Synthesis of picolines over metal modified HZSM-5 catalyst

Article abstract of DOI:10.14233/ajchem.2015.17883

A series of metal (i.e. Pb, Cd, Zn, Co, Cr) modified H-ZSM-5 catalysts were prepared by an ion-exchange method and were characterized by XRD, FT-IR, NH₃-TPD and N₂ adsorption techniques. There catalytic activity was evaluated in the Chichibabin condensation of acetaldehyde and ammonia giving 2-picoline, 4-picoline and a small amount of pyridine as the product. The catalyst coking behaviour was also characterized by TG measurement. The characterization results showed that the crystal structure of H-ZSM-5 was well reserved and the active metal ions were evenly spread in the ZSM-5 framework. The surface acidity was enhanced a lot after the metal modification. Catalytic results showed that metal incorporated catalysts greatly increased the total yield of pyridine bases, especially which of 2-picoline and 4-picoline, meanwhile the ratio of 2-picoline/4-picoline was also enhanced.

Full text of DOI:10.14233/ajchem.2015.17883

Asian Journal of Chemistry; Vol. 27, No. 7 (2015), 2415-2419
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2015.17883
Synthesis of Picolines Over Metal Modified HZSM-5 Catalyst
*
F. JIANG, J.J. HUANG, W.Y. XIAO, G.M. XIAO and H.Y. LI
School of Chemistry and Chemical Engineering, Southeast University, Nanjing, P.R. China
Corresponding author: Tel/Fax: +86 25 52090612; E-mail: xiaogm@seu.edu.cn
Received: 24 April 2014; Accepted: 27 July 2014;
*
Published online: 30 March 2015;
AJC-17047
A series of metal (i.e. Pb, Cd, Zn, Co, Cr) modified H-ZSM-5 catalysts were prepared by an ion-exchange method and were characterized
by XRD, FT-IR, NH -TPD and N adsorption techniques. There catalytic activity was evaluated in the Chichibabin condensation of
3
2
acetaldehyde and ammonia giving 2-picoline, 4-picoline and a small amount of pyridine as the product. The catalyst coking behaviour
was also characterized by TG measurement. The characterization results showed that the crystal structure of H-ZSM-5 was well reserved
and the active metal ions were evenly spread in the ZSM-5 framework. The surface acidity was enhanced a lot after the metal modification.
Catalytic results showed that metal incorporated catalysts greatly increased the total yield of pyridine bases, especially which of 2-picoline
and 4-picoline, meanwhile the ratio of 2-picoline/4-picoline was also enhanced.
Keywords: ZSM-5, Ion-exchange, 2-Picoline, 4-Picoline.
Balanced equation for key products of the CH
reaction is as follows.
3
CHO and NH
3
INTRODUCTION
Pyridine and picolines are useful intermediates in the
synthesis of herbicides, pharmaceuticals, surface-active agents,
disinfectants and other fine chemicals, such as vitamin B, nico-
tinamide and nicotinic acid. Most picolines have been mass-
produced by the Chichibabin condensation, which involves
gas-phase reactions of acetaldehyde, formaldehyde and
R1
3CH
3
CHO
+
NH3
+
3H O + H
2
2
N
R
2
1
-5
ammonia . Usually 2-picoline and 4-picoline are formed as
the by products in this reaction. However, with the development
of economy, the demand of 2-picoline and 4-picoline is increa-
sing. 2-picoline is mainly used in the synthesis of fertilizer
synergist, rubber additives, dyes intermediates, photosensitive
film material, etc. 4-Picoline is used for the synthesis of
isoniazid, phosphate-solubilizing antidote in medicine industry
and also used in the field of the pesticide, dye, rubber additives,
synthetic resin, especially for the synthesis of 4-vinyl pyridine.
Chichibabin condensation of ammonia and acetaldehyde is a
method to synthesis of 2-picoline and 4-picoline.
