New perspectives on polyoxometalate catalysts: Alcohol oxidation with Zn/Sb-polyoxotungstates

Article abstract of DOI:10.1002/chem.201202924

Catalytic belts are the crucial feature of Zn/Sb-polyoxometalates as efficient and selective catalysts for alcohol oxidation. Comprehensive theoretical, analytical, and catalytic studies identify the active role of the Sb atom in the polyoxometalate metal belt. This sheds new light on low-cost catalyst tuning strategies for crucial oxidative transformations.

Full text of DOI:10.1002/chem.201202924

COMMUNICATION
DOI: 10.1002/chem.201202924
New Perspectives on Polyoxometalate Catalysts:
Alcohol Oxidation with Zn/Sb-Polyoxotungstates
Lubin Ni,[a] Jçrg Patscheider,[b] Kim K. Baldridge,*[c] and Greta R. Patzke*[a]
The vast structural variation in polyoxometalates (POMs:
transition metal oxide clusters, preferably of W, Mo, and V)
puts them into the focus of forefront materials and catalysis
research as interfaces between solid-state and molecular
chemistry.[1] Despite POM development for sustainable
energy research and their long-standing use as “green” cata-
lysts, their (trans)formations and catalytic reaction mecha-
nisms remain to be fully explored.[2] Further insight is thus
required for the targeted construction of POM catalysts
from abundant, environmentally friendly, and low-cost ele-
ments. POM-catalyzed alcohol oxidation is a key organic
transformation that has attracted research interest for deca-
des, but on the other hand still poses synthetic and mecha-
nistic challenges.[3] As isolation and characterization of gen-
uine POM-based intermediates and active species remain
difficult, the gap between the increasing number of sand-
wich-type POM catalysts and the elucidation of their reac-
tion pathways increases.[4]
Concerning alcohol oxidation, ample spectroscopic data
have been collected to investigate POM-assisted reaction
mechanisms, but crystallographic and high-end theoretical
evidence has rarely been provided.[5] Herein, we apply a
three-level concept on the synthesis of new Zn/Sb-POM cat-
alysts as a step towards general POM design. First, the dif-
ferent a/b-[Zn2Sb2(B-ZnW9O34)2]14ꢀ catalyst forms are dem-
onstrated with ammonium cations as straightforward struc-
ture-directing agents, thus amplifying the building block po-
tential of the versatile trilacunary [ZnW9O34]12ꢀ moiety in
line with investigations on isostructural Bi-POMs[6b] and
other preceding studies.[3a,b,6,7] Second, crystallographic,
spectroscopic, and catalytic characterizations of their high-
valent a/b-[Zn2SbV (OH)2(B-ZnW9O34)2]12ꢀ analogues is pre-
2
sented to shed new light on the catalytic process. Finally, the
isomerization and catalytic behavior of the newly found
[Zn2Sb2]-POMs and their corresponding SbV species is com-
putationally verified with high-level modeling in solvent en-
vironments.[8] As such, we extend the theoretical elucidation
of POM isomerization processes from classical Keggin[9] or
Wells–Dawson types[10] and gas-phase methods,[11] towards
larger functional POMs in aqueous media. This approach
opens up new strategies for POM catalyst optimization
through chemical tuning of their “metal belt” region.
The isomeric zinc-containing polytungstoantimonate
anions
[Zn2Sb2(B-a-ZnW9O34)2]14ꢀ
and
[Zn2Sb2(B-b-
ZnW9O34)2]14ꢀ as catalysts for H2O2-assisted alcohol oxida-
tion are selectively obtained from the trilacunary precursor
Na9[B-a-SbW9O33]·19.5H2O[12] in the presence of zinc ace-
+
tate using the initial NH4 concentration as an efficient and
straightforward control parameter (see the Supporting Infor-
mation). a-NH4-[Zn2Sb2] (1a) was formed with excess
NH4Cl, whereas the b-isomer was obtained as the sodium
+
salt b-Na-[Zn2Sb2] (2a) at lower NH4 concentrations or in
the absence of NH4+. The compositions of 1a and 2a were
determined as (NH4)10[Zn
ACHTUTNGNERGUN(H2O)6]2AHCTUNGTNER[NGUN Zn2Sb2(B-a-ZnW9O34)2]
·12H2O and Na14A[Zn2Sb2(B-b-ZnW9O34)2]·46H2O, respec-
CTHUNGTRENNUNG
[a] L. Ni, Prof. Dr. G. R. Patzke
Institute of Inorganic Chemistry
University of Zurich
Winterthurerstrasse 190, 8057 Zurich (Switzerland)
Fax : (+41)44-635-6802
E-mail: greta.patzke@aci.uzh.ch
[b] Dr. J. Patscheider
Laboratory for Nanoscale Materials Science
EMPA Dꢀbendorf, 8600 Dꢀbendorf (Switzerland)
[c] Prof. Dr. K. K. Baldridge
Institute of Organic Chemistry
University of Zurich
Winterthurerstrasse 190, 8057 Zurich (Switzerland)
E-mail: kimb@oci.uzh.ch
Figure 1. Combined polyhedral/ball-and-stick representations of a/b-
2A
[Zn2SbIII (ZnW9O34)2]14ꢀ and their corresponding high-valent species a/b-
2A
[Zn2SbV2(OH) (ZnW9O34)2]12ꢀ (Zn=blue, O=red, Sb=pink, H=green;
CTHUNGTRENNUNG
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201202924.
