One-pot synthesis of 2-alkyl cycloketones on bifunctional Pd/ZrO2 catalyst

Article abstract of DOI:10.1016/j.apcata.2021.118107

2-Alkyl cycloketones are essential chemicals and intermediates for synthetic perfumes and pesticides, which are conventionally produced by multistep process including aldol condensation, separation and hydrogenation. In present work, a batch one-pot cascade approach using aldehydes and cycloketones as the raw materials, and a bifunctional Pd/ZrO₂ catalyst was developed for the synthesis of 2-alkyl cycloketones, e.g., cyclohexanone and cycloheptanone. Very high aldehydes (except for paraldehyde with large steric hindrance) conversion and high yields for 2-alkyl cycloketones (e.g., 99 % of conversion for n-butanal and 76 wt.% of yield for 2-butyl cyclohexanone) were obtained at mild temperature of 140 °C. After 10 cycles of reuse, Pd/ZrO₂ catalyst showed slight deactivation (ca. 5 % conversion and 10 % yield losses), due to the coke on the catalyst. However, the performance of the catalyst was completely recovered after an oxidative regeneration.

Full text of DOI:10.1016/j.apcata.2021.118107

Applied Catalysis A, General 616 (2021) 118107
Contents lists available at ScienceDirect
Applied Catalysis A, General
journal homepage: www.elsevier.com/locate/apcata
One-pot synthesis of 2-alkyl cycloketones on bifunctional Pd/ZrO catalyst
2
a
,
b
a
,
a,
b
a,
b
c
a
Weiyang Xue , Bin Gu *, Huiling Wu , Mengyang Liu , Songbo He , Jingmei Li ,
a
a,
Xin Rong , Chenglin Sun *
a
Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 116023 Dalian, China
b
University of Chinese Academy of Sciences, 100049 Beijing, China
c
Green Chemical Reaction Engineering, University of Groningen, Nijenborgh 4, 9747 AG Groningen, the Netherlands
A R T I C L E I N F O
A B S T R A C T
Keywords:
2-Alkyl cycloketones are essential chemicals and intermediates for synthetic perfumes and pesticides, which are
conventionally produced by multistep process including aldol condensation, separation and hydrogenation. In
present work, a batch one-pot cascade approach using aldehydes and cycloketones as the raw materials, and a
One-pot cascade approach
Bifunctional catalyst
Aldol condensation
Hydrogenation
2
bifunctional Pd/ZrO catalyst was developed for the synthesis of 2-alkyl cycloketones, e.g., cyclohexanone and
cycloheptanone. Very high aldehydes (except for paraldehyde with large steric hindrance) conversion and high
Pd/ZrO
2
yields for 2-alkyl cycloketones (e.g., 99 % of conversion for n-butanal and 76 wt.% of yield for 2-butyl cyclo-
2
-Alkyl cycloketone
◦
hexanone) were obtained at mild temperature of 140 C. After 10 cycles of reuse, Pd/ZrO
2
catalyst showed slight
deactivation (ca. 5 % conversion and 10 % yield losses), due to the coke on the catalyst. However, the perfor-
mance of the catalyst was completely recovered after an oxidative regeneration.
1
. Introduction
[4,18–20], 2-heptyl cyclopentanone [21] and biofuel [22–24]. In these
processes, ZrO , Al O , aluminum silicates, and zeolites are the most
2 2 3
Heterogeneous catalysis has several advantages compared to ho-
popular supports due to their suitable acid-base property for aldol
condensation and interaction with noble metals for hydrogenation [19,
25–27].
mogenous catalysis in terms of product separation, catalyst recycle,
equipment corrosion, and environment pollution, etc [1,2]. It is attrac-
tive to develop novel heterogenous processes and catalysts for chemicals
traditionally produced through homogenous processes. Besides, the
application of multifunctional catalysts makes it possible to integrate
those sophisticated multistep reactions into one-pot cascade processes,
which eliminates intermediates separation and other tedious operations
2-Alkyl cycloketones are essential products or intermediates for
synthetic perfumes and pesticides, which are traditionally produced
through multistep method including aldol condensation, separation and
hydrogenation. For example, 2-Butylcyclohexanone (2BCH) is the
essential intermediate for synthesis of 5(6)-decenoic acid, a widely used
milk-like spice in cream, yogurt, strawberry, etc., through the successive
Baeyer-Villiger oxidation, saponification and dehydration (Route I,
Scheme 1) [28,29]. Aldol condensation between n-butanal and cyclo-
hexanone is firstly catalyzed by NaOH aqueous. After acidification,
extraction, and distillation, the separated 2-butenylcyclohexone
[
3–6]. Although it is difficult to optimize efficient multifunctional
groups that selectively or cooperatively work at specific steps onto single
catalyst, as so far, fruitful one-pot processes have been developed in bulk
chemistry, fine chemistry and biochemistry [4,7–10].
