Oxidation of cyclohexane using a novel RuO2-zeolite nanocomposite catalyst

Article abstract of DOI:10.1139/v03-060

We report the synthesis, using an organic-template-free hydrothermal crystallization method, and catalysis of a new type of nanocomposite material, 1.3 nm-sized RuO₂ particles confined in faujasite zeolite. The zeolite-confined RuO₂ composites were fully characterized with X-ray powder diffraction, Ru K-edge X-ray absorption, and high-resolution transmission electron microscopy. XRD and X-ray fluorescence analysis indicate that the framework is faujasite zeolite with a Si:Al ratio of 1.25. Ru K-edge X-ray absorption near-edge structures indicate that the ruthenium species in the zeolite is Ru(IV) with nearest-neighbor octahedral environments similar to hydrous RuO₂, i.e., distorted RuO₆ . The k ²-weighted extended X-ray absorption fine structure indicates ithat the Ru(IV) species anchored in the zeolite likely form amorphous RuO ₂ with a 2D-chain structure, in which RuO₆ units are connected together by two shared oxygen atoms. TEM shows that the particle size of RuO₂ encapsulated inside the supercages of FAU is about 1.3 nm. The RuO₂-FAU composites display significant catalytic activity in the oxidation of cyclohexane with tBHP under mild (room temperature and 1 atm (1 atm ≡ 101.325 kPa)) conditions. The ketone and alcohol concentration can be as high as 0.26 mol L^-1 in 5 h with 48% peroxide efficiency. The catalyst is stable and reusable. Possible oxidation mechanisms are also discussed.

Full text of DOI:10.1139/v03-060

764
Oxidation of cyclohexane using a novel RuO2–
zeolite nanocomposite catalyst
Bi-Zeng Zhan, Mary Anne White, James A. Pincock, Katherine N. Robertson,
T. Stanley Cameron, and Tsun-Kong Sham
Abstract: We report the synthesis, using an organic-template-free hydrothermal crystallization method, and catalysis of
a new type of nanocomposite material, 1.3 nm-sized RuO2 particles confined in faujasite zeolite. The zeolite-confined
RuO2 composites were fully characterized with X-ray powder diffraction, Ru K-edge X-ray absorption, and high-
resolution transmission electron microscopy. XRD and X-ray fluorescence analysis indicate that the framework is
faujasite zeolite with a Si:Al ratio of 1.25. Ru K-edge X-ray absorption near-edge structures indicate that the ruthenium
species in the zeolite is Ru(IV) with nearest-neighbor octahedral environments similar to hydrous RuO2, i.e., distorted
“RuO6”. The k2-weighted extended X-ray absorption fine structure indicates that the Ru(IV) species anchored in the ze-
olite likely form amorphous RuO2 with a 2D-chain structure, in which RuO6 units are connected together by two
shared oxygen atoms. TEM shows that the particle size of RuO2 encapsulated inside the supercages of FAU is about
1.3 nm. The RuO2–FAU composites display significant catalytic activity in the oxidation of cyclohexane with tBHP un-
der mild (room temperature and 1 atm (1 atm ≡ 101.325 kPa)) conditions. The ketone and alcohol concentration can be
as high as 0.26 mol L–1 in 5 h with 48% peroxide efficiency. The catalyst is stable and reusable. Possible oxidation
mechanisms are also discussed.
Key words: nanocomposite, ruthenium oxide, catalysis, oxidation, zeolite.
