Superbasic sodium stannate as catalyst for dehydrogenation, Michael addition and transesterification reactions

Article abstract of DOI:10.1016/j.apcata.2011.08.015

It has been shown that sodium stannate with superbasic sites generated on its surface can be obtained through simple thermal treatment of sodium stannate hydrate in pure N₂. In this study, we analyzed the as-prepared materials using powder X-ray diffraction, X-ray photoelectron spectroscopy, and N₂ physisorption methods. The superbasic sites were characterized by techniques of Hammett indicators and temperature-programmed desorption using CO₂ as adsorbate. It was shown that after undergoing calcination at 623 K, there are ample superbasic sites on sodium stannate: up to 0.254 mmol/g. The superbasicity of the materials was further confirmed by employing the 1-hexene as well as cyclohexa-1,4-diene double bond isomerization reactions. The superbasicity is attributed to the higher electron-donating ability of surface O^2-. The sodium stannate samples showed excellent catalytic efficiency towards selected reactions, namely the dehydrogenation of propa-2-nol, Michael addition of electron-deficient olefins, and transesterification of cyclic carbonate with methanol. It was observed that with rise of heat-treatment temperature from 573 to 623 K, both superbasicity and catalytic activity increased, reaching a maximum at 623 K, and then declined. It is deduced that catalytic efficiency is closely related to superbasicity of the sodium stannate catalysts.

Full text of DOI:10.1016/j.apcata.2011.08.015

Applied Catalysis A: General 406 (2011) 113–118
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Superbasic sodium stannate as catalyst for dehydrogenation, Michael addition
and transesterification reactions
a
a
a,∗
a
a,b
Shu-Guo Zhang , Yu-Dan Wei , Shuang-Feng Yin , Sheng-Lian Luo , Chak-Tong Au
a
College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, Hunan, China
Department of Chemistry, Hong Kong Baptist University, Kowloon Tong, Hong Kong
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 16 May 2011
Received in revised form 15 July 2011
Accepted 12 August 2011
Available online 22 August 2011
It has been shown that sodium stannate with superbasic sites generated on its surface can be obtained
through simple thermal treatment of sodium stannate hydrate in pure N2. In this study, we analyzed
the as-prepared materials using powder X-ray diffraction, X-ray photoelectron spectroscopy, and N2
physisorption methods. The superbasic sites were characterized by techniques of Hammett indicators
and temperature-programmed desorption using CO2 as adsorbate. It was shown that after undergoing
calcination at 623 K, there are ample superbasic sites on sodium stannate: up to 0.254 mmol/g. The super-
basicity of the materials was further confirmed by employing the 1-hexene as well as cyclohexa-1,4-diene
double bond isomerization reactions. The superbasicity is attributed to the higher electron-donating abil-
ity of surface O . The sodium stannate samples showed excellent catalytic efficiency towards selected
reactions, namely the dehydrogenation of propa-2-nol, Michael addition of electron-deficient olefins, and
transesterification of cyclic carbonate with methanol. It was observed that with rise of heat-treatment
temperature from 573 to 623 K, both superbasicity and catalytic activity increased, reaching a maximum
at 623 K, and then declined. It is deduced that catalytic efficiency is closely related to superbasicity of the
sodium stannate catalysts.
Keywords:
Superbase sodium stannate
Double bond isomerization
Michael addition
Dehydrogenation
Transesterification
2
−
©
2011 Elsevier B.V. All rights reserved.
1
. Introduction
superbase materials by probe reactions, viz. double bond isomer-
ization of 1-hexene and cyclohexa-1,4-diene. It has been reported
that the probe reactions of olefins isomerization can be used for the
discrimination of strong basic and acidic sites [3–6]. Moreover, the
catalytic application of the superbases was extended to (i) dehydro-
genation of propa-2-nol, (ii) Michael addition of electron-deficient
olefins, and (iii) transesterification of cyclic carbonate with
methanol. Additionally, we conducted an in-depth discussion on
the relationship between superbasicity and catalytic activity which
is crucial for application of the superbase material in the field of
catalysis.
Solid superbases are materials possessing basic sites with
strength H- higher than 26 [1]. The preparation and application
of these materials have been studied with interest because they
catalyze reactions for the production of fine chemicals under mild
conditions with reduced waste [2–8]. However, since most of the
known superbases are sensitive to oxygen and/or CO , they are
2
complicated to prepare and cannot be applied in chemical industry
in a convenient manner [1,9–12]. For the development of base-
catalyzed processes that are eco-friendly, a new kind of superbases
has to be designed.
