Synthesis of 3-methylindole from glycerol cyclization with aniline over CuCr/Al2O3 catalysts modified by alkali earth oxides

Article abstract of DOI:10.1002/hc.21090

In the present work, CuCr catalysts supported on γ-Al ₂O₃ are prepared and modified with alkali earth elements by impregnation, characterized by N₂ adsorption-desorption, XRD, H₂-TPR (temperature-programmed reduction by H₂), CO ₂-TPD and NH₃-TPD (temperature-programmed desorption of NH₃ or CO₂), and applied in the synthesis of 3-methylindole (3-MI) with a N-heterocycle from glycerol and aniline in the fixed-bed reactor. The results show that the introduction of alkali earth elements into the CuCr/Al₂O₃ catalyst can improve the yield of target 3-MI in the order of Mg < Ca < Sr < Ba. CuCr-Ba/Al ₂O₃ gives rise to a high 3-MI yield of 39.09% and 65.17% in N₂ as a carrier gas and 20%H₂-N₂ mixture gas, respectively. According to catalysts characterization and catalytic tests, the reaction pathway of glycerol cyclization with aniline is proposed, the formation of 3-MI and 3H-indol-3-yl methanol is hypothesized to be through the aniline cyclization with 2,3-hydroxypropanal from glycerol dehydrogenation over Cu⁰ centers and basic sites. The acidic sites mainly play a role on activating aniline, which interacts with glycerol to form 3-MI or quinoline through cyclization and dehydration.

Full text of DOI:10.1002/hc.21090

Heteroatom Chemistry
Volume 24, Number 4, 2013
Synthesis of 3-Methylindole from Glycerol
Cyclization with Aniline over CuCr/Al2O3
Catalysts Modified by Alkali Earth Oxides
Yu Chen, Chenghua Xu, Chuanqi Liu, Xue Li, Jianying Liu,
Yang Cao, and Jie Yang
Air Environmental Modeling and Pollution Controlling Key Laboratory of Sichuan Higher
Education Institutes, Chengdu University of Information Technology, Chengdu, Sichuan 610225,
People’s Republic of China
Received 18 January 2013; revised 11 March 2013
cals, Inc. Heteroatom Chem 24:263–270, 2013; View
ABSTRACT: In the present work, CuCr catalysts
this article online at wileyonlinelibrary.com. DOI
supported on γ -Al2O3 are prepared and modified
10.1002/hc.21090
with alkali earth elements by impregnation, charac-
terized by N2 adsorption–desorption, XRD, H2-TPR
(temperature-programmed reduction by H2), CO2-
TPD and NH3-TPD (temperature-programmed desorp-
tion of NH3 or CO2), and applied in the synthesis
of 3-methylindole (3-MI) with a N-heterocycle from
glycerol and aniline in the fixed-bed reactor. The re-
sults show that the introduction of alkali earth ele-
ments into the CuCr/Al2O3 catalyst can improve the
yield of target 3-MI in the order of Mg < Ca < Sr <
Ba. CuCr-Ba/Al2O3 gives rise to a high 3-MI yield of
39.09% and 65.17% in N2 as a carrier gas and 20%H2–
N2 mixture gas, respectively. According to catalysts
characterization and catalytic tests, the reaction path-
way of glycerol cyclization with aniline is proposed,
the formation of 3-MI and 3H-indol-3-yl methanol
is hypothesized to be through the aniline cyclization
INTRODUCTION
Indoles or alkylindoles are of considerable indus-
trial interest and are applied as intermediates in the
production of pharmaceuticals, herbicides, fungi-
cides, dyes, etc. [1]. They are usually recovered
from the biphenylindole fraction obtained after coal
tar distillation; however, their production no longer
meets the increasing market demand. Therefore,
their chemical synthesis has attracted more and
more interest. For instance, the Fisher synthesis has
been widely applied in the preparation of indoles by
reacting arylhydrazines with ketones or aldehydes
as shown in Scheme 1 [2]. Campanati et al. [1, 3, 4]
have reported that indoles can be formed from ani-
with 2,3-hydroxypropanal from glycerol dehydrogena-
tion over Cu0 centers and basic sites. The acidic sites
mainly play a role on activating aniline, which inter-
acts with glycerol to form 3-MI or quinoline through
line (AN) cyclizaiton with 1,2-diols, which is hypoth-
esized to mainly takes place between AN and inter-
mediates (aldehyde or ketone) containing a carbonyl
group formed from diols [1,3].
