Active metal species assembled with heteropoly tungstate anion PW9O34/9- for liquid phase hydrocarbon oxidation

Article abstract of DOI:10.1016/S1381-1169(00)00118-7

Monometallic [Pd₃(PW₉O₃₄)₂]^12-, [Pd₃(PW₉O₃₄)₂Pd_nO_xH_y]^q- (n_av = 3), bimetallic [Pd₂Cu(PW₉O₃₄)₂]^12-, [Pd₂Fe(PW₉O₃₄)₂]^11-, [PdFe₂(PW₉O₃₄)₂]^10- and a mixture of [Pd₃(PW₉O₃₄)₂Pd_nO_xH_y]^q- (n_av = 10) + [(VO)₃(PW₉O₃₄)₂]^9- complexes were prepared and characterized by NMR ³¹P, ¹⁸³W, ⁵¹V, and IR spectroscopy. The complexes were tested in catalysis of O₂ + H₂ reaction and benzene oxidation to phenol with O₂/H₂. All the complexes reacted with H₂ in aqueous solution at room temperature to produce metallic Pd. The rate of reduction was controlled by H₂ diffusion. The rate of H₂ + O₂ reaction for different complexes correlated basically with effectiveness of the reduction with hydrogen. Bimetallic Pd(II)-Fe(III) complexes possessed the most substantial activity in hydroxylation of benzene. Catalytic action of Fe(III)-containing heteropoly tungstates in hydrocarbon oxidations with H₂O₂ was presented.

Full text of DOI:10.1016/S1381-1169(00)00118-7

Ž
.
Journal of Molecular Catalysis A: Chemical 158 2000 429–433
www.elsevier.comrlocatermolcata
Active metal species assembled with heteropoly tungstate
9y
anion PW9O for liquid phase hydrocarbon oxidation
34
L.I. Kuznetsova), N.I. Kuznetsova, L.G. Detusheva, M.A. Fedotov, V.A. Likholobov
BoreskoÕ Institute of Catalysis, Pr. Akademika LaÕrentieÕa 5, 630090 NoÕosibirsk, Russia
Abstract
Monometallic Pd3 PW9O34
12
y
qy
w
Ž
.2x
w
Ž
.
x
Ž . w
where on the average ns3 , bimetallic Pd2Cu-
q
,
Pd3 PW9O34 2PdnOx H y
12y
11
y
10
y
y
Ž
.2x
w
Ž
.2x
w
Ž
.2x
w
Ž
.
x
Ž .
nav f10 q
PW9O34
, Pd2Fe PW9O34
.2x
, PdFe2 PW9O34
complexes were prepared and characterized by NMR 31P, 183 W, 51V and IR spectroscopy. The
complexes were tested in catalysis of O2qH2 reaction and benzene oxidation to phenol with O2rH2. Effectiveness of the
Ž .
and a mixture of Pd3 PW9O34 2PdnOx H y
9
y
wŽ . Ž
VO PW9O34
3
Ž
.
catalytic performance depended on the composition of the complexes. Bimetallic Pd II –Fe III complexes were several
Ž .
times more active in phenol production than Pd II monometallic systems. q 2000 Elsevier Science B.V. All rights reserved.
Keywords: Benzene oxidation; O2rH2 mixture; Palladium II ; Heteropolycomplexes; NMR 31 P; 183 W; 51V
Ž .
Ž .
1. Introduction
and 3 catalyzing dioxygen complete reduction
to water. Overall, process is determined by three
reactions:
Selective oxidation of hydrocarbon substrates
by dioxygen is achieved under mild conditions,
when the process is participated by co-re-
ductant, e.g., hydrogen. Appropriate catalytic
systems are known for hydroxylation of aro-
O2 qH2 s O qH2O
Sq O sSO
O2 q2H2 s2H2O,
whose efficiency depends on a nature of active
species of the catalyst.
We have made an attempt to find connection
between the composition and properties of the
system in catalysis of benzene oxidation using
oxygen–hydrogen mixture. Choosing metal con-
taining heteropoly tungstates, we have been able
to vary the composition of the system.
w
x
matic compounds 1,2 , oxidation of cyclohex-
w x
w
x
ane 3 , and epoxidation of cyclohexene 4,5 .
Typical catalysts consist of a noble metal modi-
fied by other transition metal ions, oxides or
halide anions.