Recently, we reported in a communication the in situ generation
of a solid superbase through direct thermal treatment of sodium
stannate hydrate under nitrogen at 623 K. The superbase showed
good catalytic efficiency towards the anti-Markovnikov addition
of N–H and O–H bonds across the C C bonds of electron-deficient
olefins [13]. In the present study, different techniques (e.g., XRD,
2. Experiment
2.1. Chemicals and reagents
XPS, BET, CO -TPD) were employed to characterize the materials.
In order to further confirm their superbasicity, we studied the
The reagents and chemicals (analytic grade unless stated oth-
erwise) were obtained from Kemiou Chemical Reagent Company
2
(Tianjin, China) and Tianjin Damao Chemical Reagent Co., Ltd. We
purchased 1-hexene and cyclohexa-1,4-diene from Adamas-Beta
reagent Ltd. and J&K Chemical Ltd., respectively; they were dehy-
drated using 3 A˚ molecular sieves at room temperature before use.
Cyclohexane was dried by sodium under reflux. Sodium stannate
∗ Corresponding author. Tel.: +86 731 88821310; fax: +86 731 88821310.
E-mail addresses: sf yin@hnu.edu.cn, sfyin73@yahoo.com.cn (S.-F. Yin).
0
926-860X/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2011.08.015

1
14
S.-G. Zhang et al. / Applied Catalysis A: General 406 (2011) 113–118
(
chemically pure) was produced by Beijing Hongxing Chemical
Plant.
2.2. Catalysts preparation
To prepare the catalyst, sodium stannate hydrate was in situ
treated (using a tube furnace) at a selected temperature in the
73–873 K range for 2 h in a N2 flow (99.99% purity, Changsha Gas
5
Co., China). The samples are indicated hereinafter as Sample(X)
where X stands for the temperature for thermal treatment. For
example, the sample treated at 623 K is denoted as Sample(623).
2.3. Catalyst evaluation
Dehydrogenation of propa-2-nol ((CH ) CHOH → (CH ) C
O
3
2
3 2
+
H ) was carried out at 573 K in a fixed-bed reactor (400 mm
2
length and 10 mm diameter) connected to a nitrogen line and a gas
chromatograph. The sodium stannate hydrate sample was pressed,
crushed and sieved into 40–60 mesh particles before being loaded
Fig. 1. XRD patterns of sodium stannate hydrate and Sample(623): (᭹)
Na2SnO3·3H2O and (ꢀ) anhydrous Na2SnO3.
(
0.5 g) into the fixed-bed reactor. Before the reaction, the catalyst
CO2 temperature-programmed desorption (CO -TPD) inves-
2
was kept at a selected temperature (e.g., 623 K) for 2 h in a N flow
tigation was conducted on
a Micromeritics 2920 apparatus
2
−
1
(
15 ml min ). Then the temperature was changed to a designated
using thermal conductivity detector (TCD). The basicity
a
temperature for a particular reaction. The feed of propa-2-nol was
introduced into the closed reactor through a syringe pump with liq-
of sodium stannate samples was also determined by Ham-
mett indicators method as detailed in [13]. The probe reac-
tions employed were the isomerizations of 1-hexene into
2-hexene (CH (CH ) CH CH → CH CH CH(CH ) CH (cis/trans-
−1
uid hourly space velocity (LHSV) of 2.0 ml h in the same N2 flow
−1
rate of 15 ml min . The products were analyzed by a gas chro-
matograph (GC) equipped with a 50 m OV-101 capillary column
and FID.
3
2
3
2
3
2
2
3
2-hexene)) and cyclohexa-1,4-diene into cyclohexa-1,3-diene
((CH CH)(CH ) (CH CH) → (CH CH) (CH ) ). The isomerization
2
2
2
2 2
−
1
Anti-Markovnikov
Michael
addition
(monoaddition:
bisaddition:
reactions were carried out at 523 K with LHSV being 0.4 ml h
C6H10O + CH2 CH–CN → C H (O)CH CH CN;
following the same procedure of propa-2-nol dehydrogenation
previously described in Section 2.3. The reaction products were
analyzed by a GC equipped with a FID and 50 m OV-101 capil-
lary column. The olefin conversion and the selectivity to isomerized
products were calculated according to Eqs. (1) and (2):
6
9
2
2
NCCH CN + CH CH–CN → (NC) C(CH CH CN) ) was performed
2
2
2
2
2
2
in a glass batch reactor equipped with a magnetic stirrer. Cyclohex-
anone (5 mmol), acrylonitrile (5 mmol) and catalyst (0.025 g) were
added and the mixture was stirred at room temperature for 1 h. In
the case of using malononitrile and acrylonitrile as reactants, the
molar amount of the malononitrile was 4 mmol while that of acry-
lonitrile was 10 mmol. After the reaction, the catalyst was separated
from the mixture by centrifugation, and the reaction mixture was
analyzed using an Agilent Technologies 7820 GC equipped with
a FID and HP-5 capillary column (30 m × 0.32 mm × 0.25 ␮m).