ꢀC
cyclization and dehydration.
2013 Wiley Periodi-
As one of indoles, 3-methylindole (3-MI) has at-
tracted considerable attention due to its potential
application as perfume and synthesizing herbicides,
antidiuretic, antihypertensive, muscular relaxant,
respiratory inhibitor, and heart-stimulant medica-
ments, etc. [5]. As reported [1], 3-MI can be synthe-
sized through AN cyclization with 1,2-propanediol
Correspondence to: Chenghua Xu; e-mail: xch@cuit.edu.cn.
Contract grant sponsor: Youth Science and Technology Founda-
tion of Sichuan Province in China.
Contract grant number: 2012JQ0047.
ꢀC
2013 Wiley Periodicals, Inc.
263

264 Chen et al.
SCHEME 2
cyclization with AN. In addition, during GL cycliza-
tion with AN the obtained main product is 3-MI in a
H2-steam–N2 mixture [7] and quinoline (QN) in air
as the carrier gas [12], respectively. Therefore, the
effect of carrier gas types and reaction temperature
on yield toward target products and GL conversion
in the cyclization is investigated and a new reaction
mechanism is proposed according to the obtained
results in the present work.
SCHEME 1
over ZrO2/SiO2 as a catalyst with a yield of 48.5%.
Recently, Shi et al. [6–8] have found that glycerol
(GL) can be used as a reactant to interact with AN
to 3-MI through cyclization over Ag/SiO2 and Cu-
based catalysts. Both catalysts give rise to about 38%
of 3-MI yield in N2 as a carrier gas containing an
amount of H2. It is also hypothesized that the cy-
clization takes place between AN and an intermedi-
ate containing a carbonyl group from GL hydrode-
hydration over metal-active centers and acidic sites.
If like this, the selection of catalytic-active species
will play an important role in 3-MI synthesis from
GL. According to our previous studies [9, 10], Cu0
metallic centers exhibit an excellent catalytic activity
for hydrodehydration of alcohols. In addition, Venu-
gopal et al. [11] have discovered that the dichromate
of transition metals can improve the GL cycliza-
tion with diamines to pyrazinyl compounds con-
taining N-heterocycles. Therefore, the present work
aims to prepare a kind of CuCr/γ -Al2O3 catalysts
(CCA) by impregnation and uses them to catalyze
GL cyclization with AN to 3-MI in the fixed-bed
system.
During 3-MI synthesis from GL and AN, it is pro-
posed by Shi et al. [7, 8] that 2-hydroxypropanal is
an intermediate, which interacts with AN to 3-MI
through cyclization and is produced by GL dehydra-
tion over the acidic sites. However, it is well known
that the dehydration easily takes place between two
adjacent OH groups in the GL molecule to form
3-hydroxypropanal or hydroxyacetone. Therefore, it
seems unreasonable that 3-MI formation is from the
AN interaction with 2-hydroxypropanal as shown in
Scheme 2. To investigate the reaction pathway for
3-MI synthesis from GL and AN, the present work
introduces the basic species such as alkali earth
metal elements into CCA (the obtained catalysts are
denoted as M-CCA, where M refers to alkali earth
metal elements) and investigates their effect on GL
RESULTS AND DISCUSSION
Effect of Different Alkali Earth Metal
From Table 1, it is found that all CCA catalysts ex-
hibit a smaller specific surface area and bigger av-
erage pore size than the support γ -Al2O3, indicating
that the introduced oxide species of metals including
Cu, Cr, and even alkali earth elements preferentially
inhabit inside the micropore of support γ -Al2O3. No
obvious decrease in the total pore volume shows that
the introduced metal oxide species are able to pro-
duce some new pores.
