Noble metal silicides catalysts with high stability for hydrodesulfurization of dibenzothiophenes

Article abstract of DOI:10.1016/j.cattod.2020.08.027

Development of highly efficient and long stable hydrodesulfurization (HDS) catalysts still is a great challenge for the refining industry. In this work, a series of intermetallic noble metal silicides supported by carbon nanotubes catalysts (Pt₂Si/CNTs, Rh_xSi/CNTs, and RuSi/CNTs) have been developed by chemical vapor deposition successfully, using dichlorodimethylsilane as Si source. These materials were used as efficient catalysts for the deep HDS of dibenzothiophenes (4,6-DMDBT and DBT) and performed high selectivity to the direct desulfurization pathway. The sequence of HDS activity over noble metal silicides catalysts is in keeping with the sequence of HDS activity of the corresponding metal catalysts, which is Pt₂Si/CNTs > Rh_xSi/CNTs >> RuSi/CNTs. In addition, the Pt₂Si/CNTs performed an excellent stability in 100 h stability testing for HDS of 4,6-DMDBT. Therefore, this sulfur-tolerant noble metal silicides could be as promising catalysts for the ultra-deep HDS of fossil-fuel.

Full text of DOI:10.1016/j.cattod.2020.08.027

Catalysis Today xxx (xxxx) xxx
Contents lists available at ScienceDirect
Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Noble metal silicides catalysts with High stability for hydrodesulfurization
of dibenzothiophenes
,
b
,
,
,
Kaixuan Yanga 1, Xiao Chena 1, Zongxuan Baia, Changhai Lianga *
a State Key Laboratory of Fine Chemicals, Laboratory of Advanced Materials and Catalytic Engineering, School of Chemical Engineering, Dalian University of Technology,
Dalian 116024, China
b Green Chemistry Centre, College of Chemistry and Chemical Engineering, Yantai University, Yantai 264005, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
Development of highly efficient and long stable hydrodesulfurization (HDS) catalysts still is a great challenge for
the refining industry. In this work, a series of intermetallic noble metal silicides supported by carbon nanotubes
catalysts (Pt2Si/CNTs, RhxSi/CNTs, and RuSi/CNTs) have been developed by chemical vapor deposition suc-
cessfully, using dichlorodimethylsilane as Si source. These materials were used as efficient catalysts for the deep
HDS of dibenzothiophenes (4,6-DMDBT and DBT) and performed high selectivity to the direct desulfurization
pathway. The sequence of HDS activity over noble metal silicides catalysts is in keeping with the sequence of
HDS activity of the corresponding metal catalysts, which is Pt2Si/CNTs > RhxSi/CNTs >> RuSi/CNTs. In
addition, the Pt2Si/CNTs performed an excellent stability in 100 h stability testing for HDS of 4,6-DMDBT.
Therefore, this sulfur-tolerant noble metal silicides could be as promising catalysts for the ultra-deep HDS of
fossil-fuel.
Noble metal silicides
Deep HDS
Sulfur tolerance
DDS
Pathway
1. Introduction
in order to meet the increasingly stringent environmental requirements
and further reduce the sulfur content in gasoline and diesel oil, the
Removal of sulfur compounds from fossil-fuel and production of
clean oil products is an inevitable trend and the development of highly
efficient HDS catalysts would be a great challenge in the refining in-
dustry [1,2]. Traditional Ni(Co)Mo(W) sulfides HDS catalysts presented
good HDS activity and stability in the process of gasoline and diesel oil
refining during the implementation of relatively loose fuel oil sulfur
emission standards (<500 ug/g) due to their low cost [2–4]. With the
attention to environmental problems and increasingly stringent regu-
lations on sulfur content in fuel oil, the technology of deep and
ultra-deep desulfurization has aroused widely public concern gradually
[5]. However, due to the large steric hindrance of dibenzothiophene and
its alkylated derivatives, traditional Ni(Co)Mo(W) sulfide catalysts
performed low activity for the deep HDS of these compounds in com-
parison with the HDS of thioether and its derivatives. Deep desulfur-
ization of the fuels implies that the least reactive sulfur compounds must
be converted, which requires the application of severe operating con-
ditions and the use of especially active catalysts. Unfortunately, the HDS
process with increasing temperature and pressure are just not enough to
remove last traces of sulfur without undesired side reactions. Therefore,
development of novel highly efficient deep HDS catalysts become the
focus of scientific researchers.
