Pd/SAPO-41 Bifunctional Catalysts with Enhanced Pd Dispersion Prepared by Ultrasonic-Assisted Impregnation: High Selectivity for n-Hexadecane Hydroisomerization

Article abstract of DOI:10.1134/S1070427220040047

Two series of Pd/SAPO-41 bifunctional catalysts were synthesized via the ultrasonic-assisted impregnation (xPd/S41-U) with different treating time and conventional incipient wetness impregnation methods (0.30Pd/S41-I) on the SAPO-41 molecular sieve, respe

Full text of DOI:10.1134/S1070427220040047

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2020, Vol. 93, No. 4, pp. 502–511. © Pleiades Publishing, Ltd., 2020.
CATALYSIS
Pd/SAPO-41 Bifunctional Catalysts with Enhanced Pd Dispersion
Prepared by Ultrasonic-Assisted Impregnation: High Selectivity
for n-Hexadecane Hydroisomerization
Guozhi Jiaa, A. L. Maximovb, Wei Wanga,*, Xuefeng Baia, Xiaomeng Weia,
Xiaofang Sua, Tong Lia, Chunmu Guoa, and Wei Wua,**
a National Center for International Research on Catalytic Technology, Key Laboratory of Functional Inorganic Material
Chemistry (Ministry of Education), School of Chemistry and Material Sciences, Heilongjiang University,
Harbin, Heilongjiang, 150080 China
b Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, 119991 Russia
*e-mail: wangw@hlju.edu.cn
**e-mail: wuwei@hlju.edu.cn
Received March 24, 2020; revised March 25, 2020; accepted March 25, 2020
Abstract—The preparation of bifunctional catalysts with high catalytic selectivity for the n-alkanes
hydroisomerization still remains challenging for the production of bio-diesel. Herein, two series of Pd/SAPO-41
bifunctional catalysts are prepared by the ultrasonic-assisted impregnation (xPd/S41-U) with different treating
time and conventional incipient wetness impregnation methods (0.30Pd/S41-I) on the SAPO-41 molecular
sieve, respectively. The physico-chemical property of the synthesized SAPO-41 and prepared catalysts were
studied by XRD, SEM, ICP, N2 physical adsorption, H2 chemisorption and Py-IR measurements. The catalytic
performance for the n-hexadecane hydroisomerization over all catalysts is also studied. The characteristic results
indicate that the xPd/S41-U catalysts show stronger Brønsted acidity compared with the 0.30Pd/S41-I catalyst.
In addition, the Pd dispersion of the xPd/S41-U catalysts is almost two times higher than that of the 0.30Pd/S41-I
catalyst, which leads more Pd cluster to enter into the micropores of the SAPO-41 molecular sieve. Furthermore,
the 0.30Pd/S41-U catalyst with 0.30 wt % Pd loading shows promoted catalytic performance than that of the
0.30Pd/S41-I catalyst with the same Pd loading because of the stronger metal function and more favourable
metal-acid balance caused by the larger CPd/CH+ ratio. Therefore, the ultrasonic-assisted impregnation
prepared Pd/SAPO-41 catalysts are potential to be widely employed for the n-alkane hydroisomerization.
Keywords: ultrasonic-assisted impregnation, Pd site, SAPO-41 molecular sieve, n-hexadecane hydroisomerization,
bifunctional catalysts
DOI: 10.1134/S1070427220040047
INTRODUCTION
sulfur, nitrogen, alkenes, aromatic hydrocarbons and
other impurities, the main composition of the second-
generation bio-diesel is isomer alkanes. As a result, the
serious air pollution caused by more generated PM2.5
from incomplete combustion of traditional diesel will
be significantly suppressed [6, 7]. In addition, compared
with the first-generation biodiesel, the second-generation
bio-diesel shows more excellent blending property,
promoted low-temperature fluidity and higher energy
density [8, 9]. Furthermore, the second-generation bio-
diesel is directly obtained from renewable biomass
Inrecentyears,theemploymentofcleanrenewablefuel
hascapturedconsiderableattentionsduetotheincreasing
energy crisis and severe environmental problems [1, 2].
To achieve this purpose, the hydroisomerization of long
chain n-alkane is an effective way to improve the quality
of the second-generation bio-diesel, which is produced
by the hydrodeoxygenation of bio-oil followed by the
hydroisomerization of deoxygenated bio-oil [3–5]. In
contrast to the traditional diesel with high contents of
502

Pd/SAPO-41 BIFUNCTIONAL CATALYSTS WITH ENHANCED Pd DISPERSION
503
like vegetable oil, animal oil and waste oil, which
means the raw sources are plenty and renewable [10].
Therefore, it is necessary to develop the catalysts for
hydroisomerization of long chain n-alkanes to improve
the production of clean renewable bio-diesel.
erally above 0.5 wt % [21]. This phenomenon leads to
a high cost of the bifunctional catalysts and limits their
further applications for the industrial production. There-
fore, many strategies have been developed to promote
the metal dispersion on the surface of molecular sieves
and reduce the loading of noble metals, like depositing
noble metal nanoparticle into the molecular sieves [22]
or employing ion-exchange method [23]. But it is nota-
bly that the preparation of bifunctional catalysts through
these methods may be complicated and expensive due to
the hard encapsulation of noble metal nanoparticles and
the waste of noble metal precursors. Accordingly, it is
still essential to find simple methods for the preparation
of bifunctional catalysts with high selectivity and low
metal loading.
