A new approach to synthesize supported ruthenium phosphides for hydrodesulfurization

Article abstract of DOI:10.1016/j.materresbull.2015.10.021

Supported noble metal ruthenium phosphides were synthesized by one-step H₂-thermal treatment method using triphenylphosphine (TPP) as phosphorus sources at low temperatures. Two phosphides RuP and Ru₂P can be prepared by this method via varying the molar ratio of metal salt and TPP. The as-prepared phosphides were characterized by X-ray powder diffraction (XRD), low-temperature N₂ adsorption, CO chemisorption and transmission electronic microscopy (TEM). The supported ruthenium phosphides prepared by new method and conventional method together with contradistinctive metallic ruthenium were evaluated in hydrodesulfurization (HDS) of dibenzothiophene (DBT). The catalytic results showed that metal-rich Ru₂P was the better active phase for HDS than RuP and metal Ru. Besides this, ruthenium phosphide catalyst prepared by new method exhibited superior HDS activity to that prepared by conventional method.

Full text of DOI:10.1016/j.materresbull.2015.10.021

Materials Research Bulletin 74 (2016) 98–102
Contents lists available at ScienceDirect
Materials Research Bulletin
journal homepage: www.elsevier.com/locate/matresbu
A new approach to synthesize supported ruthenium phosphides for
hydrodesulfurization
Qingfang Wang , Zhiqiang Wang *, Xiaoqian Yin , Linxi Zhou , Minghui Zhangb,c,**
a,b
a,
b
b
a
Tianjin Key Laboratory of Water Environment and Resources, Tianjin Normal University, Tianjin 300387, China
Key Laboratory of Advanced Energy Materials Chemistry (MOE), Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), College of
b
Chemistry, Nankai University, Tianjin 300071, China
c
College of Chemistry and Environmental Science, Kashgar University, Kashgar 844006, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Supported noble metal ruthenium phosphides were synthesized by one-step H -thermal treatment
2
Received 8 August 2014
Received in revised form 4 September 2015
Accepted 7 October 2015
Available online xxx
method using triphenylphosphine (TPP) as phosphorus sources at low temperatures. Two phosphides
RuP and Ru
2
P can be prepared by this method via varying the molar ratio of metal salt and TPP. The as-
prepared phosphides were characterized by X-ray powder diffraction (XRD), low-temperature N
2
adsorption, CO chemisorption and transmission electronic microscopy (TEM). The supported ruthenium
phosphides prepared by new method and conventional method together with contradistinctive metallic
ruthenium were evaluated in hydrodesulfurization (HDS) of dibenzothiophene (DBT). The catalytic
results showed that metal-rich Ru P was the better active phase for HDS than RuP and metal Ru. Besides
2
this, ruthenium phosphide catalyst prepared by new method exhibited superior HDS activity to that
prepared by conventional method.
Keywords:
A. Inorganic compounds
B. Chemical synthesis
C. X-ray diffraction
C. Transmission electron microscopy
D. Catalytic properties
ã 2015 Elsevier Ltd. All rights reserved.
1. Introduction
phosphide and cobalt phosphide. However, this method has the
disadvantage of requiring a high temperature, which leads to the
Metal phosphides attract considerable attentions due to their
unique chemical and physical properties. They can be used as
catalytic, magnetic, electrode, and hard materials [1–6]. In
aggregation of phosphides resulting in low activity of catalyst. So, it
is necessary to synthesize ruthenium phosphide at low
temperature to get a highly active phase of catalyst. Recently,
Guan et al. had prepared RuP and Ru P used ruthenium chloride
a
particular, the VIII group phosphides (Ni
2
P, Co
2
P etc.) are widely
2
studied for catalytic applications in hydrodesulfurization which is
very important due to strict environmental legislations concerning
the sulfur content in fuels [7]. Supported nickel phosphide
catalysts have showed superior activity and stability to classical
catalysts based on molybdenum sulfide [8–13]. Many methods are
brought out for synthesizing the nickel phosphide. However, the
synthesis and catalytic activity of noble metal phosphides are less
reported than that of nickel phosphide [14–16]. Among the noble
metal phosphides, ruthenium phosphide should be considered due
to its low cost. Nowadays, several methods have been suggested to
synthesize the supported ruthenium phosphide catalyst [17–21].