Although supported noble metal catalysts are expensive and scarce,
they have much better hydrogenation performances than those of con-
ventional metal sulfides in HDS of dibenzothiophenes, which may be
used in the second reactor of a deep HDS process [6–8]. However, the
easy poisoning of the active sites by sulfur would be a major drawback,
which reduce their lifetime dramatically [9,10]. Therefore, many re-
searchers have done plenty of efforts to improve the sulfur tolerance of
noble metal catalysts. Generally, the acidic supports were employed for
supporting noble metal catalysts at HDS reaction since there are partial
transfer of electrons from the metal to acidic sites in the supports, which
would decrease the adsorption between noble metal and H2S and
improve the sulfur tolerance of noble HDS catalysts [11,12]. However,
the fossil-fuel can be decomposed and isomerized over acidic supports,
which not only decreases the yield of liquid product, but leads to the
severe deactivation because of the coking. Therefore, another effective
way to prepare the noble metal catalysts with high sulfur-tolerance
should be developed.
* Corresponding author.
E-mail address: changhai@dlut.edu.cn (C. Liang).
1
These authors contributed equally to this work.
https://doi.org/10.1016/j.cattod.2020.08.027
Received 22 January 2020; Received in revised form 16 July 2020; Accepted 24 August 2020
Available online 29 August 2020
0920-5861/© 2020 Elsevier B.V. All rights reserved.
Please cite this article as: Kaixuan Yang, Catalysis Today, https://doi.org/10.1016/j.cattod.2020.08.027

K. Yang et al.
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Fig. 1. XRD patterns of CNTs supported noble metal silicides with (a) 3 wt.% metal loading and (b) 10 wt.% metal loading. The inset images correspond to the
construction of intermetallic noble metal silicides.
The combination of noble metals with metals or non-metallic ele-
ments to form alloys or intermetallic compounds can improve the sulfur
tolerance of noble metal catalysts to some extent [13], which has
already been confirmed by Pd-Pt, Pd-Au, and Pt-Ir bimetallic catalysts
due to the synergistic effect [14–17]. Recently, the intermetallic com-
pounds have shown excellent performances on the HDS reaction. Kanda
et al. prepared a new Rh2P catalyst, which exhibited excellent activity
and stability for HDS reaction [18,19]. Richard et al. also prepared Pd-P
and Ru-P catalysts with different phases, which showed high stability
during the testing [20]. Similarly, Bussell et al. found that the Rh2P/SiO2
catalyst performed high stability during the 100 h HDS stability mea-
surement and had higher sulfur-tolerance than the metallic Rh/SiO2
catalyst [21]. The Rh2P/SiO2 catalyst preferred the hydrogenation
desulfurization (HYD) pathway for the HDS of dibenzothiophene (DBT),
which was different from that of sulfide-Rh catalyst.
Table 1
Structural properties of CNTs and CNTs-supported noble metal silicides
catalysts.
Sample
SBET
d (nm)a
Metal loading
(wt.%)
Particle size (nm)
(m2/g)a
CNTs
144
146
140
143
3.72
3.72
3.72
3.72
–
–
RhxSi/CNTs
RuSi/CNTs
Pt2Si/CNTs
2.86
2.79
2.93
2.49 ± 0.56
2.94 ± 1.10
1.33 ± 0.32
a
BET surface area (SBET) and average pore diameter (d) were determined by
using N2 adsorption-desorption isotherms measured at ꢀ 196 ◦C.
Herein, a series of intermetallic noble metal silicides supported by
carbon nanotubes catalysts (Pt2Si/CNTs, RhxSi/CNTs, and RuSi/CNTs)
have been developed and applied in the HDS of DBT and 4,6-DMDBT.
The geometrical and electronic structures and HDS performances of
intermetallic noble metal silicides catalysts have been investigated in-
depth. The Pt2Si/CNTs catalyst has shown the highest HDS activity in
comparison with the other noble metal silicides catalysts. Furthermore,
the Pt2Si/CNTs catalyst has performed an excellent stability in the HDS
of 4,6-DMDBT.
