Synthesis of an yttrium-modified bulk Ni2P catalyst with high hydrodesulfurization activity

Article abstract of DOI:10.1016/j.catcom.2014.10.010

Yttrium-modified bulk Ni₂P (Y_xNi₂P) catalysts showing high hydrodesulfurization (HDS) activity are described. The incorporation of Y into the bulk Ni₂P catalyst can suppress the formation of the Ni₅P₄ phase and therefore promote formation of the more active Ni₂P phase. Y can also greatly increase the surface area of the catalyst, leading to a smaller crystallite size and better dispersion of active Ni₂P particles. The obtained Y_xNi₂P catalysts show much higher Dibenzothiop (DBT) HDS activity than the bulk Ni₂P catalyst.

Full text of DOI:10.1016/j.catcom.2014.10.010

Catalysis Communications 63 (2015) 52–55
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Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short communication
Synthesis of an yttrium-modified bulk Ni2P catalyst with high
hydrodesulfurization activity
a
b
a
a
Hua Song a, , Xiao-Wei Xu , Hua-Lin Song , Nan Jiang , Fu-Yong Zhang
⁎
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:
Received 4 August 2014
Received in revised form 1 October 2014
Accepted 15 October 2014
Available online 22 October 2014
Yttrium-modified bulk Ni2P (YxNi2P) catalysts showing high hydrodesulfurization (HDS) activity are described.
The incorporation of Y into the bulk Ni2P catalyst can suppress the formation of the Ni5P4 phase and therefore
promote formation of the more active Ni2P phase. Y can also greatly increase the surface area of the catalyst, lead-
ing to a smaller crystallite size and better dispersion of active Ni2P particles. The obtained YxNi2P catalysts show
much higher Dibenzothiop (DBT) HDS activity than the bulk Ni2P catalyst.
© 2014 Published by Elsevier B.V.
Keywords:
Nickel phosphide (Ni2P)
Hydrodesulfurization (HDS)
Yttrium (Y)
1. Introduction
2. Experimental
Driven by the increasing use of heavy crude oil, sulfur removal
has become a pressing problem. The sulfur contents in gasoline and
diesel fuel have been stipulated to be less than 10 ppm in many parts
of the world [1,2]. It has been recognized that current commercial
hydrodesulfurization (HDS) catalysts are not adequate to meet such
low regulated sulfur levels [3]. The challenge of producing cleaner oil
from increasingly low-quality petroleum feedstocks has stimulated
the development of high-performance HDS catalysts [4–7]. Ni2P shows
the most remarkable activities among all known transition metal
catalysts [7–11].
The rare-earth metals exhibit excellent physical, chemical, optical,
and electrical properties because of their unfilled 4f electron shells
[12]. Consequently, they have been frequently used as structural and
electronic promoters to obtain better activity, selectivity, and thermal
stability of a wide range of catalysts [13]. It has been reported that the
addition of CeO2 to an Ni2P catalyst can significantly decrease the parti-
cle size and increase the specific surface area and CO uptake [14,15].
Moreover, Wei et al. [16] prepared a series of La-Ni2P/SBA-15 catalysts
and found that the addition of La increased the surface area and pore
volume.
2.1. Preparation of catalysts
The oxidic precursor of bulk Ni2P was prepared with excess phos-
phorus (Ni:P = 1:1) [18]. 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 final oxidic precursor.
Y was incorporated into the bulk Ni2P catalyst at different contents
by impregnating the as-prepared Ni2P precursor with a solution of
Y(NO3)3. The resulting solid was then dried and calcined as above.
The catalyst precursors were reduced in a fixed-bed reactor by
heating from room temperature to 400 °C at a rate of 2.5 °C/min
in a flow of H2 (200 mL/min), further heated to 500 °C at a rate of
1 °C/min, and held for 2 h. The obtained catalysts were allowed to
cool naturally to room temperature in a continuous H2 flow and then
passivated in an O2/N2 mixture (0.5 vol.% O2) with a flow rate of
20 mL/min for 2 h. The corresponding catalysts are denoted as YxNi2P,
where x represents the mole fraction of Y with respect to Ni2P.
2.2. Characterization of catalysts
In this study, yttrium (Y) has been successfully incorporated into
bulk Ni2P catalysts on the basis of our previous work [4,17]. The effects
of Y on the structure and HDS performance of the bulk Ni2P catalysts
have been investigated.
X-ray diffraction (XRD) analysis was carried out on a D/max-
2200PC-X-ray diffractometer 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. X-ray photoelectron spectroscopy (XPS) spectra were recorded
with ESCALAB MKII spectrometer. XPS measurements have been per-
formed using monochromatic Mg Kα radiation (E = 1253.6 eV) and
equipped with a hemi-spherical analyzer operating at fixed pass energy
⁎
Corresponding author. Tel./fax: +86 0459 6503167.
E-mail address: songhua2004@sina.com (H. Song).
http://dx.doi.org/10.1016/j.catcom.2014.10.010
1566-7367/© 2014 Published by Elsevier B.V.

