Mechanism of pyridine bases prepared from acrolein and ammonia by in situ infrared spectroscopy

Article abstract of DOI:10.1016/j.molcata.2015.08.014

The in situ infrared spectroscopy of acrolein and ammonia over HF/MgZSM-5 was investigated to check the adsorption reaction of acrolein and ammonia. It was proved that propylene imine intermediate came up during the condensation process of adsorbed acrolein with ammonia. The strong adsorption of C=O helps the formation of propylene imine. The reaction order and active energy were calculated according to the intensity of acrolein infrared spectroscopy. The synthesis of 3-picoline is likely to go through a flat adsorption of propylene imine and a deamination of amino dihydropyridine.

Full text of DOI:10.1016/j.molcata.2015.08.014

Journal of Molecular Catalysis A: Chemical 411 (2016) 19–26
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Mechanism of pyridine bases prepared from acrolein and ammonia by
in situ infrared spectroscopy
Xian Zhanga,b, Zhen Wub,c, Zi-sheng Chaod,∗
a
Department of Chemical Engineering, School of Erdos, Inner Mongolia University, Erdos 017000, China
Redbud Innovation Institute of Erdos, Erdos 017000, China
Membrane Technology and Engineering Research Center, Department of Chemical Engineering, Tsinghua University, Beijing 100083, China
State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, China
b
c
d
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 July 2015
Received in revised form 13 August 2015
Accepted 13 August 2015
Available online 18 August 2015
The in situ infrared spectroscopy of acrolein and ammonia over HF/MgZSM-5 was investigated to check
the adsorption reaction of acrolein and ammonia. It was proved that propylene imine intermediate came
up during the condensation process of adsorbed acrolein with ammonia. The strong adsorption of C
O
helps the formation of propylene imine. The reaction order and active energy were calculated according
to the intensity of acrolein infrared spectroscopy. The synthesis of 3-picoline is likely to go through a flat
adsorption of propylene imine and a deamination of amino dihydropyridine.
Keywords:
Acrolein
Pyridine
©
2015 Published by Elsevier B.V.
3
-Picoline
In situ infrared
Mechanism
1
. Introduction
-Picoline is an important chemical intermediate in the syn-
reported that the production of 3-picoline undergoes a process of
propylene imine formation [10], which was confirmed but never
investigated until now. Literatures [8,10–12] reported that the for-
mation of 3-picoline from acrolein or propylene imine underwent a
hydrogenation and dehydrogenation process, which is inconsistent
with the result of 3-picoline prepared from acrolein and ammo-
nium acetate in acetic acid solution with a liquid-phase reactor
[13].
3
thesis of pharmaceuticals, agriculture and fine chemicals [1,2].
Pyridine and 3-picoline was prepared from acrolein and ammo-
nia because of a higher yield with no 4-picoline [3], comparing
to that from formaldehyde, acetaldehyde and ammonia [4].
The Chichibabin mechanism [5,6] shows that the production of
pyridines from saturated aldehyde and ammonia involves imine
intermediate. Although, there is still no detailed mechanism for
the condensation of acrolein and ammonia to 3-picoline, so that
the fact that no 3-picoline could be produced between acetalde-
hyde and ammonia reaction, where the products are 2-picoline
and 4-picoline [7], is paid little attention to and admitted in some
literatures [8,9].
Caibin Wang and Li [14] concluded that the catalyst reactive
sites in favor of 3-picoline product were Brönsted acid sites over
HF-Al O3 catalyst, however, Ivanova et al. [15] insisted on the
2
interaction of weak Lewis acid sites and Brönsted acid sites of
Al O –SiO catalyst. On the other hand, a strong Lewis acid site
2
3
2
favored decomposition to pyridine product and polymerization to
tars products, while, the Brönsted acid sites were less important
than the Lewis ones. Ivanova et al. [16] preferred to the presence of
two types of Lewis acid sites exhibiting high activity and selectiv-
Acrolein was considered to be the reaction intermediate in
the condensation of formaldehyde, acetaldehyde and ammonia,
as pyridine and 3-picoline were the common pyridine products
comparing to that of acrolein and ammonia [4]. And also, it was
ity to 3-picoline over SO42 /TiO catalyst. It is necessary to analyze
−
2
and study further the catalysis of acid sites for abrogating theses
arguments. And also, it is not clear that the adsorption of acrolein
and formation of pyridine, involving to the decomposition reaction
occurring before or after the 3-picoline formation.