Interestingly, Searcy et al. studied the stability of intermetallic
compounds in the presence of H2S by chemical thermodynamics and
found that transition metal silicides could tolerate much more H2S than
the corresponding phosphides [22]. In our previous research, density
functional theory calculations (DFT) was also carried out to explore the
relationship between the electronic structure and the origin of the effi-
cient sulfur tolerance of metal silicides, which indicated that the
S-poisoning process of the active sites was suppressed or strongly
decelerated due to the special electronic structure in NiSi2 [23,24].
However, the HDS activities of non-noble metal silicides catalysts were
inferior in comparison with the those of traditional Ni(Co)Mo(W) sulfide
catalysts, despite the highly sulfur-resistant capability. Furthermore, a
high S-tolerant and efficient noble metal silicide (Pd2Si/CNTs) catalyst
was developed, which showed good stability over an 80 h lift testing and
performed 3-fold HDS activity than that over commercial Ni-Mo sulfide
catalyst [25]. The previous research results give us enlightening for
designing other highly efficient and good sulfur tolerant noble metal
silicides catalysts for the ultra-deep HDS of fossil-fuel.
2. Experiment
2.1. Materials
All the chemicals were reagent grade and used without further pu-
rifications. H2PtCl6⋅6H2O, DBT, 4,6-DMDBT, and decalin were pur-
chased from Sinopharm Chemical Reagent Co. Ltd. RuCl3⋅3H2O and
RhCl3⋅3H2O were purchased from Aladdin Co. Ltd.
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2.2. Catalysts preparation
pore size analyser. Transmission electron microscopy (TEM) and scan-
ning transmission electron microscope (STEM) was performed by using
a Tecnai G2 F30 S-Twin transmission electron microscope operating at
300 kV. Surface compositions and chemical state were investigated
using X-Ray photoelectron spectroscopy (XPS) employing an ESCA-
Intermetallic noble metal silicides supported on carbon nanotubes
(CNTs) catalysts were prepared by chemical vapor deposition (CVD) of
dichlorodimethylsilane ((CH3)2SiCl2) on M–O/CNTs (M = Pt, Rh, and
Ru) samples in H2 flow. Taking the preparation of Pt2Si/CNTs as an
example, the Pt-O/CNTs precursor was firstly synthesized by impreg-
nation the H2PtCl6⋅6H2O in CNTs and then calcinated at 350 ◦C for 2 h.
Secondly, the Pt-O/CNTs precursor was loaded in a quartz boat and put
into the middle of the horizontal quartz tube furnace, which was
reduced at 350 ◦C for 2 h with 30 sccm H2. When it reached the depo-
sition temperature (500 ◦C), (CH3)2SiCl2 maintained at 0 ◦C was carried
into the quartz tube to deposit on the reduced Pt/CNTs sample for 1 h
using H2 (10 sccm) as the carrier. The exhaust gas was adsorbed by alkali
solution. The Pt2Si/CNTs sample was cooled down to room temperature
and passivated under O2/Ar atmosphere for 12 h.
LAB250 (Thermo VG, USA) spectrometer with Al Kα (1486.6 eV) radi-
ation with a power of 150 W. The core level spectra were referenced as
the neutral C 1s peak at 284.6 eV and were deconvoluted into Gaussian
component peaks.
2.4. Catalytic testing
Typically, the catalytic HDS of DBT and 4,6-DMDBT over CNTs
supported intermetallic noble metal silicides catalysts were conducted in
a continuous flow fixed-bed reactor at 340 ◦C and 3 MPa. Before the HDS
properties testing, 0.1 g catalyst was reduced in situ in a 9 mm stainless
steel tube by pure H2 at 300 ◦C for 2 h. During the reaction, the liquid
feedstock including 1000 ppm 4,6-DMDBT or 3000 ppm DBT as reactant
and decalin as inert solvent was pumped into the reactor. The reaction
product with different reaction conditions after being condensed were
collected at room temperature after the catalyst reached steady state and
identified by Agilent 6890 N GC with 5973 MSD (HP-5 MS capillary
2.3. Catalysts characterization
X-ray diffraction (XRD) was carried out to analyze the structure and
phase of catalysts, using a D/MAX-2400 diffractometer (Cu Kα1 radia-
tion, λ= 0.15418 nm) and operated at 40 kV and 100 mA. Analysis of
element contents of Pt-Si, Rh-Si, and Ru-Si catalysts were carried out on
an inductively coupled plasma optical emission spectrometer (ICP-OES).
