Catalytic isomerisation of α-pinene oxide in the presence of ETS-10 supported ferrocenium ions

Article abstract of DOI:10.1016/j.jorganchem.2015.05.026

Ferrocenium ions, [Fc]⁺, have been immobilised in the microporous titanosilicate ETS-10 by ion exchange of Na⁺/K⁺ ions under hydrothermal conditions. The resultant hybrid inorganic-organometallic (ETS-10/[Fc]⁺) material was characterised by elemental analysis, diffuse reflectance UV-Vis spectroscopy, FT-IR spectroscopy, powder X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis. The ETS-10/[Fc]⁺ sample was tested as a catalyst for the isomerisation of α-pinene oxide (PinOx) at 35 C. With α, α, α-trifluorotoluene (TFT) as solvent, campholenic aldehyde (CPA) was the main product formed in 38% yield at 100% conversion and 30 min reaction. Other reaction products included trans-carveol, iso-pinocamphone and trans-pinocarveol. The same PinOx conversion and CPA yield could be reached within 1 min reaction time by increasing the reaction temperature (to 55 °C) and the Fe:PinOx molar ratio. Other solvents (hexane, CH₃CN, toluene) led to poorer results than TFT. Characterisation of the used catalyst, together with an analysis of the catalytic activity of the liquid phase obtained after contact of ETS-10/[Fc]⁺ with TFT, indicated that the ETS-10/[Fc]⁺ sample was resistant toward leaching of iron-containing active species. When the recovered solid was reused in a second batch run, catalytic activity was lower than in the first run, while selectivity to CPA was higher.

Full text of DOI:10.1016/j.jorganchem.2015.05.026

Journal of Organometallic Chemistry 791 (2015) 66e71
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Catalytic isomerisation of
a-pinene oxide in the presence of ETS-10
supported ferrocenium ions
*
~
Sofia M. Bruno, Ana C. Gomes, Ana C. Coelho, Paula Brandao, Anabela A. Valente ,
Martyn Pillinger, Isabel S. Gonçalves*
ꢀ
Department of Chemistry, CICECO e Aveiro Institute of Materials, University of Aveiro, Campus Universitario de Santiago, 3810-193 Aveiro, Portugal
a r t i c l e i n f o
a b s t r a c t
Ferrocenium ions, [Fc]þ, have been immobilised in the microporous titanosilicate ETS-10 by ion exchange
of Naþ/Kþ ions under hydrothermal conditions. The resultant hybrid inorganic-organometallic (ETS-10/
[Fc]þ) material was characterised by elemental analysis, diffuse reflectance UVeVis spectroscopy, FT-IR
spectroscopy, powder X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis.
Article history:
Received 10 March 2015
Received in revised form
30 April 2015
Accepted 4 May 2015
Available online 22 May 2015
The ETS-10/[Fc]þ sample was tested as a catalyst for the isomerisation of
With
a
-pinene oxide (PinOx) at 35 ꢀC.
a,a,a-trifluorotoluene (TFT) as solvent, campholenic aldehyde (CPA) was the main product formed
in 38% yield at 100% conversion and 30 min reaction. Other reaction products included trans-carveol, iso-
pinocamphone and trans-pinocarveol. The same PinOx conversion and CPA yield could be reached within
1 min reaction time by increasing the reaction temperature (to 55 ꢀC) and the Fe:PinOx molar ratio. Other
solvents (hexane, CH3CN, toluene) led to poorer results than TFT. Characterisation of the used catalyst,
together with an analysis of the catalytic activity of the liquid phase obtained after contact of ETS-10/
[Fc]þ with TFT, indicated that the ETS-10/[Fc]þ sample was resistant toward leaching of iron-containing
active species. When the recovered solid was reused in a second batch run, catalytic activity was lower
than in the first run, while selectivity to CPA was higher.
