A comparative study of ring opening of naphthalene, tetralin and decalin over Mo2C/HY and Pd/HY catalysts

Article abstract of DOI:10.1016/j.apcata.2011.06.013

The conversion of naphthalene, tetralin or decalin to ring-opened products over Mo₂C/HY, Mg- or K-Mo₂C/HY, and a commercial Pd/HY catalyst, is reported. Conversion of all reactants at 300 °C and 3 MPa was higher over the Pd/HY catalyst than the Mo₂C/HY catalysts. Tetralin was the least reactive among the three model compounds over both Pd/HY and Mo₂C/HY. With decalin as reactant, higher selectivity to C ₁₀ products was obtained over the Mo₂C/HY catalysts compared to the Pd/HY. The addition of K or Mg to Mo₂C/HY improved the Mo₂C dispersion while K also moderated the catalyst Bronsted acidity. The conversion of all three reactants was reduced by the addition of Mg or K to the Mo₂C/HY, as was the carbon deposition. For all the studied catalysts, carbon deposition was lowest after reaction with decalin compared to naphthalene or tetralin. These results suggest that the deposited carbon has as its precursor, species that are derived from naphthalene or tetralin, rather than decalin, and the coke species are generated through bimolecular reactions on acid sites. Consequently, the catalysts with higher hydrogenation activity (Pd/HY and 1% K-7% Mo₂C/HY) had lower deactivation rates.

Full text of DOI:10.1016/j.apcata.2011.06.013

Applied Catalysis A: General 403 (2011) 36–47
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Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
A comparative study of ring opening of naphthalene, tetralin and decalin over
Mo2C/HY and Pd/HY catalysts
Shahrzad Jooya Ardakani, Kevin J. Smith∗
Department of Chemical and Biological Engineering, University of British Columbia, 2360 East Mall, Vancouver, BC V6T 1Z3, Canada
a r t i c l e i n f o
a b s t r a c t
Article history:
The conversion of naphthalene, tetralin or decalin to ring-opened products over Mo2C/HY, Mg- or K-
Mo2C/HY, and a commercial Pd/HY catalyst, is reported. Conversion of all reactants at 300 ◦C and 3 MPa
was higher over the Pd/HY catalyst than the Mo2C/HY catalysts. Tetralin was the least reactive among
the three model compounds over both Pd/HY and Mo2C/HY. With decalin as reactant, higher selectivity
to C10 products was obtained over the Mo2C/HY catalysts compared to the Pd/HY. The addition of K or
Mg to Mo2C/HY improved the Mo2C dispersion while K also moderated the catalyst Bronsted acidity.
The conversion of all three reactants was reduced by the addition of Mg or K to the Mo2C/HY, as was
the carbon deposition. For all the studied catalysts, carbon deposition was lowest after reaction with
decalin compared to naphthalene or tetralin. These results suggest that the deposited carbon has as
its precursor, species that are derived from naphthalene or tetralin, rather than decalin, and the coke
species are generated through bimolecular reactions on acid sites. Consequently, the catalysts with higher
hydrogenation activity (Pd/HY and 1% K–7% Mo2C/HY) had lower deactivation rates.
Received 27 February 2011
Received in revised form 2 June 2011
Accepted 11 June 2011
Available online 17 June 2011
Keywords:
Ring-opening
Hydrogenation
Bifunctional catalyst
Molybdenum carbide
Palladium
HY zeolite
Naphthalene
Tetralin
© 2011 Elsevier B.V. All rights reserved.
Decalin
1. Introduction
The ideal process to address SCO quality issues, is selective
ring opening (RO) of cycloparaffins that reduces the number of
Bitumen-derived synthetic crude oils (SCO) have high aromatic-
ity and cylcoparaffinic content that concerns refiners as tighter
specifications on transportation fuels are promulgated. Hydro-
genation and hydrocracking are two commercially proven refining
technologies that can address the quality issues associated with
the highly aromatic SCO [1]. Conventional hydrotreating cata-
lysts help saturate aromatic rings to naphthenes (cycloparaffins or
cycloalkanes) [2,3]. However, the increase in cetane number via
hydrogenation of aromatics is insufficient to significantly increase
the quality of middle distillates because the cetane numbers of indi-
vidual cycloalkanes, such as decalin (cetane number of 35), are low.
Hydrocracking is a process designed to produce lighter and higher
quality naphtha and middle distillate fuel blending stocks by sat-
urating aromatic rings and reducing the number of ring structures
via carbon–carbon bond scission in the presence of hydrogen [4,5].
However, because of extensive overcracking there is a limited net
gain in production of desirable paraffins via this route, and the
improved distillate fuel quality results primarily from a combina-
tion of hydrogenation of aromatics and a concentration of paraffins
in a reduced volume of distillate product.
ring structures while retaining the carbon number of the reac-
tant molecule. RO involves bifunctional catalysts, with both metal
and acid sites, working at high hydrogen pressure and high tem-
perature. The acidic sites catalyze cracking, isomerization and
dealkylation, while the metal sites promote dehydrogenation,
hydrogenation, hydrogenolysis and isomerization [6]. Noble metals
supported on acidic oxides are the most preferred catalysts for RO
[7–12], but these catalysts are costly and are sensitive to poisoning
by sulfur compounds present in petroleum feedstocks.
In previous work, metal carbides and oxycarbides, supported
on HY zeolites, were investigated as alternative catalysts for RO
[13,14]. High RO activity after 1 h time-on-stream (TOS) (92% naph-
thalene conversion and 32% RO selectivity) was obtained over a
20 wt% of Mo2C/HY catalyst, with moderate HY acidity, operated at
300 ◦C, 3 MPa, and H2/naphthalene ratio of 30. Although the catalyst
was shown to have good thio-tolerance, the catalyst deactivated
because of carbon deposition on the acidic sites of the zeolite. In
subsequent work, Mg or K added to a 20 wt% Mo2C/HY catalyst
was shown [15] to increase the hydrogenation of naphthalene and
coke-precursors, whereas ring opening selectivity was reduced,
compared to the Mo2C/HY catalyst.
In the present work, Mg or K was added to Mo2C/HY catalysts
to better understand the effect of Mo2C dispersion and catalyst
acidity on the ring opening of naphthalene, tetralin and decalin.
∗
Corresponding author. Tel.: +1 604 822 3601, fax: +1 604 822 6003.
E-mail addresses: kjs@interchange.ubc.ca, kjs@chbe.ubc.ca (K.J. Smith).
0926-860X/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2011.06.013

