Nanoceria as a recyclable catalyst/support for the cyanosilylation of ketones and alcohol oxidation in cascade

Article abstract of DOI:10.1016/j.jcat.2020.09.032

The cyanosilylation of carbonyl compounds is a fundamental reaction in organic synthesis, to give cyanohydrins. Ketones are particularly reluctant to cyanosilane addition and require the action of a catalyst, and despite many soluble Br?nsted and Lewis ac

Full text of DOI:10.1016/j.jcat.2020.09.032

Journal of Catalysis 392 (2020) 21–28
Contents lists available at ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Nanoceria as a recyclable catalyst/support for the cyanosilylation of
ketones and alcohol oxidation in cascade
Francisco Garnes-Portolés a,1, Miguel Ángel Rivero-Crespo a,b,1, Antonio Leyva-Pérez a,
⇑
a Instituto de Tecnología Química (UPV-CSIC), Universidad Politècnica de València-Consejo Superior de Investigaciones Científicas, Avda. de los Naranjos s/n, 46022 Valencia, Spain
b Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology (ETH) Zürich, Vladimir-Prelog-Weg 1-5/10. 8093 Zürich. Switzerland2
a r t i c l e i n f o
a b s t r a c t
Article history:
The cyanosilylation of carbonyl compounds is a fundamental reaction in organic synthesis, to give
cyanohydrins. Ketones are particularly reluctant to cyanosilane addition and require the action of a cat-
alyst, and despite many soluble Brönsted and Lewis acids have been employed for this task, it is difficult
to find in the open literature catalytic solids able to carry out the reaction. Here, we show that commer-
cially available nanoceria catalyzes the cyanosilylation of different ketones (21 examples) at tempera-
tures between 0 and 50 °C, in high yields, under solventless conditions if required. The nanoceria
network atoms act in a cooperative way to provide a bifunctional acid-base solid catalyst for the cyanosi-
lylation reaction. The amorphization of nanoceria during reaction, due to acid release, does not hamper
the catalytic activity and, indeed, different types of nanoceria, even with supported metal nanoparticles
on surface, are active for the reaction, enabling extensive reuses after air calcination and the use of the
catalytic material for the aerobic oxidation of alcohols / cyanosilylation reaction.
Received 3 September 2020
Revised 25 September 2020
Accepted 26 September 2020
Available online 8 October 2020
Keywords:
Nanoceria
Catalysis
Cyanosilylation
Aerobic oxidation of alcohols
Cyanohydrins
Ó 2020 Elsevier Inc. All rights reserved.
1. Introduction
conjugated base, respectively [6]. This mechanism may, in princi-
ple, also occur on the surface of a bifunctional solid, such as a sim-
The cyanosilylation of carbonyl compounds is the method of
choice to synthesize cyanohydrins [1], versatile synthetic interme-
diates in organic synthesis with further reactivity through three
adjacent functional groups: the cyano, silyl and carbonyl groups
[2]. For instance, the cyanosilylation reaction is used in the phar-
maceutical and agricultural industry to synthesize the pesticide
Fenvalerate A and some non-steroid anti-inflammatory drugs,
among others [3]. While aldehydes react with trimethylsilyl cya-
nide (TMSCN) without the need of a catalyst under certain condi-
tions [4], ketones are more difficult to activate and always
require the presence of a catalyst. For that reason, a wide variety
of soluble Lewis acids have been employed to catalyze the cyanosi-
lylation of ketones [1], habitually under heating conditions, and
despite the plethora of catalytic systems reported for this reaction
so far, it is difficult to find a solid catalyst able to efficiently per-
form the cyanosilylation of ketones at 25 °C or below [5].
ple metal oxide [6b,c], provided that the latter shows the strong
acidity required to activate the carbonyl group towards the
cyanosilane [7]. Such an acid strength is not easy to achieve in a
simple metal oxide, particularly for ketones, and besides, the step-
wise cyanosilylation reaction releases corrosive HCN along the
reaction, which may modify the structure of the metal oxide [8].
These drawbacks explain why only a reduced number of simple
metal oxides catalyze the cyanosilylation reaction [9].
The advent of nanomaterials has brought new catalytic proper-
ties into old macroscopic solids [10,11]. Regarding metal oxides,
when the size is reduced to the nanoscale, the metal site can be
more accessible to external reagents by combining a higher solid
surface area and a lower coordination number around the metal
site, often accompanied by the generation of oxygen vacancies in
the solid network [11a]. These new features in nanometal oxides
invited us to explore their use as catalysts for the cyanosilylation
reaction.
