Insight into forced hydrogen re-arrangement and altered reaction pathways in a protocol for CO2 catalytic processing of oleic acid into C8-C15 alkanes

Article abstract of DOI:10.1039/c7gc01853c

A new vision of using carbon dioxide (CO₂) catalytic processing of oleic acid into C₈-C₁₅ alkanes over a nano-nickel/zeolite catalyst is reported in this paper. The inherent and essential reasons which make this achievable are clearly resolved by using totally new catalytic reaction pathways of oleic acid transformation in a CO₂ atmosphere. The yield of C₈-C₁₅ ingredients reaches 73.10 mol% in a CO₂ atmosphere, which is much higher than the 49.67 mol% yield obtained in a hydrogen (H₂) atmosphere. In the absence of an external H₂ source, products which are similar to aviation fuel are generated where aromatization of propene (C₃H₆) oxidative dehydrogenation (ODH) involving CO₂ and propane (C₃H₈) and hydrogen transfer reactions are found to account for hydrogen liberation in oleic acid and achieve its re-arrangement in the final alkane products. The reaction pathway in the CO₂ atmosphere is significantly different from that in the H₂ atmosphere, as shown by the presence of 8-heptadecene, γ-stearolactone, and 3-heptadecene as reaction intermediates, as well as a CO formation pathway. Because of the highly dispersed Ni metal center on the zeolite support, H₂ spillover is observed in the H₂ atmosphere, which inhibits the production of short-chain alkanes and reveals the inherent disadvantage of using H₂. The CO₂ processing of oleic acid described in this paper will significantly contribute to future CO₂ utilization chemistry and provide an economical and promising approach for the production of sustainable alkane products which are similar to aviation fuel.

Full text of DOI:10.1039/c7gc01853c

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Page 1 of 28
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Insight into forced hydrogen reꢀarrangement and altered reaction
pathways in a protocol for CO catalytic processing of oleic acid into
2
C ꢀC alkanes
8
15
a,b,c,d
a,b,d,e*
a,b,d
a,b,d
a,b,d,e
Shiyou Xing
, Pengmei Lv
, Haoran Yuan , Lingmei Yang , Zhongming Wang
,
a,b,d,e*
a,b,d
Zhenhong Yuan
, Yong Chen
a
Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, China
b
Key Laboratory of Renewable Energy, Chinese Academy of Sciences, Guangzhou 510640, China
c
University of Chinese Academy of Sciences, Beijing 100049, China
d
Guangdong Province Key Laboratory of New and Renewable Energy Research and Development, Guangzhou
5
10640, China
e
Collaborative Innovation Center of Biomass Energy, Henan Province, Zhengzhou 450002, China
*Corresponding authors
Eꢀmail addresses: lvpm@ms.giec.ac.cn (P. M. Lv), yuanzh@ms.giec.ac.cn (Z. H. Yuan)
Abstract
2 8
A new vision of using CO catalytic processing of oleic acid into C ꢀC15 alkanes over a
nanoꢀNi/zeolite catalyst is put forward. The inherent and essential causes making this achievable
and totally new catalytic reaction pathways of oleic acid transformation in CO atmosphere are
2
resolved clear. The yield of C
8
2
–C15 ingredients reaches 73.10 mol% in CO atmosphere, which is
much higher than the 49.67 mol% yield obtained in H
2
atmosphere. In the absence of an external
H source, aviation fuelꢀlike products are generated where aromatization of C H , oxidative
2
3
6
2 3 8
dehydrogenation involving CO and C H , and hydrogen transfer reactions are determined to
account for hydrogen liberation in oleic acid and achieve its reꢀarrangement in final alkane
products. The reaction pathway in CO atmosphere is significantly different from that in H
2
2
atmosphere, as evidenced by the presence of 8ꢀheptadecene, γꢀstearolactone, and 3ꢀheptadecene
as reaction intermediates, as well as CO formation pathway. Owing to the highly dispersed Ni
2
metal center on the zeolite support, hydrogen spillover is observed in H atmosphere, which
inhibits the production of shortꢀchain alkanes and reveals the inherent disadvantage of H in this
2
2
point. The CO ꢀprocessing of oleic acid described herein will significantly contribute to future
CO utilization chemistry and provide a hydrogenꢀeconomized, promising approach for
2
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sustainable aviation fuelꢀlike alkane production.
2
Keywords: CO ꢀenhanced processing; Oleic acid; Aviation fuel; Hydrogen reꢀarrangement;
NanoꢀNi/zeolite
1
Introduction
Severe global warming caused by the emissions of greenhouse gases from fossil fuel dependent
transportation has strongly urged the finding of alternative fuels that are environmentꢀfriendly,
1
, 2
sustainable, and renewable, such as bioethanol and biodiesel
. Biofuels are mostly used in
blends with traditional fuels because of their lower energy densities, poor oxidative stabilities, and
3
,
4
incompatibility with engines and transportation fuel infrastructure
secondꢀgeneration biofuels, comprising hydrocarbons similar to those found in traditional fuels
may well overcome these aforementioned deficiencies. Such fuels can be synthesized by the
. However, the
5
, 6
,
catalytic conversion of lipids, such as triglycerides and fatty acids found in inedible and waste oils,
through hydrodeoxygenation reactions including dehydration, hydroꢀdecarbonylation, and
7
ꢀ9
decarboxylation
.
Currently, many researches have examined the hydroconversion of lipids and fatty acids for the
production of gasolineꢀlike, keroseneꢀlike, or longꢀchain dieselꢀlike biofuels in the presence of
9
ꢀ12
hydrogen
. A typical catalytic hydrodeoxygenation process for fatty acids is consisted of
multiple liquid and gasꢀphase reactions, where hydrogen acts as a reactant for hydroꢀsaturation (eq.
1
3
1
), dehydration (eq. 2), or decarbonylation (eq. 3) .
