Good sulfur tolerance of a mesoporous Beta zeolite-supported palladium catalyst in the deep hydrogenation of aromatics

Article abstract of DOI:10.1016/j.jcat.2008.04.013

The activities of a Pd catalyst supported on mesoporous Beta zeolite (Beta-H) were evaluated for the hydrogenation of naphthalene and pyrene in the absence and presence of 200-ppm sulfur and for the hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT). Compared with Pd/Al-MCM-41, the Pd/Beta-H catalyst exhibited better sulfur tolerance for hydrogenation of naphthalene and pyrene and higher activity for HDS of 4,6-DMDBT. The ratio of the hydrogenation of the second ring naphthalene in the absence and presence of 200-ppm sulfur for Pd/Beta-H was larger than that for Pd/Al-MCM-41 (0.47 vs 0.19). The desulfurization effect of Pd/Beta-H was greater than that of Pd/Al-MCM-41 (51 vs 35%). The difference in sulfur tolerance and HDS ability of the 2 catalysts is attributed to the difference in support acidity. Beta-H exhibited more acidic sites and a higher percentage of strong acidic sites than Al-MCM-41 (552 μmol/g and 43% vs 291 μmol/g and 18%).

Full text of DOI:10.1016/j.jcat.2008.04.013

Journal of Catalysis 257 (2008) 125–133
Contents lists available at ScienceDirect
Journal of Catalysis
www.elsevier.com/locate/jcat
Good sulfur tolerance of a mesoporous Beta zeolite-supported palladium catalyst
in the deep hydrogenation of aromatics
∗
Tiandi Tang, Chengyang Yin, Lifeng Wang, Yanyan Ji, Feng-Shou Xiao
College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130023, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
The activities of
a Pd catalyst supported on mesoporous Beta zeolite (Beta-H) were evaluated for
Received 26 January 2008
Revised 9 April 2008
Accepted 20 April 2008
Available online 21 May 2008
the hydrogenation of naphthalene and pyrene in the absence and presence of 200-ppm sulfur and
for the hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT). Compared with
Pd/Al-MCM-41, the Pd/Beta-H catalyst exhibited better sulfur tolerance for hydrogenation of naphthalene
and pyrene and higher activity for HDS of 4,6-DMDBT. The ratio of the hydrogenation of the second ring
naphthalene in the absence and presence of 200-ppm sulfur for Pd/Beta-H was larger than that for Pd/Al-
MCM-41 (0.47 vs 0.19). The desulfurization effect of Pd/Beta-H was greater than that of Pd/Al-MCM-41
(51 vs 35%). The difference in sulfur tolerance and HDS ability of the 2 catalysts is attributed to the
difference in support acidity. Beta-H exhibited more acidic sites and a higher percentage of strong acidic
sites than Al-MCM-41 (552 μmol/g and 43% vs 291 μmol/g and 18%).
Keywords:
Mesoporous Beta zeolite
Palladium catalyst
Naphthalene
Pyrene
Hydrogenation
Sulfur tolerance
4,6-Dimethyldibenzothiophene
Hydrodesulfurization
© 2008 Elsevier Inc. All rights reserved.
1. Introduction
Despite their advantages, however, conventional zeolites cannot
accomplish deep hydrogenation of the bulky aromatics in diesel
The high content of aromatics in diesel fuels lowers the fuel
quality [1,2]. One solution to this problem is deep hydrogenation
of aromatics at low temperature over supported noble metal cata-
lysts [1–3]. However, the presence of sulfur strongly influences the
catalytic activity in deep hydrogenation due to the poisoning of ac-
tive sites [4,5]. Therefore, a deep hydrogenation catalyst with good
sulfur tolerance is highly desirable [2,3].
It has been reported that the catalytic activity and sulfur tol-
erance in deep hydrogenation of aromatic hydrocarbons can be
enhanced by noble metals on acidic supports, such as HY [6–8],
Beta [9], and LTL [10] zeolites. This phenomenon is attributed to
the partial electron transfer from the metal particles to the acidic
sites of zeolitic supports [1,11], and to the fact that electron-
deficient metal particles have a better resistance to sulfur poison-
ing with decreased interaction with H2S [5]. Another explanation
for the improved activity of metal particles on acidic supports is
the creation of a second hydrogenation pathway by spillover of
hydrogen atoms from the metal particles to the aromatic sulfur-
containing molecules that are adsorbed on acidic sites in the
vicinity of the metal particles [12–14]. While the metal particles
become poisoned by sulfur, they can be recovered from the hydro-
genation pathway by spillover hydrogen [15–17].
fuels, due to their pore size limitations [18–21]. Recently, meso-
porous zeolites, such as Beta and MFI, have been successfully
synthesized [22–25]. These mesoporous zeolites exhibit excellent
catalytic properties for the conversion of bulky molecules. In par-
ticular, palladium catalysts supported on mesoporous Beta zeolite
show superior performance in deep hydrogenation of bulky aro-
matic pyrene [21]. In the present work, we demonstrate that a
palladium catalyst supported on strongly acidic and hierarchically
mesoporous Beta zeolite (Pd/Beta-H) has a good sulfur tolerance in
the deep hydrogenation of polyaromatics such as relatively small
naphthalene and bulky pyrene. In contrast, palladium catalysts
supported on conventional acidic zeolites cannot convert bulky
pyrene. These features are very important for increasing fuel qual-
ity and controlling the undesirable emissions in exhaust gases.
Usually, deep hydrogenation of aromatics over supported noble
metal catalysts is carried out at low temperatures after hydrodesul-
furization (HDS) of the fuels over metal sulfide catalysts such as
sulfided CoMo and NiMo supported on γ -alumina under severe
operating conditions. Generally, after HDS, the sulfur molecules
remaining in the fuels are mainly refractory dialkyldibenzoth-
iophenes, such as 4,6-dimethyldibenzothiophene (4,6-DMDBT)
[2,26–29], due to the steric hindrance of the methyl groups present
at the 4 and 6 positions [30–32].
It has been suggested that an improvement in the acidity in the
catalyst support is favorable for the HDS of 4,6-DMDBT [33–40].
Corresponding author. Fax: +86 431 85168624.