The conversion of cyclohexanone and malononitrile was
determined by the use of biphenyl as internal standard.
Transesterification of propylene carbonate with methanol
olefin % in field − olefin % in products
Conversionolefin (%) =
× 100
olefin % in field
(1)
CxHy % in products
SelectivityCxHy (%) = ꢀ
× 100
(2)
C H % in products
x
y
3. Results and discussion
(
C H O + CH OH → CH OC(O)OCH + CH CHOHCH OH) to pro-
4
6
3
3
3
3
3
2
3
.1. Catalyst characterization
duce DMC was carried out at 353 K using 0.01 mmol propylene
carbonate, 0.10 mol of methanol and 100 mg catalyst at a glass
batch reactor equipped with condenser and a magnetic stirrer. The
analysis of the products was similar to that of anti-Markovnikov
Michael addition.
3.1.1. XRD
Fig. 1 shows the XRD patterns of sodium stannate hydrate and
Sample(623). The XRD pattern of the former shows a sharp peak at
2ꢂ = 18.7 and four small peaks at 2ꢂ = 16.9, 35.7, 21.4, 38.0, 49.2 and
◦
◦
5
8.6 ; they are attributable to Na SnO ·3H O according to the stan-
2
3
2
2
.4. Catalyst characterization
dard JCPDS (01-1115) card. After thermal treatment at 623 K, the
◦
◦
peaks of Na SnO ·3H O vanished, and peaks at 2ꢂ = 16.2 , 37.4 and
2
3
2
◦
39.3 ascribable to anhydrous Na SnO (JCPDS 30-1252) appear.
2 3
Powder X-ray diffraction experiment (XRD) was conducted on a
Rigaku Automatic Diffractometer (Rigaku D-MAX) with monochro-
matized Cu K␣ radiation (ꢀ = 0.15406 nm). X-ray photoelectron
spectroscopic (XPS) measurements were carried out on a Leybold
Heraeus-Shengyang SKL-12 electron spectrometer fitted with a VG
CLAM 4 MCD electron energy analyzer. Mg K␣ X-ray radiation
Thus, Sample(623) is anhydrous Na SnO .
2 3
3.1.2. XPS
The XPS spectrum of Sample(623) is depicted in Fig. 2; one can
see signals of the C, O, Sn and Na elements. Furthermore, according
to the Sn 3d spectrum showing spin–orbit doublet at 487.2 (3d5/2)
and 495.8 eV (3d3/2) (inset of Fig. 2), the chemical state of Sn can
be assigned to Sn(IV) [14]. Using the related sensitivity factors, it
was found that the chemical formula of the sample with thermal
treatment can be expressed as Na SnO . The result is in accord with
(
hꢁ = 1253.6 eV) was generated at 15 mA and 10 kV. Na 1s, C 1s, O 1s,
and Sn 3d peaks were recorded in intervals of 0.1 eV, and binding
energy was corrected taking the C 1s binding energy of adventitious
carbon to be 284.8 eV. The residual gas pressure of spectrometer
−7
chamber was ca. 2 × 10 Pa during data acquisition. The specific
surface areas of catalysts were determined by BET method based
on nitrogen adsorption–desorption isotherms (at 77 K) collected
over a Beckman (SA 3100) surface area analyzer.
2
3
that of XRD, further confirming that the heated sample is Na SnO .
In addition, it has been pointed out that the binding energy of O
1s peaks in XPS study can provide direct evidence of surface basicity
2
3

S.-G. Zhang et al. / Applied Catalysis A: General 406 (2011) 113–118
115
Table 1
Basicity measurements of Sample(X) catalysts.
Treatment temperature (K)
Base strengtha (H-)
Amount of superbasic
sites (mmol/g)
a
–
9.3 ≤ H- < 15.0
26.5 ≤ H- < 33.0
26.5 ≤ H- < 33.0
26.5 ≤ H- < 33.0
26.5 ≤ H- < 33.0
26.5 ≤ H- < 33.0
0
5
6
6
7
8
73
23
73
73
73
0.067
0.254
0.175
0.152
0.054
a
Experiment process as detailed in [13].