Liquidꢀphase reactions:
R′ − COOH + H → R − ꢁꢂꢂꢃ
(eq. 1)
(eq. 2)
(eq. 3)
(eq. 4)
(eq. 5)
ꢀ
R − COOH + 3H → ꢄ − ꢁꢃ + 2ꢃ ꢂ
ꢀ
ꢅ
ꢀ
R − COOH + H → ꢄ − ꢃ + ꢁꢂ + ꢃ ꢂ
ꢀ
ꢀ
R − COOH → ꢄ − ꢃ + ꢁꢂꢀ
R − COOH → ꢄ′ − ꢃ + ꢁꢂ + ꢃ ꢂ
ꢀ
ꢄ − ꢆꢇꢈꢉꢊꢇꢈꢋꢌꢍꢇꢎꢏꢐꢎꢍꢑꢊꢒꢉꢓ, ꢄ’ − ꢉꢔꢆꢇꢈꢉꢊꢇꢈꢋꢌꢍꢇꢎꢏꢐꢎꢍꢑꢊꢒꢉꢓ
Gasꢀphase reactions:
ꢁ
ꢂ + 4ꢃ ↔ ꢁꢃ + 2ꢃ ꢂ
(eq. 6)
ꢀ
ꢀ
ꢕ
ꢀ
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ꢁ
ꢂ + 3ꢃ ↔ ꢁꢃ + ꢃ ꢂ
(eq. 7)
(eq. 8)
ꢀ
ꢕ
ꢀ
ꢁ
ꢂ + ꢃ ꢂ ↔ ꢃ + ꢁꢂ
ꢀ
ꢀ
ꢀ
Consequently, large amounts of hydrogen are consumed when it is employed as a substrate in this
14, 15
process, which typically occurs at high pressures (~ 40 bar) and ambient temperature
high H pressures require the use of costly specialized equipment, and more importantly, such
processes are associated with safety concerns in terms of hydrogen recycling in scaledꢀup
. The
2
1
6
manufacturing plants . For this reason, impressive methods are developed to efficiently
deoxygenate lipids at low H pressure or in the absence of hydrogen altogether. To this end, the
2
17ꢀ19
20, 21
method of employing hydrogenꢀsource donors such as formic acids
, tetralin
, cyclohexane
22
23
,
and limonene has attracted increasing attentions in recent years because it can well simplify
the highꢀpressured equipment. However, the problems encountered by hydrogenꢀsubstitutes are
that they should be (1) widely application, easily availability, and inexpensive; (2) compatible
with biofuels after hydroprocessing; and (3) wellꢀbehaved in terms of side reactions involving the
donors.
In addition to employing hydrogen donors, the method of deoxygenating lipids and fatty acids
2
4
25
26
in the absence of hydrogen, mostly in inert atmospheres such as N
2
, He , or Ar , has also
attracted extensive interests. In the absence of hydrogen, the lipid or fatty acid carboxyl groups
can be directly removed by thermal decarboxylation (eq. 4) and decarbonylation (eq. 5), but such
27
methods usually require a high reaction temperature . However, these carboxyl groups could be
easily removed by coꢀfeeding a catalyst loaded with both noble metals (i.e., Pt, Pd, Ru, Ir, and Rh)
28ꢀ32
24
and nonꢀnoble metals (e.g., Ni) at lower temperatures
. For instance, Li et al. used different
metal acetate salts to deoxygenate stearic acid in the absence of H
2
. By using an inert gas
atmosphere, a new alkane formation pathway that occurs via an anhydride intermediate
decarbonylation was found. Notably, altering the reaction atmosphere during catalytic
deoxygenation of oxygenꢀcontaining substrates could considerably change the reaction pathways
and product distributions.
The utilization of greenhouse gas CO
2
has been an onꢀgoing worldwide objective. Several
typical applications of CO have been investigated involving its use as a weak oxidant or an
2
3
3, 34
oxidative dehydrogenation agent
. Till now, few studies reported the deoxygenation of oleic
35
acid in CO atmosphere, which employed the catalysts of hydrotalcites , Pt/SAPOꢀ11 and
2
3
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3
6
Pt/chloride Al O , etc. In these few studies, they mainly focused on the formation of oleic acid
2
3
3
7, 38
36
decarboxylation products like heptadecane
CO atmosphere, thermal decarboxylation of unsaturated acid is the only route available. The
author observed that large quantities of olefins and diolefins were produced in CO atmosphere,
. Notably, Masoudeh Ahmadi et al. found that in
2
2
which in the meantime contributed to the formation of oligomers and polymers. They also put
forward a hypothesis that the need for double bond hydrogenation is only provided through
hydrogen reꢀdistribution (dehydrogenation of the feed molecules, for example). However, along
with other studies, they did not addressed the role of CO in these catalytic processes, as well as
2
the altered reaction pathways and mechanisms in CO
Therefore, to make this CO catalytic process an approachable and feasible method for renewable
fuels production, it is critical and meaningful to focalize this new reaction systems and unearth the
role of CO acting in this process and the changed reaction pathways.
In this study, we employ HZSMꢀ5ꢀsupported nanoꢀNi metal particles as the catalyst to
deoxygenate oleic acid, the most common ingredient of fatty acids, in both CO and H
atmospheres. Distinct reaction pathways for deoxygenation of oleic acid in CO and H
atmospheres are also fully explored on the basis of reaction intermediates, the C=C bond effect on
catalytic cracking, H spillover, and hydrogen transfer for alkane production. The catalytic roles of
2 2
compared with conventional H atmosphere.
2
2
2
2
2
2
2
nanoꢀNi and the acidic sites of the zeolite are determined through separated experiments using
single Ni, single HZSMꢀ5, and nanoꢀNi/HZSMꢀ5 as catalysts. Most importantly, the cause of the
intrinsic hydrogen reꢀarrangement in oleic acid to generate the resultant liquid products in CO
2
atmosphere with no external H source is resolved.
2
2
2
Materials and methods
.1 Materials
The oleic acid feedstock (technical grade, 90.0) was purchased from SigmaꢀAldrich, Shanghai,
China. Nickel nitrate hexahydrate [Ni(NO ·6H O] (98%, Reagent Plus), citric acid (99%), and
3
)
2
2
absolute ethanol were purchased from the Tianjin Fuchen Chemical Factory. The HZSMꢀ5 support
with a Si/Al ratio of 25 was obtained from Nankai University Catalyst Co., Ltd., China, the
3
9, 40
physical and chemical properties have been provided in our previous researches
.
2 2
Cyclohexane was bought from Aladdin, China. The H and CO reaction gases were 99.999 %
pure. All materials were used as received.
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2
.2 Catalyst preparation and characterization
The catalyst used in the present study was comprised of 10 wt% Ni/HZSMꢀ5 with highly
dispersed nanoꢀNi metal particles. The catalyst was prepared by a facile citric acidꢀassisted
4
1
impregnation method from the literature . A total of 1.455 g Ni (NO
3 2 2
) •6H O and 1.575 g
C
6
H O
8 7
•H O were first dissolved into 50 mL absolute ethanol. Then, 2.655 g HZSMꢀ5 was added
2
to the solution, and the obtained mixture was stirred for 4 h at 60 ℃. After drying at 80 ℃ for 12
h, the precursor was calcinated in an air atmosphere at a rate of 10 °C/min from ambient
temperature to 500 ℃ and left for 5 h. After reduction in H atmosphere at 500 ℃ for 2 h, the
2
final catalyst was obtained. XRD measurements were performed using an X’Pert PRO MPD
diffractometer (PANalytical) operated at 40 kV and 40 mA with Cu Kα (λ = 0.15406 nm) radiation.
Scanning electron microscopy (SEM) was performed on a Hitachi Sꢀ4800 instrument operated at
10 kV. Before the SEM images were obtained, samples were placed under an E1010 ionꢀsputtering
instrument to improve their conductivity. TEM studies were performed on a Hitachi Hꢀ7560
electron microscope with an accelerating voltage of 100 kV. XPS measurements were performed
on a Thermo Scientific ESCALAB 250 Xi Xꢀray phtotoelectron spectrometer.