The XRD patterns (Fig. 1) indicate that these
catalysts mainly exhibit three obvious characteristic
diffraction peaks of γ -Al2O3 (Pdf no. 1-1308) at 2θ =
37.5o, 45.9o, and 67o, respectively [13,14]. Moreover,
CCA and those modified by alkali earth elements
only exhibit some very weak characteristic peaks for
CuO (Pdf no. 3-884) and CuCr2O4 (Pdf no. 26-509)
besides γ -Al2O3, showing that most of introduced
components are mainly dispersed in the form of the
amorphous oxides phase.
Catalytic tests (Table 1) indicate that the cycliza-
tion products from GL and AN mainly include 3-
MI, 3H-indol-3-yl methanol (3-IMol), and QN and
the formed by-products are detected by GC in-
clude acrolein, N-propylaniline, N-methylaniline, N-
ethylaniline, etc. The support γ -Al2O3 exhibits some
catalytic activity in GL cyclization with AN to 3-
MI with a yield of 12.37%, which, however, in-
creases more than twice over Cu/Al2O3 (22.89%).
Simultaneously, another two cyclization products
such as QN and 3-IMol are also formed. It is ob-
vious that 3-MI should be the product of 3-IMol hy-
drodehydration. It shows that Cu species should be
Heteroatom Chemistry DOI 10.1002/hc

Synthesis of 3-Methylindole from Glycerol Cyclization with Aniline over CuCr/Al2O3 Catalysts 265
TABLE 1 Physiochemical and Catalytic Property of Different Catalysts in GL Cyclization with AN a
Yield of Main Products (%)c
SBET
Pore Volume
Pore Size
(nm)
NH3 Uptake
GL Conversion
(%)c
b
Catalyst
(m2·g)
(cm3·g−1
)
(μmol·g−1
)
QN
3-MI
3-IMol
γ -Al2O3
Cr/Al2O3
Cu/Al2O3
CCA
Al-CCA
Mg-CCA
Ca-CCA
Sr-CCA
Ba-CCA
210.2
189.5
197.4
181.7
172.5
186.5
184.5
172.1
186.8
0.51
0.48
0.50
0.51
0.48
0.52
0.50
0.50
0.49
9.6
10.5
10.2
11.1
11.0
11.1
10.8
11.6
10.4
575
398
380
353
398
359
314
306
296
57.12
7.24
48.54
64.09
7.14
68.81
86.24
89.02
89.28
1.73
1.61
0.94
10.64
0.71
2.12
2.17
3.64
1.55
12.37
3.09
22.89
26.03
3.83
28.65
32.73
37.69
39.09
3.39
0.41
–
6.02
–
8.01
13.34
14.14
8.42
aReaction conditions: temperature 260◦C; feed rate of the liquid reactant mixture (AN/GL molar ratio = 3) 2.8 mL·h−1; catalyst 2 g; feed rate
of N2 as the carrier gas 60 mL·h−1
cGL: glycerol, QN: quinoline, 3-MI: 3-methylindole, 3-IMol: 3H-indol-3-yl methanol.
.
bData are calculated according to NH3-TPD results.
catalytic active centers for GL cyclization with AN
and 3-IMol hydrodehydration. From Table 1, it is
discovered that the Cr catalyst supported on γ -Al2O3
gives a poor GL conversion and 3-MI yield; how-
ever, the CCA exhibits a higher 3-MI yield (26.03%)
than Cu/Al2O3. It can be deduced that the Cr species
act as a promoter and the simultaneous presence of
Cu–Cr is helpful to GL cyclization with AN to 3-MI.
Moreover, it is easily found that the introduction of
alkali earth elements into CCA is able to further im-
prove the yield of the target products including 3-MI
and 3-IMol and, however, the introduction of acidic
species alumina leads to the drastic decrease in GL
conversion and yields of target products. Therefore,
it is deduced that the acid–base property of CCA cat-
alysts is probably an important factor that influences
their catalytic activity in GL cyclization with AN.
