The effect of neodymium content on dibenzothiophene HDS performance over a bulk Ni2P catalyst

Article abstract of DOI:10.1016/j.catcom.2015.05.028

Neodymium (Nd)-modified Ni₂P catalysts (Nd_xNi₂P, where x is the molar fraction of Nd to Ni₂P) have been successfully prepared. An appropriate amount of Nd can dramatically increase the surface area and promote the formation of smaller and highly dispersed Ni₂P particles. The Nd_xNi₂P catalyst with x = 0.10 exhibited the highest dibenzothiophene hydrodesulfurization activity of 97.4%, which is an increase of 35% when compared with that found for bulk Ni₂P.

Full text of DOI:10.1016/j.catcom.2015.05.028

Catalysis Communications 69 (2015) 59–62
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short communication
The effect of neodymium content on dibenzothiophene HDS
performance over a bulk Ni2P catalyst
a
b
a
a
Hua Song a, , Fuyong Zhang , Hualin Song , Xiaowei Xu , Feng Li
⁎
a
Provincial Key Laboratory of Oil & Gas Chemical Technology, College of Chemistry & Chemical Engineering, Northeast Petroleum University, Daqing 163318, Heilongjing, China
Key Laboratory of Cancer Prevention and Treatment of Heilongjiang Province, Mudanjiang Medical University, Mudanjiang 157011, China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Neodymium (Nd)-modified Ni2P catalysts (NdxNi2P, where x is the molar fraction of Nd to Ni2P) have been suc-
cessfully prepared. An appropriate amount of Nd can dramatically increase the surface area and promote the for-
mation of smaller and highly dispersed Ni2P particles. The NdxNi2P catalyst with x = 0.10 exhibited the highest
dibenzothiophene hydrodesulfurization activity of 97.4%, which is an increase of 35% when compared with that
found for bulk Ni2P.
Received 22 April 2015
Received in revised form 29 May 2015
Accepted 30 May 2015
Available online 3 June 2015
© 2015 Published by Elsevier B.V.
Keywords:
Nickel phosphide (Ni2P)
Hydrodesulfurization
Dibenzothiophene
Neodymium (Nd)
1. Introduction
In this paper, neodymium (Nd) element was successfully introduced
into bulk Ni2P and the effect of Nd content on the HDS performance of
Driven by more and more stringent environmental regulations and
the increasing use of heavy crude oil, sulfur removal from transporta-
tion fuels is becoming one of the acutest problems for the refining
industry. Among the sulfur removal methods, hydrodesulfurization
(HDS) has been widely used over the past decade. However, the current
commercially used HDS catalysts are not up to the standard set by
the regulations [1]. Hence, plenty of research has been performed to
develop a new generation of replacement materials. Transition metal
phosphides have received a lot of attention because of their high perfor-
mance in HDS. The observed activity for transition metal phosphides
in the HDS of dibenzothiophene (DBT) follows the general trend:
Fe2P b CoP b MoP b WP b Ni2P [1,2].
Rare earth metals exhibit excellent physical, chemical, optical and
electrical properties because of their unfilled 4f electron shell [3].
Therefore, they have been continually employed and investigated
as structural and electronic promoters to improve the performance
of various catalysts [4]. The addition of CeO2 to Ni2P can significantly
decrease the particle size of Ni2P, and increase the specific surface
area and CO adsorption properties, resulting in increased HDS activ-
ity [5,6]. Our previous work showed that yttrium (Y) incorporated in
the bulk Ni2P catalyst can increase the surface area of the catalyst,
leading to a smaller crystallite size and better dispersion of the active
Ni2P particles [7].
Ni2P was studied.
2. Experimental
2.1. Preparation of catalysts
The unsupported Ni2P catalysts were prepared by temperature pro-
grammed reduction (TPR) method reported by our previous study [7].