2
.3 Deoxygenation of oleic acid and product analysis
Oleic acid deoxygenation experiment was conducted in a high pressure autoclave as described
4
0
previously . Approximately 15 g feedstock and 0.7 g catalyst were added into the reactor. After
several charging and discharging cycles to evacuate the reactor of air, the system was filled with
the reaction gas at the desired pressure (i.e., 1 MPa, 2 MPa, 3 MPa, or 4 MPa). After 5 h of
reaction at the specified temperature (i.e., 320 ℃ or 360 ℃) with a mechanical agitator speed of
2
00 rpm, the reactor was immediately removed and cooled by ambient temperature water. The
reactor pressure during the deoxygenation process was recorded by a digital pressure gauge
Model: MDꢀS280, Shanghai, China). The gas product was collected in a gasꢀsampling bag, and
(
the liquid products were sampled after filtration using a 0.22 μm organic membrane. To assure
the experimental data reliable, all the experiments were repeated twice and the data shown in this
paper was an average value of two times.
The gas products (i.e., CH , CO, CO , and C –C hydrocarbons) were quantified using an
4
2
2
6
Agilent 7890A gas chromatograph (GC) equipped with a capillary column (GSꢀGASPRO, 60
m×0.32 m), a thermal conductivity detector (TCD), and a flame ionization detector (FID). All the
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gas distributions were reꢀcalculated by subtracting the used gas. The liquid product compositions
were analyzed using a GCꢀmass spectrometer (GCꢀMS, Agilent 7890Aꢀ5975C) equipped with an
Agilent HPꢀ5MS column (5% phenyl methyl silox, 30 m ×0.25 mm ×0.25 ꢁm). Prior to these tests,
the liquid products were diluted with cyclohexane at a ratio of 1:250. The GCꢀMS test parameters
were as follows: 1 ꢁL of the diluted sample was injected with a split ratio of 1:10 at 280 ℃. The
original column temperature was 60 ℃ and then reached 300 ℃ after 28.67 min at a rate of 10
℃/min. The mass detector was operated in the electronic impact (EI) mode at 70 eV. The ion
source temperature and mass transfer line temperature was set at 280 ℃ and 300 ℃, respectively.
The mass spectra were scanned in the m/z range of 34–400 at 0.2 s intervals. The major chemical
compositions were identified through a mass spectral library (NIST 2014). The FID response was
linear for each component over the concentration ranges used, and the content analysis of the
products was summarized as peak area %, which was subsequently converted into mol%.
3
3
Results and discussion
.1 Liquid products
2
First, we have catalytically processed oleic acid under H atmosphere for comparison. The
liquid product compositions in various reaction atmospheres given by GC/MS are shown in Figure
S1 in Electronic Supplementary Information (ESI). As seen, oleic acid is completely deoxygenated
at both 320 ℃ and 360 ℃. The carbon number distributions of these products at 320 ℃ in CO2
2 8
and H atmospheres are shown in Figure 1. Generally, hydrocarbons C –C15 are the main
components of aviation fuel, whereas hydrocarbons C16–C18 are considered as the diesel
3
9, 42
ingredients
pressure increases. Hydrocarbons C16–C18 and 8ꢀheptadecene are generated in yields of 56.95–
0.54 mol% and 28.79–18.64 mol%, respectively. By comparison, no C –C15 hydrocarbons are
formed in H atmosphere at the pressures investigated in this study. However, as much as 70.46
mol% of 8ꢀheptadecene is produced at 1 MPa of H
. In CO atmosphere, 43.05–59.46 mol% of C –C is formed as the reaction
2
8
1
5
4
8
2
2
pressure, which rapidly decreases to 25.93
35
36
mol% at 4 MPa of H
2
pressure. Hydrotalcites , PtꢀSAPOꢀ11 and Pt/chloride Al
2
O
3
were
reported as the catalysts to decarboxylate oleic acid, which got a over 98% oleic acid conversion.
However, their final products differed a lot with this study, where heptadecane, short chain acids
&
alkanes were obtained. While herein, as Figure 1 shows, a large amount of C
8
ꢀC15 alkanes are
achieved.
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At 360ꢍ℃, the extent of the cracking reactions is elevated (see Figure 1 (c) and (d)). As much as
7.80–73.09 mol% of C –C15 is produced as the CO pressure increases, suggesting a large
production of aviation fuelꢀlike ingredients. By comparison, no more than 49.67 mol% of C
is produced in H atmosphere (detailed information in Table S1 in ESI). Additionally, as much as
7.39 mol% of C16–C18, mostly heptadecane, is formed in 2 MPa H atmosphere. Collectively,
atmosphere enhances the production of aviation fuelꢀlike
6
8
2
8
–C15
2
6
2
these results demonstrate that using CO
2
ingredients.
(
Figure 1)
3
3
.2 Determination of the reaction pathways
.2.1 Different intermediates and initial reaction pathways
A series of experiments with increasing temperature was conducted to determine the initial
reaction pathway for the transformation of oleic acid by means of identifying the transiently
formed reaction intermediates. It is reported that in H atmosphere, oleic acid first undergoes
hydrosaturation to give stearic acid, which then converts into an extremely unstable olealdehyde
2
3
6
by dehydroxylation , as shown in Figure 2. This transient species is then quickly converted into
heptadecane and CO through decarbonylation. Meanwhile, oleic acid could equally undergo direct
decarboxylation to form 8ꢀheptadecene. Apparently, stearic acid is the first key intermediate
40
generated in oleic acid hydroprocessing . Notably, the reaction of oleic acid is completely
different in the presence of CO . As shown in Figure 3, 8ꢀheptadecene and 3ꢀheptadecene, which
2
are initially formed at 260 ℃, are produced in large quantities at 320 ℃. Additionally,
γ ꢀstearolactone (5ꢀtetradecyloxolanꢀ2ꢀone) is generated. These results indicate that
hydrosaturation of oleic acid has no way to proceed in the absence of H
intermediates (i.e., 8ꢀheptadecene, γꢀstearolactone, and 3ꢀheptadecene) are produced in the
presence of CO
2
. Thus, three
2
.
(
Figure 2)
Considering the possible reactions that could occur to oleic acid (Table 1), the corresponding
G of decarboxylation of oleic acid is large and negative, which indicates that decarboxylation
∆
will progress relatively easily since it is quite favorable. Further, dehydroxylation does not occur
in the absence of H . Thus, it is concluded that 8ꢀheptadecene is produced from the direct
decarboxylation of oleic acid.
2
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Additionally, it is clarified that, in H atmosphere, oleic acid first undergoes dehydroxylation
2
reaction to get off hydroxyl group, and then the decarbonylation reaction happens sequentially.