∗ Corresponding author.
E-mail addresses: zschao@yahoo.com, zschao@hnu.edu.cn (Z.-s. Chao).
http://dx.doi.org/10.1016/j.molcata.2015.08.014
1
381-1169/© 2015 Published by Elsevier B.V.

2
0
X. Zhang et al. / Journal of Molecular Catalysis A: Chemical 411 (2016) 19–26
Fig. 1. FT-IR spectrum of acrolein at room temperature.
Table 1
The present study describes the adsorption and reaction of
Wavenumber and assignments of IR spectra of acrolein.
acrolein and ammonia over HF/MgZSM-5 catalyst by in-situ
infrared spectroscopy in order to understand the mechanism of
pyridine and 3-picoline formation.
Wavenumber
Assignments
Bond
−
1
cm
Vibration
Intensity
3468–3395
3200–3050
3050–2950
C
O
CH2
CH
2ꢀ
ꢀ
ꢀ
Weak
Weak
Weak
2
. Experimental
2
.1. Catalyst preparation
2950–2750
CO
C
C
C
HC
C
C
C
C
H
H
C
H
O
ꢀ
Strong
Medium
Medium
Medium
Strong
Weak
Medium
Medium
Weak
2
2
2
1
750–2600
380–2200
200–2040
750–1660
2ı
2ꢀ
2g
ꢀ
ꢀ
ı
The catalyst were modified by impregnation of 130 g of HZSM-
(Si/Al = 25, Nankai University Catalyst Factory) with 100 mL 0.62 M
5
◦
Mg(NO3) solution at a temperature 90 C for 8 h and then dried.
After that, 100 mL 0.62 M NH HF2 solution followed to impregnate
the prepared solid with the same condition and then calcinated at
7
2
1630–1550
1438–1250
C
H
C
H
4
1180–1109
d
g
◦
1000–800
00 C for 4 h to get a HF/MgZSM-5 catalyst.
Note: ꢀ, ı and g denote stretching, bending and deformation; 2 denotes the double
frequency.
2.2. Characterization and methods
A varian 3100 FT-IR spectroscopy with a MCT detector and a
quartz in-situ IR transmission cell-reactor with a CaF2 window
Dalian Institute of Chemical Physics, Chinese Academy of Sciences)
into the sample holder of the IR cell-reactor and then removed
the impurities at 350 C for 2 h under vacuum condition. After the
◦
(
and a oil diffusion pump vacuum system are used to record the IR
spectrums of acrolein and its reaction products. The IR detecting
condition was followed as: speed = 40 KHz, filter = 5 Hz, resolu-
temperature was cooled down, the background spectrum was col-
lected. (2) Then, acrolein was inhaled and adsorbed on the catalyst
wafer, at the same time, the adsorption and desorption IR spec-
trum of acrolein were recorded at various temperature and vacuity.
(3) The in situ IR spectrums of adsorbed acrolein were recorded
after fresh acrolein and ammonia was inhaled respectively. (4) After
ammonia and acrolein was inhaled orderly, the in situ IR spectrums
of ammonia condensation with acrolein were recorded at various
temperature and time.
−
1
tion = 2 cm , under sampling ratio = 2, sensitivity = 1, Co-add = 32,
−
1
wavenumber = 4000–400 cm
.3. Experimental procedure
Acrolein with 95% (in mass), supplied by HuBei Xinjing new
.
2
material limited company, was firstly purified through distillation
before used. Ammonia was supplied by heating commercial ammo-
nium acetate (AR). Potassium bromide was appropriative for IR
spectroscopy and supplied by Germany Meck Company.
