Water as an additive to enhance the ring opening of naphthalene

Article abstract of DOI:10.1039/c2gc16554f

Use of water as a reaction medium or additive to enhance reaction efficiency is an important topic in green chemistry, and ring opening and contraction reactions of aromatics are crucial for upgrading diesels. In this work, we investigated the effect of water on the yields of ring opening and contraction reactions of naphthalene. A series of catalysts, such as Rh ₂O₃/HY zeolite, Mo-Ni oxide and their physical mixtures, were used as the catalysts. The influences of the amount of water, hydrogen pressure, reaction temperature and reaction time on the yields of the ring opening and contraction products (ROCP) were studied. It was found that Rh ₂O₃/HY and Mo-Ni oxide showed an excellent synergistic effect for catalyzing the reaction, and water could be used as a green and efficient additive for enhancing the yield of the ROCP. At the optimized conditions, the yield of the ROCP could be as high as 63.3%. The mechanism for the effect of water on the reactions was discussed on the basis of control experiments.

Full text of DOI:10.1039/c2gc16554f

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PAPER
Water as an additive to enhance the ring opening of naphthalene
Qian Wang, Honglei Fan, Suxiang Wu, Zhaofu Zhang, Peng Zhang and Buxing Han*
Received 3rd December 2011, Accepted 30th January 2012
DOI: 10.1039/c2gc16554f
Use of water as a reaction medium or additive to enhance reaction efficiency is an important topic in
green chemistry, and ring opening and contraction reactions of aromatics are crucial for upgrading diesels.
In this work, we investigated the effect of water on the yields of ring opening and contraction reactions of
naphthalene. A series of catalysts, such as Rh2O3/HY zeolite, Mo–Ni oxide and their physical mixtures,
were used as the catalysts. The influences of the amount of water, hydrogen pressure, reaction temperature
and reaction time on the yields of the ring opening and contraction products (ROCP) were studied. It was
found that Rh2O3/HY and Mo–Ni oxide showed an excellent synergistic effect for catalyzing the reaction,
and water could be used as a green and efficient additive for enhancing the yield of the ROCP. At the
optimized conditions, the yield of the ROCP could be as high as 63.3%. The mechanism for the effect of
water on the reactions was discussed on the basis of control experiments.
naphthalene is only 47.9%.16 So, obtaining a high yield of
ROCP from naphthalene is of great significance, but is
challenging.
Introduction
Currently, consumption of diesel is fast growing because of its
higher energy content and less greenhouse gas emission than
gasoline. The light cycle oil (LCO) with low cetane number
(CN) and high content of aromatics needs to be upgraded to
obtain high quality diesel. A high aromatic content reduces the
CN and contributes significantly to the formation of environmen-
tally harmful emissions.1,2 To meet the increasingly rigorous
environmental regulation and fuel specifications, it is necessary
to reduce the content of aromatics and increase CN. Several
methods have been used to improve CN, such as adding cetane
additives,3 blending with biodiesel,4 hydrotreating5 and selective
ring opening (SRO).6 Among the methods used, SRO improves
CN efficiently without losing the total mass, and the CN
increases from 5 to about 50 by converting aromatics to alkylaro-
matics or alkylhexanes, and the CN just locates in the range of
45–55 that is the best for the ignition of diesel engines.7 The
most efficient CN-improving products of SRO are ring opening/
contraction products (ROCP), including ring-opening products
(ROP) which are one-ring compounds of high CN and ring-con-
traction products (RCP) that are multi-ring compounds with at
least one five-membered naphthenic ring.8,9
Ring opening of aromatics can be catalyzed by Brønsted acids
such as solid acids10 and bifunctional catalysts for hydrocrack-
ing.8,17 The yields of ROCP catalyzed by solid acids are usually
low due to the large extent of overcracking and fast catalyst deac-
tivation. Bifunctional catalysts, which consist of highly dispersed
metal for hydrogenation and acidic support for cracking, are
usually more effective. Transition metals and noble metals have
been widely used as the metal components, and different acidic
supports such as zeolites have been used as the supports. Many
bifunctional catalysts have been developed, such as NiW/Al2O3-
USY,10 NiMo/zeolite,18 Ir/beta,13 Mo2C/HY,19 Pt-Ir/HY,20 Pt/
MCM-41,21 Rh/Al2O3,22,23 Ru/Al2O3,24 Pt-Rh/Al2O3,25 Rh-Ag/
TiO2 and Rh-Ge/Al2O3.27 Generally, the catalysts with tran-
26
sition metals are cheaper, but the activity is lower. While the sup-
ported noble metal catalysts are more effective, they are more
expensive.