S.J. Ardakani, K.J. Smith / Applied Catalysis A: General 403 (2011) 36–47
37
The effect of K or Mg on the deactivation of the K–Mo2C/HY
and Mg–Mo2C/HY catalysts for each of the reactants, has also
been examined. Although previous results [13,14] suggested that
Mo2C/HY catalysts were promising, no direct comparison with a
conventional, precious metal RO catalyst was made. Consequently,
in the present study, the ring opening selectivity and the rate of
deactivation of the Mo2C/HY catalysts is compared to a commercial
Pd/HY catalyst for each of the reactants.
Bronsted acid sites. n-PA pulsed adsorption and TPD of n-PA were
performed using a Micromeritics Autochem II 2920 unit, equipped
with a thermal conductivity detector. Approximately 40 mg of pas-
sivated catalyst was pretreated in He (30 ml (STP)/min) at 120 ◦C
for 1 h to remove water, followed by a 1 h treatment in H2 (30 ml
(STP)/min) at 400 ◦C to activate the passivated Mo2C, and finally a
2 h flush in He (30 ml (STP)/min) at 500 ◦C to remove adsorbed H2.
While under He flow, the catalyst was cooled to 120 ◦C and a flow
of He (30 ml (STP)/min) saturated at room temperature with n-PA
(99+%, Aldrich), was injected into the He flow in 0.5 ml pulses. The
pulses of n-PA were injected repeatedly until no further adsorption
was observed. Following the pulsed adsorption experiments, the
system was purged for 1 h in a He flow (30 ml (STP)/min) to remove
residual amine. Subsequently, TPD of n-PA from 120 ◦C to 700 ◦C
was performed at a heating rate of 5 ◦C/min. Blank experiments
were also performed to eliminate effects of n-PA physisorption
on the reactor wall or quartz wool placed under the catalyst.
The detailed interpretation of the n-PA adsorption/desorption data
have been described previously [14].
2. Experimental
2.1. Catalyst preparation
The preparation of catalysts with 7 and 20 wt% Mo2C supported
on HY zeolite has been reported previously [13,14]. The same
catalysts doped with 2 wt% Mg or 1 wt% K, were prepared by co-
impregnation of the zeolite (ZeolystTM CBV720, SiO2/Al2O3 = 30)
using a quantified aqueous solution of ammonium heptamolybdate
tetrahydrate (MoO3 81.0–83.0%, Sigma) mixed with magnesium
nitrate hexahydrate (99%, Sigma) or potassium nitrate (99.97%, BDH
Chemicals). After aging at 70 ◦C for 2 h, the impregnated support
was dried at 120 ◦C for 12 h and calcined at 500 ◦C for 4 h. Car-
burization of the calcined catalyst precursor was done in a quartz
U-tube reactor (i.d. = 7 mm) by temperature programmed reaction
in a 100 ml (STP)/min of 20% CH4/80% H2 (UHP) and a ramp rate of
5 ◦C/min up to 700 ◦C. The catalyst was held at 700 ◦C for 4 h and
then the gas was switched to H2 (UHP) to remove excess carbon by
holding at 700 ◦C for a further 2 h before cooling to room tempera-
ture. Finally, the catalysts were passivated at room temperature in
a 1% O2 in He flow (150 ml (STP)/min) before exposure to air. The
Pd/HY commercial catalyst was used as received.
2.3. Catalyst activity
Reactivity and selectivity of each of the catalysts was deter-
mined using
a stainless steel fixed-bed reactor (i.d. = 9 mm)
operated at 300 ◦C and a total pressure of 3.0 MPa with naphtha-
lene, tetralin or decalin as the reactant. About 0.5 g of the catalyst
(dp < 0.7 mm) was loaded (without dilution with inert material) into
the isothermal section of the reactor with either end of the bed
packed with glass beads (1 mm diameter). The passivated catalyst
was activated in a 60 ml (STP)/min H2 flow at 450 ◦C for 1 h. After
cooling to the reaction temperature, a 5 wt% solution of naphtha-
lene (99%, Acros Organics), tetralin (99%, Sigma Aldrich) or decalin
(anhydrous, 99+%, mixture of cis and trans, Sigma Aldrich) in hep-
tane (Fisher Scientific, HPLC grade) was pumped, using a Gilson
Model 0154E metering pump, at 0.16 ml/min into a 19 ml (STP)/min
of H2, before entering the reactor. Each catalyst was tested for
a period of 5 or 10 h and liquid products of the reaction were
collected in a condenser placed at the reactor exit. A Shimadzu
QP-2010S GC/MS equipped with a Restek RTX5 30 m × 0.25 mm
capillary column was used to identify the product selectivities.
The reaction products were grouped as hydrogenated or dehydro-
genated products (naphthalene, tetralin and decalin), ring opening
(RO) and polyaromatics (Poly). RO products, mainly alkylcyclohex-
anes, alkylbenzenes and alkylindenes were grouped based on their
carbon numbers as C7–C10 products. Poly products were aromatics
and naphthenes with more than 10 carbon atoms, mainly alkylte-
tralins. Periodic analysis of the gas phase effluent from the reactor
showed no significant quantities of cracked gas phase products. The
catalyst tests were randomly repeated to confirm the experimen-
tal reproducibility of the data and in each of the experiments the
carbon balance was better than 95%. Both diagnostic tests and cal-
culation were used to confirm that at the chosen conditions, the
catalyst activity data were free of both internal and external heat
and mass transfer effects.
2.2. Catalyst characterization
X-ray diffraction (XRD) was performed on the passivated
Mo2C/HY catalysts using a Siemens D500 diffractometer with a Cu
˚
K␣ X-ray source of wavelength 1.54 A. The analysis was performed
using a scan range of 10–90◦ with a step size of 0.04◦ and step time
of 2 s. Crystallite size (dc) estimates were made using the Scherrer
equation, as described previously [13,14].
N2 adsorption–desorption isotherms were measured at 77 K
using a Micromeritics ASAP 2020 Accelerated Surface Area and
Porosimetry analyzer, and used to determine the total BET surface
area, pore volume and average pore width of the catalysts. Approx-
imately 0.15 g of each catalyst was loaded in the sample tube for
initial degassing. The sample was evacuated at a rate of 1.33 kPa/s
and temperature ramp rate of 10 ◦C/min until the vacuum reached
40 Pa. The temperature was then held at 250 ◦C for 600 min. After
degassing, the sample was re-weighed and transferred to the anal-
ysis section for the N2 isotherm measurement.
X-ray photoelectron spectroscopy (XPS) analysis was per-
formed using an Axis-165 spectrophotometer (Kratos Analytical). A
monochromated Al K␣ (hꢀ = 1486.6 eV) source was used at a power
of 210 W and the spectra were collected in FAT mode for binding
energy ranging from 1100 to 0 eV with a pass energy of 160 eV and
step size of 0.35 eV. The catalysts were analyzed after passivation
without further treatment.
n-Propylamine (n-PA) was used to titrate the type, strength and
the quantity of acid sites on the Mo2C/HY and Pd/HY catalysts.
The n-propylammonium ion, formed by adsorption of the amine
on Bronsted acid sites, decomposes upon heating via the Hoff-
man elimination reaction, and propene and ammonia are produced.
Thus, n-PA differentiates between Lewis and Bronsted acid sites,
because the amine adsorbed on Lewis acid sites desorbs without
decomposition at low temperatures (before 300 ◦C) and the peaks
at higher temperature (above 300 ◦C) are due to n-PA cracking on
In order to study catalyst deactivation, the used catalysts from
each reaction test were characterized by N2 adsorption–desorption
at 77 K as described previously for the un-used catalysts. In addi-
tion, the carbon content of the used catalysts was determined using
a Perkin Elmer 2400 Series II CHNS/O analyzer.
3. Results
3.1. Catalyst characterization
The powder X-ray diffractograms of the 20% Mo2C/HY catalysts,
illustrated in Fig. 1, and the 7% Mo2C/HY catalysts illustrated in