3. Results and discussion
The procedure was conducted as following: (1) The HF/MgZSM-
3.1. IR spectrum of acrolein
5
catalyst and KBr were firstly mixed and milled with a mass
ration of 1:99 at a total weight of 175 mg, and then pressed into a
self-supported 13 mm transparent wafer. The wafer was mounted
On the basis of the vibrational spectroscopic study of acrolein as
reported [17], we made tentative assignments to IR bands in Fig. 1,

X. Zhang et al. / Journal of Molecular Catalysis A: Chemical 411 (2016) 19–26
21
◦
◦
Fig. 3. FT-IR spectrum of acrolein at different temperature: (A) 100 C; (B) 175 C;
(
◦
◦
C) 250 C; (D) 325 C. (For interpretation of the references to color in the text, the
reader is referred to the web version of this article.)
Fig. 2. FT-IR spectrum of acrolein at different vacuity: (A) 10 Pa; (B) 50 Pa; (C) 100 Pa;
D) 200 Pa.
(
which are listed in Table 1. The vibration peaks are in pair because
of the presence of cis- and trans- acrolein as Eq. (1).
(1)
The spectrum gives rise to C O stretching bands at 1729 and
−
1
1
713 cm , which are assigned to cis and trans conformations [18],
respectively. More cis-acrolein, who is more stable than trans-one,
has been observed as its intensity is stronger.
The vibration intensities of acrolein depress greatly at lower
vacuum, so that only the C O stretching vibration (vC=O) could
◦
Fig. 4. FT-IR spectrum of adsorbed acrolein at 325 C when fresh acrolein was
inhaled: (A) at 30 Pa before; (B) at 10 Pa before; (C) after for 30 s; (D) after for 60 s.
be observed at 10 Pa as seen in Fig. 2. At the same time, the v
C=O
−
1
frequencies of cis- and trans-acrolein (1728 and 1710 cm ) are
observed at a higher frequencies (1730 and 1712 cm−1), with new
higher temperature may produce various ketene, olefin and conju-
gated 2-metyl-2,4-pentadinenal (1680–1450 cm ) [23].
−
1
−1
bands at 1691 and 1677 cm , which are shifted to higher and lower
−1
◦
frequency from 1681 cm respectively, are assigned to weaker and
Fig. 4 displays IR spectra of acrolein at 325 C before and after
stronger C O top adsorption of trans-acrolein, comparing the band
fresh acrolein was inhaled. Bands of trans-acrolein v
disappear to
C=O
−
1
−1
at 1737 cm is assigned to weak C C adsorption of cis-acrolein
19]. Presumably, we apply these results to a weakened conjuga-
form multi-conjugated aldehyde (1653 cm ), conjugated alkenes
−
1
−1
[
(1560 and 1540 cm ) and ether species (1056 cm ) because of
the C O strong adsorption as seen in Fig. 4A [24]. Additional peak
tion effect and a strengthened physical adsorption at lower vacuum,
as a result that the physical adsorption of C O leads to a red shift,
while that of C C leads to a blue one [20].
−
1
at 1719 cm is assigned to C O adsorbed of cis-acrolein, which
adsorbed more strongly appear in Fig. 4B at lower pressure, while
−
−
1
1
Expect for the same bands shown in Figs. 2 A and 3 A and B
at lower temperature, Fig. 3C and D exhibit new IR bands due to
1744 cm
is due to vC=O from adsorbed aliphatic aldehyde and
−1
1707 cm from the trans-one, comparing to 1170 cm from vC–C
−
1
adsorbed acrolein. The new bands at 1720–1660 cm in Fig. 3C
and D are assigned to vC=O of adsorbed trans-acrolein, which is
due to the further adsorption and weaker conjugation at higher
of adsorbed acrolein [25,26]. Further more, peaks of v
shift to
C=C
−
1
−1
1614 and 1605 cm , conjugated v
shift to 1540 and 1521 cm
and vC–O shift to 1072 and
,
C=C
−
1
vC–C shift to 1365 and 1267 cm
−
1
−1
temperature. While, the bands at 1715 and 1701 cm in Fig. 3D
1039 cm
because of stronger adsorption. After fresh acrolein
−
1
are assigned to blue shift from 1712 cm
and red shift from
of trans-acrolein vC=O respectively, The 1701 cm
is dosed, the adsorption of acrolein becomes weaker that free-
−
1
−1
−1
−1
1
705 cm
is
dom phase (1728 and 1711 cm ), aliphatic aldehyde (1757 cm )
−
1
probable due to flat adsorption of cis-acrolein, but the band at 1726
and adorbed phase (1737, 1720, 1697, 1680 and 1670 cm ) are
−
1
−1
−1
and 1698 cm , red- shifted respectively from 1730 and 1701 cm
at the same time, are also considered to be the further C O adsorp-
tion after C C adsorbed [21,22]. New weak signals for v bands
observed in Fig. 3C. The vibrations at 1660–1000 cm
become
−
1
more, but only olefin (1600,1520 cm ), vC–H (1412,1370 and
−
1
−1
−1
1338 cm ), vC–C (1145 cm ) and vC–O (1071 cm ) are obvious.