To date, the bifunctional catalyst is the most widely
used catalyst in the n-alkane hydroisomerization, which
is composed of metal sites with (de)hydrogenation
function and Brønsted acid sites with isomerization and
cracking function [11]. During the hydroisomerization,
the n-alkanes are firstly dehydrogenated to alkene inter-
mediates on the metal sites. Then, the alkene interme-
diates are protonated, isomerized and deprotonated on
the Brønsted acid sites. Finally, the formed isomerized
alkene intermediates are hydrogenated to form iso-al-
kane products on the metal sites. It is worth noting that
if the balance between the functions of two active sites
is not ideal, the alkene intermediates would easily un-
dergo further cracking, which would suppress the yield
of desirable iso-alkane products [12, 13]. Generally,
the Brønsted acid sites are provided by the molecular
sieves. According to the reported works, the molecular
sieves with one-dimensional micropore system are ap-
propriate for the preparation of highly selective bifunc-
tional catalysts, including ZSM-22, ZSM-23, SAPO-
31 and SAPO-41 [14,15]. However, due to the higher
Brønsted acidity, the selectivity to iso-alkane over
zeolite-based catalysts is usually lower compared with
SAPO-based catalysts because of the stronger cracking
of iso-alkanes on the Brønsted acid sites [16, 17]. Based
on the comparison of catalytic performance for the n-oc-
tane hydroisomerization over Zeolite and SAPO based
bifunctional catalysts, Nghiem et al. found that the iso-
octane selectivity over Pt/SAPO-n catalysts were much
higher than that over Pt/ZSM-n catalysts when the reac-
tion temperature was 250°C [18]. Additionally, SAPO-
41 has been proven to show ideal catalytic behaviours
among all SAPO-n molecular sieves since the large pose
size (0.43 × 0.73 nm) of SAPO-41 is beneficial for the
formation and diffusion of desired iso-alkanes [19].
Over past years, the ultrasonic-assisted treatment
is considered to be an effective method to reduce the
metal loading of bifunctional catalysts owing to its
low cost and simple measurement [24, 25]. During the
ultrasonic treatment, the formation, growth and collapse
of bubbles can lead to high temperature and pressure to
accelerate the chemical reaction [26]. However, with the
assistance of ultrasonic treatment, the strong reductant,
the protective agents, the severe reaction conditions and
long reaction time are still necessary to achieve highly
dispersed noble metal catalysts [27]. Furthermore, the
reported works about the preparation of bifunctional
catalysts for n-alkane hydroisomerization by ultrasonic-
assisted treatment are very few. Therefore, the
combination of the ultrasonic-assisted impregnation and
hydrogenation reduction may be a simple and potential
route to improve the metal dispersion, so that the metal
loading of bifunctional catalysts can be evidently
lowered.
In this study, two series of Pd/SAPO-41 bifunctional
catalysts were prepared by ultrasonic-assisted impreg-
nation and conventional incipient wetness impregna-
tion methods, respectively. The effects of preparation
methods on metal-acid balance and the n-hexadecane
hydroisomerization over all catalysts were studied
thoroughly.
In addition to the Brønsted acid sites, the modifica-
tion of characteristics of metal sites is also very impor-
tant for the enhancement of the catalytic performance.
Because of the better catalytic stability and stronger hy-
drogenation function, noble metals (Pt and Pd) are usu-
ally employed as metal sites for bifunctional catalysts
instead of non-noble metals (Ni) [20]. However, in order
to keep the favourable metal-acid balance and high iso-
alkanes selectivity, the loading of noble metals are gen-
EXPERIMENTAL
The Synthesis of SAPO-41 Molecular Sieve
and Preparation of Pd/SAPO-41 Bifunctional Catalysts
For the synthesis of the SAPO-41 molecular
sieve, the di-n-butylamine (DBA) (95.0%, Aldrich),
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 93 No. 4 2020

504
GUOZHI JIA et al.
xPd/S41-U catalysts were also detected by inductively
coupled plasma optical emission spectrometry
(ICP-OES, PerkinElmer, Optima 5300DV). The N2
adsorption-desorption measurements of SAPO-41
and all catalysts were performed on an Autosorb-iQ2
instruments (Quantachrome). Prior to the tests, all
samples need to be degassed at 350°C in a vacuum of
1.0 × 10–3 Pa for 12 h. After that, the characterization
was carried out at liquid nitrogen temperature (–196°C).
The specific surface areas and pore volumes of samples
were determined using the method of Brunauer–
Emmett–Teller (BET) and the t-plot, respectively. The
metal dispersion of all catalysts was characterized by
using a Micromeritics AutoChem II 2920 chemisorption
analyser instrument. During the process, approximately
200 mg samples were loaded into a tube and pretreated
under hydrogen at 400°C for 1 h. Then, the sample was
treated under argon at 450°C for 2 h, cooled to room
temperature and then adsorbed by a 10% H2-Ar mixture
until saturation. The pyridine-adsorbed IR (Py-IR) of
the samples was measured on a Perkin Elmer Spectrum
Frontier transform infrared spectrometer (PE-100). At
first, all samples (diameter: 10mm, weight: about 20 mg)
were dehydrated at 350°C for 2 h under vacuum (1.33 ×
10–3 Pa), followed by the pure pyridine was adsorbed
at 90°C for 0.5 h. The pyridine was desorbed at 150°C,
250°C, 350°C orderly after that. The Brønsted acid sites
was calculated based on area of the band centered at
~1540 cm–1 [29].
orthophosphoric acid (85.0%, Tianjin Guangfu, China),
pseudoboehmite (74.1 wt % Al2O3, Catapal B, Sasol)
and silica sol (25.9 wt % SiO2, Qingdao Yumin, China)
were used as template, P, Al and Si sources, respectively.
