly kinetically formed cis-9,trans-11- and trans-10,cis-12-CLA iso-
mers are converted to the thermodynamically more stable
trans-9,trans-11- and trans-10,trans-12-CLA isomers and the
9,11 and 10,12 isomers are converted to other positional CLAs
for longer reaction times. Both phenomena are enhanced for
reduced ML concentration.
Influence of the nature of the counterion in Ru/R-USY(40)
Owing to the positive influence of a low Ru/ML ratio on the re-
action characteristics, Ru/R-USY catalysts, with R=Me, H, Na, or
Figure 4. Influence of the Ru/ML ratio on the CLA isomer product distribu-
tion (PD) during the isomerisation of methyl linoleate using a Ru/Cs-USY(40)
catalyst: A) PDct (cis-9,trans-11+trans-10,cis-12-CLA), B) PDtt (trans-9,trans-11-
+trans-10,trans-12-CLA), C) PDother CLA (other positional CLA isomers); [ML]=7
^
Cs, were tested in the isomerisation of a more concentrated
solution of ML, namely, [ML]=350 mmolLÀ1. With each cata-
lyst, much higher productivities, specific yields and selectivities
towards the desirable CLA isomers were obtained compared
(~), 21 (&), 70 (*) and 350 mmolLÀ1
( ).
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763

B. F. Sels et al.
Furthermore the Ru/Cs-USY catalyst shows the highest selec-
tivity for desirable cis-9,trans-11- and trans-10,cis-12-CLA iso-
mers (Figure 5). With the acid Ru/H-USY catalyst, faster isomeri-
sation towards the thermodynamically more stable trans,trans-
CLAs takes place, as well as positional isomerisation of the 9,11
and 10,12 isomers to both conjugated and non-conjugated
C18:2 isomers. The more basic Na- and Cs-exchanged USY cat-
alysts show a much lower initial activity for formation of trans-
9,trans-11- and trans-10,trans-12-CLA isomers and other posi-
tional CLA isomers. Only at higher conversions (around 50%
for Ru/Na-USY and around 70% for Ru/Cs-USY), are the cis-
9,trans-11- and trans-10,cis-12-CLA isomers converted to their
respective geometrical trans,trans isomers and other positional
CLA isomers. The level of non-conjugated C18:2 isomers only
slightly increases with conversion.
the Ru metal clusters (see above) is effecting this. It is known
for Pt clusters in zeolite that they receive Ir-like character (de-
crease in cluster electron density and faster hydrogenation/de-
hydrogenation) when embedded in a more acidic Y zeolite.[26]
In the present case, the opposite is clearly the case and de-
crease in metal-catalysed isomerisation is not unexpected.
In parallel, there is a reduction in the rate at which the CLA
equilibrium is reached, yielding an enhanced selectivity for
cis,trans-conjugated CLAs.
Catalyst regeneration
Finally, the optimal Ru/Cs-USY(40) catalyst was tested in a recy-
cling experiment. After the first run, the catalyst was filtered
and washed with dioxane. After drying overnight at room tem-
perature, the catalyst was directly tested in a second run, with-
out any further pre-treatment. In the same way, a third run
was also performed. The conversion and CLA yield of the three
runs are compared in Figure 6. It can be concluded that, al-
though there is some loss in activity, probably caused by loss
of active sites as a result of coke formation, the Ru/Cs-USY cat-
alyst remains very selective in the isomerisation of ML. Further
work is in progress to deal with this coke issue and catalyst de-
activation.
The reduced rate at which CLA equilibration is reached is in
line with the presence of more voluminous pore-blocking
agents, namely, Na+ and mainly Cs+ ions. The phenomenon
could therefore reflect an increased contribution of intracrystal-
line diffusion limitation. The enhanced TOF for CLAs with Ru/R-
USY(40) in the sequence R=Cs>Na>H, which can be derived
from Table 5, indicates the occurrence of a catalyst effect pro-
moting, in particular, the desired reaction, that is, the rate of
cis,trans-CLA isomer formation at positions 9,11 and 10,12. It is
not clear at this stage how enhanced basicity of the zeolite
framework, and consequently, enhanced electron density on
Figure 5. Influence of the countercation on the yield of conjugated and non-conjugated C18:2 isomers during the isomerisation of ML with Ru/H-USY(40)
(~), Ru/Na-USY(40) (&) or Ru/Cs-USY(40) (*). Reaction conditions: 1658C, [ML]=350 mmolLÀ1
.