Supercritical or near-critical water is an excellent solvent for
organic compounds, and the dissociation of water generates a
sufficiently high H+ concentration.28,29 Recently, supercritical or
near-critical water have attracted much attention as environmen-
tally benign media for chemical reactions,30–38 including some
reactions in near-critical water under microwave irradiation.39,40
It has been reported that water influences the catalytic behavior
of zeolites.41,42 At low water coverage, water reduces the density
of the Lewis acid sites and favors the formation of new Brønsted
acid sites.43–45 Water can change the distribution of Brønsted
and Lewis acid sites and inhibit the carbon deposition on zeo-
lites.46 It can also enhance the selectivity to tetralin in the
naphthalene hydrogenation and inhibit coke formation.47
There is no doubt that the study of the effect of water as an
additive on the selective ring opening of aromatics is an very
interesting topic. In this work, we studied the effect of water on
LCO consists largely of two-fused six member rings, such as
naphthalene, tetralin, and decalins, which are often used as
model compounds in the SRO studies of LCOs.10–13 Compared
with tetralin and decalin, naphthalene is more representative of
LCO for its higher aromatic content. Meanwhile, naphthalene is
more difficult to achieve high ROCP yield because the reaction
pathway is more complex. In the literature, the maximum yield
of ROCP of decalin and tetralin is about 70%,14,15 while that of
Beijing National Laboratory for Molecular Sciences, Institute of
Chemistry, Chinese Academy of Sciences, Beijing, P.R. China. E-mail:
hanbx@iccas.ac.cn; Fax: (+86) 10 6255 9373; Tel: (+86) 10 6256 2821
1152 | Green Chem., 2012, 14, 1152–1158
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the selective ring opening reaction of naphthalene, and the phys-
ical mixture of Rh2O3/HY zeolite (denoted as HY hereafter) and
Mo–Ni oxide (denoted as Mo–Ni hereafter) was used as the cata-
lyst. The influences of reaction parameters, such as amount of
water, hydrogen pressure, reaction temperature and reaction time
on the reaction were studied. Interestingly, it was found that
Rh2O3/HY and Mo–Ni had excellent synergistic catalytic proper-
ties for the reaction and water was an efficient additive to
enhance the yield of the ROCP, and the yield could reach 63.3%
at suitable conditions. The mechanism for the effect of water on
the reactions was studied on the basis of control experiments.
compounds the calculated average GC factors were adopted,
which is a commonly used method.12,48
Results and discussion
Performance of different catalysts without and with added water
Different catalysts were tested for the ring opening reaction of
naphthalene, and the results are provided in Table 1.