E-mail address: fsxiao@mail.jlu.edu.cn (F.-S. Xiao).
*
0021-9517/$ – see front matter © 2008 Elsevier Inc. All rights reserved.
doi:10.1016/j.jcat.2008.04.013

126
T. Tang et al. / Journal of Catalysis 257 (2008) 125–133
◦
(60 mL/min, STP) from room temperature to 300 C at a heating
rate of 2 C/min and held at 300 C for 100 min. After reduction,
Typical catalyst supports for HDS are γ -alumina and amorphous
aluminosilicates [1–3,41,42]. Acidic zeolites added to the alumina-
supported CoMo and NiMo catalysts enable dealkylation and iso-
merization reactions of the alkyl substituents, which may trans-
form refractory 4,6-DMDBT into more reactive species and thus
accelerate HDS [33,34]. On the other hand, although zeolites have
much stronger acidity than γ -alumina and amorphous aluminosil-
icates, the relatively small pore size of zeolites strongly hinders
the mass transport of the relatively large 4,6-DMDBT molecule
(8.7 × 12.2 Å) [43,44]. In the present work, we investigated the
possibility of sulfur removal by the conversion of 4,6-DMDBT at
◦
◦
the catalyst was purged with N2 (99.999%, 60 mL/min STP) at
◦
290 C for 1 h. After being cooled to room temperature, the re-
duced catalyst was transferred under nitrogen stream into a bottle
filled with absolute alcohol. For XPS, the alcohol in the bottle was
removed, and the residual reduced catalyst was quickly moved to
the sample holder, then transferred into the analysis chamber of
the XPS instrument, followed by evacuation [43].
2.3. Activity tests
◦
mild reaction conditions (250 C and 6.5 MPa) over Pd/Beta-H. In
contrast, conventional HDS catalysts such as CoMo/γ -Al2O3 are
used under relatively severe operating conditions.
The hydrogenation of naphthalene (5 g) was carried out in an
autoclave using dodecane (120 mL) as the solvent with 330 mg of
catalyst at 240 C. Hydrogenation of pyrene (3.5 g) was carried out
◦
2. Experimental
in an autoclave using tridecane (120 mL) as the solvent with 300
mg of catalyst at 250 C. Hydroisomerization of decalin (4.5 mL)
◦
2.1. Catalysts
was carried out in an autoclave using dodecane (120 mL) as the
solvent with 330 mg of catalyst at 240 C. The sulfur tolerance in
◦
Beta-H and Al-MCM-41 were synthesized as described in the
literature [22,45]. The H-form of the samples was ion-exchanged
the deep hydrogenation of naphthalene and pyrene was studied in
the presence of thiophene and 4,6-DMDBT (200-ppm sulfur). Hy-
drodesulfurization of 4,6-DMDBT (0.2 g, 95% purity) was carried
out using tridecane (110 mL) as the solvent with 300 mg of cat-
◦
twice with a NH4NO3 solution (1 M) at 80 C for 3 h, followed by
◦
calcination at 550 C for 4 h. The Beta-H and Al-MCM-41 supported
◦
palladium catalysts were prepared by the ion-exchange method as
described previously [21], with palladium loadings of 3.1 wt% for
Pd/Beta-H and 3.4 wt% for Pd/Al-MCM-41, as determined by the
inductively coupled plasma method (ICP; Perkin-Elmer 3300 DV).
The Pd/Beta-H and Pd/Al-MCM-41 catalysts were calcined in flow-
alyst at 250 C. In these reactions, the total pressure was 6.5 MPa
(hydrogen pressure of about 6.2 MPa), and the stirring rate was
800 rpm. To maintain the same total pressure, hydrogen was con-
tinually supplied to make up for the consumption of hydrogen in
the reaction. The reaction products were analyzed with an Agilent
6890N gas chromatograph equipped with a flame ionization detec-
tor and a mass spectrometer (TRACE MS). The Parr 5500 autoclave
had a volume of 300 mL. In a typical run, the calcined catalyst
powder (<53 μm) was reduced in flowing mixed H2–N2 gas with
◦
ing oxygen (150 mL/min, STP) from room temperature to 450 C at
◦
◦
a heating rate of 1 C/min, and then held at 450 C for 100 min.
2.2. Characterization
◦
6% H2 (80 mL/min, STP) from room temperature to 300 C at a
◦
◦
Nitrogen physisorption was carried out using a Micromeritics
ASAP 2010M system. Before the measurement, the sample was de-
heating rate of 2 C/min and held at 300 C for 100 min. After
being cooled to room temperature, the reduced catalyst was trans-
ferred under nitrogen stream into the autoclave filled with solvent
and reactant. In these reactions, the absence of mass diffusion
limitation was checked by changing the catalyst granule size and
stirring rate.
◦
gassed for 10 h at 300 C. The pore size distribution was calculated
using the BJH model. The acidities of the Beta-H and Al-MCM-
41 were determined using the stepwise temperature-programmed
desorption of ammonia [21].
The calcined Pd/Beta-H and Pd/Al-MCM-41 samples for trans-
mission electron microscopy (TEM) were reduced by mixed H2–N2
gas with 6% H2, similar to the reduction procedure in the hydro-
genation test. The used Pd/Beta-H catalyst was also observed after
the pyrene hydrogenation reaction. The TEM images were obtained
on a JEOL JSM-3010 electron microscope operating at 300 kV.
The palladium dispersion on the supported catalysts was esti-
mated from dynamic CO chemisorption measurements. In a typical
run, about 130 mg of calcined sample was reduced in flowing
mixed H2–N2 gas with 6% H2 (40 mL/min STP) from room tem-
3. Results and discussion
3.1. Catalyst characterization
Table 1 presents textural parameters and acidic properties of
the various supports and catalysts. Notably, after the loading of
Pd particles, the surface area, mesopore volume, and micropore
volume were reduced, due to the Pd particles inside the meso-
pores and micropores. In addition, Beta-H and Pd/Beta-H showed
a wide mesopore size distribution of about 5–40 nm (Figs. 1a and
1b), and Al-MCM-41 and Pd/Al-MCM-41 exhibited narrow meso-
pores of about 2.3 nm (Figs. 1c and 1d). Beta-H exhibited more
acidic sites than Al-MCM-41. For the characterization of acidity
by NH3-TPD, the acidic strength can be differentiated as weak,
middle, and strong according to the desorption temperature [47].
