Hydro-isomerization of n-dodecane on Pt–La/Beta catalyst for the production of high quality bio-jet fuel: Effect of La addition

Microporous and Mesoporous Materials 346 (2022) 112294

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Microporous and Mesoporous Materials
journal homepage: www.elsevier.com/locate/micromeso

Hydro-isomerization of n-dodecane on Pt–La/Beta catalyst for the
production of high quality bio-jet fuel: Effect of La addition
Il-Ho Choi a, Hye-Jin Lee b, Kyung-Ran Hwang a, *
a
b

Energy Resource Upcycling Research Laboratory, Korea Institute of Energy Research, Daejeon, 34129, Republic of Korea
Institute for Advanced Engineering, Yongin, 17180, Republic of Korea

A R T I C L E I N F O

A B S T R A C T

Keywords:
Isomerization
Pt–La/Beta
Jet fuel
N-dodecane
Pt dispersion

A series of Pt–La/B38 catalysts were prepared for low-temperature isomerization of n-dodecane and the effects of
La addition on the textural properties, metal dispersion, acid properties, and catalytic performance were
investigated. La co-impregnated with Pt on B38 significantly reduced the Pt size and notably enhanced the
uniformity in Pt size. A higher ratio of accessible Pt and medium-strength Brønsted acid sites and a shorter

distance between two Pt particles of Pt–La10/B38 resulted in the maximum iso-C12 yield (59.2–56.2%) in the
range of 200–250 ◦ C, due to the reasonable arrangement of active sites caused by La loading.

1. Introduction
An aqueous-phase bio-cured oil separated from the pyrolysis oil of
woody biomass contains up to 60% of the carbon in the original biomass
[1]. The aqueous fraction is composed of various oxygenated organic
compounds, mainly small carbonyl compounds such as ketones, alde­
hydes, and organic acids [2,3]. Recently, researchers have begun to
valorise carbon contained in aqueous-phase crude oil such as small
olefins and aromatics with HZSM-5 via catalytic conversion [1].
In line with the growing demand for bio-jet fuel [4], studies to pre­
pare fuel precursors through C–C bonding reactions (aldol condensa­
tion) of small oxygenates in the aqueous fraction are also being
conducted [5,6]. These medium-chain fuel precursors are transformed
to liquid biofuel (n-alkanes) through a hydro-deoxygenation process [7].
The medium-chain alkanes produced in this manner are suitable for the
carbon range of jet fuel, and further conversion into branched alkanes
through isomerization is required to obtain high quality bio-jet fuel
(Fig. A1). For reference, since n-alkanes obtained from oil-based
biomass are mainly long-chain hydrocarbons (C16 and C18),
hydro-upgrading (hydro-cracking and isomerization) is performed in the
last step to obtain high-yield and high-quality jet fuel. The catalyst used
for hydro-upgrading is a bi-functional catalyst (Pt/HY, Pt–Mg/HY,
Pt–Pd/HB, Pt/SAPO-11, etc.) wherein active metal and acid sites coexist
and the cracking and isomerization reaction of paraffin occur simulta­
neously according to the reaction mechanism [8–10].
However, unlike the existing hydro-upgrading catalysts suitable for

long chain alkanes, more careful catalyst design is required for the

isomerization of medium-chain hydrocarbons (C8, C13, etc) obtained
through the C–C bonding reactions of small oxygenates. This is because,
during the isomerization reaction on the bi-functional catalyst, a
cracking reaction of the medium-chain alkane is accompanied, thereby
lowering the yield of jet-fuel. Therefore, in order to obtain a high-yield
jet fuel while preserving the carbon number in medium-chain alkanes
synthesized from small oxygenates, a catalyst in which isomerization is
dominant rather than cracking of the medium-chain alkanes is required.
In particular, it is important to find a composition with excellent cata­
lytic performance at low temperatures, since hydro-cracking easily oc­
curs at high temperatures due to endothermic reactions [11].
Many studies have been conducted to improve the yield of isomers by
changing the catalyst properties in the isomerization reaction of
medium-chain alkanes [11,12]. As a result of performing the isomeri­
zation reaction of n-dodecane with Pt/SAPO-11 prepared under
different synthesis condition for SAPO-11 (particle sizes of 65 nm to 4.5
㎛), it is found that both suitable acidity and suitable particle size of
SAPO-11 for shorter diffusion path are closely related to the yield of
isomers [12]. In the isomerization reaction of n-octane, Ni–Cu/SAPO-11
was prepared to suppress hydrogenolysis of n-alkane [11]. Hydro­
genolysis was inhibited by reducing the active ensemble size by diluting
the active metal (Ni) with inactive Cu, resulting in an isomer yield of
about 63% at 340 ◦ C. Low-temperature isomerization of n-hexadecane
was performed using Pt–Pd/HB (Si/Al = 25) with different Pt and Pd
ratios. Bi-metallic catalysts showed an enhanced metal dispersion (92%)

