Selective hydroconversion of naphthalenes into light alkyl-aromatic hydrocarbons

Article abstract of DOI:10.1016/j.apcata.2014.12.001

2-Ring aromatics such as naphthalene and alkyl-naphthalenes constitute a high fraction in the diesel boiling point range by-products from oil refining and petrochemical plants. A two-step catalytic process, consisting of a selective hydrogenation of naphthalenes to tetralins and a subsequent hydrocracking of tetralins into light alkyl-aromatic hydrocarbons rich in BTX (benzene, toluene, xylenes), was postulated and studied in a fixed bed down-flow reactor under a moderate pressure of 3-4 MPa. For the selective hydrogenation of naphthalenes to tetralins, it was found that the catalytic performances of Mo₂C-supported catalysts were superior in terms of tetralins yield as well as selectivity to the conventional metal-supported catalysts such as Pt, Co, Ni and NiW supported catalysts. The hydrocracking of tetralin was demonstrated to produce light alkyl-aromatic hydrocarbons rich in BTX over a monofunctional H-Beta and a bifunctional Ni/H-Beta catalyst. For the high per pass yield of BTX in the hydrocracking of tetralin in which chemical equilibrium limits its conversion and product selectivity, the bifunctional Ni/H-Beta catalyst was found to be highly promising compared with the monofunctional H-Beta catalyst. The bifunctional Ni/H-Beta showed the BTX selectivity in liquid product and the total BTX yield as high as 69.5% and 40.7 wt%, respectively, at the tetralin conversion of 99.5% at 450 °C under 4 MPa. The catalytic behavior of Ni/H-Beta suggests that BTX yield can be much improved by properly controlling the hydrogenation power of metallic sites (i.e., suppressing the hydrogenation activity), the acidity of H-Beta and their balance on the bifunctional hydrocracking catalysts.

Full text of DOI:10.1016/j.apcata.2014.12.001

Applied Catalysis A: General 492 (2015) 140–150
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Selective hydroconversion of naphthalenes into light alkyl-aromatic
hydrocarbons
Yeseul Choi, Jihye Lee, Jaeuk Shin, Seulah Lee1, Donguk Kim, Jung Kyoo Lee∗
Department of Chemical Engineering, Dong-A University, Busan 604-714, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 August 2014
Received in revised form 5 November 2014
Accepted 1 December 2014
Available online 23 December 2014
2-Ring aromatics such as naphthalene and alkyl-naphthalenes constitute a high fraction in the diesel
boiling point range by-products from oil refining and petrochemical plants. A two-step catalytic process,
consisting of a selective hydrogenation of naphthalenes to tetralins and a subsequent hydrocracking
of tetralins into light alkyl-aromatic hydrocarbons rich in BTX (benzene, toluene, xylenes), was pos-
tulated and studied in a fixed bed down-flow reactor under a moderate pressure of 3–4 MPa. For the
selective hydrogenation of naphthalenes to tetralins, it was found that the catalytic performances of
Mo2C-supported catalysts were superior in terms of tetralins yield as well as selectivity to the conven-
tional metal-supported catalysts such as Pt, Co, Ni and NiW supported catalysts. The hydrocracking of
tetralin was demonstrated to produce light alkyl-aromatic hydrocarbons rich in BTX over a monofunc-
tional H-Beta and a bifunctional Ni/H-Beta catalyst. For the high per pass yield of BTX in the hydrocracking
of tetralin in which chemical equilibrium limits its conversion and product selectivity, the bifunctional
Ni/H-Beta catalyst was found to be highly promising compared with the monofunctional H-Beta catalyst.
The bifunctional Ni/H-Beta showed the BTX selectivity in liquid product and the total BTX yield as high as
69.5% and 40.7 wt%, respectively, at the tetralin conversion of 99.5% at 450 ◦C under 4 MPa. The catalytic
behavior of Ni/H-Beta suggests that BTX yield can be much improved by properly controlling the hydro-
genation power of metallic sites (i.e., suppressing the hydrogenation activity), the acidity of H-Beta and
their balance on the bifunctional hydrocracking catalysts.
Keywords:
Naphthalenes hydrogenation
Tetralin hydrocracking
BTX
Mo2C catalyst
Ni/H-Beta
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
steady reduction worldwide [5], it is highly desirable to convert
these fractions into high-value products, i.e., diesel fuel of high
In oil refining and petrochemical industries, chemically refrac-
tory heavy fractions are produced in large quantities as process
by-products. Representative examples in diesel boiling point range
are the aromatic-rich streams such as light cycle oil (LCO) from
cetane value with low aromatic and sulfur contents [2] or light alkyl
aromatic hydrocarbons such as BTX (benzene, toluene and xylenes)
[6], of which demands are steadily increasing.
There has been tremendous efforts to develop a two-stage
hydrodearomatization of these aromatic-rich fractions to decrease
the total aromatic content to less than 10 wt% along with the sul-
fur content less than 10 ppm for use in diesel [7–9]. However, much
less attention has been devoted to the production of BTX from these
fractions. Currently, the main source of BTX includes reformate
from catalytic reforming, pyrolysis gasoline from NCC and coke
oven light oil from coke oven plants. If catalytic solutions to convert
these aromatic-rich fractions into high-value BTX were available,
they could serve as a supplementary source of BTX or a new “on-
purpose” or “stand-alone” process for BTX production. Simply, the
overall process economics could be improved considering (1) the
historically high price-spread between BTX and heating oil, or (2)
the replacement of high price naphtha feedstock for the catalytic
reformer with low cost aromatic-rich fractions. Recently, such pro-
cesses have been reported and patented [6,10,11]. For example,
+
fluidized catalytic cracker (FCC) [1,2], and C10 heavy aromatics
from naphtha cracking centers (NCC) [3] and para-xylene plants.
The major refractory components included in these by-products
are naphthalene and alkyl-naphthalenes. Due to the high aromatic
hydrocarbon content, they cannot be blended in diesel pools [2]
but rather are usually disposed as low-value products such as (1)
a blending stock in heavy fuel oil for viscosity adjustment for LCO
+
[1,4] or (2) self-use in plant fuel or heating oil, etc. for C10 heavy
aromatics [3]. Since the market demand of heavy fuel oil is in its
∗
Corresponding author. Tel.: +82 51 200 7718; fax: +82 51 200 7728.
E-mail address: jklee88@dau.ac.kr (J.K. Lee).