Fig. 2. XPS spectrum of Sample(623) (inset: Sn 3d peaks).
Fig. 4. CO2-TPD profiles of (a) sodium stannate hydrate and (b) Sample(623).
range. As defined by Tanabe, materials with a basic strength higher
than 26 can be regarded as superbasic [1]. In other words, every
Sample(X) is a solid superbase. However, they are different in the
amount of superbasic sites with the one heated at 623 K showing
the highest amount (0.254 mmol/g). Based on the results, it is rea-
sonable to deduce that sodium stannate with superbasic sites on
its surface can be directly generated from sodium stannate hydrate
through a simple step of thermal treatment.
Fig. 3. O 1s spectrum of (a) sodium stannate hydrate and (b) Sample(623).
3
.1.3.2. CO -TPD. The CO -TPD results of sodium stannate hydrate
2 2
of metal oxides [15]. Fig. 3 shows the O 1s peaks of Na SnO ·3H O
2
3
2
and Sample(623) are depicted in Fig. 4. It is clear from Fig. 4 that the
former shows poor CO2 adsorption, displaying only low-intensity
signals at around 403 and 853 K. Over Sample(623), intense des-
orption peaks are observed at ca. 573, 803, and 973 K. The CO2
desorption at 973 K can be considered as a clear indication of super-
basicity [4]. The results confirm the presence of superbasic sites
on Sample(623), in good agreement with the results of Hammett
indicators method (Table 1).
and Sample(623). It is known that the electron-donating ability of
electron pairs of a metal oxide is related to O 1s binding energy: a
lower O 1s binding energy implies higher ability of donating the
electron pairs. The O 1s binding energy of Na SnO ·3H O is ca.
2
3
2
5
31.0 eV whereas that of Sample(623) is 530.0 eV. The lowering of
binding energy from ca. 531.0 to 530.0 eV can be considered as an
enhancement of surface basicity [16]. It is reasonable to deduce that
the enhanced basicity (including superbasicity) of Sample(623) is a
The basicity distribution of Sample(623) according to the
2−
result of the higher electron-donating ability of surface O [17,18].
In other words, the surface O2− ions of Sample(623) can function
as active basic sites.
CO -TPD results and those of Hammett indicator-Benzoic acid
2
titration (as described in [13]) are listed in Table 2. According
to the data of titration, Sample(623) possesses weak (7.2–15.0),
strong (15.0–26.5) and super (26.5–33.0) basic sites, in amounts
of 1.317, 1.225 and 0.254 mmol/g, respectively, giving a total of
3.1.3. Basicity characterization
In order to confirm the surface superbasicity of the calcined
2.796 mmol/g. In the CO -TPD investigation, desorbed peaks at 573,
2
Na SnO , Hammett indicators and CO -TPD approaches were
803 and 973 K indicate weak, strong and super basic sites, respec-
tively. The amounts of these basic sites were calculated by the
integral method based on the area of the corresponding desorp-
tion peaks; they are 1.286, 1.025 and 0.243 mmol/g, respectively
2
3
2
employed. Moreover, the superbasicity of these materials were
probed by 1-hexene as well as cyclohexa-1,4-diene double bond
isomerization reactions.
(Table 2). It is apparent that the distributions of base strength
3
.1.3.1. Hammett indicators method. The base strength (H-) and
obtained based on the results of Hammett indicators and CO2-TPD
methods are in good agreement with each other (Table 2).
amount of basic sites of samples were measured using the Ham-
mett indicators method (Table 1). One can see that sodium stannate
hydrate shows weak basicity (9.3 ≤ H- < 15.0). After heating sodium
stannate hydrate at temperatures ranging from 573 to 873 K, the
as-obtained samples exhibit basic strength in the 26.5 ≤ H- < 33.0
3.1.3.3. Double bond isomerization of 1-hexene and cyclohexa-1,4-
diene. The probe reactions are applied to characterize basic sites
that are different in strength [1,3–6]. Isomerization of 1-hexene and

1
16
S.-G. Zhang et al. / Applied Catalysis A: General 406 (2011) 113–118
Table 2
Basicity distribution of Sample(623) measured by Hammett indicators method and CO2-TPD.
Method
Base strength H- distribution (mmol/g)
7.2–15.0 (weak)
15.0–26.5 (strong)
26.5–33.0 (super strong)
Total basicity
Hammett indicators methoda
CO2-TPD
1.317
1.276
1.225
1.035
0.254
0.243
2.796
2.554
a
Experiment process as detailed in [13].
