PtSnNa/SUZ-4: An efficient catalyst for propane dehydrogenation

Article abstract of DOI:10.1016/S1872-2067(17)62750-5

The structure and catalytic properties of PtSn catalysts supported on SUZ-4 and ZSM-5 zeolite have been studied by using various experimental techniques including XRD, nitrogen adsorption, NH₃-TPD, TG, H₂-TPR and TPO techniques combined with propane dehydrogenation tests. It has been shown that SUZ-4-supported PtSnNa (PtSnNa/SUZ-4) was determined to be a better catalyst for propane dehydrogenation than conventional catalysts supported on ZSM-5, owing to its higher catalytic activity and stability. Dibenzothiophene poisoning experiments were performed to investigate the detailed structures of the two supported catalysts. The characterization of the two catalysts indicates that the distribution of Pt on the porous support affects the activity. In contrast to ZSM-5-supported catalysts, Pt particles on the PtSnNa/SUZ-4 are primarily dispersed over the external surface and are not as readily deactivated by carbon deposition. This is because that the strong acid sites of the SUZ-4 zeolite evidently prevented the impregnation of the Pt precursor H₂PtCl₆ into the zeolite. In contrast, the weak acid sites of the ZSM-5 zeolite led to more of the precursor entering the zeolite tunnels, followed by transformation to highly dispersed Pt clusters during calcination. In the case of the PtSnNa/ZSM-5, the interactions between Sn oxides and the support were lessened, owing to the weaker acidity of the ZSM-5 zeolite. The dispersed Sn oxides were therefore easier to reduce to the metallic state, thus decreasing the catalytic activity for hydrocarbon dehydrogenation.

Full text of DOI:10.1016/S1872-2067(17)62750-5

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Chinese Journal of Catalysis 38 (2017) 529–536
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
PtSnNa/SUZ‐4: An efficient catalyst for propane dehydrogenation
Hualan Zhou a, Jingjing Gonga, Bolian Xu a, Shengcai Denga, Yuanhua Ding b, Lei Yu a,b,*,
Yining Fan a,#
a Key Laboratory of Mesoscopic Chemistry of MOE, Jiangsu Provincial Key Laboratory of Nanotechnology, School of Chemistry and Chemical Engineering,
Nanjing University, Nanjing 210046, Jiangsu, China
b Jiangsu Key Laboratory of Environmental Material and Environmental Engineering, School of Chemistry and Chemical Engineering, Yangzhou Universi‐
ty, Yangzhou 225002, Jiangsu, China
A R T I C L E I N F O
A B S T R A C T
Article history:
The structure and catalytic properties of PtSn catalysts supported on SUZ‐4 and ZSM‐5 zeolite have
been studied by using various experimental techniques including XRD, nitrogen adsorption,
NH3‐TPD, TG, H2‐TPR and TPO techniques combined with propane dehydrogenation tests. It has
been shown that SUZ‐4‐supported PtSnNa (PtSnNa/SUZ‐4) was determined to be a better catalyst
for propane dehydrogenation than conventional catalysts supported on ZSM‐5, owing to its higher
catalytic activity and stability. Dibenzothiophene poisoning experiments were performed to inves‐
tigate the detailed structures of the two supported catalysts. The characterization of the two cata‐
lysts indicates that the distribution of Pt on the porous support affects the activity. In contrast to
ZSM‐5‐supported catalysts, Pt particles on the PtSnNa/SUZ‐4 are primarily dispersed over the ex‐
ternal surface and are not as readily deactivated by carbon deposition. This is because that the
strong acid sites of the SUZ‐4 zeolite evidently prevented the impregnation of the Pt precursor
H2PtCl6 into the zeolite. In contrast, the weak acid sites of the ZSM‐5 zeolite led to more of the pre‐
cursor entering the zeolite tunnels, followed by transformation to highly dispersed Pt clusters dur‐
ing calcination. In the case of the PtSnNa/ZSM‐5, the interactions between Sn oxides and the
support were lessened, owing to the weaker acidity of the ZSM‐5 zeolite. The dispersed Sn oxides
were therefore easier to reduce to the metallic state, thus decreasing the catalytic activity for
hydrocarbon dehydrogenation.