The conventional method to synthesize ruthenium phosphide is
the reduction of ruthenium salt using phosphate as phosphor
source, which is the also classic method to synthesize nickel
and hypophosphite as precursors at the temperature of 673 K [22],
but the obtained ruthenium phosphide needed post-treatment to
remove salt impurity formed in the process of decomposition of
hypophosphite.
2 2
We once prepared Ni P/SiO catalyst using triphenylphosphine
(TPP) as phosphorus source in a reducing atmosphere, and the
catalyst exhibited high catalytic activity for high dispersion of
active phase due to low synthesis temperature [23]. Since TPP is
widely used as a ligand and forms complexes with noble metals
[24,25], noble metal phosphides may be prepared through the
above process. In this work, we tried to prepare SiO
ruthenium phosphide catalysts using ruthenium chloride and TPP
as precursors in a flow of hydrogen, and both RuP/SiO and Ru P/
SiO catalysts can be successfully synthesized. Unlike the method
using hypophosphite as phosphorus source, this method does not
need post-treatment. As-synthesized supported Ru P and RuP
2
-supported
2
2
2
2
catalysts with 2.0 wt.% ruthenium loading exhibited higher
catalytic activity in the HDS of DBT than supported RuP by
conventional method as well as Ru catalyst with the same
*
*
Corresponding author. Fax: +86 22 23507730.
* Corresponding author. College of Chemistry, Nankai University, Tianjin 300071,
China.
E-mail address: zhangmh@nankai.edu.cn (M. Zhang).
http://dx.doi.org/10.1016/j.materresbull.2015.10.021
025-5408/ã 2015 Elsevier Ltd. All rights reserved.
0

Q. Wang et al. / Materials Research Bulletin 74 (2016) 98–102
99
ruthenium loading. Besides this, metal-rich Ru
2
P was proved to be
measure the surface areas of samples using a Micromeritics ASAP
2010 instrument. The samples were degassed before analysis at
200 C for 12 h under vacuum. Surface areas were computed based
on the Brunauer–Emmett–Teller (BET) adsorption method. CO
chemisorptions of the catalysts were performed using Micro-
meritics ChemSorb 2750 gas adsorption equipment. The sample
a promising HDS active phase, and showed excellent HDS
performance than RuP. This method offers another choice to
synthesize high active noble metal phosphide catalysts at a low
temperature.
ꢀ
2
. Experimental section
was loaded into a quartz reactor and pretreated in a 10% H
2
/Ar flow
ꢀ
at 400 C for 3 h. After cooling in He, pulses of 10% CO/He in a He
ꢀ
2.1. Synthesis of supported ruthenium phosphides
carrier were injected at 25 C.
2
.1.1. Synthesis of RuP/SiO
All of the chemical reagents used are of analytical pure grade
without further purification. SiO supported ruthenium phos-
2
and Ru
2
P/SiO
2
by TPP method
2.3. HDS activity tests
2
The HDS reaction of dibenzothiophene (DBT 0.5 wt.% in decalin)
phides were prepared as followed. The silica support (BET surface
area: 340 m /g from Tianjin Chemical Institute) was dried at 393 K
for 3 h and calcined at 773 K for 6 h before impregnation. The
was performed in a fixed-bed continuous-flow reactor. Prior to
2
evaluation,1.0 g (about 2 ml ) catalyst (20–40 mesh) was reduced at
À1
0.3 MPa pressure with H
2
(flow rate of 60 ml min ) at 673 K for 3 h.
ruthenium-TPP solution was prepared by dissolving RuCl
3
Á
3H
2
O
Catalytic activities were measured under a hydrogen pressure of
3.0 MPa. The weight hourly space velocity (WHSV) was 10 h . The
À1
(
2.556 g) with TPP (7.869 g) at the molar ratio of ruthenium to
phosphorus of 1:3 in 100 ml ethanol and stirring at the
temperature of 333 K in a water bath for 2 h (samples with
different molar ratios of ruthenium to phosphorus were prepared
by changing the amount of TPP). A certain amount of silica support
was added to the solution and stirred for 6 h, followed by drying at
liquid samples were collected at 1 h interval after a stabilization
period of 3 h and were analyzed by gas chromatography with an
OV-101Capillary Column. The HDS properties of RuP and Ru P
2
catalysts prepared by the TPP method, the RuP prepared by the
conventional method of phosphate as phosphor source and
metallic Ru with the same 2.0 wt.% metal loading were evaluated
under the above reaction conditions.