* Corresponding author.
E-mail address: (K.-R. Hwang).
/>Received 22 August 2022; Received in revised form 3 October 2022; Accepted 17 October 2022
Available online 28 October 2022

1387-1811/© 2022 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license ( />

I.-H. Choi et al.

Microporous and Mesoporous Materials 346 (2022) 112294

relative to mono-metallic catalysts (54%) and the conversion was also
increased along with the metal dispersion (65%–77%) [13].
A small amount (0.5 wt%) of rare earth metals (Ce, La, and Re) were
loaded on Pt/ZSM-22 to suppress the Pt sintering during reduction
treatment since the Pt dispersion is important in the low-temperature
isomerization of alkane [14]. Ce or La oxides helped to protect the
nano-sized Pt metal and induced an electron-deficiency state of Pt.
However, the Ce-modified Pt/ZSM-22 showed better isomerization
performance than the La-modified catalyst due to the strong interaction
of a Pt–O–Ce bond. Rare earth metal (Ce, La, Nd, and Yb) - exchanged
Pt/HB catalysts were also prepared [15,16]. The Ce-exchanged HB
(0.2–0.8 wt% loading) exhibited higher conversion and selectivity for
isomerized products than the parent HB catalyst due to the reducibility
of Pt species facilitated by the ion-exchanged Ce [16]. On the other
hand, in the case of La-exchanged Pt/HB, only a small amount of loading
(0.3 wt%) had a slight positive effect on the isomerization performance
due to the formation of new Lewis acid sites [15]. As such, in the
bi-functional catalytic system, the catalytic performance for the isom­
erization reaction of n-paraffin is greatly affected by the pore size and
acid site strength and density [12], the residence time of the olefinic
intermediate in the pores [17,18], the metal dispersion (distance be­
tween metals) [11,13], and the metal/acid balance [17,19], as well as
the reaction conditions, and studies are being conducted to increase the
degree of isomerization at relatively lower temperatures. Nevertheless,

it is still necessary to explore catalyst compositions that can maximize
the isomer yield while minimizing the cracking reaction, in order to
achieve high-yield and high-quality fuel through isomerization of
medium-chain alkanes.
In this work, a series of Pt–La/HB (Beta zeolite, Si/Al = 38) catalysts
were prepared for low-temperature isomerization of n-dodecane as a
model compound of medium-chain alkane. In general, a Pt catalyst
impregnated on an acidic support with a low Si/Al ration is more active
but less selective for the isomerization reaction. However, beta zeolite
with a low Si/Al ratio (B38) was selected to increase the conversion of nalkane at relatively low temperatures and La was added on Pt/B38. The
textural properties, metal dispersion, and acid properties of the La-

loaded catalysts were characterized using various techniques and the
accessible metal/acid ratio and an average acid step between two metal
sites were discussed to highlight the importance of balancing the
accessible metal and acid sites related to conversion and isomer yield.
2. Experimental
2.1. Catalyst preparation
CP814C (B38) as a powder type beta zeolite was purchased from
Zeolyst, and the zeolite was calcined before use at 500 ֠C for 1 h in air. As
Pt and La precursors, chloroplatinic acid solution (Sigma-Aldrich, 5 wt
%) and lanthanum nitrate hexahydrate (Samchun Chem., >98%) were
used. The catalyst was prepared by the wetness impregnation method
using a mixed aqueous solution of Pt and La precursors, followed by
calcination at 450 ֠C for 4 h in air. To determine the effect of La addition,
the loading amount of Pt was fixed at 1 wt%, and the prepared catalysts
were denoted as follows: Pt–La’x’/B38, where x is the tentative La
content.
2.2. Characterization
To determine the textural properties of the prepared catalyst, a