Nitrogen adsorption-desorption isotherms were constructed using the
column, 0.32 mm ×0.25
μ
m × 30 m), and analyzed by Agilent GC 7890A
with FID (HP-5 capillary column, 0.32 mm ×0.25
μ
m × 30 m).
◦
multi-points method at -196 C with an Autosorb IQ surface area and
Fig. 2. STEM image and STEM-EDX element mapping images of Pt2Si/CNTs sample.
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3. Results and discussion
silicides.
Nitrogen adsorption-desorption isotherms of the CNTs support and
M-Si/CNTs (M = Pt, Rh, and Ru) samples were measured to study the
impacts of CVD treatment on the pore structure. All the BET surface area
and average pore sizes of those catalysts are shown in Table 1. The
specific surface area of the CNTs supported noble metal silicides cata-
lysts show a slight decline compared with the CNTs support, except that
of RhxSi/CNTs. There is no change on the average pore sizes of those
catalysts. Besides, the ICP results in Table 1 also show that the metal
loading of those catalysts still maintain at ca. 3 wt.% after the CVD
treatment. These results indicate that there is almost no negative effect
on the structure of support after the Si deposition.
3.1. Characterization of supported noble metal silicides catalysts
The structure and crystal phases of the as-prepared Pt2Si/CNTs,
RhxSi/CNTs, and RuSi/CNTs samples are confirmed by XRD patterns.
For all the XRD patterns of the samples in Fig. 1, there are three same
diffraction peaks at ca. 26.2◦, 44.2◦, and 54.0◦ corresponding to CNTs. In
the XRD pattern of Pt2Si/CNTs sample, there are two tiny peaks at 32.1◦
and 44.7◦, which are corresponding to the (1, 1, 0) and (1, 1, 2) lattice
planes of Pt2Si (JCPDS # 17-0683). However, there is no peaks corre-
sponding to noble metal or noble metal silicides in the XRD patterns of
RhxSi/CNTs and RuSi/CNTs samples, which may be attributed to the
low metal loading and low crystallinity. In order to find the direct evi-
dence to prove the formation of noble metal silicides after CVD, RhxSi/
CNTs, Pt2Si/CNTs, and RuSi/CNTs samples with 10 wt.% metal loading
are also prepared by CVD at the same reaction conditions. As shown in
Fig. 1b, the peaks of Pt2Si/CNTs and RuSi/CNTs samples match well
with the standard pattern of Pt2Si (JCPDS # 19-0893) and RuSi (JCPDS
# 50-1242), respectively. It indicates that single-phase Pt2Si and RuSi
intermetallic compounds can be prepared successfully by CVD treat-
ment. However, there are two phases including RhSi (JCPDS # 12-0513)
and Rh3Si2 (JCPDS # 39-0793) in the RhxSi/CNTs sample. In addition,
the crystal structure of Pt2Si, RuSi, RhSi, and Rh3Si2 are inserted in
Fig. 1b. Clearly, it shows that each Si atom is surrounded by metal atoms
in those noble metal silicides intermetallic compounds. Similar with the
intermetallic Pd2Si sample, the active noble metal is partially isolated by
Si atoms, which would lead to electronic structure modification and
endow the metal with different catalytic performance [25]. Combined
with the XRD results above all, the CVD method using (CH3)2SiCl2 as the
Si source is a general way to prepare supported noble metal silicides
catalysts, especially for the preparation of single-phase noble metal
In order to reveal the particle distribution and crystalline structure,
the as-prepared RhxSi/CNTs, Pt2Si/CNTs, and RuSi/CNTs samples were
characterized by TEM and STEM-EDX measurements. The EDX element
mappings in Fig. 2 and Fig. S1 confirm the elemental composition and
indicate the presence of Si in these three noble metal silicides after the
CVD treatment. Fig. 3 displays the TEM images and the particle size
histograms of the as-prepared RhxSi/CNTs, Pt2Si/CNTs, and RuSi/CNTs
catalysts. As shown in Fig. 3, all these noble metal silicides nanoparticles
are highly dispersed on CNTs and there is no apparent aggregation
observed. The particle sizes of the noble metal silicides nanoparticles
from statistical analysis is centered at 2.49 ± 0.56 nm, 1.33 ± 0.32 nm,
and 2.94 ± 1.10 nm for the RhxSi/CNTs, Pt2Si/CNTs, and RuSi/CNTs,
respectively. As shown in Fig. 3b, the observed lattice spacing of the
particle in RhxSi/CNTs is ca. 2.09 Å, which matches well with the (1, 1,
0) plane of RhSi with a tetragonal structure. Similarly, the measured
lattice spacings of 2.03 Å and 2.35 Å are corresponding to the (1, 1, 2)
plane of Pt2Si, the (2, 0, 0) plane of RuSi, respectively. The results are
corresponding to the XRD results, which further prove that highly
dispersed noble metal silicides nanoparticles supported on CNTs were
synthesized by CVD method successfully.