The oxidic precursor of bulk Ni2P was prepared with excess phosphorus
(Ni:P = 1:1) to compensating the loss of phosphorus during the reduc-
tion stage [8]. A mixture of Ni(NO3)2 and (NH4)2·HPO4 solution was
stirred and the water was evaporated to obtain a solid product. The
resulting solid was dried at 120 °C for 12 h and calcined at 500 °C for
3 h to obtain the oxidic precursor (PNi2P). Nd was incorporated into
the bulk Ni2P by impregnating the PNi2P with a solution of Nd(NO3)3.
The resulting solid was treated as PNi2P to obtain the final oxidic precur-
sor (PNdNi2P). Finally, the PNi2P and PNdNi2P were reduced and passiv-
ated as our previous study [7]. The corresponding catalysts are denoted
as Ni2P and NdxNi2P, where x represents the molar fraction of Nd with
respect to Ni2P.
2.2. Characterization of catalysts
XRD analysis was carried out on a D/max-2200 PC-X-ray diffractom-
eter using Cu Kα radiation under the setting conditions of 40 kV, 30 mA,
scan range from 10 to 80° at a rate of 10°/min. The typical physico-
chemical properties of catalysts were analyzed by BET method using
⁎
Corresponding author.
E-mail address: songhua2004@sina.com (H. Song).
http://dx.doi.org/10.1016/j.catcom.2015.05.028
1566-7367/© 2015 Published by Elsevier B.V.

60
H. Song et al. / Catalysis Communications 69 (2015) 59–62
appropriate amount of Nd can promote smaller Ni2P particles and a bet-
ter dispersion of Ni2P. Our previous work [5] studied the effect of the
rare-earth metal (Y) on bulk Ni2P. We found Y can greatly increase the
surface area of the catalyst, promoting a smaller crystallite size (Dc)
and better dispersion of active Ni2P.
3.2. BET
Table 1 summarizes the textural properties of Ni2P and NdxNi2P. The
surface area and pore volume of the Ni2P catalysts were 11.17 m2·g−1
and 0.060 cm3·g−1, respectively. Upon increasing the Nd content, the
specific surface area of NdxNi2P showed a significant increase initially,
reaching a maximum at x = 0.1 and then decreased with further in-
creases in the Nd content. The surface area of the Nd0.10Ni2P catalyst
was 25.64 m2·g−1, which was an almost twofold increase when com-
pared with that found for bulk Ni2P. This indicates that an appropriate
amount of Nd was beneficial to the formation of smaller and highly dis-
persed Ni2P particles in the catalyst (see Table 1, column 5).
Fig. 1. XRD patterns of the Ni2P and NdxNi2P catalysts.
Micromeritics adsorption equipment of NOVA2000e. CO uptake mea-
surements were performed in a Micromeritics ASAP 2010 apparatus
under static volumetric conditions. The XPS spectra were acquired
using ESCALAB MKII spectrometer.
3.3. CO uptake
The CO uptake measurements were used to titrate the surface Ni
atoms and to provide an estimate of the active CO uptake sites on the
catalysts [8]. Although CO molecules may also be adsorbed P sites,
their amount may be very small and they can be neglected [11]. The
measured CO adsorption capacities at room temperature for all the sam-
ples are presented in column 6 of Table 1. The CO adsorption of the bulk
Ni2P sample was determined to be 171 μmol·g−1. The CO adsorption of
the NdxNi2P catalysts was dramatically higher than that of bulk Ni2P,
which showed that introducing Nd to the catalyst can improve the dis-
persion of active Ni2P. The CO uptake of the Nd0.12Ni2P catalyst was
lower than that found for the Nd0.10Ni2P sample. This was attributed
to the decrease in surface area in Nd0.12Ni2P upon increasing x from
0.10 to 0.12 (Table 1) because the surface area has a great effect on
the dispersion of Ni sites. In addition, the excess Nd would occupy the
some of the Ni sites leading to a decrease in the amount of exposed Ni
sites on the catalyst's surface. This will be discussed further with the
XPS analysis.