Pd(NO3)2 solution (5 wt %, Shanxi Kaida, China) was
used as metal precursor solution to prepare Pd/SAPO-41
bifunctional catalysts.
The SAPO-41 molecular sieve was synthesized
accordingtoourpreviouslyworks,whilethecomposition
of initial gel was of Al2O3 : SiO2 : DBA : P2O5 : H2O =
1.0 : 0.6 : 3.0 : 1.0 : 55.0 [28]. The obtained sample
was denoted as S41. For the Pd/SAPO-41 bifunctional
catalysts prepared by ultrasonic-assisted impregnation
method, 2 g SAPO-41 was impregnated of 50 mL
Pd(NO3)2 solution (0.01 mol/L) with an ultrasonic
bath at a frequency of 25 kHz and an input power of
300 W for 40, 80 and 120 min, respectively. Then, the
obtained samples were washed by deionized water,
dried overnight at 110°C, followed by the calcination
in air at 600°C for 4 h and reduction at 400°C for 1 h
with 40 mL/min hydrogen in a fixed-bed reactor. The
prepared catalysts were denoted as xPd/S41-U, in
which the x was the Pd loading (wt %) of the catalyst
with different treating time. For comparison, the
preparation of Pd/SAPO-41 bifunctional catalyst by the
conventional incipient wetness impregnation method
was carried out as follows: the 2 g SAPO-41 molecular
sieve was impregnated with 0.12 g Pd(NO3)2 solution
(0.01 mol/L) and 1.87 g deionized water to maintain the
Pd loading was 0.30 wt % and the following steps were
the same as those of xPd/S41-U catalysts. The prepared
conventional Pd/SAPO-41 bifunctional catalyst was
denoted as 0.30Pd/S41-I.
Catalytic Performance Tests
The hydroisomerization of n-hexadecane was carried
out in a fixed-bed reactor with 1.0 g catalyst (20–40 mesh)
over all catalysts. Before the test, the catalyst was placed
into the reaction tube and treated under a flow of H2 at
400°C for 1 h. Furthermore, the tests were conducted at
weight hourly space velocity (WHSV) of 3.70 h–1, H2
pressure of 2.0 MPa, H2/n-hexadecane molar ratio of
8.72 and reaction temperature at the range of 280–370°C.
The reaction products were analyzed by using the Agilent
6820 gas chromatograph, which was equipped with
a flame ionization detector (FID) and a HP-1 capillary
column (60 m × 0.25 mm × 1.00 μm). The conversion of
n-hexadecane (%) and the yield of iso-hexadecane (%)
are calculated by the following formula:
Characterization of SAPO-41 Molecular Sieve
and Pd/S41 Bifunctional Catalysts
The Powder X-ray diffraction (XRD) patterns of the
synthesized SAPO-41 molecular sieve was measured
using a Bruker D8 Advance X-ray diffractometer with
the standard CuKα (λ = 1.5406 Å, 40 kV, 40 mA) over the
range of angles 5–55°. The crystal phase and diffraction
peaks of the SAPO-41 were identified by the JCPDS
database. The scanning electronic microscopy (SEM)
images of SAPO-41 molecular sieves were obtained on
S-4800 (Hitachi, Japan) at 30 kV. The metal loading of
the amount of n-hexadecane consumed
100%,
Conversion of n-hexadecane 

,
the amount of n-hexadecane in feed
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 93 No. 4 2020

Pd/SAPO-41 BIFUNCTIONAL CATALYSTS WITH ENHANCED Pd DISPERSION
505
the amount of iso-hexadecane formed
100%,
100,
Selectivity to iso-hexadecane 
amount of n-hexadecane consumed
the amount of iso-hexadecane formed
100%,
100,
Yield of iso-hexadecane 
the amount of n-hexadecane in feed
RESULTS AND DISCUSSION
to 0.27 wt %. But when the treating time becomes
120 min, the Pd loading of 0.30Pd/S41-U catalyst is
0.30 wt %, which increases slightly compared with the
0.27Pd/S41-U catalyst. This phenomenon suggests that
the growth of Pd deposition amount is not linear as the
treating time changes longer. The textural properties
of the SAPO-41 molecular sieve and all Pd/SAPO-41
bifunctional catalysts are determined by N2 physical
adsorption measurements. The N2 adsorption-desorption
isotherms of all samples are shown in Fig. 2 and the
calculated textural properties are listed in Table 1. The
isotherm of SAPO-41 exhibits a sharp increase at the
relative pressure (P/P0) of 10–6. In addition, a hysteresis
loop is found at high P/P0 for all samples, which are
assigned to the intergranular mesopores formed by the
crystal aggregation. For all Pd/SAPO-41 catalysts, the
isotherms are similar to that of the SAPO-41 but the
textural properties change evidently. Compared with
the SAPO-41 molecular sieve, the micropore surface
area (Smicro) and the micropore volumes (Vmicro) of the
xPd/S41-U catalysts are both lower due to the partial
micropores blockages of SAPO-41 molecular sieve after
the deposition of Pd nanoparticles [30]. In addition, as
the Pd loading of xPd/S41-U catalysts increases, the
Smicro and Vmicro both decrease continuously, indicating
more micropore blockages because of the higher Pd
deposition amount. Furthermore, it is notably that
Characteristics of SAPO-41 Molecular Sieve and All
Pd/SAPO-41 Bifunctional Catalysts
Figure 1a shows the XRD pattern of the SAPO-41
molecular sieve synthesized by using DBA as template.