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Hydrogen-Free Production of Conjugated Linoleic Acids
Experimental Section
Materials
Zeolite samples were from Zeolyst (ZSM-5=CBV28014, Y=CBV100,
USY=CBV720, CBV760 and CBV780, BETA=CP811C-300), whereas
the commercial Ru/C catalyst was from Johnson Matthey (5 wt%
Ru, Type 97). ML was from Sigma–Aldrich with a purity of >99%,
n-decane was from Acros with a purity of >99%. CLA references
for peak identification, namely, cis-9,trans-11-, trans-10,cis-12-,
trans-9,trans-11-, cis-9,cis-11- and cis-10,cis-12- (C18:2) CLA, were
from Matreya LLC.
Figure 6. Recycling experiment with Ru/Cs-USY(40) recorded after reaction
for 300 min (gray=conversion of ML(350 mmolLÀ1), white=yield of CLA,
stripes=selectivity towards CLA).
Catalyst preparation
The supports were loaded with 0.5 wt% Ru ion exchange for 24 h
under stirring of the aqueous zeolite slurry (200 mL water per
gram of dry zeolite), containing the required amount of Ru precur-
sor ([RuIII(NH3)6Cl3]). Afterwards, the Ru–hexamine-exchanged zeo-
lite powder was filtered, washed with distilled water and dried
overnight at 508C. Prior to metal loading, the zeolite powder was
changed from the proton to the NH4 form by adding an aqueous
solution of ammonia (0.015m) for 16 h (200 mLgÀ1). The obtained
NH4 zeolite was transformed into the Na form by two successive
room-temperature ion-exchange steps (16 h) with a 1m aqueous
solution of NaCl (200 mL per gram of dry zeolite). The caesium
form was obtained by exchanging the sodium zeolite twice with a
0.1m aqueous solution of caesium acetate (25 mLgÀ1 zeolite) for
48 and 72 h. After each exchange step, the slurry was filtered, the
solids were washed three times with distilled water and air-dried at
1008C.
Prior to activation, the dry powders were compressed, crushed and
sieved. The 0.25–0.50 mm fraction was retained for further use. Ac-
tivation was conducted in a flow reactor in two steps under a flow
of nitrogen (120 mLminÀ1 gÀ1). First, the reactor was heated from
RT to 2008C at 28CminÀ1 and then from 200 to 3508C at
38CminÀ1. Optionally, a reduction step at 4008C (58CminÀ1) under
a flow of hydrogen (120 mLminÀ1 gÀ1) was performed. The catalyst
pellets were then transferred from the flow reactor to a stirred
batch reactor, requiring a short exposure to air at room tempera-
ture.
Conclusions
The results presented clearly show that, compared with other
heterogeneous processes reported in the literature, high pro-
ductivities of and selectivities for CLA from ML can be ob-
tained by heterogeneous catalysis when highly dispersed RuO2
species are present in Si-rich USY catalysts, at least when
added to the batch reactor. When the reactions are performed
under an inert atmosphere, almost no hydrogenated products
are formed, whereas conjugation seems to be performed by
means of hydrogen transfer between the fatty acids and the
active Ru metal clusters on the catalyst, that is, according to a
classical Horiuti–Polanyi mechanism, since cis,trans-CLAs at po-
sitions 9,11 and 10,12 were shown to be primary products con-
verted consecutively into trans,trans isomers with double
bonds at the same and finally other positions. Unwanted side
reactions are coke formation and formation of hydrogenated
products. The latter increase in selectivity when enhanced
amounts of activated hydrogen are present due to presence of
hydrogen during activation or reaction. Faster equilibration
among the CLAs is obtained when the size of the charge-com-
pensating cations is reduced (Cs+ >Na+ >H+). This can be the
result either of enhanced intracrystalline diffusional resistance
or of enhanced activity of Ru metal clusters in a more basic
catalyst support.