◦
◦
perature to 300 C at a heating rate of 2 C/min and then held
◦
at 300 C for 100 min. After reduction, the catalyst was purged
◦
with He (99.999%, 40 mL/min STP) at 290 C for 2 h to eliminate
chemisorbed hydrogen, followed by cooling to 30 C in a He flow.
◦
Subsequently, 100 μL of CO was injected to the reduced catalyst at
10-min intervals by the pulse method until saturation adsorption
was observed. The estimated dispersion and average particle size
of the palladium particles are based on spherical geometry and an
adsorption stoichiometry of CO/Pd = 1. The average Pd particle size
was calculated by the following equation [46]:
◦
Beta-H had higher concentrations of relatively strong (250–350 C,
234 μmol/g) and strong (>350 C, 237 μmol/g) acidic sites com-
◦
pared with Al-MCM-41 (105 and 53 μmol/g, respectively, Table 1).
Fig. 2 shows TEM images of the samples. The Pd particles were
located in both disordered mesopores (Fig. 2b; particle size about
5 nm) and ordered micropores (insert in Fig. 2b; particle size
<1 nm) of Pd/Beta-H, which is consistent with the fact that the
Beta-H sample contains both hierarchical mesopores (5–40 nm)
and ordered micropores (0.7 nm). After pyrene hydrogenation, the
TEM images of the Pd/Beta-H catalyst showed that the Pd particles
were still located in the mesopores and micropores of the sample
d = 1.1289/D,
where d and D represent palladium particle size (in nm) and dis-
persion, respectively.
X-ray photoelectron spectroscopy (XPS) of reduced catalysts
was performed using a Thermo ESCA LAB 250 system. The cal-
cined catalyst was reduced in a mixed H2–N2 gas with 6% H2

T. Tang et al. / Journal of Catalysis 257 (2008) 125–133
127
Table 1
Textural and acidic parameters of the samples
BET surface
External surface
Mesoporous
Microporous
Acidic amounts of the support (μmol/g)
Samples
area (m2/g)
areaa (m2/g)
volume (cm3/g)
volume (cm3/g)
◦
◦
◦
150–250
81
C
250–350
234
C
>350 C
Total
552
Beta-H
524
466
799
721
151
134
–
0.24
0.21
0.62
0.54
0.17
0.15
–
237
Pd/Beta-H
Al-MCM-41
PdAl-MCM-41
133
105
53
291
–
–
a
Mesoporous surface area is included.
Table 2
XPS and CO-chemisorption data over Pd/Beta-H and Pd/Al-MCM-41 catalysts
Catalysts
Pd loading
(wt%)
Binding energy
Pd 3d5/2 (eV)
CO-chemisorption
CO/Pd
d (nm)
Pd/Beta-H
Pd/Al-MCM-41
3.1
3.4
335.5
335.0
0.47
0.52
2.4
2.2
Naphthalene hydrogenation can be basically considered an irre-
versible pseudo-first-order consecutive reaction under a pressure
◦
>3.1 MPa and a reaction temperature <275 C, the second step
being the slow step [48]. In our case, the reaction pressure was
◦
6.5 MPa and the reaction temperature was 240 C; therefore, naph-
thalene hydrogenation was considered an irreversible pseudo-first-
order consecutive reaction.
Fig. 5 illustrates the time dependence of naphthalene conver-
sion over the Pd/Beta-H and Pd/Al-MCM-41 catalysts. Notably, the
activities of Pd/Beta-H and Pd/Al-MCM-41 were quite different for
the conversion of tetralin to decalin; for example, after reaction
for 180 min, this conversion was 82% over Pd/Beta-H but only
20% over Pd/Al-MCM-41. The conversion of naphthalene to tetralin
◦
at 240 C was close to 100% over both catalysts; however, when
◦
the reaction temperature was decreased to 200 C, this conver-
sion (at 80 min of reaction time) dropped to 92% over Pd/Beta-H
and 66% over Pd/Al-MCM-41. These results indicate that Pd/Beta-H
had greater hydrogenation activity than Pd/Al-MCM-41 catalyst in
naphthalene hydrogenation.
Fig. 6 shows the time dependence of naphthalene conversion
over the Pd/Beta-H and Pd/Al-MCM-41 catalysts in the presence
of 200-ppm sulfur in the form of thiophene. Compared with the
results in Fig. 5, here the catalytic activity in the hydrogenation
of naphthalene to tetralin over Pd/Beta-H was hardly influenced
by the addition of 200-ppm sulfur, but the same amount of sul-
fur resulted in a significant reduction of the catalytic activity over
Pd/Al-MCM-41. Furthermore, the catalytic activity in the hydro-
genation of tetralin to decalin was significantly suppressed over
both Pd/Beta-H and Pd/Al-MCM-41 by the presence of 200-ppm
sulfur, but the poisoning effect was much stronger over Pd/Al-
MCM-41 than over Pd/Beta-H; for example, at a reaction time
of 180 min, the conversion of tetralin to decalin was 46% for
Pd/Beta-H, compared with only 3% for Pd/Al-MCM-41. These re-
sults indicate that Pd/Beta-H had a much better sulfur tolerance in
the hydrogenation of naphthalene compared with Pd/Al-MCM-41.
Table 3 presents the product selectivity in naphthalene hydro-
genation over Pd/Beta-H and Pd/Al-MCM-41 in the absence and
presence of 200-ppm sulfur in the form of thiophene for a re-
action time of 60 min. Compared with Pd/Al-MCM-41, Pd/Beta-H
exhibited much higher activity for the conversion of tetralin and
selectivity for decalins in the absence and presence of 200-ppm
sulfur (runs 1–4).
Fig. 1. Pore size distribution curves of (a) Beta-H, (b) Pd/Beta-H, (c) Al-MCM-41, and
(d) Pd/Al-MCM-41.