C=O
−1
at 1691–1660 cm in Fig. 3D suggest stronger adsorption of trans-
For a long time, the intensity of adsorbed acrolein, especially
−
1
acrolein or acrolein dimmers for the dimerization of acrolein at
the band at 1698 cm , becomes weaker and the bands of

2
2
X. Zhang et al. / Journal of Molecular Catalysis A: Chemical 411 (2016) 19–26
Fig. 5. Adsorption forms of acrolein over catalyst surface.
non-conjugated aldehyde (1757 cm−1) and flat-adsorbed phase
The adsorption of acrolein will draw stronger and flatter at higher
temperature and lower pressure, when acrolein will polymerize to
form dimmers. It is meaning that the weak (w) physical adsorption
is converted to medium (m) and strong (s) chemical adsorption
and the point adsorption to the flat adsorption. The adsorption will
become more complicated as acrolein and its adsorption products
would be adsorbed on Brönsted, weaker and stronger Lewis acid
sites over the zeolite catalyst surface.
−
1
(
1720 cm ) disappear in Fig. 4D. It is suggested that the reaction
of acrolein caused by flat-adsorbed and point-adsorbed acrolein as
−
1
new bands of muti-conjugated vC=O (1660 and 1653 cm ) could be
seen, at the same time, other bands of vC=C decrease as their weaker
adsorption with the catalyst.
Above all, it is said that trans-crolein is more active and eas-
ier to be adsorbed than cis-crolein, of which C C is easier to be
adsorbed than C O comparing that of trans-crolein is opposite.

X. Zhang et al. / Journal of Molecular Catalysis A: Chemical 411 (2016) 19–26
23
3.2. Adsorption of acrolein
The electron affinity of acrolein double bands, which are
easy to be adsorbed over catalyst surface as their higher elec-
tron density, follow the order: 1
C
2
C >
3
C
4
O > C
1
2
C
3
C
4
O.
The electron density and electrophilic ability of atoms follow
4
2
1
3
the order: O > C ≈ C > C, so that a single point adsorption
3
4
(
␩ –ꢁ) of the oxygen atom happens more easily on
while a dual site adsorption (␩ –ꢂ) of
C
O,
1
1
2
C
C is priority. The
2
adsorption of acrolein, which is determined to the surface
structure [27,28], environment [29] and properties [30,31], is
followed in Fig. 5 as summarized by the count of adsorption
sites.
(
A) The single point (ꢃ ) adsorption. The ␩ -s adsorption of sig-
1
1
nal atom will produce a carbenium ion, which is not steady and
4
difficulty to be observed as seen in Fig. 5A-s. Only the [ O] ␩ -w
1
Fig. 6. FT-IR spectrum of acrolein and ammonia: (A) before NH3 inhaled; (B) after
NH3 inhaled for 1 min; (C) after NH3 inhaled for 18 min. (For interpretation of the
references to color in the text, the reader is referred to the web version of this article.)
adsorption of trans-acrolein shown in Fig. 5A-w could be observed
clearly as it is full of unpaired electron. Comparatively, the ␩ -w
1
adsorption of other atoms is so weak that their vibration is consis-
tent with that of unabsorbed acrolein.
␩3-w and cis-␩4-w and adsorption at high temperature and low
pressure in Fig. 4A, meanwhile, the ␩3-m, ␩3-m and ␩4-s at high
temperature and lower pressure in Fig. 4B.