2.3. Catalytic activities
The HDS of DBT over prepared catalysts was performed in a flowing
high-pressure fixed bed reactor using a feed consisting of a decalin solu-
tion of DBT (1 wt.%). The conditions of the HDS reaction were 340 °C,
3.0 MPa, WHSV = 1.5 h−1, and hydrogen/oil ratio of 500 (V/V). Prior
to reaction, 0.8 g of the NdxNi2P were pretreated in situ with flowing
H2 (40 mL/min) at 500 °C for 2 h. Sampling of liquid products was
started 2 h after the steady reaction conditions had been achieved.
The feed and reaction product was analyzed by FID gas chromatography
with a GC-14C-60 column.
3. Results and discussion
3.1. XRD
The XRD patterns of all samples are shown in Fig. 1. For all samples,
strong diffraction peaks at 2θ = 40.6°, 44.5°, 47.1° and 54.1° (PDF:
03-0953) can be attributed to the Ni2P phase, which indicates that
the active phase formed is mainly Ni2P. The Ni2P shows weak diffraction
peaks at 2θ = 28.8°, 30.2°, 31.6°, 43.9°, 47.8° and 53.0° (PDF: 18-0883),
which were ascribed to small amounts of the Ni5P4 phase. However,
NdxNi2P exhibits a broad peak owing to an amorphous phase at the cor-
responding position. This suggests that the addition of Nd to Ni2P can
suppress the formation of the Ni5P4 phase. It is worth noting that with
an increasing Nd content in the catalysts, the Ni2P phase peaks initially
become more intense and broadened, and then become less intense. In
general, an increase in the peak width exhibits a decrease in the crystal-
lite size (Dc) of the Ni2P. The crystallite sizes (Dc) (column 5 of Table 1),
calculated from Scherrer's equation [9,10], initially decrease and then
increase, reaching a minimum of 39 nm at x = 0.10, which shows an
3.4. XPS
In order to gain further insight into the surface composition of the
samples and the influence of Nd content, the XPS technique of samples
was performed. The XPS spectra of the Ni2P and NdxNi2P samples in the
Ni(2p) and P(2p) regions are shown in Fig. 2 and the binding energies
are presented in Table 2. As shown in Fig. 2(a), all spectra were
decomposed, taking into account the spin-orbital splitting of the Ni
2p3/2 and Ni 2p1/2 lines (about 17 eV) and the presence of satellite
peaks at about 5 eV higher than the binding energy of the parent sig-
nal [12]. For all catalysts, the bands centered at 852.1–852.7 eV and
856.1–856.7 eV can be attributed to the Niδ+ species in the Ni2P
phase and Ni2+ species interacting with phosphate as a consequence
of a superficial passivation, respectively [12,13]. As shown in
Fig. 2(b), the peaks centered at 128.8–129.9 eV can be assigned to
Table 1
The textural characterization and HDS catalytic performance of the Ni2P and NdxNi2P catalysts.
Sample
SBET (m2·g−1
)
Vp (cm3·g−1
)
d (nm)
Dca (nm)
CO uptake (μmol·g−1
)
Conversion (%)
Selectivity (%)
TOF (10−3·s−1
)
CHB
BP
Ni2P
11.17
14.10
25.64
15.13
16.0
0.060
0.066
0.129
0.074
0.086
21.7
20.2
18.7
19.6
20.1
54
50
39
43
21
171
229
326
291
314
62.1
75.9
97.4
89.5
92.0
35
32
31
33
28
65
68
69
67
72
8.5
7.3
6.5
6.9
6.9
Nd0.01Ni2P
Nd0.10Ni2P
Nd0.12Ni2P
Y
0.10Ni2P
a
Calculated from the Dc = Kλ/β cos(θ) (Scherrer equation) based on the Ni2P {1 1 1}.

H. Song et al. / Catalysis Communications 69 (2015) 59–62
61
Fig. 2. XPS spectra of the Ni2P and NdxNi2P catalysts.
Pδ− species in the Ni2P phase [12] and the peak at 134.1–134.8 eV can
3.5. HDS activity
be attributed to phosphate (P5+) due to superficial oxidation of the Ni2P
particles [14,15].
