Conversion of palmitic acid to jet fuel components over Mo/H-ZSM-22 bi-functional catalysts with high carbon reservation

Article abstract of DOI:10.1016/j.apcata.2020.117847

The optimal preparation conditions of Mo/H-ZSM-22 bi-functional catalysts were obtained via the sublimation phenomenon of MoO₃ at high calcination temperatures, which was beneficial for the well-dispersion of MoO_x species with 5?10 nm particles. High reduction temperature enhanced the reduction from Mo⁶⁺ to Mo⁴⁺ and even from Mo⁴⁺ to Mo°, which would be beneficial for iso-alkanes formation with higher carbon reservation. Importantly, 89.3 % selectivity of C₁₆ alkanes of which 61.7 % were iso-C₁₆ alkanes were obtained with complete deoxygenation of palmitic acid, which was the highest selectivity of C₁₆ alkanes over Mo/H-ZSM-22 bi-functional catalyst prepared at a calcination temperature of 550 °C and at a reduction temperature of 600 °C. The results would offer a novel candidate of bi-functional catalysts for upgrading of microalgae-based bio-oil to high-value jet fuel components with high selectivity of iso-alkanes and carbon reservation.

Full text of DOI:10.1016/j.apcata.2020.117847

AppliedCatalysisA,General608(2020)117847
Contents lists available at ScienceDirect
Applied Catalysis A, General
journal homepage: www.elsevier.com/locate/apcata
Conversion of palmitic acid to jet fuel components over Mo/H-ZSM-22 bi-
functional catalysts with high carbon reservation
Jimei Zhanga,c, Yanchun Shia,*, Hongbin Caoa, Yulong Wub,*, Mingde Yangb
a CAS Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, China
b Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing, 100084, China
c School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
The optimal preparation conditions of Mo/H-ZSM-22 bi-functional catalysts were obtained via the sublimation
phenomenon of MoO3 at high calcination temperatures, which was beneficial for the well-dispersion of MoOx
species with 5−10 nm particles. High reduction temperature enhanced the reduction from Mo6+ to Mo4+ and
even from Mo4+ to Mo°, which would be beneficial for iso-alkanes formation with higher carbon reservation.
Importantly, 89.3 % selectivity of C16 alkanes of which 61.7 % were iso-C16 alkanes were obtained with complete
deoxygenation of palmitic acid, which was the highest selectivity of C16 alkanes over Mo/H-ZSM-22 bi-func-
tional catalyst prepared at a calcination temperature of 550 °C and at a reduction temperature of 600 °C. The
results would offer a novel candidate of bi-functional catalysts for upgrading of microalgae-based bio-oil to high-
value jet fuel components with high selectivity of iso-alkanes and carbon reservation.
Mo/H-ZSM-22
Palmitic acid
Hydrodeoxygenation
Isomerization
1. Introduction
exhibits the unique advantage with eliminate oxygen in the form of
H2O, compared to decarboxylation and hydrodecarbonylation.
The depleting petroleum and the increasing CO2 emission have been
generally considered as two big challenges of the development for air
transport industry, which motivated researchers to seek for other re-
newable energy sources. Currently, many publications have reported
that bio-oil obtained from hydrothermal liquefaction of microalgae (so
called “microalgae-based bio-oil”), was recognized as one of the most
promising alternatives to produce jet fuel alkanes [1,2]. Moreover, it
could alleviate energy shortages and reduce greenhouse gas CO2
emissions beyond 55 % [3]. Microalgae-based bio-oil containing a large
amount of C14-C22 long-chain fatty acids, has similar carbon numbers
with jet fuel components; while such high oxygen content (10−40 wt
%) causes many unsatisfactory properties such as poor ignition, inferior
heating value, thermal instability and so on [4–7]. Therefore, deox-
ygenation of microalgae-based bio-oil is necessary for its upgrading,
and palmitic acid (C15-COOH) or stearic acid (C17-COOH) are usually
selected as model compounds to study their deoxygenation perfor-
mance [8–14]. According to published literatures [13–19], three
deoxygenation routes of fatty acids have been summarized as follows:
decarboxylation (DCX: R-COOH → R-H + CO2), hydrodecarbonylation
(HDC: R-COOH + H2 → R-H + CO + H2O) and hydrodeoxygenation
(HDO: R-COOH + 3H2 → R-CH3 + 2H2O). From the perspective of
atomic economy, hydrodeoxygenation (HDO) without carbon loss
Conventional metal catalysts, including sulfided NiMo and CoMo,
noble metal and transition metal (Ni/Co/Mo) with no acidity of sup-
ports, have been reported. However, these catalysts can only convert
microalgae-based bio-oil or its model compounds into n-alkanes
[20–23]. As well known, the freezing point is a crucial standard to
evaluate the quality of jet fuel [24]. In comparison with n-alkanes as
shown in Table 1 [25], iso-alkanes are considered as one of the ideal
components for jet fuel with the low freezing point. Thus, deoxygenated
products of n-alkanes need to be isomerized to meet the requirement for
the low freezing point of jet fuel ranges components [24–26]. Based
upon above analysis during upgrading of microalgae-based bio-oil or its
model compounds (palmitic acid or stearic acid) to iso-alkanes in jet
fuel, the catalysts must possess two functions with the hydrogenation-
deoxygenation of oxygenated compounds and further isomerization of
deoxygenated products (n-alkanes). Recently, metal/zeolite bi-func-
tional catalysts, such as Mo/ZSM-22, Ni/Beta, Ni/ZSM-5 and so on
[16,27–30], have been developed for upgrading microalgae-based bio-
oil to hydrocarbons. In our previous work [16], Mo/H-ZSM-22 bi-
functional catalyst, prepared via the wetness impregnation method, has
been developed for upgrading palmitic acid (C15-COOH) to high se-
lectivity of iso-alkanes (59.7 %) and C16 alkanes (75.5 %) with beyond
99.9 % conversion of palmitic acid, which indicated that H-ZSM-22
⁎ Corresponding authors.