2
4
-Picoline: R
1
1
= H, R
2
= CH
3
-Picoline: R
= CH
3
, R
2
= H
The activity of the catalyst is in connection with its acidity
which is an important property that governs the yield and
selectivity . In order to adjust the surface acidity of the
catalyst, several methods have been used to modify H-ZSM-
, such as impregnation , ion-exchange , chemical vapor
deposition (CVD) , atom-planting method
mation treatment . To our best of knowledge, study of the
influence of incorporated metal on the catalytic performance
in the condensation of acetaldehyde and ammonia are limited.
Therefore, in the present work, ion-exchange technique was
employed to prepare a series of metal incorporated H-ZSM-5
catalysts. The investigated metals include Pb, Cd, Zn, Co and
Cr. The catalytic performance of these catalysts for the conden-
sation of acetaldehyde and ammonia was evaluated and the
coking performance was also investigated.
5
,10
5
,6,11
5
5
1
2,13
14,15
and subli-
1
6
ZSM-5 zeolite has intrinsic acidity, capability to incor-
porate trivalent cations other than Al in framework and three-
dimensional porosity and therefore, has been explored exten-
sively as a catalyst for the aldehyde-ammonia condensation
4-9
reaction in recent years . It is expected that the zeolite shape-
selectivity plays an important role in condensation reactions,
leading to pyridine, 2-picoline and 4-picoline and limiting the
formation of bulkier reaction intermediates. The reactions
include condensation, cyclization and dehydrogenation.

2
416 Jiang et al.
Asian J. Chem.
-
1
flow of 30 mL min . After cooling to 373 K, NH was intro-
3
EXPERIMENTAL
Catalyst preparation: The original HZSM-5 zeolite
duced by a pulsed injection with the He flow until saturation.
The sample was quenched again at the temperature for 1 h to
remove the excess NH . Desorption was then performed under
(
SiO /Al = 120 mol/mol) was supplied by Nanjing Refinery,
2
O
2 3
3
which was calcined at 823 K for 5 h before using.
The metal was incorporated respectively by an ion-
exchange technique with water as the solvent. The metal
-1
the same He flow with a ramp of 10 K min to 973 K.
RESULTS AND DISCUSSION
precursors used to prepare the catalysts were: Pb(NO ) ,
3
2
XRD patterns of all the samples show the characteristic
MFI diffraction peaks and similar peak positions in Fig. 1,
which indicates that the ZSM-5 crystal structure is not
destroyed during the ion-exchange treatment . Moreover, no
metal containing phases are detected suggesting a highly dis-
persed metal species on the zeolite.
Cd(NO
Co(NO
3
)
2
·4H
2
O, Cr(NO
3
)
3
·9H
2
O, Zn(NO
3
)
2
·6H O and
2
3
)
2
·6H O. In a typical experiment, 3 g HZSM-5 was
2
added into 75 mL nitrate salt aqueous solution with a concen-
tration of 0.125 mol/L. After stirring at 363 K for 24 h, the
slurry was filtrated and washed with distilled water. Finally,
the samples were dried at 373 K for 6 h and then calcined at
5
8
23 K for 4 h. These samples were denoted as Pb-ZSM-5, Cd-
ZSM-5, Cr-ZSM-5, Zn-ZSM-5 and Co-ZSM-5, respectively.
Activity measurements: The vapor phase condensation
of ammonia and acetaldehyde was carried out in a fixed bed
reactor (ϕ 20 × 6) at 673 K and atmospheric pressure. The
catalyst bed temperature was measured with a thermocouple
placed at the center of reactor cross-section. The 20 wt. %
acetaldehyde aqueous solution was fed from the top of the
reactor using a chromatographic pump (USA). Ammonia was
fed from a pressurized cylinder and adjusted by mass flow
controllers. Prior to this, 1 g of the catalyst diluted with 1.5 g
quartz sand was loaded into the reactor. A 1: 7 molar ratio of
aldehyde/ammonia was introduced into the reactor at GHSV
-1
of 1000 h . The product was cooled and condensed using ice-
cold water and collected per hour at the bottom. A sufficient
number of ice-cooled traps were used to collect all lower
boilings. The products were finally analyzed by GC 9160
equipped with FID using a capillary column of FFAP.Yield of
pyridine bases (2-picoline, 4-picoline and pyridine) were
calculated on the basis of carbon balance with calibration. As
a result of the polymerization of acetaldehyde, the content of
acetaldehyde consumed can't be calculated. The selectivity was
calculated based on the content of carbon in the acetaldehyde
reacted is the same with the content of carbon in pyridine, 2-
picoline and 4-picoline. The yield ratio of 2-picoline/4-picoline
was also calculated and discussed.