Keywords:
ETS-10
Ferrocenium
a
-pinene oxide
Isomerisation
Campholenic aldehyde
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
Furthermore, ETS-10 has been shown to be active in the photo-
catalytic decomposition of organic compounds [10e15]. Surpris-
ETS-10 (Engelhard Titanosilicate Structure 10) is a crystalline
titanosilicate possessing three-dimensional pore system of
ingly, few studies have employed ETS-10 as a catalyst support. Most
of these center around the immobilisation of nobel metal nano-
particles (NPs), e.g. Pt NPs in NOx mediated carbon oxidation [16]
and n-hexane reforming [17], Ag NPs for bactericidal activity [18],
Au NPs for oxidation of 1-phenylethanol with oxygen [19], and Ru
NPs for the dry reforming of methane [20].
a
elliptical channels defined by 12-membered rings with a maximum
pore diameter of 7.6 Å [1,2]. The framework structure, which was
solved by Anderson et al. [3], consists of corner-sharing TiO6
octahedra and corner-sharing SiO4 tetrahedra. Each titanium atom
contributes a net negative charge of ꢁ2 that is compensated by
extraframework charge-balancing cations (Naþ and Kþ in the as-
synthesised material). The OeTieOeTieO (titania) chains in ETS-
10 can be considered as one-dimensional semiconducting quan-
tum wires embedded inside an insulating matrix of SiO2. ETS-10
containing alkali cations exhibits catalytic activity for base-
catalysed reactions such as the dehydration of tert-butanol [4],
the dehydrogenation of alcohols [4,5], the aldol condensation of
acetone [6], the transesterification of soybean oil [7], the isomer-
We recently reported that ferrocenium ions, [Fe(C5H5)2]þ
([Fc]þ), could be incorporated into ETS-10 by ion-exchange [21]. To
the best of our knowledge, this was the first report describing the
use of ETS-10 as a support for an organometallic species. The
successful encapsulation of [Fc]þ in ETS-10 is not surprising when
the pore size characteristics of the support are examined in detail.
Thus, a study on the photocatalytic activity of ETS-10 for the
conversion of organic substrates with different molecular widths
[13], backed up by theoretical analysis of the ETS-10 structure [22],
indicates that the pore limiting diameter of ETS-10 is about 5.6 Å.
This is almost an exact match with the shortest dimension of the
[Fc]þ ion, which can be considered a cylinder with dimensions of
6.8 Å ꢂ 5.65 Å [23]. Indeed, it is known, for example, that the
isation of
D-glucose [8], and Knoevenagel condensation [9].
* Corresponding authors.
E-mail addresses: atav@ua.pt (A.A. Valente), igoncalves@ua.pt (I.S. Gonçalves).
http://dx.doi.org/10.1016/j.jorganchem.2015.05.026
0022-328X/© 2015 Elsevier B.V. All rights reserved.

S.M. Bruno et al. / Journal of Organometallic Chemistry 791 (2015) 66e71
67
ferrocenium cation can fully penetrate the cavity of the organic
host cucurbit[7]uril [24], which has a cavity opening diameter of
5.4 Å [25], to form a highly stable inclusion complex.
Ferrocenium salts such as [Fc]PF6 have attracted some interest
as catalysts, especially for reactions promoted by Lewis acids, e.g.
the DielseAlder reaction [26], aminolysis of epoxides [27], cyano-
silyation of carbonyl compounds [28], Strecker reactions of ketones
and aldehydes [29], Mannich reaction of aldehydes, anilines, and
(0.50 g), ferrocenium hexafluorophosphate (0.25 g, 0.76 mmol) and
millipore deionised water (20 mL), and the mixture heated in an
oven at 100 ꢀC for 19 h. The resultant blue solid was isolated, washed
with water (4 ꢂ 30 mL), acetone (4 ꢂ 30 mL), and finally vacuum-
dried. Anal. Calcd for Na0.5K0.3(C10H10Fe)0.4(H3O)0.8[TiSi5O13]$
0.5H2O: C, 9.27; H, 1.44; Fe, 4.31. Found: C, 9.25; H, 1.60; Fe, 4.3%.
Selected FT-IR (KBr, cmꢁ1):
n
¼ 3446 (br), 3155 (w), 3128 (w), 1639
(m), 1423 (m), 1025 (vs), 982 (sh), 858 (sh), 763 (s), 551 (s), 501 (w),
431 (s), 384 (m), 323 (w).
