Synthesis of Ni-P-B amorphous nanoparticles with uniform size as a potential hydrodeoxygenation catalyst

Article abstract of DOI:10.1039/c4nj01770f

An Ni-P-B amorphous nano-catalyst was synthesized using a facile chemical reduction method. The amorphous degree was enhanced and the transferred electron decreased with an increase of P content in Ni-P-B. In the hydrodeoxygenation (HDO) of p-cresol, the conversion using Ni-P-B was high up to 98.9% with a selectivity of 6.5% for toluene and a deoxygenation degree of 96.8% at 498 K.

Full text of DOI:10.1039/c4nj01770f

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Synthesis of Ni–P–B amorphous nanoparticles with
uniform size as a potential hydrodeoxygenation
catalyst†
Cite this:DOI: 10.1039/c4nj01770f
Received (in Montpellier, France)
ab
a
a
a
a
a
Weiyan Wang,* Pengli Liu, Kui Wu, Kun Zhang, Lu Li, Zhiqiang Qiao and
10th October 2014,
ab
Accepted 25th November 2014
DOI: 10.1039/c4nj01770f
www.rsc.org/njc
Yunquan Yang*
An Ni–P–B amorphous nano-catalyst was synthesized using a facile Hence, an amorphous catalyst seems to be a good candidate for
chemical reduction method. The amorphous degree was enhanced the HDO reaction.
2
4
and the transferred electron decreased with an increase of P content
Li et al. have demonstrated that the presence of P in an
in Ni–P–B. In the hydrodeoxygenation (HDO) of p-cresol, the con- Ni–B amorphous catalyst could strengthen its hydrogenation
version using Ni–P–B was high up to 98.9% with a selectivity of 6.5% activity and selectivity owing to an increase in unsaturated
2
5
for toluene and a deoxygenation degree of 96.8% at 498 K.
coordination. Moreover, Cecilia et al. have reported that the
unreduced phosphorus in a Ni–P catalyst acted as the Br o¨ nsted
Amorphous material, possessing a unique homogeneous isotropic acid site for the deoxygenation reaction. Until now, there are no
structure and high concentration of coordinative unsaturated sites reports regarding Ni–P–B as a HDO catalyst because Ni–P–B
is expected to display some special properties, especially for prepared using a chemical reduction method has high hydro-
1
–5
catalytic applications. The techniques generally used for the genation activity but low deoxygenation activity. If it can increase
preparation of metal–metalloid amorphous catalysts have con- the Br ¨o nsted acid sites of the Ni–P–B catalyst with the precondition
centrated on: (1) rapid quenching method and (2) chemical of insuring its high hydrogenation activity, the prepared catalyst
reduction method. For the rapid quenching method, the amor- will exhibit good HDO activity. Therefore, aiming at improving the
phous catalysts prepared have a very small surface area and deoxygenation activity, we used NiSO , NaH PO and NaBH as
4
2
2
4
need further treatment for activation, which is not suitable for raw materials, (NH ) SO and Na C H O (sodium citrate) as the
4
2
4
3 6 5 7
practical industrial catalysis. Hence, most amorphous catalysts buffer agent to prepare Ni–P–B amorphous catalyst in this study.
are prepared using a chemical reduction method.
Their catalytic activity was tested using the HDO reaction of
We have prepared Ni(Co)–Mo(W)–B amorphous catalysts using p-cresol as a probe.
a chemical reduction method for the hydrodeoxygenation (HDO)
The Ni–P–B amorphous catalysts were characterized by XPS
These catalysts and the binding energies of each element and surface composi-
exhibited high hydrogenation activity, making the HDO of tion summarized in Table 1. The binding energy of Ni 2p at
6–10
of oxygen–containing compounds in bio–oil.
2
6,27
phenols via a hydrogenation–dehydration (HYD) route. It verified around 852.2–852.8 eV was ascribed to metallic Ni.