Accordingly, this mechanism would explain the large amount of CO produced in the gaseous
products when oleic acid is processed in H
2
2
atmosphere (see Section 3.2.4). In CO atmosphere,
the above reaction pathways are restricted because of the absence of H
2
. Thus, two pathways to
generate CO are possible: decarbonylation followed by dehydration or vice-versa. However, no
hydrocarbons containing two C=C bonds or one C≡C bond in the liquid products are observed.
Therefore, it is concluded that it is much difficult for decarbonylation to proceed separately if
dehydroxylation does not occur first.
1
3
Table 1 Possible reactions of oleic acid.
Equation ∆G573(kJ/mol) ∆H573(kJ/mol)
RꢀCOOH→RꢀH + CO (g)
RꢀCOOH→R’ꢀH + CO(g) + H O(g)
Reaction
Decarboxylation
Decarbonylation
2
ꢀ83.5
ꢀ17.0
ꢀ67.6
ꢀ86.1
9.2
179.1
48.1
ꢀ115
2
RꢀCOOH + H
Hydrodehydration RꢀCOOH + 3H
Rꢀsaturated alkyl group, R’ꢀunsaturated alkyl group
Figure 3)
2
(g)→RꢀH +CO(g)+H
2
O(g)
2
→RꢀCH + 2H O(g)
3
2
(
Particularly, γꢀstearolactone (5ꢀtetradecyloxolanꢀ2ꢀone) is observed at 280 ℃ and increases
significantly at 320 ℃. This suggests that the zeolite acidic sites possibly catalyze a carbenium
ion transfer reaction involving the intrinsic C=C bond of oleic acid to shift from carbon No. 9 to
No. 15, as illustrated in Figure 4. After this C=C shift, lactonization reaction occurs to give rise of
γꢀstearolactone. This step is followed by the decarboxylation of γꢀstearolactone to generate
3
ꢀheptadecene, which is detected in the liquid products. It is extensively known that carbenium
ions usually form in hydrocarbon’s CꢀC bond, especially in olefin’s C=C bond , which leads to the
formation of cracking products. However, no cracking products in the heating period, as Figure 3
shows herein, demonstrates that carbenium ions are not easy to be formed at C=C bonds sites
before the removal of carboxyl group in oleic acid. This interesting phenomenon could be
explained as: when the acid strength of acid sites on HZSMꢀ5 is not strong enough to get off the
carboxyl group of oleic acid, instead, a carbenium ion is formed in αꢀcarbon of carboxyl group,
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which induces C=C shifting. Thereafter, the lactonization and decarboxylation reactions occur
subsequently. Besides the acid sites, Ni/HZSMꢀ5 also contains plentiful Ni metal centers, which
could catalyze the decarboxylation reaction of oleic acid effectively, as well verified as in Section
3
.3.
(
Figure 4)
3
.2.2 Catalytic cracking: double bond effect on carbenium ion reactivity
It is understood that cracking reactions of longꢀchain alkanes on zeolites follows a carbenium
ion and βꢀscission mechanism. However, the issue of which site the carbenium ion is first
generated on the oleic acid structure remains unclear, though it has been suggested that
43
protonation of unsaturated fatty acids may initiate at the double bond . Inspired by this, stearic
acid was chosen for the catalytic conversion experiments to compare with the results of oleic acid.
(
Figure 5)
Stearic acid shares a similar molecular structure with oleic acid but it does not have a C=C bond.
The results of CO ꢀprocessed experiments on stearic acid (Figure 5) show that the major liquid
2
product is heptadecane at both 320 ℃ and 360 ℃, which occurs via the deoxygenation of oleic
acid. However, relatively few hydrocarbons with <17 carbon atoms are formed. These results
strongly suggest that the catalytic cracking reaction does not proceed efficiently in the absence of
the substrate’s C=C bond. By comparison, substantial cracking products are formed when oleic
acid is the substrate (Table 2). Clearly, the intrinsic C=C bond in oleic acid is crucial to carbenium
ion formation, which promotes cracking. Moreover, hydrocarbons with 8 and 9 carbon atoms are
the major liquid products, suggesting the preferential cracking of 8ꢀheptadecene. Notably, a wide
variety of hydrocarbons with 10–16 carbons are also formed, indicating a migrated behavior of
C=C bond in the carbon chain of 8ꢀheptadecene. However, fewer hydrocarbons with a higher
number of carbon atoms are produced, indicating that the C=C bond does not migrate easily to the
sites close to the end of carbon chain.
Overall, these results demonstrate that the catalytic cracking reaction most likely initiates at the
intrinsic C=C bond where the carbenium ion is first formed and βꢀscission occurs, resulting in the
high yields of C and C hydrocarbons. Additionally, the location of the carbenium ion shifts
8
9
within the 8ꢀheptadecene carbon chain to produce other hydrocarbons.
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Table 2. Molar distribution of C –C products in CO atmosphere at 320 ℃.
8
17
2
Retention
time (min)
Reaction pressure (MPa) / (mol %)
Compounds
Formula
1
2
3
4
Ethylbenzene,
3
.91, 4.02
C
8
H
10
6.6
7.3
8.5
11.3
1
1
2
1
,3ꢀDimethyꢀbenzene
ꢀOctene, 4ꢀOctene,(E)ꢀ,
ꢀOctene
3
.03, 3.07, 3.12
C H
7.3
7.4
9.4
12.5
8
16
ꢀEthylꢀ3ꢀmethylꢀbenzene
5.48
4.35
C H
1.3
1.1
4.4
0.7
2.8
0.4
7.2
1.3
0.8
7.3
41.2
1.1
0.7
4.6
0.9
3.1
0.7
7.5
1.7
0.9
7.7
43.6
1.5
0.7
4.6
1.1
3.4
0.3
7.8
1.6
1.2
7.6
47.7
2.6
1.1
5.5
1.4
4.1
0.4
7.7
2.2
1.0
6.8
56.6
9
12
18
20
cisꢀ4ꢀNonene
Nonane
C H
9
4.39
C H
9
4
ꢀDecene
Decane
ꢀMethylꢀnaphthalene
5.91
C
10
H
20
22
10
24
26
30
32
5.99
C H
10
2
10.71
7.61
C H
11
Undecane
Dodecane
C H
11
9.15
C
12
C
14
C
15
H
H
H
2
,3,5,8ꢀTetramethylꢀdecane
Pentadecane
Total C –C15 hydrocarbons
10.60
13.23
8
1
6.33, 16.45,
16.50, 16.59,
7.11
8
ꢀHeptadecene
C
C
17
17
H
34
29.1
26.6
25.3
18.8
1
Undercylꢀcyclohexane
Heptadecane
18.32
16.68
4.48
H
34
36
6.2
16.7
2.5
6.0
15.8
2.1
5.8
14.6
2.1
5.5
13.2
2.8
C H
17
Cyclohexanone
C H O
6 10
Phenylethyl alcohol
8.02
C H O
0.8
0.5
1.1
0.7
8
10
2ꢀDodecanone
11.95
C
12
H
24
O
0.6
0.8
0.6
0.7
3
.2.3 Hydrogen spillover and its effect on cracking/hydrogenation reaction
It is noteworthy that no cracking occurs at 320 ℃ in H atmosphere though it does at 360 ℃.