ketones to give
ides with alcohols [31]. Recently, we started to explore organo-
metallic complexes for the catalytic isomerisation of -pinene
b-amino-ketones [30], and ring-opening of epox-
a
2.3. Catalytic tests
oxide (PinOx) to campholenic aldehyde (CPA), a reaction that is
usually promoted by Lewis acid catalysts. Encouraging results were
The catalytic reactions were carried out in a magnetically stir-
red, closed borosilicate reaction vessel (10 mL capacity), which was
immersed in an oil bath thermostated at 35 ꢀC. Typically, the
reactor was loaded with catalyst in an amount equivalent to
obtained for the indenyl allyl dicarbonyl derivative (
h
5-Ind)Mo(h3
-Cl)}2]
-
C3H5)(CO)2 [32], the dimeric complex [{(
h
5-Ind)Mo(CO)2(
m
[33] and methyltrioxorhenium(VII) [34]. CPA is useful as an aroma
chemical and as a synthetic intermediate for other aroma chemicals
and also for some pharmaceuticals [35,36]. In particular, CPA is used
in the manufacture of commercial sandalwood-like fragrances, e.g.
Sandalore® and Javanol® (Givaudan), Bacdanol® (IFF), Brahmanol®
(Dragoso) and Polysantol® (Firmenich). The isomerisation of PinOx
is a good test reaction and has been used to probe the Lewis acidity
and catalytic activity of various materials, for example metal-
organic frameworks [37]. We therefore chose this reaction to
probe the catalytic potential of ETS-10-supported ferrocenium ions,
and report the results in this paper.
7.7 mmol of iron, a-pinene oxide (170 mmol) and organic solvent
(0.5 mL). The solvent and catalyst were mixed at 35 ꢀC for 10 min
prior to addition of PinOx (taken as the instant the reaction began).
The course of the reaction was monitored using a Varian 3800 GC
equipped with a BR-5 (Bruker) capillary column (30 m ꢂ 0.25 mm;
0.25 mm) and a flame ionisation detector, using H2 as the carrier gas
and cyclododecane epoxide as internal standard. The reaction
products were identified by GCeMS (Trace GC 2000 Series (Thermo
Quest CE Instruments) - DSQ II (Thermo Scientific)), equipped with
a capillary DB-5 type column (30 m ꢂ 0.25 mm; 0.25
mm) and using
He as carrier gas. After a batch run, the solid phase was separated
from the reaction mixture by centrifugation and washed (3 ꢂ 1 mL)
with n-hexane. For the reaction using TFT as solvent, the recovered
solids were washed with n-hexane or TFT. The solids were dried at
room temperature overnight and then under vacuum (0.1 bar) for
1 h, at 40 ꢀC, giving the recovered solids referred to as ETS-10/
[Fc]þ(W-Hex/run2) and ETS-10/[Fc]þ(W-TFT/run2), respectively.
Contact tests were performed for ETS-10/[Fc]þ by mixing the
material with a solvent (without substrate) at 35 ꢀC for 30 min.
Afterwards, the mixture was centrifuged and the liquid phase was
2. Experimental
2.1. Materials and methods
Ferrocenium hexafluorophosphate (97%), acetone (99%), a,a,a-
trifluorotoluene (TFT; anhydrous, >99%), toluene (anhydrous,
99.8%), acetonitrile (anhydrous, 99.8%), and n-hexane (anhydrous,
95%) were acquired from SigmaeAldrich, and
(PinOx, 97%) was supplied by TCI. ETS-10 was prepared as described
previously [38].
a-pinene oxide
separated using a 0.22 mm PTFE membrane, and transferred to a
Elemental analysis for carbon and hydrogen were performed at
the University of Aveiro using a Leco TruSpec 630-200-200 analy-
ser. Fe contents were determined by ICP-OES at C.A.C.T.I., the Uni-
versity of Vigo, Spain. Powder X-ray diffraction (XRD) data were
collected at ambient temperature using a PANalytical Empyrean
instrument equipped with a PIXcel 1D detector set at 240 mm from
the sample. Cu-Ka1,2 X-radiation. (l1 ¼1.540598 Å; l2 ¼ 1.544426 Å)
filtered with a nickel foil was used along with a standard trans-
mission sample holder. Operating conditions for the X-ray tube
were 45 kV and 40 mA. Intensity data were collected in continuous
separate reactor, where it was preheated at 35 ꢀC for 10 min.
Subsequently, PinOx was added in a molar amount equivalent to
that used under the typical reaction conditions. The solid obtained
from the contact test was vacuum-dried at 40 ꢀC for 1 h, charac-
terised and used in a catalytic batch run.