E-mail addresses: ycshi@ipe.ac.cn (Y. Shi), wylong@tsinghua.edu.cn (Y. Wu).
https://doi.org/10.1016/j.apcata.2020.117847
Received 28 June 2020; Received in revised form 20 September 2020; Accepted 21 September 2020
Availableonline23September2020
0926-860X/©2020ElsevierB.V.Allrightsreserved.

J. Zhang, et al.
AppliedCatalysisA,General608(2020)117847
Table 1
adsorption-desorption isotherms recorded by a Micromeritics ASAP
2010 instrument with outgassing at 90 °C for 1 h and at 350 °C for 15 h
under vacuum. X-ray fluorescence (XRF) spectrometer (MagiX, Philips)
determined the elemental analyses of the solid sample and X-ray pho-
toelectron spectroscopy (XPS) detected states and concentration of Mo
species. NH3-TPD was performed to characterize the acidity of catalysts
on Autochem II 2920. Temperature programmed reduction by hy-
drogen (H2-TPR) was used to determine the interaction between metal
and support and reducibility of these bi-functional catalysts.
Freezing points of paraffin [23].
Carbon number
Freezing point (oC)
n-Paraffin
2-Methylparaffin
5-Methyparaffin
C16
C18
C20
18
28
37
−10
6
−31
−20
−7
18
possessed excellent isomerization of n-alkanes. The sublimation of
MoO3 occurred under certain conditions [16,31–33], would be more
effective for gas to diffuse into zeolitic channels than solids in theory.
According to the results of SEM, TEM, XRF and TEM-EDS character-
izations in our previous work [16], no obvious observation of MoO3
over these calcinated Mo/ZSM-22 catalysts but MoO2 particles were
observed clearly, which was ascribed to the sublimation of MoO3 ex-
isted at high energy spotting in TEM/TEM-EDS analysis and at beyond
550 °C calcination [16,31–33]. The dispersion and state of MoOx further
influence the catalytic performance and final products distribution.
Therefore, we tried to optimize the preparation conditions of Mo/H-
ZSM-22 catalysts for upgrading of long-chain fatty acids to high-value
added jet fuel with more iso-alkanes just via the phenomenon of MoO3
sublimation at high temperature (> 500 °C). In this paper, we in-
tentionally designed MoOx/H-ZSM-22 bi-functional catalysts via tai-
loring the calcination temperatures (450 °C, 550 °C and 650 °C for 5 h)
and reduction temperatures (500 °C, 600 °C and 700 °C for 4 h), to study
the optimal preparation conditions for Mo/H-ZSM-22 bi-functional
catalysts and to upgrade palmitic acid (model compounds of micro-
algae-based bio-oil) for more iso-alkanes in jet fuel ranges as possible as
decreasing carbon loss.
2.3. Catalytic performance
Palmitic acid (0.5 g), n-decane (50 mL), and catalyst (0.1 g) were
put to the stainless-steel autoclave with 100 mL. Pure hydrogen under
ambient temperature was introduced into the autoclave for three times
in order to replace the air inside the autoclave, and then sealed reactor
was pressurized to 4 MPa with hydrogen. Finally, the system was he-
ated to 260 °C and conducted for 4 h at a stirring speed of 300 rpm. The
final liquid phase products were analyzed by GC–MS (Agilent 7890-
597-5, FSFS J &W 122-5532- 30 m × 250 μm × 0.25 μm) equipped
with a flame ionization and mass spectrometry detection using the area
normalization method [40,41]. The conversion of palmitic acid and
selectivity of products were calculated as follows:
moles of converted palmitic acid
moles of the starting palmitic acid
Conversion of palmitic acid=(
)×100%
moles of each product
moles of total products
Selectivity of products=(
)×100%
3. Results and discussion
3.1. Physicochemical properties
2. Experimental
According to XRD patterns of all materials in Fig. 1, there were si-
milar diffraction peaks between these Mo/HZ-22 catalysts and HZ-22
parent zeolite without any other compete crystalline phase, except for
the diffraction peaks of MoOx species, which obviously indicated that
all Mo/HZ-22 catalysts possessed parent zeolite HZ-22 structure even at
high calcination and reduction temperatures. Compared to HZ-22, some
decrease of diffraction intensities for Mo/HZ-22 catalysts was observed.
The diffraction intensities of Mo/HZ-22-650C-500R, Mo/HZ-22-550C-
600R and Mo/HZ-22-550-700R were decreased significantly, which
may illustrate the obvious destruction of parent zeolite caused by too
2.1. Catalysts preparation
Firstly, commercial H-ZSM-22 zeolite was offered by Sinopec
Research Institute of Petroleum Processing (Beijing, China) as parent
support, which was synthesized via the conventional hydrothermal
method [39]. Secondly, (NH4)6Mo7O24·4H2O (Sinopharm Chemical
Reagent Co. Ltd, Shanghai, China) was purchased, which were further
dissolved in distilled water with the mass ratio of
1
((NH4)6Mo7O24·4H2O) to 10 (H2O) for Mo source. Thirdly, we in-
tentionally prepared a series of Mo/H-ZSM-22 precursors with 20 wt%
Mo loading by a wetness impregnation method according to our pre-
vious work [16]. And then, different calcination (450 °C, 550 °C or
650 °C for 5 h) and reduction (500 °C, 600 °C or 700 °C for 4 h in hy-
drogen) temperatures were carried out for optimizing the preparation
conditions of Mo/H-ZSM-22 bi-functional catalysts to achieve the
higher selectivity of iso-alkanes with complete deoxygenation of pal-
mitic acid. A series of Mo/H-ZSM-22-n bi-functional catalysts were
named as Mo/HZ-22-450C-500R, Mo/HZ-22-650C-500R, Mo/HZ-22-
550C-600R and Mo/HZ-22-550C-700R based upon calcination and re-
duction temperatures, respectively. It’s worth noting that Mo/HZ-22-
550C-500R bi-functional catalyst was calcined at 550 °C for 5 h and
reduced at 500 °C for 4 h, as the same sample as in previous work [16].