Fig. 3. TEM images and high-resolution TEM images of RhxSi/CNTs, Pt2Si/CNTs, and RuSi/CNTs samples. The inset images correspond to particle size distribution
and associated fast Fourier transformation, respectively.
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The surface chemical properties of the Pt2Si, RuSi, and Rh-Si samples
and their corresponding noble metal catalysts are tested in the HDS of
4,6-DMDBT and DBT at different reaction conditions. Based on GC–MS
analyses results, the reaction network of the HDS of 4,6-DMDBT over as-
prepared noble metal silicides catalysts has been proposed, as shown in
Scheme 1. There are five main products including 4,6-dimethylbiphenyl
(4,6-DMBP), 4,6-dimethyltetrahydrodibenzothiophene (4,6-DM-TH-
DBT), 4,6-dimethylhexahydrodibenzothiophene (4,6-DM-HH-DBT),
4,6-dimethylcyclohexylbenzene (4,6-DM-CHB), and 4,6-dimethylbicy-
clohexyl (4,6-DM-BCH). 4,6-DMBP is observed as the only product
through DDS pathway. The intermediate products (4,6-DM-TH-DBT,
4,6-DM-HH-DBT, and 4,6-DM-CHB), and the fully hydrogenated product
(4,6-DM-BCH) are observed as the products through HYD pathway. The
selectivity to 4,6-DMBP (SDMBP) is used for measuring the selectivity to
DDS pathway, while 1-SDMBP represents selectivity to HYD pathway.
Normally, there are two different adsorption modes on the surface of
active sites in the HDS of 4,6-DMDBT, which are vertical adsorption
(adsorption to S atom) and horizontal adsorption (adsorption to benzene
ring) [37,38]. The horizontal adsorption mode is positive to the HYD
pathway, while the vertical adsorption mode for 4,6-DMDBT occurs on
the edge sites, which would be beneficial to the DDS pathway [38].
Because of the steric hindrance of methyl, the HDS of 4,6-DMDBT over
supported catalysts normally choose to go through HYD pathway but not
are investigated by XPS (as shown in Fig. 4). There are two peaks at 74.0
eV and 78.1 eV belonging to 4f7/2 and 4f5/2 of Pt in PtOx, which are
derived from the slight surface oxidation of platinum silicide phase [26,
27]. The binding energy of the Pt 4f7/2 and Pt 4f5/2 at ca. 72.9 eV and
76.3 eV can be attributed to the Pt2Si intermetallic compound, which are
consistent with the reported by Morgan et al. [28,29]. In comparison
with the XPS spectrum of metallic Pt 4f, the binding energy of Pt in Pt2Si
shifts to higher binding energy, which indicates that there is electron
transfer from Pt to Si atoms [30]. As shown in Fig. 4f, the Rh peaks in
spectrum of Rh 3d5/2 are at 307.1 eV and 307.6 eV, which are higher
than the binding energy of metal Rh [31,32]. It indicates indirectly that
the Rh combined with Si, leading to the higher binding energy of Rh.