Résumé : Faisant appel à une méthode de cristallisation hydrothermique sans gabarit organique on a effectué la syn-
thèse d’un nouveau matériau nanocomposite, des particules de RuO2 d’une taille de 1,3 nm confinées dans un zéolite
de faujasite, et on a examiné ses propriétés comme catalyseur. Les composites de RuO2 confinées dans le zéolite ont
été caractérisés par diffraction des rayons X sur des poudres, absorption de rayons X par l’arête K du Ru et par mi-
croscopie électronique de transmission à haute résolution. L’analyse de la diffraction et de la fluorescence des rayons X
indiquent que le squelette est le zéolite de faujasite avec un rapport de Si:Al de 1,25. Les structures près des rebords
obtenues par absorption de rayons X par l’arête K du Ru indiquent que l’espèce ruthénium du zéolite est le Ru(IV)
avec un environnement octaédrique pour les voisins immédiats, comme dans le cas du RuO2 hydratée c’est-à-dire du
« RuO6 » déformé. La structure fine d’absorption étalée des rayons X indique que l’espèce Ru(IV) ancrée dans le zéo-
lite forme vraisemblablement du RuO2 amorphe avec une structure en chaîne bidimensionnelle dans laquelle les unités
de RuO6 sont reliées entre elles par deux atomes d’oxygène partagés. La méthode « TEM » montre que la taille des
particules de RuO2 encapsulées dans les supercages de FAU est d’environ 1,3 nm. Les composites RuO2–FAU présen-
tent une activité catalytique significative dans l’oxydation du cyclohexane par le tBHP dans des conditions douces
(température ambiante et 1 atm (1 atm ≡ 101.325 kPa)). Les concentrations de cétone et d’alcool peuvent atteindre une
valeur de 0,26 mol L–1 en 5 h, avec une efficacité de peroxyde de 48%. Le catalyseur est stable et peut être réutilisé.
On discute aussi des mécanismes d’oxydation possibles.
Mots clés : nanocomposite, oxyde de ruthénium, catalyse, oxydation, zéolite.
[Traduit par la Rédaction]
Zhan et al. 769
Introduction
catalytic processes for the oxidation of cyclohexane to
cyclohexanol and cyclohexanone (1–9). To achieve satisfac-
tory selectivity (>80%), yield usually must be sacrificed
(~4% conversion) because of free-radical autoxidation pro-
cesses (5). Incorporation of transition metal compounds into
molecular sieves offers one of the most promising ap-
Oxidation of cyclohexane under mild conditions is one of
the most interesting and challenging topics in oxidation
chemistry (1–4). Considerable effort has been made to de-
velop novel homogeneous and heterogeneous catalysts and
Received 19 December 2002. Published on the NRC Research Press Web site at http://canjchem.nrc.ca on 24 June 2003.
Dedicated to Professor Don Arnold for his contributions to chemistry.
B.-Z. Zhan, M.A. White,1 J.A. Pincock, K.N. Robertson, and T.S. Cameron. Department of Chemistry and Institute for
Research in Materials, Dalhousie University, Halifax, NS B3H 4J3, Canada.
T.-K. Sham. Department of Chemistry, The University of Western Ontario, London, ON N6A 5B7, Canada.
1Corresponding author (e-mail: Mary.Anne.White@dal.ca).
Can. J. Chem. 81: 764–769 (2003)
doi: 10.1139/V03-060
© 2003 NRC Canada

Zhan et al.
765
Fig. 1. XRD patterns for synthetic RuO2–FAU composites and
proaches to enhance the selectivity because the free radicals
generated by autoxidation are constrained by the well-
defined porous system. Various metals and metallo-
complexes have been incorporated into zeolites, silicates,
SAPO, ALPO, and mesoporous materials and used as cata-
lysts for alkanes and alkenes oxidation (5–10). Among them,
zeolite-confined metallophthalocyanines have displayed the
attractive activity of cyclohexane oxidation with tBHP at
room temperature (8, 9). However, there are several draw-
backs in these systems, such as the complicated synthetic
procedures and the use of expensive metallo-complexes. De-
velopment of an efficient and recyclable catalyst for alkane
oxidation under mild conditions is still a significant chal-
lenge.
pure FAU. The numbers in parentheses are RuO2 concentrations
in the FAU zeolites in mmol g–1.