(Fig. 2c), suggesting that the Pd particles in Beta-H did not readily
aggregate in pyrene hydrogenation. In the Pd/Al-MCM-41 catalyst,
the Pd particles were located mainly in mesopore channels of Al-
MCM-41, with an average particle size of about 2.2 nm (Fig. 2d).
Table 2 presents the results of XPS and CO chemisorption of
Pd/Beta-H and Pd/Al-MCM-41. The binding energies of the Pd 3d5/2
peak of Pd/Beta-H (335.5 eV) and Pd/Al-MCM-41 (335.0 eV) clearly
differed (Fig. 3), suggesting that Pd clusters on Pd/Beta-H were
electron-deficient compared with those on Pd/Al-MCM-41. This is
due to the close contact between the strong acid site and the small
cluster of Pd atoms, which allows withdrawal of electrons from the
noble metal, creating an electron-deficient metal particle [5,11].
Furthermore, estimation of Pd particle size by CO chemisorption
showed average Pd particle sizes of 2.4 nm on Beta-H and 2.2 nm
on Al-MCM-41.
We also analyzed the byproducts of naphthalene hydrogena-
tion. We found no byproducts for Pd/Al-MCM-41 but found sev-
eral byproducts for Pd/Beta-H, including octahydro-2,5-dimethyl-
pentalene, 1-butyl-cyclohexene, 1-butyl-cyclohexane, and light hy-
drocarbons (C5–C9). This suggests that hydrocracking of naph-
thalene occurred over Pd/Beta-H. After 60 min, the selectivity
3.2. Naphthalene hydrogenation
Fig. 4 shows the proposed network of naphthalene hydrogena-
tion. The hydrogenation of naphthalene occurs in two steps: the
conversion to tetralin, followed by the formation of decalin [48].

128
T. Tang et al. / Journal of Catalysis 257 (2008) 125–133
Fig. 2. TEM images of Pd/Beta-H and Pd/Al-MCM-41 catalysts. (a) Large-scale TEM image of the reduced Pd/Beta-H, (b) high resolution TEM images of the reduced Pd/Beta-H,
(c) high resolution TEM image of the used Pd/Beta-H, (d) the reduced Pd/Al-MCM-41. Insert in (b): TEM image of Pd particles in micropores.
(a)
(b)
Fig. 3. XPS spectra of (a) Pd/Beta-H and (b) Pd/Al-MCM-41catalysts.
Fig. 4. Network of naphthalene hydrogenation.
for byproducts was 4.6% (run 1 in Table 3); when the reaction
hydrogenation of the second ring of naphthalene in the absence
(k2c) and presence (k2s) of thiophene [43,48] over Pd/Beta-H and
Pd/Al-MCM-41 (Table 4). The rate constants were normalized to
per mol of metal atoms. Both k2s and k2s/k2c for Pd/Beta-H were
much higher than those for Pd/Al-MCM-41, confirming the bet-
ter sulfur tolerance of Pd/Beta-H. The different sulfur tolerance in
time was increased to 180 min, the selectivity for byproducts
reached 25%. The formation of byproducts from hydrocracking may
be associated with strongly acidic sites on the Pd/Beta-H catalyst.
To carefully compare sulfur tolerance, we estimated the rate
constants derived with the pseudo-first-order assumption for the

T. Tang et al. / Journal of Catalysis 257 (2008) 125–133
129
Table 3
Product selectivities in naphthalene hydrogenation over Pd/Beta-H and Pd/Al-MCM-
41 catalysts for reaction time of 60 min
Run Catalyst
Tetralin
conversion
(%)
Product selectivity (%)
Tetralin t-Decalin c-Decalin By-product Total
decalins
1
2
3
4
Pd/Beta-H
36.3
17.4
5.5
0
63.7
82.6
94.5
71.5
17.2
8.3
3.2
0
14.5
7.3
2.4
0
4.6
1.8
0
31.7
Pd/Beta-Ha
15.6
5.6
0
Pd/Al-MCM-41
Pd/Al-MCM-41a
0
a
The presence of 200-ppm sulfur in the form of thiophene.
Table 4
Comparison of the rate constants of the hydrogenation of the second ring of naph-
thalene over Pd/Beta-H and Pd/Al-MCM-41 in the absence and presence of 200-ppm
sulfur in the form of thiophene
Catalysts
k2 (L/molM h)
k2c
k2s
k2s/k2c
Fig. 5. Dependence of the naphthalene and tetralin conversion on reaction time in
the absence of thiophene. (2) Naphthalene conversion over Pd/Beta-H; (") naph-
thalene conversion over Pd/Al-MCM-41; (Q) tetraline conversion over Pd/Beta-H;
(a) tetralin conversion over Pd/Al-MCM-41.
Pd/Beta-H
Pd/Al-MCM-41
521
92
243
18
0.47
0.19
Fig. 7. Dependence of the ratio of trans-decalin/cis-decalin in naphthalene hydro-
genation on reaction time in the absence and presence of 200-ppm sulfur in
the form of thiophene. (2) In the absence of thiophene over Pd/Beta-H; (") in
the presence of thiophene over Pd/Beta-H; (Q) in the absence of thiophene over
Pd/Al-MCM-41; (a) in the presence of thiophene over Pd/Al-MCM-41.
Fig. 6. Dependence of the naphthalene and tetralin conversion on reaction time in
the presence of 200-ppm sulfur in the form of thiophene. (2) Naphthalene conver-
sion over Pd/Beta-H; (") naphthalene conversion over Pd/Al-MCM-41; (Q) tetraline
conversion over Pd/Beta-H; (a) tetralin conversion over Pd/Al-MCM-41.
interaction with the strongly Brönsted acidic sites of the zeolite
to form electron-deficient Pt particles of enhanced hydrogenation
activity and improved sulfur tolerance. In this work, the Beta-H
zeolite with strong and abundant acidic sites (which also could
make the electrons withdraw from the palladium atoms) resulted
in good sulfur tolerance in naphthalene hydrogenation.
these two catalysts may be due to their different acidities; sim-
ilar phenomena have been reported previously [6–10]. The close
contact between the strong acidic sites and the small clusters
of palladium may cause withdrawal of electrons from the pal-
ladium atoms, thereby creating electron-deficient palladium par-
ticles, which decreases the bond strength between the electron
acceptor, such as sulfur, and the electron-deficient palladium [5,
11]. This explanation is supported by the change in the binding
energy of Pd 3d5/2 for Pd/Beta-H (335.5 eV) and Pd/Al-MCM-41
(335.0 eV) (Table 2), in good agreement with those reported by
other groups [5,43,48]. Cooper and Donnis [5] proposed that the
close contact between the strong acidic sites and the small clus-
ters of Pt and Pd atoms allows withdrawal of electrons from the
noble metal, thereby creating an electron-deficient metal particle.