The mechanism of the catalytic cyanosilylation reaction is
widely described as an acid-base manifold, where the carbonyl
and the cyanosilane compound are activated by the acid and its
Here we show that a facile, high-yielding, room temperature
cyanosilylation of ketones occurs with different types of crystalline
nanosized cerium oxide as catalysts [12]. The nanoceria shows a
high catalytic activity after calcination, to remove water and car-
bonates strongly adsorbed to the Ce4+ Lewis sites, with concomi-
tant amorphization during use, which nevertheless does not
⇑
Corresponding author.
E-mail address: anleyva@itq.upv.es (A. Leyva-Pérez).
These authors contributed equally to the manuscript.
Current address.
1
2
https://doi.org/10.1016/j.jcat.2020.09.032
0021-9517/Ó 2020 Elsevier Inc. All rights reserved.

F. Garnes-Portolés, Miguel Ángel Rivero-Crespo and A. Leyva-Pérez
Journal of Catalysis 392 (2020) 21–28
hamper the catalytic activity and tolerates extensive reuses. With
this result in hand, the aerobic oxidation of alcohols/cyanosilyla-
tion reaction was performed with Au nanoparticles (NPs) sup-
ported on nanoceria.
then heated at 80 °C for 5 h. After the reaction, acetone was added
and the catalyst was separated by centrifugation. The mixture was
analyzed by GC-MS, and the conversion and selectivity were deter-
mined by GC using n-nonane or n-dodecane as an external stan-
dard. The used catalyst was calcinated at 400 °C for 4 h, and
introduced in a flask (20 mg, 2.4 Au%) with the synthesized ketone
(0.42 mmol) and TMSCN (0.5 mmol), and the mixture was stirred
at 25 °C for 8 h. The products in solution were analyzed by GC-
MS, and conversion and selectivity were determined by GC using
n-nonane or n-dodecane as an external standard.
2. Materials and methods
General. Reagents were obtained from commercial sources
(Merck-Aldrich) and used without further purification otherwise
indicated. Nanosized cerium oxide was purchased from Rhodia
Co. The other nanoceria materials were prepared acording to pre-
viously published methods [13a]. The metal content of the solids
was determined by inductively coupled plasma-atomic emission
spectroscopy (ICP-AES) after disaggregation of the solid in aqua
regia and later dilution, except for nanoceria where H2O2 (30 vol
%) was used instead of the acid mixture. Dried and deaerated sol-
vents were obtained after treatment with purification resins, hav-
ing less than 50 ppm of water. All the products obtained were
characterized by GC-MS, and 1H, 13C NMR, and DEPT were used
in some cases to further confirm the product structure. When
available, the characterization given in the literature was used
for comparison. Gas chromatographic analyses were performed
in an instrument equipped with a 25 m capillary column of 1%
3. Results and discussion
3.1. Cyanosilylation catalyzed by nanoceria
Table 1 shows the results for the cyanosilylation of acetophe-
none 1 with TMSCN 2 after 1 h reaction time, with different cat-
alytic nanomaterials and solvents. It can be seen there that the
reaction does not proceed without a catalyst nor in the presence
of some representative nanoparticulated metal oxides, such as sil-
icoalumina, titania nor zirconia (entries 1–4), but the reaction pro-
ceeds well with commercially available nanoceria catalyst (entry
5), at 25 °C and with n-hexanes as a solvent.
phenylmethylsilicone. GC-MS analyses were performed on a spec-
trometer equipped with the same column as the GC and operated
under the same conditions. NMR were recorded in a 300 MHz
instrument using the appropriate solvent containing TMS as an
internal standard. Absorption spectra in solution were recorded
on open cells in an UV/Vis spectrophotometer. Solid IR spectra
were recorded on a spectrophotometer by previous mixture of
the solid with dried KBr. Thermogravimetric analyses were per-
formed on 0.5–0.8 mm pelletized samples under a dry N2 atmo-
sphere with a thermobalance operating at a heating rate of
10 °CÁminÀ1. N2 adsorption-desorption isotherms were performed
at 77 K on sieved materials after outgassing for 16 h under vacuum.
Electron microscopy studies were performed on a microscope
operated at 100–200 kV after impregnating a dispersion of the
solid sample on a Cu grid and leaving to evaporate for, at least, 4 h.