Aldol condensation is a fundamental pathway for C = C bond for-
mation, which conventionally applies liquid acid-base catalysts.
Recently, attentions have been drawn by using heterogenous catalysts,
such as solid alkali hydroxide, carbonates, metal oxides, metal-organic
framework and supported KF [11–15]. Unsaturated C = C hydrogena-
tion is also an important reaction in petrochemistry and fine chemistry,
which is mainly catalyzed by e.g., Pd, Pt, Ru, and Ni supported catalysts
=
(2BCH ) is sequentially hydrogenated by Pd/C catalyst to produce
2BCH. The disadvantages of this process, such as vast wastewater
emission (about 15 tons wastewater per ton of 2BCH), severe equipment
corrosion, sophisticated operation, and low conversion and yield, have
afflicted enterprises for a long time. Therefore, the development of green
and simplified synthesis of 2BCH, e.g., by using the one-pot heteroge-
nous system, is necessary.
[
16,17]. One-pot process cascading aldol condensation and hydroge-
nation have been applied to synthesize methyl isobutyl ketone (MIBK)
2
Herein, a bifunctional heterogeneous Pd/ZrO catalyst was prepared
*
Corresponding authors.
E-mail addresses: gubinseven12@dicp.ac.cn, 849716032@qq.com (B. Gu), clsun@dicp.ac.cn (C. Sun).
https://doi.org/10.1016/j.apcata.2021.118107
Received 9 February 2021; Received in revised form 10 March 2021; Accepted 12 March 2021
Available online 16 March 2021
0
926-860X/© 2021 Elsevier B.V. All rights reserved.

W. Xue et al.
Applied Catalysis A, General 616 (2021) 118107
Scheme 1. The conventional homogeneous (Route I, black) and the one-pot cascade heterogeneous (Route II, magenta) synthesis for 2BCH and the side re-
actions (blue).
and applied for 2BCH synthesis through one-pot cascade process (Route
II, Scheme 1), where ZrO provided acid-base sites for aldol condensa-
tion and Pd was active for C = C hydrogenation. The synergistic effect
between ZrO and Pd was investigated. Furthermore, the established
The contents of Pd in the catalysts were measured by inductively
coupled plasma mass spectrometry (ICP-MS) on PerkinElmer NexION
300D apparatus under the Kinetic Energy Discrimination mode (KED).
2
1
13
2
H and C NMR spectras of 2BCH isolated by vacuum distillation
process and catalyst were extended to synthesis of other 2-alkyl cyclo-
ketone homologs and isomers.
and dissolved in CDCl
Avance III.
3
solution were analyzed on 400 MHz Bruker
N
2
physisorption was obtained at 77 K on Quantachrome Quadrasorb
SI. The specific surface areas were calculated using the Brunauer-
Emmett-Teller (BET) method. The total pore volumes (V ) were esti-
mated from the adsorbed amount at a relative pressure (P/P ) of ca.
.98.
CO
was measured on Micromeritics AutoChem 2910 with mass spectrom-
etry detector. Catalysts were saturated by 100 % CO or 10 vol% NH
He (at 50 C and 100 C, respectively) and desorbed at a heating rate of
2
. Experiments
t
2
.1. Materials
o
0
Hexachloroplatinic acid hexahydrate (H
2
PtCl
O) ), ruthenium chloride
, 37 wt.% Ru), and palladium chloride (PdCl , 58 wt.% Pd)
were used as metal precursors. γ-Al and ZrO were obtained from
commercial pseudoboehmite and zirconium hydroxide by calcination at
6
(H
2
O)
6
, 37.5 wt.% Pt),
2 3 2 3
or NH temperature programmed desorption (CO /NH -TPD)
nickel chloride hexahydrate (NiCl
RuCl (H O)
2
(H
2
6
(
3
2
x
2
2
3
/
◦
-1
◦
2
O
3
2
◦
10 C min .
The H temperature programmed reduction (H
on a Finesorb-3010 under the condition of 10 vol% H
2
◦
6
00 C for 4 h. Aluminium silicate, magnesium oxide (MgO), ceria
2
2
-TPR) was measured
balanced with Ar.