Received 16 November 2016
Accepted 17 December2016
Published 5 March 2017
Keywords:
SUZ‐4 zeolite
PtSnNa catalyst
Propane dehydrogenation
Catalyst stability
Pt distribution
© 2017, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
1. Introduction
genation is considered to be one of the most important petro‐
chemical processes because of the rapidly growing demand for
It is well reported that supported bi‐component Pt‐Sn cata‐
lysts can be employed in many reactions, including alkane de‐
hydrogenation [1–3], hydrocarbon rearrangement [4], low
temperature carbon monoxide oxidation [5], and alcohol elec‐
tro‐oxidation [6]. Among these applications, propane dehydro‐
propylene [2,7–9]. Supported Pt‐Sn catalysts have been widely
used because of their high activities and environmentally
friendly characteristics [1,2]. Aluminium oxide (Al2O3) is the
most common support for these materials, owing to its high
surface area and acidity. However, Al2O3‐supported Pt‐Sn cata‐
* Corresponding author. Tel: +86‐13665295901; Fax: +86‐514‐87975244; E‐mail: yulei@yzu.edu.cn
# Corresponding author. Tel: +86‐25‐83594620; Fax: +86‐25‐83317761; E‐mail: ynfan@nju.edu.cn
This work was supported by the Jiangsu Planned Projects for Postdoctoral Research Funds (1301080C), NNSFC (21202141, 21173182), Key Science
& Technology Specific Projects of Yangzhou (YZ20122029), the Innovation Foundation of Yangzhou University (2015CXJ009).
DOI: 10.1016/S1872‐2067(17)62750‐5 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 38, No. 3, March 2017

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
530
Hualan Zhou et al. / Chinese Journal of Catalysis 38 (2017) 529–536
lysts are deficient in terms of poor stability and lack of durabil‐
ity during recovery [1,10,11]. Thus, the development of novel
supports to improve the stability of these catalysts is not only
highly desirable but also timely.
H‐SUZ‐4 or H‐ZSM‐5 with an aqueous mixture of H2PtCl6 and
SnCl4 (H2PtCl6 = 5 mg/mL, SnCl4 = 5.85 mg/mL) and with
aqueous NaCl (0.5 mol/L). The impregnated samples were
dried at 110 °C for 4 h, calcined at 520 °C for 4 h, and then
dechlorinated in air containing water vapor at 530 °C for 4 h.
In recent years, zeolites such as SUZ‐4 and ZSM‐5 have been
found to be good supports because of their high surface areas,
good thermal stabilities, large pore volumes and tunable acidity
[12–14]. SUZ‐4 is a new type of synthetic zeolite patented by
the British Petroleum Company in 1992. In the three dimen‐
sional topological structure of this material, straight
ten‐membered channels intersect with two eight‐membered
channels at an angle of approximately 74°, which is similar to
the structure of ZSM‐5 zeolite [15,16]. SUZ‐4‐supported cata‐
lysts have been widely used in many processes, such as the
conversion of n‐hexane [16], the synthesis of dimethyl ether
from methanol [17], and the elimination of nitrogen oxides
[18]. However, there have not yet been any reports concerning
the application of SUZ‐4‐supported catalysts to propane dehy‐
drogenation, while ZSM‐5‐supported catalysts have attracted
significant attention in this regard [13,19]. In contrast to
γ‐Al2O3, the three‐dimensional microporous ZSM‐5 zeolite has
a well‐defined, ten‐membered, ring‐crossed channel system
that prevents the formation of large hydrocarbon molecules,
thus improving the catalyst’s stability [13]. Recently, Zhou’s
group [20] investigated propane dehydrogenation over
ZSM‐5‐supported Pt‐Sn catalysts and found that the propylene
selectivity was significantly improved by introducing promot‐
ers to neutralize the support acidity. The addition of hydrogen
to the reaction system effectively inhibited the cracking of pro‐
pane to C1 and C2 products and also reduced carbon deposi‐
tion on the catalyst surface, thus improving both the dehydro‐
genation selectivity and catalytic stability [21]. Despite this, the
ZSM‐5‐based catalysts were still easily deactivated by carbon
deposition under the chosen reaction conditions. To resolve
this issue, our own group developed the SUZ‐4‐supported cat‐
alyst PtSnNa/SUZ‐4, which afforded a 20% propylene yield.
Although propylene can be obtained in similar 18%–23%
yields by increasing the Sn loading when using a PtSn/ZSM‐5
catalyst [22], our catalyst has the advantage of being more ro‐
bust and undergoing very little deactivation due to carbon
deposition.