2.2. Characterization
XRD patterns of Mo/H-ZSM-22 bi-functional catalysts in the 2θ
range of 5° to 80° were characterized by D/MAX-III X-ray diffractometer
(Rigaku Corporation, Japan) equipped with a Cu Kα radiation source
working at 35 kV and 35 mA. The morphology of these catalysts was
obtained using on a FEI Quanta scanning electron microscope (SEM)
and transmission electron microscopy (TEM). The surface areas and
pore volumes of these catalysts were obtained according to nitrogen
Fig. 1. XRD patterns of parent zeolite H-ZSM-22 (a) and Mo/H-ZSM-22 (b: Mo/
HZ-22-450C-500R; c: Mo/HZ-22-550C-500R; d: Mo/HZ-22-650C-500R; e: Mo/
HZ-22-550C-600R; f: Mo/HZ-22-550C-700R) bi-functional catalysts.
2

J. Zhang, et al.
AppliedCatalysisA,General608(2020)117847
Table 2
Textural properties of Mo/H-ZSM-22 bi-functional catalysts.
Samples
SiO2/ Al2O3
Mo (wt %)
SBET (m2/g)
Smicro (m2/g)
Sext (m2/g)
Vmicro (cm3/g)
Vtotal (cm3/g)
The ratios of Weak/Medium strong sites
HZ-22
75
75
75
75
75
75
–
204
44
54
25
50
52
161
12
21
5
43
33
33
20
42
44
0.080
0.005
0.009
0.002
0.003
0.003
0.31
0.12
0.24
0.06
0.13
0.17
0.27
3.17
0.82
2.57
0.77
0.96
Mo/HZ-22-450C-500R
Mo/HZ-22-550C-500R
Mo/HZ-22-650C-500R
Mo/HZ-22-550C-600R
Mo/HZ-22-550C-700R
19.8
20.3
22.4
21.2
21.6
8
8
high calcination and reduction temperature. Characteristic diffraction
peaks of MoO2 phase were observed at 2θ = 36.8° and 53.3° over Mo/
HZ-22-450C-500R, Mo/HZ-22-550C-500R and Mo/HZ-22-650C-500R
[16], indicating that reduction procedure at 500 °C allowed to obtain
the desired Mo4+ species. Additionally, Mo° species of 2θ = 40.6° were
obviously observed over Mo/HZ-22-550C-600R and Mo/HZ-22-550C-
700R catalysts, which disclosed that Mo4+ was further reduced to Mo°
at reduction temperature of 600 °C and 700 °C for 4 h. The intensity of
Mo° diffraction peak increased with the rising of reduction temperature,
while the diffraction peak intensities of HZ-22 zeolite of Mo/HZ-22
catalysts were opposite. That is, high reduction temperature could
improve more Mo° formation; on the contrary, too high reduction
temperature destructed the structure of parent zeolite support resulting
in low relative crystallinity.
Clearly, there was no any significant particles over calcinated Mo/HZ-
22 catalysts (a: Mo/HZ-22-450C, b: Mo/HZ-22-550C; c: Mo/HZ-22-
650C) according to SEM images, which looked like the smooth noddle-
shape as well as parent zeolite HZ-22 (a and Fig. 2a and Fig. 3a).
Especially, Mo/HZ-22-650C seemed to be out of parent zeolite HZ-22
shape to some extent caused by the destruction of structure at too high
calcination temperature (650 °C). Based upon TEM analysis in Fig. 4d,
no obvious particles of MoO3 species were observed over Mo/HZ-22-
550C bi-functional catalyst before reduction, which was in accordance
with our previous work [16]. Based upon the TEM-EDS analysis, it has
been proven directly the presence of Mo contents over Mo/HZ-22-550C
in Fig. 4e, which seemed to be much lower (area 1: 11.3 wt%; area 2:
8.1 wt%; area 3: 10.6 wt%) than XRF analysis (20.3 wt% Mo). This
phenomenon may be caused by the sublimation of MoO3 owing to high
energy spotting in TEM-EDS conditions and/or at high calcination
temperature [16,31–33], while it could be seen clearly the particles of
reduced MoOx species over HZ-22 supports for Mo/HZ-22 bi-functional
catalysts (Fig. 2 and Fig. 3).
The main textural properties of HZ-22 and Mo/HZ-22 bi-functional
catalysts are summarized in Table 2 based upon BET and XRF analysis.
There were identical ratios of SiO2/Al2O3 (75) and similar Mo loading
(19.8 wt% for Mo/HZ-22-450C-500R, 20.3 wt% for Mo/HZ-22-550C-
500R, 22.4 wt% for Mo/HZ-22-650C-500R, 21.2 wt% for Mo/HZ-22-
550C-600R, and 21.6 wt% for Mo/HZ-22-550C-700R). The surface area
and volume of all Mo/HZ-22 bi-functional catalysts presented much
decrease than parent zeolite HZ-22 in Table 2, due to the obvious pores
blockage by MoOx species. While it is worth noting that the surface area
and volume of Mo/HZ-22-650C-500R was much less than other Mo/HZ-
22 bi-functional catalysts, which was in accordance with XRD analysis
(Fig. 1d) based upon the serious destruction of parent zeolite. Too high
calcination (650 °C) temperature may cause the obvious destruction of
parent zeolites during preparation of Mo/HZ-22 bi-functional catalysts.
Compared to calcination temperatures, reduction temperatures even at
600 °C and 700 °C showed less influence on the structure of Mo/HZ-22
catalysts owing to the protection of structure in hydrogen atmosphere
to some extent (Table 2).