(
B) The double points (␩ ) adsorption. Due to the lowest elec-
2
tron density, the ␩ -w adsorption of acrolein containing 3-C could
2
3
4
be observed difficultly except for that of [ C, O], comparing that
containing 4-O will make the v red shift. On the contrary, the
-w adsorption of [ C, C] will make a blue shift. Because of the
3.3. Reaction of acrolein and ammonia
C=O
1
2
␩2
conformation resistance, the ␩ -w adsorption is more possibly hap-
Fig. 6 shows the adsorption spectra of acrolein before and after
NH3 inhaled for a time. After NH3 was dosed for 1 min comparing
2
pened to the cis-acrolein than trans-acrolein. The ␩ -m and ␩ -s
2
2
1
2
1
2
adsorption of acrolein except for that of [ C, C], producing aliphatic
aldehyde, and [ C, O], producing ether, could not be observed
because of their activation as seen in Fig. 5B.
Fig. 6B to Fig. 6A, one can see that cis-, trans-␩ -w [ C, C] and trans-
2
3
4
␩ -w adsorption of acrolein decrease while trans-␩ -w adsorption
1
3
of acrolein keeps unchanged. At the same time, the new band at
−
1
(
C) The three points (␩ ) adsorption. As the same reason above,
1670 cm observed in Fig. 6B appear indicating the existence of
3
3
4
the ␩ -s and ␩ -m adsorption of acrolein could not be observed
C N group [34], with also a trans-␩ -w [ C, O] adsorbed C O band
2
3
3
1
−
1
−1
because of the carbonion formation. Due to the atom electron den-
at 1684 cm blue shifted from 1677 cm . It says that the acrolein
have been converted to propylene imine, who is probably a cis-
1
2
4
sity order of acrolein, the ␩ -w and ␩ -m adsorption of [ C, C, O],
3
3
2
1
2
which are due to the further ␩ -w and ␩ -s adsorption of [ C, C]
one as the ␩ -w adsorption of trans- acrolein is depressed most
2
2
1
−
1
−1
respectively, is the more possible one than the others as seen in
Fig. 5C-w and C-m2.
greatly. That the trans-␩ -w band at 1698 cm shifts to 1694 cm
1
shows also a weaker adsorption after NH dosed in Fig 6B and D.
3
−
1
(
D) The four points (␩ ) adsorption. The ␩4 adsorption of
The bands at 1660 and 1653 cm disappear gradually and a new
band at 1647 cm is easy to be considered to be a multi-conjugated
vC=N. Additionally, the new bands at 1612 and 1521 cm indicate
4
−
1
acrolein, which is usually called flat adsorption as all atoms interact
with the surface as seen in Fig. 5D, is attributed to the ␩3 further
adsorption that the ␩ -m2 and ␩ -m3 adsorption of acrolein could
−
1
the conjugated C C or cyclic C C [23], who was partly converted
4
4
−
1
hardly be observed. Due to the coadsorption of both C C and C O,
to olefin [26] at 1600 and 1506 cm as seen in Fig 6C and D. And
−
1
the energy and stability of ␩ -w adsorption increase and are close
also the 1360 cm band of ıC–H is shifted to higher frequency as
acrolein decrease. Moreover, the new bands at 1540 and 1448 cm
indicate the existence of pyridine [35], however, more 3-picoline
appear at 1531 and 1430 cm after a long time [36,37]. It suggests
that 3-picoline appears after the production of pyridine, which
may be produced at stronger acid sites. As a following, NH3 would
occupy those strong acid sites leading to weak acid ones and pre-
ferring to produce 3-picoline product.
4
−
1
to that of ␩ -s adsorption. The ␩ -m and ␩ -s adsorption need so
2
4
1
4
more energies that the acrolein may probably decompose at some
extent.