Brunauer-Emmett-Teller (BET) analysis was conducted by using 3Flex
(Micromeritics Co., LTD.). The sample was degassed at 200 ֠C overnight,
and was cooled to − 196 ֠C for N2 adsorption. The structural property was
estimated by an X-ray diffraction analysis (XRD, SmartLab 9kW/Rigaku
Co. Ltd.). To observe the acidity of the catalyst’s surface, NH3-temper­
ature programmed desorption (NH3-TPD) and Fourier transform
infrared spectroscopy (FTIR) were utilized by using a BELCAT II catalyst
analyzer (BELCAT) and a Nicolet iS50+ (Thermo Scientific), respec­
tively. In the case of NH3-TPD, NH3 was adsorbed on the sample at 50 ֠C,
and then desorbed with increasing temperature to 800 ֠C. Meanwhile,
pyridine, employed as a probe molecule in the FTIR analysis, was
adsorbed at 100 ֠C, and then desorbed. In the desorption profiles of
pyridine at below 300 ֠C, two bands overlap around 1445–1444 cm− 1,

Fig. 1. FE-STEM/TEM and EDS images of the prepared catalysts: (a) Pt/B38, (b) Pt–La2/B38, and (c) Pt–La10/B38 (the yellow arrow in the figure points to a Pt
particle). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)
2


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Microporous and Mesoporous Materials 346 (2022) 112294

corresponding to pyridine interacting with the hydroxyl group and
pyridine bonded to a relatively stronger Lewis site, respectively. Thus,
we chose the pyridine desorption profile of 300 ֠C to confirm the strong
Lewis site because the pyridine bonded to the hydroxyl group disappears
below 300 ֠C. A H2-temperature programmed reduction (H2-TPR)
experiment was carried out to evaluate the temperature at which
hydrogen consumption for Pt oxides occurred using an AutoChem II

(Micromeritics). The contents of Pt in the prepared catalysts were
determined by using inductively coupled plasma – optical emission
spectroscopy (ICP-OES, OPTIMA7300DV/PerkinElmer), and a CO-pulse
chemisorption (BELCAT II catalyst analyzer/BELCAT) was used for
measuring the Pt dispersion and size. Visual images of the catalysts were
obtained by using a field emission-scanning transmission electron mi­
croscope (FE-S/TEM, HF5000/Hitachi Co. Ltd.) equipped with an en­
ergy dispersive spectrometer (EDS). Before the TEM analysis, the
catalysts were reduced at 350 ֠C for 1 h with H2.

are summarized in Table 1. The specific surface area and total pore
volume decreased with the impregnation of Pt and La on the bare B38
support. In particular, an increase in the amount of impregnated La had
a greater effect on the reduction of micropore volume than the meso/
macropore volume. As a result, the mean pore diameter increased from
2.15 nm to 2.29 nm. This reduction in micropores and increase in mean
pore diameter are advantageous in terms of reducing the cracking re­
action of olefinic intermediates, because retention of the intermediate in
micropores induces cracking reactions at acid sites. The Pt dispersion of
the Pt/B38 catalyst was 41.7%, whereas the Pt dispersion increased to
more than 60% when impregnated with La on Pt/B38.
The XRD patterns of the prepared catalyst are shown in Fig. A2.
Compared with the XRD pattern of B38, the intensity of the character­
istic peak of B38 decreased as the loading amount of La on the catalyst
increased. Also, no characteristic peaks related to La were found even
when 12 wt% of La was impregnated on the B38. This indicates that an
amorphous lanthanum oxide (LaOx) was formed, which can be
confirmed from the TEM images presented later. FE-STEM/TEM and
EDS images of the prepared catalysts (Pt/B38, Pt–La2/B38, and
Pt–La10/B38) are shown in Fig. 1 and Fig. A3. In the case of Pt/B38