CHTUNGTRENNUNG
photographs: crystal color and morphology).
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tively, from X-ray crystallography data, in combination with
elemental and thermogravimetric analyses (see Table S1 and
Figure S20 in the Supporting Information). Both 1a and 2a
(Figure 1) contain a central belt of four coplanar ZnII and
SbIII cations sandwiched between two [B-a/b-ZnW9O34]12ꢀ
trivacant Keggin subunits. The two six-coordinate Zn atoms
display octahedral environments, whereas the two Sb atoms
exhibit five-coordinate square-pyramidal geometries. Bond
valence sum (BVS)[13] values of zinc (2.04 and 2.15 for 1a,
2.02 and 2.14 for 2a), antimony (3.08 for 1a, 3.04 for 2a),
and tungsten atoms (5.88–6.00 for 1a and 5.82–6.03 for 2a)
are in line with their respective oxidation states of +2, +3,
and +6 (see Table S3 in the Supporting Information).
identical (see Figure S11), indicating the stability of the
POM in solution. The ESI-MS spectra of compounds 1a and
2a in a mixture of deionized water and acetonitrile (80:20)
are very similar and show the presence of the intact [Zn2Sb2-
AHCTNUGERT(GNNNU ZnW9O34)2] cluster with various amounts of associated cati-
ons and water molecules. Two main distributions of peaks
arise from quadruply and quintuply charged species (see
Figures S26 and S27).
Next, the reactivity of catalysts 1a and 2a with hydrogen
peroxide was investigated. The SbV-containing derivatives of
1a and 2a, Na
·28H2O (3) and Na2A
N
[Zn2SbV (OH)2(B-a-ZnW9O34)2]
8ACHTUNGTERNNUNG
2
U
·20H2O (4), were obtained in single crystalline form by
treatment with H2O2 at 858C (see Table S2 in the Support-
ing Information for the crystallographic details).[21] Decolori-
zation of the yellow solution indicates the oxidation of SbIII
centers in 1a and 2a to SbV, likely through attack of H2O2.
Whereas the basic POM frameworks of 1a and 2a remain
unchanged, the coordination geometry of Sb in a-
[Zn2SbV (OH)2] (3) and b-[Zn2SbV (OH)2] (4) is extended
The two newly synthesized isomers 1a and 2a display
flexible isomerization and interconversion processes with b-
Na-[Zn2Sb2] (2a) playing a central role (see the Supporting
Information). In NH4+/Na+-containing solutions, spontane-
ous isomerization of the b-isomer 2a into the a-form 1a
very slowly sets in. Likewise, b-Na-[Zn2Sb2] (2a) equili-
+
brates with a-Na-[Zn2Sb2] (1b) in the absence of NH4 ions.
2
2
Furthermore, b-Na-[Zn2Sb2] (2a) can undergo a cation ex-
from square-pyramidal to octahedral (Figure 1). BVS values
of 4.63 (Sb1), 2.16 (Zn1), 2.29 (Zn2), and 5.88–5.98 (W) in 3
and 1.99, 2.23 (Zn1, Zn2), 4.95 (Sb1), as well as an average
of 5.94 for W in 4 correspond to ZnII, SbV and WVI in both
compounds. Furthermore, BVS values of 0.91 and 0.87 in 3
and 4, respectively, clearly identify O35 as hydroxo ligand
(see Table S4).