333 K overnight. The dry solid was subsequently treated in flowing
hydrogen (60 ml/min) with increasing the temperature from room
temperature to final temperature at a rate of 20 K/min and then
kept at final temperature for 5 h. The synthetic temperature range
was from 573 K to 823 K. The treated sample was cooled to RT in
3. Results and discussion
flowing H
2
and then passivated in a flow of 1 vol.% O
2
2
/N . By
3.1. Synthesis of supported ruthenium phosphide by TPP method
controlling the final treated-temperature and adjusting the molar
ratio of ruthenium to phosphorus, different type of ruthenium
3.1.1. The influence of temperature on ruthenium phosphide by TPP
method
2
phosphides RuP and Ru P will be obtained.
In order to illuminate the formation of ruthenium phosphide
process clearly, higher loading ruthenium phosphide was pre-
2.1.2. Synthesis of RuP/SiO
2
using NH PO as phosphorus source by
4
H
2
4
conventional method
2
pared. Fig. 1 shows the XRD patterns of the SiO -supported
For comparison, the ruthenium phosphide was also prepared by
conventional method [8]. The solutions of ruthenium phosphate
ruthenium-TPP precursor with 23 wt.% Ru loading and Ru/P molar
ratio of 1:3 treated at different temperatures in the hydrogen
atmosphere for 5 h. After sample being treated at 573 K and 623 K,
precursors were prepared by dissolving RuCl
3
2
Á3H O with
ꢀ
NH PO (the molar ratio of Ru and P was 1:2) in distilled water,
H
4 2
4
only a broad peak at 22.0 which is attributed to the amorphous
and the resulted solution was used to impregnate silica by the
incipient wetness method. After the impregnation, the obtained
sample was dried at 333 K overnight. Then the powder was
2
phase of SiO support is observed. When the temperature is
2
reduced in H flow of 60 ml/min with increasing the temperature
from RT to 723 K at a rate of 4 K/min and from 723 to 873 K at a rate
of 1 K/min. Finally, the temperature was kept at 873 K for 5 h. The
resulted sample was cooled to RT in flowing H
2
, and then
passivated in a flow of 1 vol.% O /N
2
2
.
2.1.3. Synthesis of supported metallic Ru
To prepare the supported Ru catalyst, RuCl 3H O was dissolved
3 2
Á
in distilled water to obtain incipient solution. Then the silica was
added into the solution and stirred for 3 h. After the impregnation,
the obtained sample was dried at 333 K overnight. The powder was
reduced for 3 h at 673 K in a 30 ml/min H
.2. Catalyst characterization
X-Ray diffraction (XRD) characterization was conducted using a
2
flow.
2
Rigaku D/max-2500 powder X-ray diffractometer employing Cu Ka
radiation (40 kV and 40 mA). Transmission electron microscopy
(
TEM) images were acquired using a TECNAI G2T20 high-resolu-
tion transmission electron microscope. The TEM samples were
thoroughly ground and then suspended in ethanol using an
ultrasonic bath. One drop of the suspension was placed on a
carbon-coated copper grid that was placed on filter paper, and left
2
Fig. 1. The XRD patterns of the RuP/SiO catalysts prepared by TPP methods at
2
in air to dry. Low temperature N adsorption was employed to
different temperature (a) 573 K, (b) 623 K, (c) 673 K, (d) 723 K and (e) 823 K.

100
Q. Wang et al. / Materials Research Bulletin 74 (2016) 98–102
increased to 673 K, three weak peaks appear at 2
u
= 31.8, 44.2 and
presented. The average Ru
SiO and RuP crystallite size of 10 nm for the RuP/SiO
calculated by the Scherrer equation. It can also be seen from above
results that the synthesis of RuP and Ru P can be controlled by
2
P crystallite size of 13 nm for the Ru
2
P/
ꢀ
46.0 , which are attributed to the RuP phase, indicating the
2
2
were
formation of RuP. As the reaction temperature increases to 823 K,
the intensity of these peaks increases which suggests the growing
2
up of RuP crystalline size. Seven diffraction peaks locating at about
simply adjusting Ru/P molar ratio. The phosphor content in the
precursor before heat treatment was higher than that in the final
ꢀ
2
u
= 29.1, 31.8, 32.5, 35.8, 44.2, 46.0, and 53.6 are observed at the
treatment temperature of 823 K (Fig. 1e), which could be identified
to the (0 0 2), (0 01), (110), (111), (112), (211) and (0 31)
crystallographic planes of RuP, respectively. The XRD patterns for
RuP are similar to that reported previously [26], while the
synthetic temperature (673 K) was much lower in the current
method.