(
CeO ), zinc oxide (ZnO), calcia (CaO), titanium oxide (TiO ) and all
2
2
organic reagents were purchased from Macklin Co., Ltd., which are
analytical grade and used without any treatment.
2
.4. One-pot synthesis of 2-alkyl cycloketones from aldehydes and
cycloketones
2
.2. Preparation of catalysts
Take 2BCH as example, 18 g (0.25 mol) n-butanal, 54 g (0.55 mol)
cyclohexanone, and 3.7 g catalysts were added into a 250 mL autoclave.
Pd based catalysts were prepared via a wet impregnation method.
Typically, 10 g powdered carrier was dispersed in 25 mL aqueous so-
lution of stoichiometric PdCl and stirred at room temperature for 3 h,
2 2
Oxygen in autoclave was displaced thrice by 0.2 MPa N and 0.5 MPa H
2
in sequence. Then, 3.5 MPa H
was charged into the autoclave at room
2
followed by filtration and washing with deionized water for three times.
◦
temperature. The reaction was carried out at 140 C for 400 min under
stirring at 400 rpm followed by cooling to room temperature naturally.
The other 2-alkyl cycloketones were synthesized with the same cyclo-
ketone/aldehyde molar ratio.
◦
xPd/Y catalysts were obtained after drying at 80 C overnight and
◦
calcination at 450 C for 4 h, where x refers to the weight percentage
(
wt.%) of Pd and Y represents the carrier. Besides, another three ZrO
2
supported catalysts containing 0.2 wt.% of Pt, 0.2 wt.% of Ru, and 5.0
wt.% of Ni were also prepared by following the above procedure and
using the corresponding metal salts.
=
For comparison, 2BCH was also synthesized by conventional ho-
mogenous method. Briefly, 60 mL 1 wt.% NaOH aqueous and 24 g of
cyclohexanone were added into a 250 mL flask at room temperature.
Then, 8 g n-butanal was slowly dropped into the flask during 10 min
under violent stirring. After stirring for another 1.5 h and settling for 12
h, the organic phase was obtained by separation, extraction with ethyl
acetate, and drying with anhydrous sodium sulfate.
2
.3. Characterizations
Powder X-ray diffraction (PXRD) was recorded on PANalytical X’Pert
PRO X-ray diffractometer with Cu K
α
radiation (40 kV and 40 mA).
The liquid products were filtrated and analyzed on Agilent 7890A
gas chromatograph (GC) equipped with HP-5 ms ((5%-phenyl)-meth-
ylpolysiloxane, 30 m) capillary column, flame ionization detector (FID),
and mass spectrometry detector (MS).
Transmission electron microscopy (TEM) images were taken on JEOL
JEM-2100 microscopy at an accelerating voltage of 200 kV equipped
with an energy dispersive X-ray (EDX) detector.
Thermogravimetric analyses (TGA) were performed on Netzsch STA
n-Butanal conversion (X), products selectivities (S
i
) and 2BCH yields
◦
ꢀ 1
4
49 F3 at a heating rate of 10 C min in air.
(Y ) were calculated as follows:
i
2

W. Xue et al.
Applied Catalysis A, General 616 (2021) 118107
Fig. 3. Two H
2
-consumption peaks were observed at 123℃ and 249℃,
respectively. The former was ascribed to PdO and the latter was
attributed to Pd species of Pd-O-Zr, which evidenced the existence of
SMSI on Pd/ZrO
.2Pd/ZrO catalyst was applied to synthesize 2BCH through a one-
pot method, where ZrO provided suitable acid-base sites for
2
[35].