(Fig. 1(a) and Fig. A3(a)), large Pt particles (approximately, 26–36 nm)
are exposed to the external surface of the support, and small size Pt
particles are distributed between them. Small Pt appears to be present
within the pores rather than on the surface of the catalyst particles. The
low Pt dispersion confirmed by the CO pulse method (Table 1) appears
to be due to the large Pt particles exposed to the outside. As shown in
Fig. 1(b) and Fig. A3(b), when Pt and a small amount of La were
impregnated on B38, large and small Pt particles were also mixed.
However, it is observed that, unlike Pt/B38, the size of Pt exposed to the
outside was drastically reduced (approximately, 6–14 nm). As observed
in the EDS mapping of the Pt–La2/B38, Pt is distributed evenly on the
support with La. It appears that co-impregnated La improves the
dispersion of Pt, as shown in Table 1 (Pt dispersion). When 10 wt% of La
was co-impregnated with Pt on B38 (Pt–La10/B38), all large-sized Pt
particles disappeared and nano-sized Pt particles (~approximately, 3.3
nm) were uniformly distributed (Fig. 1(c) and Fig. A3(c)). It thus can be
seen that as the amount of co-impregnated La increases, the uniformity
and dispersion of nano-sized Pt particles appear to increase. However,
unlike the STEM/TEM images, the Pt dispersion (63.7–68.4%) measured
by the CO pulse (Table 1) was similar regardless of the amount of La
loading for the Pt–La5~12/B38 catalysts. This appears to be due to the
Pt size gradually decreasing when the amount of La loading exceeds a
certain amount (about 5 wt%), whereas as the catalyst surface is covered
with lanthanum, the number of externally exposed Pt (accessible Pt)
decreases little by little. However, they still show higher dispersions
(more than about 63.7%) than Pt/B38.
As shown in the STEM image (Figs. 1(c-3)), amorphous LaOx was
observed, which is consistent with the XRD result where La-related
peaks did not appear (Fig. A2). Nevertheless, as shown in both EDS
mapping (Figs. 1(c-4)) and line-EDS (Fig. A3(c)), La and Pt are well

distributed throughout.
H2-TPR was employed to further confirm the reduction in size of Pt
particles by La addition to Pt/B38 (Fig. A4). For Pt/B38, the reduction
peaks centered at 80 ◦ C and 355 ◦ C were attributed to the reduction of
PtOx particles loaded on the external surface and dispersed in the in­
ternal pores of B38, respectively [19]. The reduction temperature for
PtOx loaded on the external surface of B38 was gradually shifted to
higher temperatures (above 200 ◦ C) as the loading amount of La in­
creases. This indicates that the size of PtOx particles loaded on the
external surface of the support becomes smaller, which is accordant with
the results of the FE-S/TEM analysis. However, excessive loading of La
(12 wt%) reduced the amount of Pt species exposed on the surface, and
thus the hydrogen consumption was relatively reduced. La thus appears
to play a role in preventing agglomeration of co-impregnated Pt and
facilitating uniform nano-size dispersion.
Table 2 summarizes acid properties of the prepared catalysts, based

2.3. Hydro-isomerization reaction
Low-temperature hydro-isomerization was conducted with low
temperature and atmospheric pressure in a continuous fixed bed reac­
tion system. The prepared catalyst (400 mg) was inserted into the
tubular reactor (quartz, I.D. 5 mm), and then the reactor was mounted
on a furnace. Hydrogen (Special Gas Co. Ltd., 99.999%) was injected
with a flow of 100 ml/min into the reaction system. The reactor was
heated to 350 ֠C for the catalyst’s reduction, and then the hydroisomerization was progressed at 160–340 ֠C. The temperature devia­
tion was maintained below 1%. As a model compound, n-dodecane
(Sigma-Aldrich, >99%) was employed and pumped into the reaction
system with 5.85 h− 1 weight hourly space velocity (WHSV) by an HPLC
pump (Optos 1HM, Eldex). The liquid sample was collected by using a
cold trap, and the trap was cooled by ice to condense the products

derived from the reactor.
The collected sample was analyzed by a gas chromatograph (GC,
Simadzu Co. Ltd./GC-2010 plus) equipped with a frame ionization de­
tector (FID) and mass spectroscopy (MS, Simadzu Co. Ltd./GCMSQP2010 SE). Both instruments used the same RTX-5 column (30 m ×
0.25 mm x 0.25 μm) and oven program (held to 50 ֠C for 1 min, heated to
220 ֠C (10 ֠C/min and held for 1 min), and further heated to 280 ֠C (15 ֠C/
min and held for 3 min)). To quantitatively measure unconverted ndodecane and isomerized products (iso-C12), n-pentadecane (Aldrich,
>99%) was used as an internal standard, and the response factor of
isomerized products was assumed to be the same with n-dodecane. The
terminologies were defined by the following equations:
Conversion (%) =