38
S.J. Ardakani, K.J. Smith / Applied Catalysis A: General 403 (2011) 36–47
16
•
•
•
• Zeolite ∗ Mo2C
•
•
•
14
12
10
8
•
•
•
•
•
•
•
20% Mo2C/HY
∗
∗
∗
∗
∗
∗
∗
Zeolite HY
•
•
•
•
•
•
•
•
•
•
2%Mg-7%Mo2C/HY
2% Mg-20% Mo2C/HY
∗
∗
∗
∗
∗
∗
∗
2%Mg-20%Mo2C/HY
6
•
1% K-20% Mo2C/HY
∗
∗
∗
∗
∗∗
∗
4
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
0.0
0.2
0.4
0.6
0.8
1.0
2 Theta
Relative pressure (P/P0)
Fig. 1. XRD of 20% Mo2C/HY, 1% K–20% Mo2C/HY and 2% Mg–20% Mo2C/HY catalysts.
Fig. 3. Nitrogen adsorption–desorption isotherm for zeolite HY, 2% Mg–7% Mo2C/HY
and 2% Mg–20% Mo2C/HY catalysts measured at 77 K.
Fig. 2, confirmed the presence of the Mo2C phase. In the case of
the 7% Mo2C/HY catalyst, the Mo2C peak intensity was near the
diffractometer’s detection limit. The X-ray data also show that the
crystallinity of the HY zeolite was maintained after preparation of
the Mg- or K-doped Mo2C/HY, indicating no obvious framework
collapse associated with the high temperature preparation proce-
dure.
The physicochemical properties of the catalysts are summarized
in Table 1, with the HY zeolite included for reference. Increased
Mo2C loading significantly reduced the surface area, pore volume
as well as the micropore area and micropore volume of the cata-
lysts compared to the HY support. Surface areas and pore volumes
were further suppressed upon addition of 2% Mg or 1% K. However,
changes in micropore area and micropore volume of the Mo2C/HY
catalysts upon doping with 2% Mg or 1% K were small. The zeolite
HY crystallite size (Table 1), calculated from the strongest reflec-
tion of the HY zeolite at 2ꢁ = 16◦, decreased upon addition of Mo2C,
suggesting that the presence of Mo2C had some influence on the
long-range order of the HY crystallites. Although the effect of Mg
addition on the HY crystallite size was small, doping of the Mo2C/HY
catalyst with K decreased the HY crystallite size significantly. The
effect of Mg and K addition on the Mo2C crystallite size in the case
of 7% Mo2C/HY was not measurable by XRD. However, the addition
of both Mg and K decreased the Mo2C crystallite size of the 20%
Mo2C/HY catalyst, showing improved dispersion of Mo2C on these
catalysts [15].
The XPS data of Table 1 show no measurable change in the
Mo/(Si + Al) atom ratio upon the addition of Mg or K to the 7%
Mo2C/HY catalyst, however, this ratio increased upon addition of
K to the 20% Mo2C/HY catalyst and decreased upon addition of the
Mg, despite the XRD data described above, that showed improved
Mo2C dispersion with K or Mg addition to the Mo2C/HY catalyst.
The N2 adsorption–desorption isotherm of the 2% Mg–20%
Mo2C/HY catalyst is shown in Fig. 3 and is compared to that of cal-
cined HY and the 2% Mg–7% Mo2C/HY catalyst. Fig. 3 shows that 2%
Mg–20% Mo2C/HY had reduced N2 uptake and hence BET surface
area and total pore volume compared to the 2% Mg–7% Mo2C/HY.
Of note is the reduced hysteresis observed for the 2% Mg–20%
Mo2C/HY compared to 2% Mg–7% Mo2C/HY that suggests that the
Mo2C is located in the mesopores of the HY. The HY mesoporosity
is presumably a consequence of agglomeration of HY microcrys-
tallites. The pore size distribution data of Fig. 4 show the reduced
•
• Zeolite ∗ Mo2C
•
•
˚
volume associated with the mesopores in the range 30–50 A for
•
•
•
the 1% K–7% Mo2C/HY and the 2% Mg–7% Mo2C/HY compared to
the 7% Mo2C/HY and the HY alone. Fig. 5 shows the reduced meso-
pore volume of the 20% Mo2C/HY compared to the 7% Mo2C/HY
(Fig. 4) which is further reduced by doping, especially with 2% Mg.
Fig. 6 compares the micropore size distribution of the 2% Mg–20%
Mo2C/HY catalyst with the HY zeolite. Clearly, there was no signifi-
cant change in the zeolite micropore size distribution upon doping
with Mg, although there was a small reduction in the micropore
volume as already noted (Table 1). Since the Mo2C crystals are too
large (Table 1) to enter the micropores of the zeolite, the reduction
in micropore volume presumably reflects blockage of the zeolite
micropore mouth by Mo2C. Together these data suggest that the
Mo2C and MgO/K2O (the metal oxides present after calcination and
reduction) are located throughout the zeolite mesopores and block
some of the zeolite micropores.
•
•
•
•
•
•
•
7% Mo2C/HY
∗
∗
∗
∗
∗
∗
•
•
•
•
•
•
•
•
2% Mg-7% Mo2C/HY
∗
∗
∗
∗
∗
∗
•
•
•
1% K-7% Mo2C/HY
∗
∗
∗
∗
∗
∗
∗
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
The n-propylamine temperature programmed desorption (n-
PA TPD) profile for the HY zeolite, the Mo2C/HY and the Pd/HY
catalysts were used to quantify the total, Lewis and Bronsted acid-
2 Theta
Fig. 2. XRD of 7% Mo2C/HY, 1% K–7% Mo2C/HY and 2% Mg–7% Mo2C/HY catalysts.