Catalyst characterisation
For investigations with TEM, the sample was dispersed in ethanol
and deposited on a holey carbon grid for analysis. Bright-field TEM,
HAADF-STEM and STEM-EELS spectrum image mapping was car-
ried out in a FEI Titan 80-300 “cubed” microscope equipped with a
Gatan Quantum spectrometer. The convergence angle, a, was
about 20 mrad, the collection semi-angle, b, was about 100 mrad.
The maps were generated by integrating the background-subtract-
ed signal from the carbon K edge, oxygen K edge, ruthenium M4,5
edge and the Si K edge in each EELS spectrum. The scanned area
was 69ꢁ125 nm divided into 61ꢁ67 pixels in the spectrum image.
Ru K-edge EXAFS spectroscopy experiments were carried out at
the Diamond Light Source in Didcot, UK, beamline B18 (Core XAS).
A double-crystal monochromator Si(311) was used. The measure-
ments were performed in fluorescence mode by using a nine-ele-
ment Ge solid-state detector. The spectra were calibrated by using
a Rh foil (1st maximum 1st derivative: 23220 eV). The samples
were prepared by pressing around 50 mg of the activated catalyst
pellets into tablets. These tablets were placed into a sample holder
with kapton film as an X-ray transparent window. The experiments
Though in physicochemical terms the presence of highly Ru
oxide clusters was clearly demonstrated on the reduced cata-
lyst exposed to air at room temperature, it was assumed that
such clusters in reaction conditions were transformed into
highly dispersed Ru metal clusters through the autoxidation of
ML by RuÀO.
Because of the very high productivities obtained with the
Ru/Cs-USY(40) catalyst, this process could be a major break-
through in the production of bio-based drying oils, paints and
plastics. Moreover, because the beneficial CLA isomers are the
main products with the Ru/Cs-USY catalyst, this research may
also accelerate the development of CLA-enriched functional
foods.
ChemSusChem 2011, 4, 757 – 767
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765

B. F. Sels et al.
were performed at room temperature. XAS data processing and
EXAFS analysis were performed by using IFEFFIT[27] with the Horae
package (Athena and Artemis).[28] The crystallographic RuO2 data
(space group 136; a=b=4.919, c=3.1066 ꢂ) were used as a start-
ing fitting model.[20] Ru K-edge EXAFS fitting results (the error is
the last digit in parentheses): 2RuO at 2.01(2) ꢂ, Debye–Waller
factor s2 =0.001(1) ꢂ2, 4RuO at 1.95(4) ꢂ, s2 =0.006(6) ꢂ2, 2RuRu at
3.16(3) ꢂ, s2 =0.009(3) ꢂ2, E0 =À5.1(2) eV, R factor 2.3%; fitting
ranges 1.49 <k <11.18 ꢂÀ1; 1.00<R<3.11 ꢂ, 12 independent data
points, k2-weighted fit, amplitude 1.0 (fixed).
mond Light Source for provision of XAS beamtime and the staff
of B18 for help with data collection.
Keywords: conjugation · fatty acids · heterogeneous catalysis ·
isomerization · ruthenium
[1] R. D. O’Brien, Fats and Oils: Formulating and Processing for Applications,
3rd ed., Taylor & Francis, Boca Raton, 2009.
[2] a) T. F. Bradley, US 2 350 583, 1944; b) R. T. Sleeter, US 5719301, 1998.
[3] Y. Lu, R. C. Larock, ChemSusChem 2009, 2, 136–147.
[4] a) A. Bhattacharya, J. Banu, M. Rahman, J. Causey, G. Fernandes, J. Nutr.
Biochem. 2006, 17, 789–810; b) M. W. Pariza, Y. Park, M. E. Cook, Prog.