Fig. 6. Activity of Sample(X) catalysts as a function of thermal treatment tempera-
ture (X) in double bond isomerization of cyclohexa-1,4-diene (inset: a plot of initial
conversion of cyclohexa-1,4-diene versus superbasicity). Reaction conditions: tem-
−
1
−1
perature, 523 K; LHSV, 0.4 ml h ; N2 flow rate, 15 ml min .
cyclohexa-1,4-diene, the effect of X on catalytic activity is sim-
ilar to that of 1-hexene isomerization but much clearer (Fig. 6).
With an increase in X, the activity for double bond isomerization of
cyclohexa-1,4-diene first increased, reaching a maximum at 623 K,
and then decreased. The results imply the existence of superbasic
sites [3–6], consistent with the results of CO -TPD and Hammett
2
indicators methods. Similar results were obtained over KF/alumina,
a solid catalyst of strong base, as described by Kabashima et al. [9].
As seen in Tables 1 and 2, Sample(X) is similar in basic strength
but different in the amount of superbasic sites, and Sample(623) is
the highest in terms of the amount of superbasic sites. The insets of
Figs. 5 and 6 show the relationship between activity and amount of
superbasic sites of the catalysts. In the case of 1-hexene isomeriza-
tion, both 1-hexene conversion and cis/trans ratio increased linearly
with rise of superbasic sites. A similar trend can also be seen in the
case of double bond isomerization of cyclohexa-1,4-diene. Thus, the
activity of Sample(X) correlated with the basic strength as well as
the amount of superbasic sites: the more the amount of superbasic
sites or the stronger the base strength, the higher the catalytic activ-
ity. It is obvious that 623 K is the optimal treatment temperature to
obtain superbasic sites for catalytic efficiency. Thus, Sample(623)
was chosen for further investigation.
Fig. 5. Activity of Sample(X) catalysts as a function of thermal treatment tem-
perature (X) in double bond isomerization of 1-hexene. (A): Initial conversion of
1
-hexene (inset: a plot of initial 1-hexene conversion versus superbasicity); (B) ini-
tial cis/trans ratios of 2-hexene (inset: a plot of initial cis/trans ratios of 2-hexene
−
1
versus superbasicity). Reaction conditions: temperature, 523 K; LHSV, 0.4 ml h
;
−1
N2 flow rate, 15 ml min
.
cyclohexa-1,4-diene was employed in this study for this purpose.
The isomerization of olefins has been applied to probe solid bases of
strong basicity [3–6]. The reaction is initiated by the abstraction of
allylic H by basic sites to generate cis and trans forms of allyl anion
in which the former is more stable than the latter. Therefore, cis is
predominantly formed in the initial stage of the reaction [19]. A high
cis/trans ratio is a characteristic feature of isomerization catalyzed
by catalysts of strong or super basicity.
Fig. 5 shows the conversion of 1-hexene and initial cis/trans
ratios of 2-hexene over Sample(X). A rise in treatment tempera-
ture (X) from 573 to 623 K would result in increase of 1-hexene
conversion and cis/trans ratio, and the highest cis/trans ratio (1.58)
was observed over Sample(623). Further rise in X would result in
sharp decline in catalytic activity, and Sample(873) only showed
low activity. For Sample(923), no activity was detected even when
the reaction temperature was elevated to 623 K.
3.1.4. N2 adsorption/desorption isotherm
The N2 adsorption/desorption isotherm of Sample(623) is typ-
ical of type-IV isotherm, showing little uptake at high partial
pressure (Fig. 7). According to the hystersis loop, Sample(623) is
mesoporous in nature [4]. According to SEM pictures (not shown
here), the mesopores of the material are generated between the
particles rather than inside the particles. Generally, the pores of
such a dimension would allow easy diffusion of small reactants
into the catalyst [1]. The specific surface area of Sample(623) is
2
−1
3
2.5 m g , and the low specific surface area implies that the sur-
face density of basic and superbasic sites is high. With basic and
superbasic sites located on the external surface as well as on the
surface of mesoporous channels, Sample(623) is suitable for base-
catalyzed reactions.
The reported activity for 1-hexene isomerization was usu-
ally low [19–21]. In the case of double bond migration of

S.-G. Zhang et al. / Applied Catalysis A: General 406 (2011) 113–118
117
Table 3
catalyst has wide application in chemical industries because coke
formation on catalysts in some high-temperature reactions can be
retarded.
Acetone yield in the decomposition of 2-propanol and DMC yield in the transester-
ification of PC with methanol over Sample(623) at different reaction times.