It can be found that the sharp characteristic diffraction
peaks existing at 6.8°, 9.7°, 13.7°, 18.3°, 16.3° and
20.5–25.7°, which are ascribed to the AFO topology of
SAPO-41. The strong intensity of these peaks suggests
that the synthesized SAPO-41 molecular sieve is highly
crystalline. Simultaneously, no additional peaks are
observed, indicating that the synthesized SAPO-41
molecular sieve is free from impure phase. The SEM
image of SAPO-41 in Fig. 1b presents the typical
morphology of the AFO topology, which are columnar-
shaped aggregates with 2.5 μm of diameter and 5.0 μm
of length [28]. Moreover, the SEM image confirms the
absence of amorphous species and demonstrates the
high crystallinity of the synthesized SAPO-41, which is
consistent with the results of XRD pattern.
The Pd loading of xPd/S41-U catalysts is investigated
by ICPmeasurement and the results are shown inTable 1.
The ICP results reveal that as the time of the ultrasonic-
assisted impregnation increases from 40 to 80 min,
the Pd loading of xPd/S41-U changes from 0.10 wt %
(a)
(b)
SAPO-41
5
10 15 20 25 30 35 40 45 50 55
2θ, deg
Fig. 1. (a) XRD pattern and (b) SEM image of the SAPO-41 molecular sieve.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 93 No. 4 2020

506
GUOZHI JIA et al.
Table 1. The ICP results and textural properties of the SAPO-41 molecular sieve and all Pd/SAPO-41 catalysts
Surface area, m2/g
Pore volume, cm3/g
Samples
S41
Pd loadinga, wt %
b
c
d
e
SBET
251
219
204
199
194
Smicro
Sext
23
29
39
41
30
Vtotal
Vmicro
0.081
0.073
0.065
0.062
0.065
Vmeso
–
228
190
165
158
164
0.132
0.147
0.161
0.156
0.097
0.051
0.074
0.096
0.094
0.032
0.10Pd/S41-U
0.27Pd/S41-U
0.30Pd/S41-U
0.30Pd/S41-I
0.10
0.27
0.30
0.30
a Determined by ICP; b determined by BET method; c determined by t-plot method; d determined at P/P0 = 0.995; e Vmeso = Vtotal – Vmicro
.
Table 2. The Py-IR and H2 chemisorption results of the SAPO-41 molecular sieve and all Pd/SAPO-41 catalysts
Brønsted aciditya, μmol/g
c
CPd
,
d
Sample
DPdb, %
CPd/CH+
–
μmol/g
total
89.4
45.3
41.0
39.9
43.2
weak
9.9
medium
23.3
9.2
strong
56.2
29.1
27.7
20.1
24.9
S41
–
–
0.10Pd/S41-U
0.27Pd/S41-U
0.30Pd/S41-U
0.30Pd/S41-I
7.0
51.2
53.5
61.1
27.3
4.8
0.11
0.33
0.43
0.18
5.2
8.1
13.6
17.2
7.7
9.3
10.5
7.5
10.8
a Determined by Py-IR method. b Calculated by H2 chemisorption method. c Calculated from the loading and dispersion of Pd. d The amount
ratio of exposed Pd atoms (CPd) to total Brønsted acid density
the 0.30Pd/S41-U catalyst reveals smaller micropore
surface and pore volume than those of 0.30Pd/S41-I
catalyst with the same Pd loading. This result may be
originated from the entrance of more Pd cluster into
the microporous channels caused by the increase of
Pd dispersion, which is further confirmed by the H2
chemisorption measurement.
In order to investigate the Pd dispersion of all Pd/
SAPO-41 catalysts, the H2 chemisorption measurement
is carried out and the results are listed in Table 2. It can
be found that the Pd dispersion of xPd/S41-U catalysts
is significantly higher compared with the 0.30Pd/S41-I
catalyst. Especially for the 0.30Pd/S41-U catalyst, the
61.1% of the Pd dispersion is two times higher than
that of the 0.30Pd/S41-I catalyst (27.3%). This result
demonstrates that the ultrasonic-assisted impregnation
method is very effective to increase the Pd dispersion
of the bifunctional catalysts. This is because the high
temperature and pressure generated by the ultrasonic
treatment can evidently improve the diffusion of Pd2+
ions, which is beneficial for the entrance of more Pd2+
ions into the microporous channels or highly disperse
outside of the SAPO-41 molecular sieve [27]. Based on
the Pd dispersion, the exposed Pd atoms (CPd value) are
calculated and the results are listed in Table 2.Among all
catalysts, the 0.10Pd/S41-U catalyst reveals the smallest
CPd value because of the lowest Pd loading. Moreover,
the CPd values of the 0.27Pd/S41-U and 0.30Pd/S41-U
320
280
240
200
160
120
80
0.30Pd/S41-I
+200
+150
0.30Pd/S41-U
0.27Pd/S41-U
+100
+50
0.10Pd/S41-U
S41
40
0
0.0
0.2
0.4
0.6
0.8
1.0
P/P
0
Fig. 2. N2 adsorption-desorption isotherms of the SAPO-41
molecular sieve and all Pd/SAPO-41 catalysts.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 93 No. 4 2020

Pd/SAPO-41 BIFUNCTIONAL CATALYSTS WITH ENHANCED Pd DISPERSION
507
(a)
(b)
1400
1440
1480 1520
Wavenumber, cm–1
1560 1600
1400
1440
1480 1520
Wavenumber, cm–1
1560 1600
(c)
1400
1440
1480 1520
Wavenumber, cm–1
1560 1600
Fig. 3. Py-IR spectra of all Pd/SAPO-41 catalysts at (a) 150°C, (b) 250°C and (c) 350°C.