Ruthenium compounds have considerable potential for ox-
idation of alkanes and alkenes because of their rich redox
properties (11 oxidation states, ranging from Ru–II to RuVIII
)
(11–13). Recently, RuO2, especially RuO2(110), has been re-
ceiving considerable attention for its extraordinarily high
catalytic activity (14–18). The outstanding catalytic ability
of the RuO2(110) surface is attributed to the existence of
coordinatively unsaturated ruthenium atoms (14–16). Inter-
estingly, a structure similar to RuO2(110) was found in
amorphous hydrous RuO2 (19). Nanomaterials can be novel
catalysts because of the large surface area and the high den-
sity of active sites (20–21). Thus, it is expected that zeolite-
confined hydrous nano-RuO2 could exhibit favourable oxida-
tion chemistry. Recently, we have reported the synthesis of
faujasite zeolites (FAU) with controllable particle size and
surface properties by using an organic-additive-free hydro-
thermal crystallization approach (22, 23). This organic-
additive-free synthetic method makes it possible to synthe-
size zeolite-based host–guest materials in a simple one-step
modification or build-the-bottle-around-the-ship approach
(10), namely directly adding guest molecules into the fresh-
prepared aluminosilicate gel before hydrothermal crystalliza-
tion. Furthermore, FAU zeolites have a unique and well-
defined pore system: ~1.3 nm supercages are tetrahedrally
connected by 12-membered-ring channels with ~0.74 nm
openings (24). Therefore, physically trapped nanoparticles
or molecules with sizes between about 0.74 and 1.3 nm can-
not diffuse out of the supercages unless the strict framework
of the zeolite is destroyed (8–10). In this paper, we report
the synthesis and catalysis of novel nanocomposite materi-
als, viz. faujasite zeolites with confined RuO2 nanoclusters
(abbreviated as RuO2–FAU) with a one-step modification of
the hydrothermal synthetic method for FAU. The catalytic
results indicate that these materials are very efficient and
stable catalysts for cyclohexane oxidation at room tempera-
ture.
at 2θ values of 12.6°, 18.6°, 21.8°, 28.2°, and 33.5°, indicat-
ing the presence of small amounts of NaP-1 zeolite impurity
(25). In comparison with the XRD pattern of pure FAU zeo-
lite, the 2θ values of the diffraction peaks of RuO2–FAU
composites are slightly higher, and they increase with in-
creased RuO2 loading. Figure 2 gives an example of the shift
of the hkl(642) diffraction peak as a function of RuO2 load-
ing. This shift demonstrates encapsulation of RuO2 inside
the cages of FAU zeolite using our hydrothermal crystalliza-
tion method. No new diffraction peaks belonging to RuO2
compounds were found, indicating that the RuO2 in the zeo-
lite is amorphous.
The Ru K-edge X-ray absorption near-edge structures of
all the RuO2–FAU composites resemble those of hydrous
RuO2 (26). This indicates that the ruthenium species in the
zeolite is Ru(IV) with nearest-neighbor octahedral environ-
ments similar to hydrous RuO2, i.e., distorted “RuO6” (19).
It also shows that all the Ru(III) species are oxidized to
Ru(IV) under the hydrothermal synthetic conditions. Fur-
thermore, the k2-weighted extended X-ray absorption fine
structure of RuO2–FAU composites is virtually the same as
that of amorphous RuO2·2.32H2O (26) indicating that the
Ru(IV) species anchored in the FAU zeolite likely form
amorphous RuO2 with a 2D-chain structure, in which RuO6
units are connected together by two shared oxygen atoms
(19). This is consistent with the XRD results. A schematic
structure of a RuO2 nanocluster in FAU zeolite is given in
Scheme 1.
Results and discussion
Figure 3 shows a typical high-resolution transmission
electron microscopy (TEM) image taken at the RuO2–
FAU(0.78) sample. The dark spots, homogeneously distrib-
uted through the sample and not seen in the pure FAU, are
reasonably attributed to the RuO2 particles. Figure 3 clearly
indicates that these particles are very uniform, in the size
range 1.3 0.2 nm. This is the same size as the supercages
of FAU zeolite. Likely the RuO2 nanoclusters are incorpo-
rated into the supercages of FAU zeolite during the hydro-
All the synthesized zeolite-confined hydrous RuO2 sam-
ples were characterized by X-ray powder diffraction as
shown in Fig. 1. The XRD patterns of as-synthesized RuO2–
FAU samples match very well with simulated XRD results
for faujasite zeolites (25). For our sample with the highest
RuO2 loading, RuO2–FAU(1.63) (where the number in
brackets refers to RuO2 concentration in mmol g–1; see the
Experimental section for details), a few weak peaks appear
© 2003 NRC Canada

766
Can. J. Chem. Vol. 81, 2003
Fig. 2. XRD pattern showing the shift of the hkl(642) diffraction
Fig. 3. Typical TEM image of the RuO2–FAU(0.78) composite.