the amount of converted n − dodecane (g)
× 100
the amount of injected n − dodecane (g)

iso − HC12 yield (%) =

the amount of produced iso − C12 (g)
× 100
the amount of injected n − C12 (g)

iso − HC12 selectivity (%) =

the amount of produced iso − C12 (g)
× 100
the amount of converted n − C12 (g)

iso − HC12 in product (g)
iso − HC12/n − HC ratio ( − ) =

, and
12
n − HC12 in product (g)

nPt/
nBA ( − ) =

(
)
the amount of exposed Pt metal mmol/g

(
)
the amount of medium − strength Brønsted acid sites mmol/g

3. Results and discussion
3.1. Catalyst characteristics
The textural properties and Pt dispersion of the prepared catalysts
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Microporous and Mesoporous Materials 346 (2022) 112294

Table 1
Textural properties and metal dispersion of the prepared catalysts.
Catalysts

BET surface area (m2/g)

a

B38
Pt/B38
Pt–La2/B38
Pt–La5/B38
Pt–La7/B38
Pt–La10/B38
Pt–La12/B38
a
b
c
d
e

b

Micro

Meso

680.4
608.9
561.6
523.5
517.8
464.1
457.3

102.5

83.4
80.5
83.3
86.0
73.3
79.3

Total pore volume (cm3/g)
b

Macro

Total

c

a

b

Micro

Meso

0.4
0.7
0.7
0.7
0.3
0.6

0.6

680.9
606.9
579.6
539.3
529.6
467.2
465.9

0.212
0.196
0.178
0.165
0.163
0.146
0.141

0.114
0.098
0.095
0.093
0.102
0.093
0.095

b

Mean pore diameterd (nm)

Pt dispersione (%)

2.12
2.15
2.16
2.21
2.20
2.28
2.29

–
41.7
60.7
65.9
63.8
68.4
63.7

c

Macro

Total

0.010
0.015
0.015
0.015
0.008
0.014

0.014

0.341
0.301
0.288
0.275
0.272
0.241
0.243

calculated from T-plot data.
calculated from BJH desorption data.
calculated from specific BET data.
calculated from BJH adsorption data, and.
calculated from CO pulse (accessible Pt) and ICP data (Pt content).

Fig. 2. Results of hydro-isomerization of n-dodecane using B38, Pt/B38 and Pt–La10/B38 catalysts (WHSV = 5.85/h).

on the results of NH3-TPD and pyridine-FTIR (Fig. A5). When 2 wt% of
La was loaded on Pt/B38, the total acid sites increased. However, as the
amount of La was further increased, the amount of acid sites decreased
slightly because the amorphous lanthanum oxides covered the acid sites.
(Fig. 1 and A3). However, they still have more acid sites than B38 or Pt/
B38. In addition, the Brønsted acid sites related to the skeleton isom­
erization of the reactant also decreased according to the La loading,
while Lewis acid sites were generated due to the formation of amor­
phous LaOx. Considering the ratio of accessible Pt and Brønsted acid
sites (nPt/nBA), Pt–La2~10/B38 had a higher nPt/nBA value
(0.117–0.132) than that of Pt/B38 (0.076), but there was not a

significant difference among the values. It is noteworthy that although
nPt/nBA shows similar values, the size of accessible Pt becomes smaller
as the amount of loaded La increases (Fig. 1, Fig. A3, and Fig. A4).
3.2. Low-temperature isomerization of n-dodecane
The desired isomerization reaction entails dehydrogenation of nalkane on Pt site, skeleton rearrangement of olefinic intermediate on
active acid sites, and hydrogenation of iso-olefin on Pt site occurring
continuously and smoothly, while preserving the number of carbons in
the reactant. Fig. 2 shows the conversion and the selectivity of iso4


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Microporous and Mesoporous Materials 346 (2022) 112294

Table 2
Acid properties measured with NH3-TPD and pyridine-FTIR of the prepared catalysts.
Catalysts
B38
Pt/B38
Pt–La2/B38
Pt–La5/B38
Pt–La7/B38
Pt–La10/B38
Pt–La12/B38
a
b
c

Acid site (mmol/g)
Weak

Medium

Strong

Total

0.955
0.933
1.428
1.246
1.146
1.116
1.104

0.358
0.442
0.614
0.618
0.597
0.579
0.547

0.193
0.248
0.4
0.299
0.281
0.273
0.147

1.506
1.623
2.442
2.163
2.024
1.968
1.798

B/L ratioa (− )