Current address: Research Center for Green Catalysis, Korea Research Institute
1
of Chemical Technology, Daejon 305-600, Republic of Korea.
http://dx.doi.org/10.1016/j.apcata.2014.12.001
0926-860X/© 2014 Elsevier B.V. All rights reserved.

Y. Choi et al. / Applied Catalysis A: General 492 (2015) 140–150
141
UOP LLC commercialized the LCO-X process in which catalytic pro-
cesses such as the hydrotreatment of LCO to reduce contaminants,
the conversion of hydrotreated LCO and the aromatic maximization
unit are incorporated in series [6].
selectivity to tetralin over decalins were compared with those
from the conventional metal-supported catalysts, Ni/␥-Al2O3,
Co/␥-Al2O3, Pt/␥-Al2O3 and NiW/␥-Al2O3. Finally, the hydrocrack-
ing of tetralin was studied over a monofunctional H-Beta and
a bifunctional Ni/H-Beta catalyst to demonstrate the two-stage
catalytic process (Scheme 1) for the production of BTX from heavy-
aromatics rich in naphthalenes.
To achieve high per pass yield of BTX from aromatic-rich frac-
tions, it is important to convert the 2- and 3-ring aromatics
into single-ring products in high selectivity. In this regard, we
postulated the following two-stage catalytic process (outlined in
Scheme 1) to convert naphthalene (for example) into high-value
BTX. In the scheme, one ring of naphthalene is selectively hydro-
genated into tetralin in the first stage (1) and the naphthenic ring
of tetralin is cracked in the second stage (2) to yield BTX and crack-
ing products. By removing polynuclear aromatics in the first stage,
the two-stage process would better guarantee the catalyst stabil-
ity in the second stage since they are highly susceptible to coke
formation on the acid sites of subsequent hydrocracking catalyst.
In Scheme 1, the final BTX yield will be primarily determined by
the hydrogenation selectivity, i.e., naphthalene hydrogenation to
tetralin versus to decalins, since the complete hydrogenation of
naphthalene to decalins in step (1) will lead to mostly hydrocracked
products (LPG and naphtha) instead of high-value BTX along with
extensive hydrogen consumption in the hydrocracking step (2).
Fundamental studies concerning the kinetic, mechanistic,
thermodynamic and catalytic chemistry aspects of aromatic hydro-
genation over conventional hydrogenation catalysts including
noble metals and sulfide catalysts were well documented in the
literature [8,12]. There are chemical equilibrium limitations on
aromatic hydrogenation within the normal operating range of
hydrofining over conventional Co-Mo and Ni-Mo sulfide catalysts
which become active only at relatively high temperature [8,13,14].
Noble metals including Pt, Pd and Rh are well known active hydro-
genation catalysts but are costly and have relatively low resistance
to sulfur poisoning. Furthermore, noble metal catalysts used in
naphthalene hydrogenation are not selective to tetralin but give
high selectivity to decalins at high naphthalene conversion levels
[15–19] due to their high catalytic hydrogenation activity. Thus, it
is desirable to look for low-cost, contaminant-tolerable and active
aromatics hydrogenation catalysts that have high selectivity to
tetralin in the first stage of Scheme 1 above. For this purpose,
molybdenum carbide (Mo2C) is of interest due not only to its simi-
lar catalytic activity to noble metals [20–23] but its high tolerance
to sulfur [24–27] and high hydrotreating (HDT) capability of gas oils
similar to the commercial HDT catalysts such as NiMo-S and CoMo-
S catalysts [25,26]. Recently, Pang et al. [28] prepared Mo2C/AC
(Mo2C supported on activated carbon) by a microwave-assisted
pyrolysis method and showed that the Mo2C/AC has a moderate
hydrogenating capability to give high selectivity to tetralin in the
hydrogenation of naphthalene. Mo2C-supported HY catalytic sys-
tems were intensively studied as a replacement for noble metal
loaded catalysts, aimed at the conversion of naphthalene into high-
cetane diesel components via the hydrogenation and ring opening
of naphthalene [27,29–31]. Others have studied the direct hydro-
conversion of methyl-naphthalene to alkyl-benzenes [4,32] or the
hydrocracking of tetralin [33–36] as the probe reaction for the pur-
pose of heavy-oil upgrading to high quality diesel fuel rather than
to high-value BTX. The product distribution from hydrocracking is
strongly dependent upon zeolites employed in the hydrocracking
catalysts at fixed metallic functions. Some previous reports on the
hydrocracking of 1-methyl naphthalene [4,32] and tetralin [33] on
metal-supported USY zeolite catalysts revealed that the BTX selec-
tivity in the product was not high enough for the purpose of high
value BTX production.
2. Experimental
2.1. Preparation of catalysts
2.1.1. Hydrogenation (HYD) catalysts
The catalysts for the HYD of naphthalenes, Mo2C(x)/␥-Al2O3
with x = 5, 10 and 20, Mo2C(20)/Na-Y, Ni(5)/␥-Al2O3, Co(5)/␥-
Al2O3, Pt(1)/␥-Al2O3 and NiW (NiO = 3.5 wt%; WO3 = 24.0 wt%)/␥-
Al2O3 catalysts were prepared, where the numbers in the
parenthesis denote the weight % of metal on the catalysts.
The Mo2C-supported catalysts were prepared by temperature-
programmed reaction of molybdenum oxides in CH4 (20%)/H2 flow
following the procedure in the literature [30]. ␥-Al2O3 (Alfa Aesar)
and Na-Y (CBV100, Zeolyst) were employed as the supports of HYD
catalysts.
The ammonium heptamolybdate tetrahydrate ((NH4)6Mo7O24
·4H2O) aqueous solution containing the required amount of Mo,
was impregnated on the supports. After aging at room temperature
for 1 h, the Mo impregnated catalysts were dried at 80 ◦C in air
overnight followed by calcination at 500 ◦C for 4 h under O2 flow.
The calcined catalysts were placed in a quartz reactor with frit
and heated to 700 ◦C at a rate of 5 ◦C/min in a CH4/H2 flow (20%
CH4) and held at 700 ◦C for 4 h. The catalysts were then held for
2 h in a H2 stream to remove excess carbon before cooling down to
room temperature. Finally, the catalysts were passivated in an O2
(1%)/He flow for 45 min and stored in a globe box filled with Ar.