2.2. Catalyst characterization
The powder X‐ray diffraction (XRD) patterns of all samples
were obtained with a Philips X’pert pro diffractometer using Cu
Kα radiation at 40 kV and 40 mA, from 5° to 50°. Surface areas
were calculated by the BET method based on N2 adsorption
isotherms recorded at the temperature of liquid nitrogen using
a Micromeritics ASAP2010 analyzer. The samples were
degassed at 300 °C and 0.133 Pa prior to analysis, after which
isotherms were acquired at −196 °C. NH3‐TPD profiles of the
specimens were obtained in a flow‐type fixed‐bed reactor at
ambient pressure. The catalysts were pre‐treated at 500 °C for
2 h under an Ar flow. The NH3 adsorption temperature was 100
°C, and the temperature was raised at a rate of 10 °C/min. The
desorbed NH3 was detected by a gas chromatograph (GC)
equipped with a thermal conductivity detector (TCD).
H2 chemisorption on the supported PtSnNa catalysts was
assessed both before and after the propane dehydrogenation
reaction according to a previously described procedure [25].
Each of the catalysts was reduced in a H2 flow at 500 °C for 2 h
and then out‐gassed in an Ar flow at 540 °C for 2 h before H2
chemisorption measurements.
The amount of carbonaceous material deposited on each
catalyst during the propane dehydrogenation reaction was
measured using thermo‐gravimetric (TG) analysis (STA
449C‐Thermal star 300 TA‐MS apparatus). Catalyst samples
(each approximately 0.02 g) obtained after a 10‐h reaction
were heated from room temperature to 900 °C in O2 (at 25
mL/min) at a heating rate of 10 °C/min, and the amounts of
coke on the specimens was calculated from the resulting TG
curves.
Temperature‐programmed oxidation (TPO) was deter‐
mined with the same apparatus as used for the H2
chemisorption experiments. An approximately 0.1‐g sample
was placed in a quartz reactor and then heated to 800 °C in a
mixture of O2 (at 3.0 mL/min) and Ar (at 30 mL/min) at a
heating rate of 10 °C/min. Temperature‐programmed
reduction (TPR) was performed using the same apparatus em‐
ployed during the TPO assessments. In these trials, approxi‐
mately 0.1‐g samples were placed in a quartz reactor and sub‐
sequently heated in a flow of 5% H2‐95% Ar (at 20 mL/min) at
a heating rate of 10 °C/min.
2. Experimental
2.1. Catalyst preparation
An SUZ‐4 zeolite with the molar ratio SiO2/Al2O3 = 21 and a
ZSM‐5 zeolite with the molar ratio SiO2/Al2O3 = 20 were
prepared by methods previously described in the literature
[23,24]. In each case, the resulting solid phase was filtered,
washed with distilled water several times, dried at 110 °C for
12 h and then calcined at 550 °C for 4 h. This was followed by
Purposely poisoned catalysts (containing 0.02% S) were
prepared by impregnating the reduced PtSnNa/SUZ‐4 or
PtSnNa/ZSM‐5 catalysts with an ethanol solution of
dibenzothiophene (0.2 mg/mL), followed by flushing with
nitrogen for 1 to 2 h to evaporate residual ethanol and drying at
110 °C for 4 h.
All catalysts were reduced in H2 at 500 °C for 2 h before
catalytic evaluation. The propane dehydrogenation reaction
was carried out in a quartz tubular micro‐reactor under
+
NH4 exchange in aqueous NH4Cl (1 mol/L). H‐SUZ‐4 and
H‐ZSM‐5 were obtained by calcining the ammonium forms of
SUZ‐4 and ZSM‐5 at 550 °C for 4 h. PtSnNa catalysts supported
on either the SUZ‐4 or the ZSM‐5 zeolite (Pt = 0.5%, Sn = 2.0%,
Na = 1.0%) were prepared by sequentially impregnating the

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Hualan Zhou et al. / Chinese Journal of Catalysis 38 (2017) 529–536
531
selectivity were likely due to the excessive concentrations of
acid sites on these materials, leading to carbon deposits and
undesirable cracking reactions, respectively. The PtSnNa‐based
catalysts, including both PtSnNa/SUZ‐4 and PtSnNa/ZSM‐5,
were much more advanced. Between these two, the
PtSnNa/SUZ‐4 was found to be superior based on its higher
stability and propylene selectivity (Fig. 1(a), curves (3) vs. (4);
Fig. 1(b), curves (3) vs. (4)). Moreover, the PtSnNa/SUZ‐4
afforded the highest propylene yields of up to 20% (Fig. 1(c),
curves (3) vs. (1,2) and (4.5)). It should be noted that, even
without a catalyst, some small amount of propane was still
transformed, although with poor selectivity, because of
cracking reactions (Figs. 1(a–c), curves (5)).