As can be seen from Fig. 3, the HDS activities for all the catalysts
gradually increased and then remained stable with time. The DBT con-
version of bulk Ni2P was only 62% after 8 h. The DBT conversion signif-
icantly increased and then decreased upon increasing the Nd content.
The Nd0.10Ni2P catalyst showed the maximum HDS activity of 97.4%
after 8 h, an increase of 35% when compared with that found for Ni2P.
This was attributed to Nd0.10Ni2P possessing smaller sized particles
and a better dispersion of the active Ni2P phase, as well as the higher
surface area and lower coverage of phosphorus when compared with
the other samples, which showed that an appropriate amount of Nd
was beneficial for the HDS process.
The HDS activities, TOF and CO uptake of samples after reaction 8 h
are presented in columns 6–10 of Table 1. The DBT conversion and
TOF of bulk Ni2P were 62% and 8.5 × 10−3 s−1, respectively. Both the
DBT conversion and CO uptake of NdxNi2P increase very quickly,
reaching a maximum at x = 0.10, and then decrease. On the contrary,
variation of the TOF has a reverse trend. Hence, the higher CO uptake
and lower TOF value were beyond that expected for the samples,
which indicated that the metal sites do not accurately represent the ac-
tual active sites for HDS but just provide the initial active sites in HDS re-
action [16]. The results obtained show that a nickel phosphosulfide
active phase was generated during the HDS reaction [8,10].
The HDS catalytic selectivities of the catalysts are given in columns 8
and 9 of Table 1. For all the samples, the yield of BP is much higher than
that of CHB, indicating that DBT primarily removed by the DDS pathway
over all the catalysts [17]. Compared with Ni2P, the selectivity to BP over
NdxNi2P is slightly higher, showing that the HDS route was not changed
much by addition of Nd [18]. For comparison, the textural characteriza-
tion and HDS activities of Y0.10Ni2P reported in reference [7] are listed in
line 7 of Table 1. It can be seen that the DBT conversion of Nd0.10Ni2P
with a higher CO uptake is obviously superior to that of Y0.10Ni2P,
while the selectivity to BP over Y0.10Ni2P is slightly higher than that of
Nd0.10Ni2P.
XPS analyses for the Ni2P and NdxNi2P catalysts were used to calcu-
late the surface Niδ+/ΣNi and P/Ni atomic ratios (Table 2). The Niδ+/ΣNi
ratios of the samples increased with Nd content, reaching a maximum at
x = 0.10 and then decreased. This indicates that the addition of an ap-
propriate amount of Nd promotes the formation of active Ni2P, which
improves the performance of the catalysts. Moreover, the P/Ni molar
ratio of the NdxNi2P samples were lower than that found for bulk Ni2P,
which indicates that the addition of Nd to Ni2P can suppress the enrich-
ment of P on the surface. The result obtained gives rise to more nickel
sites being exposed on the surface of the samples, which may also influ-
ence the catalysts' performances.
Table 2
Spectral parameters obtained by XPS analysis.
Sample
Binding energy (eV)
Superficial
atomic ratio
Ni 2p3/2
P 2p3/2
Ni2+
Satellite
Niδ+
P5+
Pδ−
Niδ+/ΣNi
P/Ni
Ni2P
856.7
856.2
856.4
856.1
861.2
860.9
861.7
861.2
852.7
852.1
852.5
852.4
134.8
134.2
134.6
134.1
128.8
129.2
129.9
129.4
0.041
0.043
0.055
0.047
3.0
2.8
2.2
2.3
Nd0.01Ni2P
Nd0.10Ni2P
Nd0.12Ni2P
4. Conclusions
In the present work, Nd-modified unsupported Ni2P (NdxNi2P) cata-
lysts, which have higher HDS activity have been successfully prepared.