Meng et al. [43] reported a greater binding energy of Pd 3d5/2
on strongly acidic HY zeolite (335.5 eV) than on weaker acidic
HUSY zeolite (335.1 eV). Their catalytic tests in naphthalene hy-
drogenation showed that the Pd/HY sample was more active than
the PdPt/HUSY sample in the presence and absence of thiophene.
Corma et al. [48] reported that small Pt clusters were localized in
the supercages of the USY zeolite and were subjected to greater
Fig. 7 illustrates the time dependence of the trans-decalin/cis-
decalin (t-D/c-D) ratio during naphthalene hydrogenation over
Pd/Beta-H and Pd/Al-MCM-41. For Pd/Al-MCM-41, the ratio of t-
D/c-D quickly reached a constant value of 1.3–1.4 in the absence
of sulfur. In contrast, the ratio of t-D/c-D over Pd/Beta-H increased
with reaction time in the absence and presence of 200-ppm sulfur.
This phenomenon is attributed to the isomerization of cis-decalin
to trans-decalin on the Pd/Beta-H, which was further confirmed by
the hydroisomerization of pure decalin (Fig. 8). Comparing Figs. 7
and 8 shows a t-D/c-D close to 1.7 in naphthalene hydrogena-
tion over Pd/Beta-H for a reaction time of 180 min, compared
with the 8.8 in hydroisomerization, indicating the suppression of
hydroisomerization by the presence of naphthalene and tetralin.
Huang and Kang [49] also reported that the presence of tetralin
in naphthalene hydrogenation strongly limited the conversion of
c-decalin to t-decalin.

130
T. Tang et al. / Journal of Catalysis 257 (2008) 125–133
Fig. 8. Dependence of trans-decalin and cis-decalin content and trans-decalin/
cis-decalin ratio in decalin hydroisomerization on reaction time over Pd/Beta-H. (2)
Trans-decalin content; (1) cis-decalin content; (") trans-decalin/cis-decalin ratio.
Fig. 10. Dependence of the pyrene conversion on reaction time in the absence and
presence of 200-ppm sulfur in the form of thiophene. (2) Over Pd/Beta-H in the ab-
sence of sulfur; (") over Pd/Al-MCM-41 in the absence of sulfur; (a) over Pd/Beta-H
in the presence of thiophene; (Q) over Pd/Al-MCM-41 in the presence of thiophene.
Fig. 9. The proposed network of pyrene hydrogenation. (A) Pyrene; (B) 4,5-dihydro-
pyrene; (C) 1,2,3,6,7,8-hexahydropyrene; (D) 1,2,3,3a,4,5-hexahydropyrene; (E) 4,5,9,
10-tetrahydropyrene; (F) 1,2,3,3a,4,5,5a,6,7,8-decahydropyrene; (G) 1,2,3,3a,4,5,9,10,
10a,10b-decahydropyrene; (H) perhydropyrene.
Fig. 11. Decreased percentages of DHP in pyrene hydrogenation versus reaction time
after addition of 200-ppm sulfur in the form of thiophene. (Q) Over Pd/Beta-H;
(a) over Pd/Al-MCM-41.
3.3. Pyrene hydrogenation
Fig.
9 shows the proposed network of pyrene hydrogena-
products (the sum of hexahydropyrene, decahydropyrene, and per-
hydropyrene; DHP) over Pd/Beta-H was almost twice that of over
Pd/Al-MCM-41, demonstrating Pd/Beta-H’s much greater deep hy-
drogenation ability.
tion [21]. Pyrene hydrogenation is a consecutive reaction that
first creates dihydropyrene, followed by the formation of tetrahy-
dropyrene, hexahydropyrene, decahydropyrene, and perhydropy-
rene [21].
Furthermore, after addition of 200-ppm sulfur in the form of
thiophene (runs 2 and 5 in Table 5), Pd/Beta-H still exhibited a
much higher conversion rate for pyrene than Pd/Al-MCM-41 (94.5
vs 69.1%). Furthermore, the hydrogenation products dihydropyrene,
tetrahydropyrene, hexahydropyrene, decahydropyrene, and perhy-
dropyrene were observed over Pd/Beta-H, whereas only dihydropy-
rene, tetrahydropyrene, and hexahydropyrene were observed over
Pd/Al-MCM-41. These findings indicate that DHP products were
greatly suppressed over the two catalysts after the addition of 200-
ppm sulfur in the form of thiophene.
In contrast, after addition of 200-ppm sulfur in the form of 4,6-
DMDBT (runs 3 and 6 in Table 5), the conversion of pyrene and
the DHP content were only slightly decreased, but the Pd/Beta-
H still exhibited much greater catalytic activity than Pd/Al-MCM-
41. Furthermore, comparing pyrene hydrogenation in the presence
of thiophene with 4,6-DMDBT (Table 5) clearly showed that 4,6-
DMDBT has less poisoning effect than thiophene. Generally, both
Fig. 10 illustrates the time dependence of pyrene conversion
over Pd/Beta-H and Pd/Al-MCM-41 in the absence and presence of
thiophene. Obviously, the conversion of pyrene over the two cata-
lysts was significantly reduced by the addition of 200-ppm sulfur
in the form of thiophene, but the suppression of the catalytic activ-
ity over Pd/Al-MCM-41 was more serious than that over Pd/Beta-
H; for example, after 90 min, pyrene conversion was 94% over
Pd/Beta-H and 90% over Pd/Al-MCM-41 in the absence of sulfur
and 87 and 57%, respectively, in the presence of 200-ppm sulfur.