S.J. Ardakani, K.J. Smith / Applied Catalysis A: General 403 (2011) 36–47
39
Table 1
Physicochemical properties of Mo2C/HY and Pd/HY catalysts.
a
Catalyst
SBET (m2/g)
SMicro (m2/g)
VP (cm3/g)
VP,
(cm3/g)
dP (nm)
XRD particle size (nm)
XPS
Micro
HY
Mo2C
Mo/(Si + Al)
HY
783
666
522
627
641
462
444
589
543
487
385
469
484
358
337
418
0.49
0.45
0.36
0.41
0.41
0.30
0.32
0.46
0.25
0.23
0.18
0.22
0.23
0.17
0.16
0.19
2.52
2.67
2.76
2.63
2.58
2.60
2.84
3.09
–
54.3
47
53.1
38.8
47.3
41.7
–
–
–
22
–
–
7% Mo2C/HY
0.02
0.08
0.02
0.02
0.05
0.10
-
20% Mo2C/HY
2% Mg–7% Mo2C/HY
1% K–7% Mo2C/HY
2% Mg–20% Mo2C/HY
1% K–20% Mo2C/HY
Pd/HY
–
10
14
–
a
Average pore diameter.
0.012
0.010
0.008
0.006
0.004
0.002
0.000
0
50
100 0
50
100 0
50
100
0
50
100
Pore size, Å
Pore size, Å
Pore size, Å
Pore size, Å
Fig. 4. Pore size distribution of zeolite HY, 7% Mo2C/HY, 1% K–7% Mo2C/HY and 2% Mg–7% Mo2C/HY catalysts measured at 77 K.
0.012
0.010
0.008
0.006
0.004
0.002
0.000
0
50
100 0
50
100 0
50
100
0
50
100
Pore size, Å
Pore size, Å
Pore size, Å
Pore size, Å
Fig. 5. Pore size distribution of zeolite HY, 20% Mo2C/HY, 1% K–20% Mo2C/HY and 2% Mg–20% Mo2C/HY catalysts measured at 77 K.

40
S.J. Ardakani, K.J. Smith / Applied Catalysis A: General 403 (2011) 36–47
3.2. Catalyst activity
0.20
0.18
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
3.2.1. Comparison of Mo2C/HY and Pd/HY catalysts
Table 3 shows the conversion of naphthalene, tetralin and
decalin and the product selectivities after 2 h time-on-stream (TOS)
over the 7% Mo2C/HY, 20% Mo2C/HY and Pd/HY catalysts. A sum-
mary comparing the conversion and RO selectivity of these catalysts
with all three reactants is presented in Fig. 7. The naphthalene con-
version data show that the 20% Mo2C/HY had higher activity than
the 7% Mo2C/HY. Although selectivity toward the hydrogenated
products (tetralin and decalin) was almost the same for these two
catalysts (Table 3), the RO selectivity was slightly higher for the 20%
Mo2C/HY compared to the 7% Mo2C/HY catalyst. The Pd/HY had
higher conversion of naphthalene and RO selectivity than both the
Mo2C/HY catalysts. Table 3 shows that, compared to both Mo2C/HY
catalysts, the Pd/HY catalyst had a lower tetralin selectivity and
higher decalin selectivity and a significantly higher RO selectivity
(52.5% after 2 h TOS).
Similar trends were observed with tetralin as reactant. The 20%
Mo2C/HY had higher conversion than the 7% Mo2C/HY whereas
the Pd/HY had the highest tetralin conversion. The RO selectivity
followed the same trend with a RO selectivity of 77.7% after 2 h
TOS over the Pd/HY. In addition, there was a decreased selectiv-
ity toward naphthalene (dehydrogenated product) and increased
selectivity toward decalin (hydrogenated product) over the Pd/HY
when compared to the Mo2C/HY catalysts. There was a high selec-
tivity toward polymerization products over the Mo2C/HY catalysts
compared to the Pd/HY catalyst. Although the tetralin conversion
over the Mo2C/HY and Pd/HY catalysts was lower than the naphtha-
lene conversion, the RO yields were higher with tetralin as reactant
compared to naphthalene.
HY
2% Mg-20% Mo2C/HY
5
6
7
8
9
10
11
12
Pore width (Ao)
Fig. 6. Micropore size distribution of zeolite HY and 2% Mg–20% Mo2C/HY catalysts.
Table 2
Acidity of the HY zeolite support, HY supported Mo2C and Pd/HY catalysts.
Catalyst
Acidity (mmol/g)a
Lewis
Bronsted
Total
HY
0.42 (24)
0.40 (30)
0.48 (37)
0.73 (54)
0.14 (14)
0.09 (9)
1.38 (76)
0.91 (70)
0.81 (63)
0.61 (46)
0.83 (86)
0.93 (91)
0.56 (82)
1.27 (65)
1.80
1.31
1.29
1.34
0.97
1.02
0.68
1.95
7% Mo2C/HY
1% K–7% Mo2C/HY
2% Mg–7% Mo2C/HY
20% Mo2C/HY
2% Mg–20% Mo2C/HY
1% K–20% Mo2C/HY
Pd/HY
The Pd/HY catalyst was the most active catalyst with decalin
as reactant, with 92% conversion after 2 h TOS. There was
no selectivity toward dehydrogenated or polymerized products
over the Pd/HY catalyst and similar results were obtained over
the Mo2C/HY catalysts. Interestingly, the 20% Mo2C/HY showed
lower conversion than the 7% Mo2C/HY for the ring opening of
decalin.
0.12 (18)
0.68 (35)
a
The numbers in brackets are the percentage of Lewis and Bronsted acid sites.
ity, as summarized in Table 2. Comparing total acidities shows
that increased Mo2C loading decreased the total acidity of the
Mo2C/HY catalysts. Furthermore, with increased Mo2C loading the
percent of Lewis acid sites decreased marginally while the per-
cent of Bronsted acid sites increased. Although doping of the 7%
Mo2C/HY with 2% Mg or 1% K did not change the total acidity of
the catalyst, it reduced the Bronsted acidity of the catalyst notice-
ably in favor of increasing Lewis acidity. In the case of the 20%
Mo2C/HY, doping with 2% Mg had negligible effect on the total
acidity but doping with 1% K reduced the total acidity and also the
Bronsted acidity. The total acidity and the Bronsted acidity of the
commercial Pd/HY catalyst were higher than any of the Mo2C/HY
catalysts.
Fig. 7 also shows that with naphthalene as reactant, the loss in
conversion with TOS was small for the Pd/HY catalyst, however the
ROP selectivity decreased significantly with TOS. The deactivation
of all the catalysts was lowest with decalin as reactant, compared
to when unsaturated polyaromatics (naphthalene or tetralin) were
used. The selectivity to Poly products followed the same trend,
with the lowest selectivity occurring with decalin as reactant for
all catalysts (Table 3).
The ring opening product carbon number distribution over
the Mo2C/HY and Pd/HY catalysts with naphthalene, tetralin and
decalin as reactants is illustrated in Fig. 8. The ring opening prod-
ucts included C10 species resulting from ring opening without
further cracking or hydrogenolysis of C–C bonds, whereas the C7–C9
Table 3
Comparative activities of 7% Mo2C/HY, 20% Mo2C/HY and Pd/HY catalysts using different reactants.
Experiment
Reactant
Catalyst
Conv. (%)
Selec. (%)
Naph.
RO Yield (%)
Tet.
Dec.
RO
9.2
13.1
52.5
57.5
67.6
77.7
99.8
Poly
E1
E2
E3
E4
E5
E6
E7
E8
E9
Naphthalene
Naphthalene
Naphthalene
Tetralin
Tetralin
Tetralin
Decalin
Decalin
Decalin
7% Mo2C/HY
20% Mo2C/HY
Pd/HY
7% Mo2C/HY
20% Mo2C/HY
Pd/HY
7% Mo2C/HY
20% Mo2C/HY
Pd/HY
77
95
98
25
35
71
72
61
92
–
–
–
8.9
8.8
1.0
0
0
0
81.7
81.4
29.5
–
–
–
0.1
0
0
0.5
2.4
17.6
14.8
13.1
20.7
–
8.6
3.2
0.5
18.8
10.4
0.5
0.1
0
7.1
12.4
51.5
14.4
23.7
55.2
71.9
61.0
92.0
–
–
100
100
0
Reaction conditions: time on stream: 2 h; catalyst weight: 500 mg; T: 300 ◦C; P: 3 MPa; WHSV (H2 plus naphthalene, tetralin or decalin): 1 h−1
.