From NH3-TPD (temperature-programmed des-
orption of NH3) results (Table 1), the introduction
of Cu, Cr, and alkali earth elements decreases the
NH3 uptakes of catalysts; it means that the surface
acidic sites are decreased. CO2-TPD (temperature-
programmed desorption of CO2) curves of different
catalysts (Fig. 2) indicate that γ -Al2O3 support gives
a desorption peak below 100◦C, which is weakened
after introducing Cu, Cr, or alkali earth components.
This peak is assigned to the strong physical adsorp-
tion in the pore of samples. The presence of Cu and
Cr can lead to the production of weak or medium-
strong basic sites; they give rise to CO2 desorption
FIGURE 1 XRD patterns of catalysts such as (1) Al2O3, (2)
CCA, (3) Al-CCA, (4) Mg-CCA, (5) Ca-CCA, (6) Sr-CCA, and
(7) Ba-CCA.
FIGURE 2 CO2-TPD curves of different catalysts such as
(1) Al2O3, (2) Al-CCA, (3) CCA, (4) Mg-CCA, (5) Ca-CCA, (6)
Sr-CCA, and (7) Ba-CCA.
Heteroatom Chemistry DOI 10.1002/hc

266 Chen et al.
FIGURE 3 Effect of Ba loading on the catalytic property
of Ba-CCA in GL cyclization with AN. Reaction conditions:
temperature 260◦C; feed rate of the liquid reactant mixture
(AN/GL molar ratio 3) 2.8 mL·h−1; catalyst 2 g; rate of N2 as
FIGURE 4 CO2-TPD patterns of Ba-CCA catalysts with
Ba/Cu molar ratio of (1) 0, (2) 0.1, (3) 0.3, (4) 0.5 and (5)
0.7.
the carrier gas 60 mL·h−1
.
nique is introduced to characterize the effect of Ba
loading on the state of copper species.
peaks at about 200 and 380◦C, respectively. The pres-
ence of alkali earth elements leads to the appearance
of another desorption peak at 680◦C, which is at-
tributed to the strong basic sites. In addition, the in-
troduction of alkali earth elements can also increase
the amount of medium-strong basic sites and the
basicity of weak basic sites whose desorption peak
shifts to a higher temperature in the order of Mg <
Ca < Sr < Ba, which is obviously coincident with
the order of increase in the catalytic activity of cor-
responding catalysts. It indicates that the presence
of basic sites is favorable to GL cyclization with AN.
From Fig. 5, it is clearly observed that a strong
H2-TPR peak at about 300◦C, attributed to the reduc-
tion of Cu2+ to Cu0 [9, 10], appears for CuCr/Al2O3
without Ba loading. In addition, the intensities of
this peak are weakened and a new H2-TPR band
at a higher temperature range of 490–600◦C comes
forth after Ba loading. It is probably because that the
presence of redundant Ba species will result in the
Effect of Ba Loading
From above results, it can be concluded that the in-
troduction of Ba plays an excellent function on im-
proving 3-MI production. Therefore, the effect of Ba
loading on catalytic properties of the Ba-CCA cata-
lyst is further investigated in this work. From Fig. 3,
Ba-CCA with a Ba/Cu molar ratio of 0.1 exhibits the
highest GL conversion and 3-MI yield with 89.28%
and 39.09%, respectively. With the further increase
in Ba loading, both GL conversion and 3-MI yield are
significantly declined. CO2-TPD results (Fig. 4) indi-
cate that the increase in Ba loading increases the
amount of basic centers including weak, medium-
strong, and strong basic sites. It is obvious that the
effect of the Ba loading amount on the catalytic prop-
erty of Ba-CCA seems to be contrary to the above
-obtained results. To investigate this, the H2-TPR
(temperature-programmed reduction by H2) tech-
FIGURE 5 H2-TPR profiles of Ba-CCA catalysts with a
Ba/Cu molar ratio of (1) 0, (2) 0.1, (3) 0.3, (4) 0.5, and (5)
0.7.