For the catalyst Rh2O3/HY, hydrogenation was the dominant
reaction, and decalin was the main product (entry 1). When HY
+ Mo–Ni was used as the catalyst, hydrogenation also dominated
the reaction (entry 3), but the yield of decalin was much lower
than that catalyzed by Rh2O3/HY, indicating that Rh is more
active for hydrogenation than the Mo–Ni catalyst. When sulfur
was added, the catalysts Rh2O3/HY and HY + Mo–Ni showed
the similar product distribution (entries 5 and 7). Entries 1 and 5
indicate that sulfur reduced the activity of Rh2O3/HY for the
hydrogenation reaction. But the yield of the ROCP catalyzed by
HY + Mo–Ni was improved by adding sulfur (entries 3 and 7),
mainly because sulfur can improve the hydrogenation activity of
Mo–Ni and promote the cleavage of C–C bonds.49 All the
results demonstrate that high yield of ROCP could not be
reached using Rh2O3/HY or HY + Mo–Ni. However, when they
were combined, a higher yield of the ROCP could be achieved
(entries 9, 11, 13, 15, 17 and 19), especially when the mass ratio
of Rh2O3/HY and Mo–Ni was 1 : 0.3. Generally, the ring
opening reaction of a six-member ring is much easier after iso-
merization to a five-member ring. Therefore, the catalysts with
the functions of isomerization and cracking simultaneously
should be highly efficient for ring-opening reaction. It was
reported that MoO2 from the hydrogenation reduction and MoS2
possess the ability of catalyzing isomerization and ring opening
by the formation of Brønsted Mo–OH and Mo–SH acidic group
(s) on the surface,50,51 and the hydrogenation activity of Rh will
not be affected by Mo–Ni.50 Therefore, we can deduce that the
Rh and Mo–Ni catalyzed hydrogenation, and HY and Mo–Ni
promoted the isomerization and ring opening reactions.
The influence of water added on the performances of different
catalysts was studied. Using Rh2O3/HY as the catalyst, the
ROCP yield increased from 21.5% to 26.3% and the yield of HC
was reduced from 15.2% to zero with the addition of water
(entries 1 and 2). The water on the zeolite can form new
Brønsted acid sites,43–46,52 which may enhance the ring opening
reaction and therefore the ROCP yield can be higher. At the
same time, the water molecules adsorbed on the HY zeolite com-
peted with reactants and inhibited bimolecular reactions, which
reduced the yield of HC. The influence of water on the yield of
ROCP catalyzed by Mo–Ni + HY was not considerable, both the
ROCP yields with and without water were about 11% (entries 3
and 4). The tetralin yield decreased, and decalin and ROCP
yields increased after adding water for Rh2O3/HY + S (entries 5
and 6) and Mo–Ni + S + HY (entries 7 and 8), indicating that
water improved the hydrogenation activity of the metallic com-
ponents and enhanced the acidity of the HY zeolite. The yield of
ROCP was increased considerably when Mo–Ni and Rh2O3/HY
were combined (Rh2O3/HY + Mo–Ni), and water could also
improve the yield of ROCP (entries 9 to 14).
Experimental
Naphthalene was purchased from Shantou Xilong Chemical
Factory (Guangdong, China). Sulfur powder, rhodium chloride
and n-hexane were obtained from Beijing Chemical Reagent
Company. All the above chemicals were of analytical grade and
used without further purification. The HY zeolite was provided
by Zibo Taixing Chemicals Co. Ltd (Shandong, China). The
Mo–Ni catalyst used was the same as that used previously.42 The
Rh2O3/HY catalyst with 2 wt% Rh2O3 was prepared by an
impregnation method using RhCl3 solution followed by calcina-
tion at 823 K. X-ray photoelectron spectroscopy (XPS) data were
obtained with an ESCALab220i-XL electron spectrometer from
VG Scientific using 300 W AlKα radiation. The base pressure
was 3 × 10−9 mbar. The binding energies were referenced to the
C1s line at 284.8 eV from adventitious carbon.