peak of FAU zeolites as a function of RuO2 loading.
loading in the FAU zeolites (entries 2, 3, and 5, Table 1).
This clearly demonstrates that RuO2 incorporated in the
zeolitic framework provides the catalytically active sites for
the alkane oxidation. The turnover number (TON) of RuO2–
FAU(0.15) is about 630, which is close to the best results
(990) achieved with FePcY-PDMS as the catalyst (entry 6,
Table 1), although our oxidation reaction was carried out in
a simple batch reactor (8). Higher RuO2 concentrations can
increase catalytic activity, i.e., cyclohexane conversion, but
give lower TONs because of the partial blockage of zeolitic
channels by the RuO2 nanoclusters. Comparing the cyclo-
hexane conversion, TON value, and peroxide efficiency, we
conclude that the optimum concentration of RuO2 in RuO2–
FAU is ca. 0.78 mmol g–1, e.g., about one RuO2 nanocluster
in every two to three supercages.
Scheme 1. The 2D-chain structure of RuO2 in zeolite.
Cyclohexanol (ol) and cyclohexanone (one) are the pre-
dominant products (about 90 mol%). The one:ol ratio in-
creases from 1.3 in RuO2–FAU(0.15) to 3.3 in RuO2–
FAU(1.63) (entries 2 and 5, Table 1), showing that higher
RuO2 concentration can lead to further oxidation of the alco-
hol to the ketone. The high oxidation activity of RuO2–FAU
is also revealed from the low proportion (<8 mol%) of
cyclohexyl hydroperoxide (CHHP) in the products. The only
observed side product, tert-butyl cyclohexyl peroxide, is rel-
atively minor (<5 mol%). No over-oxidation products, such
as adipic acid, were found. Furthermore, no dicyclohexyl
by-product was found in the oxidation mixture, which con-
trasts with the Ce/silicate catalysts (27). It appears that, be-
cause of the steric constraints imposed by the zeolitic
channels and (or) cages, two cyclohexyl radicals cannot be
created in one channel and (or) cage at the same time. This
provides strong evidence that RuO2 is indeed confined in the
supercages of FAU zeolite. The shape-selectivity of RuO2–
FAU nanocomposites to both substrates and products is also
observed in other catalysis experiments such as the oxidation
of alcohols (26) and alkyl-aromatics.2
thermal crystallization process and the growth of RuO2
clusters is strictly constrained by the rigid zeolitic frame-
work. The encapsulation of nano-RuO2 inside the zeolite is
further confirmed by catalytic results (vide infra). It is esti-
mated that, on average, every 1.3 nm RuO2 cluster contains
five Ru atoms, as deduced from the bond lengths.