These results indicate the superior sulfur tolerance of Pd/Beta-H in
pyrene hydrogenation.
Table 5 presents the product selectivities in pyrene hydrogena-
tion over the Pd/Beta-H and Pd/Al-MCM-41 catalysts in the absence
and presence of 200-ppm sulfur in the form of thiophene or 4,6-
DMDBT at a reaction time of 180 min. Although pyrene conversion
in the absence of sulfur (runs 1 and 4 in Table 5) was simi-
lar over the two catalysts, the selectivity for deep hydrogenation

T. Tang et al. / Journal of Catalysis 257 (2008) 125–133
131
Table 5
Product selectivities in pyrene hydrogenation over Pd/Beta-H and Pd/Al-MCM-41 catalysts for reaction time of 180 min
Run
Catalyst
Pyrene
Product selectivity (%)
conversion (%)
B
E
C
D
F
G
H
DHPc
1
2
3
4
5
6
Pd/Beta-H
96.3
94.5
95.2
94.0
69.1
92.6
10.5
24.5
12.9
23.4
40.7
24.4
24.2
39.3
27.5
37.8
21.0
38.7
24.9
16.2
23.1
12.8
4.2
6.2
5.7
5.8
5.3
2.7
5.5
11.8
2.7
9.9
5.8
0
10.7
3.4
9.5
4.2
0
8.1
2.7
6.5
4.7
0
61.6
30.7
54.8
32.8
7.4
Pd/Beta-Ha
Pd/Beta-Hb
Pd/Al-MCM-41
Pd/Al-MCM-41a
Pd/Al-MCM-41b
12.1
4.6
3.1
2.4
27.7
a
b
c
The presence of 200-ppm sulfur in the form of thiophene.
The presence of 200-ppm sulfur in the form of 4,6-DMDBT.
The sum of C, D, F, G, and H (deep hydrogenation products, DHP).
Fig. 12. Network of 4,6-DMDBT hydrodesulfurization.
thiophene and 4,6-DMDBT can be adsorbed on catalytically active
sites, leading to poisoning of the catalysts; however, 4,6-DMDBT
is more strongly adsorbed. In addition, under the same reaction
conditions, the sulfur in the thiophene molecule is more readily
hydrodesulfurized to H2S; therefore, the concentration of H2S in
the reaction is relatively high, resulting in serious catalyst poison-
ing.
3.4. Hydrodesulfurization of 4,6-DMDBT
As a refractory compound of the dialkyldibenzothiophenes in
fuels hydrotreated over supported metal sulfide catalysts [2,51],
4,6-DMDBT was hydrodesulfurized over Pd/Beta-H and Pd/Al-
MCM-41. Fig. 12 shows the proposed network of 4,6-DMDBT
hydrodesulfurization [52]. Compared with hydrogenation route
(HYD), the rate for direct desulfurization (DDS) of 4,6-DMDBT is
To quantitatively analyze the change in DHP products in the
absence and presence of 200-ppm sulfur in the form of thiophene
over the Pd/Beta-H and Pd/Al-CMC-41 catalysts, Fig. 11 illustrates
the time dependence of the decrease in the percentage of DHP
(i.e., the percentage of DHP difference before and after addition of
sulfur). The decrease in the percentage of DHP was much smaller
over Pd/Beta-H than over Pd/Al-MCM-41, indicating the much bet-
ter sulfur tolerance of Pd/Beta-H. The difference in sulfur tolerance
in pyrene hydrogenation over the two catalysts is also attributed
to their different acidity, as was discussed earlier for naphthalene
hydrogenation. In addition, the Beta-H support has the advantages
of both microporosity and mesoporosity, and, of course, the palla-
dium particles are located in the micropores as well as the meso-
pores (Fig. 2b). Due to pore size limitations, hydrogenation of the
bulky pyrene molecule occurs only in the mesopores. The palla-
dium sites located in the mesopores that are poisoned by adsorbed
sulfur may possibly be partially recovered by spillover hydrogen
coming from the micropores [2,50].
ꢀ
very slow [51,52]. In our experiments, the product of 3,3 -dimeth-
ꢀ
ylbiphenyl (3,3 -DM-BP) was undetectable, confirming the slow
DDS rate. The hydrogenation of a phenyl ring of 4,6-DMDBT im-
parts flexibility to the methyl group, resulting in the formation of
flexible intermediates with reduction of the steric hindrance, fol-
lowed by desulfurization [51]. Figs. 13 and 14 illustrate the time
dependence of 4,6-DMDBT conversion and the remaining sulfur
content in the liquid phase over Pd/Beta-H and Pd/Al-MCM-41.
The conversion of 4,6-DMDBT was lower over Pd/Beta-H than over
Pd/Al-MCM-41 (Fig. 13), due to the larger number of exposed Pd
atoms for 4,6-DMDBT in Pd/Al-MCM-41 (with Pd particles inside
mesopores) compared with Pd/Beta-H (with Pd particles inside
both mesopores and micropores). However, analysis of reactants
and products by the sulfur analyzer demonstrated a much higher
sulfur content remaining in the reaction system over Pd/Al-MCM-
41 than over Pd/Beta-H (Fig. 14), indicating Pd/Beta-H’s much
greater desulfurization ability. As discussed earlier for the hy-

132
T. Tang et al. / Journal of Catalysis 257 (2008) 125–133
ꢀ
benzothiophene (4,6-DM-PH-DBT), and 3,3 -dimethylbicyclo-
ꢀ
hexyl (3,3 -DM-BCH) [52,54–56] were formed over Pd/Al-
MCM-41. 4,6-DM-TH-DBT, 4,6-DM-HH-DBT, and 4,6-DM-PH-
DBT were the intermediates in the hydrogenation of 4,6-
ꢀ
DMDBT, and 3,3 -DM-BCH resulted from the hydrodesulfu-
rization of 4,6-DM-PH-DBT [54,56], suggesting that the hy-
drodesulfurization of 4,6-DMDBT over Pd/Al-MCM-41 occurred
via the HYD pathway. This finding is in good agreement with
the results obtained for Pd/γ -Al2O3 and Pt-Pd/γ -Al2O3 re-
ported previously [54–56].