The Ni(5)/␥-Al2O3, Co(5)/␥-Al2O3, Pt(1)/␥-Al2O3 and NiW/␥-
Al2O3 catalysts were also prepared by
a wet-impregnation
method with the metal precursors, nickel(II) nitrate hexahydrate
(Ni(NO3)2·6H2O), cobalt nitrate hexahydrate (Co(NO3)2·6H2O),
ammonium metatungstate hydrate ((NH4)6(H2W12O40)·5H2O) and
hexachloroplatinic acid (H2PtCl6), respectively. After aging at room
temperature for 1 h, the metal-impregnated catalysts were dried
at 80 ◦C in air overnight. The Ni/␥-Al2O3, Co/␥-Al2O3 and NiW/␥-
Al2O3 catalysts were calcined at 500 ◦C in air for 2–3 h while
the Pt/␥-Al2O3 catalyst was calcined at 350 ◦C in an O2 flow for
4 h.
2.1.2. Hydrocracking (HYC) catalysts
The catalyst for the HYC of tetralin, Ni(2)/H-Beta, was pre-
pared by wet-impregnation of aqueous solution of nickel(II)
nitrate hexahydrate (Ni(NO3)2·6H2O) on H-Beta (CP811E-75,
SiO2/Al2O3 = 75, Zeolyst) using the same procedure for the prepa-
ration of Ni/␥-Al2O3 catalyst. The Ni loading amount was 2 wt%.
H-Beta (CP811E-75, SiO2/Al2O3 = 75, Zeolyst) was also employed
as a monofunctional HYC catalyst for reference.
2.2. Characterization of the catalysts
The catalysts were characterized by powder X-ray diffraction
(XRD), X-ray photoelectron spectroscopy (XPS), transmission elec-
tron microscopy (TEM), temperature programmed reduction (TPR)
and pulse chemisorption of CO or H2. X-ray powder diffraction pat-
terns were obtained using a Rigaku Miniflex 600 with a Cu K␣ X-ray
˚
In the present work, Mo2C-supported catalysts, Mo2C/␥-Al2O3
and Mo2C/Na-Y, were prepared and tested in the hydrogenation of
naphthalene and methyl-naphthalene under a moderate H2 pres-
sure of 3 MPa. Their catalytic activity and the resulting product
source of wavelength 1.54 A. Measurement was performed using
a scan range 5–80◦ with a step width of 0.02◦ and scan speed of
0.2◦/min. XPS analysis was done using a Theta Probe AR-XPS Sys-
tem (Thermo Fisher Scientific, UK) with a monochromated Al K˛

142
Y. Choi et al. / Applied Catalysis A: General 492 (2015) 140–150
LPG, Naphtha
+
2
1
Naphthalene
Tetralin
BTX
1
LPG, Naphtha
2
Decalin
Scheme 1. Catalytic scheme for naphthalene conversion into BTX.
(hꢀ = 1486.6 eV) at a power of 150 W. All XPS spectra were corrected
to the C 1s peak at 284.6 eV. TEM images were obtained to deter-
mine the size of particles using a JEM-2010 (JEOL, Japan). Pulse
chemisorptions of CO or H2 were employed to analyze the metal
dispersions for Mo2C-supported catalysts or the other conventional
metal supported catalysts, respectively, at 308 K using a BEL-CAT
instrument (BEL Japan, Inc.) equipped with a thermal conductiv-
ity detector. The chemisorption stoichiometries were CO/M = 1 for
Mo2C-supported catalysts [37] and H/M = 1 for the other metal sup-
ported catalysts. Typically, the catalyst (0.1–0.14 g) was reduced in
H2 flow at the specific condition given in the following catalytic
activity test section and then purged in He flow at the reduction
temperature for 30 min. After cooling to 308 K, the CO or H2 pulse
chemisorption was started.
The reactor effluent was introduced on-line into a liquid–gas
separator with a liquid sampling port and a cooling jacket con-
nected to a coolant circulator. Once a steady-state was reached
after 4 h of time-on-stream, the liquid product sampled from the
separator bottom was analyzed by an off-line GC equipped with
a capillary column (HP-INNOWax, 60 m × 0.32 mm × 0.5 ␮m) con-
nected to an FID. The GC-FID peaks were further identified with a
GC–MS (Agilent 5973) coupled to a GC-FID (Agilent 6890) equipped
with a capillary column (DB-1 ms, 30 m × 0.25 mm × 0.25 ␮m).
The gas products from separator overhead were analyzed by
an on-line GC equipped with a capillary column (HP Plot-Q,
60 m × 0.32 mm × 0.5 ␮m) connected to an FID.
2.3.2. HYC of tetralin
The HYC catalysts, H-Beta and Ni(2)/H-Beta, were pre-pelletized
and sieved into 250–500 ␮m fractions. Typically, 0.58 g of sieved
catalyst was loaded in the reactor. Then, the catalyst was sub-
jected to the same pretreatment procedure as for the HYD catalyst
described above. After reduction, the reactor temperature was
reduced to 120 ◦C, and tetralin feed was introduced into the reactor
by using an HPLC pump at WHSV = 2 h−1 with the H2/tetralin molar
ratio of 8. The reactor pressure was raised to 4 MPa followed by the
reactor temperature increase to the 400–450 ◦C range. The liquid
and gas products were analyzed by the same procedure as the HYD
reaction of naphthalenes.
2.3. Catalytic activity tests
2.3.1. HYD of naphthalenes
The HYD of naphthalenes was conducted in a fixed-bed down-
flow reactor heated by an electrical furnace under the total pressure
of 3 MPa. The pressure in the reactor was maintained by means
of a back pressure regulator and the feed H2 flow rate was con-
trolled by using a mass flow controller. Catalysts were pelletized
and sieved into 250–500 ␮m fractions. In each HYD reaction, the
sieved catalyst (0.3 g) was loaded in a stainless steel reactor (3/8 in.
O.D.). The upper space of the catalyst bed was filled with glass beads
(1–1.25 mm) which served as preheating and distribution zones of
feed stream. Then, the Mo2C-supported catalysts and Ni/␥-Al2O3
catalysts were reduced at 450 ◦C (ramping rate of 5 ◦C/min) for
1 h in H2 flow (60 cc/min). The Co/␥-Al2O3 and Pt/␥-Al2O3 cata-
lysts were reduced at 400 ◦C (ramping rate of 5 ◦C/min) for 1 h and
350 ◦C (ramping rate of 2.5 ◦C/min) for 2 h in H2 flow (60 cc/min),
respectively. After reduction, the reactor temperature was cooled
to 120 ◦C, and the reaction feed mixture was introduced into the
reactor. The reactor pressure was raised to 3 MPa followed by the
reactor temperature increase to the desired temperature. The reac-
tant (5 wt% of naphthalene or methyl-naphthalene) dissolved in
n-heptane was introduced to the reactor using a HPLC pump at
WHSV = 0.7 h−1 (for naphthalene or 2-methyl-naphthalene) and
the reaction tests were conducted at the reaction temperature of
250–400 ◦C with the H2/naphthalene (or 2-methyl-naphthalene)
molar ratio of 30.