Additionally, the reduction temperature (500 °C, 600 °C and 700 °C)
effects on Mo/HZ-22 preparation were investigated as shown in Fig. 2
and Fig. 3. Compared to Mo/HZ-22-550C-500R (c and Fig. 2c and
Fig. 3c), more reduced MoOx species were significantly observed over
Mo/HZ-22-550C-600R (e and Fig. 2e and Fig.3e) and Mo/HZ-22-550C-
700R (f and Fig. 2f and Fig. 3f). The higher reduction temperature re-
sulted in the more MoO2 and Mo species obtained over HZ-22 parent
zeolite. While too high reduction temperatures (700 °C) probably led to
the obvious destruction of HZ-22 parent zeolite, like the case of Mo/HZ-
22-650C-500R at high calcination temperature. Mo/HZ-22-550C-700R
also exhibited shorter and broader noodle-like shapes, compared to
parent zeolite HZ-22 (a and Fig. 2a and 3a). Importantly, reduced MoOx
species particles over HZ-22 supports were regular shape and uniform
distribution based upon SEM and TEM analysis, and the particle size
distributions was summarized in Fig.3, suggesting that reduced MoOx
species size of all catalysts centered at about 5−10 nm. For Mo/HZ-22-
650C-500R, reduced MoOx species particles were slightly larger than
other catalysts, which may be due to higher calcination temperature
leading to serious destruction of parent zeolite. The diameters of these
MoOx species were more than 20 times as comparison of parent zeolite
HZ-22 channels. Thus, some of reduced MoOx species were exposed on
the external surface of HZ-22, as well as some lied in channels, resulting
in blocking the pores, as shown in Table 2 by BET analysis. Such uni-
form dispersion of reduced MoOx species over HZ-22 supports also il-
lustrated the sublimation of MoO3 via the gas-phase diffusion during
the process of catalysts preparation, compared to liquid-phase via the
wet impregnation method. According to the above analysis, too high
calcination and reduction temperatures usually led to the obvious de-
struction of zeolite supports with out of noodle-like shapes. Therefore,
it could predict that Mo/HZ-22-550C-600R bi-functional catalyst would
be one of the best candidates for upgrading palmitic acid to produce
more iso-alkanes without loss of carbon numbers, and the catalytic
performance would be discussed in detailed in next section.
3.2. Morphology of Mo/HZ-22 bi-functional catalysts
The influence of calcination temperature (450 °C, 550 °C and 650 °C)
on the morphology of Mo/HZ-22-n-500R (n = 450C/550C/650C) was
performed over SEM and TEM analysis in Fig. 2 and Fig. 3. It could be
seen that Mo/HZ-22-450C-500R and Mo/HZ-22-550C-500R had similar
noodle-like shape with HZ-22, which disclosed that 450 °C and 550 °C
calcination did not change the shape of parent zeolites. There were
many reduced MoOx species over the external surface of HZ-22, which
was not like parent zeolite HZ-22 with smooth shape. The noodle-like
shape of Mo/HZ-22-450C-500R and Mo/HZ-22-550C-500R seemed
shorter than parent zeolite HZ-22. However, much shorter and broader
noodle-like shapes were observed over Mo/HZ-22-650C-500Rd and
(Fig. 2d and Fig. 3d) than those over Mo/HZ-22-450C-500R and Mo/
HZ-22-550C-500R, which may be due to the obvious destruction of
parent zeolite at too high calcination temperature (650 °C). SEM and
TEM images were in accordance with XRD (Fig. 1) and BET results
(Table 2), which suggested that calcination temperature at 550 °C
would be one of appropriate candidates for Mo/HZ-22 bi-functional
catalysts.
3.3. Active centers analysis
SEM, TEM and TEM-EDS analysis of Mo/HZ-22 calcinated at
450 °C/550 °C/ 650 °C for 5 h were carried out as shown in Fig. 4.
The acidic properties of HZ-22 and Mo/HZ-22 bi-functional
3

J. Zhang, et al.
AppliedCatalysisA,General608(2020)117847
Fig. 2. SEM images of parent zeolite H-ZSM-22 (HZ-22) and Mo/H-ZSM-22 (a: Mo/HZ-22-450C-500R; b: Mo/HZ-22-550C-500R; c: Mo/HZ-22-650C-500R; d: Mo/
HZ-22-550C-600R; e: Mo/HZ-22-550C-700R) bi-functional catalysts.
catalysts were detected by NH3-TPD, as shown in Fig. 5 and Table 2.
Firstly, HZ-22 exhibited a large number of medium strong acid sites
around 380 °C and a small number of weak acid sites around 200 °C.
Compared with parent zeolite HZ-22, the weak acidic sites increased
significantly over all Mo/HZ-22 bi-functional catalysts, and the weak
acid strength became stronger around at 230 °C. This result may be the
contribution of MoOx species in the global acidity, like the cases of
reported literatures [34–36]. Secondly, medium strong acid sites of Mo/
HZ-22 bi-functional catalysts seem to be determined by the various
calcination and reduction temperatures. As for Mo/HZ-22-450C-500R,
medium acid sites were covered by MoOx species due to blockage ef-
fects of pore windows at 450 °C (low calcination temperature) to some
extent. Mo/HZ-22-550C-500R, Mo/HZ-22-550C-600R and Mo/HZ-22-
550C-700R catalysts showed similar acidity, in whose acid sites were
slightly more than HZ-22, as well as even medium strong acid sites.
High reduction temperature of Mo6+ into Mo4+ and Mo° was beneficial
for the acidity presentation. However, Mo/HZ-22-650C-500R gave
much poorer medium strong acid sites than other Mo/HZ-22 bi-func-
tional catalysts, which was related to the obvious destruction of parent
zeolite after high calcination temperature (650 °C: Fig. 1d, Fig. 2d and
Fig. 3d). Additionally, the ratios of medium strong acid to weak acid
were as followed: 0.32 for Mo/HZ-22-450C-500R, 1.22 for Mo/HZ-22-
550C-500R, 0.38 for Mo/HZ-22-650C-500R, 1.29 for Mo/HZ-22-550C-
600R, 1.03 for Mo/HZ-22-550C-700R, in comparison with 3.67 for HZ-
22. It could be clearly seen that Mo/HZ-22-550C-500R, Mo/HZ-22-
550C-600R and Mo/HZ-22-550C-700R retained more medium strong
4

J. Zhang, et al.
AppliedCatalysisA,General608(2020)117847
Fig. 3. TEM images of parent zeolite H-ZSM-22 (HZ-22) and Mo/H-ZSM-22 (a: Mo/HZ-22-450C-500R; b: Mo/HZ-22-550C-500R; c: Mo/HZ-22-650C-500R; d: Mo/
HZ-22-550C-600R; e: Mo/HZ-22-550C-700R) bi-functional catalysts.
acid sites than Mo/HZ-22-450C-500R and Mo/HZ-22-650C-500R, in-
dicating that 550 °C was may be appropriate calcination temperature
for preparing Mo/HZ-22 bi-functional catalysts to be beneficial for acid-
catalysis (dehydration and isomerization).