Brønsted acid siteb (mmol/g)

Lewis acid siteb (mmol/g)

nPt/nBAc (− )

1.48
1.40
0.89
0.74
0.74
0.65
0.80

1.12
1.15
0.92
0.87
0.92

0.88
0.99

0.76
0.88
1.04
1.18
1.25
1.36
1.23

–
0.076
0.123
0.132
0.118
0.117
0.103

the ratio of Brønsted acid (B) and Lewis acid (L) of pyridine-FTIR profile.
calculated from NH3-TPD data and the ratio of B and L of pyridine-FTIR profile.
the ratio of total amount of exposed Pt sites to the total amount of medium-strength B site.

dodecane (a), the yield of iso-dodecane (b), and the distribution of
product (c and d) for B38, Pt/B38, Pt–La10/B38, and La10/B38. B83
and La10/B38 were inactive for isomerization of n-dodecane at reaction
temperature below 280 ◦ C, but n-dodecane started to be converted
above 300 ◦ C where a severe cracking reaction was predominant, and
thus the liquid product was hardly recovered. In the case of Pt/B38, ndodecane stared to be converted at 180 ◦ C and showed 100% conversion
at 240 ◦ C. However, most cracked hydrocarbons with less than five

carbons and gases were generated in the high conversion section (Fig. 2
(c)), and as the conversion increased according to the reaction temper­
ature, the selectivity of iso-C12 fell inversely. As a result, the maximum
yield (22.9%) of the desired iso-C12 was obtained at 200 ◦ C with a
conversion of about 30% (Fig. 2(b)). For Pt–La10/B38, the conversion
was delayed by about 20 ◦ C compared to that of Pt/B38, but the selec­
tivity of iso-C12 was maintained high in the range of 200–250 ◦ C. The
selectivity of iso-C12 at 260 ◦ C, which showed 100% conversion,
decreased sharply, and the maximum iso-C12 yield (59.2–56.2%) was
thus obtained in the range of 240–250 ◦ C (Fig. 2(b)). As shown in Fig. 2
(c), distributions (mono-branched and multi-branched isomers and
cracked hydrocarbons) in the product varied according to the conver­
sion of n-dodecane over the bi-functional catalyst. n-dodecane was
mainly transformed into cracked hydrocarbons over B38 acid catalyst.
In the case of Pt/B38, isomers were mainly produced at low conversion
(less than about 30%), but as the conversion increased, cracked products
became the dominant species due to their secondary transformation.
This appears to be due to poor hydrogenation resulting from low nPt/
nBA (0.076). This trend was similar when La was co-impregnated with
Pt on B38, but the conversion at which the secondary transformation
began to appear in Pt–La10/B38 was delayed by about two times (at
about 60% conversion). For comparison, hydro-isomerization of ndodecane was performed using a Pt/SAPO-11 which is one of the wellknown catalysts for hydro-isomerization (not shown here). The con­
version of 64.9% and the isomer yield of 52.1% were obtained at 300 ◦ C.
Thus, Pt–La10/B38 shows better catalytic performance even at 250 ◦ C
than Pt/SAPO-11 that have been studied recently.
The ratio of cracked product and isomer (C/I ratio) and the ratio of
multi- and mono-branched isomers (multi/mono ratio) are provided in
Fig. 2(d). Both C/I and multi/mono ratios of Pt–La10/B38 were lower
than those of Pt/B38. This means that skeleton isomerization and hy­
drogenation of n-dodecane are balanced on the Pt–La/B38 catalyst. In

conclusion, as shown in Table 2, it can be seen that the high nPt/nBA
(0.117) of Pt–La10/B38 is suitable for producing iso-C12 under the
present reaction conditions, where the carbon number of the feed (ndodecane) is preserved while minimizing the cracking reaction in the
range of low reaction temperature.
The average number of active acid sites that one n-dodecane mole­
cule encountered during the catalytic reaction, nas, was estimated based
on the initial product distribution to observe the characteristics of the
diffusion path of olefinic intermediates between two Pt metal sites and
the results are summarized in Table 3 [18]. B38 was converted at high
temperature (above 280 ◦ C in Fig. 2(a)) because there was no metal