Heteroatom Chemistry DOI 10.1002/hc

Synthesis of 3-Methylindole from Glycerol Cyclization with Aniline over CuCr/Al2O3 Catalysts 267
occlusion of Cu2+ species, leading to the decrease
in production of the surface Cu0 species during the
pretreatment with H2. The results show that the Cu0
species play an important role in GL cyclization with
AN besides the basicity of Ba-CCA catalysts. The Cu0
species probably promote the dehydrogenation or
dehydration of GL to intermediates containing the
carbonyl group, which can interact with the NH2
group in AN molecules to imines Schiff base (SB),
and SB further cyclization to 3-MI, 3-Imol, and even
QN easily takes place in the Cu0-active species [1,3].
improved by introducing an amount of H2 into the
carrier gas and reaches up to the highest value of
57.05% when using 20%H2–N2 as the carrier gas. Al-
though the main product in GL cyclization with AN
over Cu/SiO2-Al2O3 and Ag/SiO2 has been reported
by Shi et al. [6–8] to be 3-MI in N2 or a N2–H2 mixture
gas; the obtained 3-MI yield over both catalysts is
not too high (only 38%). It indicates that the present
catalyst Ba-CCA with the Ba/Cu molar ratio of 0.1
exhibits a good catalytic activity in GL cyclization
with AN to 3-MI.
Effect of Reaction Temperature
Effect of the Carrier Gas Composition
The effect of temperature on GL cyclization with AN
over the Ba-CCA catalyst is investigated. As shown in
Fig. 7, GL conversion increases when the tempera-
ture shifts from 220 to 300◦C. A 3-MI yield of 41.36%
is obtained at 220oC and reaches up to 65.17% when
increasing the reaction temperatur◦e to 240◦C. How-
ever, a higher temperature (>260 C) will lead to a
gradual decrease in the 3-MI yield. It indicates that a
higher reaction temperature probably results in the
side reaction from GL. From GC analysis of products
mixture, the by-products involve N-methylaniline,
N-ethylaniline, N-propylaniline, and acrolein. Any-
way, it seems that 240oC is the optimum tempera-
ture for 3-MI synthesis from GL and AN over the
Ba-CCA catalyst. It is obvious that the highest 3-MI
yield obtained in the present work is much higher
than that reported by Shi et al. [7,8].
As mentioned above, GL dehydrogenation or de-
hydration to intermediates containing the carbonyl
group is probably an important pathway for GL cy-
clization with AN. According to our previous stud-
ies [9,10], Cu0 centers can exhibit a catalytic activity
for hydrodehydration of alcohols with H2. Therefore,
the present work also investigates the GL cyclization
with AN over the Ba-CCA catalyst in N2 as the car-
rier gas by introducing a different amount of H2 or
O2. The results (Fig. 6) indicate that the Ba-CCA cat-
alyst gives a low GL conversion and yield toward
3-MI and 3-IMol; the product is mainly QN in oxida-
tive carrier gases including air or 5%O2–N2 mixture,
which is coincident with those results reported by
Reddy and Ganesh [12] by using N2 as the carrier
gas; 3-MI with a yield of 39.09% is obtained as a
main product. Moreover, 3-MI yield can be further
FIGURE 6 Effect of the carrier gas on the catalytic property
of the Ba-CCA catalyst with Ba/Cu = 0.1. Reaction condi-
tions: temperature 260◦C; a feed rate of liquid reactant mix-
ture (AN/GL molar ratio 3) 2.8 mL·h−1; catalyst 2 g; rate of
FIGURE 7 Effect of temperature on the cyclization over the
Ba-CCA catalyst with Ba/Cu = 0.1. Reaction conditions: the
feed rate of the liquid reactant mixture (AN/GL molar ratio 3)
2.8 mL·h−1; catalyst 2 g, the rate of 20%H2–N2 as the carrier
the carrier gas 60 mL·h−1
.
gas 60 mL·h−1
.