The reaction was carried out in a high-pressure cylindrical-
shaped 316 stainless reactor of 6 mL. In a typical experiment, a
desired amount of naphthalene, catalysts, S powder (S is com-
monly used to activate the transition metal catalyst in oil
refineries), and water were added into the reactor. The reactor
was purged with hydrogen three times to remove the air and then
pressurized to the desired pressure. The loaded reactor was
placed into a preheated isothermal furnace. After a desired reac-
tion time, the reactor was taken out of the furnace and cooled in
a water bath to quench the reaction quickly. The cooled reactor
was then opened and the reaction mixture was transferred into a
10 mL vial. The reactor was then rinsed with n-hexane and the
washings were added to the above vial. Then an internal stan-
dard, biphenyl, was added into the vial for analysis. The reaction
products were analyzed by an Agilent 4890D gas chromatograph
equipped with an SUPELCOWAX-10 capillary column (30 m)
and an FID detector. GC-MS analysis of the compounds was
performed on a SHIMADZU-QP2010.
The products include mainly hydrogenation products (tetralin
and decalin), ring opening/contracting products (ROCP) (e.g.,
alkyl-benzene, alkyl-hexane, methyl-indans and decalin skeletal
isomers), cracking products (less than 10 carbon atoms), and
heavy compounds (HC) (more than 11 carbon atoms). Naphtha-
lene conversion was calculated from (Minitial − Mun)/Minitial
,
where Minitial is the initial mass of naphthalene, and Mun is the
mass of naphthalene unreacted. The yield to product i (Yi) is
defined as Mi/Minitial, where Mi is the mass of product i. For
hydrogenation products and naphthalene, GC calibration factors
were obtained using pure reference compounds. For the other
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Table 1 Selective ring opening of naphthalene with different catalysts with and without water
Yield (%)
Decalin
Entry
Catalyst
Water (mg)
Conv. (%)
Tetralin
ROCP
HC
1
2
3
4
5
6
7
8
Rh2O3/HY
Rh2O3/HY
HY + Mo–Ni(1 : 0.3)
HY + Mo–Ni(1 : 0.3)
Rh2O3/HY + S
Rh2O3/HY + S
HY + Mo–Ni (1 : 0.3) + S
HY + Mo–Ni (1 : 0.3) + S
Rh2O3/HY + Mo–Ni(1 : 0.1)
Rh2O3/HY + Mo–Ni(1 : 0.1)
Rh2O3/HY + Mo–Ni(1 : 0.3)
Rh2O3/HY + Mo–Ni(1 : 0.3)
Rh2O3/HY + Mo–Ni(1 : 1.2)
Rh2O3/HY + Mo–Ni(1 : 1.2)
Rh2O3/HY + Mo–Ni(1 : 0.1) + S
Rh2O3/HY + Mo–Ni(1 : 0.1) + S
Rh2O3/HY + Mo–Ni(1 : 0.3) + S
Rh2O3/HY + Mo–Ni(1 : 0.3) + S
Rh2O3/HY + Mo–Ni(1 : 1.2) + S
Rh2O3/HY + Mo–Ni(1 : 1.2) + S
0
2
0
2
0
2
0
2
0
2
0
2
0
2
0
2
0
2
0
2
100
100
99.6
100
99.6
99.7
99.7
99.8
100
100
100
100
100
100
99.7
100
100
100
100
99.5
57.6
67.4
41.5
42.2
24.3
36.3
35.0
38.5
18.9
24.2
10.4
16.7
10.1
13.1
37.2
37.4
17.9
24.3
6.7
0.4
0.2
42.3
41.0
30.2
19.1
27.3
21.1
0
0
0
0
23.1
26.8
0
0
0.4
0
21.5
26.3
11.4
11.6
23.4
28.9
19.5
28.3
38.8
44.8
47.4
53.1
36.9
39.2
43.9
50.8
50.7
63.3
42.2
47.5
15.2
0
1.2
0
14.6
1.7
11.8
1.3
9
19.4
11.2
27.3
14.5
22.1
14.8
10.2
1.6
12.3
0
13.9
1.7
10
11
12
13
14
15
16
17
18
19
20
28.0
31.2
10.1
Reaction conditions: naphthalene 6 mg, H2 5 MPa, 613 K, 4 h, Rh2O3/HY contains 2 wt% Rh2O3, Si/Al = 4.6 in HY, total mass of the catalyst
6.5 mg, S 3 mg, the ratios in the second column from the right side are the mass ratio of Rh2O3/HY: Mo–Ni or HY: Mo–Ni, the volume of the reactor
was 6 mL.