Table 3
The initial weight distribution in the product and estimated average number of
active acid steps involved in the n-C12 transformation between two Pt sites.
Catalysts

Conversion
(%)

Monobranched
C12 (wt.
fraction)

Multibranched
C12 (wt.
fraction)

Cracked
products (wt.
fraction)

naas

B38
Pt/B38
Pt–La10/
B38

6.17
5.59
2.29

0.06
0.71
0.93

0.03
0.29
0.07

0.91
0.00
0.00

3.78
1.43
1.11

a

nas = (mono-branched C12 × 1) + (multi-branched C12 × 2.5)+(cracked
products × 4) [8,18].

active site for dehydro/hydrogenation, and mostly cracked products
were produced, traveling approximately 3.8 acid steps. When Pt was
impregnated on B38, isomers were mainly generated in the initial re­
action, and the number of active acid sites involved in the trans­
formation was greatly reduced. In the case of Pt–La10/38, the nas value
was close to 1.1. This is considered a result of the reduced the distance
between nano-sized Pt particles, as can be seen from TEM images and Pt
dispersion. This is consistent with the results of previous studies [18].
However, it is difficult to find a significant difference between nas values
estimated from the initial reaction of two catalysts (Pt/B38 and
Pt–La10/B38). This is because the possibility that inactive acid sites
exist under the operating conditions (180 and 200 ◦ C) cannot be
excluded. This is confirmed by observing the change of nas values ac­
cording to the reaction temperature, shown in Fig. A6. As the conversion
of n-dodecane increased, the nas values of two bifunctional catalysts
increased. This indicates that the increase of the reaction temperature
causes more acid sites to become active, and also increases the diffu­
sivity of the olefinic intermediates. However, it is clear that
Pt–La10/B38 still shows lower nas values than Pt/B38 at similar con­
versions, and the gap between the two values increases as the temper­
ature (conversion) increases. This means that in the Pt–La10/B38
catalyst with well dispersed nano-sized Pt particles, even if the reaction
temperature rises, the average number of active acid sites that the in­
termediates encounters while traveling through the surface of the cat­
alysts is small due to the short distance between Pt particles.
Fig. 3 shows the results of hydro-isomerization of n-dodecane ac­
cording to the La content impregnated on the Pt/B38 at 250 ◦ C.

Although the conversion was close to 100% on Pt/B38 at 250 ◦ C, the
recovered iso-C12 yield was very low due to the predominant cracking
reaction (Fig. A7). As the amount of La loading increased, the conversion
of dodecane decreased, but the selectivity and yield of the desired iso-C12
tended to increase. The maximum yield of iso-C12 was obtained in the
10% La impregnated catalyst.
The reason for the change in catalytic properties (conversion,
selectivity and yield) in the Pt–La series catalysts even with similar nPt/
nBA values is (1) an increase of uniformity of nano-sized Pt and (2) the
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Microporous and Mesoporous Materials 346 (2022) 112294

smaller distance between two Pt particles caused by La loading, result­
ing in predominant hydrogenation of the olefinic intermediates. That is,
the optimal loading of La reduce the distance between Pt particles and
enhances the intimacy between the uniformly distributed nano-sized Pt
and the active acid sites. A further increase of the La loading (more than
12 wt%) resulted in lowered catalytic performance, likely due to the
coverage of the Brønsted acid and Pt sites by LaOx with Lewis acid sites,
as discussed in the results of FE-S/TEM and H2-TPR, consistent with a
previous study showing that the conversion is related to the externally
exposed Pt over the catalyst [19]. For the Pt–La2~10/B38 catalysts, the
ratio of iso-C12/n-C12 was greater than 2.1. Note that the ratio decreases
as the content of La increases because uncovered n-dodecane remains.
Fig. 4 shows the time-on-stream stability of Pt–La10/B38 in hydroisomerization of n-dodecane. Initial conversion and isomer yield were
86% and 57%, respectively, but the isomer yield gradually decreased