Heteroatom Chemistry DOI 10.1002/hc

268 Chen et al.
is probably a slow reaction step. The former eas-
ily forms QN through dehydration, and the latter
produces 3-MI through the hydrodehydration. More-
over, both reactions should be a fast reaction, which
can be improved by H2 in the carrier gas. It indi-
cates that the actual function of H2 is not to pro-
mote GL hydrodehydration to intermediate, but to
accelerate 3-IMol conversion to 3-MI. In addition, it
seems contrary that a high 3-MI yield is obtained in
N2 as the carrier gas without H2. In this case, H2
as the raw material for 3-IMol hydrodehydration to
3-MI is mainly from GL dehydrogenation over Cu0-
active centers or basic sites (Scheme 4).
Obviously, the intramolecular cyclization of SB
is an important step for the production of N-
heterocycle products such as 3-IMol, 3-MI, or QN.
As shown in Scheme 4, an achievement of this step
and even production of the final products such as
3-MI and QN are through dehydration. It is pro-
posed that dehydration mainly is carried out over
the acidic sites, which has also been proved by NH3-
TPD (Table 1). In addition, there is still another
fact that the acidic Al2O3, CCA and even other Cu-
based catalysts such as Cu/SiO2–Al2O3 reported by
Shi et al. [7, 8] also lead to the 3-MI formation.
It is probably because that acidic sites can acti-
vate AN molecules through chemical adsorption of
NH2 groups, which can directly interact with OH
groups in GL molecules to SB as shown in Scheme 5.
Certainly, the Cu0-active species in acidic Cu-based
catalysts also probably catalyze dehydrogenation of
GL in the same way as shown in Scheme 4, which
will also easily interact with the activated AN. More-
over, Cu0-active species are also the catalytic centers
Proposed Cyclization Pathway
As proposed by Shi et al. [7, 8, 12], GL cycliza-
tion with AN takes place mainly through cycliza-
tion of SB, which is produced by N-alkylation of
AN with carbonyl groups from dehydration of GL
molecules. As well known, GL dehydration can pro-
duce two kinds of intermediates containing the car-
bonyl group such as 3-hydroxypropanal and acetol
and is promoted by using Cu0 as catalytic active
centers in the presence of H2. Thus, the cycliza-
tion of SB should lead to the easy formation of QN
and 2-methylindole (2-MI) as shown in Scheme 3. It
seems easy to illustrate the formation of by-products
QN and acrolein through further dehydration of 3-
hydroxypropanal. However, 2-MI as a cyclization
product is not detected in our reaction system. In
addition, it can not also explain that the formation of
QN in N2 as the carrier gas without H2 and a higher
yield of 3-MI has been obtained in N2 or the H2–N2
mixture gas (Fig. 6). Therefore, the cyclization path-
way as shown in Scheme 3 seems unreasonable for
explaining the formation of 3-IMol and 3-MI.
From results of the above catalytic tests, it is ob-
served that the introduction of Cu-active species and
basic species improves 3-MI formation, and another
cyclization product such as 3-IMol is also found to
be formed. As reported [15–17], the basic sites are
typical catalytic centers for dehydrogenation of alco-
hols to aldehydes. Therefore, it is proposed that the
formation of SB is from AN and intermediate 2,3-
dihydroxypropanal produced by the dehydrogena-
tion of GL molecules [3] over Cu0 particles or basic
sites (Scheme 4). SB occurs intramolecular cycliza-
tion to 3,4-dihydroquinolin-3-ol and 3-IMol, which
SCHEME 3
SCHEME 4
Heteroatom Chemistry DOI 10.1002/hc

Synthesis of 3-Methylindole from Glycerol Cyclization with Aniline over CuCr/Al2O3 Catalysts 269
desorption isotherms at −196◦C using an SSA-4200
analyzer (Builder Instrument Co., Beijing, China).
Powder X-ray diffraction (XRD) analysis of catalysts
was carried on a DX-2700 X-ray powder diffractome-
ter (Fangyuan Instrument Co., Dandong, China) op-
erated at 30 kV and 20 mA, using Cu Kα radiation.