S.J. Ardakani, K.J. Smith / Applied Catalysis A: General 403 (2011) 36–47
41
NAPHTHALENE
TETRALIN
DECALIN
100
80
60
40
20
100
80
60
40
20
100
80
60
40
20
0
0
0
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5
100
100
100
95
90
85
80
75
70
80
60
40
20
0
80
60
40
20
0
7% Mo2C/HY
20% Mo2C/HY
Pd/HY
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5
TOS, h
TOS, h
TOS, h
Fig. 7. Conversion and ring-opening product (ROP) selectivities as a function of time-on-stream (TOS) over 7% Mo2C/HY, 20% Mo2C/HY and Pd/HY catalysts with naphthalene,
tetralin and decalin as model reactants. The reaction condition for all the experiments—T: 300 ◦C; P: 3 MPa; WHSV (H2 plus naphthalene, tetralin or decalin): 1 h−1
.
species arise from reactants that have undergone ring opening and
cracking or hydrogenolysis. Fig. 8 shows that on Pd/HY, most of the
ring opened products were C10 when naphthalene was the reac-
tant, but the selectivity to C7–C9 species increased with tetralin
and decalin as reactant. In the case of the 7% Mo2C/HY and the 20%
Mo2C/HY catalysts (Fig. 8), very small amounts of C10 species were
produced from naphthalene. However, C10 species were produced
selectively with tetralin and decalin as reactant. Of particular note
is the much higher selectivity to C10 species obtained with decalin
as reactant over the Mo2C/HY catalysts, compared to the Pd/HY
catalyst.
three reactants. Furthermore, the 1% K–7% Mo2C/HY showed higher
conversion and RO selectivity compared to the 2% Mg–7% Mo2C/HY.
The lower activity of the 7% Mo2C/HY catalyst upon doping is most
obvious in the conversion of tetralin and decalin. The highest yield
to RO products was obtained with decalin as reactant, although it
decreased dramatically upon adding 2% Mg or 1% K to the 7% Mo2C.
Of note is the significantly reduced deactivation rate for the 1% K–7%
Mo2C/HY catalyst compared to the un-doped catalyst, especially
with decalin as reactant (Fig. 9). The 1% K–7% Mo2C/HY catalyst also
had much lower selectivity to ploymerization products (Table 4)
than the 2% Mg–7% Mo2C/HY and the 7% Mo2C/HY catalysts, and
this trend is likely a consequence of the reduced Bronsted acidity
of the K-doped catalyst (Table 2).
3.2.2. Effect of K and Mg doping of Mo2C/HY catalysts
The comparison of activity and RO selectivity of the un-doped
and 2% Mg or 1% K doped 20% Mo2C/HY catalysts is presented
in Fig. 10 and the conversions and selectivities toward all prod-
ucts after 2 h TOS are given in Table 5. Similar to the 7% Mo2C/HY,
doping the 20% Mo2C/HY with 2% Mg or 1% K decreased the conver-
sion of naphthalene and tetralin whereas the conversion of decalin
Fig. 9 summarizes the reactivity and selectivity of the un-doped
and 2% Mg or 1% K doped 7% Mo2C/HY catalyst with naphtha-
lene, tetralin and decalin as reactants. Table 4 reports the activity
and selectivity of the same catalysts after 2 h TOS. Doping the 7%
Mo2C/HY catalyst with 1% K or 2% Mg decreased the activity (con-
version) of the catalyst compared to the un-doped catalyst for all
Table 4
Catalytic activity of 7% Mo2C/HY, 1% K–7% Mo2C/HY and 2% Mg–7% Mo2C/HY using different reactants.
Experiment
Reactant
Catalyst
Conv. (%)
Selec. (%)
Naph.
RO yield (%)
Tet.
Dec.
RO
9.2
12.1
8.9
57.5
66.8
58.4
99.8
99.4
99.7
Poly
E10
E11
E12
E13
E14
E15
E16
E17
E18
Naphthalene
Naphthalene
Naphthalene
Tetralin
Tetralin
Tetralin
Decalin
Decalin
Decalin
7% Mo2C/HY
77
67
57
25
13
9
72
32
28
–
–
–
8.9
12.0
3.1
0
81.7
84.2
83.1
–
–
–
0.1
0.4
0
0.5
0.8
0.2
14.8
11.8
20.8
–
8.6
2.9
7.8
18.8
9.5
17.7
0.1
7.1
8.1
5.1
14.4
8.7
5.3
71.9
31.8
27.9
1% K–7% Mo2C/HY
2% Mg–7% Mo2C/HY
7% Mo2C/HY
1% K–7% Mo2C/HY
2% Mg–7% Mo2C/HY
7% Mo2C/HY
1% K–7% Mo2C/HY
2% Mg-7% Mo2C/HY
0
0
–
–
0.2
0.3
Reaction conditions: time on stream: 2 h; catalyst weight: 500 mg; T: 300 ◦C; P: 3 MPa; WHSV (H2 plus naphthalene, tetralin or decalin): 1 h−1
.