Table 1
Propane conversion, propylene selectivity and propylene yield values
following a 10 h reaction for samples with different sodium ion con‐
tents.
Propane
conversion selectivity
(mol %)
12.8
19.7
Propylene
Propylene
yield
(mol %)
10.8
Entry
Catalyst a
(mol %)
84.2
93.0
92.4
93.5
1
2
3
PtSn/SUZ‐4
PtSnNa(0.5)/SUZ‐4
PtSnNa(1.0)/SUZ‐4
PtSnNa(2.0)/SUZ‐4
18.3
18.9
8.1
20.5
8.9
4
a
Values in parentheses indicate the sodium ion content by mass frac‐
tion (%).
reaction conditions of 0.1 MPa, 590 °C, C3H8/H2 = 1/3 (molar
ratio) and a propane weight hourly space velocity (WHSV) of
3.0−1. The reaction products (C3H6, CH4, C2H6 and C2H4) were
analyzed by an online GC (Shimadzu GC‐14A, Japan) with a TCD
and an Al2O3 packed column.
3.2. Structure and surface properties of the catalysts
Each of the specimens was assessed by XRD. As shown in
Fig. 2, no crystalline phase signals attributable to Pt, Sn or Na
were observed after the impregnation, calcination or hydrogen
reduction steps, possibly due to the low concentrations and/or
the high dispersion states of these metals (Fig. 2, curves (2) and
(5)) [18]. Moreover, compared with the original structures of
the SUZ‐4 and ZSM‐5 zeolite supports, the XRD patterns of the
supported catalysts do not show any characteristic changes
(Fig. 2, curves (1) vs. (2); (4) vs. (5)). After the propane
dehydrogenation reaction was performed for 10 h, the signals
of the SUZ‐4 and ZSM‐5 zeolites are also observed in the XRD
patterns of the catalysts, as shown in Fig. 2, curves (3) and (6),
indicating that the supports were stable during the reaction.
3. Results and discussion
3.1. Propane dehydrogenation
A series of catalysts with different sodium ion contents were
prepared and tested for their activity during propane dehy‐
drogenation. The addition of sodium ions improved both the
propane conversion and the propylene selectivity (entries 2,3
vs. 1), as shown in Table 1. A sodium content of 1.0% was found
to be optimal (entries 3 vs. 2,4 ) and so was used in the follow‐
ing experiments. It is known that the by‐products of this reac‐
tion are methane and ethane due to the cracking of propane or
propylene on catalyst acid sites. As shown in Fig. 1, the pure
zeolite catalysts H‐SUZ‐4 and H‐ZSM‐5 exhibited high initial
reaction activities but very poor stability, as reflected in the
rapidly decreased propane conversions (Fig. 1(a), curves (1)
and (2)). In addition, the H‐SUZ‐4 and H‐ZSM‐5 both showed
very low propylene selectivity (Fig. 1(b), curves (1) and (2)),
which is an even more crucial property for industrial
production. The evident deactivation and low propylene
Fig.
3
presents the nitrogen adsorption‐desorption
isotherms of the catalysts. The H‐SUZ‐4 and H‐ZSM‐5 generated
types I and IV adsorption‐desorption isotherms, respectively
(curves (2) and (4)), corresponding to microporous and
mesoporous materials. Furthermore, the adsorption‐
desorption isotherms of the supported catalysts are similar to
those of the supports (curves (1) vs. (2), (3) vs. (4)). This
result indicates that the uniform pore structures of the
supports were maintained after loading of the Pt, Sn and Na
components.
25
100
90
100
90
(c)
(b)
(3)
(4)
(a)
(3)
(4)
20
15
10
5
80
70
60
50
40
30
20
10
0
(1)
80
70
60
50
40
30
20
10
0
(2)
(3)
(5)
(1)
(2)
(5)
(2)
(1)
(4)
(5)
0
2
4
6
8
10
0
2
4
6
8
10
2
4
6
8
10
t/h
t/h
t/h
Fig. 1. (a) Propane conversion, (b) propylene selectivity and (c) propylene yield over time for different catalysts. (1) H‐SUZ‐4; (2) H‐ZSM‐5; (3) PtSn‐
Na/SUZ‐4; (4) PtSnNa/ZSM‐5; (5) without a catalyst. Reaction conditions: 590 °C, H2/C3H8 = 1/3 (molar ratio), m (cat.) = 0.3 g, WHSV = 3.0 h−1.