catalysts are both larger compared with 0.30Pd/S41-I
catalyst due to the higher Pd dispersion, suggesting that
more accessible Pd active sites are formed on these two
catalysts.
difference of Py-IR spectra recorded at different
temperature. From Table 2, the total Brønsted acid
density of all Pd/SAPO-41 catalysts is lower compared
with the SAPO-41 molecular sieve owing to the
deposition of Pd nanoparticles. Simultaneously, the
total Brønsted acid density of the xPd/S41-U catalysts
decrease gradually as the Pd loading increases, which
may be originated from the larger coverage of Brønsted
acid sites located outside of the SAPO-41 molecular
sieve and more micropore blockages caused by the
entrance of highly dispersed Pd cluster[11]. In addition,
compared with the 0.30Pd/S41-I catalyst, although the
total Brønsted acid density of the 0.30Pd/S41-U catalyst
is lower due to the higher Pd dispersion, the adsorption
band of pyridine on Brønsted acid sites of the 0.30Pd/
S41-U catalyst (1544–1546 cm–1) is higher. This
phenomenon indicates that the Brønsted acid strength
of 0.30Pd/S41-U catalyst is greater. Furthermore, by
combining the results of H2 chemisorption and Py-IR
spectra, the ratio of exposed Pd atoms to total Brønsted
Beyond the characteristics of Pd sites, the Brønsted
acid density is also very important for the improvement
of the catalytic performances over the bifunctional
catalysts. To study the Brønsted acidity with different
strength, the Py-IR measurements are conducted for
the SAOP-41 molecular sieve and all catalysts, and the
results are shown in Fig. 3 and Table 2. In the Py-IR
spectra of all samples, the band located at ~1543 and
~1445 cm–1 are assigned to the adsorption of pyridine
on the Brønsted and Lewis acid sites respectively, while
the band at ~1490 cm–1 is assigned to the adsorption
on two acid sites. Accordingly, the ~1543 cm–1 band
area of Py-IR spectrum recorded at 150 and 350°C are
attributed the total and strong Brønsted acid density,
respectively. Then, the weak and medium Brønsted
acid density can also be calculated based on the area
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 93 No. 4 2020

508
GUOZHI JIA et al.
Table 3. The catalytic test results over all Pd/SAPO-41 catalysts at about 90% of n-hexadecane conversion
Items
0.10Pd/S41-U 0.27Pd/S41-U 0.30Pd/S41-U 0.30Pd/S41-I
n-Hexadecane conversion, %
88.4
65.5
57.9
89.7
80.1
71.8
90.0
95.8
86.2
91.5
91.7
83.9
iso-Hexadecane selectivity, %
iso-Hexadecane yield, %
Mono-branched iso-hexadecane distribution, %
2-MeC15
7.6
8.6
7.8
8.8
9.9
12.2
12.0
12.6
10.5
6.0
7.6
9.0
3-MeC15
4-MeC15
8.3
8.5
8.8
5-MeC15
8.1
8.5
9.2
6-MeC15
7.5
7.8
9.0
7,8-MeC15
15.6
55.7
44.3
1.9
16.0
57.4
42.6
4.0
15.6
59.2
40.8
11.0
Total MeC15
63.2
36.8
22.8
Total multi-branched iso-hexadecane distribution, %
I/C ratios
acid density (CPd/CH+) is calculated, which is commonly
employed to characterize the balance between metal
function and acid function of the prepared bifunctional
catalysts [31]. As shown in Table 2, the CPd/CH+ ratio of
the 0.30Pd/S41-U (0.43) catalysts are 2.4 times of the
0.30Pd/S41-I catalyst (0.18), suggesting that the 0.30Pd/
S41-U catalysts prepared via the ultrasonic-assisted
impregnation method reveals a stronger metal function.