42
S.J. Ardakani, K.J. Smith / Applied Catalysis A: General 403 (2011) 36–47
20%Mo C/HY
2
7%Mo C/HY
50
40
30
20
10
0
2
50
40
30
20
10
0
Naphthalene
C
C
C
C
7
Naphthalene
C
C
C
C
7
8
8
9
9
10
10
1
2
2
2
3
3
4
4
4
5
5
5
1
2
2
2
3
4
4
5
5
5
50
40
30
20
10
0
50
40
30
20
10
0
Tetralin
Tetralin
1
1
3
100
80
60
40
20
0
100
80
60
40
20
0
Decalin
Decalin
1
3
1
3
4
TOS, h
TOS, h
Pd/HY
50
40
30
20
10
0
Naphthalene
C
7
C
C
C
8
9
10
1
2
2
2
3
4
4
4
5
5
5
50
40
30
20
10
0
Tetralin
1
3
100
80
60
40
20
0
Decalin
1
3
TOS, h
Fig. 8. Ring opening product (ROP) carbon number selectivity as a function of time-on-stream (TOS) over the 7% Mo2C/HY, 20% Mo2C/HY and Pd/HY catalysts with naphthalene,
tetralin and decalin as model reactants. The reaction condition for all the experiments—T: 300 ◦C; P: 3 MPa; WHSV (H2 plus naphthalene, tetralin or decalin): 1 h−1
.
was negligible. Unlike the case of 7% Mo2C/HY, the activity of 2%
Mg–20% Mo2C/HY was higher than the 1% K–20% Mo2C/HY with
naphthalene and tetralin as reactants.
Figs. 11 and 12 show the carbon number distribution of ring
opened products obtained over the doped 7% Mo2C/HY and 20%
Mo2C/HY catalysts. The trends observed for all the doped-Mo2C/HY
catalysts were very similar to those discussed for the undoped-
Mo2C/HY catalyst, wherein with decalin as reactant, a very high RO
selectivity to C10 products was obtained.
3.3. Catalyst deactivation
The physical properties of all the catalysts after 5 h TOS reaction
with naphthalene, tetralin and decalin are summarized in Table 6.
The used catalysts all showed some loss in surface area and sig-
nificant carbon deposition after reaction, with each of the three
reactants. However, the loss in surface area and the extent of carbon
deposition was greatest after reaction with naphthalene compared
to decalin and tetralin.
Table 5
Catalytic activity of 20% Mo2C/HY, 1% K–20% Mo2C/HY and 2% Mg–20% Mo2C/HY using different reactants.
Experiment
Reactant
Catalyst
Conv. (%)
Selec. (%)
Naph.
RO yield (%)
Tet.
Dec.
RO
13.1
4.6
5.6
67.6
76.9
58.0
100
96.4
100
Poly
E19
E20
E21
E22
E23
E24
E25
E26
E27
Naphthalene
Naphthalene
Naphthalene
Tetralin
Tetralin
Tetralin
Decalin
Decalin
Decalin
20% Mo2C/HY
95
62
81
35
10
17
61
2
–
–
–
8.8
1.7
14.7
0
81.4
91.8
90.0
–
–
–
0
0
0
2.4
3.1
1.3
13.1
18.9
15.6
–
3.2
0.6
3.2
10.4
2.5
11.8
0
12.4
2.9
4.5
23.7
7.7
9.9
61
1% K–20% Mo2C/HY
2% Mg–20% Mo2C/HY
20% Mo2C/HY
1% K–20% Mo2C/HY
2% Mg–20% Mo2C/HY
20% Mo2C/HY
1% K–20% Mo2C/HY
2% Mg–20% Mo2C/HY
0
0
–
–
3.6
0
1.9
2.0
2
Reaction conditions: time on stream: 2 h; catalyst weight: 500 mg; T: 300 ◦C; P: 3 MPa; WHSV (H2 plus naphthalene, tetralin or decalin): 1 h−1
.

S.J. Ardakani, K.J. Smith / Applied Catalysis A: General 403 (2011) 36–47
43
NAPHTHALENE
TETRALIN
DECALIN
100
80
60
40
20
0
100
80
60
40
20
0
100
80
60
40
20
0
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5
100
80
60
40
20
0
100
80
60
40
20
0
100
95
90
85
80
75
70
7% Mo2C/HY
1% K-7% Mo2C/HY
2% Mg-7% Mo2C/HY
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5
TOS, h
TOS, h
TOS, h
Fig. 9. Conversion and ring-opening product (ROP) selectivities as a function of time-on-stream (TOS) over 7% Mo2C/HY, 1% K–7% Mo2C/HY and 2% Mg–7% Mo2C/HY catalysts
with naphthalene, tetralin and decalin as model reactants. The reaction condition for all the experiments—T: 300 ◦C; P: 3 MPa; WHSV (H2 plus naphthalene, tetralin or
decalin): 1 h−1
.
NAPHTHALENE
TETRALIN
DECALIN
100
80
60
40
20
0
100
80
60
40
20
0
100
80
60
40
20
0
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5
100
80
60
40
20
0
100
80
60
40
20
0
100
95
90
85
80
75
70
20% Mo2C/HY
1% K-20% Mo2C/HY
2% Mg-20% Mo2C/HY
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5
TOS, h
TOS, h
TOS, h
Fig. 10. Conversion and ring-opening product (ROP) selectivities as a function of time-on-stream (TOS) over 20% Mo2C/HY, 1% K–20% Mo2C/HY and 2% Mg–20% Mo2C/HY
catalysts with naphthalene, tetralin and decalin as model reactants. The reaction condition for all the experiments—T: 300 ◦C; P: 3 MPa; WHSV (H2 plus naphthalene, tetralin
or decalin): 1 h−1
.

44
S.J. Ardakani, K.J. Smith / Applied Catalysis A: General 403 (2011) 36–47
Table 6
Properties of the used catalysts after reaction in naphthalene, tetralin and decalin.
Catalyst
SBET (m2/g)
Carbon wt%
Fresh
Fresh
After reaction with
Naphthalene
After reaction with
Naphthalene
Tetralin
Decalin
Tetralin
Decalin
Pd/HY
7% Mo2C/HY
589
666
627
641
472
467
450
641
589
340
321
428
459
321
374
422
–
426
510
490
403
389
446
423
–
527
542
542
–
408
438
425
560
495
–
8.17
19.98
12.74
11.64
11.76
7.87
10.18
–
6.81
13.81
8.58
10.44
9.31
3.33
7.98
–
3.07
8.34
4.19
7.16
6.80
6.11
5.36
9.14
5.81
0.09
0.26
0.09
–
0.44
0.57
0.09
–
2% Mg–7% Mo2C/HY
1% K–7% Mo2C/HY
20% Mo2C/HY
2% Mg–20% Mo2C/HY
1% K–20% Mo2C/HY
1% K–7% Mo2C/HY-10 ha
Pd/HY-10 ha
–
–
–
–
The reaction condition for all the experiments—T: 300 ◦C; P: 3 MPa; WHSV (H2 plus naphthalene, tetralin or decalin): 1 h−1, reaction time: 5 h.
a
Catalyst used for 10 h reaction time with decalin.
Fig. 13 summarizes the conversion of decalin and RO selec-
tivity over the 1% K–7% Mo2C/HY and Pd/HY catalysts for a 10 h
reaction period. The reaction conditions were the same for both
Fig. 13 shows that both catalysts appear to deactivate at a similar
rate, whereas the RO selectivity remained constant. Comparing the
loss in surface area and the carbon content of both catalysts after
10 h reaction (Table 6) showed that although both catalysts lose
experiments—T: 300 ◦C; P: 3 MPa; WHSV (H2 plus decalin): 1 h−1
.
1%K-7%Mo2C/HY
1%K-20%Mo2 C/HY
50
50
40
30
20
10
0
Naphthalene
C
C
C
C
7
40
30
20
10
0
Naphthalene
C
7
8
C
C
C
8
9
9
10
10
1
2
2
2
3
3
4
4
4
5
5
1
2
2
2
3
3
4
4
4
5
5
5
100
80
60
40
20
0
100
80
60
40
20
0
Tetralin
Tetralin
1
1
100
80
60
40
20
0
100
80
60
40
20
0
Decalin
Decalin
1
3
5
1
3
TOS, h
TOS, h
2%Mg-7%Mo2 C/HY
2%Mg-20%Mo2C/HY
50
40
30
20
10
0
50
Naphthalene
C
7
Naphthalene
C
7
8
9
40
30
20
10
0
C
C
C
8
C
C
C
9
10
10
1
2
2
2
3
3
4
4
4
5
5
5
1
2
3
3
4
5
5
5
60
50
40
30
20
10
0
50
40
30
20
10
0
Tetralin
Tetralin
1
1
2
4
100
80
60
40
20
0
100
80
60
40
20
0
Decalin
Decalin
1
2
3
4
1
3
TOS, h
TOS, h
Fig. 11. Ring opening product (ROP) carbon number selectivity as a function of time-
on-stream (TOS) over the 1% K–7% Mo2C/HY and 2% Mg–7% Mo2C/HY catalysts with
naphthalene, tetralin and decalin as model reactants. The reaction condition for
all the experiments–T: 300 ◦C; P: 3 MPa; WHSV (H2 plus naphthalene, tetralin or
Fig. 12. Ring opening product (ROP) carbon number selectivity as a function of time-
on-stream (TOS) over the 1% K–20% Mo2C/HY and 2% Mg–20% Mo2C/HY catalysts
with naphthalene, tetralin and decalin as model reactants. The reaction condition
for all the experiments—T: 300 ◦C; P: 3 MPa; WHSV (H2 plus naphthalene, tetralin
decalin): 1 h−1
.
or decalin): 1 h−1
.