+
change into b-NH4-[Zn2Sb2] (2b) upon addition of NH4
.
The isomerization of 2a into 1a or 1b, respectively, is ther-
modynamically favored. Initially, the a- or b-form can be se-
+
lectively accessed by switching the initial NH4 concentra-
tion. Crystal structure details for 1b and 2b are provided in
Table S1 in the Supporting Information.[21]
Calculated energetics of 1a and 2a show a relative energy
difference of approximately 1.0 kcalmolꢀ1, with 1a being the
lower energy form (for details on the computational meth-
ods see the Supporting Information). This energy difference
is commensurate with what one would expect given the de-
scribed experimental isomerization process. The fully opti-
mized structural results were found to be in excellent agree-
ment with the crystallographically determined values. Solid-
state UV/Vis spectra of compounds 1a and 2a show visible-
light absorption (Figure S9) with band gap values of 2.78
(2.65) and 2.88 (2.71) eV, respectively, in relatively good
agreement with computationally predicted values shown in
parentheses.
The phase purity of compounds 1a, 1b, 2a, and 2b ob-
tained in this study was confirmed with PXRD measure-
ments (see Figures S14–S17). Cyclic voltammograms (CVs)
of aqueous solutions of 1a and 2a are strongly pH-depend-
ent (see Figures S21 and S22). The redox signals become
weaker and finally disappear with higher solution pH due to
protonation effects.[14] The quasi-reversible peak (I–I’) be-
tween ꢀ0.5 and ꢀ1.0 V at pH 4.0 corresponds to the redox
processes of the WVI centers. The irreversible oxidation
Solid-state and solution FT-IR spectra of the SbV-contain-
ing compound 3 agree well with the SbIII precursor 1a,
which underlines the oxidative stability of the POM motif
(see Figure S11). In line with the observed color change, the
UV/Vis spectra of POMs 3 and 4 exhibit a considerable
blue shift with respect to those of 1a and 2a (see Figure S9).
PXRD measurements confirm the phase purity of 3 and 4
(see Figures S18 and S19). The CV curves of 3 and 4 are
similar to those of 1a and 2a; however, cyclovoltammetric
determination of the SbIII/SbV redox couple is difficult due
to the electro-inactivity of SbV, which hinders the electron
transfer (see Figures S23 and S24).[16] ESI-MS investigations
of compounds 3 and 4 show that three main distributions of
peaks arise from quadruply, quintuply, and sextuply charged
species. All of the main peaks can be assigned to the expect-
ed {Zn2Sb2(OH)2ACHTNUGTRENGN(U ZnW9O34)2} cluster polyanion with differ-
ent cations and charges (see Figures S28 and S29).
X-ray photoelectron spectroscopy (XPS) of the Sb 3d3/2
peak was employed to confirm the SbV valence state in 3
and 4, as the Sb 3d5/2 peak could not be used due to overlap-
ping with the O1s peak in Sb/O-containing compounds (see
Figure S30a). In addition, Sb 4d is almost entirely masked
by the W 4f line of much higher intensity, and is therefore
not available for analysis. The peak at 540.5 eV is assigned
to the 3d3/2 state of SbV in 3, whereas the peak at 539.7 eV
corresponds to the 3d3/2 state of SbIII in 1a.[17] The binding
energy of the Sb 3d3/2 is slightly shifted due to the different
binding sites of the SbIII and SbV cations in 3 and 1a (see
Figure S30a). 121Sb NMR spectra also support the existence
peak (II’) around 0.27 V is assigned to the oxidation of met-
[15]
allic Sb0 to oxygenic Sb3+
.
FT-IR and Raman spectra of
1a and 2a in the solid state are closely related, and the char-
acteristic peaks are assigned to W–O vibrations (see Figur-
es S10, S12, and detailed assignment in Table S13). POM
stability in aqueous media was confirmed by FT-IR spectro-
scopy and electrospray ionization mass spectra (ESI-MS).