By comparison, the cracking extent in CO atmosphere is much higher, as evidenced by the higher
yield of C –C hydrocarbons (see Figure 1). These results demonstrate distinct reaction behaviors
2
2
8
15
in two reaction atmospheres. Hydrogenation catalysts are commonly prepared with loaded metal
4
4ꢀ46
sites, like Pt, Zn, and Pb
, where hydrogen is easily spilled contributing to the mass production
of atomic hydrogen. The spilledꢀover hydrogen then transfers to the acidic sites located at the
47
surface of the HZSMꢀ5 support, leading to effective hydrogenation reactions. Zhang et al.
considered that the spilled over H produced by Pt played an important role in the stabilization of
+
48
an iꢀC
5
intermediate, which contributed to the high isomerization selectivity. Kusakari et al.
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found a low isomerization rate of pentane over zeolite beta in the presence of H or a mixture of
2
2
Pt/SiO and zeolite beta in the presence of helium. The reason for this behavior is an overꢀlow or
overꢀhigh yield of pentene in the absence of spilledꢀover hydrogen to balance the pentene
production. Evidently, hydrogen spillover at metal centers is much in favor of catalytically
hydrogenation reactions.
4
9, 50
A Ni metal center also possesses excellent hydrogen spillover ability
. Herein, the highly
dispersed Ni nanoꢀparticles (see Figure 6(b), the XRD and XPS results are in Figure S2 in ESI) on
catalyst provide many more opportunities for hydrogen splitting. However, in contrast to the
4
7, 48
isomerization results of spilledꢀover hydrogen reported by Zhang and Kusakari
, none of
isomerized alkane derived from 8ꢀheptadecene is observed at 320 ℃, except nꢀheptadecanes in
liquid products. This suggests that 8ꢀheptadecene is easily hydrogenated but difficult to isomerize
or crack because of the availability of atomic hydrogen. In contrast, cracking 8ꢀheptadecene into
hydrocarbons with requisite carbon number for aviation fuel occurs relatively easily in CO
2
atmosphere. In this case, there is no hydrogen spillover effect because of the lack of external
hydrogen. Overall, these results strongly suggest that eliminating hydrogen spillover enhances the
cracking ability of the catalyst’s acidic sites, as illustrated in Figure 7. Notably, in the presence of
2
H , when reaction temperature increases to 360 ℃ 8ꢀheptadecene cracks. However, the cracking
extent is still lower than that in CO atmosphere. This illustrates yet again the restriction of
2
spilledꢀover hydrogen on catalyst cracking ability.
(
(
Figure 6)
Figure 7)
3
.2.4 H
As shown in Table S2, approximately 47 mol% of alkanes is produced in CO
20 ℃. This suggests the production of H which contributes to the formation of alkanes. Hence,
source. It is acknowledged that the typical catalytic cracking
product of long chain alkanes is C . Nevertheless, it is easily to be hydrogenated into C in
the presence of H , which is in accordance with the low C but high C yield in Figure 8.
Interestingly, similar case is found in CO atmosphere. This is justified by the occurrence of
2
source and hydrogen transfer reactions for alkane production
2
atmosphere at
3
2
it is necessary to explore the H
2
H
3 6
3 8
H
2
3
H
6
3 8
H
2
aromatization reaction amongst C
3
H
6
(see Figure S3 in ESI), which produces aromatic
3 8
will hydrogenate C to C H .
hydrocarbons and H simultaneously. In turn, the generated H
2
2
3
H
6
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The above two factors contribute to the low C H but relative high C H yield in CO atmosphere.
3
6
3
8
2
Then it is concluded that in CO
hydrogen and contributes to alkane’s production.
Notably, as shown in Figure 8, a large amount of CO is produced in both H
atmospheres. It has been widely acknowledged that the formation of CO in H atmosphere
originates from decarbonylation reaction. However, as discussed in Section 3.2.1, decarbonylation
does not initially occur in CO atmosphere, nor does it occur easily afterward. It is therefore much
perplexing for the formation of CO with large quantities in CO atmosphere. Experimentally, the
2
atmosphere, aromatization of C
3
H
6
takes place to generate
2
and CO
2
2
2
2
CO
after experiments at 320 ℃ and 360 ℃, respectively, suggesting an CO
reaction. Simultaneously, the yield of C H in CO atmosphere is much lower than that in H
2
pressure , with an initial value of 4 MPa, shows a decrease of 11.6 % and 20.9 % before and
2
consumption in the
3
8
2
2
8
2
(
Figure 8). Therefore, it is very likely that an oxidative dehydrogenation (ODH) reaction of C
occurs with CO as follows: C + 3CO → 6CO + 4H , which consumes both C and CO
and generates amounts of both H and CO.
The ODH reaction of C with CO has been reported to be catalyzed by CrꢀMSUꢀx , WO
3
H
2
H
3 8
2
2
3 8
H
2
51
H
3 8
2
x
–
5
2
53
VO
x
/SiO
2
, and Au . However, the reaction has not been catalyzed by nanoꢀNi/HZSMꢀ5 before,
the catalyst investigated in this study. Accordingly, nanoꢀNi/HZSMꢀ5 was used to catalyze the
ODH reaction. As evidenced by the presence of CO and H (see Figure 8(e)), the reaction
2
proceeds favorably. Further, C
the methanation reaction between the generated CO and H
remains to be further explored since the complicated nature of ODH reactions making this
3 8
conversion process still unclear. Nevertheless, it can be concluded that H generated from C H
H
2 6
and CH
4
4
are also generated. The formation of CH results from
2
(eq. 7). The occurrence of C
2 6
H
2
via the ODH reactions during the conversion of oleic acids contributes to the hydrogenation of
cracked olefins into alkanes.
(
Figure 8)
Over 45 mol% alkanes are produced at 320 ℃ in CO
2
atmosphere when there is no external H
2
source. As shown in Table 3, when reaction temperature increases to 360 ℃, almost all of the
liquid products are converted into alkanes with 8–17 carbon atoms, with a small amount of
8
ꢀheptadecene and no shortꢀchain olefins. To examine this more fully, an average molecular
formula for liquid products is defined as C ꢃ to give the observed product distribution, in
ꢖ
ꢀꢖꢗꢘ
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which the values of x are calculated (Figure 9 (a)). Olefins and alkanes are represented by x values
of 0 and 2, respectively. As seen, the formula represents the saturation degree of liquid products
rather well. Higher x values are indicative of more alkaneꢀlike saturation. In the presence of CO
2
at 320 ℃, the low x value close to 0.2 indicates that the products are primarily olefins, which is
consistent with the results in Table 2. Notably, the x value increases substantially to 1.25 when the
temperature increases to 360 ℃, signifying an elevated level of products saturation. The highly
saturated products at 360 ℃ strongly indicate the occurrence of hydrogen transfer reactions
amongst these small olefins, which mainly proceeds in the form of ꢍolefin + ꢍolefin → alkane +
5
4
aromatic and one sample is illustrated in Figure 10.