1
0
20
30
(°)
Fig. 1. XRD patterns of metal modified and original samples
40
50
2θ
Fig. 2 shows the IR spectra of the samples. The absorption
-1
bands at 1220, 1100, 800 and 455 cm are typical of siliceous
materials. These absorption bands are the external asymmetric
stretching, internal asymmetric stretching, external symmetric
stretching and the bending vibration peak of the T-O (Si or
Al), respectively . As a result of the asymmetric stretching
mode in double-ring blocks, a characteristic band at 551 cm
16
-1
Catalyst characterization: The X-ray diffraction (XRD)
patterns were recorded on a Rigaku D/MAX 2000 instrument
with CuK (λ = 1.5406 Å) radiation. Thermal analysis was
α
carried out using a simultaneous DSC-TGA instrument (SDT
Q600, TA, USA) and performed at a uniform heating rate of
-1
2
0 K min under air atmosphere. The surface area and pore
characteristics of the samples were measured by means of a
Beishide 3H-2000 instrument. Before the adsorption of N at
7 K, the samples were degassed at 673 K for 3 h. Total specific
2
7
surface areas (SBET) of the samples were determined by
applying the BET (Brunauer-Emmett-Teller) model to nitrogen
adsorption data obtained in the relative pressure range from
0
.01 to 0.12. Total pore volumes were estimated from the
amount of nitrogen absorbed at a relative pressure of 0.99.
The t-plot method was employed to evaluate the volume of
1600
1400
1200
1000
800
600
400
p
micropore (Vmicrop). The average pore diameter (D ) was obtained
–1
Wavenumber (cm )
from the BET data. NH -TPD was carried out with a quartz
3
reactor, a TCD detector and 100 mg sample at atmospheric
pressure. The system was quenched at 823 K for 1 h in a He
Fig. 2. IR spectra of (a) H-ZSM-5, (b) Pb-ZSM-5, (c) Co-ZSM-5, (d) Cd-
ZSM-5 and (e) Zn-ZSM-5 samples

Vol. 27, No. 7 (2015)
Synthesis of Picolines Over Metal Modified HZSM-5 Catalyst 2417
is observed in each of the catalysts, which suggests that all the
catalysts have the MFI structure. As reported, the optical
-1
density ratio of the 550 and 450 cm is about 0.72 for the pure
17
-1
MFI sample . The intensity ratios of the 550 and 450 cm for
a) HZSM-5, (b) Pb-ZSM-5, (c) Co-ZSM-5, (d) Cd-ZSM-5
(
and (e) Zn-ZSM-5 are 0.47, 0.77, 0.86, 0.75 and 0.66, respec-
tively. It is concluded that metal incorporated has a certain
influence on the crystallinity of HZSM-5 and the MFI structure
of these catalysts is well reserved. These results are in accor-
dance with the XRD results.
Table-1 summarizes the BET surface area, pore volume
and average pore size of the samples. It can be seen that the
specific surface area decreases slightly after the modification.