3. Results and discussion
3.1. Properties of the catalysts
The properties of HYD catalysts obtained from BET measure-
ments and chemisorptions are summarized in Table 1. The XRD
patterns of Na-Y and Mo-loaded on Na-Y before and after temper-
ature programmed reaction (TPR) are compared in Fig. 1. After the
calcinations of Mo-loaded on Na-Y in O2, MoO3 were formed as the
major phase with some other molybdenum oxides (Fig. 1b). After
the TPR, intense diffraction peaks consistent with Mo2C [20,29]
were clearly observed at 2ꢁ = 34.2◦, 38.0◦, 39.5◦, 52.2◦, 61.6◦, 69.6◦
and 74.7◦ as indexed in Fig. 1c. The high crystallinity of the Na-Y
zeolite was maintained after TPR, while the crystalline MoO3 phase
[38] was not detected (Fig. 1c). Hence, the Mo2C phase was success-
fully formed without obvious framework collapse of Na-Y support
by the TPR process. The XRD patterns of Mo loaded on ␥-Al2O3
are shown in Fig. 2. On the calcined precursor for the Mo2C(20)/␥-
Al2O3, the obvious peaks at 2ꢁ = 23.4◦, 25.8◦, 27.3◦ and 49.4◦
corresponding to (1 1 0), (0 4 0), (0 2 1) and (0 0 2) planes of MoO3
[38] were clearly observed in Fig. 2b. After TPR of MoO3/␥-Al2O3,
all the MoO3 peaks disappeared. However, in contrast to the XRD
pattern of Mo2C(20)/Na-Y, the Mo2C diffraction peaks were hardly
observed on Mo2C/␥-Al2O3 catalysts (Fig. 2c–e) except for the small
discernible Mo2C (1 0 1) one at 2ꢁ = 39.5◦ on the Mo2C(20)/␥-Al2O3
Prior to the HYD of naphthalene over NiW/␥-Al2O3 catalyst,
the catalyst was dried at 400 ◦C under He flow (20 cc/min) for 2 h.
After drying, the catalyst was sulfided in situ by introducing a sul-
fur containing feed (16.5 vol% of dimethyl sulfide (DMS) in decane,
0.1 cc/min) and H2 (50.5 cc/min) at 120 ◦C under the pressure of
3 MPa. The sulfidation was conducted at 400 ◦C for 2 h, with a heat-
ing rate of 5 ◦C/min. For the HYD of naphthalene over sulfided
NiW/␥-Al2O3 catalyst, 100 ppm of DMS was added in the reaction
feed described above.

Y. Choi et al. / Applied Catalysis A: General 492 (2015) 140–150
143
Table 1
Properties of HYD catalysts.
a
b
c
Catalysts
SABET (m2 g−1
)
VP, total (cm3/g)
VP, micro (cm3/g)
VP, meso (cm3/g)
CO uptake (␮mol/g)
H2 uptake (␮mol/g)
Na-Y
Mo2C(20)/Na-Y
␥-Al2O3
Mo2C(5)/␥-Al2O3
Mo2C(10)/␥-Al2O3
Mo2C(20)/␥-Al2O3
NiW/␥-Al2O3
Ni(5)/␥-Al2O3
Co(5)/␥-Al2O3
Pt(1)/␥-Al2O3
736
61
0.29
0.05
0.75
0.67
0.62
0.51
0.50
0.71
0.68
0.76
0.27
0.02
0.00
0.00
0.00
0.00
0.01
0.00
0.00
0.00
0.03
0.03
0.74
0.66
0.61
0.50
0.50
0.70
0.67
0.75
–
30
–
–
–
1580
–
–
–
–
–
–
–
–
–
–
–
50
360
550
225
198
186
153
177
218
207
241
a
Total pore volume at P/P0 = 0.99.
Micropore volume determined by t-plot analysis.
Mesopore volume determined by BJH method.
b
c
Fig. 1. XRD patterns of HYD catalysts; (a) Na-Y, (b) MoO3(20)/Na-Y and (c) Mo2C(20)/Na-Y.
(Fig. 2c) whose Mo2C content was the highest. The relatively high
Mo2C content (20 wt%) implies that the Mo2C particles were well
dispersed on the Mo2C/␥-Al2O3, consistent with previous reports
[39,40]. The XRD patterns of calcined Ni, Co, Pt and NiW-supported
on ␥-Al2O3 catalysts are given in Fig. 3. The strong Co3O4 peaks
were found on the Co(5)/␥-Al2O3 in Fig. 3c, while the nickel,
platinum and NiW oxide peaks were near the diffractometer’s
detection limit indicating the high dispersion of metal oxides on the
support.
The surface chemical states of the oxygen passivated
Mo2C(20)/Na-Y and Mo2C(20)/␥-Al2O3 were investigated by
an ex situ XPS. The Mo 3d regions of the XPS spectra with
the deconvolutions are given in Fig. 4. For the O2-passivated
Mo2C(20)/Na-Y, two peaks corresponding to the Mo 3d of Mo2C
Fig. 2. XRD patterns of HYD catalysts; (a) ␥-Al2O3, (b) MoO3(20)/␥-Al2O3, (c) Mo2C(20)/␥-Al2O3, (d) Mo2C(10)/␥-Al2O3 and (e) Mo2C(5)/␥-Al2O3.

144
Y. Choi et al. / Applied Catalysis A: General 492 (2015) 140–150
Fig. 3. XRD patterns of HYD catalysts; (a) ␥-Al2O3, (b) Ni(5)/␥-Al2O3, (c) Co(5)/␥-Al2O3, (d) Pt(1)/␥-Al2O3 and (e) NiW/␥-Al2O3.
Fig. 4. The Mo 3d regions of the XPS spectra of (a) Mo2C(20)/Na-Y and (b) Mo2C(20)/␥-Al2O3.
were clearly detected at 227.8 and 231.1 eV but their integrated
areas were smaller than those corresponding to the Mo 3d of MoOx
(Mo6+ at 232.2–235.4 eV and Mo4+ at 229.4–232.7 eV, respectively)
due to partial surface oxidation during the passivation step with
dilute O2 stream during the preparation. For the O2-passivated
Mo2C(20)/␥-Al2O3, the Mo2C peaks were present at 228.3 and
231.6 eV but their intensities were much smaller than those in
Mo2C(20)/Na-Y possibly due to severe surface oxidation of smaller
Mo2C particles as evidenced in the XRD analysis. The XPS data indi-
cates the presence of Mo2C on Na-Y and ␥-Al2O3 while its phase
was not apparent from the XRD pattern for Mo2C(20)/␥-Al2O3
catalyst.