−
1
The ␲, di-␴ and di-␲ adsorption reported in literatures [32,33]
are correspond to ␩ -w, ␩ -s, and ␩ -w adsorption. Except for the
2
2
4
weak physisorption, Loffreda [17] reported the strong adsorption
4
1
2
3
4
1
2
of [ O] trans-␩ , [ C, C] trans- and cis-␩ , [ C, O] trans-␩ , [ C, C,
1
2
2
4
O] trans- and cis-␩ , trans- and cis-␩ were present over Lewis acid
Fig. 7 shows the spectra of acrolein with NH3 dosed before
3
4
sites. Akita [29] admitted that as the coverage increasing, cis-␩ and
acrolein for a certain time at different temperatures. New v
3
C=O
−
1
trans-␩ adsorption, which is more stable than trans-␩ adsorption,
Bands of adsorbed acrolein at 1750–1680 cm and pyridines at
4
1
−
1
will be converted to trans- and cis-␩ -s adsorption. After all, it is
1540 and 1454 cm
are observed in Fig. 7D and E. It indicates
2
difficult to confirm the active carbonion intermediate from strong
adsorption. Although, we could conclude that flat, strong and trans
adsorption are favored at lower pressure, while point, strong and
cis adsorption are favored at higher temperature and stronger acid
sites and adsorption of C O is favored over polar surface, on the
contrary, that of C C is favored over non-polar surface.
that pyridines are more easily to be produced when NH3 is over-
dosed before acrolein and at a temperature exceeding 523 K, at
which acrolein is activated by adsorption of trans-acrolein. It shows
that pyridines are mainly produced from trans-acrolein and higher
temperature as the intensity of trans-acrolein decrease and that
of pyridines increase at 598 K comparing that at 523 K. However,
−
1
Based on the vibrational spectroscopic studies of acrolein under
various condition, we made tentative assignments to IR bands are
listed in Table 2. Therefore, the ␩ -w and ␩ -w adsorption of and
other bands at 1556 and 1470 cm show not only the present of
pyridine products but other byproduct.
Fig. 8 shows the HC O peak area (A) of acrolein versus tem-
perature (T) and time (t), and also the curve of ln(−dA/dt) versus
1
2
gaseous acrolein are present at low pressure as seen in Fig. 2B. The
␩2-s, trans-␩ -w and trans-␩ -w adsorption of acrolein are present
at high temperature as seen in Fig. 3D, comparing the ␩ -m, cis-
−
1
lnA. The absorbance of acrolein HC O peak area (1750–1680 cm
)
3
4
and its concentration accords with the Lambert–Beer’s Law
3

2
4
X. Zhang et al. / Journal of Molecular Catalysis A: Chemical 411 (2016) 19–26
Table 2
Frequencies and assignments of IR spectra of acrolein adsorption over catalyst surface.
Absorption
HC OConjugated
Wavenumber (cm−1)
Types
Gas
Atoms
Cis C3H4O
Trans C3H4O
None
4O
O
Yes
Yes
No
1729–1731
1728
1145
1710–1713
1696–1690
1071
␩
1
w
s
4
␩
2
w
w
w
s
1C, 2C
Yes
Yes
Yes
No
1737–1738
1719–1720
1726
1715
1707
1684–1675
1757
1
3
1
3
C, O; 2C, 4
4
O
4
C,
C,
C,
O
C
2
4
s
O
No
1172–1056
1
2
1
1
C, 2C, 4
␩
␩
3
4
w
w
w
m2
O
O
O
O
Yes
Yes
Yes
No
1726
1705
1691
1691
1734
3
4
4
4
C, C,
1719–1720
1719–1720
1744
3
C, C,
2
C, C,
1C, 2C, 3C, 4O
w
m1
s
Yes
No
No
1726
1736
1072–1039
1701
1707
1
2
3
4
C, C, C,
O
C, 2C, 3C, 4O
Fig. 7. FT-IR spectra of ammonia and acrolein for 30 min at different temperatures:
A) 298 K; (B) 373K; (C) 448 K; (D) 523 K; (E) 598 K.
(
[
38]: A = K × C (the value of molar absorptivity K is a constant,
1
−
−1
L × mol × cm ). The conversion (˛) of HC O group, which is
consistent with that of acrolein at this low pressure, is calculated
as ˛ = (A − At)/A × 100%= 92.21% when T = 598 K and t = 30 min
0
0
in Fig. 8a. For that, the initial HC O absorbance of acrolein is
described for A , and the absorbance of acrolein at t moment is
0
described for At. The equation of reaction rate for acrolein and
ammonia is evolved as Eq. (2), in which k is the reaction velocity
−1
constant (k, min ) and n is the reaction order (n). The reaction
order n is consistent with the curve slope of ln(−dA/dt) versus
lnA in Fig. 8b. The results show the standard curve function:
y = a + b × x = −2.4477 + 0.9932 × x, and the square of linear correla-
2
tion coefficient: R = 0.9906. It shows n = 0.9932≈1, which meaning
the ln(−dA/dt)−lnA curve is consisted with the first-order kinet-
ics mode. Probably, propylene imine is the first main intermediate
from acrolein and ammonia and HC O group is the main activated
site [11,12].