The modification of Cd, Zn, Co and Cr make the pore volume
and pore size slightly increase, while that of Pb behaviour the
opposite way. The expanding pore volume and pore size may
be due to the destruction of zeolite framework in the ion-
exchange process, for these aqueous solutions of metal nitrates
have weak acidity which can lead to the dealumination of
the framework and result in the meso- or macro-pores in the
5
00
600
700
800
900
Temperature (K)
3
Fig. 3. NH -TPD curves of the original and metal modified ZSM-5 samples
Result of thermal analysis of the samples used after 8 h is
presented in Fig. 4. The slightly declining of TG curve before
1
8,19
zeolite . The declining pore volume and pore size may be
ascribed to the much bigger Pb atom replacing the original
small H atom during the ion-exchange process. Consequently,
the decrease of XRD peak intensity in Fig. 1 can be explained
as the framework of zeolite was partly destroyed, or the incor-
porated metal covered the zeolite structure. On the whole, the
surface area and pore characteristics do not change too much
during the ion-exchange process.
4
73 K is ascribed to desorption physically adsorbed water, for
water is one of the products in this reaction. The one occurred
from 573 to 1073 K is undoubtedly due to the burning of coke
formed during the reaction of acetaldehyde and ammonia. The
content of coke is equal to the losing weight of catalysts. We can
see that the carbon deposition of modified catalysts is higher
than that of the parent HZSM-5, which is probably ascribed to
the covered surface pores and the destruction of ZSM-5 frame
3
The NH -TPD curves of the samples are depicted in Fig. 3.
21
work which would restrict the diffusion of the products . How-
ever, that of Pb-ZSM-5 is the lowest among the modified samples.
The curves have two peaks corresponding to two kinds of acid
sites, i.e. the weak sites associated with the TPD peak at around
4
7
80-650 K and the strong sites related to the peak at around
00-850 K. After the metal modification, the peak area of the
1
00
9
9
9
9
9
8
7
6
weak acid sites increases largely, while that of the strong acid
sites decreases. The top temperature of the weak peak also
slightly shifts to higher position when the curve of metal modi-
fied sample is presented. The change of Pb-ZSM-5 is the
biggest, of which the top temperature shifts to 570 K with that
of the original sample 550 K. Since the ion-exchange process
a
b
c
+
95
is the exchange of H in the ZSM-5 framework to metal ions,
it is deduced that the declining strong acid sites are mainly
Brønsted acid sites and the increasing weak acid sites are mainly
Lewis acid sites. The meal incorporation greatly increases the
total amount of acid sites, especially that of the weak acid
sites. The ratio of the acid amount of HZSM-5/Co-ZSM-5/
Zn-ZSM-5/Cd-ZSM-5/Cr-ZSM-5/Pb-ZSM-5 is about 1: 1.36:
9
4
3
d
e
9
f
92
400
600
800
1000
1200
Temperature (K)
1
.35: 1.29: 1.15: 1.68. The influence of Pb metal on the catalyst
Fig. 4. TG curves of used samples: (a) H-ZSM-5, (b) Cr-ZSM-5, (c) Pb-
ZSM-5, (d) Zn-ZSM-5, (e) Cd-ZSM-5 and (f) Co-ZSM-5
surface acidity is the most significant.
TABLE-1
TEXTURAL PROPERTIES OF DIFFERENT CATALYSTS
2
3
3
3
a
Sample
H-ZSM-5
Pb-ZSM-5
Cd-ZSM-5
Zn-ZSM-5
SBET (m /g)
357
Vtotal (cm /g)
Vmicrop (cm /g)
Vmesop (cm /g)
Dp (nm)
3.33
3.26
3.44
3.85
0.297
0.290
0.303
0.328
0.390
0.298
0.075
0.089
0.069
0.072
0.104
0.078
0.222
0.201
0.234
0.256
0.286
0.217
356
352
340
342
Cr-ZSM-5
Co-ZSM-5
4.56
3.42
346
a
Vmesop = Vtotal-Vmicrop

2
418 Jiang et al.
Asian J. Chem.