0
2
2
2
Fig. 1. XRD patterns of fresh 0.2Pd/ZrO catalyst.
i
ꢀ nf
n
nꢀ butanal
nꢀ butanal
X
nꢀ butanal(%) =
× 100%
i
n
nꢀ butanal
x∙n
nꢀ butanal
i
S
i
(%) =
× 100%
nꢀ butanal
i
f
n
ꢀ n
X
nꢀ butanal × S
i
2 2
Fig. 3. H -TPR curve of 0.2Pd/ZrO .
Y
i
(%) =
1
00
Where ni
and n
f
are the initial and final contents of n-
nꢀ butanal
nꢀ butanal
butanal, respectively; ni is the final molar quantity of product i and x
refers to the number of n-butanal molecules needed for yielding one i
molecule.
3
. Results and discussion
3
.1. Performance of Pd/ZrO
2
The actual Pd loading of 0.2Pd/ZrO
2
determined by ICP-MS was
0
.216 %, which was very close to the theoretical value. The XRD pattern
of fresh 0.2Pd/ZrO
2
catalyst was displayed in Fig. 1, which showed
◦
◦
primary diffraction peaks of monoclinic ZrO
2
at 2theta = 28.2 , 31.4
◦
and 50.1 [30] as well as a weak diffraction peak of tetragonal ZrO
2
at
◦
2
theta = 30.3 [31]. No diffraction peaks of Pd or PdO were observed
due to the relatively low Pd content. TEM images of 0.2Pd/ZrO catalyst
Fig. 2) showed no visible Pd nanoparticle or cluster. These results
2
(
2
indicated that Pd species were highly dispersed on ZrO , which was
Fig. 4. Product distributions for one-pot (Pd/ZrO
syntheses. Repeated results for 2-butyl cyclohexanone synthesis via one-pot
cascade approach over 0.2Pd/ZrO catalyst of different batch. Conditions:
.25 mol n-butanal, 0.55 mol cyclohexanone, 3.7 g 0.2 wt.%Pd/ZrO , 3.5 MPa
2
) and homogenous (NaOH)
probably due to the strong metal-support interaction (SMSI) between Pd
and ZrO [32]. As reported [33,34], highly dispersed Pd species are
highly selective and active for C = C hydrogenation.
The reducibility of Pd/ZrO was measured by H -TPR and shown in
2
2
0
2
◦
2
2
H
2
, reaction temperature of 140 C, reaction time of 400 min.
2
Fig. 2. TEM images and EDX results (at S1 sites) of fresh 0.2Pd/ZrO catalyst.
3

W. Xue et al.
Applied Catalysis A, General 616 (2021) 118107
Fig. 5. Stability and regeneration of Pd/ZrO
2
(green: n-butanal conversion, orange: 2BCH selectivity). Conditions: 0.25 mol n-butanal, 0.55 mol cyclohexanone, 3.7 g
◦
0
.2 wt.%Pd/ZrO
2
, 3.5 MPa H
2
, reaction temperature of 140 C, reaction time of 400 min (For interpretation of the references to colour in this figure legend, the
reader is referred to the web version of this article).
2
Fig. 6. TEM images and EDX results (at S1 sites) (a and b), XRD (c) and TG-DTG curves (d) of spent 0.2Pd/ZrO catalyst after 10 cycles.
condensation and Pd was responsible for selective hydrogenation of as-
formed C = C bond. Experiment was repeated four times (Fig. 4), which
showed excellent repeatability. As shown in Fig. 4, 99 % of n-butanal
conversion and 76 % of 2BCH yield were achieved under reaction
3.2. Stability and regeneration of Pd/ZrO
2
Stability of 0.2Pd/ZrO
2
catalyst was studied by a 10 times of reuse
catalyst was sepa-
experiment. After each reuse, the used 0.2Pd/ZrO
2
◦
temperature of 140 C and catalyst dose (the weight ratio of catalyst to
rated by sedimentation only and reused without any treatment. As
shown in Fig. 5, in the first six reuses, the catalyst showed benign sta-
bility with negligible decay of n-butanal conversion and 2BCH yield.
Afterward, a slight deactivation occurred, leading to 95 % of n-butanal
conversion and 67 % of 2BCH yield after 10 times of reuse.