Lipid Res. 2001, 40, 283–298.
[5] a) M. Coakley, M. C. Johnson, E. McGrath, S. Rahman, R. P. Ross, G. F. Fitz-
gerald, R. Devery, C. Stanton, Nutr. Cancer 2006, 56, 95–102; b) Y. Lee,
J. P. Vanden Heuvel, J. Nutr. Biochem. 2010, 21, 490–497; c) J. Ecker, G.
Liebisch, W. Patsch, G. Schmitz, Biochem. Biophys. Res. Commun. 2009,
388, 660–666.
Ruthenium dispersions were determined by using CO chemisorp-
tion. Catalyst pellets loaded in a tubular reactor were activated ac-
cording to the pre-treatment procedure described previously and
cooled to room temperature under a flow of helium. For the titra-
tion of the Ru surface, pulses of pure CO (5 mL) at an interval of
2 min were added to a helium flow of 10 mLminÀ1. The CO con-
centration in the outlet stream was followed continuously by ion
monitoring at m/z 28 with a Pfeiffer Omnistar quadrupole mass
spectrometer. For the calculation of the dispersion, adsorption of
one CO per accessible Ru atom was assumed. In the same way,
pulses of pure H2 or O2 were added to a helium flow for the H2
and O2 titration experiments, respectively. The concentration of H2
and O2 in the outlet stream was determined by ion monitoring at
m/z 2 and 32, respectively. The same setup was also used for the
determination of the decomposition products during the activation
of the catalysts under N2. By monitoring at m/z 16, 17 and 18, the
concentrations of NH2+, NH3 and H2O species, respectively, were
followed.
[6] C. R. Kepler, K. P. Hirons, J. J. McNeill, S. B. Tove, J. Biol. Chem. 1966, 241,
1350–1354.
[7] a) J. Fritsche, S. H. , Z. Lebensm. Unters. Forsch. 1998, 206, 77–82; b) K. L.
Ritzenthaler, M. K. McGuire, R. Falen, T. D. Shultz, N. Dasgupta, M. A.
McGuire, J. Nutr. 2001, 131, 1548–1554; c) S. Mushtaq, E. H. Mangia-
pane, K. A. Hunter, Br. J. Nutr. 2010, 103, 1366–1374; d) J. Jiang, A.
Wolk, B. Vessby, Am. J. Clin. Nutr. 1999, 70, 21–27; e) L. Laloux, L. du
Chaffaut, L. Razanamahefa, L. Lafay, Eur. J. Lipid Sci. Technol. 2007, 109,
918–929.
[8] a) C. Ip, M. Singh, H. J. Thompson, J. A. Scimeca, Cancer Res. 1994, 54,
1212–1215; b) H.-J. Song, I. Grant, D. Rotondo, I. Mohede, N. Sattar,
S. D. Heys, K. W. J. Wahle, Eur. J. Clin. Nutr. 2005, 59, 508–517; c) J.-M.
Gaullier, J. Halse, K. Hoye, K. Kristiansen, H. Fagertun, H. Vik, O. Gud-
mundsen, J. Nutr. 2005, 135, 778–784; d) H. Blankson, J. A. Stakkestad,
H. Fagertun, E. Thom, J. Wadstein, O. Gudmundsen, J. Nutr. 2000, 130,
2943–2948.
[9] a) A. Saebo, C. Skarie, D. Jerome, G. Haroldsson, US 6 410 761 B1, 2002;
b) A. Westfechtel, W. Albiez, L. Zander, P. Horlacher, US 20060106238 A1,
2006.
[10] A. Westfechtel, S. Busch, E. Grundt, P. Horlacher, US 7067684 B2, 2006.
[11] a) R. C. Larock, X. Dong, S. Chung, C. K. Reddy, L. E. Ehlers, J. Am. Oil
Chem. Soc. 2001, 78, 447–453; b) P. Pertici, V. Ballantini, S. Catalano, A.
Giuntoli, C. Malanga, G. Vitulli, J. Mol. Catal. A: Chem. 1999, 144, 7–13;
c) R. T. Sleeter, US 6696581 B1, 2004.