Decomposition of 2-propanola
Reaction time (h) Acetone yield (%)
Transesterificationb
Reaction time (h)
DMC yield (%)
3.2.2. Michael addition
0
0
1
2
3
3
.25
.75
.5
.25
.0
88.8
73.7
75.9
71.5
7.6
1
3
5
7
9
53.2
64.5
72.6
73.0
71.8
72.3
Michael addition is for C–C bond formation and is widely used
in organic synthesis [27]. The reaction is commonly catalyzed by
strong bases [28]. In the application of Na SnO3 in the Michael
2
addition of cyclohexanone to acrylonitrile, we observed monoad-
dition product. However, in the case of malononitrile, bis-addition
product was obtained. We confirmed that proportionate yield of
bis-addition product was obtained whether the molar amount of
acrylonitrile used in the reaction was equal to or less than that of
malononitrile. On the other hand, the use of excess cyclohexanone
did not furnish any bis-addition product under similar reaction con-
dition. In Michael addition, although mono-adduct was obtained
with all conventional basic reagents [29–36], the generation of bis-
adduct is not unprecedented. It was reported to be possible by
Alvarez et al. in Michael addition of acrylonitrile to malononitrile
over a solid ruthenium(II) complex [37]. Furthermore, the use of our
superbase materials has the advantages of being short in reaction
time (ca. 5 min) and relatively high in yield (99.2%) at room tem-
perature and atmosphere pressure, demonstrating that the strong
.75
6.2
11
a
−1
;
Reaction conditions: temperature, 573 K; LHSV, 2.0 ml h
N2 flow rate,
−
1
1
5 ml min
.
b
Reaction conditions: catalyst, 100 mg; propylene carbonate, 0.01 mmol;
methanol, 0.10 mol; reaction temperature, 353 K.
basic sites on Na SnO3 are apt for this kind of base-catalyzed pro-
2
cesses.
3.2.3. Transesterification of cyclic carbonate with methanol to
produce DMC
Transesterification of ester with alcohol is important in the syn-
thesis of fine chemicals, and this kind of reactions is commonly
catalyzed by basic materials [38–40]. We used Sample(623) to
catalyze the transesterification of propylene carbonate (PC) with
methanol to produce dimethyl carbonate (DMC) and propylene gly-
col (PG). The results are shown in Table 3. A 72.6% yield of DMC
was achieved after reaction time of 5 h under atmospheric pres-
sure, higher than those recorded in the literature [41–44]. The DMC
yield kept almost constant even the reaction was prolonged to 11 h,
suggesting that the reaction was limited by thermodynamic equi-
librium [45].
Fig. 7 N2. adsorption/desorption isotherm of Sample(623).
3
.2. Catalytic applications
In a recent communication, we reported the high catalytic
activity of Na SnO3 for the anti-Markovnikov hydroamination and
2
hydroalkoxylation of electron-deficient olefins with nucleophiles
13]. In this study, we applied the catalyst to (i) dehydrogenation
of propa-2-nol, (ii) Michael addition of electron-deficient olefins,
and (iii) transesterification of propylene carbonate with methanol.
[
It was suggested that both moderately and strongly basic
sites are active for the transesterification of cyclic carbonate with
methanol to produce DMC [46,47]. In other words, the DMC yield
depends on the total amounts of basic sites. It is interesting to
point out that 1-alkoxy-2-propanol and 2-alkoxy-1-propanol were
not detected as by-products in our study. According to the basicity
distribution of Sample(623) displayed in Table 2, there are ample
amount of sites that are strongly basic on the surface. It is plausible
that the availability of these sites is a determining factor for high
selectivity to DMC.
3
.2.1. Dehydrogenation of propa-2-nol
Catalytic decomposition of propa-2-nol promoted by solid base
catalysts is important for the production of acetone [3]. Strongly
basic catalysts used to promote the decomposition of propa-2-nol
usually enjoy supremacy such as being high in acetone selectivity
and yield [22–25]. The industrial application of the procedure is
extremely promising since the cost of propa-2-nol is much lower
than that of acetone. The yield of acetone in the decomposition of
propa-2-nol at 573 K over Sample(623) at different reaction times is
shown in Table 3. The catalyst is highly active: acetone yield as high
as 88.8% was obtained at 0.25 h. At reaction time of 2.25 h, the yield
declined to 71.5% but acetone selectivity was above 97.0%. There
was a big decline in yield when reaction time exceeded 2.5 h due
to a big drop in propa-2-nol conversion (to 7.6%). Nonetheless, the
catalytic efficiency is better than that reported in the literature [3],
noted that in the present study the reaction temperature was lower
and acetone selectivity and yield were much higher. It was observed
that when reaction time exceeded 3.75 h, the color of the catalyst
changed from white to gray, suggesting that the deactivation was
a result of coking. Unlike the solid acid catalysts on which coke for-
4. Conclusions
A solid superbase catalyst can be generated simply by thermal
treatment of sodium stannate hydrate under a flow of pure N2.