=
total feeding of organics) of 5 wt.%. Trace amount (< 2%) of 2BCH still
existed, which was not completely hydrogenated. Side reactions, such as
n-butanal hydrogenation to 1-butanol (BOH), self-condensation of n-
=
butanal to 2-ethylhexaldehyde (2EH) and 2-ethylhexenal (2EH ), and
further condensation to 2,6-dibutyl/dibutenyl cyclohexanone (C14
)
The TEM images (Fig. 6a and b) of deactivated catalyst showed that
Pd species were not aggregated, which indicated the good stability of
were inevitable. However, they were dramatically suppressed in the
one-pot synthesis. In comparison, conventional multistep method
2
0.2Pd/ZrO catalyst. XRD pattern of the used catalyst (Fig. 6c) indicated
(
labeled as NaOH in Fig. 4) gave n-butanal conversion of 95 % and
that the crystallization of the catalyst was well kept. The Pd content of
deactivated catalyst measured by ICP-MS was 0.204 %, which was
comparable to fresh catalyst (0.216 %) by taking experimental error in
consideration. All above results indicated the good structural stability of
=
2
BCH yield of 68 %. So, the yield of 2BCH through further hydroge-
nation of the latter by Pd/C would be even lower, which was thus
considerably lower than that obtained from the one-pot cascade method
in present study.
2 2
0.2Pd/ZrO catalyst. Therefore, the deactivation of 0.2Pd/ZrO was
most likely related to the Pd coverage by organic impurities rather than
the intrinsic structure change of the catalyst [36]. This speculation is
evidenced by TG analysis (Fig. 6d), showing that 3.5 wt.% of coke was
4

W. Xue et al.
Applied Catalysis A, General 616 (2021) 118107
2 2
Fig. 7. Product yields over Pd/ZrO with respect to reaction temperature (a), catalyst dose (b), Pd loading (c), reaction time (d) and product yields over pure ZrO
versus reaction time (e).
formed on the used catalyst. Notably, the soft coke could be removed by
2BCH yield were relatively low (64 % and 14 %, respectively) due to the
◦
an oxidative regeneration at a low temperature of ca. 450 C.
deficient active sites for both condensation and hydrogenation pro-
◦
=
The deactivated 0.2Pd/ZrO
2
catalyst was then regenerated at 450 C
cesses. The high amount of 2BCH suggested that Pd sites were inade-
in air for 4 h. After the removal of coke, the activity of Pd/ZrO
2
was
quate. By increasing catalyst dosage, both n-butanal conversion and
2BCH selectivity were improved, accompanied with the dramatically
completely recovered [37], showing an excellent regenerability of this
heterogeneous catalyst. The good stability and excellent regenerability
=
decreased 2BCH . n-Butanal conversion and 2BCH yield were linearly
of Pd/ZrO
2
catalyst would lower the cost of one-pot cascade process,
increased with catalyst dosage from 2% to 5%. Further increasing
catalyst dosage made negligible change for 2BCH yield.
even though more reaction-regeneration cycles are still needed to be
considered.
The effect of Pd loading on catalytic activity was further investigated
2
and showed in Fig. 7c Over the ZrO carrier without loading Pd, 70 % of
n-butanal was converted. However, 2BCH yield is only 4%. Instead,
3
.3. Optimizations of reaction conditions
=
2
BCH showed a very high yield of 41 %. These results indicated that
ZrO
hydrogenation. Interestingly, by loading trace amount (0.05 wt.%) of Pd
on ZrO , the 2BCH yield remarkably rose to 61 %, along with an
2
was mainly responsible for aldol condensation but not active for
The temperature dependence results (Fig. 7a) showed that n-butanal
conversion and 2BCH yield were positively related to the reaction
◦
◦
2
temperature. At stage of temperature from 100 C to 140 C, n-butanal
conversion and 2BCH yield were almost linearly increased with the re-
increased n-butanal conversion to 90 % and a significantly decreased
=
2
BCH yield to 5%. With loading more Pd, e.g., 0.05ꢀ 0.2 wt.%, n-
◦
action temperature. When reaction temperature reached 140 C, n-
butanal conversion and 2BCH yield rised proportionally. However,
excess Pd loading (0.53 wt.%) improved the side reaction, e.g., self-
hydrogenation of n-butanal to 1-Butanol (BOH, Scheme 1), leading to
a slight decrease of 2BCH yield.
butanal was nearly completely (> 99 %) converted. Further increasing
◦
temperature to 160 C made little change for n-butanal conversion,
while a slightly increased 2BCH yield (from 76 % to 80 %) was obtained.