2. In addition to 4,6-DM-TH-DBT, 4,6-DM-HH-DBT, and 4,6-DM-
PH-DBT, we found a significant amount of light hydrocarbons
(C5–C9) over Pd/Beta-H, which may be hydrocracking products
of intermediates formed from 4,6-DMDBT. In particular, we
found cyclohexane, suggesting that demethylation and scission
of the C–C bond connecting the two rings in cyclohexylben-
zene may occur over Pd/Beta-H.
3. The difference in the products between Pd/Beta-H and Pd/Al-
MCM-41 also is related to the change in the Beta-H zeolite
and Al-MCM-41 supports, because the palladium loadings and
particle sizes are almost the same for the two catalysts. The
higher acidity is favorable for demethylation and scission of
the C–C bond connecting the two rings [51]. Similar phenom-
ena have been reported over alumina-supported CoMo and
NiMo catalysts modified by acidic zeolites [33,34] and by the
addition of phosphorus and fluorine [36–38].
Fig. 13. Dependences of 4, 6-DMDBT conversions on reaction time. (2) Pd/Beta-H;
(") Pd/Al-MCM-41.
Recently, Niquille-Röthlisberger and Prins [57,58] compared the
catalytic activity in HDS of 4,6-DMDBT over Pd supported on
amorphous silica-alumina (ASA) and over alumina and found that
the ASA-supported Pd catalyst had a much higher activity than
the alumina-supported Pd catalyst. They have suggested that the
more strongly acidic ASA support is beneficial for the creation of
electron-deficient Pd particles, leading to better sulfur resistance
and improved hydrogenation properties [57]. This was further con-
firmed by catalytic results in the presence of pyridine and piperi-
dine [58]. In addition, Niquille-Röthlisberger and Prins suggested
that a new reaction might occur: hydrogenation by spillover of hy-
drogen atoms to 4,6-DMDBT molecules adsorbed on the support
in the vicinity of the Pd particles [57]. In our case, compared with
Al-MCM-41, the strongly acidic Beta-H support may have an ad-
vantage in the creation of electron-deficient Pd particles and the
adsorption of 4,6-DMDBT molecules on acidic sites near the Pd
particles [57], leading to significantly improved catalyst activity.
Fig. 14. Dependences of the remaining sulfur content in 4,6-DMDBT-hydrogenation
system on reaction time. (2) Pd/Beta-H; (") Pd/Al-MCM-41.
drogenation of naphthalene and pyrene, because of Pd/Beta-H’s
superior hydrogenation ability, deep hydrogenation or C-S bond-
breaking of 4,6-DMDBT, which facilitates the HDS of 4,6-DMDBT,
occurred more readily on Pd/Beta-H than on Pd/Al-MCM-41. For
example, when the reaction time reached 180 min, the sulfur
content in the liquid phase was 165 ppm over Pd/Beta-H, com-
pared with 226 ppm over Pd/Al-MCM-41. These results indicate
Pd/Beta-H’s higher activity for hydrodesulfurization of 4,6-DMDBT.
Recently, Lee et al. [53] reported the HDS of 4,6-DMDBT over Co-
MoS catalysts supported on nanoporous carbon. They obtained a
4. Conclusion
Compared with Pd/Al-MCM-41, Pd/Beta-H exhibited good sul-
fur tolerance in the hydrogenation of naphthalene and pyrene and
greater activity in the HDS of 4,6-DMDBT. These findings are at-
tributed to the differing support acidity of Beta-H zeolite and Al-
MCM-41.
◦
4,6-DMDBT conversion of 55.4% at 4.0 MPa, 320 C, and a reaction
time of 240 min in an autoclave. In our case, under mild conditions
(6.5 MPa, 250 C, 180 min), the Pd/Beta-H catalyst demonstrated a
Acknowledgments
◦
4,6-DMDBT conversion of 77%. These results confirmed that nobel
metal catalysts supported on acidic mesoporous zeolites are very
helpful for the deep HDS of 4,6-DMDBT.
This work was supported by the State Basic Research Project
of China (grant 2004CB217804) and the National Natural Science
Foundation of China (grants 20573044 and 20773049).
To gain insight into the difference in catalytic activity for
the HDS of 4,6-DMDBT, we analyzed the products catalyzed by
Pd/Beta-H and Pd/Al-MCM-41 by GC-MS, and obtained the follow-
ing results:
References
[1] A. Stanislaus, B.H. Cooper, Catal. Rev. Sci. Eng. 36 (1994) 75.
[2] C. Song, X.L. Ma, Appl. Catal. B 41 (2003) 207.
[3] C. Song, Catal. Today 86 (2003) 211.
[4] J. Barbier, E. Lamy-Pitara, P. Marecot, J.P. Boitiaux, J. Cosyns, F. Verna, Adv. Catal.
37 (1990) 279.
1. Such compounds as 4,6-dimethyl-1,2,3,4-tetrahydrodibenzo-
thiophene (4,6-DM-TH-DBT), 4,6-dimethyl-1,2,3,4,4a,9b-hexadi-
benzothiophene (4,6-DM-HH-DBT), 4,6-dimethylperhydrodi-
[5] B.H. Cooper, B.L. Donnis, Appl. Catal. A 137 (1996) 203.

T. Tang et al. / Journal of Catalysis 257 (2008) 125–133
133
[6] C. Song, A.D. Schmitz, Energy Fuels 11 (1997) 656.
[32] F. Bataille, J.L. Lemberton, P. Michaud, G. Pérot, M. Vrinat, M. Lemaire, E. Schulz,
M. Breysse, S. Kasztelan, J. Catal. 191 (2000) 409.
[7] H. Yasuda, N. Matsubayashi, T. Sato, Y. Yoshimura, Catal. Lett. 54 (1998) 23.
[8] H. Yasuda, T. Sato, Y. Yoshimura, Catal. Today 50 (1999) 63.
[9] B. Pawelec, R. Mariscal, R.M. Navarro, S. van Bokhorst, S. Rojas, J.L.G. Fierro,
Appl. Catal. A 225 (2002) 223.
[10] J.T. Miller, D.C. Koningsberger, J. Catal. 162 (1996) 209.