2
product of RuP or Ru P, which can be explained by that the part of
TPP will be evaporated at the temperature of 723 K higher than its
boiling temperature (650 K).
For comparison, the SiO
2
supported RuP with 23 wt.% Ru
loading was also prepared by conventional phosphate as phosphor
source. The XRD patterns of samples reduced at different
temperatures are shown in Fig. S1. It can be seen that the RuP
can be synthesized by conventional method at 873 K for 6 h. This
result was similar to the others reported [8].
3.2. The influence of molar ratio of ruthenium and phosphorus on
ruthenium phosphide
2
For HDS reaction of DBT, the SiO supported RuP with 2.0 wt.%
2
Besides this, the Ru P can also be obtained by changing molar
ruthenium content was synthesized. The XRD patterns of
ratio of Ru/TPP from 1:3 to 1.5:1. The XRD patterns of samples with
3 wt.% Ru loading prepared at 723 K and different Ru/TPP molar
ratios are shown in Fig. 2. When the molar ratio of Ru and P was
phosphide catalysts prepared by TPP and conventional methods
ꢀ
2
are shown in Fig. S2. Only the peak at 22.9 attributed to SiO
2
was
observed due to the low loading or high dispersion of metal which
is beyond the detection limit of XRD.
ꢀ
ꢀ
ꢀ
below 1:1, the main peaks at 31.8 , 44.2 and 46.0 corresponding
to RuP phase were observed. As the Ru/P ratio was changed to 2:1,
ꢀ
ꢀ
the peaks at 38.1 and 47.1 attributed to Ru
2
P phase appeared.
3.3. TEM images of samples
ꢀ
However, the peak at 44.0 belonging to metal Ru existed. And
when the molar ratio was 1.5:1, the peaks at 30.5 , 38.1 , 40.6 , 47.1
and 53.5 all corresponding to Ru
ꢀ
ꢀ
ꢀ
ꢀ
2
TEM investigation of 2.0 wt.% RuP/SiO catalyst prepared by TPP
method reveals that the particle size of RuP was about 2–5 nm and
ꢀ
2
P phase (JCPDS 65-2382) can be
sphere-shaped RuP particles uniformly dispersed on the surface of
SiO (Fig. 3b). Meanwhile, the morphology of RuP/SiO with same
2 2
loading prepared by the conventional phosphate as phosphor
source was also shown in Fig. 3a. It can be seen that the RuP
obviously existed in the form of aggregation with a larger particle
size of 5–15 nm. It suggests the effectiveness of the TPP method in
increasing the dispersion of the active species. As shown in Fig. 3c,
the particle size of Ru
–5 nm and sphere-shaped Ru
of SiO . Besides this, Ru
coexisted. The particle size of RuP prepared by phosphate as
phosphor source was bigger than that prepared by TPP method
because that the higher temperature causes the sintering of the
phosphide. It is also seen from the TEM investigation that
2
P prepared by TPP method was about
P particles dispersed on the surface
P with the bigger particle size (ꢁ 10 nm)
2
2
2
2
2
the particle size of RuP and Ru P prepared by TPP method was
similar.