Hydrogen transfer is a bimolecular reaction where one hydrogen atom is transferred from an
adsorbed surface alkoxide to one hydrocarbon molecule (e.g., cyclic, acyclic alkane, or alkene).
Branchedꢀchain alkanes are facile hydrogen donors compared with linear alkanes because of the
stabilizing influence of carbocations in transition structures. Further, alkenes show a higher
reactivity for hydrogen donation, especially for multiply unsaturated olefins (e.g., with tertiary
5
5
allylic CꢀH bonds), because of more effective charge delocalization to form carbocations
.
However, the identity and reactivity of such molecules eludes experimental probes on account of
56
their subsequent dehydrogenation to form aromatics rapidly , which is consistent with the results
of this study.
2
Moreover, the increased hydrogen production with increased CO pressure (Figure 9(b))
indicates an elevated level of dehydrogenation in conjunction with hydrogen transfer, as well as
C H dehydrogenation by CO . The slight increase of hydrogen yields with increased temperature
3
8
2
is correlated with the extent of dehydrogenation, where the hydrogen requirement to produce
alkanes is also well satisfied.
Table 3. Molar distribution of classified products in CO
2
atmosphere at 360 ℃.
Retention
Reaction pressure (MPa) / (mol %)
Compounds
Formula
time (min)
1
2
3
4
Alkanes
Octane
Nonane
3.03
4.39
5.99
7.61
9.14
C
8
H
18
13.7
11.0
7.2
20.2
11.5
8.4
13.4
11.8
8.4
15.0
12.1
7.9
C H
9
20
Decane
C
C
C
10
11
12
H
22
24
26
Undecane
Dodecane
H
H
9.9
6.7
10.2
4.6
9.3
4.8
5.3
4.7
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Tridecane
Tetradecane
10.59
11.94
13.22
14.42
15.56
16.28
C
C
C
13
14
15
H
H
H
28
30
32
34
36
34
2.9
1.5
2.8
1.5
3.5
1.8
15.7
5.8
3.0
1.7
3.0
1.7
Pentadecane
10.2
2.9
7.4
10.6
6.2
Hexadecane
C H
1
1.2
6
Heptadecane
C
17
17
H
H
16.7
5.8
13.4
4.8
12.4
3.6
Undercylꢀcyclohexane
C
Total
86.6
83.2
79.9
86.5
Olefins
8
ꢀHeptadecene
Aromatics
Ethylbenzene
,3ꢀDimethylꢀbenzene
14.94–15.93
C
17
H
34
6.7
8.9
7.5
4.6
3.91
4.01
6.98
C
8
H
10
1.7
4.8
0.0
6.5
2.0
4.7
1.2
7.9
3.0
6.4
2.1
5.4
1.4
8.9
1
C H
8
10
1
ꢀMethylꢀ2ꢀpropylꢀbenzene
C
10
H
14
3.0
Total
12.4
(
Figure 9)
Figure 10)
.3 Reaction pathways and catalytic mechanisms in CO
In CO atmosphere, the catalytic processing of oleic acid consists of deoxygenation, catalytic
cracking, CO dehydrogenation of C , and hydrogen transfer reactions, as shown in Figure 11.
(
3
2
atmosphere
2
2
3 8
H
Because of no (E)ꢀhexadecꢀ8ꢀenꢀ1ꢀol or (E)ꢀheptadecaꢀ1,9ꢀdiene in liquid products, the
decarbonylation of oleic acid does not occur. Instead, oleic acid decarboxylates directly to give
8
ꢀheptadecene, or it is first converted to γꢀstearolactone (5ꢀtetradecyldihydrofuranꢀ2(3H)ꢀone)
through C=C bond migration and cyclization, and then decarboxylates into 3ꢀheptadecene.
Subsequently, the formed heptadecenes crack into various shortꢀchain olefins. The aromatization
of C H and dehydrogenation of C H8 by CO2 contribute to hydrogen production and is
3
6
3
accompanied by hydrogen transfer amongst these shortꢀchain olefins, all of which drive the
production of aviation fuelꢀlike alkanes.
4
0
As elaborated in our early work , the hydrodeoxygenation pathways under H
include direct decarboxylation or dehydroxylation followed by decarbonylation to give
ꢀheptadecene. Herein, heptadecenes are further hydrogenated to form heptadecanes and almost
no further cracking is observed compared to that in CO atmosphere, especially at 320 ℃. The
2
atmosphere
8
2
effect of hydrogen spillover accounts for this observed behavior. Hydrogen atoms could be easily
available by nanoꢀNi metal particles in large quantities, then spilling onto the acidic sites on
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catalyst’s surface. With numerous H atoms, the intrinsic C=C bonds in heptadecenes are easily
hydrogenated, whereas their cracking are largely inhibited.
(
Figure 11)
The Ni metal center and zeolite acidic sites constitute the catalytic active sites for oleic acid
conversion. First, the catalytic active centers required for the ODH reaction of C with CO are
H
3 8
2
determined using pure Ni and HZSMꢀ5 as catalysts. The results in Figure 12 clearly shows that the
reaction is catalyzed by acidic sites.
(
Figure 12)
The catalytic mechanisms in CO
2
atmosphere have also been investigated separately by means
of using pure Ni metal and HZSMꢀ5 to catalyze the conversion of oleic acid. All oleic acids are
transformed with pure Ni as the catalyst (Figure 13(a)), indicating that the metal sites can
deoxygenate oleic acid alone through decarboxylation. However, almost all of the liquid products
are C17 hydrocarbons. Thus, under CO
2
atmosphere, Ni metal center possesses an extremely weak
capacity to crack the hydrocarbons, even in the presence of C=C bonds, which is consistent with
40
the results of our previous study .
For the HZSMꢀ5 zeolite, all oleic acids are similarly converted, demonstrating that acidic sites
can also catalyze decarboxylation reactions. However, large amounts of hydrocarbons with <17
carbon atoms are formed in liquid products, as evidenced by the GC/MS spectra (Figure 13(b)),
indicating that significant cracking occurs using HZSMꢀ5. This is caused by the presence of strong
11
Brønsted acid sites on zeolite surface, which possess high cracking activity . Collectively, these
results also account for the large amount of C –C hydrocarbons produced by employing the
8
15
nanoꢀNi/HZSMꢀ5 catalyst, as mentioned in Section 3.1.