Figs. 5-7 depicts the yield of 2-picoline, 4-picoline, total
ZSM-5), 42.4 % (Cd-ZSM-5), 31.8 % (Zn-ZSM-5), 25.4 %
(Cr-ZSM-5), 22.5 % (Co-ZSM-5) and 15.7 % (Mg-ZSM-5),
respectively. The highest one (47.1 %) is almost three times
as that of the initial H-ZSM-5 catalyst (17.5 %). Such increase
in 2-picoline yield is not only due to the increase of pyridine
bases yield from 42.5 to 84.1 %, but also due to the increase
of 2-picoline selectivity from 41 to 56 %.
pyridine bases and selectivity of 2-picoline and 4-picoline as
a function of time on stream (TOS), respectively. Although
the influence of time on stream is small, the following trends
are observed. The total yield of pyridine bases increases to a
maximum value with an initial increase in time on stream prior
to declining with further increase in time on stream and it seems
to be steady after reaction for 2 or 3 h for most samples except
Pb-ZSM-5, the time of which is 5 h. The highest yields of
pyridine bases over these catalysts are also obtained when the
reaction proceeds for 2 or 3 h, which are 50.3 % (Co-ZSM-5),
65
6
0
5
8
5
4.1 % (Pb-ZSM-5), 61.1 % (Zn-ZSM-5), 56.2 % (Cr-ZSM-
), 73.2 % (Cd-ZSM-5) and 42.5 % (HZSM-5), respectively.
5
The yields of metal modified catalysts are superior to that of
HZSM-5. The HZSM-5 catalyst used in the synthesis of 2-
picoline and 4-picoline was less reported. From the reported
50
4
5
0
5
,14,16
literatures
, we can see that the yield of pyridine and 3-
4
picoline is about 55-70 %, which is lower than that of Pb-
20
ZSM-5 catalyst in the present work. Sile et al. reported that
the yields of 2-picoline and 4-picoline catalyzed by theAl
3
5
0
2
O -
3
5
6
CrCl
that the total yield of 2-picoline and 4-picoline catalyzed by
the Pb-Cr-Al -SiO catalyst was 80.6 %. These yields of 2-
picoline and 4-picoline are also lower than that of our work.
3
catalyst were 27 and 11 %, respectively. Rao et al. reported
45
40
35
30
25
20
15
10
O
2 3
2
90
80
70
60
50
40
1
2
3
4
5
6
7
8
Time on stream (h)
Fig. 6. Yield and selectivity of 2-picoline versus time on stream. (a) H-
ZSM-5, (b) Co-ZSM-5, (c) Pb-ZSM-5, (d) Zn-ZSM-5, (e) Cr-ZSM-
5, (f) Cd-ZSM-5
Fig. 7 shows the influences of TOS on the yield and
selectivity of 4-picoline. As is shown in this figure, sample of
H-ZSM-5 occupies the highest place in the selectivity plot, of
which the selectivity is about 53.8 %. The following line
belongs to Co-ZSM-5 with a value of about 50.7 %. The selec-
tivity of the other catalysts is below 50 %, about 40 % (Cd-
ZSM-5, Pb-ZSM-5) and 44 % (Zn-ZSM-5, Cr-ZSM-5). In
general, the selectivity of metal incorporated catalysts is lower
than the original H-ZSM-5. The highest yields of 4-picoline
are also obtained at reaction for 2 or 3 h, which are 34.1 %
(Pb-ZSM-5), 27.7 % (Cd-ZSM-5), 25.8 % (Zn-ZSM-5), 26.0 %
(Cr-ZSM-5) and 25.5 % (Co-ZSM-5), respectively. Comparing
with the initial HZSM-5 catalyst (21.4 %), the highest one
(34.1 %) increases by 12.7 %. Such increase in 4-picoline yield
is mainly due to the promotion of pyridine bases.
Fig. 8 depicts the change of 2-picoline to 4-picoline ratios
as a function of TOS. These catalysts had a high initial 2-
picoline to 4-picoline ratio, varied from 0.7 to 1.6 and no
specific trend was observed with the increase of TOS. As can
been seen that the ratio of Cd-ZSM-5, Pb-ZSM-5 and Zn-ZSM-
5 samples are bigger than 1, which are varied from 1.44 to
1.60, 1.36 to 1.49, and 1.17 to 1.28, respectively. That of the
other two samples are below 1, which are in the range of 0.94-
1.07 (Cr-ZSM-5), and 0.86-1.01 (Co-ZSM-5), respectively.