Therefore, Mo/HZ-22 bi-functional catalysts were prepared by appro-
priate calcination (550 °C) and reduction temperatures (500 °C and
600 °C) according to above characterization results. Reduction tem-
perature at 700 °C was too high to destruct the structure of HZ-22
support.
After high reduction temperatures at 600 °C and 700 °C, acid sites
over Mo/HZ-550C-600R and Mo/HZ-550C-700R bi-functional catalysts
could recover and even increase obviously. One is that high tempera-
tures (600 °C and 700 °C) in H2 atmosphere improved the reduction of
Mo6+ to Mo4+ and Mo°, which may be beneficial for the recovery of
acid sites; the other is the contribution of MoOx species in total acidity
based upon literatures [34–36]. The morphology, porosity and acidity
of Mo/HZ-22-550C-600R were similar with Mo/HZ-22-550C-500R,
while diffraction intensities of these two catalysts decreased obviously.
Based on H2-TPR results in Fig. 6, the broad peak was observed
around at 573 °C for Mo/HZ-22-450C precursor, 620 °C for Mo/HZ-22-
550C precursor and 660 °C for Mo/HZ-22-650C precursor, respectively,
which was assigned to the reduction of Mo6+ to Mo4+. Clearly, the
higher calcination temperature of Mo/HZ-22 bi-functional catalysts
usually led to more MoOx into HZ-22 pores/channels, and then resulted
in the higher reduction temperature of Mo6+ to Mo4+. The high cal-
cination temperature of preparation catalysts facilitated the
5

J. Zhang, et al.
AppliedCatalysisA,General608(2020)117847
Fig. 4. SEM (a: Mo/HZ-22-450C; b: Mo/HZ-22-550C; c: Mo/HZ-22-650C), TEM (d: Mo/HZ-22-550C) and TEM-EDS (e: Mo/HZ-22-550C) analysis of Mo/H-ZSM-22
after calcination.
sublimation of MoO3 to allow more MoO3 gas-phase into HZ-22 pores/
channels, which also increased the difficulty reduction of MoO3 re-
duction. As for Mo/HZ-22-650C precursor, hydrogen adsorption peak at
Additionally, there was a small peak at 160 °C for Mo/HZ-22-450C
precursor, which was probably contributed to the adsorbed hydrogen of
partial MoOx exposed over HZ-22 external surface at low calcination
temperature (450 °C).
720 °C was ascribed to the reduction of Mo4+
→ Mo° [18].
6

J. Zhang, et al.
AppliedCatalysisA,General608(2020)117847
with XRD and H2-TPR analysis (Fig. 1). High reduction temperature
enhances more Mo4+ and even Mo° formation: Mo°/Mo4+ = 2.34,
Mo°/Mo6+ = 0.56 and Mo4+/Mo6+ = 0.27 for Mo/HZ-22-550C-600R;
Mo°/Mo4+ = 1.45, Mo°/Mo6+ = 0.63 and Mo4+/Mo6+ = 0.49 for
Mo/HZ-22-550C-700R. Too high reduction temperature led to the de-
struction of HZ-22 support with out of noodle-like shape as shown in
Fig. 1, Fig. 2 and Fig. 3. Therefore, 600 °C was considered as the most
appropriate reduction temperature for Mo/H-22-550C compared to
500 °C and 700 °C. It is well known that Mo4+/Mo6+ ratio of Mo/HZ-
22-550C-500R directly influenced HDO/HDC selectivity, and Mo4+ (or
MoO2) was proven to improve HDO without any carbon atom loss [16].
It is anticipated for the better catalytic performance over Mo° and M4+
active centers of Mo/HZ-22-550C-600R catalyst without carbon loss
during the process of palmitic acid conversion.
3.4. Catalytic performance over Mo/HZ-22 bi-functional catalysts
In our previous work [16], it concluded that the stronger acid sites
were, the more iso-alkanes formed was and the less C16 produced was
over Mo/HZ-22-550-500R via HDC route. The acidity of bi-functional
catalysts generally influences the distribution of final products through
dehydration and isomerization of intermediates during palmitic acid
conversion. On the other hand, Mo4+/Mo6+ ratio significantly de-
termined HDO/HDC selectivity over Mo/HZ-22-550-500R bi-functional
catalyst. Mo6+ supported HDC route with one carbon atom loss, while
Mo4+ facilitated HDO route without carbon atom loss. At 260 °C in
presence of 4 MPa H2 for 4 h, palmitic acid could be completely con-
verted to hydrocarbons over Mo/HZ-22-550C-500R [16]. Thus, Mo/HZ-
22 with different calcination and reduction temperatures catalyzed
palmitic acid to hydrocarbons at identical conditions as shown in
Table 4 and Fig. 8, which could seek for the optimal conditions for
preparation of Mo/HZ-22 bi-functional catalyst to achieve the higher
iso-alkanes without loss of carbon numbers. It is worth noting that the
parallel tests of palmitic acid conversion over Mo/HZ-22 bi-functional
catalysts were performed, and the repeatability of data were excellently
stable as shown in Fig. 8. It could be seen that the error bar of mono.iso-
Fig. 5. NH3-TPD curves of parent zeolite H-ZSM-22 (HZ-22) and Mo/H-ZSM-22
(Mo/HZ-22-450C-500R; Mo/HZ-22-550C-500R; Mo/HZ-22-650C-500R; Mo/
HZ-22-550C-600R; Mo/HZ-22-550C-700R) bi-functional catalysts.
C
16 alkanes, multi.iso-C16 alkanes and n-C16 alkanes were all below 5 %.