Notably, many of the liquid products using only HZSMꢀ5 are aromatic hydrocarbons (AHCs)
(
see Figure 13(b)), such as ethylbenzene and σꢀxylene, which extremely differs from the product
compositions when using nanoꢀNi/HZSMꢀ5 (see Table 2 and Table 3). Therefore, a positive
catalytic effect of loaded nanoꢀNi metal sites is present, which hydroꢀsaturates the cracked
products and inhibits excessive cracking and aromatization at acidic sites. The strong acidic sites
in HZSMꢀ5 easily lead to the production of AHCs, whereas the loaded Ni particles decrease the
amount of acidic sites of the catalyst because of their partial coverage. The highly dispersed
nanoꢀNi particles prepared by citric acidꢀassisted impregnation described herein (see Figure 6)
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have an even smaller particle size and more dense distribution, which creates more coverage of the
4
0
acidic sites relative to our former conventional impregnation method . This explains the high
inhibition of AHC formation by using nanoꢀNi/HZSMꢀ5 catalyst. In terms of the hydrogen transfer
reaction which is kept to carbenium ion mechanism, it strongly depends on catalyst acidic sites
that are provided by HZSMꢀ5 zeolite support. In summary, these results demonstrate that the
production of aviationꢀlike alkanes under CO
both the nanoꢀNi metal centers and the acidic sites of the catalyst.
Figure 13)
Also, we checked the changes of catalyst acid site density before and after reaction in CO
atmosphere, respectively. The results shown in Table 4 indicate that the amounts of catalyst
acid sites in H atmosphere decrease more than that in CO atmosphere. Both of them is due to the
2
atmosphere relies on the coordinated actions of
(
2
and
H
2
2
2
generation of deposited coke, as shown in Figure 14. This is consistent with the results of total
carbon number calculation (see Table S3 in ESI). The carbon loss in liquid products indicates the
formation of coke. Moreover, the SEM observations suggest that different types of deposited coke
are formed in this two atmospheres. The deposited coke formed in CO
removed by cyclohexane, and the loaded nano Ni metal particles can be clearly observed.
However, it is totally different in H atmosphere where the catalyst surface is almost completely
2
atmosphere is easy to be
2
covered. The coke formation in catalytic process has been an intractable but haveꢀtoꢀface problem.
Various types of techniques have been employed to characterize the coke species and its formation
5
7
13
58
59
process, like TPO/TGA
,
C NMR and confocal fluorescence microscopy , etc. Recently,
6
0
Mance et al used an advanced DNPꢀsupported solidꢀstate NMR technique to characterize the
deposited carbon species in fluid catalytic cracking process. They found that the coke mainly
consists of aromatic and aliphatic coke species in which the former one is the main type. This
result can explain the reason of the hardꢀtoꢀremove aromatic coke species in H
whereas in CO , the reactions between CO and aromatic coke species probably contribute to the
decrease of itself and leave aliphatic coke species on catalyst surface. The results of
thermogravimetric analysis in Figure 14 also indicates the higher amounts of coke formation in H
2
atmosphere,
2
2
2
atmosphere compared to CO atmosphere. In this point, CO atmosphere shows a positive role in
2
2
the inhibition of coke formation.
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Table 4. Acid amounts of the catalyst before and after used in H and CO atmosphere.
2
2
a
Acid amounts (mmol/g)
Samples
Brønsted acid
0.073
Lewis acid
0.049
b
Catalyst
c
Catalyst used in H atmosphere
0.029
0.043
2
c
Catalyst used in CO
2
atmosphere
0.039
0.048
a
b
c
values obtained at 473 K, refers to the fresh catalyst of 10 wt% nanoꢀNi/HZSMꢀ5, before
PyꢀIR testing, the catalyst is calcinated and reduced in H atmosphere.
2
(
Figure 14)
4
Conclusions
A facile citric acidꢀassisted impregnation method is used to generate highly dispersed nanoꢀNi
particles on a HZSMꢀ5 support. By employing this catalyst, a much higher content of C –C15
8
hydrocarbon aviation fuel ingredients is attained in CO
i.e., 73.09 mol% vs. 49.67 mol%) using 15 g oleic acid and 0.7 g 10 wt% Ni/HZSMꢀ5 at a
temperature and pressure of 360ꢍ℃ꢍ and 4 MPa, respectively.
This present study provides an entirely new protocol of using the greenhouse gas CO
deoxygenate oleic acid to produce C –C15 aviation fuelꢀlike alkanes. In CO atmosphere, the
aromatization reactions amongst C and the ODH reactions involving C and CO liberate
2 2
atmosphere than that in H atmosphere
(
2
to
8
2
3
H
6
H
3 8
2
hydrogen in oleic acid for subsequent reaction to produce aviation fuelꢀlike alkanes. Such alkanes
are also generated via hydrogen transfer reactions between the initially produced olefins.
2
The reaction pathways and catalytic mechanisms in CO atmosphere have been fully explored.
Heptadecenes are formed by direct decarboxylation of oleic acid or γꢀstearolactone which is
originated from C=C bond shift and lactonization of oleic acid. Catalytic cracking of heptadecenes
is initiated at the intrinsic C=C bond where the carbenium ion is formed, resulting in a large
number of C and C hydrocarbons. Additionally, the phenomenon of hydrogen spillover is
8
9
observed in H
2
catalytic processing of oleic acid. In this case, the complete inhibition of catalytic
cracking action on acidic sites at 320 ℃ is observed, which indicates a disadvantage of using H
atmosphere in this point.
2
Both of catalyst Ni metal centers and acidic sites are able to decarboxylate oleic acid in CO
2
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atmosphere. The catalytic cracking reaction can only occur at the catalyst acidic sites. Ni metal
centers are of great importance for the production of aviation fuelꢀlike alkanes by means of
hydrogenation. Another important pathway for alkane production occurs via hydrogen transfer
reactions, which depend strongly on the catalyst’s acidic sites.
The results presented herein demonstrate an innovative approach to CO
2
utilization chemistry
and prove unequivocally that CO ꢀprocessing of oleic acid over nanoꢀNi/zeolite catalyst can
2
produce sustainable and clean aviation fuelꢀlike alkanes in an efficient and effective manner.
Acknowledgments
The work was financially supported by the National Natural Science Foundation of China (No.
21576260), the Natural Science Foundation of Guangdong Province (No. 2016A030308004), the
Special Funds of Applied Science and Technology Research of Guangdong Province (No.
2
015B020241002) and the Natural Science Foundation of Guangdong Province (No.
015A030313720).