The structure of metal catalysts was further investigated by
TEM. The TEM images of the Mo2C catalysts and the other reduced
metal-supported catalysts are shown in Figs. 5 and 6, respectively.
On the TEM images of Mo2C(20)/Na-Y catalyst shown in Fig. 5a
and b, Mo2C nanoparticles were found to be well dispersed in
the micro-pores of Na-Y crystals due to the high BET surface area
(736 m2 g−1) of Na-Y (see Table 1). The Mo2C nanoparticles of
1–3 nm size in diameter were formed in the pores of Na-Y as shown
in Fig. 5a and in the inset. Larger particles of 10–60 nm size in
diameter were also found on the catalyst (Fig. 5a and b), indicat-
ing relatively inhomogeneous particle size distribution on Na-Y.
According to the physical–chemical properties of catalysts sum-
marized in Table 1, both the BET surface area and the total pore
volume (mainly micropore volume) of Mo2C/Na-Y were substan-
tially lowered to 61 m2 g−1 and 0.05 cm3/g, respectively, from the
corresponding values of 736 m2 g−1 and 0.29 cm3/g for parent Na-Y
support, indicating that (1) a large fraction of Mo2C particles were
located inside the micropores of Na-Y and/or (2) some portion of
the Na-Y microstructure collapsed during the TPR at elevated tem-
perature. The average particle size of Mo2C as determined by the
Scherer’s formula with the line broadening of the two distinctive
XRD peaks at 2ꢁ = 34.2◦ and 39.5◦ is ∼27 nm. On the bright field
TEM image of Mo2C(20)/␥-Al2O3 in Fig. 5c, Mo2C particles were
not clearly observed compared to those on Mo2C(20)/Na-Y. In the
corresponding dark field image in Fig. 5d, white images correspond-
ing partly to a number of small Mo2C nanoparticles whose sizes
are of several nanometers and partly to large ones characterized
by elongated cylindrical shapes were observed. With the increase
of Mo2C content on Mo2C/␥-Al2O3 catalysts, the BET surface area
and total pore volume (mainly mesopore volume) were lowered

Y. Choi et al. / Applied Catalysis A: General 492 (2015) 140–150
145
Fig. 5. TEM images of (a) and (b) Mo2C(20)/Na-Y, (c) and (d) Mo2C(20)/␥-Al2O3 catalyst.
as shown in Table 1. The TEM images of Ni/␥-Al2O3, Co/␥-Al2O3
and Pt/␥-Al2O3 catalysts are also shown in Fig. 6. Ni and Co parti-
cles on the order of 5–20 nm in diameter were observed in Fig. 6a
and b while the Pt particles of several nm in diameter were found
in Fig. 6c. As can be seen in Table 1, the textual properties of Ni,
Co and Pt catalysts were not significantly affected by metal load-
ing on ␥-Al2O3. The CO or H2 chemisorption results are also given
in Table 1. The CO uptake of the Mo2C(20)/␥-Al2O3 catalyst was
much larger than that of Mo2C(20)/Na-Y, consistent with the XRD
and TEM results. However, the CO uptake for the Mo2C(20)/Na-Y
catalyst was too low considering the average particle size of Mo2C
of ∼27 nm by XRD. This could possibly be due to the fact that a
large number of Mo2C located inside the micropores of Na-Y are
inaccessible to CO under the dynamic condition of pulse chemisorp-
tions, which is in consistence with the substantial loss of micropore
volume (92.5% reduction, i.e., 0.27 cm3/g for Na-Y → 0.02 cm3/g for
Mo2C(20)/Na-Y as shown in Table 1 by Mo2C loading on Na-Y. Even
in the case of Mo2C(20)/␥-Al2O3, less than 1% of the total Mo is avail-
able at the surface of the Mo2C. The H2 chemisorption results for
the Ni/␥-Al2O3 (0.5 ␮mol/g) and Co/␥-Al2O3 (3.6 ␮mol/g) catalysts
revealed that the Ni and Co dispersions were very low compared
to the particle sizes observed by TEM as frequently observed with
a dynamic pulse system due to strong metal–support interactions
[41]. The Pt dispersion was 21.5% which was well in line with the
TEM observation.
3.2. Hydrogenation of naphthalenes
The naphthalene conversion and product selectivity from the
hydrogenation of naphthalene over Mo2C-supported catalysts as a
function of reaction temperature are shown in Fig. 7a and b, respec-
tively. Detailed product distributions at the reaction temperature
of 350 ◦C are listed in Table 2. The Mo2C(20)/Na-Y catalyst showed
very high levels of naphthalene conversion, i.e., 98.8–99.4%, at the
reaction temperature range of 250–350 ◦C. The Mo2C(20)/␥-Al2O3
catalyst with the same Mo2C content as Mo2C(20)/Na-Y also
showed high naphthalene conversion of >96% at 300–350 ◦C. For
the Mo2C(5)/␥-Al2O3 and Mo2C(10)/␥-Al2O3, naphthalene conver-
sions were low at temperatures below 300 ◦C but increased up to
>91% at 350 ◦C. For all the Mo2C-supported catalysts, naphthalene
conversions started to decrease at 400 ◦C due to the equilib-
rium limitation [8,13,14]. Fig. 7b compares tetralin and decalins
selectivities in the product obtained from Mo2C-supported cat-
alysts. All the Mo2C/␥-Al2O3 catalysts showed very high tetralin
Fig. 6. TEM images (a) Ni(5)/␥-Al2O3, (b) Co(5)/␥-Al2O3 and (c) Pt(1)/␥-Al2O3 catalysts.

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Y. Choi et al. / Applied Catalysis A: General 492 (2015) 140–150
Table 2
Naphthalene hydrogenation over various HYD catalysts.