Fig. 8. Peak area of acrolein HC O group: (a) versus temperature (T) and time (t);
b) ln(−dA/dt) versus ln A. (b) Peak area of acrolein HC O group ln(−dA/dt) versus
ln A.
(
As the reaction order n is equal or approximate to 1, the equation
of reaction rate could be evolved as Eq. (3).
−
dC
dt
1
dA
dt
k
n
dA
n
= K × A ⇒ − dt = k × K1−n × A
n
n
v =
= k × C ⇒ −K ×
−
dC
−dC
v =
= k × C ⇒
= k × dt ⇒ ln C = ln C − k × t
dA
0
ln(− dt ) = ln(k × K1−n) + n × ln A
dt
C
⇒
(2)
⇒
ln A = ln A − k × t
(3)
0

X. Zhang et al. / Journal of Molecular Catalysis A: Chemical 411 (2016) 19–26
25
−
1
Fig. 9 shows the curves of lnA versus t and the curve of lnk versus
/T. The curve slope of lnA versus t shown in Fig. 9a is the negative
119 − 16 = 103 kJ × mol
in trans-one with Extended Hückel
1
Mode and ChemBio 3D soft. It is also confirmed that propylene
value of the reaction velocity constant (k), which is 0.0037 at 523 K
imine is the reaction intermediate as the reaction E is close to the
a
and 0.085 at 598 K. The Arrhenius relation could be evolved as Eq.
ꢄE of propylene imine and acrolein.
0
1/2
−1
(
4), in which A is the Aleniwus factor (M × min ) and Ea is the
activity energy.
3.4. Mechanism of condensation between acrolein and ammonia
Ea
0
(−Ea/RT)
0
k = A × e
⇒ ln k = ln A −
(4)
The result that pyridine products is more easily to be produced
over stronger Lewis sites is also observed in this paper due to a
stronger adsorption of trans-acrolein [16]. A Diels–Alder conden-
sation is proposed to be present as shown in Eq. (5), which is similar
to the acrolein dimerization and decarbonylation [25].
RT
The curve slope of lnk versus 1/T shown in Fig. 9b is
calculated as −Ea/RT = −13163, so the activity energy
(5)
The stronger C O adsorption of trans-acrolein could also pro-
duce olefin products and polymerization products [11,15] as seen
in Eqs. (6) and (7), which are related to stronger and cis-adsorption
at some extent.
(6)
(7)
The production of 3-picoline is considered to be related to a
weak and flat adsorption of trans-propylene imine as seen in Eq.
(8). As the adsorption over Brönsted and weaker Lewis acid sites
are weaker than that over stronger Lewis acid site,the 3-picoline is
probably produced on the former two catalytic sites [14,16]. It is
concluded that the hydrogenation of acrolein is not necessary for
the formation of 3-picoline.
(8)
Ea = 13,163 × 8.314 = 109.4 kJ × mol−1.
The
energy
differ-
ence (ꢄE) of propylene imine and acrolein is calculated
to be 120 − 9 = 110 kJ × mol−
1
in cis-conformation and

2
6
X. Zhang et al. / Journal of Molecular Catalysis A: Chemical 411 (2016) 19–26
The pyridine product is produced from cis- propylene imine and
O double-adsorbed trans-acrolein through a Diels–Alder reac-
C
tion and decarbonylation of C O adsorption over strong Lewis acid
site. However, the 3-picoline is preferred to be produced from flat
adsorbed trans-acrolein and trans-propylene imine over Brönsted
and weaker Lewis acid sites.
Acknowledgements
We are grateful to the financial supports from the Project
#
21376068 for National Natural Science Foundation (NSFC), the
Colleges and Universities’ Scientific Research Project of Inner
Mongolia Autonomous Region (NJZZ13017) and the Innovation
training program of Inner Mongolia University.
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