2
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Green Chemistry
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DOI: 10.1039/C7GC01853C
a)80
1MPa (b)80
C8-C15
C16-C18
8-Heptadecene
(
100
80
C8-C15
C16-C18
8-Heptadecene
2MPa
3MPa
4MPa
70
60
50
40
30
20
10
0
70
60
50
40
30
20
10
0
100
80
60
40
20
0
6
0
0
4
1
2
3
4
20
0
Pressure(MPa)
1
2
3
4
Pressure(MPa)
1MPa
2
3
4
MPa
MPa
MPa
C8
C9
C10 C11 C12 C13 C14 C15 C16 C17
C8
C9 C10 C11 C12 C13 C14 C15 C16 C17= C17
Carbon number
Carbon number
C8-C15
C16-C18
Heptadecane
C8-C15
C16-C18
Heptadecane
(
c) 70
(d)70
100
100
1MPa
2MPa
80
60
40
20
0
80
60
50
40
30
20
10
0
60
50
40
30
20
10
0
3
4
MPa
MPa
60
40
20
0
1
2
3
4
1
2
3
4
Pressure(MPa)
Pressure(MPa)
1MPa
2MPa
3MPa
4MPa
C8
C9
C10 C11 C12 C13 C14 C15 C16 C17
C8
C9
C10 C11 C12 C13 C14 C15 C16 C17
Carbon number
Carbon number
Figure 1. Distribution of the number of carbons and yields of liquid products at a reaction
temperature of 320 ꢀ in an atmosphere of CO (a) and H (b), and a reaction temperature of 360
in an atmosphere of CO (c) and H (d). “C17=” in (b) refers to the C17 hydrocarbon
2
2
ꢀ
2
2
containing C=C bond.
2
Figure 2. Oleic acid conversion pathways in H atmosphere.

Green Chemistry
Page 22 of 28
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DOI: 10.1039/C7GC01853C
8-Heptadecene
3-Heptadecene
γ−Stearolactone
o
3
20 C
Oleic acid
o
3
00 C
o
2
80 C
o
2
60 C
o
2
40 C
3
4
14
15
16
17
18
19
20
21
22
Retention time (min)
Figure 3. GC/MS spectra of the liquid products during the heating period. Reaction conditions: 15
g oleic acid, 0.7 g 10 wt% Ni/HZSM-5, 4 MPa CO
2
.
Figure 4. Reaction pathway to generate 3-heptadecene in CO atmosphere.
2
Heptadecane
o
3
60 C
Heptadecane
o
3
20 C
2
3
4
12
13
14
15
16
Retention time (min)
Figure 5. GC/MS spectra of the liquid products at 320 ꢀ and 360 ꢀ. Reaction conditions: 15
g stearic acid, 0.7 g 10 wt% Ni/HZSM-5, 4 MPa CO , 5 h.
2

Page 23 of 28
Green Chemistry
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DOI: 10.1039/C7GC01853C
Figure 6. SEM and TEM images of the catalyst: (a) SEM of HZSM-5, (b) SEM of
nano-Ni/HZSM-5 with a Ni particle distribution, (c) TEM of HZSM-5, (d) TEM of
nano-Ni/HZSM-5.
2 2
Figure 7. Depictions of the possible reactions under H and CO atmosphere.

Green Chemistry
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DOI: 10.1039/C7GC01853C
(
a)100
CO (b)100
CO
CO2
CO2
C3H6
C3H8
C2H6
CH4
C3H6
C3H8
8
6
4
2
0
0
0
0
0
C2H6
CH4
80
60
40
20
0
1
2
3
4
1
2
3
4
Gas pressure (MPa)
Gas pressure (MPa)
(
c)100
H2 (d)100
H2
CO
C3H6
C3H8
C2H6
CH4
CO
C3H6
C3H8
80
60
40
20
0
C2H6
CH4
80
60
40
20
0
1
2
3
4
1
2
3
4
Gas pressure (MPa)
Gas pressure (MPa)
(
e) 60
Products of C H dehydrogenation with CO
2
3
8
4
0
0
0
2
CO
H2
CH4
C2H6
Figure 8. Distributions of the produced gas in oleic acid conversion at two reaction atmospheres:
a) H at 320 ꢀ, (b) H at 360 ꢀ, (c) CO at 320 ꢀ, (d) CO at 360 ꢀ and (e) gas products of
via the ODH reactions involving CO with the following reaction conditions: 18.04% C
vs. 81.96 % CO , 2 MPa, 360ꢁꢀ, 5 h.
(
2
2
2
2
C
H
3 8
2
3 8
H
2

Page 25 of 28
Green Chemistry
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DOI: 10.1039/C7GC01853C
o
2
1
1
0
0
.0
.5
.0
.5
.0
0.24
320
360
C
(a)
o
C
o
CO -H-360 C
2
o
0.20
CO -H-320 C
2
0
0
0
0
.16
.12
.08
.04
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0.00
1
2
3
4
Hydrogen pressure (MPa)
Carbon dioxide pressure (MPa)
2 2
Figure 9. Calculated x values (a) and H production (b) at 320 ꢀ and 360 ꢀ in CO .
Octane
H
2
1-Octene
Cyclization
(E)-octa-1,3-diene
(3E,5E)-octa-1,3,5-triene
Ethylbenzene
1
-Octene
Figure 10. One proposed pathway for hydrogen transfer process.
2 2
Figure 11. Proposed reaction pathways for oleic acid in CO and H atmospheres.

Green Chemistry
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DOI: 10.1039/C7GC01853C
1
8
6
4
2
0
0
(
c) 80
Before reaction
After Ni catalysis
After HZSM-5 catalysis
60
40
20
0
C3H8 CO2
CO
H2
CH4
C2H6
Figure 12. C
3
H
8
ODH reaction products for pure Ni and HZSM-5 catalyzing experiments,
respectively.
C17 hydrocarbons
(a)
o
Ni-360 C
C17 hydrocarbons
o
Ni-320 C
2
4
6
13
14
15
16
17
Retention time(min)
(b)
3
2
5
4
8
11
12
6
9
10
1
7
13
o
HZSM-5-360 C
14
o
15
HZSM-5-320 C
2
4
6
8
13
14
15
16
17
Retention time(min)
Figure 13. GC/MS spectra of the liquid products (a) and (b) for pure Ni and HZSM-5 catalyzing
experiments, respectively. The hydrocarbons in (b) are: (1) 1,2,3-trimethyl-cyclopentene, (2)
ethylbenzene, (3) σ-xylene, (4) nonane, (5) 1-ethyl-3-methyl-benzene, (6) decane, (7)
1
-methyl-3-propyl-benzene, (8) undecane, (9) dodecane, (10) tridecane, (11) hexadecane, (12)
heptadecane, (13) undecyl-cyclohexane, (14) 3-nonyl-cyclohexene, and (15) 1-decyl-cyclohexene.

Page 27 of 28
Green Chemistry
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DOI: 10.1039/C7GC01853C
Figure 14. SEM images and thermogravimetric analysis of the catalyst used in CO and H2
2
atmospheres. Before testing, the used catalyst is washed by cyclohexane.

Green Chemistry
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DOI: 10.1039/C7GC01853C
TOC+Sentence:
A protocol for CO
2
8
-enhanced processing of oleic acid for C -C15 alkane production is proposed,
3 6 3 8
where C H aromatization, C H oxidative dehydrogenation and hydrogen transfer reactions
contribute to achieving intrinsic hydrogen in oleic acids re-arrangement in final liquid alkanes.