As for Mo/HZ-22-550C-500R in our previous work, its catalytic
performance (iso-alkanes/n-alkanes = 1.5 and C16/C16-x = 3.1) were
shown in Table 4 (line 2) and Fig. 8b [16]. Compared to Mo/HZ-22-
550C-500R, Mo/HZ-22-450C-500R with lower calcination temperature
could also completely convert palmitic acid to hydrocarbons with 100
% selectivity. While there was less iso-alkanes and C16 alkanes forma-
tion with iso-alkanes/n-alkanes = 1.0 and C16/C16-x = 2.8, which was
ascribed to the less acid sites especially for strong acid sites (Fig. 5 and
Table 2). It is worth noting that calcination temperature at 650 °C was
considered as too high to destruct seriously structure of parent zeolite
HZ-22, thus Mo/HZ-22-650C-500R catalyst was not considered as one
of the candidates to upgrade palmitic acid. Combining the character-
ization and catalytic performance, 550 °C is considered as the appro-
priate calcination temperature for Mo/HZ-22 bi-functional catalysts.
Additionally, Mo/HZ-22-550C-600R and Mo/HZ-22-550C-700R also
converted completely palmitic acid to achieve 100 % selectivity of al-
kanes at identical conditions (Table 4 and Fig. 8). With similar iso-al-
kanes selectivity (Fig. 8c and 8d), much more C16 alkanes were formed
over Mo/HZ-22-550C-600R (C16/C16-x = 8.4) and Mo/HZ-22-550C-
700R (C16/C16-x = 6.8), which directly disclosed that Mo° (Fig. 1 and
Table 3) emerged at higher reduction temperature was apt to enhance
HDO reaction without carbon atom loss. Meanwhile, more MoO3 spe-
cies were reduced over HZ-22, which led to the recovery of more acid
sites (Fig. 5) and further the production of more iso-alkanes.
Fig. 6. H2-TPR curves of Mo/H-ZSM-22 precursors.
The Mo 3d XPS spectra of Mo/HZ-22-n bi-functional catalysts was
depicted in Fig. 7, and it could be seen that the reduction temperature
significantly affected the chemical state of Mo species. The concentra-
tion of MoOx species was also different at different calcination and
reduction temperatures (the XPS analysis of Mo/HZ-22-650C-500R did
not performed due to the obvious destruction of parent zeolite structure
at calcination temperature of 650 °C). According to XPS spectra of Mo/
HZ-22 bi-functional catalysts, Mo°/Mo4+, Mo°/Mo6+ and Mo4+/Mo6+
ratios for Mo/HZ-22-450C-500R, Mo/HZ-22-550C-500R, Mo/HZ-22-
550C-600R and Mo/HZ-22-550C-700R were calculated and listed in
Table 3. The peaks at binding energy (BE) value of 229.0 and 232.6 eV
were assigned to Mo4+, the peaks emerged at 231.7 and 234.9 eV were
attributed to Mo6+, and the peaks centered at 227.5 eV and 231.0 eV
were assigned to metallic Mo. Firstly, increasing calcination tempera-
ture would be helpful the dispersion of MoO3 due to its sublimation,
which might also be further beneficial for the reduction of Mo6+ to
Mo4+ at identical reduction temperature (500 °C), as comparison of
Mo/HZ-22-450C-500R (Mo4+/Mo6+ = 0.30) with Mo/HZ-22-550C-
500R (Mo4+/Mo6+ = 0.58). Secondly, Mo° species (227.5 eV and
231.0 eV) was detected for Mo/HZ-22-550C-600R and Mo/HZ-22-
550C-700R bi-functional catalysts [16,37,38], which was in accordance
The similar level of conversion (85.6 % over Mo/HZ-22-550C-500R
for 150 min, 83.7 % over Mo/HZ-22-550C-600R for 120 min, 84.6 %
over Mo/HZ-22-550C-700R for 120 min) lower than 100 % was ob-
tained as shown in Fig. 9 at 260 °C in presence of 4.0 MPa H2 for dif-
ferent reaction time, which indicated that Mo/HZ-22-550C-600R and
7

J. Zhang, et al.
AppliedCatalysisA,General608(2020)117847
Fig. 7. XPS curves of Mo/H-ZSM-22 (Mo/HZ-22-450C-500R; Mo/HZ-22-550C-500R; Mo/HZ-22-550C-600R; Mo/HZ-22-550C-700R) bi-functional catalysts.
550C-500R with 59.6 % alkanes and 26.0 % iso-alkanes selectivity
(10.2 % n-C15, 5.3 % multi-iso-C16, 20.7 % mono-iso-C16 and 23.4 % n-
Table 3
XPS analysis of Mo/H-ZSM-22 bi-functional catalysts.
C
16), more alkanes and iso-products were obtained over Mo/HZ-22-
Catalysts
Mo0/Mo4+
Mo0/Mo6+
Mo4+/Mo6+
550C-600R (81.1 % and 44.4 %) and Mo/HZ-22-550C-700R (85.7 %
and 40.8 %), which was ascribed to more amounts of acid sites over
Mo/HZ-22 after higher reduction temperature. According to iso-alkanes
especially for multi-iso-C16 selectivity, it could be seen that Mo/HZ-22-
550C-600R presented the best isomerization activity among these three
Mo/HZ-22 bi-functional catalysts. In all, Mo/HZ-22-550C-600R catalyst
exhibited the best catalytic performance during palmitic acid conver-
sion among Mo/HZ-22 bi-functional catalysts.