Table 2 Selective ring opening of naphthalene with different amounts
of water
and that of the hydrogenated compounds increased with further
increasing the amount of water added. The reason may be that
some acidic sites for cracking reaction were covered by water. As
the water added exceeded 100 mg, no ROCP could be detected,
and conversion of naphthalene and the yields of the hydrogen-
ated compounds decreased significantly, indicating that addition
of too much water reduced the activity of the catalyst for all the
reactions by covering the surface of the catalyst.
Yield (%)
Entry Water (mg) Conv. (%) Decalin Tetralin ROCP HC
1
2
3
4
5
6
7
0
2
6
10
50
100
400
100
100
100
100
99.1
97.8
59.6
17.9
24.3
21.3
50.9
55.0
13.7
2.6
0
0
4.9
4.6
22.3
79.2
51.6
50.7
63.3
55.6
49.2
16.1
0.4
12.3
0
0
0
0
0
0
Effect of temperature on the reaction
0
The effect of the temperature on the reaction is shown in Fig. 1.
At the lower temperature, the hydrogenation products, decalin
and tetralin, were mainly produced, and their yields decreased
with increasing temperature. The ROCP yield increased with
increasing temperature and reached a maximum at 613 K, and
then decreased with further increasing temperature. The main
reason was that at the lower temperature the reaction rate of the
hydrogenation was much faster than the ring opening reaction,
and the ring opening reaction became faster as the temperature
was raised, which was favorable to yielding the ROCP. As the
temperature was too high, significant overcracking occurred and
the yield of the ROCP decreased.
Reaction conditions: naphthalene 6 mg, H2 5 MPa, 613 K, 4 h, Rh2O3/
HY contains 2 wt% Rh2O3, Si/Al = 4.6 in HY, total mass of the catalyst
6.5 mg; S 3 mg, Rh2O3/HY: Mo–Ni 1 : 0.3, the volume of the reactor
was 6 mL.
When Rh2O3/HY + Mo–Ni + S was used as the catalyst, the
yield of the ROCP was 50.7% (entry 17). After adding water, the
maximum ROCP yield was as high as 63.3% (entry 18), which
was considerably higher than the yield reported in the literature
(47.9%).16 In addition, water could also inhibit the formation of
the HC.
Effect of the amount of added water on the reaction
Influence of hydrogen pressure on the reaction
The effect of the amount of added water on the reaction cata-
lyzed by Rh2O3/HY + Mo–Ni + S was studied and the results
are presented in Table 2. Addition of 2 mg water could reduce
the yield of HC significantly and increase the yield of ROCP
considerably because of the formation of Brønsted acid sites on
the surface of the catalysts.53 But the yield of ROCP decreased
The influence of hydrogen pressure on the yields of different
products is illustrated in Fig. 2. Both the yields of ROCP and
decalin increased with hydrogen pressure at the beginning and
then decreased after about 5 MPa. This is understandable
because hydrogenation is necessary for the ring open cracking
and contraction reactions. At the lower hydrogen pressure, the
1154 | Green Chem., 2012, 14, 1152–1158
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Fig. 3 The effect of reaction time on product distribution of naphtha-
lene hydrocracking; ■ ROCP, ● tetralin, ▲ decalin. Reaction con-
ditions: naphthalene 6 mg, H2 5 MPa, 613 K, water 2 mg, Rh2O3/HY
contains 2 wt% Rh2O3, Si/Al = 4.6 in HY, total mass of the catalyst
6.5 mg, S 3 mg, Rh2O3/HY: Mo–Ni 1 : 0.3, the volume of the reactor
was 6 mL.