H. Song et al. / Catalysis Communications 63 (2015) 52–55
53
of 40 eV. The typical physico-chemical properties of catalysts were ana-
lyzed by BET method using micromeritics adsorption equipment of
NOVA2000e. All the samples were outgassed at 200 °C until the vacuum
pressure was 6 mm Hg. The adsorption isotherms for nitrogen were mea-
sured at −196 °C. CO chemisorption uptake measurements were per-
formed in a Micromeritics ASAP 2010 apparatus under static volumetric
conditions. After pretreatment in a continuous N2 flow, CO pulses were
injected into N2, and the CO uptake was measured using a TCD until
there was no further CO uptake after consecutive injections.
increasing Y content, indicating that the incorporation of Y could pro-
mote better dispersion of Ni2P, which may also influence the DBT HDS
conversion and product distribution. Wang et al. [14,15] have studied
the effect of rare earth metal Ce on the particle size of the Ni2P, they
found that the presence of Ce have a positive effect on the dispersion
of the Ni2P particles. The strong interaction between nickel metals and
certain reducible oxides (such as CeO2) may constrain the growth of
the particle size of nickel and thus the final Ni2P particles. [15]
3.2. BET
2.3. Catalytic activities
Table 1 summarizes the textural properties of YxNi2P catalysts as
well as bulk Ni2P. The surface area and pore volume of the Ni2P sample
were determined as 6.1 m2 · g−1 and 0.025 cm3 · g−1, respectively. It is
worth noting that all of the YxNi2P catalysts showed a gradual increase
in specific surface area and pore volume with increasing Y content.
Compared with the bulk Ni2P catalyst, the surface area and pore volume
of Y0.10Ni2P (16.0 m2 · g−1 and 0.086 cm3 · g−1, respectively) were
almost twofold higher. This indicates that Y could promote greater dis-
persion of the Ni2P phase, which is consistent with the results obtained
by XRD.
The HDS of DBT was carried out in a flowing high-pressure fixed-bed
reactor using a feed consisting of a decalin solution of DBT (1 wt.%).
Catalytic activities were measured at 340 °C, 3.0 MPa, hydrogen/oil
ratio of 500 (V/V) and weight hourly space velocities (WHSV) of
1.5 h−1. Prior to reaction, 0.8 g of the catalysts were pretreated in situ
with flowing H2 (40 mL/min) at 500 °C for 2 h. Sampling of liquid prod-
ucts was started 2 h after the steady reaction conditions had been
achieved. The liquid samples which mainly contain the formed biphenyl
(BP) and cyclohexylbenzene (CHB) were collected every hour and ana-
lyzed by FID gas chromatography with a GC-14C-60 column.
3.3. CO uptake
3. Results and discussion
CO uptake measurements were used to effectively “titrate” the sur-
face metal atoms and to provide an estimate of the number of active
sites and their dispersion on the catalysts, ignoring the very low degree
of adsorption at P sites [18,20]. The measured CO adsorption capacities
of Ni2P and YxNi2P catalysts are presented in column 7 of Table 1. The
3.1. XRD
As can be seen from Fig. 1, XRD diffractograms of Ni2P and YxNi2P
precursor present broad feature peak centered at 2θ = 32°, which can
be assigned to the amorphous NixPyOz phases [19]. For all of the