Catalysts
Naphthalene conversion (%)
Tetralin selectivity (%)
Products in liquid (wt%)
Tetralin
Decalin
Naphthalene
Mo2C(20)/Na-Y
Mo2C(20)/␥-Al2O3
Mo2C(10)/␥-Al2O3
Mo2C(5)/␥-Al2O3
NiW/␥-Al2O3
Ni(5)/␥-Al2O3
Co(5)/␥-Al2O3
Pt(1)/␥-Al2O3
98.8
99.0
92.4
91.0
97.8
74.3
98.7
98.9
89.3
100.0
100.0
99.5
80.3
83.2
43.2
8.8
88.3
99.0
92.4
90.5
78.6
61.8
42.6
8.7
10.6
0.0
0.0
1.2
1.0
7.6
9.0
2.2
25.7
1.3
1.1
0.5
19.2
12.5
56.1
90.2
Reaction conditions: time on stream = 4 h; catalyst weight = 0.3 g; T = 350 ◦C; P = 3 MPa; WHSV (naphthalene) = 0.7 h−1; H2/naphthalene molar ratio = 30/1.
Fig. 8. (a) Naphthalene conversion with reaction temperature over Ni, Co and Pt sup-
portedcatalystsand(b)tetralinanddecalinsselectivitieswithreactiontemperature;
solid-lines for tetralin selectivity, dashed-lines for decalins selectivity.
Fig. 7. (a) Naphthalene conversion with reaction temperature over Mo2C and NiW
supported catalysts and (b) tetralin and decalins selectivities with reaction temper-
ature over Mo2C and NiW supported catalysts; solid-lines for tetralin selectivity and
dashed-lines for decalins selectivity.
Pt/␥-Al2O3 catalyst showed a naphthalene conversion of 60.5%
with the tetralin and decalins selectivities of 29.4 and 70.6%,
respectively. At the reaction temperature of 250–350 ◦C, an almost
complete conversion of naphthalene into decalins was observed.
The Co/␥-Al2O3 catalyst also converted naphthalene mostly
into decalins at lower temperatures (250–300 ◦C). The tetralin
selectivity steadily increased with the further raise of reaction tem-
perature along with the decrease of naphthalene conversion due
to the equilibrium limitation [8,13,14]. At 350 ◦C, the tetralin and
decalins selectivities were almost 1:1 at the naphthalene conver-
sion of 98.7%. The Ni/␥-Al2O3 catalyst showed a moderate level of
naphthalene conversion and tetralin selectivity at 300–350 ◦C. For
example, the tetralin selectivity was 83.2% with a significant for-
mation of decalins (16.8%) at the naphthalene conversion of 74.3%
at 350 ◦C. Others have also reported the co-production of tetralin
and decalins in the naphthalene hydrogenation with Ni/␥-Al2O3
catalysts in the wide range of naphthalene conversion level [42,43].
In summary, the Mo2C-supported catalysts exhibited high
tetralin selectivity at high naphthalene conversion level in naph-
thalene hydrogenation while conventional hydrogenation catalysts
such as Pt, Co, Ni- and NiW-supported catalysts produced a
moderate or substantial amount of decalins due to rather high
selectivity (>96.8%) with decalins selectivity below 2% at most.
On the other hand, a substantial amount of decalins were formed
on the Mo2C(20)/Na-Y catalyst. The selectivity to decalins over
Mo2C(20)/Na-Y was as high as 10.7% at 350 ◦C (Table 2) and showed
no clear dependence on reaction temperature. Even though the
cause of relatively high decalins selectivity over Mo2C/Na-Y in
comparison to Mo2C/Al2O3 is uncertain at the moment, the inher-
ent acidity of Na-Y on Mo2C/Na-Y might be responsible in terms of
enhanced hydrogen spill-over or strong metal-support interaction.
The NiW/␥-Al2O3 catalyst showed naphthalene conversion levels
close to those over Mo2C(20)/Al2O3 as shown in Fig. 7a. However,
it showed much lower selectivity to tetralin than Mo2C(20)/Al2O3
due to the enhanced formation of decalins as compared in Fig. 7b
and Table 2. Overall, Mo2C-supported catalysts are highly selective
in the hydrogenation of naphthalene into tetralin at the high
conversion level of naphthalene, in which supports with low
acidity are preferred.
Fig. 8a and b compares the naphthalene conversions and
tetralin/decalins selectivities obtained from naphthalene hydro-
genation over Ni-, Co- and Pt-supported catalysts. The detail
product distributions are also given in Table 2. At 200 ◦C, the

Y. Choi et al. / Applied Catalysis A: General 492 (2015) 140–150
147
were below 30% and benzene was the largest among BTX. The
BTX yield accounting for the liquid product yield (i.e., 94.0%) and
the BTX selectivity (i.e., 29.3%) in liquid product was only 27.6%
at 425 ◦C. On the other hand, a large amount of naphthalenes
(naphthalene plus methylnaphthalenes) were formed in the liquid
products mainly due to the chemical equilibrium between naph-
thalene and tetralin [8,13,14]. Furthermore, heavy by-products
+
such as C10–C11 aromatics were formed in large quantity result-
ing from the non-selective cracking of tetralin, re-alkylation and
hydrogen transfer between products on the acid sites of H-Beta
[44]. The high yield of naphthalenes and heavy by-products are
of concern because they can form coke on the acid sites that can
lead to catalyst deactivation in the long term. As seen in Table 4,
the tetralin conversion at 450 ◦C decreased to 83.7% due to catalyst
deactivation mainly by coke formation even though BTX yield was
slightly higher than 425 ◦C. Overall, the monofunctional H-Beta cat-
alyst showed its limitations in the tetralin HYC to BTX considering
(1) the limited tetralin conversion due to the equilibrium involved
in the reaction, (2) non-selective cracking of tetralin and (3) the
Fig. 9. Tetralin yield as a function of naphthalene conversion over various HYD
catalysts.
+
large yield of heavy by-products of C10–C11 aromatics. In the gas
hydrogenation activity. The yield of tetralin as a function of
naphthalene conversion is plotted in Fig. 9 for all the hydrogena-
tion catalysts. The yield vs. conversion plot obviously presents
the coincidence of data with dotted line-trajectory. The Co- and
Pt-supported catalysts possessing strong hydrogenation activity
are located on the right-bottom edge in the plot, while all the
Mo2C-supported catalysts are located on the right-top edge in
the plot indicating their superiority in selective hydrogenation of
naphthalene into tetralin possibly resulting from the moderate
hydrogenation activity of Mo2C.
products, C3 and C4 fragments were mainly produced via catalytic
cracking as shown in Fig. 10.