3. Results and discussion
3.1. Synthesis and characterisation
mode in the ca. 3.5ꢃ 2
q
ꢃ 70ꢀ range, in 0.02ꢀ
2q
steps with a
A
mixture
comprising
ETS-10,
ferrocenium
hexa-
counting time of 50 s per step. Scanning electron microscopy (SEM)
and energy dispersive X-ray spectrometry (EDS) were carried out
on a Hitachi S-4100 microscope. Samples were prepared by depo-
sition on aluminium sample holders followed by carbon coating
using an Emitech K 950 carbon evaporator. Thermogravimetric
analyses (TGA) were performed using a Shimadzu TGA-50 system
with a heating rate of 5 ꢀC minꢁ1 under air. Room-temperature FT-
IR spectra (range 4000e300 cmꢁ1) were recorded with a Mattson
7000 spectrometer, using a globar source, a DTGS detector, and
potassium bromide cells, with 4 cmꢁ1 resolution. Diffuse reflec-
tance (DR) UVeVis spectra were recorded in the range
220e850 nm at ambient temperature using a Jasco V-560 spec-
trometer equipped with a JASCO ISV-469 integrating sphere.
fluorophosphate and water was heated at 100 ꢀC for 19 h in a hy-
drothermal digestion bomb, giving a deep blue solid. This colour is
characteristic of [Fc]þ and the presence of this ion was confirmed by
electronic absorption measurements in the visible region, which
showed an absorption maximum at 618 nm, equal to the absorption
maximum of [Fc]PF6 (Fig. 1). This band is assigned as a ligand-to-
metal chargeetransfer transition. Further proof for the presence
of [Fc]þ ions in the hybrid material ETS-10/[Fc]þ was obtained by
measuring the FT-IR spectrum, which showed the characteristic
bands of [Fc]þ at 3128 and 1423 cmꢁ1, corresponding to the CeH
and C]C stretching modes of the cyclopentadienyl (Cp) ring
(Fig. 2). Whereas the salt [Fc]PF6 exhibits strong bands at 557 and
833 cmꢁ1 due to PFꢁ6 , these bands are absent for the sample ETS-10/
[Fc]þ, which indicates that immobilisation of [Fc]þ ions took place
mainly through ion exchange of Naþ and/or Kþ ions in ETS-10
(Fig. 3). Concerning the bands for the host framework, no signifi-
cant changes occurred in the SieO bands (at about 1025 cmꢁ1),
2.2. Synthesis of ETS-10/[Fc]þ
A Teflon-lined stainless-steel autoclave was charged with ETS-10

68
S.M. Bruno et al. / Journal of Organometallic Chemistry 791 (2015) 66e71
Fig. 3. Ion-exchange scheme showing the structure of ETS-10 (polymorph B) and
ferrocenium ion, [Fc]þ
.
Fig. 1. Diffuse reflectance UVeVis spectra of ETS-10 (e $ e $ e), [Fc]PF6 (e e e e), and
ETS-10/[Fc]þ (eeeee).
constant composition, although some iron rich particles were found.
Average Fe/Ti, Si/Ti and (Fe þ Na þ K)/Ti atomic ratios were 0.45, 5
and 1.2, respectively. Values of 5 and 1.2 were also obtained for the
Si/Ti and (Na þ K)/Ti ratios in the ETS-10 starting material. Micro-
analysis and ICP-OES measurements for ETS-10/[Fc]þ gave a carbon
content of 9.25% and an iron content of 4.3%, which indicate a fer-
rocenium loading of 0.8 mmol gꢁ1. Taking these data together with
the EDS-determined atomic ratios allows us to propose the formula
(Na,K)0.8([Fc])0.4(H3O)0.8[TiSi5O13].0.5H2O for the hybrid material.
while, on the other hand, the TieO stretching mode at 725 cmꢁ1
underwent a shift to 763 cmꢁ1
.
Fig. 4 shows representative SEM images of as-synthesised ETS-10
and ETS-10/[Fc]þ. ETS-10 displays the typical truncated bipyramidal
crystal morphology, with crystal sizes ranging between 2.5 and 5 mm.