All the synthetic RuO2–FAU nanocomposites were em-
ployed as catalysts for cyclohexane oxidation at room tem-
perature using tert-butyl hydroperoxide (tBHP) as the
oxidant. The catalytic oxidation results are given in Table 1,
along with the results of the FePcY-PDMS catalyst (8). Sev-
eral control experiments were carried out to determine the
catalytically active sites of RuO2–FAU catalysts: no catalytic
products were observed when unmodified FAU zeolite was
used as the “catalyst” (entry 1, Table 1), showing that pure
FAU does not have any catalytic activity at room tempera-
ture even in the presence of tBHP. No oxidation products
were detected on mixing cyclohexane with RuO2–FAU with-
out tBHP. In the absence of cyclohexane, tBHP is decom-
posed to tert-butyl alcohol, O2, and a very small amount of
tert-butyl peroxide (t-BuOOt-Bu). Very high catalytic activ-
ity of cyclohexane oxidation was observed using RuO2–FAU
composites as catalysts. Furthermore, cyclohexane conver-
sion was found to increase with increased RuO2 nanocluster
If we assume that 1 mol of ketone product is formed for
every 2 mol of peroxide, the peroxide efficiency is about
48% for both RuO2–FAU(0.78) and RuO2–FAU(1.63) cata-
lysts (entries 3 and 5, Table 1), which is higher than the
observed 35% efficiency in FePcY-PDMS (8). The concen-
2 B.-Z. Zhan, M.A. White, J.A. Pincock. To be submitted.
© 2003 NRC Canada

Zhan et al.
767
Table 1. Catalytic results for cyclohexane oxidation.
Conc.
Effic.
(%)e
TONc
No.
Catalyst
Products (mol%)a
Conv. (%)b
(mol L–1)d
ol
one
CHHP
tBCP
ane
tBHP
1
2
3
4
5
6
FAU
—
39
25
33
—
50
66
56
69
—
8
5
7
5
—
3
5
5
5
—
—
47
74
68
84
—
—
—
36
48
44
48
35
RuO2–FAU(0.15)
RuO2–FAU(0.78)
RuO2–FAU(0.78)f
RuO2–FAU(1.63)
FePcY-PDMS (8)g
4.5
8.6
7.6
9.4
—
630
190
170
100
990
0.13
0.23
0.21
0.26
—
21
(main products are ol + one)
aol = cyclohexanol, one = cyclohexanone, CHHP = cyclohexyl hydroperoxide, tBCP = tert-butyl cyclohexyl peroxide.
bConversion (ane = cyclohexane, tBHP = tert-butyl hydroperoxide).
cTON = turnover number on tBHP per RuO2 nanocluster in 5 h.
dConcentration of ol + one after 5 h of reaction.
eEfficiency of tert-butyl hydroperoxide, i.e., the percentage of peroxide used for substrate oxidation.
fCatalytic results from a third run. After each run, the solid catalyst was separated by centrifugation and then fully washed with acetone and reused for
a next run under the same conditions.
gReaction was carried out with 0.32 g of FePcY-PDMS in a counter-current membrane reaction with 40 mmol of tBHP as a 7% solution in water,
300 mmol of cyclohexane.
tration of one
+ ol with RuO2–FAU(1.63) reached
Ru-oxo oxidation mechanism
0.26 mol L–1 in 5 h at RT (entry 5). Furthermore, RuO2 is
physically occluded in the zeolite supercage, making the cat-
alyst reusable. After reaction, a clear, colorless organic
phase was separated by centrifugation. Leaching of RuO2 in
the filtrate is negligible: the concentration of Ru in the or-
ganic phase is less than 30 ppb (ICP analysis). Further stir-
ring of the organic phase with tBHP did not change the
product composition, showing that trace amounts of Ru did
not cause any oxidation under the experimental conditions,
e.g., RT and 1 atm (1 atm ≡ 101.325 kPa). About 90% of the
reactivity, e.g., the conversion of both ane and tBHP, re-
mained in the third run (entries 3 and 4, Table 1).
The high activity of RuO2–FAU can be related to the oxi-
dation mechanism. A competitive oxidation of C6H12–C6D12
over RuO2–FAU(0.78) catalyst at RT showed an isotopic ef-
fect of kH/kD = 8.3 0.2 (extrapolated to 0% conversion).