Active species of the catalysts combine dif-
Ž .
ferent functions, which are 1 generation of a
specific form of oxygen through partial reduc-
Ž .
tion of dioxygen with hydrogen, 2 assistance
In our previous study, catalytic systems based
of oxygen transfer to hydrocarbon substrate S,
Ž .
on Pd II complexes with heteropoly tungstate
y
anion PW11O739 were studied in benzene oxida-
w x
Ž .
)
tion 6 . Of the same type Pd II complexes
were precursors of supported catalysts which
Corresponding author. Fax: q7-383-234-2453.
Ž
.
E-mail address: kuznina@catalysis.nsk.su L.I. Kuznetsova .
1381-1169r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved.
Ž
.
PII: S1381-1169 00 00118-7

(
)
430
L.I. KuznetsoÕa et al.rJournal of Molecular Catalysis A: Chemical 158 2000 429–433
operated in liquid-phase oxidation of benzene
3. Results and discussion
w x
and cyclohexane 7 . In the course of this work,
y
we have used PW9O934 anion as a matrix carry-
3.1. Characterization of the complexes
w
x
Ž .
ing three transition metal ions 8,9 . Pd II
Ž .
Ž .
Ž
.
Ž .
Ž .
mono-, bimetallic Pd II –Fe III , Pd II –Cu II
Ž .
and a mixture of Pd II and V V complexes
with this heteropoly anion were prepared and
applied to catalysis.
We selected heteropoly tungstate anion which
could serve as a ligand for palladium and other
metal ions, and at the same time, participate in
the catalytic process. A number of complexes of
12
y
w
Ž
.2 x
the composition M3 PW9O34
are known
Ž .
Ž .
Ž .
for metal ions M s Co II , Cu II , Sn II
8,9,11 . Analogous Pd II complex was also
assumed 9 . We have characterized Pd II com-
plex which was obtained in solution at PW9
2. Experimental
w
x
Ž .
w x
Ž .
Ž .
Monometallic Pd II complexes with the
PW9O934 anion were prepared by adding solid
concentration 0.02 M, a Pd II to PW9 molar
ratio of 3:2 and pHf4. According to NMR 31
y
Ž .
2
q
w
Ž
.4x
Na8HPW9O34 P24H2O to the Pd H2O
so-
P
Ž .
lution in H2SO4 immediately after adding of
Na2CO3 solution until pH 1.6. The mixture was
stirred to dissolving the solid and neutralized to
pH 3.7–4.0 with Na2CO3 solution.
To prepare bimetallic complexes, Pd H2-
and Fe2 SO4 3 or CuSO4, or NaVO3
solutions were mixed before adding heteropoly
data, a signal of the complex y12.45 ppm
comprised 80% of total phosphorus. Admixtures
identified in solution were phosphate anions
5
y
Ž
.
w
Ž
.
x
Ž
.
f0 ppm , Pd PW11O39
y12.8 ppm ,
PW12O40 y15.3 ppm . In NMR 183W spec-
trum Pd II complex concentrated to 0.1 M
PW9 exhibited two signals y69.6 and y85.5
ppm with intensities ratio of 2:1, that confirmed
3
y
w
Ž
Ž
.
2
q
.
O
4x
Ž
.
Ž
.
Ž .
Ž
.
tungstate.
12y
w
Ž
.2 x
In the resulting solutions the concentration of
heteropoly tungstate anion was 0.02 M, the total
the structural type of M3 A-a-PW9O34
w
x
9,11 . Of this type, complexes have three
Ž .
Ž
. Ž
Ž .
concentration of Pd II plus Fe III or Cu II ,
metal–oxygen polyhedron located between two
y
Ž ..
or V V was 0.03 to 0.06 M.
A-a-PW9O934 fragments: each M atom is
5
y
w
Ž
.x
Preparation of Pd PW11O39
complexes
bonded to four oxygen atoms of both heteropoly
anions; water molecule or another particles may
occur as additional ligands of M.
w x
was previously described in Ref. 6 .
10y
w
Ž
. x
Pd2WO AsW9O33 2
was prepared as de-
14y
w
x
w
x
Ž .
scribed in Ref. 10 by mixing As2W19O67
No Pd II hydroxide and, from the other hand,
the same NMR 31P signal y12.45 ppm were
2
q
w
Ž
.4x
and Pd H2O
solutions and neutralizing to
Ž
.