The ETS-10/[Fc]þ sample presents similar morphology. EDS analyses
carried out on different crystals of ETS-10/[Fc]þ generally showed a
Fig. 2. FT-IR spectra in the ranges 250e1550 cmꢁ1 and 2750-4000 cmꢁ1 of (a) ETS-10,
(b) [Fc]PF6, and (c) ETS-10/[Fc]þ. The frequencies of selected bands are indicated.
Fig. 4. Representative SEM images of (a) ETS-10 and (b) ETS-10/[Fc]þ
.

S.M. Bruno et al. / Journal of Organometallic Chemistry 791 (2015) 66e71
69
Thermogravimetric analysis of ETS-10/[Fc]þ revealed a weight
loss of 3.4% from ambient temperature to 250 ꢀC, attributed to loss
of water, followed by a loss of 10.6% up to 500 ꢀC, attributed to
decomposition of encapsulated ferrocenium ions (Fig. 5). The TGA
curve for as-synthesised ETS-10 is shown for comparison, and re-
veals a 13.3% weight loss from ambient temperature to 300 ꢀC, but
no mass loss step in the temperature range of 300e500 ꢀC.
Fig. 6 shows the powder XRD patterns of the starting materials
(as-synthesised ETS-10 and [Fc]PF6) and the ETS-10/[Fc]þ sample.
After treatment with [Fc]þ, the reflections characteristic of ETS-10
are maintained at the same positions, although there are signifi-
cant changes in the relative intensities of some peaks. No re-
flections characteristic of [Fc]PF6 are present, providing further
evidence for the successful encapsulation of [Fc]þ ions within the
channels of the titanosilicate host material.
3.2. Catalysis
The ETS-10/[Fc]þ sample was tested as a catalyst for the iso-
merisation of a
-pinene oxide (PinOx), using TFT as solvent, at 35 ꢀC
(Table 1). Campholenic aldehyde (CPA) was the main product
formed in 38% yield at 100% conversion and 30 min reaction
(Scheme 1). Other reaction products included trans-carveol, iso-
pinocamphone and trans-pinocarveol. The turnover frequency
(TOF, calculated from the conversion at 1 min reaction) was 17 mol
ꢁ1
mol minꢁ1. With ETS-10 (without [Fc]þ) as catalyst, the PinOx
Fe
reaction was sluggish (15% conversion at 24 h), and CPA yield was
less than 3%. Hence, the active species which promote the iso-
merisation reaction contain iron. The catalytic performance of ETS-
10/[Fc]þ was compared with that for the ferrocenium salt ([Fc]PF6)
on the basis of the same initial molar ratio Fe:PinOx of 1:22. The salt
[Fc]PF6 led to slightly higher reaction rate and lower CPA selectivity
than ETS-10/[Fc]þ, which may be due to differences in the chemical
nature of the iron species and/or catalyst stability (Table 1).
Increasing the initial Fe:PinOx molar ratio from 1:22 to 1:6.3, and
the reaction temperature from 35 ꢀC to 55 ꢀC, led to similar CPA yield
(38%) at 100% conversion, but in a shorter period of time (1 min,
Fig. 6. Powder XRD patterns of (a) [Fc]PF6, (b) ETS-10, (c) ETS-10/[Fc]þ, (d) ETS-10/
[Fc]þ(W-TFT/run2), (e) ETS-10/[Fc]þ(W-Hex/run2), and (f) ETS-10/[Fc]þ-TFTct
.
Table 1). Several iron based heterogeneous catalysts have been pre-
viously investigated for the isomerisation of PinOx to CPA: iron oxide
supported on TiO2 [39], SiO2 [40], ZreSiO2 [40], mesoporous SiO2 [41]
andMCM-41[42]; iron(II) and iron(III)-containing MCM-41 [43];FeCl3
supported on SiO2 or TiO2 nanoparticles [44]; iron(III)-containing
mesoporous and microporous nickel phosphate molecular sieves
[45]; iron-containing zeolites [46] and iron(III)-containing MOFs [47].
In comparison to titania-supported iron oxide, the results for ETS-10/
[Fc]þ arefairlygood;theformerledto38%CPAyieldat95%conversion,
using cyclohexane as solvent, at 70 ꢀC and 325 min [39].