Typical reaction procedure for cyanosilylation reactions with
nanoceria. In a typical cyanosilylation reaction, 10 to 20 wt% of
nanoceria catalyst was weighed under nitrogen in a 2 ml glass vial
equipped with a magnetic stirrer. Then, 0.3 ml of n-hexanes,
0.25 mmol of carbonyl compound and 0.3 mmol of TMSCN were
added, the vial was capped, and the mixture magnetically stirred
at 25 °C for the indicated time. The final composition of the mix-
ture was analyzed by GC-MS, and the conversion and selectivity
were determined by GC using n-nonane or n-dodecane as an exter-
nal standard.
The solid acids were calcined at 400 °C prior to reaction, since
otherwise no catalysis occurs, and Fig. 1A shows
a high
resolution-transmission electron microimage (HR-TEM) of the cat-
alytic nanoceria after this treatment (higher resolution micro-
images of this commercially available material can be found else-
where) [12d]. The material consists in crystalline NPs of ꢀ7 nm
particle size, without any water adsorbed on surface. Different
organic solvents can be used (entries 5–10), although with less effi-
ciency than n-hexanes, and the same yield of 3 is obtained when
decreasing the amount of nanoceria from 50 to 20 wt% (entries
11–13). A tentative explanation on the solvent effect might be that
the relative concentration of starting materials increases in the
proximity of the catalyst surface when the most apolar solvent of
all the solvents tested, i.e. n-hexanes, is used, which makes the
reaction go faster. This explanation is supported by the fact that
the reaction works faster under neat conditions (see ahead).
Kinetic studies (Fig. S1) show that the yield of 3 nearly achieves
a plateau after 20 min reaction time regardless the amount of solid
catalyst employed (20 and 50 wt%), and filtration at 20% conver-
sion stops the reaction completely, which strongly supports that
the cyanosilylation of 1 is heterogeneously catalyzed by nanoceria
(Fig. S2).
The yield of 3 is further increased by calcination of nanoceria
at > 400 °C (entry 14), regardless if the calcination atmosphere is
air, vacuum or N2, and yields only decrease at calcination temper-
atures > 600 °C (Fig. S3). In contrast, calcination at 600 °C did not
increase the yield of 3 for nanotitania and nanozirconia (entries
3–4 in Table 1). Thermogravimetric analyses show that the weight
loss in nanoceria does not only correspond to the typical adsorbed
water but also to strongly adsorbed species at 500 °C (Fig. S4), and
Typical reaction procedure for the aerobic oxidation of alcohols/-
cyanosilylation reaction catalyzed by Au-nCeO2. The corresponding
alcohol (4.85 mmol) was added over Au-nCeO2 catalyst (200 mg,
1 Au mol%, 30 wt% nCeO2; in cases where the alcohol is solid,
6 ml of hexane were also added, 0.8 M) in a glass reactor equipped
with a stirring bar at 5 bar of O2, and the resulting mixture was
22

F. Garnes-Portolés, Miguel Ángel Rivero-Crespo and A. Leyva-Pérez
Journal of Catalysis 392 (2020) 21–28
Table 1
and
a
shift of the band corresponding to atmospheric CO2
(1690 cmÀ1) [14]. The combined kinetic and IR results suggest that
the removal of adsorbed carbonates is essential for nanoceria to act
as a catalyst in the cyanosilylation of acetophenone 1. Indeed, an
induction time for the reaction was observed when lower calcina-
tion temperatures were employed, which may correspond to the
time required for the desorption of carbonates. Together, these
results strongly support that the Lewis acidity required for the
cyanosilylation reaction is only achieved on the nanoceria surface
after removal of the strongly adsorbed water and carbonate mole-
cules, which may constitute a simple strategy to use nanoceria as a
strong acid catalyst in organic synthesis.
Results for the cyanosilylation reaction of acetophenone 1 with TMSCN 2 catalyzed by
nanoparticulated solid acids, calcined at 400 °C, after 1 h at 25 °C under inert
atmosphere.