3
.4. Activity measurements
2 2 2
The activities of RuP/SiO and Ru P/SiO catalysts prepared by
TPP, RuP/SiO
with Ru/SiO
2
prepared by phosphate as phosphor source, together
catalyst were tested in the hydrodesulfurization
2
(
HDS) of DBT. The HDS activities of the four catalysts at different
reaction temperatures were shown in Table 1. The conversions of
DBT on these catalysts increased with increasing reaction
temperature. And the supported noble metal phosphides of RuP
and Ru
Ru/SiO
2
P prepared by TPP method exhibited higher activity than
catalyst. The HDS reaction network of DBT was shown in
2
Scheme S1. The HDS products were analyzed and summarized in
Table S1, and it can be seen that the selectivity of cyclo-
hexylbenzene (hydrogenation product) over phosphides was
higher than that over ruthenium catalyst which indicated the
hydrogenation activity of ruthenium phosphides was higher than
that of ruthenium. The result was consistent with that reported by
Bowker et al. [21]. It is known that hydrogenation of DBT favored
the HDS process. Compared with the RuP/SiO
phosphate as phosphor source, the RuP/SiO
method presented much higher HDS activity in the test. In
particular, the 37.6% initial activity of RuP/SiO prepared by the TPP
method is higher than that of RuP/SiO prepared by conventional
2
catalyst prepared by
2
prepared by TPP
Fig. 2. The XRD patterns of the ruthenium phosphides prepared by TPP methods
from Ru/P molar ratio (a) 1:3, (b) 1:2, (c) 1:1, (d) 1.5:1, and (e) 2:1
2
2

Q. Wang et al. / Materials Research Bulletin 74 (2016) 98–102
101
Fig. 3. The TEM micrographs of 2.0 wt.% RuP supported on silica prepared (a) by the conventional method using NH
c) Ru P supported on silica prepared by TPP method.
4
H
2
PO
4
as phosphor source, (b) by TPP method as well as
(
2
Table 1
Conversion of DBT on SiO
2
-supported ruthenium phosphide catalysts prepared by different methods
Ru contentc
wt.%)
BET surface area (m /g)
2
CO uptake (mmol/g)
Conversion of DBT (%) at different reaction temperatures
TOF (603 K)
Catalysts
À3 À1
(
583 K
603 K
623 K
10
s
RuP/SiO a
1.8
1.8
1.7
1.9
328
301
310
340
3.5
3.2
3.6
4.1
56.7
34.5
89.4
53.2
75.8
42.9
97.4
63.1
92.9
55.3
100.0
74.9
16.3
10.1
20.5
11.6
2
b
RuP/SiO
2
a
Ru
2
P/SiO
2
Ru/SiO
2
a
The catalyst prepared by TPP method.
The catalyst prepared by method of phosphate as phosphor source.
Analyzed by ICP-AES.
b
c
method and reached 92.9% at 623 K. The main reason for the
difference of catalytic activity between the TPP method and the
conventional method may be due to the higher preparation
temperature of the latter. The particle size of active species was
large because of the aggregation of phosphide on the carrier
prepared by conventional method, hence affected the catalytic
4. Conclusions
Our results demonstrate that SiO
catalysts can be easily prepared by hydrogen-thermal treatment of
a complexe precursor. Compared with SiO supported metallic Ru
catalyst and RuP/SiO catalyst prepared by phosphate as phosphor
source, the as-prepared RuP/SiO and Ru P/SiO by TPP method
2 2
supported RuP and Ru P
2
2
activity. The supported metal-rich phosphide Ru
2
P prepared by
2
2
2
TPP method exhibited the highest activity among all the tested
catalysts, and its activity reached 89.4% at 583 K and ultimately
shows excellent catalytic activity. Futher studies are focused on
exploring this method for the synthesis of other noble metal
reached 100% at 623 K. Although The Ru/SiO
highest amount of CO chemisorption, its turnover of frequency
TOF) was lower than Ru P and RuP prepared by TPP method.
Among these catalysts, the Ru P was the most active phase due to
its highest TOF value. The reaction time of HDS on Ru P/SiO
catalyst with 2.0 wt.% Ru loading was also prolonged to 42 h and
the result was shown in Fig. 4. It can be seen that HDS conversion
slightly decreased after 7 h and maintained at 80 %. The decline of
activity may be due to the absorption of organic products.
2
catalyst had the
2 2 5 2
phosphides (such as PtP , Rh P, Pd P , etc.).
(
2
Acknowledgements
2
2
2
TheauthorsthankthesupportsfromNaturalSciencesFoundation
ofChina(No.21576140, 51103105 andNo. 41173096),NaturalScience
Foundation of Tianjin (14JCYBJC20000), MOE Innovation Team
(IRT13R30 and IRT13022) of China, the National Science &
Technology Pillar Program (No. 2012AA03A601 and No.
2
012BAC07B02), Tianjin basic education during the 12th Five Year
Planeducation scientific researchproject(KT-12th five year-002-zd-
21) and the innovation team training plan of the Tianjin Education
0
Committee (TD12-5037).
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.
materresbull.2015.10.021.
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