Fig. 1 Effect of temperature on the yield of different products; ■
ROCP, ● tetralin, ▲ decalin. Reaction conditions: naphthalene 6 mg,
H2 5 MPa, water 2 mg, 4 h, Rh2O3/HY contains 2 wt% Rh2O3, Si/Al =
4.6 in HY, total mass of the catalyst 6.5 mg, S 3 mg, Rh2O3/HY: Mo–Ni
1 : 0.3, the volume of the reactor was 6 mL.
the beginning, the main product was tetralin. With increasing
time, more tetralin was converted to decalin and ROCP. After
that, extending the reaction time would result in more overcrack-
ing. Therefore, both the yields of decalin and ROCP decreased,
as shown in Fig. 3.
Characterization of the catalysts
The Rh2O3/HY + Mo–Ni catalysts with and without sulfur
(entries 12 and 18 of Table 1) were characterized before and
after the reaction by XPS. The results with and without sulfur
are shown in the left and right columns of Fig. 4, respectively.
Fig. 4(a) shows that Mo6+ (232.5 eV) was fully converted to
MoS2 (228.9 eV) with addition of sulfur after the reaction, while
Fig. 4(d) illustrates that Mo6+ was partly reduced to Mo4+ (229.2
eV) after the reaction without sulfur. Therefore, in the reaction,
the Mo in the reaction system existed as MoS2 in the presence of
sulfur, and as MoO3 and MoO2 without sulfur. MoO3 dissociated
hydrogen into H atoms, and the bonding of H to surface O
atoms led to the formation of Brønsted acidic Mo–OH groups on
the MoO2 surface. In the sulfide catalyst, the dissociated H
atoms form the Mo–SH group on MoS2 surface. The acidity of
MoS2 is weaker than MoO2.51 But MoS2 is more active for
hydrogenation than MoO2.52 So the acidity of the oxide system
is higher than that of the sulfide system. Too high acidity usually
causes overcracking and condensation, which produces HC.54
This can explain in part why the yield of HC is much lower
when the sulfide catalyst was used.
Fig. 2 The effect of hydrogen pressure on the yield of different pro-
ducts; ■ ROCP, ● tetralin, ▲ decalin. Reaction conditions: naphtha-
lene 6 mg, 613 K, water 2 mg, 4 h, Rh2O3/HY contains 2 wt% Rh2O3,
Si/Al = 4.6 in HY, total mass of the catalyst 6.5 mg, S 3 mg, Rh2O3/
HY: Mo–Ni 1 : 0.3, the volume of the reactor was 6 mL.
concentration of hydrogen on the catalyst surface was low, and
therefore the yields of the ROCP and decalin increased with
pressure. However, the overcracking was more significant at the
higher pressure, and the yields decreased with increasing
pressure. As expected, the yield of tetralin, the partially hydro-
genated compound, decreased monotonously with pressure.
There are four peaks at 307.95 eV, 308.55 eV, 309.8 eV and
310.5 eV in Rh 3d figures Fig. 4(b) and 4(e), and they are
assigned to Rh, Rh2+, Rh3+ and Rh sulfide, respectively. In the
presence of sulfur, a part of Rh3+ was reduced to Rh, and part
was converted to Rh sulfide that is inactive for hydrogenation.