Entry
Solid catalyst (wt%)
Solvent
3 (yield, %)
1
None
n-Hexanes
n-Hexanes
n-Hexanes
n-Hexanes
n-Hexanes
Toluene
DCM
Diethyl ether
DMF
0
5
2[a]
3[b]
4[b]
5[c]
6
nanoSiO2ÁAl2O3 (20 wt%)
nanoTiO2 (20 wt%)
nanoZrO2 (20 wt%)
nanoCeO2 (50 wt%)
18 (9)
1 (1)
58
39
27
42
18
7
56
55
26
(67)
(72)
7[d]
8
9[d]
10[d]
11
Fig. 2A shows that the nanoceria catalyst is still very active for
the cyanosilylation of 1 at 0 °C (see also Table 1, entry 14), and
Fig. 2B shows that the reaction can also be run without any solvent,
which is a clear advantage from an industrial point of view, to
achieve a 72% yield after 1 h (see also Table 1, entry 15). Fig. 2C
shows that the used solid catalyst is not active after simple wash-
ings with n-hexanes, and the corresponding FT-IR spectrum
(Fig. S5) shows the appearance of new bands between 1100 and
1450 cmÀ1, assignable to remaining organic impurities, which
may block the active sites and produce the rapid deactivation of
the catalyst at ꢀ60% conversion. Since a simple calcination should
remove these organic impurities, the used nanoceria catalyst was
calcined at 400 °C to recover full activity for, at least, 10 uses, as
shown in Fig. 2D, without any significant depletion of the intrinsic
catalytic activity, as indicated by the similar initial rates. Notice
that a higher calcination temperature is not required to recycle
THF
nanoCeO2 (30 wt%)
nanoCeO2 (20 wt%)
nanoCeO2 (10 wt%)
nanoCeO2 (20 wt%)
nanoCeO2 (20 wt%)
n-Hexanes
n-Hexanes
n-Hexanes
n-Hexanes
–
12
13
14[b,e]
15[b]
[a]
[b]
[c]
[d]
13 wt% alumina.
Between parentheses, result for the solid catalyst calcined at 600 °C.
<5% of 3 with non-calcined solid.
DCM stands for dichloromethane, DMF for N,N-dimethylformamide and THF for
tetrahydrofurane.
[e]
61% and 58% of 3 at 0 °C and 50 °C reaction temperature, respectively.
Fourier-transformed infrared spectroscopy (FT-IR, Fig. S5) shows
the progressive disappearance with the calcination temperature
of the band corresponding to adsorbed carbonates (1384 cmÀ1
)
Fig. 1. High resolution-transmission electron microimages (HR-TEM) of commercially available nanoceria (A) and in-house synthesized ceria nanorods (B), nanooctahedra (C)
and nanocubes (D), after calcination at 400 °C under air.
23

F. Garnes-Portolés, Miguel Ángel Rivero-Crespo and A. Leyva-Pérez
Journal of Catalysis 392 (2020) 21–28
B)
A)
0 ºC
25 ºC
50 ºC
n
-Hex.
No solv.
Time (min)
C)
Time (min)
D)
Fresh catalyst
Washedwith
Calcined at 400 ºC
n
-Hex.
Time (min)
Time (min)
Fig. 2. (A) Kinetics for the cyanosilylation reaction of acetophenone 1 with TMSCN 2 at different reaction temperatures, under inert atmosphere and catalyzed by nanoceria
(20 wt%) calcined at 600 °C. (B) With and without solvent. (C) Reuse of nanoceria after washing or calcination. (D) Yield-time plot for 10 uses of the nanoceria catalyst, after
calcination.
Fig. 3. Initial turnover frequency (TOF0) vs. the Brunauer, Emmett and Teller (BET) surface of the different nanoceria catalysts for the cyanosilylation reaction of acetophenone
1 with TMSCN 2 at 25 °C and under inert atmosphere. Yields refer to 1 h reaction time.
the solid since carbonates are not present any more in the used cat-
alyst according to the FT-IR spectrum, and only organic impurities
must be removed.
These materials were used as catalysts under typical reaction con-
ditions and the results show a decrease of the catalytic activity for
all the doped nanoceria materials tested, thus strongly suggesting
the lack of any catalytic role for oxygen vacancies (Fig. S7). To fur-
The catalytic activity of a nanocrystalline solid often depends on
the crystallographic face exposed to reactants.[13a] To check if that
is the case here, ceria nanorods, nanooctahedra and nanocubes,
which expose on surface the 111, 110, and 100 crystallographic
planes, respectively, were prepared, and representative microim-
ages are shown in Fig. 1B–D (see Fig. S6 for further images and
Table S1 for calcination procedures and corresponding BET surface
areas) [13,15]. The catalytic results for these materials, shown in
Fig. 3, indicate that the catalytic activity linearly correlates with
the total surface area of nanoceria and does not have any apparent
relationship with the exposed face.