There are ample superbasic sites (0.254 mmol/g) on the surface
with strength in the 26.5 ≤ H- < 33.0 range. Maximum superbasic-
ity and catalytic efficiency were observed over the sample that
was heated at 623 K. Moreover, there is a correlation between the
superbasicity and catalytic activity in the selected base-catalyzed
reactions: the higher the superbasicity and/or the more the super-
basic sites, the better the catalytic activity. The thermal treatment of
sodium stannate hydrate for the generation of superbasic sites can
be performed in situ prior to reaction, making storage of superbasic
materials not a concern. It is envisaged that this solid superbasic
mation was fast [26], the superbase Na SnO3 catalyst has better
resistance towards coking. Moreover, a deactivated catalyst can be
easily regenerated by calcination in air or O flow, followed by ther-
mal treatment in a flow of high-purity N . With such advantage, the
2
2
2

1
18
S.-G. Zhang et al. / Applied Catalysis A: General 406 (2011) 113–118
material will find wide applications in reactions that are catalyzed
by basic materials.
[17] H. Vinek, H. Noller, M. Ebel, K. Schwarz, J. Chem. Soc. Faraday Trans. 1 (1977)
34–746.
18] K. Tanaka, H. Yanashima, M. Minobe, G. Suzukamo, Appl. Surf. Sci. 121–122
1997) 461–467.
[19] Y.X. Rao, J.J. Kang, D. Antonelli, J. Am. Chem. Soc. 130 (2008) 394–395.
7
[
(
Acknowledgments
[
20] Y.N. Li, S.L. Liu, Z.K. Zhang, S.J. Xie, X.X. Zhu, L.Y. Xu, Appl. Catal. A: Gen. 338
2008) 100–113.
(
This project was financially supported by Hunan Provincial Nat-
ural Science Foundation of China (10JJ1003), the National Natural
Science Foundation of China (20873038), Doctoral Program Foun-
dation of Institutions of Higher Education of China (Grant No.
[
21] S. Pariente, P. Trens, F. Fajula, F.D. Renzo, N. Tanchoux, Appl. Catal. A: Gen. 307
(2006) 51–57.
[
[
22] P.E. Hathaway, M.E. Davis, J. Catal. 116 (1989) 263–278.
23] J. Weitkamp, M. Hunger, U. Rymsa, Micropor. Mesopor. Mater. 48 (2001)
255–270.
2
00805320001), Outstanding Young Research Award of National
[24] A. Gervasini, A. Aroux, J. Catal. 131 (1991) 190–198.
[25] M.A. Aramendía, V. Borau, C. Jiménez, J.M. Marinas, A. Porras, F.J. Urbano, J.
Catal. 161 (1996) 829–838.
Natural Science Foundation of China (Grant No. E50725825), the
Fundamental Research Funds for the Central Universities, and
National 863 Program of China (2009AA05Z319). C.T. Au thanks
the Hunan University for an adjunct professorship.
[
26] J.L. Dong, J.H. Zhu, Q.H. Xu, Appl. Catal. A: Gen. 112 (1994) 105–115.
[27] M.E. Jung, Comprehensive Organic Synthesis, vol. 4, Pergamon, Oxford, 1991.
[28] P. Perlmutter, Conjugate Addition Reactions in Organic Synthesis, Pergamon,
Oxford, 1992.
[
29] D.Y. Kim, S.C. Huh, S.M. Kim, Tetrahedron Lett. 42 (2001) 6299–6301.
References
[30] J. Christoffers, Eur. J. Org. Chem. (1998) 1259–1266.
[
31] M.M. Dell’Anna, V. Gallo, P. Mastrorilli, C.F. Nobile, G. Romanazzi, G.P. Suranna,
Chem. Commun. (2002) 434–435.
[
[
[
[
1] K. Tanabe, M. Misono, Y. Ono, H. Hattori, New Solid Acids and Bases, Their
Catalytic Properties, Kodansha, Tokyo, 1989, p. 3.
2] X. Li, G.Z. Lu, Y.L. Guo, Y. Guo, Y.Q. Wang, Z.G. Zhang, X.H. Liu, Y.S. Wang, Catal.