Solid-state and solution FT-IR spectra for 1a are practically
2ACTHNUTRGNEUNG
of a-[Zn2SbV (OH) (ZnW9O34)2]12ꢀ in solution. A solution of
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Polyoxometalate Catalysts
COMMUNICATION
3 in CH3CN displays a strong, broad resonance at 220 ppm
ꢀ
(relative to SbF6 , W1/2 =3600 Hz, Figure S30c). However,
no such signal was detected for SbIII-containing a-NH4-
[Zn2Sb2] (1a), consistent with previous reports.[18]
The formation of high-valent hydroxo species 3 and 4 was
further verified with computational methods. The energetic
preference for a-species 3 over the b-form 4 is larger than
the respective difference between 1a and 2a (ca. 10 kcal
molꢀ1) and the ionization potential for a-[Zn2SbV (OH)2] (3)
2
is also predicted to be 0.6–0.7 eV higher than for 1a and 2a.
Calculated electrophilic HOMO density plots for 1a and 2a
show the highest probability for an electrophilic attack the
vicinity of the SbIII atoms, which are probable targets for
two hydroxyl radicals arising from the homolytic cleavage of
H2O2 that subsequently oxidize SbIII to SbV to form the hy-
droxometal species 3 or 4 and hydroxyl ions (see Figure 2
and Equation (1)).
14ꢀ
a=b-½Zn2SbIII2ðZnW9O34Þ2ꢁ
þ 2 Hþ þ 2 H2O2
!
ð1Þ
a=b-½Zn2SbV2ðOHÞ2ðZnW9O34Þ2ꢁ
þ 2 H2O
12ꢀ
The isomers 1a and 2a exhibit remarkable catalytic activi-
ties for the oxidation of various alcohol types to the corre-
sponding ketones or aldehydes with H2O2 (see Table 1 and
the Supporting Information).[19] Liquid cyclic alcohols are
converted into the corresponding cyclic ketones in high
yields. However, solid cyclic alcohols are less active due to
insufficient homogeneous interaction.[20] Dissolution of 2-
adamantanol in 1,2-dichloroethane partially affords the cor-
responding ketone 2-adamantanone, which could be further
oxidized to 4-oxahomodamatan-5-one through Baeyer–Vil-
liger oxidation due to ring-strain effects. Secondary benzylic
alcohol and propargylic alcohol were also efficiently oxi-
dized. A 1, 3-diol was completely oxidized to yield the 3-
keto alcohol, whereas the effi-
Figure 2. BP86/Def-TZVPP calculated HOMO (left, contour level 0.02)
a) for a-[Zn2Sb2ACTHNUGTRENNUG 2ACHUTNGTRENNGUN
(ZnW9O34)2]14ꢀ and b) for b-[Zn2Sb (ZnW9O34)2]14ꢀ to-
gether with electrophilic density plots (contour level 0.05; blue/red=
highest/lowest probability of electrophilic attack).
high efficiency of catalysts 1a and 2a. Their overall alcohol
oxidation performance ranks equal with industrially attrac-
tive and recently discovered polyoxometalate catalysts.[3c]
After alcohol oxidation was complete, the catalysts could
simply be recycled by phase separation. These catalysts re-
trieved from initial fresh catalysts 1a and 2a still maintain
cient oxidation of 2-hexanol to
Table 1. Oxidation of various alcohols with a-NH4-[Zn2Sb2] (1a) and b-Na-[Zn2Sb2] (2a).[a]
the corresponding 2-hexanone
turned out to be more difficult.
Moreover, we observed no reac-
tivity in the oxidation of pri-
mary alcohols. Only benzyl al-
cohol as an aromatic alcohol
could be oxidized to benzylalde-
hyde and further to benzoic
acid (selectivity 3:2) with either
isomeric catalyst. Combined re-
sults for catalysts 1a and 2a
lead to the following order of
relative activity in alcohol oxi-
dation: benzylic > propargylic,
cyclic, acyclic 1,3-diols > allylic,
primary aromatic > secondary
acyclic @ primary acyclic. Ref-
erence experiments in the ab-
sence of catalyst under identical
Substrate
Alcohol conv. [mol%][b]
Product selectivity [mol%][b]
1a
2a
no catalyst
1a
2a
cyclopentanol
cyclohexanol
cyclooctanol
98
>99
90
99
>99
92
0
6
5
cyclopentanone
cyclohexanone
cyclooctanone
2-adamantanone
4-oxahomoadamatan-5-one
benzaldehyde
benzoic acid
acetophenone
1-phenyl-2-propyn-1-one
2-ethyl-3-oxo-1-hexanol
2-hexanone
100
100
100
80
20
60
100
100
100
50
50
60
2-adamantanol[d]
54
75
21
benzyl alcohol
83
82
0
40
40
1-phenylethanol[c]
1-phenyl-2-propyn-1-ol[c]
2-ethyl-1,3-hexanediol
2-hexanol
>99
88
96
92
14
7
100
100
100
100
100
100
100
100
100
100
>99
23
>99
36
0
0
1-hexen-3-ol
85
90
0
1-hexen-3-one
[a] Reaction conditions: 0.25 mmol substrate, 1.25 mmol (30%) H2O2, 1.0 mmol catalyst, 0.50 mL H2O, 85 8C,
7 h. [b] Organic products were identified and quantified by GC-MS and GC with calibrations using pure corre-
sponding standards and dodecane as an internal standard. [c] 1-Phenylethanol and 1-phenyl-2-propyn-1-ol: 2
molar excess was sufficient. [d] 0.5 mL 1,2-dichloroethane added instead of H2O. Product distributions were
conditions (Table 1) confirm the not significantly affected by carrying out the reactions in N2 atmosphere.