´
´
ther confirm this point, 3,3,5,5-tetramethylbenzidine (TMB) was
used as an active radical oxygen species (ROS) indicator for the
nanoceria catalyst before and after the cyanosilylation reaction of
acetophenone 1 with TMSCN 2 [16e]. Absorption UV–visible spec-
troscopic measurements of the solutions (Fig. S8) show the
expected band for protonated TMB at ꢀ 450 nm (a yellow colour
solution is also visible by the naked eye) and the absence of any
band indicative of TMB oxidation with ROS, at 650 nm (blue colour
by the naked eye). This simple test confirms the lack of ROS in
nanoceria during the catalyzed reaction.
Nanoceria is well-known to possess a high number of oxygen
vacancies [16]. However, the fact that the crystalline phase is irrel-
evant for the catalysis here, suggests that oxygen vacancies will
most probably not play any role during the catalytic cyanosilyla-
tion, since a change in the crystalline phase of nanoceria implies
a significant change in the oxygen vacant number (Table S2)
[16a]. To further check this, the number of oxygen vacancies in
nanoceria was increased by doping with different atoms, including
metals (Ga, Sm, Al and Fe) [17] and by treatment with HCl [18].
Once determined that the catalytic activity of nanoceria does
not come from particular crystalline faces nor oxygen vacancies,
the role of Lewis and Brönsted acid sites in nanoceria during the
cyanosilylation reaction was studied. Fig. 4 shows the catalytic
results with nanoceria after addition of 10 mol% of either pyridine
or di-tert-butylpyridine. While the former quenches the Lewis and
Brönsted sites, the latter only quenches the Brönsted sites, and the
results show that both amine bases decrease significantly the cat-
alytic activity of nanoceria, particularly pyridine.
24

F. Garnes-Portolés, Miguel Ángel Rivero-Crespo and A. Leyva-Pérez
Journal of Catalysis 392 (2020) 21–28
Fig. 4. (A) Kinetics for the cyanosilylation reaction of acetophenone 1 with TMSCN 2 after adding different pyridine quenchers (10 mol%), and (B) nanoceria exchanged with
Na+ and exchanged back with H+.
Fig. 4 also shows that if the H+ in nanoceria is exchanged by Na+
[19], the catalytic activity decreases considerably, and this catalytic
activity is partially recovered after exchanging back the H+ cations.
Calcination of nanoceria under a H2 atmosphere prior to reaction
(Fig. S3, right) dramatically decreases the catalytic activity, which
also supports the presence of catalytically active and reducible
Lewis metal sites in nanoceria. These results, together, strongly
suggest that the catalytic activity of nanoceria for the cyanosilyla-
tion reaction comes from both Lewis and Brönsted acid sites [20].
The sharp stopping of the catalytic activity of nanoceria during
the cyanosilylation reaction, at ꢀ60% conversion, could in part be
explained by the deposition of silicon and aminated organic mole-
cules on the acid sites, thus blocking further catalytic cycles [20c].
However, a somewhat unexpected morphological issue was found
during the examination of nanoceria after reaction. Fig. 5 shows a
HR-TEM image with the corresponding energy-dispersive X-ray
spectroscopy (EDS) mapping of a catalytic nanoceria rod after reac-
tion, where an external layer containing a cerium/oxygen ratio
slightly higher than in the bulk can be clearly seen, indicative of
the presence of oxygen vacancies on surface. These catalytically
inactive nanoceria phase, plenty of oxygen vacancies, can be gener-
ated by the release of HCN during reaction, just as HCl does, and
explains the rapid deactivation of the nanoceria catalyst [13a,21].
Indeed, the recovery of the catalytic activity after calcination under
air at 400 °C (see above) supports this explanation, since this air
calcination regenerates the oxygen sites and restore the original
catalytic material [22].
Fig. 6 shows the scope of the cyanosilylation reaction with
TMSCN 2 for different ketones 4–16, using commercially available
nanoceria as a catalyst. The results show that TMS-protected
cyanohydrins with aryl (products 17–18), alkyl (products 22–27)
and alkenyl (products 28–29) substituents can be formed in good
Fig. 5. HR-TEM with energy dispersive X-ray spectroscopy (EDS) of a representative ceria nanorod after reaction. The formation of an amorphous layer around the nanorod,
just where the catalytic events have occurred, is clearly observed. EDS analysis shows a slight increase in the Ce/O ratio of the amorphous area, notice the lower green-to-red
intensity ratio in the amorphous shell, so the generation of catalytically inactive oxygen vacancies can be inferred.