Mo/HZ-22-450C-500R
Mo/HZ-22-550C-500R
Mo/HZ-22-550C-600R
Mo/HZ-22-550C-700R
–
–
0.30
0.58
0.27
0.49
–
–
2.34
1.45
0.56
0.63
Mo/HZ-22-550C-700R exhibited higher hydrogenation activity than
Mo/HZ-22-550C-500R based upon shorter reaction time. C15−CHO
and C15−CH2−OH selectivity were 29.1 % and 11.3 % over Mo/HZ-
550C-500R, 15.2 % and 3.7 % over Mo/HZ-22-550C-600R, 12.2 % and
2.1 % over Mo/HZ-22-550C-700R, also disclosing the hydrogenation
activity increased in order: Mo/HZ-22-550C-500R < Mo/HZ-22-550C-
600R < Mo/HZ-22-550C-700R. That is, Mo° and Mo4+ especially for
Mo° possessed high hydrogenation activity. Compared to Mo/HZ-22-
Based upon above results, the possible reaction pathway was pro-
posed as shown in Scheme 1: (i) hydrodeoxygenation and then iso-
merization for n-C16 and iso-C16 alkanes, (ii) hydrodecarbonylation and
then isomerization for n-C15 and iso-C15 alkanes, (iii) direct cracking
deoxygenation for n-C14 alkane. It could be seen that enhancement in
dehydration and isomerization reactions would decrease the con-
centration of n-alkanes in these consecutive reactions over acid sites,
Table 4
Upgrading of palmitic acid over Mo/H-ZSM-22 bi-functional catalysts reacted for 4 h in presence of 4 MPa H2 at 260 °C.
Catalysts
Conv. (%)
Selectivity (mol/mol%) of each product after reaction
iso-alkanes/n-alkanes (mol/mol)
C16 /C16-x (mol/mol)
alkanes
n-C14
n-C15
multi. iso-C16
mono. iso-C16
n-C16
Mo/HZ-22-450C-500R
Mo/HZ-22-550C-500R
Mo/HZ-22-550C-600R
Mo/HZ-22-550C-700R
> 99.9
> 99.9
> 99.9
> 99.9
100
100
100
100
1.5
0.9
3.2
4.4
24.8
23.6
7.5
9.4
41.7
44.1
31.4
28.5
22.6
15.8
27.6
25.7
1.0
1.5
1.7
1.6
2.8
3.1
8.4
6.8
15.6
30.3
32.9
8.5
8

J. Zhang, et al.
AppliedCatalysisA,General608(2020)117847
which could motivate hydrogenation forward. Moreover, enhancement
in hydrogenation lead to increasing the concentration of
C
15−CH2−OH over Mo4+ and/or Mo° active centers, which would
drive the dehydration and isomerization reactions moving to produce
the more iso-alkanes. That is, the interaction between metal active
centers and acid sites and their influence on the overall reaction over
Mo/H-ZSM-22 bi-functional catalysts during upgrading of palmitic
acid. It is a pity that too high reduction temperature (700 °C) resulted in
some destruction and out of noodle-like shape for Mo/HZ-22-550C-
700R (Fig. 2f and 3ff and f). Mo/HZ-22-550C-600R bi-functional cat-
alyst presented the outstandingly catalytic performance, which ob-
tained about 61.7 % iso-alkanes selectivity and 89.3 % selectivity of C16
alkanes during complete deoxygenation of palmitic acid.
4. Conclusions
Different calcination and reduction temperatures were selected to
optimize the conditions for preparing Mo/H-ZSM-22 bi-functional cat-
alysts, which would apply in upgrading palmitic acid to iso-alkanes with
minimizing loss of carbon numbers. Parent zeolite support was ser-
iously destructed after too high calcination and/or reduction tempera-
tures. Reduced MoOx species with well dispersion of 5−10 nm over H-
ZSM-22, were successfully prepared at 550 °C calcination and 600 °C
reduction. After reduction at 500 °C, only Mo4+ centers were observed;
while Mo° was detected over Mo/H-ZSM-22 with high reduction tem-
peratures (600 °C and 700 °C). Importantly, more n-C16 alkanes were
obtained over Mo/H-ZSM-22 bi-functional catalysts via 550 °C calci-
nation and 600 °C reduction, which may be caused by Mo° species ex-
hibited higher hydrodeoxygenation (HDO) activity than Mo4+ centers.
Furthermore, the selectivity of iso-alkanes was reached up to 61.7 %.
Mo/H-ZSM-22 bi-functional catalysts could achieve simultaneously
deoxygenation and isomerization during upgrading of palmitic acid to
jet fuel ranges iso-/n- alkanes with less carbon loss, which may be afford
new strategy to design bi-functional catalysts for conversion of micro-
algae-based bio-oil to jet fuel in future.
Fig. 8. Selectivity of C16 alkanes over different Mo/H-ZSM-22 (a: Mo/HZ-22-
450C-500R; b: Mo/HZ-22-550C-500R; c: Mo/HZ-22-550C-600R; d: Mo/HZ-22-
550C-700R) bi-functional catalysts (General conditions: 50 mL n-decane, 0.5 g
palmitic acid, 0.1 g Mo/HZ-22-n catalysts, 4 MPa H2, stirring at 300 rpm).
CRediT authorship contribution statement
Jimei Zhang: Investigation, Software, Writing - original draft.
Yanchun Shi: Writing - review & editing, Visualization. Hongbin Cao:
Resources. Yulong Wu: Validation, Methodology, Conceptualization,
Supervision. Mingde Yang: Formal analysis.
Fig. 9. Conversion and selectivity of products over Mo/HZ-22-550C, Mo/HZ-
22-550C-600R and Mo/HZ-22-550C-700R bi-functional catalysts (General
conditions: 50 mL n-decane, 0.5 g palmitic acid, 0.1 g Mo/HZ-22-n catalysts,
4 MPa H2, stirring at 300 rpm).
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to
Scheme 1. Possible reaction pathway over Mo/H-ZSM-22 bi-functional catalysts during palmitic acid conversion.
9

J. Zhang, et al.
AppliedCatalysisA,General608(2020)117847
influence the work reported in this paper.
18 (2016) 4633–4648.
[17] B.X. Peng, Y. Yao, C. Zhao, J.A. Lercher, Angew. Chem. Int. Ed. 51 (2012)
2072–2075.
Acknowledgment
[18] R.R. Ding, Y.L. Wu, Y. Chen, H. Chen, J.L. Wang, Y.C. Shi, M.D. Yang, Catal. Sci.
Technol. 6 (2016) 2065–2076.
[19] C. Zhao, T. Brück, J.A. Lercher, Green Chem. 15 (2013) 1720–1739.