Ž .
observed at a Pd II to PW9 ratio as high as 3:1.
pH 6.5 Na2CO3 . Acidity of the resulting solu-
tion was adjusted to pH 4 by adding H2SO4 just
before catalytic experiments.
w
Ž
That indicated formation of Pd3 PW9-
q
y
.
x
O34 2 Pd3Ox H y
species, which have been
The oxidation reactions were performed in
thermostatic reactor supplied with magnetic stir-
rer and connected to burette for measuring gas
consumption. NMR spectra were registered on a
Bruker MSL-400 spectrometer at room tempera-
ture. The resonance and accumulation frequen-
cies were 161.98 MHz and 0.05 Hz for 31P,
16.67 MHz and 0.05 Hz for 183W, 105.15 MHz
and 20 Hz for 51V. IR spectra of Cs-salts in KBr
were registered on a Specord IR-75 instrument.
precipitated with Csq cations, and P:W:Pd ratio
was conformed by elemental analysis. Addi-
tional palladium ions are, probably, combined
into oligomeric hydroxo fragments, as previ-
Ž .
ously determined for Pd II complexes with
7
y
w
x
w x
anion 6 .
PW11O39
When starting from solutions containing
Ž .
Pd II and the second metal ion, we obtained
10y, 11yor 12y
w
Ž
.2 x
complexes Pdx M3yx PW9O34
for MsFe III , Cu II and xs1 or 2. Insertion
Ž
.
Ž .

(
)
L.I. KuznetsoÕa et al.rJournal of Molecular Catalysis A: Chemical 158 2000 429–433
431
Ž .
of the paramagnetic ions changed the width of
the NMR 31P signal from sharp for the
inated in the absence of Pd II . The rest of
Ž .
phosphorus was found in the Pd II complex
12y
9y
w
Ž
.
2 x
Ž
with PW9O34 anion f10%, dsy12.45
6y
Pd3 PW9O34
According to NMR 31P spectra, the most part
of heteropoly tungstate occurred in bimetallic
complex to broad peak.
.
ppm . Only small amounts of PW9V3O40 iso-
3yn
w
xy
w x
mers and other PW12 V O40
anions 12
yn
n
Ž .
Ž
.
Ž
.
Pd II –Fe III complexes. Issuing from intensi-
were presented -10%, dsy13.2–13.5 ppm .
NMR 51V spectrum of the solution consisted
mainly of one signal at y535 ppm. NMR 183W
spectrum consists of four signals at y72.1,
y87.2, y102, y104 ppm with intensities
ties of the signals y66 and y45 ppm in spectra
Ž .
Ž
.
for Pd II :Fe III : PW9 s1:2:2 ratio and for
Ž .
Ž
.
Pd II : Fe III : PW9 s2:1:2 ratio, the signals
can be assigned to PdFe2 PW9O34
10
y
w
Ž
.2 x
and
.
11
y
w
Ž
.
2 x
Ž
Ž .
Pd2 Fe PW9O34
, respectively. Fe III q
2:1:4:8, the first two of them belong to Pd II
9y
Ž .
PW9O34 solution in the absence of Pd II gave
a broad signal in positive region of chemical
shifts.
complex and the last two can be assigned to a
new complex. There is a little doubt that the
solution contained two monometallic complexes
12y
qy
w
Ž
.
2 x
w
Ž
.
x
Ž .
Bimetallic Pd2Cu PW9O34
complex
Pd3 PW9O34 2 PdnOx H y
probably, according to NMR data, VO -
nav f 10 and,
Ž .
Ž .
wŽ
.
3
formed when Pd II , Cu II and PW9 ions were
taken in ratio of 2:1:2. In the NMR 31P spec-
trum predominated signal at y22 ppm. Minor
signals at approximately y32–39 ppm arised
9
y
Ž
.2 x
PW9O34
in a ratio of approximately 1:10.
Structural type of V V -complex was confirmed
by IR spectrum that was found to be typical to
Ž .
Ž .
w
Ž
.
x Ž .
anions Table 1 .
2
from Cu II monometallic complexes.
M3 PW9O34
w
Ž
.2 x
The structural type M3 PW9O34
prepared bimetallic complexes, as well as over-
of the
3.2. Catalysis
Ž .
stoichiometric Pd II -species was supported by
Ž .
IR spectra. The data of IR spectroscopy for the
The catalytic performance of the Pd II com-
plexes was tested for two oxidation reactions:
complete reduction of oxygen to water and hy-
droxylation of benzene to phenol in two-phase
Ž .
Ž .
Ž
.