XRD analysis indicated that the addition of Nd into the bulk Ni2P can
suppress the formation of the Ni5P4 phase and thereby promote the
formation of the active Ni2P phase. The crystallite size of Ni2P first
decreases, reaching a minimum at x = 0.10, and then increases upon in-
creasing the Nd content. Moreover, the value of x has a large influence
on the surface area of the catalyst and an appropriate amount of Nd
(x = 0.10) was found to significantly increase the surface area, resulting
in a better dispersion of the active Ni2P phase. In addition, incorporation
Fig. 3. The HDS activity of the Ni2P and NdxNi2P catalysts. Temperature, 340 °C; pressure,
3.0 MPa; H2/oil ratio, 500 (V/V); WHSV, 1.5 h−1
.

62
H. Song et al. / Catalysis Communications 69 (2015) 59–62
[3] I. Hayao, O. Akira, H. Eitetsu, J. Catal. 96 (1985) 139–145.
[4] N. Phonthammachai, M. Rumruangwong, E. Gulari, A.M. Jamieson, S. Jitkarnka, S.
Wongkasemjit, Colloids Surf. A Physicochem. Eng. Asp. 247 (2004) 61–68.
[5] X. Li, Y.L. Zhang, A.J. Wang, Y. Wang, Y.K. Hu, Catal. Commun. 11 (2010)
1129–1132.
[6] Z.C. Sun, X. Li, A.J. Wang, Y. Wang, Y.Y. Chen, Top. Catal. 55 (2012) 1010–1021.
[7] H. Song, X.W. Xu, H.L. Song, N. Jiang, F.Y. Zhang, Catal. Commun. 63 (2015) 52–55.
[8] S.T. Oyama, X. Wang, Y.K. Lee, K. Bando, F.G. Requejo, J. Catal. 210 (2002)
207–217.
[9] X. Wang, P. Clark, S.T. Oyama, J. Catal. 208 (2002) 321–331.
[10] S.T. Oyama, X. Wang, Y.K. Lee, W.J. Chun, J. Catal. 221 (2004) 263–273.
[11] K.A. Layman, M.E. Bussell, J. Phys. Chem. B 108 (2004) 10930–10941.
[12] I.K. Tamás, V. Zdeněk, G.P. Dilip, R. Ryong, S.K. Hei, J.M.H. Emiel, J. Catal. 253 (2008)
119–131.
[13] Y.N. Guo, P.H. Zeng, S.F. Ji, N. Wei, H. Liu, C.Y. Li, Chin. J. Catal. 31 (2010) 329–334.
[14] H. Song, M. Dai, Y.T. Guo, Y.J. Zhang, Fuel Process. Technol. 96 (2012) 228–236.
[15] D. Kanama, S.T. Oyama, S. Otani, D.F. Cox, Surf. Sci. Spectra 8 (2001) 220–224.
[16] A.E. Nelson, M.Y. Sun, A.S.M. Junaid, J. Catal. 241 (2006) 180–188.
[17] H. Song, X.W. Xu, M. Dai, H.L. Song, Chem. J. Chin. Univ. 34 (2013) 2609–2616.
[18] S.T. Oyama, Y.K. Lee, J. Catal. 258 (2008) 393–400.
of an appropriate amount of Nd (x = 0.10) can suppress the enrichment
of P on the surface of the catalyst and therefore increase the number of
exposed nickel atoms, leading to the highest CO uptake. The Nd0.10Ni2P
catalyst exhibits the highest DBT HDS activity of 97.4%, which was an in-
crease of 35% when compared with that found for bulk Ni2P.
Acknowledgment
The authors acknowledge the financial supports from the National
Natural Science Foundation of China (21276048), the Natural Science
Foundation of Heilongjiang Province (ZD201201) and the Project of
Education department of Heilongjiang Province (12541060).
References
[1] S.T. Oyama, T. Gott, H.Y. Zhao, Y.K. Lee, Catal. Today 143 (2009) 94–107.
[2] L. Yang, X. Li, A.J. Wang, R. Prins, Y. Wang, Y.Y. Chen, X.P. Duan, J. Catal. 317 (2014)
144–152.