Commun. 8 (2007) 1969–1972.
[32] B.C. Ranu, M. Saha, S. Bhar, Synth. Commun. 27 (1997) 621–626.
[33] K. Shimizu, M. Miyagi, T. Kan-no, T. Kodama, Y. Kitayama, Tetrahedron Lett. 44
(2003) 7421–7424.
[34] N. Srivastava, B.K. Banik, J. Org. Chem. 68 (2003) 2109–2114.
[35] J.S. Yadav, B.V.S. Reddy, G. Baishya, A.V. Narsaiah, Chem. Lett. 34 (2005)
102–103.
[36] Z. Zhang, Y.W. Dong, G.W. Wang, K. Komatsu, Synlett (2004) 61–64.
[37] S.G. Alvarez, S. Hasegawa, M. Hirano, S. Komiya, Tetrahedron Lett. 39 (1998)
5209–5212.
[38] G. Stoica, S. Abelló, J. Pérez-Ramírez, Appl. Catal. A: Gen. 365 (2009)
252–260.
[39] S.R. Jagtap, M.D. Bhor, B.M. Bhanage, Catal. Commun. 9 (2008) 1928–1931.
[40] H. Abimanyu, C.S. Kim, B.S. Ahn, K.S. Yoo, Catal. Lett. 118 (2007) 30–35.
[41] R. Juárez, A. Corma, H. García, Green Chem. 11 (2009) 949–952.
[42] S.G. Liu, J. Ma, L.X. Guan, J.P. Li, W. Wei, Y.H. Sun, Micropor. Mesopor. Mater.
117 (2009) 466–471.
3] Y. Wang, W.Y. Huang, Y. Chun, J.R. Xia, J.H. Zhu, Chem. Mater. 13 (2001)
6
70–677.
4] L.B. Sun, J. Yang, J.H. Kou, F.N. Gu, Y. Chun, Y. Wang, J.H. Zhu, Z.G. Zou, Angew.
Chem. Int. Ed. 47 (2008) 3418–3421.
[5] H. Matsuhashi, M. Oikawa, K. Arata, Langmuir 16 (2000) 8201–8205.
[
6] J. Kije n´ ski, P. Radomski, E. Fedory n´ ska, J. Catal. 203 (2001) 407–425.
[7] H. Gorzawski, W.F. Höelderich, Appl. Catal. A: Gen. 179 (1999) 131–137.
[8] R.M. Bota, K. Houthoofd, P.J. Grobet, P.A. Jacobs, Catal. Today 152 (2010) 99–103.
[9] H. Kabashima, H. Tsuji, S. Nakata, Y. Tanaka, H. Hattori, Appl. Catal. A: Gen.
1
94–195 (2000) 227–240.
[
[
10] Y. Wang, J.H. Zhu, W.Y. Huang, Phys. Chem. Chem. Phys. 3 (2001) 2537–2543.
11] L.B. Sun, J.H. Kou, Y. Chun, J. Yang, F.N. Gu, Y. Wang, J.H. Zhu, Z.G. Zou, Inorg.
Chem. 47 (2008) 4199–4208.
[
[
[
12] U. Meyer, H. Gorzawski, W.F. Hölderich, Catal. Lett. 59 (1999) 201–206.
13] S.G. Zhang, Y.D. Wei, S.F. Yin, C.T. Au, Catal. Commun. 12 (2011) 712–716.
14] Z.J. Wang, Z.Y. Li, J.H. Sun, H.N. Zhang, W. Wang, W. Zheng, C. Wang, J. Phys.
Chem. C 114 (2010) 6100–6105.
15] G. Busca, Chem. Rev. 110 (2010) 2217–2249.
16] Q. Li, S.E. Brown, L.J. Broadbelt, J.G. Zheng, N.Q. Wu, Micropor. Mesopor. Mater.
[43] T. Wei, M.H. Wang, W. Wei, Y.H. Sun, B. Zhong, Green Chem. 5 (2003) 343–346.
[44] C. Murugan, H.C. Bajaj, R.V. Jasra, Catal. Lett. 137 (2010) 224–231.
[45] K. Torii, T. Iwasaki, Catal. Lett. (1986) 2021–2024.
[46] S. Fujita, B.M. Bhanage, Y. Ikushima, M. Shirai, K. Torii, M. Arai, Catal. Lett. 79
(2002) 95–98.
[
[
[47] B.M. Bhanage, S. Fujita, Y. Ikushima, M. Arai, Appl. Catal. A: Gen. 219 (2001)
259–266.
5
9 (2003) 105–111.