catalysts, the peaks at 2θ = 40.6°, 44.5°, 47.1°, and 54.1° (PDF no.
03–0953) can be ascribed to Ni2P, indicating this to be the principal
active phase for all samples. Bulk Ni2P shows weak diffraction peaks at
2θ = 28.8°, 30.2°, 31.6°, 36.1°, 43.9°, 45.1°, 47.8°, and 53.0° (PDF no.
18–0883), which can be assigned to a small amount of Ni5P4 phase.
However, YxNi2P exhibits a broad peak due to an amorphous phase at
the corresponding position. This suggests that Y suppresses formation
of the Ni5P4 phase. The diffraction peaks of the Ni2P phase in YxNi2P be-
come more broadened with increasing Y content. In general, an increase
in peak width can be attributed to a decrease in the crystallite size of the
Ni2P. The calculated mean crystallite sizes (Dc) of Ni2P in the catalysts
based on Scherrer's equation are listed in column 2 of Table 1. The
Ni2P crystallite size in the YxNi2P catalysts is seen to decrease with
CO uptake of the bulk Ni2P sample was determined as 171 μmol · g−1
.
The CO uptake of the YxNi2P samples was clearly considerably higher
than that of bulk Ni2P, and increased with increasing Y content, indicat-
ing that the addition of Y can improve the dispersion of active Ni2P. This
may be because for bulk Ni2P the lower surface area leads to a poor dis-
persion of the particles and the accumulation of phosphate leads to less
nickel sites being exposed on the surface (see discussion of the XPS
results). For YxNi2P, the higher CO uptake can be attributed to the smaller
Ni2P particles, as observed in the XRD analysis. It should also be noted
that the CO uptakes are below the theoretical surface metal site density
calculated from the average particle size determined by XRD analysis.
This indicates that some nickel sites were covered by excess phosphorus,
which was enriched on the surfaces of all of the catalysts. This will be
discussed further in relation to the XPS results.
3.4. XPS
The XPS spectra for Ni2P and YxNi2P catalysts 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 Ni 2p3/2 and Ni 2p1/2 lines
(17.5 eV) and the presence of satellite peaks at about 5 eV higher than
the binding energy of the parent signal [21,22]. For all catalysts, the Ni
2p3/2 spectrum consists of three contributions. The bands centered at
852.5–852.7 eV and 856.1 ~ 856.7 eV can be attributed to the Niδ+ spe-
cies in Ni2P phase and Ni2+ species interacting with phosphate as a con-
sequence of a superficial passivation, respectively [22–24]. The bands
centered at 860.8–861.2 eV can be assigned to the shake-up satellite
[4,21]. As shown in Fig. 2(b), the peaks centered at 128.8–130.3 eV
can be assigned to Pδ+ species in the Ni2P phase [22,25], and the peak
at 134.5–134.8 eV can be attributed to phosphate (P5+) due to superfi-
cial oxidation of the Ni2P particles [24]. It is worth noting that the P 2p3/2
binding energy corresponding to phosphide phase increases with in-
creasing Y content in the catalyst due to the electron transfer from phos-
phide species to yttrium.
The ratios of the Niδ+ species to total Ni of Ni2P phase (R Niδ+) in Ni
2p3/2 are also illustrated in column 7 Table 2. It is worth noting that the
Fig. 1. XRD patterns of the Ni2P and YxNi2P catalysts and precursors.