Hence, bifunctional HYC catalysts containing metallic compo-
nents are desirable in the conversion of tetralin to BTX. Thus, the
Ni(2)/H-Beta catalyst was employed as an example of bifunctional
ones in the tetralin HYC. As shown in Table 4, the Ni(2)/H-
Beta showed much higher tetralin conversions (98.9–99.5%) with
much less yield of heavy by-products such as naphthalenes and
+
heavy C10–C11 aromatics than the monofunctional H-Beta cata-
lyst. These results can be ascribed to the hydrogenation activity of
nickel on the bifunctional Ni(2)/H-Beta catalyst. The BTX selectiv-
ity in the liquid product substantially increased with the reaction
temperature increase. For example, it was 54.4% and 69.5% at
425 ◦C and 450 ◦C, respectively. The BTX content was in the order
of toluene > xylenes > benzene and toluene > benzene > xylenes at
425 ◦C and 450 ◦C, respectively, while benzene was the largest
among BTX over the H-Beta catalyst. The big difference in the liq-
uid product distributions from the hydrocracking of tetralin over
H-Beta and Ni(2)/H-Beta is apparent in Fig. 11. According to the
previous report [33] on the hydrocracking of tetralin over NiW-
supported USY catalyst, benzene and alkylbenzene selectivity was
very low indicating that USY zeolite is not as selective as H-Beta in
the hydrocracking of diesel boiling range feedstock such as tetralin
into alkyl-aromatics rich in BTX.
The total liquid yields over Ni(2)/H-Beta catalyst were very
low and they were in the range of 53.3–58.5 wt% compared to
94–95.5 wt% over H-Beta catalyst. The final BTX yield over Ni(2)/H-
Beta catalyst, accounting for the liquid yield and the BTX selectivity
in the liquid product, was 30.2 wt% at 425 ◦C, and further increased
up to 40.7 wt% at 450 ◦C. Over the Ni(2)/H-Beta catalyst, it is
remarkable that the nonaromatics composed of light alkane prod-
ucts of C4–C7 range constitute as much as 42.5 wt% in the liquid
product at 400 ◦C and they were substantially lowered down to
24 wt% and 11 wt% in the liquid product at 425 and 450 ◦C, respec-
tively, which were in the opposite trend of the increase in BTX
yield with the increase of reaction temperature. Considering the
very low yield (3.7–6.4 wt%) of nonaromatics over H-Beta cata-
lyst, it is believed that the light alkane products are formed as
by-products due to cracking of decalins over Ni(2)/H-Beta as shown
in Scheme 1. At a relatively low temperature, at 400 ◦C for example,
tetralin can be further hydrogenated to decalins on the metal-
lic Ni sites and decalins can be readily cracked on the acid sites
of bifunctional Ni(2)/H-Beta. Actually the decalins selectivity in
naphthalene hydrogenation at 400 ◦C over Ni(5)/Al2O3 was more
than 22% at the pressure of 3 MPa as shown in Fig. 8. By increas-
ing temperature, however, the equilibrium will remain toward
3.3. Hydrogenation of 2-methylnaphthalene (2-MN)
In most of aromatic-rich fractions of diesel boiling point range,
a substantial amount of methyl-naphthalenes are included. Thus,
2-methylnaphthalene (2-MN) was also employed as a model com-
pound and was hydrogenated over a Mo2C(20)/␥-Al2O3 catalyst
under the same conditions as the naphthalene hydrogenation. The
results at the reaction temperature of 250 and 300 ◦C are sum-
marized in Table 3. In the hydrogenation of 2-MN, two different
methyltetralins, i.e., 6-methyltetralin (6-MT) and 2-methyltetralin
(2-MT), were co-produced with 6-MT selectivity being 2.5–2.9
times more than 2-MT. The higher selectivity of 6-MT than 2-
MT could primarily be attributed to the larger steric hindrance
for the methyl-substituted ring to form ␲-complex on metal sur-
faces than for the methyl-free ring. At high 2-MN conversion level,
only a trace amount of 2-methyldecalin (2-MD) was detected on
GC–MS indicating that that the reaction is sequential as shown in
Scheme 2. Hence, a Mo2C/␥-Al2O3 catalyst was also found to be
highly active and selective in the hydrogenation of methylnaph-
thalene to methyltetralins.
3.4. Hydrocracking (HYC) of tetralin into light alkyl-aromatics
Finally, the hydrocracking of tetralin was conducted over H-
Beta and Ni(2)/H-Beta catalysts, representing the monofunctional
and the bifunctional HYC catalysts, respectively, to produce light
alkyl-aromatics rich in BTX. The reactions were carried out at
WHSV = 2 h−1 with H2/tetralin molar ratio of 8.0 under the total
pressure of 4 MPa at the increasing mode of reaction temperature
in the range of 400–450 ◦C. The reaction products were collected at
each temperature at steady-state after more than 2 h of time-on-
stream. The results are summarized in Table 4.
Over the monofunctional H-Beta catalyst, the tetralin conver-
sions were 76.4% and 88.3% at 400 ◦C and 425 ◦C, respectively.
At both temperatures, the BTX selectivities in the liquid product

148
Y. Choi et al. / Applied Catalysis A: General 492 (2015) 140–150
Table 3
2-Methylnaphthalene hydrogenation over Mo2C(20)/␥-Al2O3 catalyst.
Temp. (◦C)
2-MN conversion (%)
Methyltetralins selectivity (%)
Products in liquid (wt%)
2-MT
6-MT
2-MN
250
300
97.2
89.4
100.0
100.0
24.8
25.8
72.4
63.6
2.8
10.6
Reaction conditions: Mo2C(20)/␥-Al2O3 catalyst; catalyst weight: 0.3 g; time on stream = 4 h; P = 3 MPa; WHSV (2-methylnaphthalene) = 0.7 h−1; H2/2-methylnaphthalene
molar ratio = 30/1.
Scheme 2. Hydrogenation of 2-methylnaphthalene (2-MN) over Mo2C/␥-Al2O3 catalyst.
Table 4
Results of tetralin hydrocracking over H-Beta and Ni/(2)/H-Beta catalysts.
Catalysts
H-Beta
Ni(2)/H-Beta
Reaction temperature, ◦
WHSV, h−1
C
400
2
425
2
450
2
400
2
425
2
450
2
Total pressure, MPa
Tetralin conversion, %
4
76.4
4
88.3
4
83.7
4
98.9
4
98.9
4
99.5
Liquid products, wt%
Nonaromatics (Nonaro.)