Besides, there are two peaks at 308.8 eV and 314.4 eV belonging to 3p3/2
and 3p5/2 of Rh in RhOx, which are derived from the slight surface
oxidation of Rh silicide phase [33,34]. Similarly, the Ru peak at 462.4
eV and 466.8 eV in spectrum of Ru 3p can be attributed to the Ru of RuSi
and Ru of RuOx, respectively [35,36].
3.2. HDS performances of supported noble metal silicides catalysts
The HDS performances of as-prepared noble metal silicides catalysts
Fig. 4. XPS spectra of all elements in (a) Pt2Si, (c) RuSi, and (e) Rh-Si, (b) Pt 4f region, (d) Ru 3p region, and (f) Rh 3d region in these samples.
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Scheme 1. Reaction network of 4,6-DMDBT conversion over noble metal silicides catalysts.
DDS pathway, especially over the noble metal catalysts with a powerful
hydrogenation capability of benzene ring.
silicides catalysts, the RhxSi/CNTs and RuSi/CNTs catalysts present
almost no activity under 340 ◦C and 3 MPa. However, as shown in
Fig. 5d, the Pt2Si/CNTs catalyst shows good activity for the HDS of 4,6-
DMDBT. When the contact time closed to 0.6 min, the conversion of 4,6-
DMDBT can reach to 50 %. The selectivity to 4,6-DMBP through the DDS
route is as much as 40 %, which is much higher than that over the metal
Pt/CNTs catalyst. A similar phenomenon occurred during HDS of 4,6-
DMDBT over Pd2Si/CNTs catalyst, where the selectivity to DDS
pathway was enhanced when the formation of intermetallic Pd2Si [25].
Combining the geometric structure (Pt atoms isolated by Si atoms) and
the electronic structure (electron transferred from Pt to Si) of interme-
tallic Pt2Si, we can deduce that the modification of Si element to metallic
Pt atoms would decrease the activation capacity of H2, which is negative
Fig. 5 present the conversion of 4,6-DMDBT and the selectivity to
DDS/HYD pathway over CNTs supported noble metal catalysts with
◦
different contact time at 340 C and 3.0 MPa total pressure. It clearly
demonstrates that the HDS activity decreases in the following order: Pt/
CNTs > Rh/CNTs >> Ru/CNTs. The conversion of 4,6-DMDBT over Pt/
CNTs and Rh/CNTs catalysts are 94.7 % and 43.2 % at the same contact
time (τ =0.74 min), respectively, which are much higher than those over
Ru/CNTs (< 5%). In addition, the selectivity to HYD reaction pathway
over Pt/CNTs, Rh/CNTs, and Ru/CNTs are more than 85 % in the HDS of
4,6-DMDBT.
For the HDS of 4,6-DMDBT over CNTs supported noble metal
Fig. 5. 4,6-DMDBT conversion and selectivity to DDS/HYD over (a) Pt/CNTs, (b) Ru/CNTs, (c) Rh/CNTs, and (d) Pt2Si/CNTs catalysts. Reaction conditions: 340 ◦C,
3 MPa, and H2/substrate = 300.
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Fig. 6. DBT conversion and selectivity to DDS/HYD over (a) Pt2Si/CNTs, (b) RhxSi/CNTs, and (c) RuSi/CNTs catalysts. Reaction conditions: 340 ◦C, 3 MPa, and H2/
substrate = 300.
to the hydrogenation of benzene ring in 4,6-DMDBT, leading to the high
selectivity to DDS pathway and preventing form the hydrogen con-
sumption [25,39–41].
Table 2
Catalytic performances of noble metal and metallic compounds catalysts for the
HDS of DBT.
In addition, the RhxSi/CNTs, Pt2Si/CNTs, and RuSi/CNTs catalysts
are used for the HDS of DBT. As shown in Fig. 6, the HDS activity of DBT
over those three metal silicides catalysts are much higher than that of
4,6-DMDBT, because of the absence of methyl steric-hindrance effect.