25

F. Garnes-Portolés, Miguel Ángel Rivero-Crespo and A. Leyva-Pérez
Journal of Catalysis 392 (2020) 21–28
Fig. 6. Scope of the cyanosilylation reaction of ketones 4–16 with TMSCN 2 catalyzed by nanoceria at 25 °C for 1 h under inert atmosphere (yields after 24 h reaction time in
parentheses).
to excellent yields. However, electron-donor substituents (prod-
ucts 19–21) tend to hamper the reaction. Indeed, when an
equimolecular amount of anisole is added to the highly reactive
ketone adamantone 14, the formation of the corresponding pro-
duct 27 is nearly stopped (Fig. S9). A Hammett plot with different
substituents in the para-position of acetophenone 1 shows a q > 0,
which corresponds to a nucleophilic reaction, and a clear correla-
tion with the r+ parameters indicates building of positive charge
in the transition state, most probably the activation of the carbonyl
group of the ketone (Fig. S10). The approximation of
q = 0 for
Fig. 7. Scope for the aerobic oxidation of alcohols/cyanosilylation reaction catalyzed by Au/nCeO2 at 25 °C for 5 h under inert atmosphere. Two-step combined GC yields.
26

F. Garnes-Portolés, Miguel Ángel Rivero-Crespo and A. Leyva-Pérez
Journal of Catalysis 392 (2020) 21–28
halide substituents is indicative that the activation of TMSCN 2
takes control at some point on the cyanosilylation rate, in accor-
dance with the expected acid/base mechanism of the reaction.
Acknowledgements
Financial support by MINECO (Spain) (Project CTQ 2017-86735-
P and Excellence Unit ‘‘Severo Ochoa” SEV-2016-0683) is acknowl-
edged. F.G.-P. thanks ITQ for a contract and M.A.R-C. thanks Iber-
drola Foundation for a fellowship.
3.2. Aerobic oxidation of alcohols/cyanosilylation reaction catalyzed by
Au-nCeO2
A sustainable organic synthesis demands the optimization of
chemical steps during reaction, if possible by grouping several
steps in one-pot and, ideally, over a recoverable solid catalyst
[23]. In view that the cyanosilylation reaction proceeds in both cat-
alytic amorphous and crystalline nanoceria, even under air, it was
envisioned here the use of metal-supported nanoceria catalysts as
bifunctional catalysts for the aerobic oxidation/cyanosilylation
reactions [24]. In this way, nanoceria will act as both catalyst
and support, enabling the cyanosilylation reaction after the
metal-catalyzed oxidation reaction. This approach does not only
engage two very different catalytic reactions, i.e. a dehydrogena-
tion reaction mediated by ROS and a typical Lewis acid-catalyzed
reaction [25], but also the activation of the bifunctional solid, since
one single calcination of the solid will concomitantly fix the metal
phase on the nanoceria surface, after impregnation with the metal
precursor, and also activate the nanoceria framework for the
cyanosilylation reaction, thus saving catalyst preparation steps.
Gold NPs on nanoceria (Au/nCeO2, 5 Au wt%), prepared by a
reported procedure with the commercial nanoceria catalyst active
for the cyanosilylation reaction as a support [24a], was chosen as a
model catalyst for the one-pot reaction. First, Au/nCeO2 was tested
in the aerobic oxidation of different alcohols, and the results show
that the corresponding aldehydes and ketones are obtained in
excellent yields with 1 Au mol% (Fig. S11). Then, Au/nCeO2 was
tested as a catalyst for the cyanosilylation reaction of acetophe-
none 1, with the amount of catalyst required for complete alcohol
oxidation (1 Au mol%, 30 nCeO2 wt%) and under optimized condi-
tions (see above), to give 81% yield of cyanohydrin 3, a better yield
than the corresponding bare nanoceria catalyst under the same
reaction conditions (56%). With this encouraging result in hand,
the Au/nCeO2 catalyst was employed for both aerobic oxidation/-
cyanosilylation reactions. The results for different alcohols are
shown in Fig. 7. Good to excellent yields were obtained in most
cases, which demonstrates that two mechanistically different
metal NP- and nanoceria-catalyzed reactions are compatible over
a same metal-supported nanoceria catalyst.
Appendix A. Supplementary material
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.jcat.2020.09.032.
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Nanoceria catalyzes the cyanosilylation of different ketones at
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solventless conditions. After simple calcination, the solid catalyst
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Other inorganic nano-oxides tested did not show this catalytic
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Declaration of Competing Interest
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