[20] R. Sotelo-Boy, Y. Liu, T. Minowa, Ind. Eng. Chem. Res. 50 (2011) 2791–2799.
[21] I. Simakova, O. Simakova, P. Maki-Arvela, A. Simakov, M. Estrada, D.Y. Murzin,
Appl. Catal. A. Gen. 355 (2009) 100–108.
The authors are grateful for the financial supports National Science
Foundation of China (No. 21838006, No. 21776159 and No.
21576155).
[22] M. Snare, I. Kubickova, P. Maki-Arvela, K. Eranen, D.Y. Murzin, Ind. Eng. Chem.
Res. 45 (2006) 5708–5715.
References
[23] M.F. Wagenhofer, E. Barath, O.Y. Gutierrez, J.A. Lercher, ACS Catal. 7 (2017)
1068–1076.
[24] H. J. Robota, J. C. Alger, U. S. Patent, 9012710 B2, 2015.
[25] G. Knothe, R.O. Dunn, J. Am. Oil Chem. Soc. 86 (2009) 843–856.
[26] M. Krár, T. Kasza, S. Kovács, D. Kalló, J. Hancsók, Fuel Process. Technol. 92 (2011)
886–892.
[1] J. Cheng, T. Li, R. Huang, J.H. Zhou, K.F. Cen, Bioresour. Technol. Rep. 158 (2014)
378–382.
[2] C.Y. Yang, R.F. Nie, J. Fu, Z.Y. Hou, X.Y. Lu, Bioresour. Technol. Rep. 146 (2013)
569–573.
[27] D.R. Wang, B. Ma, B. Wang, C. Zhao, P. Wu, Chem. Commun. 51 (2015)
15102–15105.
[3] B. Ma, J.J. Zhang, H.M. Cui, M.Y. He, C. Zhao, Sci. China Chem. 4 (2015) 350–360.
[4] X.H. Zhang, T.J. Wang, L.L. Ma, Q. Zhang, T. Jiang, Bioresour. Technol. Rep. 127
(2013) 306–311.
[28] B. Ma, C. Zhao, Green Chem. 17 (2015) 1692–1701.
[29] W.J. Song, C. Zhao, J.A. Lercher, Chem. Eur. J. 19 (2013) 9833–9842.
[30] Y.H. Liu, L. Yao, H. Xin, G.S. Wang, D. Li, C.W. Hu, Appl. Catal. B: Environ. 174-175
(2015) 504–514.
[5] B. Ma, J.B. Hu, Y.M. Wang, C. Zhao, Green Chem. 17 (2015) 4610–4617.
[6] W.J. Song, Y.S. Liu, E. Barath, C. Zhao, J.A. Lercher, Green Chem. 17 (2015)
1204–1218.
[31] M. Ferroni, V. Guidi, E. Comini, G. Sberveglieri, A. Vomiero, G. Della Mea,
G. Martineli, J. Vac, Sci. Technol. B 21 (2003) 1442–1448.
[32] R.K. Sharma, G.B. Reddy, J. Appl. Phys. 114 (2013) 184310.
[33] N. Floquet, O. Bertrand, J.J. Heizmann, Oxid. Met. 37 (1992) 253–279.
[34] J.A. Botas, D.P. Serrano, A. García, J. de Vicente, R. Ramos, Catal. Today 195
(2012) 59–70.
[7] C. Zhao, J.A. Lercher, Angew. Chem. 51 (2012) 6037–6042.
[8] S.P. Zou, Y.L. Wu, M.D. Yang, C. Li, J.M. Tong, Energy Environ. Sci. 3 (2010)
1073–1078.
[9] C. Miao, O. Marin-Flores, S.D. Davidson, T.T. Li, T. Dong, D.F. Gao, Y. Wang,
M. Garcia-Perez, S.L. Chen, Fuel 166 (2016) 302–308.
[10] B. Yoosuk, P. Sanggam, S. Wiengket, P. Prasassarakich, Renew. Energy 139 (2019)
1391–1399.
[35] E. Mannei, F. Ayari, M. Mhamdi, M. Almohalla, A. Guerrero Ruiz, G. Delahay,
A. Ghorbel, Microporous Mesoporous Mater. 219 (2016) 77–86.
[36] F.G. Denardin, O.W. Perez-Lopez, Microporous Mesoporous Mater. 295 (2020)
109961.
[11] I. Hachemi, N. Kumar, P. Maki-Arvela, J. Roine, M. Peurla, J. Hemming, J. Salonen,
D.Y. Murzin, J. Catal. 347 (2017) 205–221.
[12] M. Peroni, G. Mancino, E. Barath, O.Y. Gutierrez, J.A. Lercher, Appl. Catal. B.
Environ. 180 (2016) 301–311.
[37] B. Brox, I. Olefjord, Surf. Interface Anal. 13 (1988) 3–6.
[38] D. Valencia, L. Diaz-Garcia, L.F. Ramirez-Verduzco, A. Qamar, A. Moewes,
J. Aburto, RSC Adv. 9 (2019) 18292–18301.
[13] H. Xin, W.J. Zhou, K.Y. Zhou, X.Z. Du, D. Li, C.W. Hu, Catal. Today 319 (2019)
182–190.
[39] W. X. Fang, X.T. Shu, Y. B. Luo, China, 103058214A, 2013.
[40] W.J. Song, Y.S. Liu, E. Barath, C. Zhao, J.A. Lercher, Green Chem. 17 (2015)
1204–1218.
[14] H. Xin, K. Guo, D. Li, H. Yang, C.W. Hu, Appl. Catal. B: Environ. 187 (2016)
375–385.
[15] B.X. Peng, X.G. Yuan, C. Zhao, J.A. Lercher, J. Am. Chem. Soc. 134 (2012)
9400–9405.
[41] A. Kumar, A. Kumar, B. Biswas, J. Kumar, S.R. Yenumala, T. Bhaskar, Renew.
Energy 151 (2020) 687–697.
[16] Y.C. Shi, Y.Y. Cao, Y.N. Duan, H. Chen, Y. Chen, M.D. Yang, Y.L. Wu, Green Chem.
10