Ž .
Ž .
Pd II , Pd II –Fe III and Pd II –Cu II com-
plexes isolated from solution as Cs-salts are
presented in Table 1. Vibration frequencies of
`
Ž
.
P O and W5O bands are identical for the
complexes obtained here and known in the liter-
ature Co II and Sn II compounds. Specific
interaction of different metal ions with the het-
eropoly tungstate was reflected in relative inten-
water–benzene medium Table 2 . These data
should be considered, taking into account the
reducibility of the complexes with hydrogen.
It was determined that the complexes
Ž .
Ž .
12
y
w
Ž
.
2 x
w Ž .
Pd3 PW9O34
,
Pd3 PW9O34 2 Pd3Ox-
q
y
10y
` `
` `
x
w
Ž
.
2 x
w
sities of W O W and W O M bands.
H y , PdFe2 PW9O34
as well as Pd-
2
q
5
When mixing NaVO3, Pd H2O
and
PW11O39 y, and the mixture of two com-
w
Ž
.
4x
Ž
.x
w
PW9O934 in a ratio of 4:2:2, the NMR 31P
spectrum indicated formation of a new complex
giving a signal at y12.3 ppm, that also predom-
plexes Pd 3 PW9O34 2 Pd nOx H y
and
react with H2 in aqueous
y
qy
Ž
.
x
9
y
wŽ
. Ž
.2 x
VO PW9O34
3
solution at room temperature to produce metal-
Table 1
Ž
.
Ž
.
IR spectra of Cs 1–4 - and K 5–6 -salts of the complex anions
y1
y1
`
`
`
O
` `
.
W and W O M
Ž
.
Ž
.
Ž
No.
Composition
n P O , cm
n W5O , cm
n W
Ref.
12y
w
w
w
Ž
.2 x
Ž .
Ž
Ž
Ž
Ž
Ž
Ž
.
.
.
.
.
.
Ž .
945 s
Ž
.
.
.
.
Ž
Ž
Ž
.
.
.
Ž .
Ž .
1
2
3
4
5
6
Pd3 PW9O34
1075 s , 1013 m
Ž .
935 s
Ž .
880 w , 785 vs , 695 m
Present work
11y
Ž
Ž
.2 x
.2 x
Ž
Pd2 Fe PW9O34
Pd2Cu PW9O34
1080 s , 1020 m
885 m , 790 vs , 700 sh
12y
Ž .
Ž .
Ž
Ž
.
Ž .
1073 s , 1015 m
943 s
890 w , 790 vs , 750 sh , 705 sh
9y
wŽ . Ž
.2 x
Ž .
Ž .
Ž
Ž .
VO PW9O34
1070 s , 1045 m
Ž .
950 s
Ž .
790 vs , 700 sh
Ž .
w
w
Ž 3
.2 x
Ž .
w x
12y
Co3 PW9O34
Sn3 PW9O34
1060 s , 1020 m
Ž .
930 s
Ž .
800 vs , 715 s
Ž .
8
12y
Ž
.2 x
Ž
.
Ž .
Ž .
w
x
1074 s , 1025 m
940 s
890 m , 807 s , 758 s ,712 s
11

(
)
432
L.I. KuznetsoÕa et al.rJournal of Molecular Catalysis A: Chemical 158 2000 429–433
Table 2
Ž .
Ž .
Ž .
Data on H2 to H2O I and C6 H6 to phenol II oxidation in the presence of Pd II -containing complexes. Conditions: O2rH2 s1r2, pH 4
Ž
.
Ž . Ž .
I 5 ml of 0.01 M solution of complex, T 208C; II 0.3 ml of 0.01 M solution of complex, 1 ml of
except for 3 , reaction time 1 h;
Ž
.
Ž
.
benzene, T 258C T 208C for 3, 4 ; turnover numbers TN of catalysts were calculated per 1 g-atom of palladium
Ž .
I
Ž .
II
No.
Catalyst composition
Phenol, 106 mol
TN phenol
Ž
.
Ž
.
TN H2O
12y
w
w
w
w
w
w
w
w
w
Ž
Ž
.2 x
1
2
3
4
5
6
7
8
9
Pd3 PW9O34
11
16
34
16
0
3.1
5.2
4.0
1.0
0
5.3
21
15
0.35
0.30
1.30
0.30
0
0.90
3.50
5.0
qy
.
x
Pd3 PW9O34 2 Pd3Ox H y
5y
Ž
.x
.x
Ž
.