However, higher reaction temperature could lead to higher energy
consumption and severer equipment requirement.
Product distribution with respect to reaction time on Pd/ZrO
lyst and ZrO carrier were studied (Fig. 7d and e). As shown in Fig. 7d,
during the first 50 min, the condensation on Pd/ZrO was very fast due
2
cata-
2
The effect of catalyst dosage was also investigated and displayed in
Fig. 7b. In the case of 1% catalyst dosage, n-butanal conversion and
2
5

W. Xue et al.
Applied Catalysis A, General 616 (2021) 118107
Table 1
reaction results of catalysts with varied active metals and supports.
ꢀ
Conv. /%
n-butanal
Yield/%
2BCH
S
BET
2
/
t
V /mL g
1
Entry
Catalysts
ꢀ 1
m
g
=
=
2BCH
BOH
2 EH
2 EH
C14
1
2
3
4
5
6
7
8
9
Pt/ZrO
Ru/ZrO
2
37
25
32
0.15
0.13
0.14
0.66
0.59
0.04
0.01
0.05
0.01
0.23
97
36
16
8
23
43
46
2
8
1
10
6
17
20
33
4
2
a
98
9
1
Ni/ZrO
Pd/Al
2
99
1
1
5
2
O
3
160
203
8
97
55
50
52
10
55
52
14
18
13
26
80
4
16
16
2
1
Pd/MgO
Pd/CaO
Pd/ZnO
97
4
0
12
8
100
100
86
3
1
4
1
1
0
2
Pd/TiO
Pd/CeO
Pd/Al SiO
2
8
2
14
6
6
4
2
2
87
12
14
5
0
11
5
1
0
2
5
52
49
7
8
0
◦
Conditions: 0.25 mol n-butanal, 0.55 mol cyclohexanone, 3.7 g catalyst (0.2 wt.% metal loading), 3.5 MPa H
2
, reaction temperature of 140 C, reaction time of 400
a
min. The active metal content is 5 wt.%.
which was atomic economic.
Table 2
NH and CO
3
2
TPD results.
NH (TPD)
3
CO
2
(TPD)
3.4. Effects of active metals and supports
Top
NH
g)
3
uptake (μmol/
Top
CO
g)
2
uptake ( mol/
μ
Catalysts
peak
peak
Pt, Ru and Ni, the commonly-used metals for hydrogenation, were
o
o
(
C)
( C)
also loaded on ZrO
ZrO , Ru/ZrO and Ni/ZrO
version (> 97 %). However, the yield of 2BCH over these catalysts are
2
carrier for this study (Entry 1–3 in Table 1). Pt/
Pd/ZrO
2
212.7
178.2
150.4
296.3
674.4
675.7
79.5
94.1
94.0
20.2
31.7
4.8
2
2
2
catalysts showed excellent n-butanal con-
Pd/Al
Pd/
2 3
O
much lower than that over Pd/ZrO
2
. Products distributions show that
, Ru/ZrO and Ni/ZrO
Al
2
SiO
5
=
large amount of 2BCH are produced on Pt/ZrO
2
2
2
,
Pd/MgO
n.d.
n.d.
120.5
31.8
related to the insufficient C = C hydrogenation. Notably, with the in-
=
crease of 2BCH yields, the yields of C14 are simultaneously increased in
to the high concentration of n-butanal and cyclohexanone, resulting in
the order of Pd/ZrO (6%)<Pt/ZrO (17 %)<Ru/ZrO (20 %)<Ni/ZrO
2
2
2
2
=
=
rapid increase of 2BCH yield, while the formation of 2BCH was hys-
(33 %). This is ascribed to the more active -H of 2BCH than 2BCH to
α
teretic. With the proceeding of reaction, the concentration of n-butanal
further condense with n-butanal and higher thermodynamic stability of
2,6-dibutenyl cyclohexanone [1]. In brief, Pd has great superiority over
other metals for selective synthesis of 2BCH through one-pot method
[34].