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
532
Hualan Zhou et al. / Chinese Journal of Catalysis 38 (2017) 529–536
505
(6)
(5)
(4)
(3)
(2)
(1)
430
(4)
(3)
(2)
(1)
0
100
200
300
400
T/oC
500
600
10
20
30
40
50
Fig. 4. NH3‐TPD profiles of the catalysts. (1) H‐ZSM‐5; (2) PtSn‐
Na/ZSM‐5; (3) H‐SUZ‐4; (4) PtSnNa/SUZ‐4.
2/(o )
Fig. 2. XRD patterns of the catalysts. (1) H‐SUZ‐4; (2) PtSnNa/SUZ‐4; (3
PtSnNa/SUZ‐4 after reaction for 10 h; (4) H‐ZSM‐5, (5) PtSnNa/ZSM‐5;
(6) PtSnNa/ZSM‐5 after reaction for 10 h.
of coke deposited on each catalyst during the reaction could be
determined from TG analysis and are presented in Table 2. The
pore sizes of both catalysts were increased following the reac‐
tion. In addition, the H2 uptake of the fresh PtSnNa/SUZ‐4
catalyst was close to that of the fresh PtSnNa/ZSM‐5 catalyst,
which is consistent with their similar catalyst activities in the
initial reaction stage (Fig. 1(a)). Compared with the
PtSnNa/SUZ‐4, the H2 uptake of the PtSnNa/ZSM‐5 catalyst was
decreased to a greater extent (ca. 36%) after coke deposition (9
wt.%). However, the differences in the performance of these
two catalysts during propane dehydrogenation cannot be
attributed to the insignificant difference in the deposited coke
amounts. These results indicate that there might be some other
reasons for the rapid deactivation of the PtSnNa/ZSM‐5
catalyst.
140
130
(4)
120
110
(3)
100
90
(2)
80
(1)
70
60
0.0
0.2
0.4
0.6
0.8
1.0
To obtain more information regarding the reaction
mechanism, the acidities of the different catalysts were
examined by NH3 temperature‐programmed desorption (TPD).
The NH3‐TPD profiles are displayed in Fig. 4 while the detailed
data are given in Table 3. Here the acid amount is proportional
to the corresponding desorption peak area. The different
crystal structures of the H‐ZSM‐5 and H‐SUZ‐4 zeolite resulted
in variations (both in strength and amount) in the surface
acidity of the supports, and loading with PtSnNa led to a more
obvious change. Two NH3 desorption peaks appear in these
TPD profiles. The first signal, in the range of 190 to 200 °C, is
attributed to weak acid absorption, while the second peak, at
420 to 520 °C, results from strong acid sites (Fig. 4) [26,27].
The TPD profile of the PtSnNa/ZSM‐5 is quite different from
that of the H‐ZSM‐5. A broadened peak showing stronger NH3
desorption at low temperature appears, while the strong acid
Relative pressure (p/p0)
Fig. 3. Nitrogen adsorption‐desorption isotherms of the catalysts. (1)
PtSnNa/SUZ‐4; (2) H‐SUZ‐4; (3) PtSnNa/ZSM‐5; (4) H‐ZSM‐5.
Table 2 summarizes the characterization data for different
catalysts. It is evident that the pore volumes (Vp) and surface
areas of the supported catalysts were decreased (entry 2 vs. 1;
entry 4 vs. 3) and that these values were further reduced fol‐
lowing the reaction (entries 2 and 4). These results can possi‐
bly be attributed to blocking of the support pores by the Pt or
by coke. Compared with the PtSnNa/ZSM‐5, the Vp of the PtSn‐
Na/SUZ‐4 after the reaction was decreased by a smaller
amount, clearly showing that the pores in this new material
were less likely to be blocked by coke deposition. The amounts
Table 2
The pore volumes, surface areas, pore sizes, H2 uptakes and the amounts of coke deposited on the different catalysts a.
Entry
Catalyst
H‐SUZ‐4
PtSnNa/SUZ‐4
H‐ZSM‐5
VP/( cm3/g)
0.14
0.13(0.11)
0.20
ABET/(m2/g)
291
277(213)
313
D/nm
1.89
1.92(2.15)
2.06
H/(mL/g)
—
22(19)
—
25(16, 24b)
C/(wt%)
1
2
3
4
—
8
—
9
PtSnNa/ZSM‐5
0.17 (0.13)
297 (239)
2.10(2.29)
a Data in parentheses are the value for catalysts after a 10‐h reaction. b H2 uptake of the catalyst after partial oxidation trials (vide infra, Fig. 6(b)).