in the order of 0.30Pd/S41-U > 0.27Pd/S41-U > 0.10Pd/
S41-U, which is consistent with the order of CPd/CH+
ratios. This result indicates that the metal-acid balance
may demonstrate stronger influences to the conversion
of n-hexadecane compared with the total Brønsted acid
density when the metal density is low and the (de)hydro-
genation is a speed control step. In addition, as shown in
Figs. 4b, 4c, the order of the iso-hexadecane selectivity
and yield over all catalysts at n-hexadecane conversion
of about 90% is the same as that of the n-hexadecane
conversion. Especially for the 0.30Pd/S41-U catalyst,
the iso-hexadecane selectivity is 95.8% at the n-hexa-
decane conversion of 90.0%, which is relatively high
among reported catalysts with much higher noble metal
loading (listed in Tables 3 and 4). This result suggests
that the larger CPd/CH+ ratio is also beneficial for the
improvement of metal-acid balance and the promotion
of iso-hexadecane yield. During the hydroisomerization
process (illustrated in Fig. 4d), the n-alkane molecular is
firstly dehydrogenated on the Pd sites to become the n-
alkene intermediates. Then, the n-alkene intermediates
transformed to the iso-alkene intermediates on the Brøn-
sted acid sites followed by the hydrogenation on the Pd
sites to form the desired iso-alkane products. Therefore,
in order to achieve the ideal catalytic performance, the
metal function of bifunctional catalysts should exceed
the Brønsted acid function. This is because an insuffi-
cient amount or a weak hydrogenation function of metal
sites can lead to stronger cracking reactions of isomers
on the Brønsted acid sites [32]. For the 0.10Pd/S41-U
Catalytic Behaviours over All Pd/SAPO-41
Bifunctional Catalysts for the n-Hexadecane
Hydroisomerization
It is well known that the Brønsted acidity, metal func-
tion and metal-acid balance have direct influences on
the catalytic behaviours of n-alkane hydroisomerization
over bifunctional catalysts. Therefore, to further investi-
gate the positive effects of ultrasonic-assisted impregna-
tion method on the catalytic performances of prepared
xPd/S41-U catalysts compared with the 0.30Pd/S41-I
catalyst prepared by the conventional incipient wetness
impregnation method, the n-hexadecane hydroisomeri-
zation is tested over all Pd/SAPO-41 catalysts.
The catalytic performances for the n-hexadecane
hydroisomerization over xPd/S41-U catalysts are pre-
sented in Fig. 4 and Table 3. From Fig. 4a, it can be
found that the n-hexadecane conversion over all cata-
lysts increases as the reaction temperature changes from
280 to 370°C. At the same reaction temperature, the
conversion of n-hexadecane over all catalysts decreases
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 93 No. 4 2020

Pd/SAPO-41 BIFUNCTIONAL CATALYSTS WITH ENHANCED Pd DISPERSION
509
100
80
60
40
20
0
100
80
60
40
20
0
(a)
(b)
280
(c)
300
320
340 360
380
0
20
40
60
80
100
Temperature, °C
Conversion of n-hexadecane, %
100
80
60
40
20
0
(d)
n-C16
SAPO-41
0
20
40
60
80
100
Ymax of iso-C16 = 86.2%
Conversion of n-hexadecane, %
Fig. 4. The catalytic performance of n-hexadecane hydroisomerization over xPd/S41-U catalysts. (a) The n-hexadecane conversion
versus the reaction temperature; (b) the iso-hexadecane selectivity versus the n-hexadecane conversion; (c) the iso-hexadecane yield
versus the n-hexadecane conversion and (d) the illustration of n-hexadecane hydroisomerization over xPd/S41-U bifunctional catalysts.
catalyst with the smallest CPd/CH+ ratio, the metal func-
tion is too weak to keep the favourable balance with the
Brønsted acid function, so that the isomer alkene inter-
mediates interact with more Brønsted acid sites to un-
dergo further cracking before the hydrogenation on the
Pd metal sites. As a result, the yield of iso-hexadecane
over the 0.10Pd/S41-U catalyst (57.9%) is the lowest
among all catalysts. On the contrary, for the 0.30Pd/
S41-U catalyst with the highest CPd/CH+ ratio, the iso-
mer alkene intermediates are faster hydrogenated to
become iso-hexadecanes on Pd sites instead of further
cracking owing to the more favourable metal-acid bal-
Table 4. The relevant work done for the performance of n-alkanes hydroisomerization over bifunctional catalysts.
Reaction
temperature, °C
n-Alkanes
conversion, %
iso-Alkanes
selectivity, %
Catalyst
n-Alkanes
Reference
0.3Pd/SAPO-11
0.8Pd/SAPO-41
0.5Pt/SAPO-11
0.5Pd/SAPO-11
0.5Pd/SAPO-31
1.0Pt/SAPO-11
0.30Pd/S41-U
n-C10
n-C16
n-C12
n-C10
n-C10
n-C12
n-C16
360
340
340
350
380
300
320
90.8
94.0
93.5
85.8
80.0
92.1
90.0
89.8
94.6
75.8
89.4
90.6
83.2
95.8
[15]
[18]
[33]
[34]
[35]
[36]
This work
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 93 No. 4 2020

510
GUOZHI JIA et al.
ance, which leads to the highest iso-hexadecane yield
among all catalysts. This conclusion is also proved by
the the distribution of mono- and multi-branched iso-
hexadecane products over all Pd/SAPO-41 catalysts. As
listed in the Table 3, the distribution of mono-branched
iso-hexadecane products over 0.30Pd/S41-U catalyst is
the highest among all catalysts, while the ratio of iso-
hexadecane products to cracking products (I/C ratios) is
the lowest. This result indicates that the further isomeri-
zation and cracking of alkene intermediates over the
0.30Pd/S41-U catalyst is suppressed due to the highest
CPd/CH+ ratio and strongest metal function. Addition-
ally, the comparison of the catalytic performances over
0.30Pd/S41-U and 0.30Pd/S41-I catalysts is also shown
in Table 3. It can be found that the n-hexadecane con-
version, the maximum iso-hexadecane yield, the mono-
branched iso-hexadecane distribution and the I/C ratio
of the 0.30Pd/S41-U catalyst are all higher than those of
the 0.30Pd/S41-I catalyst. This result confirms that the
higher CPd/CH+ ratio of the 0.30Pd/S41-U catalyst leads
to the promoted catalytic performance compared with
the catalysts prepared by the conventional incipient wet-
ness impregnation method.