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K. K. Baldridge, G. R. Patzke et al.
their high catalytic activity over five cycles as shown by the
cyclohexanone yields of 98% and 94%, respectively (see
Table S25). However, the presence of 1a or the SbV-contain-
ing derivative 3 in the white-colored recycled catalyst is im-
possible to distinguish with FT-IR methods due to closely
related spectra of both compounds (see Figure S11). Com-
parison of the Sb 3d3/2 XPS regions for recycled samples of
1a and 3, which were regenerated after alcohol oxidation
(Figure S31a), demonstrates identical oxidation states for
both compounds. Furthermore, both recycled 1a and 3 con-
tain SbV as evident from the characteristic peak positions for
the 3d3/2 state of SbV at 540.5 eV and 540.2 eV, respectively
(see Figure S31a).[17] This finding is further corroborated by
comparing the valence band spectra (see Figure S31b),
which show the onset of the density of states at about
1.7 eV for SbIII (reference: Sb2O3), whereas that of SbV (re-
cycled catalysts and reference KSb(OH)6) lies at about 3.1–
3.4 eV.
the isomeric catalysts 1a and 2a is preceded by a long in-
duction period, 3 shows a clean first-order reaction over a
wider range time of 200 min without any induction period
(Figure 3b). This indicates a transformation of pre-catalysts
1a or 2a with H2O2 to form the catalytically reactive species
3 or 4, consistent with the above-mentioned crystal struc-
tures of 3 and 4, which were isolated from the reaction of
1a and 2a with H2O2. Stoichiometric oxidation reactions
with 3 were investigated (Figure 4) and no significant initial
To gain further insight into the catalytic mechanism, ki-
netic model experiments with cyclohexanol and compounds
1a, 2a, and 3 were performed. Both 1a and 2a displayed
sigmoidal curves (Figure 3a), whereas an exponential curve
was recorded for 3. Whereas oxidation of cyclohexanol with
Figure 4. Dependence of the stoichiometric oxidation of cyclohexanol on
the [H2O2]/[cyclohexanol] ratio. Conditions: 1) 0.125 mmol cyclohexanol,
0.0625 mmol a-[Zn2SbV2(OH)2] (3), (0–1.25 mmol) H2O2, 1 mL H2O,
858C, 7 h; 2) 0.125 mmol cyclohexanol, (0–1.25 mmol) H2O2, 1 mL H2O,
858C, 7 h.
stoichiometric oxidation of cyclohexanol was observed with
3 in the absence of hydrogen peroxide. However, treatment
of species 3 with hydrogen peroxide drastically enhances the
catalytic efficiency. The cyclohexanone yield can be im-
proved from around 9% to 93% by increasing amounts of
hydrogen peroxide from 0.25 to 10 equiv relative to cyclo-
hexanol (Figure 4). It is obvious that this oxidation reaction
process is independent of the H2O2 concentration in the ab-
sence of 3 or 4 (Figure 4).
Based on these results, we propose a new catalytic
scheme for alcohol oxidation with hydrogen peroxide cata-
lyzed by 1a or 2a (Scheme 1). Initially 1a or 2a reacts with
hydrogen peroxide to form the high-valent SbV-containing
derivatives 3 or 4, where the induction period observed in
the catalytic oxidation points to an irreversible step. Next, 3
or 4, respectively, are involved in the catalytic cycle as
active catalyst and react further with hydrogen peroxide to
probably form some reactive intermediate. Finally, the SbV
catalyst 3 or 4 can be recycled for new runs, again affording
the corresponding alcohol oxidation products. The conver-
sion of the SbIII-POM 1a into a SbV species 3 after catalysis
and the persistence of SbV in recycled catalysts (see Fig-
ure S31) provide further strong evidence that the catalytic
cycle is initiated and maintained by high-valent SbV com-
pounds 3 or 4. Despite intense efforts, we have not been
able to further monitor and directly isolate any competent
intermediate from 3 or 4 with H2O2 in the catalytic cycle.