Thermogravimetric analysis (TGA) was performed on a TGA Q500
(TA Instruments) instrument, while heating the sample from RT to
7008C (58CminÀ1) under oxygen.
Isomerisation reaction
Isomerisation of ML at 1658C was carried out in a 100 mL Parr au-
toclave with a sampling device and under 3.5 bar of N2 with con-
stant stirring (500 rpm). In a typical experiment, n-decane (40 g),
ML (0.1–5.0 g) and 0.5Ru–zeolite (0.8 g) catalyst (or 5Ru/C (0.08 g))
were used.
[12] a) V. M. Deshpande, R. G. Gadkari, D. Mukesh, C. S. Narasimhan, J. Am.
Oil Chem. Soc. 1985, 62, 734–738; b) A. Bernas, P. Laukkanen, N. Kumar,
P. Mꢃki-Arvela, J. Vꢃyrynen, E. Laine, B. Holmbom, T. Salmi, D. Y. Murzin,
J. Catal. 2002, 210, 354–366; c) A. Bernas, N. Kumar, P. Mꢃki-Arvela, E.
Laine, B. Holmbom, T. Salmi, D. Y. Murzin, Chem. Commun. 2002, 10,
1142–1143; d) M. Kreich, P. Claus, Angew. Chem. 2005, 117, 7979–7983;
Angew. Chem. Int. Ed. 2005, 44, 7800–7804; e) P. Bauer, P. Horlacher, P.
Claus, Chem. Eng. Technol. 2009, 32, 2005–2010; f) O. A. Simakova, A.-R.
Lleino, B. Campo, P. Mꢃki-Arvela, K. Kordas, J.-P. Mikkola, D. Y. Murzin,
Catal. Today 2010, 150, 32–36; g) A. Bernas, N. Kumar, P. Laukkanen, J.
Vꢃyrynen, T. Salmi, D. Y. Murzin, Appl. Catal. A: Gen. 2004, 267, 121–
133; h) A. Bernas, N. Kumar, P. Mꢃki-Arvela, N. V. Kul’kova, B. Holmbom,
T. Salmi, D. Y. Murzin, Appl. Catal. A: Gen. 2003, 245, 257–275.
[13] a) R. Oukaci, A. Sayari, J. G. Goodwin, J. Catal. 1986, 102, 126–139; b) R.
Oukaci, J. C. S. Wu, J. Catal. 1987, 107, 471–481.
Analysis methods
The fatty acid methyl esters were analysed by using a Hewlett
Packard HP 6890 gas chromatograph with a split injection system
(split ratio=100:1) and N2 as the carrier gas. A 100 m CP-SIL 88
highly polar capillary column with an internal diameter of 0.25 mm
and a film thickness of 0.2 mm was used for separation. Initially, the
column temperature was maintained at 1808C for 50 min and then
raised at 108CminÀ1 to 2258C and held there for 15 min. The FID
detector used was maintained at 2808C. Heptadecane was used as
the internal standard. Most CLA isomers were identified based on
retention times, using references from Matreya LLC. Other CLA iso-
mers were identified based on literature data[29]
.
[14] a) S. Narasimhan, D. Mukesh, R. Gadkarl, V. M. Deshpande, Ind. Eng.
Chem. Prod. Res. Dev. 1985, 24, 324–326; b) D. Mukesh, C. S. Narasim-
han, V. M. Deshpande, K. Ramnarayan, Ind. Eng. Chem. Res. 1988, 27,
409–414.
Acknowledgements
[15] a) A. Philippaerts, S. Paulussen, S. Turner, O. I. Lebedev, G. Van Tendeloo,
H. Poelman, M. Bulut, F. De Clippel, P. Smeets, B. Sels, P. Jacobs, J. Catal.
2010, 270, 172–184; b) A. Philippaerts, S. Paulussen, A. Breesch, S.
Turner, O. I. Lebedev, G. Van Tendeloo, B. Sels, P. Jacobs, Angew. Chem.