No.21706053), Intergovernmental International Science
and Technology Innovation Cooperation Key Project
(2018YFE0108800), National Ministry of Education
“Silk Road 1+1” Research Cooperation Project, the
Transformation for Science and Technology Achieve-
ments in University of Department of Education of Hei-
longjiang Province (TSTAU-C2018015) and Heilongji-
ang University graduate student innovation research
project funding (YJSCX2019-175HLJU).
CONFLICT OF INTEREST
Co-author A.L. Maksimov claims to be the editor-in-chief
of the Journal ofApplied Chemistry; the remaining co-authors
have no conflict of interest.
REFERENCES
1. Avinash, A. and Murugesan, A., Fuel, 2018, vol. 216,
pp. 322–329.
https://doi.org/10.1016/j.fuel.2017.12.029
2. Uvarkina, D.D., Piryutko, L.V., Danilova, I.G.,
Budukva, S.V., Klimov, O.V., Kharitonov, A.S., and
Noskov, A.S., Russ. J. Appl. Chem., 2015, vol. 88, no. 11,
pp. 1827–1838.
CONCLUSIONS
https://doi.org/10.1134/S10704272150110142
3. Jeon, Y., Chi, W.S., Hwang, J., Kim, D.H., Kim, J.H.,
and Shul, Y.G., Appl Catal B-Environ., 2019, vol. 242,
pp. 51–59. https://doi.org/10.1016/j.jiec.2019.07.029
In this work, the ultrasonic-assisted impregnation
method is employed to prepare a series of xPd/S41-U
catalysts with high Pd dispersion. By simply changing
the treating time from 40 to 120 min, the Pd loading on
the SAPO-41 molecular sieve increases from 0.10 wt %
to 0.30 wt %. Compared with the 0.30Pd/S41-I catalyst
prepared by the conventional incipient wetness
impregnation method, the 0.30Pd/S41-U catalyst with
the same Pd loading demonstrates evidently higher Pd
dispersion and CMe/CH+ ratio. In addition, the catalytic
performance over the 0.30Pd/S41-U catalyst is excellent
due to the enhanced metal function and more favourable
metal-acid balance. Therefore, the ultrasonic-assisted
impregnation method is a simple and effective method to
prepare highly selective bifunctional catalysts with low
noble metal loading for the n-alkane hydroisomerization
and other (de)hydrogenation reaction in petroleum
refining and petrochemical industrial production.
4. Gaile, A.A., Saifidinov, B.M., Kolesov, V.V., and
Koldobskaya, L.L., Russ. J. Appl. Chem., 2010, vol. 83,
no. 3, pp. 464–472.
https://doi.org/10.1134/S1070427210030171
5. Li, P., Sakuragi, K., and Makino, H., Fuel Process.
Technol., 2019, vol. 193, pp. 295–303.
https://doi.org/10.1016/j.fuproc.2019.05.009
6. Liu, X., Deng, B., Fu, J., Xu, Z., Liu, J., Li, M., Li, Q.,
Ma, Z., and Feng, R., Chem. Eng. J., 2019, vol. 355,
pp. 170–180. https://doi.org/10.3390/app9183721
7. Pimerzin, A.A., Savinov, A.A., Ishutenko, D.I.,
Verevkin, S.P., and Pimerzin, A.A., Russ. J. Appl. Chem.,
2019, vol. 92, no. 12, pp. 1772–1779.
https://doi.org/10.1134/S1070427219120198
8. Mantovani, M., Mandelli, D., Gonçalves, M., and
Carvalho, W.A., Chem. Eng. J., 2018, vol. 348, pp. 860–
869. https://doi.org/10.1016/j.cej.2018.05.059
ACKNOWLEDGMENTS
9. Singh, D., Sharma, D., Soni, S.L., Sharma, S., and
Kumari, D., Fuel, 2019, vol. 253, pp. 60–71.
https://doi.org/10.1016/j.fuel.2019.04.174
This work is supported by the National Natu-
ral Science Foundation of China (No.21676074,
10. Santamaria, L., Lopez, G., Arregi, A., Amutio, M.,
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 93 No. 4 2020

Pd/SAPO-41 BIFUNCTIONAL CATALYSTS WITH ENHANCED Pd DISPERSION
511
Artetxe, M., Bilbao, J., and Olazar, M., Appl. Catal.
B-Environ., 2019, vol. 242, pp. 109–120.
https://doi.org/10.1016/j.apcatb.2018.09.081
23. Samad, J.E., Blanchard, J., Sayag, C., Louis, C., and
Regalbuto, J.R., J. Catal., 2016, vol. 342, pp. 203–212.
https://doi.org/10.1016/j.jcat.2016.08.004
24. Nemamcha, A., Rehspringer, J.L., and Khatmi, D.,
J. Phys. Chem. B., 2006, vol. 110, pp. 383–387.
https://doi.org/10.1021/jp0535801
11. Wang, W., Liu, C., and Wu, W., Catal. Sci. Technol.,
2019, vol. 9, pp. 4162–4187.
https://doi.org/10.1039/C9CY00499H
25. Su, X., Vinu, A., Aldeyab, S.S., and Zhong, L., Catal.
Lett., 2015, vol. 145, pp. 1388–1395.