Temperature-programmed reduction by H2 (H2-
TPR) and temperature-programmed desorption of
NH3 or CO2 (NH3-TPD or CO2-TPD) were performed
on a TP-5080 adsorption instrument (Xianquan Co.,
Tianjing, China) equipped with a thermal conduc-
tivity detector. In a typical H2-TPR experiment,
20 mg of the sample placed in a quartz tube was
first degassed under 30 mL·min−1 of N2 at 300◦C for
30 min and then cooled to room temperature. The
TPR profiles were recorded from room temperature
to 850◦C with a heating rate of 10◦C·min−1 under
30 mL·min−1 of 5% H2–N2 mixture. For TPD, 20 mg
of catalysts were pretreated in N2 at 300◦C for
SCHEME 5
for 3,4-dihydroquinolin-3-ol dehydration to QN and
3-IMol hydrodehydration to 3-MI, respectively.
With the increase in reaction temperature
(>240◦C), SB as shown in Schemes 4 and 5 is easily
converted to a by-product such as N-propylaniline
through the fast hydrodehydration. Moreover, high
temperature can also lead to the improvement on
GL drastic dehydration to acrolein and even the
30 min. The adsorption of NH3 or CO2 was carried
out by feeding 10 vol% NH3 or CO2 in 30 mL·min−1
of N2 at room temperature. Samples were washed
with dry N2 for another 2 h to remove physisorbed
molecules. The obtained samples were heated in He
at a heating rate of 10◦C·min−1 from 50 to 850◦C for
NH3 or CO2 desorption.
C
C leakage of GL to aldehyde and formaldehyde
,which interact with AN to N-ethylaniline and N-
methylaniline, respectively.
Catalytic Test
The catalytic tests were carried out in a fixed-bed
quartz microreactor (i.d. 15 mm, length 40 cm)
placed in an electronically controlled oven and oper-
ating at atmospheric pressure. Prior to activity test,
2 g catalysts were in situ pretreated in 40 mL·min−1
of H2 at 300◦C for 2 h. After 60 mL·min−1 of the
given carrier gas was switched and temperature was
decreased to a desired value (220–300◦C), the liq-
uid mixture containing GL and AN with a molar
ratio of 1:3 was pumped into the reactor at a feed
rate of 2.8 mL·h−1. The tested period was 4 h, and
the products liquid mixture was collected by an ice-
salt cool trap and analyzed qualitatively and quan-
titatively on the SC-2000 gas chromatograph (GC;
Chongqing Chuanyi Analyzer, China) equipped with
an Agilent CAM capillary column (30 m × 0.32 mm
× 0.25 μm film thickness) and a flame ionization
detector. The residual reactants concluding GL and
AN and products were ascertained according to the
GC retention time of the corresponding standard
substances; their amounts were calculated accord-
ing to their GC peak area and the corresponding
correction factors. Yields of target products were ob-
tained based on GL conversion.
EXPERIMENTAL
Catalyst Preparation and Modification
Preparation and modification of CuCr/Al2O3 (CCA)
catalysts were carried out by coimpregnation. Typi-
cally, 20 g of dried commercial γ -Al2O3 (SBET = 210
m2·g−1, particle size 0.8–1.2 mm) as support were
crushed to the desired particles with a size of 0.45–
0.85 mm and impregnated in the aqueous solution
containing Cu(NO3)2, Cr(NO3)3, and/or nitrates of Al
or alkali earth metals (such as Mg, Ca, Sr, and Ba)
for 2 h at room temperature. Wherein, the molar ra-
tio of Cu:Cr:M was 1:2:0.1 except those mentioned
especially, the total weight percentare of Cu and Cr
was controlled to 5 wt% in comparison with the sup-
port. The samples were dried at 80◦C for 12 h, and
then calcined at 550 oC for 7 h to obtain the M-CCA
catalysts, wherein M referred to Al, Mg, Ca, Sr, or Ba.
Catalyst Characterization
BET surface areas (SBET), pore volume, and pore size
of the catalysts were measured by the N2 adsorption-
Heteroatom Chemistry DOI 10.1002/hc

270 Chen et al.
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Heteroatom Chemistry DOI 10.1002/hc