=
decreased along with the accumulation of 2BCH , the reaction rate of
hydrogenation became higher than that of condensation. Thereafter, the
=
yield of 2BCH gradually decreased to a relatively low level. Similar
=
trend was also observed for 2 EH and 2 EH although their total yields
For the bifunctional catalyst, support is as important as metals,
which provides the acid-base sites for aldol condensation [1]. Therefore,
in order to understand the effect of supports, commonly used supports,
=
were much lower than 2BCH and 2BCH. On the contrary, yields of
=
=
2
unsaturated 2BCH and 2 EH increased steadily on pure ZrO in the
first 300 min and then keep unchanged (Fig. 7e). In this case, the final
such as acidic Al O3 [38], strong basic MgO, CaO [39,40] and weak
2
=
yield of 2BCH (42 %) was twice as the highest value on Pd/ZrO
2
but
basic ZnO [41], TiO2 [42], CeO2 [43] and amorphous alumina silicate
still was lower than the 2BCH yield. Therefore, compared with multistep
approach, the one-pot cascade process improved the yield of 2BCH,
(Al SiO ) [44], were also studied. As shown in Table 1 (Entry 4 to 7),
2
5
Pd/Al O , Pd/MgO, Pd/ZnO and Pd/CaO showed comparable n-butanal
2
3
Table 3
One-pot synthesis of 2-alkyl cycloketones from cycloketone and aldehyde.
[
a]
[a]
Entry
ketone
R of 2
Conv. /%
Yield of 3a or 3b/%
1
2
3
4
5
6
7
8
9
i-C
n-C
tert-C
3
H
7
-
92
99
10
99
99
99
98
84
98
29
95
96
96
97
76
84
<1
84
86
88
87
65
70
1
4
H
9
-
4 9
H
1a
n-C
5
n-C
6
n-C
7
n-C
8
H
H
H
H
11
13
15
17
-
-
-
-
3 7
i-C H -
4
n-C H
9
-
10
11
12
13
14
4 9
tert-C H
1b
n-C
5
n-C
6
n-C
7
n-C
8
H
H
H
H
11
13
15
17
-
-
-
-
75
71
74
76
◦
[a]
Conditions: 0.25 mol aldehyde, 0.55 mol ketone, 3.7 g 0.2 wt.%Pd/ZrO
2
, 3.5 MPa H
2
, reaction temperature of 140 C, reaction time of 400 min.
Conversion and
yield were calculated by area normalization method of GC. 2-alkyl cycloketones were determined by the molecular ion peak detected by GC–MS.
6

W. Xue et al.
Applied Catalysis A, General 616 (2021) 118107
conversion with Pd/ZrO
2
, while the 2BCH yields (< 55 %) on these
. This was due to the
Declaration of Competing Interest
catalysts were much lower than that on Pd/ZrO
2
high selectivities of side reactions like self-condensation and n-butanal
hydrogenation on these catalysts. On the contrary, much lower n-buta-
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
nal conversions were obtained on Pd/TiO
owing to their lower intrinsic activity than Pd/ZrO
ZrO was the most suitable support, which was probably due to its
suitable acid-base properties. In order to demonstrate this, NH -TPD and
CO -TPD measurements were applied for Pd/ZrO , Pd/Al , Pd/Al
SiO and Pd/MgO (Table 2). Quantities of weak or medium basic sites
were observed on Pd/ZrO , Pd/Al and Pd/MgO, while those on
Pd/Al SiO was much lower. Considering the fact that n-butanal con-
2
, Pd/CeO
2 2 5
and Pd/Al SiO ,
2
. So, in this system,
2
Acknowledgements
3
2
2
2
O
3
2-
This work was supported by National Natural Science Foundation of
China (Grant No. 21802135). We thank Dalian Luck Fine Chemical Co.,
Ltd for providing standard samples.
5
2
2 3
O
2
5
versions were higher than 97 % on the formers but only 49 % on the
latter, we could conclude that the condensation step was primarily
catalyzed by base sites. However, higher amount of base site also
partially contributed to higher self-condensation of n-butanal, which
Appendix A. Supplementary data
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.apcata.2021.118107.
leads to lower 2BCH yield on Pd/Al
Pd/ZrO . No obvious correlations between acid sites and catalytic per-
formance were observed on these catalysts, so the hydrogenation of
2 3
O and Pd/MgO than that on
2
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