For ETS-10/[Fc]þ, the type of solvent (TFT, hexane, toluene,
CH3CN) influenced significantly the catalytic reaction (Table 1). The
reaction of PinOx was sluggish with hexane or CH3CN as solvent, at
35 ꢀC. Considerable improvements were observed for toluene or
TFT (higher reaction rates and CPA yields), the latter leading to the
best catalytic results. For all solvents tested, the solids were
recovered and characterised by FT-IR spectroscopy, and exhibited
weak bands attributed to the cyclopentadiene ring of the supported
species (3128 and 1423 cmꢁ1, Fig. 7). The differences in catalytic
results for the different solvents may be due to competitive
adsorption effects, and/or differences in catalyst stability.
In order to check for leaching of active species, a contact test
(described in Section 2.3) was performed for ETS-10/[Fc]þ using TFT
as solvent (without substrate), at 35 ꢀC. The liquid phase obtained
after separating the catalyst by filtration was colourless, suggesting
that no iron-containing species were desorbed from the catalyst
into the liquid phase. The substrate PinOx was added to the liquid
phase obtained from the contact test and the solution was left to
react under typical conditions for 4 h. The results were comparable
with those obtained without catalyst, giving only 10% conversion
and 2% CPA yield, with TFT as solvent. Hence, ETS-10/[Fc]þ seems to
be stable towards metal leaching. The solid obtained from the
contact test of ETS-10/[Fc]þ with TFT (denoted ETS-10/[Fc]þ-TFTct)
Fig. 5. TGA curves of as-synthesised ETS-10 (dd), ETS-10/[Fc]þ (e e e), ETS-10/
[Fc]þ(W-TFT/run2) (e e e), and ETS-10/[Fc]þ(W-Hex/run2) (e $ e).

70
S.M. Bruno et al. / Journal of Organometallic Chemistry 791 (2015) 66e71
Table 1
Catalytic isomerisation of PinOx in the presence of ETS-10/[Fc]þ and [Fc]PF6.
Catalyst
Fe:PinOxa
T/ꢀC
Solvent
Time
Conv. (%)b
CPA Sel. (%)c
ETS-10/[Fc]þ
1:6.3
1:22
1:22
1:22
1:22
1:22
1:22
e
55
35
35
35
35
35
35
35
35
TFT
TFT
Hexane
Toluene
CH3CN
TFT
TFT
TFT
TFT
1 min
1 min/30 min
4 h
24 h
24 h
100
76/100
10
59
19
38
35/38
18
47
28
ETS-10/[Fc]þ
ETS-10/[Fc]þ
ETS-10/[Fc]þ
ETS-10/[Fc]þ
ETS-10/[Fc]þ (W-Hex/run2)d
ETS-10/[Fc]þ (W-TFT/run2)d
ETS-10e
24 h
41
51
4 h/24 h
1 h/24 h
1 min/30 min
56/74
4/15
94/100
62/57
16/15
25/29
f
[Fc]PF6
1:22
a
Initial amount of catalyst based on Fe:PinOx molar ratio.
PinOx conversion at the indicated reaction time.
CPA selectivity at the indicated reaction time.
b
c
d
Catalysts correspondþto the solids recovered after a baþtch run using ETS-10/[Fc]þ as catalyst and TFT as solvent; the used solid was washed with hexane or TFT, and dried at
40 ꢀC, giving ETS-10/[Fc] (W-Hex/run2) and ETS-10/[Fc] (W-TFT/run2), respectively.
e
Catalyst used in a similar mass amount as that used for ETS-10/[Fc]þ
.
f
Catalyst used in a similar molar amount of iron as that used for ETS-10/[Fc]þ
.
was characterised by FT-IR spectroscopy (Fig. 7) and powder XRD
(Fig. 6). The FT-IR spectrum shows bands attributed to the cyclo-
pentadiene ring of the supported species, while the powder XRD
pattern is unchanged from that for ETS-10/[Fc]þ, confirming that
the hybrid material has good stability towards metal leaching un-
der the catalytic reaction conditions used.
hexane or TFT, and vacuum-dried at 40 ꢀC, giving ETS-10/[Fc]þ(W-
Hex/run2) and ETS-10/[Fc]þ(W-TFT/run2), respectively. The
washed and dried solids were characterised and tested in a second
batch run. The FT-IR spectra and powder XRD patterns (Fig. 6) of
ETS-10/[Fc]þ(W-Hex/run2) and ETS-10/[Fc]þ(W-TFT/run2) were
similar to those for the original catalyst ETS-10/[Fc]þ. The PinOx
conversion at 24 h was greater for ETS-10/[Fc]þ(W-TFT/run2) than
for ETS-10/[Fc]þ(W-Hex/run2) (Table 1), suggesting that TFT is a
more efficient solvent than hexane for the catalyst recovery.