(46%) until 4 h of time-on-stream. After shutting down the reaction
system, the catalyst was in-situ cleaned with acetone without any other
regeneration process. In the subsequent reaction, the conversion and
isomer yield were maintained within 75–80% and 55–60%, respectively,
which means that the catalyst can be regenerated only by washing with
acetone.
Based on the above results, the hydro-isomerization reaction over the
bifunctional catalysts is schematically drawn in Fig. 5. The mechanism
of hydro-isomerization on the bi-functional catalyst has been well
documented in several studies [13]. In general, the n-alkane is dehy­
drogenated to the alkene intermediates on the Pt active site and the
intermediates are protonated and isomerized on the Brønsted acid sites,
and then hydrogenated on the nearby Pt active site to form a desired
iso-alkane. Meanwhile, the low nPt/nBA value and the diffusion limi­
tation of the intermediates in the microporous channels of acid supports
increases the contact opportunity and the contact time with the acid
sites, resulting in further cracking to obtain unwanted cracking prod­
ucts. That is, a proper arrangement of metal and acid sites is very
important in bi-functional catalysts, as well as the textural structure of
the catalysts. For Pt–La10/B38, the size of Pt was very small and uni­
form. Such uniformly distributed nano-sized Pt particles (~approxi­
mately, 3.3 nm) give the reactant many opportunities for
dehydro/hydrogenation reactions, resulting in the production of many
olefinic intermediates at the same time. The intermediates undergo
skeletal rearrangement at an adjacent acid site and then hydrogenate at
a nearby Pt site to form isomers. In addition, the La loading reduces the
volume of micropores, thereby suppressing the cracking reaction that
occurs from the diffusion limitation of the intermediates.

Fig. 4. The time-on-stream stability of Pt–La10/B38 in hydro-isomerization of

n-dodecane (250 ◦ C and WHSV = 5.85/h).

4. Conclusion
A series of Pt–La/B38 catalysts were prepared for low-temperature
isomerization of n-dodecane and the effect of La addition on the cata­
lytic performance (conversion, selectivity and yield) was investigated.
Based on the results of CO pulse chemisorption, FE-S/TEM images, and a
H2-TPR analysis, La (10 wt%) co-impregnation in Pt/B38 resulted in an
increase of the Pt dispersion (41.7%–68.4%). Moreover, the size of Pt
loaded on the external surface of B38 was significantly reduced from
approximately 26–36 nm–~3.3 nm and the uniformity in Pt size was
notably enhanced. La thus appears to play a role in preventing
agglomeration of co-loaded Pt and facilitating uniform nano-size Pt
dispersion. Pt/B38 showed good activity at relatively low reaction
temperature (100% conversion at 220 ◦ C), but most cracked hydrocar­
bons with less than five carbons and gases were generated in the high
conversion section, resulting in a maximum yield, 22.9%, for the desired
iso-C12. Meanwhile, for Pt–La10/B38, the conversion was delayed by
about 20 ◦ C compared to that of Pt/B38, but the selectivity of iso-C12 was
maintained high in a range of 200–250 ◦ C, resulting in the maximum isoC12 yield (59.2–56.2%). Both the C/I and multi/mono ratios of Pt–La10/
B38 were lower than those of Pt/B38, indicating that skeleton isomeri­
zation and hydrogenation of n-dodecane are balanced on the Pt–La/B38
catalyst. In conclusion, the desirable arrangement of active sites with
higher nPt/nBA (0.1777) and lower nas (1.11) caused by La loading in
the Pt–La/B38 catalyst enhances the catalytic performance for lowtemperature isomerization of n-dodecane.
Funding
A National Research Foundation of Korea grant funded by the Korea
government.
CRediT authorship contribution statement
Il-Ho Choi: Writing – review & editing, Writing – original draft,

Methodology, Investigation, Formal analysis, Conceptualization. HyeJin Lee: Methodology, Formal analysis. Kyung-Ran Hwang: Writing –
review & editing, Supervision, Project administration, Investigation,
Conceptualization.
Declaration of competing interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence

Fig. 3. Results of hydro-isomerization of n-dodecane using Pt/B38 and a series
of Pt–La/B38 catalysts (250 ◦ C and WHSV = 5.85/h).
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Microporous and Mesoporous Materials 346 (2022) 112294

Fig. 5. Schematic drawing of the isomerization reaction of n-dodecane on the prepared bi-functional catalysts (Pt/B38, Pt–La2/B38, and Pt–La10/B38).

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Data availability
Data will be made available on request.
Acknowledgements
This work was supported by a National Research Foundation of

Korea (NRF) grant funded by the Korea government (MSIT) (No.
NRF2020M1A2A2079802).
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.micromeso.2022.112294.
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