This indicates the existence of an electrophilic oxo-species
(e.g., eqs. [1] and [2]) (8, 28). The relative reactivity of pri-
mary, secondary, and tertiary C—H bonds provides further
evidence for the presence of Ru-oxo species. In adamantane
oxidation over RuO2–FAU(0.78) zeolite, we found the ter-
tiary C—H bonds to be 9.7 times more reactive than second-
ary C—H bonds (secondary:tertiary product ratio of 0.31;
statistical factor of 3). This product ratio is significantly
higher than 0.05 with Fenton chemistry and 0.14 for
hydroxyl radicals (29), but remains in the range required for
oxo-chemistry as observed in P-450 and its model systems
(8, 30, 31). However, we cannot rule out a small contribution
from a free-radical pathway (e.g., eqs. [3]–[7]), as we ob-
serve a small amount of CHHP, tBCP, and O2 products in the
cyclohexane oxidation. Quite likely, two competitive oxida-
tion pathways are involved since there are different Ru(IV)
environments in the RuO2–FAU composite catalyst. Looking
at the 2D-chain RuO2 structure, two different coordination
environments of Ru(IV) are found: in a five-Ru-atom RuO2
nanocluster, the two end Ru atoms are completely different
from those three Ru in the middle. Two types of oxygen,
e.g., bridged and terminal, could also be involved in the oxi-
dation process.
[1]
[2]
t-BuOOH + Ru(IV) → t-BuOH + Ru(VI)=O
Ru(VI)=O + C6H12 → Ru(IV) + C6H11OH
Free-radical oxidation mechansim
[3]
[4]
[5]
[6]
[7]
t-BuOOH + Ru(IV) → t-BuOO· + Ru(III) + H+
2t-BuOO· → 2t-BuO· + O2
t-BuO· + C6H12 → t-BuOH + C6H11·
2t-BuO· → t-BuOOt-Bu
t-BuO· + C6H11· → t-BuOOC6H11
Conclusions
We have synthesized a new type of nanocomposite mate-
rial, nanosized RuO2 in a faujasite zeolite, using an organic-
template-free hydrothermal crystallization approach. The
ruthenium encapsulated inside the supercages of FAU is
amorphous hydrous RuO2 with a particle size of 1.3 nm. It
has a 2D-chain structure in which RuO6 units are connected
together by sharing two oxygen atoms (26). The RuO2–FAU
composites display significant catalytic activity in the oxida-
tion of cyclohexane with tBHP under mild (room tempera-
ture and 1 atm (1 atm ≡ 101.325 kPa)) conditions. The
ketone and alcohol concentration can be as high as
0.26 mol L–1 in 5 h with 48% peroxide efficiency. Further-
more, RuO2 is physically trapped in the zeolite supercage,
making the catalyst potentially reusable.
Experimental details
Chemical reagents included fumed silica (11 nm, Sigma),
tetraethylorthosilicate (Aldrich), NaOH (Aldrich), NaAlO2
(Allied Chemical), Al(OH)3 (McArthur Chemical),
RuCl3·3H2O (Aldrich), and RuO2 (A.D. Mackay). All other
organic and inorganic chemicals were reagent grade and
were used without further purification.
© 2003 NRC Canada

768
Can. J. Chem. Vol. 81, 2003
ditions are the same as described above. Without tBHP: the
mixture of 0.1 g RuO2–FAU catalyst, 10 mmol cyclohexane,
and 2 mL acetone was stirred for 5 h. Without cyclohexane:
0.1 g RuO2–FAU catalyst, 4 mmol tBHP, and 2 mL acetone
were mixed together and stirred for 5 h at room temperature.
Reaction products were analyzed with GC.
Synthesis of pure faujasite zeolite
The pure faujasite zeolite was synthesized by hydrother-
mal crystallization in an oil bath with both controllable tem-
perature and stirring rate. Unmodified faujasite zeolite was
synthesized using hydrothermal crystallization methods re-
ported previously (22, 23). Aluminosilicate gel was prepared
by mixing freshly prepared aluminate and silicate solutions
together in the molar ratio 5.5Na2O:1.0Al2O3:4.0SiO2:190H2O.
The powdered products were recovered with centrifugation
and washed with deionized (DI) water until pH < 8, and then
dried at room temperature for 24 h for further characteriza-
tion. X-ray fluorescence analysis showed that the Si:Al ratio
for the 4-day crystallization sample was 1.25, within the
range of 1.0 ~ 1.5 for faujasite-X zeolite.