Benzene
Toluene
3.7
14.9
2.4
2.5
0.1
6.4
24.0
5.0
4.1
0.4
9.6
27.5
6.7
4.4
0.6
42.5
3.0
15.4
3.3
23.9
11.1
25.7
5.2
11.0
20.3
32.0
5.1
Ethylbenzene (EB)
ꢀ
xylenes
16.4
17.5
17.2
(para-xylene)
(meta-xylene)
(0.0)
(0.1)
(0.0)
9.7
(0.0)
(4.0)
(5.7)
(0.1)
(0.2)
(0.0)
9.7
(0.0)
(4.4)
(5.3)
(0.1)
(0.3)
(0.1)
7.1
(0.0)
(3.1)
(3.9)
(4.0)
(8.7)
(3.7)
6.8
(6.0)
(0.2)
(0.6)
(4.3)
(9.3)
(4.0)
5.3
(4.4)
(0.2)
(0.6)
(4.1)
(9.0)
(4.0)
4.3
(3.5)
(0.3)
(0.5)
(ortho-xylene)
ꢀ
C9 aromatics
(trimethylbenzenes)
(indane)
(other C9 aromatics)
Decalin
Tetralin
Naphthalene
0.0
23.6
11.0
22.7
2.3
0.0
11.7
10.8
20.3
3.1
0.0
16.3
8.3
15.2
2.5
0.1
1.1
0.2
10.1
0.2
1.1
0.0
1.0
0.2
8.5
0.5
0.9
0.0
0.5
0.7
6.4
1.4
1.0
ꢀ
(other C10 aromatics)
Methylnaphthalenes
ꢀ
(other C11 and C+ aromatics)
7.2
4.5
1.8
Total
100.0
100.0
100.0
100.0
100.0
100.0
ꢀ
(l-ring aromatics), wt%
54.2
17.3
95.5
16.6
62.3
29.3
94.0
27.6
59.1
34.8
95.2
33.1
55.5
34.7
53.3
18.5
73.7
54.3
55.6
30.2
85.7
69.5
58.5
40.7
BTX in liquid, wt%
Liquid yield, wt%
BTX yield, wt%
Fig. 10. Comparison of gas product distributions from tetralin hydrocracking over H-Beta and Ni(2)/H-Beta catalysts at (a) 425 ◦C and (b) 450 ◦C.

Y. Choi et al. / Applied Catalysis A: General 492 (2015) 140–150
149
Fig. 11. Comparison of liquid product distributions from tetralin hydrocracking over (a) H-Beta and (b) Ni(2)/H-Beta catalysts at 450 ◦C.
Table 5
Estimation of the theoretical BTX yield in tetralin hydrocracking reaction.
Hydrocracking feed
Scenarios of
Normalized B/T/X yield
at each scenario, wt%
Normalized B/T/X yield
applied to the B/T/X
hydrocracked products
based on C and H
balance only
distributions at 450 ◦
over Ni/H-Beta, wt%
C
(1)
(2)
57.3
67.6
57.3 × 0.29 = 16.6
67.6 × 0.46 = 31.1
(3)
77.9
77.9 × 0.25 = 19.5
Calculated B/T/X yield, wt%
67.6
67.2
Case-1: B/T/X = equimolar ratio
Case-2: B/T/X = 0.29/0.46/0.25 wt ratio
tetralin over decalins and thus tetralin cracking will be facilitated
over decalins cracking, which can lead to increased liquid product
yield as well as increased BTX yield at higher temperature on the
bifunctional Ni(2)/H-Beta catalyst, which is apparent from Table 4.
Over the bifunctional Ni(2)/H-Beta catalyst, the C1–C2 fragments
were formed in substantial quantities comparable to the C3–C4
fragments in the gas product indicating cracking on the metal sur-
face via hydrogenolysis (Fig. 10) [45].
The Ni(2)/H-Beta catalyst showed BTX yield as high as 40.7 wt%
at 450 ◦C in the tetralin HYC. However, it still produced a large
amount of light alkane products (11.0 wt%) with low liquid yield
(58.5 wt%). The high yield of BTX obtained at high temperatures
can be partly ascribed to the equilibrium shift toward tetralin at
high temperature. Here, the theoretical BTX and liquid yield can be
simply calculated with ideal scenarios ((1)–(3)) shown in Table 5.
The scenarios set forth for estimation are based on the assump-
tions of (1) complete tetralin conversion to benzene or toluene or
xylene and (2) the gaseous cracked products are simply assumed
to be saturated light alkanes of C2–C4, which is the case in a typical
hydrocracking, by taking into account of C and H balance between
hydrocracking feed and products without considering the crack-
ing/ring opening mechanisms of tetralin in detail. The normalized
B/T/X yield, which is the same as liquid yield in this calcula-
tion, should be 67.6 wt% or 67.2 wt% with the B/T/X distribution
of equimolar proportions or the same as the case at 450 ◦C over
Ni/H-Beta, respectively.
The BTX yield of 40.7 wt% obtained at 450 ◦C over Ni(2)/H-Beta
is still far below the theoretical BTX yield of 67.2–67.6 wt%. This
suggests that there is a large room of catalyst improvement in terms
of (1) the hydrogenation activity of metallic sites, (2) the acidity of
zeolite and (3) the balance between metallic and acidic sites, to
obtain the BTX yield close to the theoretical one at the reaction
temperature as low as possible.
4. Conclusions
Naphthalenes constitute a high fraction in the diesel boiling
point range by-products from oil refining and petrochemical plants.

150
Y. Choi et al. / Applied Catalysis A: General 492 (2015) 140–150
A two-step catalytic process consisting of selective hydrogena-
tion of naphthalenes to tetralins and subsequent hydrocracking
of tetralins was postulated and studied to produce light alkyl-
aromatics rich in BTX. For this purpose, the catalytic performances
of Mo2C-supported catalysts for the selective hydrogenation were
superior in terms of naphthalenes’ conversion and tetralins’ yield
as well as selectivity to the conventional metal-supported catalysts
such as Pt, Co, Ni and NiW supported on alumina. The hydrocrack-
ing of tetralin was demonstrated to produce light alkyl-aromatics
rich in BTX over monofunctional H-Beta and bifunctional Ni/H-Beta
catalysts. For the high per pass yield of BTX in the hydrocrack-
ing of tetralin in which chemical equilibrium limits conversion
and product selectivity, a bifunctional catalyst containing metallic
component was desirable and out-performed over monofunctional
one. The Ni/H-Beta showed the BTX yield as high as 40.7 wt% at
the tetralin conversion of 99.5% at 450 ◦C. However, the BTX yield
should be much improved by properly controlling (1) the hydro-
genation power of metallic sites (suppress the HYD activity), (2)
the acidity of H-Beta for cracking and (3) their balance in the
bifunctional catalyst, which will be subjected to future study.
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