S.J. Ardakani, K.J. Smith / Applied Catalysis A: General 403 (2011) 36–47
45
coke by chain reactions. The relationship between the proper-
ties of the catalysts of the present study and their ring opening
activity as a function of the three reactants investigated herein
is conveniently discussed in view of these same mechanistic
proposals.
100
80
60
40
20
0
Previous studies have shown that ring opening is favored over
zeolites with a low density of Bronsted acid sites, since strong and
high density of Bronsted acidity usually leads to extensive cracking,
dealkylation and carbon deposition [16,17]. However, in the case
of naphthalene and tetralin as reactants, bifunctional active centers
that are increased with Mo2C loading [14], are necessary to achieve
an initial hydrogenation and isomerization of the reactants, as
shown in Fig. 14. Accordingly, in the present study, the conversion
of naphthalene and tetralin increased with increased Mo2C loading
(E2 and E5 of Table 3). However, the conversion of decalin decreased
at higher Mo2C loading (or dispersion) (E8 of Table 3), showing
that in the case of decalin, acidity is the major factor determining
catalyst activity, consistent with Fig. 14 that shows the direct iso-
merization of decalin on acid sites as the precursor to ring opening.
The decalin conversion on the Mo2C/HY and Pd/HY catalysts cor-
relates with the catalyst Bronsted acidity. Pd/HY had the highest
decalin conversion (92%) (E9 of Table 3) and the highest Bron-
sted acidity (1.27 mmol/g) followed by 72% conversion over the 7%
Mo2C/HY with a Bronsted acidity of 0.91 mmol/g and 61% conver-
sion over the 20% Mo2C/HY with a Bronsted acidity of 0.83 mmol/g.
Decalin conversion yielded similarly high RO selectivities over both
Pd/HY and Mo2C/HY catalysts. However, the Mo2C/HY RO prod-
ucts were mainly C10 isomers, whereas significant cracking and
hydrogenolysis occurred, yielding C7–C9 products over the Pd/HY
(Fig. 8). These differences in ring-opened product selectivities are
also likely a result of the acidity differences between the catalysts,
with the higher acidity of the Pd/HY enhancing the rate of cracking
reactions compared to the Mo2C/HY.
The conversion of naphthalene, tetralin and decalin was higher
on the Pd/HY than the Mo2C/HY catalysts (E3, E6 and E9 of Table 3).
Among the reactants examined, tetralin was the least reactive over
both Pd/HY and Mo2C/HY catalysts. There was also a noticeable dif-
ference in product distribution over the Pd/HY catalyst compared
to the Mo2C/HY catalysts. Pd/HY showed decreased selectivity to
tetralin and increased selectivity to decalin and RO products com-
pared to the Mo2C/HY catalysts with naphthalene as reactant. There
was also a decreased selectivity to dehydrogenated (naphthalene)
products and increased selectivity to hydrogenated (decalin) and
RO products compared to Mo2C/HY catalysts with tetralin as reac-
tant. In terms of the monomolecular reaction mechanism described
above, both the Mo2C/HY and Pd/HY were effective in achieving
isomerization and ring opening, but not as effective in hydrogenat-
ing tetralin to decalin. Clearly the hydrogenation/dehydrogenation
activity of the Mo2C was less than that of Pd for the conditions of
the present study.
1
2
3
4
5
6
7
8
9
10
100
90
80
70
1% K-7% Mo2C/HY
Pd/HY
1
2
3
4
5
6
7
8
9
10
TOS, h
Fig. 13. Conversion and ring-opening product (ROP) selectivities as a function of
time-on-stream (TOS) over 1% K–7% Mo2C/HY and Pd/HY catalysts with decalin as
model reactant. The reaction condition for both experiments—T: 300 ◦C; P: 3 MPa;
WHSV (H2 plus decalin): 1 h−1
.
surface area and have significant carbon deposition, the deactiva-
tion of Pd/HY by carbon deposition is less than that of the Mo2C/HY.
4. Discussion
Analysis by XRD confirmed that Mo2C was successfully syn-
thesized on the 1% K- and 2% Mg-doped 20% Mo2C/HY and 7%
Mo2C/HY catalysts, as well as on the un-doped 20% Mo2C/HY and
7% Mo2C/HY catalysts. The Mo2C dispersion increased as the Mo2C
loading increased from 7% to 20% [14], and the Mo2C crystallite size
data (Table 1) show that addition of Mg or K to the 20% Mo2C/HY
also increased Mo2C dispersion [15]. The increase in the Mo/(Si + Al)
ratio (determined by XPS, Table 1) upon doping the 20% Mo2C/HY
with 1% K confirmed the increased Mo2C dispersion. However, 2%
Mg addition to the 20% Mo2C/HY resulted in a decrease in the
Mo/(Si + Al) ratio, suggesting that some of the Mg must be closely
associated with, or be located on top of the Mo2C. The Mo/(Si + Al)
ratio for the 7% Mo2C/HY catalysts were unchanged upon addition
of the Mg or K, and these results suggest that in the case of low
Mo2C loading, the interaction between the Mg or K and the Mo2C
is reduced. An increase in the Mo2C loading also decreased the total
acidity of the catalysts, as did the addition of the K, whereas addition
of the Mg had no impact on total acidity [14,15].
In previous work [14], the reaction of naphthalene over
Mo2C/HY catalysts was discussed in terms of two competing reac-
tion mechanisms shown in Fig. 14. Accordingly, naphthalene is
hydrogenated to tetralin and small amounts of decalin on Mo2C
sites by a monomolecular mechanism. The hydrogenated inter-
mediates migrate to acid sites where further hydrogenation, by
spillover hydrogen migrating from Mo2C sites, and isomerization
and rupture of saturated naphthenic rings occur, leading to the
desired ring opened products. However, when an effective sup-
ply of hydrogen to the zeolite acid sites is limited, reactions can
follow a bimolecular mechanism. In this scheme, a carbenium
ion of alkylbenzene is formed on a Bronsted acid site from one
tetralin molecule, which is a consequence of hydride transfer reac-
tions of naphthalene over acidic sites. This carbenium ion molecule
then attacks one naphthalene molecule leading to alkylnaphtha-
lene and multinuclear aromatics that are further transformed into
Similar conclusions are drawn from an analysis of the cata-
lyst deactivation and carbon deposition on these catalysts. Carbon
deposition, the main cause of catalyst deactivation, was lowest
after reaction on the Pd/HY catalyst compared to Mo2C/HY cat-
alysts (Table 6). Also, for all of the catalysts of Table 6, carbon
deposition was lowest after reaction with decalin compared to
naphthalene and tetralin. These results suggest that the deposited
carbon has as its precursor, species that are derived from naphtha-
lene or tetralin, rather than decalin. This assertion is consistent with
the coke species being generated through bimolecular reactions on
acid sites [14] and consequently, catalysts with high hydrogena-
tion activity reduce coke formation. Furthermore, the selectivity
to Poly products (coke precursors) was highest with naphthalene
and tetralin reactants and lowest on Pd/HY, consistent with hydro-
genation of the polyaromatics being key to controlling catalyst
deactivation.