Isotope effect
The reaction was conducted in sealed vials containing a
mixture of 0.1 g RuO2–FAU catalyst, 5 mmol C6H12,
5 mmol C6D12, 4 mmol tBHP, and 2 mL acetone as solvent.
The reaction products taken at different reaction times were
analyzed and quantified by GC.
Adamantane reaction
Synthesis of RuO2–FAU composites
The reaction was conducted in sealed vials containing a
mixture of 0.1 g RuO2–FAU catalyst, 2 mmol adamantane,
4 mmol tBHP, and 2 mL acetone as solvent. The reaction
products taken at different reaction times were analyzed and
quantified by GC and identified by GC–MS.
The RuO2–FAU nanocomposites were synthesized with
one-step modification to the method for pure FAU, namely
adding RuCl3·3H2O into the freshly prepared aluminosilicate
gel, before hydrothermal crystallization. A measured amount
of RuCl3·3H2O was added to an aluminosilicate gel contain-
ing 5.34 g NaOH, 2.42 g NaAlO2, 3.43 g SiO2, and 50.0 g
H2O. The gel was aged for 2 days and then crystallized at
90°C for 15 h with stirring. The resultant black powder was
separated from solution by centrifugation and then washed
thoroughly with DI water to remove any physically absorbed
species. All the synthesized samples were dried at room
temperature for further characterization and catalytic investi-
gations. ICP–MS analysis indicated that three RuO2–FAU
samples with different RuO2 loadings were synthesized:
RuO2–FAU(0.15), RuO2–FAU(0.78), and RuO2–FAU(1.63),
where the numbers in the parentheses are RuO2 concentra-
tions in the FAU zeolites in mmol g–1. These correspond, re-
spectively, to one RuO2 nanocluster in every ca. 10, 2.2, and
1.1 supercages of FAU (on average, every 1.3 nm RuO2
nanocluster contains five Ru atoms, as deduced from the
bond lengths).
Characterization
X-ray powder diffraction patterns were recorded on a
Rigaku Miniflex System using Cu-Kα radiation, 30 kV,
15 mA with a scanning speed of 1° (2θ) min–1, T = 20°C. Ru
K-edge XAFS measurements were made at the Bending
Magnet Beamline of the PNC (Pacific Northwest Consor-
tium)-CAT (Collaborative Access Team) at the Advanced
Photon Source (APS) at Argonne National Laboratory. APS
is a 7 GeV, third-generation electron storage ring, operating
typically at 100 mA injection current. All the measurements
were conducted in fluorescence mode using a Xe-filled ion
chamber with filter and solar slit arrangements. High-
resolution TEM images were recorded with a FEI Tecnai-12
operated at 80 kV.
Acknowledgements
Cyclohexane oxidation
The oxidation reactions were carried out in sealed vials
containing a mixture of 0.1 g RuO2–FAU catalyst, 10 mmol
cyclohexane, 4 mmol tBHP, and 2 mL acetone as solvent.
The reaction products were analyzed and quantified by GC
after 5 h of room-temperature reaction, and identified by ei-
ther GC–MS or GC with standard samples. All the reactions
were run under aerobic conditions. All the GC analyses were
performed on a Supelco MDN-55 column (30 m × 0.25 mm ×
0.50 µm) with a Perkin-Elmer Auto System GC equipped
with an FID. GC–MS for the product identification was con-
ducted using a Perkin-Elmer Auto System XL GC with a
Perkin-Elmer TurboMass mass spectrometer. Chlorobenzene
was chosen as the internal standard for GC analyses. Cyclo-
hexyl peroxide was converted to cyclohexanol for quantifica-
tion. This was done by reacting the oxidation mixture with
excess triphenyl phosphine at room temperature for 20 min,
followed by GC analysis. The consumption of tert-butyl
hydroperoxide was directly calculated from the GC results.
The authors thank K.V.R. Rao for XAFS assistance. This
work was financially supported by the Natural Sciences and
Engineering Research Council of Canada (NSERC) and the
Killam Trusts (the latter for a postdoctoral research fellow-
ship to BZZ and research professorship to MAW).
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