12. Guisnet, M., Catal. Today, 2013, vol. 218, pp. 123–134.
https://doi.org/10.1016/j.cattod.2013.04.028
https://doi.org/10.1007/s10562-015-1537-0
13. Pastvova, J., Kaucky, D., Moravkova, J., Rathousky, J.,
Sklenak, S., Vorokhta, M., Brabec, L., Pilar, R.,
Jakubec, I., Tabor, E., Klein, P., and Sazama, P., ACS
Catal., 2017, vol. 7, no. 9, pp. 5781–5795.
26. Li, J., and Bai, X., J. Mater. Sci., 2016, vol. 51, pp. 9108–
9122.
https://doi.org/10.1007/s10853-016-0164-5
27. Li, J., Bai, X., and Lv, H., Ultrason. Sonochem., 2020,
vol. 60, pp. 104746.
https://doi.org/10.1021/acscatal.7b01696
14. Smit, B., and Maesen, T.L., Nature, 2008, vol. 451,
pp. 671–678. https://doi.org/10.1038/nature06552
15. Song, X., Bai, X., Wu, W., Kikhtyanin, O.V., Zhao, A.,
Xiao, L., Su, X., Zhang, J., and Wei, X., Mol. Catal.,
2017, vol. 433, pp. 84–90.
https://doi.org/10.1016/j.ultsonch.2019.104746
28. Wei, X., Kikhtyanin, O.V., Parmon, V.N., Wu, W., Bai, X.,
Zhang, J., Xiao, L., Su, X., Zhang, Y., J. Porous Mater.,
2017, vol. 25, pp. 235–247.
https://doi.org/10.1007/s10934-017-0437-7
https://doi.org/10.1016/j.mcat.2016.12.017
29. Schmidt, F., Hoffmann, C., Giordanino, F., Bordiga, S.,
Simon, P., Carrillo-Cabrera, W., and Kaskel, S., J. Catal.,
2013, vol. 307, pp. 238–245.
16. Yue, T., Liu, W., Li, L., Zhao, X., Zhu, K., Zhou, X., and
Yang, W., J. Catal., 2018, vol. 364, pp. 308–327.
https://doi.org/10.1016/j.jcat.2018.06.003
https://doi.org/10.1016/j.jcat.2013.07.020
17. Park, K.C., and Ihm, S.K., Appl. Catal. A-Gen., 2000,
vol. 203, pp. 201–209.
30. Zhang, Y., Wang, W., Jiang, X., Su, X., Kikhtyanin, O.V.,
and Wu, W., Catal. Sci. Technol., 2018, vol. 8, pp. 817–
828. https://doi.org/10.1039/C7CY02106B.
https://doi.org/10.1016/S0926-860X(00)00490-7
18. Nghiem, V.T., Sapaly, G., Mériaudeau, P., and
Naccache, C., Top. Catal., 2000, vol. 14, pp. 131–138.
https://doi.org/10.1023/A:1009071403372
31. Alvarez, F., Ribeiro, F.R., Perot, G., Thomazeau, C., and
Guisnet, M., J. Catal., 1996, vol. 162, pp. 179–189.
https://doi.org/10.1006/jcat.1996.0275
19. Mériaudeau, P., Tuan, V.A., Sapaly, G., Nghiem, V.T., and
Naccache, C., Catal. Today, 1999, vol. 49, pp. 285–292.
https://doi.org/10.1016/S0920-5861(98)00435-0
32. Kim, J., Han, S.W., Kim, J.C., and Ryoo, R., ACS Catal.,
2018, vol. 8, no.11, pp. 10545–10554.
https://doi.org/10.1021/acscatal.8b03301
20. Kim, M.Y., Lee, K., and Choi, M., J. Catal., 2014,
vol. 319, pp. 232–238.
33. Ge, L., Yu, G., Chen, X., Li, W., Xue, W., Qiu, M., and
Sun, Y., New J. Chem., 2020, vol. 44, no. 7, pp. 2996–
3003. https://doi.org/10.1039/C9NJ06215G
https://doi.org/10.1016/j.jcat.2014.09.001
34. Yang, L., Wang, W., Song, X., Bai, X., Feng, Z., Liu, T.,
and Wu, W., Fuel Process. Technol., 2019, vol. 190,
pp. 13–20. https://doi.org/10.1016/j.fuproc.2019.02.027
21. Parmar, S., Pant, K.K., John, M., Kumar, K., Pai, S.M.,
and Newalkar, B.L., J. Mol. Catal. A-Chem., 2015,
vol. 404, pp. 47–56.
https://doi.org/10.1016/j.molcata.2015.04.012
35. Yang, J., Kikhtyanin, O.V., Wu, W., Zhou, Y.,
Toktarev, A.V., Echevsky, G.V., and Zhang, R., Micropor.
Mesopor. Mat., 2012, vol. 150, pp. 14–24.
22. Liu, Y., Li, Z., Yu, Q., Chen, Y., Chai, Z., Zhao, G., Liu, S.,
Cheong, W.C., Pan, Y., Zhang, Q., Gu, L., Zheng, L.,
Wang, Y., Lu, Y., Wang, D., Chen, C., Peng, Q., Liu, Y.,
Liu, L., Chen, J., and Li, Y., J. Am. Chem. Soc., 2019,
vol. 141, pp. 9305–9311.
https://doi.org/10.1016/j.micromeso.2011.09.020
36. Kim, M.Y., Lee, K., and Choi, M., J. Catal., 2014,
vol. 319, pp. 232–238.
https://doi.org/10.1016/j.jcat.2014.09.001
https://doi.org/10.1021/jacs.9b02936
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 93 No. 4 2020