[11] W.M.H. Sachtler, A.Y. Stakheev, Catal. Today 12 (1992) 283.
[12] S.D. Lin, M.A. Vannice, J. Catal. 143 (1993) 539.
[33] M.V. Landau, D. Berger, M. Herskowitz, J. Catal. 159 (1996) 236.
[34] T. Isoda, S. Nagao, X.L. Ma, Y. Korai, I. Mochida, Energy Fuels 10 (1996) 1078.
[35] E. Lecrenay, K. Sakanishi, I. Mochida, Catal. Today 39 (1997) 13.
[36] E. Lecrenay, K. Sakanishi, I. Mochida, T. Suzuka, Appl. Catal. A 175 (1998) 237.
[37] C. Kwak, M.Y. Kim, K. Choi, S.H. Moon, Appl. Catal. A 185 (1999) 19.
[38] C. Kwak, J.J. Lee, J.S. Bae, K. Choi, S.H. Moon, Appl. Catal. A 200 (2000) 233.
[39] I.I. Abu, K.J. Smith, J. Catal. 241 (2006) 356.
[13] S.D. Lin, M.A. Vannice, J. Catal. 143 (1993) 563.
[14] S.D. Lin, M.A. Vannice, J. Catal. 143 (1993) 554.
[40] I.I. Abu, K.J. Smith, Appl. Catal. A 328 (2007) 58.
[15] L.J. Simon, J.G. van Ommen, A. Jentys, J.A. Lercher, J. Phys. Chem. B 104 (2000)
11644.
[41] A.J. Wang, L.F. Ruan, Y. Teng, X. Li, M.H. Lu, J. Ren, Y. Wang, Y.K. Hu, J. Catal. 229
(2005) 314.
[16] L.J. Simon, J.G. van Ommen, A. Jentys, J.A. Lercher, J. Catal. 201 (2001) 60.
[17] L.J. Simon, J.G. van Ommen, A. Jentys, J.A. Lercher, J. Catal. 203 (2001) 434.
[18] A.H. Janssen, A.J. Koster, K.P. de Jong, Angew. Chem. Int. Ed. 40 (2001) 1102.
[19] A.H. Janssen, A.J. Koster, K.P. de Jong, J. Phys. Chem. B 106 (2002) 11905.
[20] S. van Donk, A.H. Janssen, J.H. Bitter, K.P. de Jong, Catal. Rev. 45 (2003) 297.
[21] T.D. Tang, C.Y. Yin, L.F. Wang, Y.Y. Ji, F.S. Xiao, J. Catal. 249 (2007) 111.
[22] F.-S. Xiao, L.F. Wang, C.Y. Yin, K.F. Lin, Y. Di, J.X. Li, R.R. Xu, D.S. Su, R. Schlögl,
T. Yokoi, T. Tatsumi, Angew. Chem. Int. Ed. 45 (2006) 3090.
[23] H. Wang, T.J. Pinnavaia, Angew. Chem. Int. Ed. 45 (2006) 7603.
[24] M. Choi, H. Cho, R. Srivastava, C. Venkatesan, D. Choi, R. Ryoo, Nat. Mater. 5
(2006) 718.
[42] X. Li, A.J. Wang, S. Zhang, Y.Y. Chen, Y.K. Hu, Appl. Catal. A 316 (2007) 134.
[43] X.C. Meng, Y.X. Wu, Y.D. Li, J. Porous Mater. 13 (2006) 365.
[44] H.J. Zhang, X.C. Meng, Y.D. Li, Y.S. Lin, Ind. Eng. Chem. Res. 46 (2007) 4186.
[45] L.Y. Chen, Z. Ping, G.K. Chuah, S. Jaenicke, G. Simon, Micro. Meso. Mater. 27
(1999) 231.
[46] J.J.F. Scholten, A.P. Pijpers, A.M.L. Hustings, Catal. Rev. Sci. Eng. 27 (1985) 151.
[47] W.M. Zhang, P.G. Smirniotis, M. Gangoda, R.N. Bose, J. Phys. Chem. B 104 (2000)
4122.
[48] A. Corma, A. Martínez, V. Martínez-Soria, J. Catal. 169 (1997) 480.
[49] T.C. Huang, B.C. Kang, Ind. Eng. Chem. Res. 34 (1995) 1140.
[50] C. Song, CHEMTECH 29 (1999) 26.
[25] R. Srivastava, M. Choi, R. Ryoo, Chem. Commun. (2006) 4489.
[26] T. Fujikawa, O. Chiyoda, M. Tsukagoshi, K. Idei, S. Takehara, Catal. Today 45
(1998) 307.
[27] K.G. Knudsen, B.H. Cooper, H. Topsøe, Appl. Catal. A 189 (1999) 205.
[28] H. Schulz, W. Böhringer, P. Waller, F. Ousmanov, Catal. Today 49 (1999) 87.
[29] C. Li, Z.X. Jiang, J.B. Gao, Y.X. Yang, S.J. Wang, F.P. Tian, F.X. Sun, X.P. Sun, P.L.
Ying, C.R. Han, Chem. Eur. J. 10 (2004) 2277.
[51] S.K. Bej, S.K. Maity, U.T. Turaga, Energy Fuels 18 (2004) 1227.
[52] M. Egorova, R. Prins, J. Catal. 224 (2004) 278.
[53] J.J. Lee, S. Han, H. Kim, J.H. Koh, T. Hyeon, S.H. Moon, Catal. Today 86 (2003)
141.
[54] A. Niquille-Röthlisberger, R. Prins, J. Catal. 235 (2005) 229.
[55] P. Kukula, V. Gramlich, R. Prins, Helv. Chim. Acta 89 (2006) 1623.
[56] A. Niquille-Röthlisberger, R. Prins, J. Catal. 242 (2006) 207.
[57] A. Niquille-Röthlisberger, R. Prins, Catal. Today 123 (2007) 198.
[58] A. Niquille-Röthlisberger, R. Prins, Ind. Eng. Chem. Res. 46 (2007) 4124.
[30] M.V. Landau, Catal. Today 36 (1997) 393.
[31] V. Meille, E. Schulz, M. Lemaire, M. Vrinat, J. Catal. 170 (1997) 29.