1
2
3
4
5
6
7
8
Time on stream (h)
Fig. 5. Total yield of pyridine bases versus time on stream. (a) H-ZSM-5,
b) Co-ZSM-5, (c) Pb-ZSM-5, (d) Zn-ZSM-5, (e) Cr-ZSM-5, (f)
(
Cd-ZSM-5
Fig. 6 depicts the yield and selectivity of 2-picoline over
varied samples. Fig. 6 showed that the influence of TOS on
selectivity is negligible for all the samples. Samples of Cd-
ZSM-5 and Pb-ZSM-5 occupy the highest place in the selec-
tivity plot, of which the selectivity is about 58 and 56 %,
respectively. The following line belongs to Zn-ZSM-5 with a
value of about 52 %. Selectivities of the other catalysts are
below 50 %, about 45 % (Co-ZSM-5, Cr-ZSM-5) and 41 %
(
HZSM-5). In general, the selectivity of metal incorporated
catalysts is higher than the original HZSM-5, which indicates
that the introduction of metal species could change the product
distribution and make it prone for 2-picoline production. As a
result of the behaviour of total pyridine bases yield and 2-
picoline selectivity, the trends of 2-picoline yield are similar to
that of yield of pyridine bases: the highest yields of 2-picoline
are obtained at reaction for 2 or 3 h, which are 47.1 % (Pb-

Vol. 27, No. 7 (2015)
Synthesis of Picolines Over Metal Modified HZSM-5 Catalyst 2419
2
1,22
reaction . The increasing amount of surface acidity may be
the reason for the high picoline yield, while the increasing
amount of weak acid sites are account for the unique selectivity
of 2-picoline.
5
5
4
4
5
0
5
0
Conclusion
Highly dispersed and MFI structure well reserved Pb, Cd,
Zn, Co, Cr modified ZSM-5 catalysts were obtained by the
ion-exchange method. The surface area and pore properties
were also showed small change after the modification. How-
ever, the amount of surface acidity, especially the weak acidity,
increased a great deal of the modified samples. Catalytic
experiments revealed that the metal incorporated catalysts gave
higher yields of pyridine bases than the original HZSM-5.
Among them, performance of Pb-ZSM-5 and Cd-ZSM-5 was
better than that of the rest catalysts in terms of yields of total
pyridine bases and selectivity of 2-picoline. The yields of pyri-
dine bases for Pb-ZSM-5 and Cd-ZSM-5 were 84.1 % and
36
32
28
24
20
16
73.2 %, respectively and the selectivity of 2-picoline were 56.3
and 58.6 %, respectively. However, the coking of the metal
incorporated catalysts was worse than the initial zeolite, which
may be due to the restriction of diffusion of the products after
modification. Moreover, the coking of Pb-ZSM-5 was the least
among the modified samples which also gave the highest yield
of pyridine bases.
1
2
3
4
5
6
7
8
Time on stream (h)
Fig. 7. Yield and selectivity of 4-picoline versus time on stream. (a) H-
ZSM-5, (b) Co-ZSM-5, (c) Pb-ZSM-5, (d) Zn-ZSM-5, (e) Cr-ZSM-
5, (f) Cd-ZSM-5
ACKNOWLEDGEMENTS
The authors thank the National Natural Science Foundation
of China (21276050) and the Scientific Research Foundation
of Graduate School of Southeast University (YBJJ1341).
The ratios of all the metal incorporated catalyst are higher
than that of H-ZSM-5 (0.75-0.82) in addition to that of Mg-
ZSM-5 catalyst at the reaction carrying on 2 and 5 h. Ion-
exchange treatment increases the selectivity of 2-picoline but
decreases that of 4-picoline.
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(
Cd-ZSM-5
All these results discussed above show that the yield of
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only enhances the yield of picolines, but also has a unique
selectivity to 2-picoline. This may be due to the change of
distribution of surface acidity, which is a very important factor
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