Pd PW11O39
Pd PW11O39
Pd2Cu PW9O34
pH 2
5y
Ž
12y
Ž
.2 x
qy
9y
Ž
.
x
wŽ . Ž
.2 x
Pd3 PW9O34 PdnOx H y q VO PW9O34
32
2
3
11y
Ž
.2 x
Pd2 Fe PW9O34
.2 x
10y
10y
Ž
PdFe2 PW9O34
30
0
Ž
.2 x
Pd2WO AsW9O33
1.0
0.15
lic palladium. The rate of reduction was con-
ric data, only 10% to 30% of complexes decom-
posed to produce palladium metal.
Ž
.
trolled by H2 diffusion curves 1, 2 in Fig. 1 .
Based on the amount of the gas consumed,
Ž .
The results of testing Pd II containing com-
Ž .
complete reduction of Pd II was achieved in
plexes in benzene hydroxylation with O2rH2
are also given in Table 2. Inactive in water
Ž .
Ž .
Ž .
Ž
.
Pd II and Pd II –Fe III complexes, whereas in
Pd II –V V system not only complete reduc-
tion of Pd II , but also partial reduction of V V
was observed. Pd2Cu PW9O34
plex of tentative composition Pd2WO As-
reacted very slowly, but the rate
increased with time, probably, because of ap-
12
y
Ž .
Ž .
w
Ž
.
2 x
w
production Pd21C0u PW9O34
and Pd2-
WO AsW9O33 2 ycomplexes possessed very
low if any activity in hydroxylation. On this
basis, it can be assumed that O2rH2 hydroxyl-
ation, as well as formation of water, needs the
presence of Pdo species. As we believe, the
considerable condition for effective hydroxyl-
Ž .
and com-
Ž
. x
12
y
w
Ž
.2 x
w
Ž
10y
.
x
W9O33 2
pearance of metallic palladium catalyzing fol-
Ž
.
lowing reduction curves 3, 4 in Fig. 1 .
As revealed, the rate of H2 qO2 reaction for
Ž
.
different complexes Table 2 correlated basi-
cally with effectiveness of the reduction with
hydrogen. Slowly reduced complexes showed
zero activity in O2 qH2 consumption. Equi-
12
y
w
Ž
.
2 x
Ž .
1
molar solutions of the Pd3 PW9O34
5
y
w
Ž
.
x
Ž .
4 complexes showed
close activity referred to the amount of palla-
and Pd PW11O39
5
y
w
Ž
Ž .
.x
dium, however, Pd PW11O39
prepared in
more acidic solution 3 was more active.
The presence of readily reducible polyhy-
droxo fragments in the complex was a signifi-
cant factor for the H2 qO2 reaction that was
w
responsible for the high activity of Pd3-
q
y
Ž
.
x
Ž .
2
Ž .
Ž .
PW9O34 2 Pd3Ox H y
and Pd II –V V
Fig. 1. Dependence on time of H2 consumption with aqueous
Ž .
w
Ž
.
Pd3 PW9O34 -
2
solutions of heteropolycomplexes.
1
,
—
2
system 6 .
qy
9y
x
wŽ
. Ž
.2 x
w Ž
PdFe2 PW9-
PdnOx H y
.2 x
q
VO PW9O34
—
Ž .
3
In the course of the reaction, all Pd II -con-
taining complexes were kept in solution. After 1
h of reaction, according to the spectrophotomet-
O34 10y, 3 — Pd2Cu PW9O34 12y, 4 — Pd2WO AsW9-
w
Ž
.2 x
w
Ž
O33 10y, pH 4, 0.02 M P 1–3 , 0.04 M As 4 , 208C, Vs5
.2 x
Ž
.
Ž .
cm3.

(
)
L.I. KuznetsoÕa et al.rJournal of Molecular Catalysis A: Chemical 158 2000 429–433
433
ation is stabilizing the Pdo species in solution
Acknowledgements
w x
by means of heteropoly tungstate 6 .
On the other hand, it is well known that
hydroxylation of benzene is participated by an
appropriate oxygen transfer agent. This function
This work was supported by the National
Grant for Leading Scientific Schools of Russian
Ž
.
Federation No. 96-15-97557 .
9
y
w
Ž
. Ž
.2 x
was realized by the VO PW9O34
plex in the system 6 that was more active than
com-
3
Ž .
Ž .
Pd II monometallic complexes. As far as the
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.
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