However, the reaction for the two solids was slower than for the
original catalyst. TGA (Fig. 5) and elemental analysis (carbon con-
tent of 10 wt%) data for ETS-10/[Fc]þ(W-TFT/run2) were similar to
those for ETS-10/[Fc]þ, suggesting that the catalyst was efficiently
washed and dried, and did not contain reaction products. The same
applies for the solid obtained from the catalytic reaction with
hexane as solvent, washed with hexane and vacuum-dried 40 ꢀC
The solid ETS-10/[Fc]þ-TFTct was tested for the isomerisation of
PinOx under typical conditions, and led to 29% conversion and 44%
CPA selectivity, which was poorer than that observed for the orig-
inal catalyst (76% conversion and 35% CPA selectivity). Possibly, the
chemical nature of the supported iron species changes and/or
active sites are passivated by adsorption of reaction products. PinOx
can undergo cationic ring-opening polymerisation to give ether
polymers [48]. To the best of our knowledge there are no reports on
the polymerisation of PinOx in the presence of iron catalysts.
Nevertheless, in an attempt to improve the catalyst recovery by
simple washing, the solid recovered from a 30 min batch run of the
reaction of PinOx (with TFT as solvent) was washed (W) with
Fig. 7. Selected regions of the FT-IR spectra of the solids recovered after a batch run
using ETS-10/[Fc]þ as catalyst and the solvent (a) TFT, (b) toluene, (c) CH3CN or (d)
Scheme 1. Products formed in the isomerisation of PinOx catalysed by ETS-10/[Fc]þ
.
hexane, and of (e) ETS-10/[Fc]þ-TFTct
.

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E.J.M. Hensen, C. Li, J. Phys. Chem. C 116 (2012) 17124e17133.
71
(carbon content of 9.6 wt%). The lower catalytic activity may be due
ꢀ
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Nevertheless, the CPA selectivity at ca. 75% conversion was greater
for ETS-10/[Fc]þ(W-TFT/run2) than for the original catalyst (57%
and 35% selectivity, respectively, Table 1).
4. Conclusions
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the channels of ETS-10 has been achieved by performing a single
ion exchange cycle with an aqueous solution of ferrocenium hex-
afluorophosphate under hydrothermal conditions. The ETS-10/
[Fc]þ sample exhibited catalytic activity for the liquid-phase iso-
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a-pinene oxide (PinOx), under moderate reaction
conditions (35e55 ꢀC, air). In comparison to the salt [Fc]PF6, the
supported catalyst ETS-10/[Fc]þ was less active, and slightly more
selective to campholenic aldehyde (38% yield at 100% conversion).
The catalyst is stable toward metal leaching, based on contact tests.
However, the used catalyst (washed with TFT and dried) exhibited
lower activity than the original one, suggesting that the chemical
nature of the supported iron species changed. Nevertheless, the
recovered catalyst led to significantly higher CPA selectivity than
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materials based on ferrocenium ions immobilised in porous sup-
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This work was developed in the scope of the project CICECO-
[33] S.M. Bruno, A.C. Gomes, C.A. Gamelas, M. Abrantes, M.C. Oliveira, A.A. Valente,
~
^
Aveiro Institute of Materials [FCT (Fundaçao para a Ciencia e a
Tecnologia) ref. UID/CTM/50011/2013], financed by national funds
through the FCT/MEC and when applicable co-financed by FEDER
(Fundo Europeu de Desenvolvimento Regional) under the PT2020
Partnership Agreement. We acknowledge funding by FEDER
through COMPETE (Programa Operacional Factores de Com-
petitividade) and by national funds through the FCT within the
project FCOMP-01-0124-FEDER-029779 (FCT ref. PTDC/QEQ-SUP/
1906/2012, including the research grant with ref. BPD/UI89/4864/
2013 to A.C.G.). The FCT and the European Union are acknowledged
for a post-doctoral grant to S.M.B. (ref. SFRH/BPD/46473/2008)
cofunded by MCTES and the European Social Fund through the
program POPH of QREN.
~
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3172e3180.
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