Int. Ed. 2011 (accepted).
A.P. acknowledges the F.W.O.-Vlaanderen (Research Foundation
Flanders) for a doctoral fellowship. We are grateful to the Flemish
government for long-term sponsorship (Methusalem, CASAS). S.T.
gratefully acknowledges the financial support from the Fund for
Scientific Research Flanders (FWO). M.T. acknowledges the Dia-
[16] J. W. Ward, J. Catal. 1968, 10, 34.
[17] R. T. Sanderson, Polar Covalence, Academic Ed., New York, 1976.
766
www.chemsuschem.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemSusChem 2011, 4, 757 – 767

Hydrogen-Free Production of Conjugated Linoleic Acids
[18] a) J. J. Verdonck, P. A. Jacobs, J. C. S. Faraday I 1980, 76, 403–416;
b) Y. W. Chen, H. T. Wang, J. G. Goodwin, J. Catal. 1983, 83, 415–427.
[19] a) R. Oukaci, A. Sayari, J. G. Goodwin, J. Catal. 1987, 106, 318–322; b) M.
Goldwasser, J. F. Dutel, C. Naccache, Zeolites 1989, 9, 54–58; c) S. J. Cho,
S. M. Jung, Y. G. Shul, R. Ryoo, J. Phys. Chem. 1992, 96, 9922–9927;
d) L. E. Pedersen, J. H. Lundsford, J. Catal. 1980, 61, 39–47.
[20] C. E. Boman, Acta Chem. Scand. 1970, 24, 116–122.
[21] B.-Z. Zhan, M. A. White, T.- K. Sham, J. A. Pncock, R. J. Doucet, K. V. R.
Rao, K. N. Robertson, T. S. Cameron, J. Am. Chem. Soc. 2003, 125, 2195–
2199.
Lçffler, M. Muhler, J. Catal. 2001, 202, 296–307; c) J. Wang, C. Y. Fan, Q.
Sun, K. Reuter, K. Jacobi, M. Scheffler, G. Ertl, Angew. Chem. 2003, 115,
2201–2204; Angew. Chem. Int. Ed. 2003, 42, 2151–2154.
[26] N. Kaufherr, M. Dufaux, J. Bandiera, B. Imelik, ACS Symp. Ser. 1977, 40,
538–548.
[27] M. Newville, J. Synchrotron Radiat. 2001, 8, 322–324.
[28] B. Ravel, M. Newville, J. Synchrotron Radiat. 2005, 12, 537–541.
[29] M. P. Yurawecz, J. K. G. Kramer, O. Gudmundsen, M. W. Pariza, S. Banni,
Advances in Conjugated Linoleic Acid Research, Vol. 3, AOCS Press, Cham-
paign, 2006.
[22] J. Horiuti, M. Polanyi, Transactions of the Faraday Society 1934, 30,
1164–1172.
[30] O. Berdeaux, L. Voinot, E. Angioni, P. Juaneda, J. L. Sebedio, J. Am. Oil
Chem. Soc. 1998, 75, 1749–1755.
[23] H. Pines, W. M. Stalick, Base Catalyzed Reactions of Hydrocarbons and Re-
lated Compounds, Academic Press, New York, 1977.
[31] A. Bernas, N. Kumar, P. Mꢃki-Arvela, B. Holmbom, T. Salmi, D. Y. Murzin,
Org. Process Res. Dev. 2004, 8, 341–352.
[24] P. A. Jacobs, Carboniogenic Activity of Zeolites, Elsevier, Amsterdam,
1977.
[25] a) H. Over, Y. D. Kim, A. P. Seitsonen, S. Wendt, E. Lundgren, M. Schmid,
P. Varga, A. Morgante, G. Ertl, Science 2000, 287, 1474–1476; b) H. Mad-
havaram, H. Idriss, S. Wendt, Y. D. Kim, M. Knapp, H. Over, J. Abmann, E.
Received: January 12, 2011
Published online on April 19, 2011
ChemSusChem 2011, 4, 757 – 767
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemsuschem.org
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