54
H. Song et al. / Catalysis Communications 63 (2015) 52–55
Table 1
The properties and HDS catalytic performance of the Ni2P and YxNi2P catalysts.
Sample
Dc (nm)a
SBET
Vp
Metal site density
CO uptake
Conversion (%)
Selectivity (%)
TOF
b
(m2 · g−1
)
(cm3 · g−1
)
(μmol · g−1
)
(μmol · g−1
)
(10−3 · s−1
)
CHB
BP
Ni2P
Y0.01Ni2P
42
37
30
21
6.1
0.025
0.057
0.070
0.086
339
383
459
508
171
240
287
314
62
77
91
92
35
40
36
28
65
60
64
72
8.5
7.5
7.4
6.9
10.4
12.9
16.0
Y
Y
0.03Ni2P
0.10Ni2P
a
Calculated from the Dc = Kλ/β cos(θ) (Scherrer equation) based on the Ni2P {1 1 1}.
Calculated from theL ¼ Snf, where f is the fractional weight loading of the sample (gnickel phosphide/gcat.), which is 1 in this paper, n is the average surface metal atom density, which for
b
Ni2P is 1.01 × 1015 atoms · cm−2, S is the effective surface area of the crystallites (assuming cubic or spherical geometry) and which can be calculated from the S = 6/ρDc (ρ is the density
of nickel phosphides taken as 7.09 g · cm−3) [17].
ratios of the YxNi2P catalysts obviously increase with increasing Y con-
tent. The RNiδ+ of bulk Ni2P is only 0.041, whereas that of the
P on the surface. This leads to more nickel sites being exposed on the
surface of the samples, which may also influence the DBT HDS conver-
sion. This is discussed below.
Y
0.10Ni2P catalyst is fivefold higher at 0.054. This result suggests that
the addition of a small amount of Y promotes the formation of active
Ni2P particles, which would improve the HDS activity.
3.5. HDS activity
In addition, Table 2 also lists the surface P/Ni atomic ratios calculated
by XPS analyses. The theoretical P/Ni molar ratio used to prepare the
precursor materials was 1.0. However, after reduction, this ratio in-
creases considerably for all of the catalysts because of an enrichment
of phosphorus on their surfaces. Compared with bulk Ni2P, the P/Ni
molar ratios of YxNi2P are low and decrease with increasing Y content,
showing that the addition of Y to Ni2P can suppress the enrichment of
The Ni2P and YxNi2P catalysts are evaluated by the HDS of DBT, and
the results are shown in Fig. 3. The HDS activities of all of the catalysts
first increased and then remained stable with time. The DBT conversion
of bulk Ni2P was only 62% after 8 h. The DBT conversions of all of the
YxNi2P catalysts were dramatically higher than that of bulk Ni2P, and
increased with increasing Y content. The DBT conversion with Y0.10Ni2P
reached 92% after 8 h, increasing by 30% with the addition of Y. The
dramatically increased HDS activity with the YxNi2P catalysts may be
attributed to the smaller size and better dispersion of the active Ni2P
phase, as well as the higher surface area of the catalysts and lower cover-
age of phosphorus on their surfaces.
The HDS catalytic activities, TOF and CO uptake of Ni2P and
YxNi2P catalysts after reaction 8 h are given in column 6–8 of Table 1.
The bulk Ni2P catalyst showed a DBT conversion of 62% and a TOF of
8.5 × 10−3 s−1. The HDS activities of the prepared YxNi2P catalysts
increased significantly with increasing Y content. However, higher CO
uptakes but lower TOF values were unexpectedly observed for the
catalysts modified with Y. This indicates the metal sites just provide
the initial active sites in HDS reaction, which do not accurately repre-
sent for the actual active sites for HDS. [26] This is similar to the results
obtained by Oyama et al. [8,9,18], indicating that the actual active phase
is a nickel phosphosulfide produced during the HDS reaction.
It is worth noting that the selectivity for BP is much higher than that
for CHB (Table 1, column 8,9), indicating that DBT is mainly transformed
through the desulfurization (DDS) pathway during HDS over Ni2P and
YxNi2P catalysts [18]. For YxNi2P catalysts, the selectivity for BP in-
creased with increasing Y content, which may be attributed to more
Ni(1) sites (involved in the DDS route) being exposed on the surface
of the samples [7,27].
4. Conclusions
Y-modified bulk Ni2P (YxNi2P) catalysts with high HDS activity have
been prepared. XRD analysis has shown that the incorporation of Y into
Table 2
Spectral parameters of the Ni2P and YxNi2P catalysts obtained by XPS analysis.
Sample
Binding energy (eV)
Superficial
atomic ratio
Ni 2p3/2
P 2p
Ni2+
Satellite
Niδ+
P5+
Pδ–
P/Ni
Niδþ
∑Ni
Ni2P
856.7
856.1
856.4
861.2
860.8
860.9
852.7
852.5
852.6
134.8
134.5
134.6
128.8
129.0
130.3
0.041
0.048
0.054
3.0
2.7
2.4
Y0.03Ni2P
0.10Ni2P
Fig. 2. XPS spectra of the Ni2P and YxNi2P catalysts (a) Ni 2p core level spectra, (b) P 2p core
level spectra.
Y

H. Song et al. / Catalysis Communications 63 (2015) 52–55
55
Foundation of Heilongjiang Province (ZD201201), the Education De-
partment of Heilongjiang Province (12541060).
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.catcom.2014.09.027. These data include MOL files
and InChiKeys of the most important compounds described in this
article.
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the bulk Ni2P catalyst can suppress the formation of the Ni5P4 phase and
thereby promote the formation of more of the active Ni2P phase. The
crystallite size of Ni2P decreased with increasing Y content. Y can greatly
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the active Ni2P particles. With increasing Y content, the enrichment of
P on the surface of the catalysts decreases and therefore the number
of exposed nickel atoms increases, leading to a higher CO uptake. The
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The authors acknowledge the financial supports from the National
Natural Science Foundation of China (21276048), the Natural Science