Among these catalysts, the Pt2Si/CNTs has the highest activity, which
probably attribute to the high intrinsic activity of the corresponding
metal Pt. The small particle size of the Pt2Si/CNTs is also beneficial to
the HDS of DBT. The RuSi/CNTs is the less active for the HDS of DBT.
The sequence of HDS activity over the metal silicides catalysts is in
keeping with the sequence of HDS activity over the corresponding metal
catalysts, which indicates that the corresponding metal is the principal
factor on the activity of metal silicides catalysts. Particularly noteworthy
is that all these three kinds of metal silicide catalyst have superiorly high
selectivity to DDS pathway during the HDS of DBT. As shown in Table 2,
these noble metal silicides catalysts perform the highest selectivity to
DDS under the similar conversion of DBT, in comparison with all the
reported noble metal (Rh, Pt, and Ru) catalysts and noble intermetallic
compounds (Rh2P, Ru2P, and RuP) catalysts [7,20,21,42].
Catalysts
Con.%
Sel.% to DDS
Reaction conditions
Ref.
Pt2Si/CNTs
RhxSi/CNTs
RuSi/CNTs
Rh/SiO2
100
100
26
30
99
70
100
99
–
95
92
100
76
4
340 ◦C, 3.0 MPa
340 ◦C, 3.0 MPa
340 ◦C, 3.0 MPa
275 ◦C, 3.0 MPa
275 ◦C, 3.0 MPa
275 ◦C, 3.0 MPa
348 ◦C, 3.0 MPa
348 ◦C, 3.0 MPa
325 ◦C, 3.0 MPa
325 ◦C, 3.0 MPa
340 ◦C, 3.0 MPa
275 ◦C, 5.0 MPa
This work
This work
This work
[21]
Rh2P/SiO2
[21]
sulfided Rh/SiO2
Ru2P/MCM-41
RuP/MCM-41
RuP/SiO2
52
26
27
60
78
26
42
[21]
[42]
[42]
[20]
Sulf. Ru/SiO2
Ru/MCM-41
Pt/AlM-I
–
[20]
55
84
[42]
[7]
The stability of Pt2Si/CNTs catalyst for the HDS of 4,6-DMDBT has
been detected, as shown in Fig. 7. The conversion of 4,6-DMDBT is ca. 45
%. There is no obvious deactivation even after 100 h stability testing. In
addition, the selectivity to DDS pathway is almost unchanged, main-
taining at ca. 40 %. Comparing with the previous report that the metallic
Pt catalyst with neutral support (Si-MCM-41) has shown a significantly
deactivation during 8 h stability testing in HDS of DBT [43], the
Pt2Si/CNTs catalyst has a high sulfur resistance during the HDS of 4,
6-DMDBT. Combing the XRD and XPS results, the isolation effect and
strong interaction between Pt and Si normally lead to a higher energy
barrier for the combination between Pt (in Pt2Si) and S, which could be
the main reason for the excellent stability of Pt2Si/CNTs in the test.
4. Conclusions
In summary, intermetallic noble metal silicides supported by CNTs
catalysts (Pt2Si/CNTs, RhxSi/CNTs, and RuSi/CNTs) have been prepared
by the CVD method successfully. Compared with the RhxSi/CNTs and
RuSi/CNTs, Pt2Si/CNTs catalyst shows the best HDS activity in the HDS
of DBT and 4,6-DMDBT. These three catalysts perform superior selec-
tivity to DDS pathway comparing with the corresponding noble metallic
catalyst, which save the consumption of hydrogen to some extent. In
Fig. 7. Stability testing for 4,6-DMDBT conversion and selectivity to products
over Pt2Si/CNTs catalyst. Reaction conditions: 340 ◦C, 3 MPa, and H2/substrate
= 300.
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´
´
[4] A.E. Cruz Perez, Y. Torrez Jimenez, J.J. Velasco Alejo, T.A. Zepeda, D.M. Frías
addition, due to the active-site isolation by Si element and electron
transfer between Pt and Si atoms, Pt2Si/CNTs catalyst performs the
excellent stability and sulfur resistance during the long-stream stable
testing. Therefore, Pt2Si/CNTs with highly efficient activity and good
sulfur-tolerance as a novel inorganic material is a promising catalyst for
the HDS of fossil-fuel.
´
´
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