46
S.J. Ardakani, K.J. Smith / Applied Catalysis A: General 403 (2011) 36–47
Fig. 14. Proposed reaction schemes for the main products from naphthalene, tetralin and decalin on Mo2C/HY catalysts from [14]. A: acid sites, M: metal sites; ISO:
isomerization; DS: desorption; RO: ring opening.
The product distributions obtained over the Pd/HY catalyst with
naphthalene and tetralin as reactant (Table 3), suggest that the
main reaction mechanism is the monomolecular mechanism of
Fig. 14, as is the case for the Mo2C/HY catalysts. The bimolecular
mechanism is much more inhibited in the case of Pd/HY cata-
lyst compared to the Mo2C/HY catalyst, presumably by a more
efficient generation of activated hydrogen on the Pd sites of the
Pd/HY catalyst. Consequently, the carbon deposition caused by the
bimolecular path is less for the Pd/HY after 5 h TOS than that for
Mo2C/HY and this is valid for all three reactants of naphthalene,
tetralin or decalin (Table 6).
For all three reactants, the addition of K or Mg to the Mo2C/HY
catalysts resulted in a significant decrease in conversion compared
to the undoped Mo2C/HY catalyst. The impact of the K or Mg on
product selectivity, especially RO selectivity, was much less pro-
nounced. The 1% K–7% Mo2C/HY (E11, E14 and E17 of Table 4)
showed higher conversion and RO selectivity compared to 2%
Mg–7% Mo2C/HY (E12, E15 and E18 of Table 4). Although the total
acidity of the 7% Mo2C/HY did not change by doping with 1% K
or 2% Mg (Table 2), the percent of Bronsted acid sites or bifunc-
tional active centers available for hydrogenation, isomerization and
ring opening, decreased from 70% to 63% and 46%, respectively.
The decreased total and Bronsted acidity of 1% K–20% Mo2C/HY
compared to the undoped 20% Mo2C/HY and 2% Mg–20% Mo2C/HY
catalysts (Table 2) also seems to be the main reason for its lower
conversion of naphthalene and tetralin (E20 and E23 of Table 5)
compared to that of the un-doped 20% Mo2C/HY (E19 and E22) and
the 2% Mg–20% Mo2C/HY (E21 and E24 of Table 5) catalysts. The dra-
matic decrease in decalin conversion over the 1% K and 2% Mg doped
20% Mo2C/HY catalysts compared to the un-doped 20% Mo2C/HY
catalyst is assigned to the noticeably decreased Lewis acidity upon
doping of the 20% Mo2C/HY with 1% K or 2% Mg.
The major effect of the addition of K or Mg to the Mo2C/HY
catalyst was to decrease the deactivation rate of the catalysts in
the presence of all three reactants. Comparing the carbon deposi-
tion on the catalysts after 5 h TOS shows that addition of 2% Mg or
1% K to the Mo2C/HY decreased the carbon deposition relative to
that obtained on the un-doped Mo2C/HY with each of naphthalene,
tetralin and decalin reactant. Among the three reactants, the low-
est carbon deposition occurred after reaction with decalin (Table 6).
Similarly, the selectivity to Poly products (Table 4) decreased upon
addition of K or Mg to the Mo2C/HY. This confirms the enhanced
monomolecular pathway that occurs for the doped 7% Mo2C/HY
catalysts compared to the un-doped 7% Mo2C/HY catalyst. Fig. 9

S.J. Ardakani, K.J. Smith / Applied Catalysis A: General 403 (2011) 36–47
47
shows that there was obvious deactivation in all cases, however,
Acknowledgement
a significantly reduced deactivation rate for the 1% K–7% Mo2C/HY
catalyst was observed, especially with decalin as the feed. Although
among the studied catalysts, higher Bronsted acidity is favored for
decalin conversion, the deactivation is considerably reduced when
the 1% K–7% Mo2C/HY catalyst with a moderate percent of Bron-
sted acid sites (63%) was used (Table 2). K moderates the Bronsted
acid sites of the 7% Mo2C/HY catalyst and consequently the coke
precursors from acid catalyzed polymerization reactions (bimolec-
ular pathway) are greatly reduced. The highest selectivity to C10
products, also obtained on the 1% K–7% Mo2C/HY catalyst with
decalin as reactant, is consistent with a reduced acidity that limits
the cracking of RO products, whereas in the case of Pd/HY using the
same reactant, lower C10 selectivity was observed because of acid
cracking reactions.
Funding for the present study from Natural Resources Canada
through the Climate Change Technology and Innovation Initiative
is gratefully acknowledged.
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Although Pd/HY showed higher activity and RO selectivity than
the 7% Mo2C/HY, the latter showed higher selectivity to C10 prod-
ucts when decalin was used as reactant. Furthermore, with the
addition of 1% K to 7% Mo2C/HY catalyst, the deactivation rate
and loss in RO selectivity were all but eliminated with decalin as
reactant. Catalyst deactivation associated with both the Pd/HY and
Mo2C/HY catalysts was more pronounced with naphthalene and
tetralin as reactant. The results suggest that catalyst deactivation
would best be overcome by pre-hydrogenating the feedstock to sat-
urate polyaromatics prior to ring opening and the latter could be
achieved with high selectivity using the 1% K–7% Mo2C/HY catalyst.
The lower cost and higher thio-tolerance of the 1% K–7% Mo2C/HY
catalyst compared to the Pd/HY catalyst are considered an impor-
tant advantage.