Figure 3. a) Kinetic profiles for the oxidation of cyclohexanol catalyzed
by a-NH4-[Zn2SbIII2] (1a), b-Na-[Zn2SbIII2] (2a), and a-[Zn2SbV2(OH)2]
(3). b) Kinetic profile for a-[Zn2SbV2(OH)2] (3) of the first 200 min as a
first-order plot (reaction conditions: 1.0 mmol catalyst: 0.25 mmol alcohol,
1.25 mmol H2O2 (30%), T=858C, yield (%)=[cyclohexanone]/initial [cy-
clohexanol] ꢂ 100%, C0 =initial [cyclohexanol], C=initial [cyclohexa-
nol]ꢀ[cyclohexanone]).
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Polyoxometalate Catalysts
COMMUNICATION
Keywords: alcohol oxidation · antimony · computational
methods · homogeneous catalysis · polyoxometalates
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Scheme 1. Proposed catalytic scheme for alcohol oxidation with catalysts
1a and 3 or 2a and 4.
Such intermediates are probably very short lived, that is,
beyond the detection timescale of conventional FT-IR,
Raman, and NMR spectroscopy. As a consequence, they
have never been identified for POM-assisted oxidations.[4a–c]
Catalytic intermediate isolation thus poses a major physico-
chemical challenge in its own right, which we will tackle as a
long-term goal with advanced time-resolved spectroscopy
methods.
In conclusion, two a/b-isomers of the [Zn2SbIII
-
2
(ZnW9O34)2]14ꢀ polyanion (1a and 2a) were selectively ob-
+
tained by using NH4 as a straightforward inorganic addi-
tive, and both forms showed high catalytic activity for alco-
hol oxidation. The observed spontaneous isomerization of b-
into a-isomer is consistent with high-level theoretical studies
in solution environments. The catalytic cycle proceeds via
2ACTHNUTRGNEUNG
their respective a/b-[Zn2SbV (OH) (ZnW9O34)2]12ꢀ high-
2
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valent SbV-containing derivatives 3 and 4.
Complementary crystallographic and analytical evidence
together with computational results shed new light on the
still unknown pathways of POM-catalyzed alcohol oxida-
tion. The introduction of active Sb centers into the “belt”
region of sandwich-type POM catalysts opens up the possi-
bility to strategically replace noble metals with low-cost
components. We will further develop this comprehensive ap-
proach towards informed POM catalyst design for urgent
applications in “green” synthetic and energy technologies.
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Acknowledgements
This work was supported by the Swiss National Science foundation
(SNSF Professorship PP00P2_133483/1 and Sinergia Grant No.
CRSII2_136205/1) and by the University of Zurich. L. N. thanks the Chi-
nese Scholarship Council for a PhD fellowship. We are grateful to Dr.
Thomas Fox (University of Zurich) for NMR measurements. We thank
Dr. Urs Stalder and Dr. Laurent Bigler (University of Zurich) for ESI-
MS measurements.
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K. K. Baldridge, G. R. Patzke et al.
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Received: August 15, 2012
Published online: && &&, 0000
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Chem. Eur. J. 0000, 00, 0 – 0
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These are not the final page numbers!

Polyoxometalate Catalysts
COMMUNICATION
Polyoxometalates
L. Ni, J. Patscheider, K. K. Baldridge,*
G. R. Patzke* ................. &&&& — &&&&
New Perspectives on Polyoxometalate
Catalysts: Alcohol Oxidation with Zn/
Sb-Polyoxotungstates
Catalytic belts are the crucial feature
of Zn/Sb-polyoxometalates as efficient
and selective catalysts for alcohol oxi-
dation. Comprehensive theoretical,
analytical, and catalytic studies identify
the active role of the Sb atom in the
polyoxometalate metal belt. This sheds
new light on low-cost catalyst tuning
strategies for crucial oxidative transfor-
mations.
Chem. Eur. J. 2012, 00, 0 – 0
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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These are not the final page numbers!