Without sulfur, Rh oxide was reduced to Rh after reaction,
which is active for the hydrogenation. So the Rh was less active
in the sulfide catalyst than the oxide catalyst. The decalin yield
of entry 5 is lower than that of entry 1 in Table 1 because the
hydrogenation activity of Rh is reduced by sulfur. However,
Effect of reaction time on the reaction
The effect of reaction time on the distribution of the products is
shown in Fig. 3. Tetralin was the main product at 1 h and its
yield decreased with increasing reaction time. The yields of
ROCP and decalin increased with time up to 4 h, and the yields
decreased with further increasing reaction time. This is consist-
ent with the argument that the hydrogenation rate of naphthalene
to tetralin is much higher than that of tetralin to decalin due to
the strong adsorption of naphthalene on the metal surface.53 At
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Fig. 4 X-ray photoelectron spectra for the catalysts with and without sulfur before and after the reaction: (a) and (d) Mo 3d level, (b) and (e) Rh 3d
level, (c) and (f) Ni 2p level. The left column is for the Rh2O3/HY + Mo–Ni + S, the right column is for the Rh2O3/HY + Mo–Ni.
when Rh was combined with Mo–Ni, the hydrogenation activity
reduction of Rh can be compensated by the enhanced activity of
Mo–Ni sulfide, as can be known by the comparison of entries 12
and 18 in the table.
naphthalene catalyzed by a bifunctional catalyst can be illustrated
by Scheme 1.8,55 On the bifunctional catalysts, the selective ring
opening reaction is accompanied by hydrogenation, isomeriza-
tion and cracking. Naphthalene is first converted to tetralin and
decalin with the aid of the hydrogenation catalyst. The acidic
support promotes the isomerization and ring opening reaction.
The overcracking reaction can yield some small molecules. HC
is produced by condensation reactions, forming the precursors of
coke. In this work, the Rh and Mo–Ni sulfide are active for the
hydrogenation, and the HY and Mo–Ni sulfide promote the iso-
merization and cracking. Some new Brønsted acid sites were
formed on the HY and Mo–Ni sulfide in the presence of water,
which enhances the isomerization and cracking. Besides, the
water molecules adsorbed on the zeolite inhibited the conden-
sation reaction, which reduced the probability to form the HC.
All the factors were favorable to achieving a higher yield of
ROCP.
Fig. 4(c) and 4(f) show the Ni 2p level XPS spectrum. In the
presence of sulfur, there was a very weak peak for Ni sulfide
(852.7 eV), and a strong peak for Ni oxide (855.5 eV), indicat-
ing that the Ni existed mainly in the form of Ni oxide. Without
sulfur, the peak for the Ni oxide increased to 856.1 eV. The Ni
oxide was not reduced to Ni (852 eV) by hydrogen in the reac-
tion. In the presence of sulfur, a small part of Ni was sulfided
and Ni also existed mainly in the form of Ni oxide. In our exper-
imental conditions, the main form of Ni in the catalysts was Ni
oxide with and without S. So the effect of sulfur on the function
of Ni should be very limited.
Based on our results and the related work in the literature, the
reaction pathway for the selective ring opening reaction of
1156 | Green Chem., 2012, 14, 1152–1158
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Scheme 1 The possible reaction pathway of naphthalene hydrocracking.
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100 749, 2009.
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We have studied the effect of water on the ring opening and con-
traction reactions of naphthalene promoted by different catalysts.
The results indicate that Rh2O3/HY and Mo–Ni + S can catalyze
the reaction synergistically. The best ratio of Rh2O3/HY and Mo–
Ni is 1 : 0.3 for the reaction. In the reaction, Rh and Mo–Ni
sulfide are active for the hydrogenation, and the HY and Mo–Ni
sulfide provide acid sites for isomerization and cracking reac-
tions. Water can be used as an effective green additive for enhan-
cing the yield of the ROCP catalyzed by Rh2O3/HY + Mo–Ni +
S because it can improve the hydrogenation activity of the cata-
lyst, produce new Brønsted acid sites on the HY and Mo–Ni
sulfide, which enhances the isomerization and cracking. In
addition, the water molecules adsorbed on the zeolite can
prevent the condensation reaction, which inhibits the formation
of heavy compounds. All the factors are favorable to achieving
higher yield of ROCP. This work provides new and useful
knowledge for improving the CN of diesel in a greener and
efficient way. We believe that water as green additive has great
potential for promoting some other chemical reactions.
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