that the HDO catalyst requires two components: a metal like site level, two binding energies at 187.2–187.6 eV and 190.9–191.8 eV
for hydrogenation and a Br o¨ nsted acid site for deoxygenation.
For the B 1s
11
were attributed to boron interacting with nickel and oxidized
An optimum molar ratio of these two types of sites ensures the boron,26,27 respectively. Similar to the B 1s level, the binding
best HDO activity. Besides, several kinds of catalysts, such as energies at 129.5–129.7 eV and 130.0–130.4 eV for P 2p were
sulfides, phosphides, nitrides, carbides and noble metals have assigned to phosphorus interacting with nickel and oxidized
1
2–23
24,28
also been applied into the HDO reaction.
Only some noble phosphorus, respectively.
When compared with the standard
metal catalysts have high hydrogenation properties, leading to binding energies of Ni (853.0 eV), B (187.0 eV) and P (130.0 eV),
moderate HDO reaction conditions, but the cost is very high. it indicated boron donated part of electrons to nickel and
phosphorus accepted electrons from nickel, which was in
a
29
School of Chemical Engineering, Xiangtan University, Xiangtan, Hunan, 411105,
agreement with previous reports. We need to point out that
P. R. China. E-mail: wangweiyan@xtu.edu.cn
the transferred electrons decreased while the P oxide on the
catalyst surface increased with the molar ratio of P/B, suggesting
that the hydrogenation activity declined slowly while the deoxy-
b
National & Local United Engineering Research Centre for Chemical Process
Simulation and Intensification, Xiangtan University, Xiangtan 411105,
P. R. China. E-mail: yangyunquan@xtu.edu.cn
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nj01770f genation activity enhanced gradually. The surface composition
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Table 1 XPS binding energies and surface composition of the Ni–P–B samples
Ni (%)
B (%)
P (%)
0
2+
0
3+
0
n+
Catalysts
Ni–B
Ni 2p (eV)
852.2
B 1s (eV)
P 2p (eV)
—
Surface composition
Ni
Ni
B
B
P
P
187.6
191.8
Ni1.00
Ni1.00
Ni1.00
Ni1.00
B
1.11
B
1.89
B
2.22
B
2.63
30.6
54.8
50.1
23.3
69.4
45.2
49.9
76.7
16.2
39.4
54.8
30.5
83.8
60.6
45.2
69.5
—
—
8
8
55.6
61.0
Ni–P–B-0.5
Ni–P–B-1
Ni–P–B-6
852.3
187.6
191.7
129.5
133.0
P
0.38
P
1.07
P
1.19
44.0
47.6
31.8
56.0
52.4
68.2
8
8
55.4
60.4
852.5
187.3
190.9
129.6
133.0
8
8
55.8
60.6
852.8
187.2
190.9
129.7
133.4
8
8
56.3
61.5
of the Ni–P–B catalyst showed that the B content on the surface
was increased with a decrease in the amount of NaBH added,
which was ascribed to the following reason. NaBH was added
4
4
2
+
dropwise into the system and then reacted with Ni to produce
Ni–B. This Ni–B can act as a catalyst for promoting the reaction
À
2+
of H
PO
2 2
with Ni . Because of an excess of reducing agent,
2
+
after a certain time, Ni reacted completely, but NaBH
4
was still
added and then hydrolysed, leading to a high B content on the
catalyst surface.
The XRD patterns of Ni–B and Ni–P–B are shown in Fig. 1. All the
Ni–B and Ni–P–B samples presented only one broad peak at around
30,31
2y = 451, characteristic of a typical amorphous structure.
It has
been reported that amorphous B and P oxides show peaks at
32
around 20–301. However, no other peaks except for one broad
peak at 2y = 451 were observed, indicating a high dispersion of these
oxides. Notably, the intensity of the peak at 2y = 451 decreased with Fig. 2 SEM images of Ni–B, Ni–P–B-0.5, Ni–P–B-1 and Ni–P–B-6.
the amount of P added. The peak width corresponded to the
24
amorphous degree, which demonstrated the lowest amorphous
degree for Ni–B and the highest amorphous degree for Ni–P–B-6.
Fig. 2 shows the SEM images of Ni–B, Ni–P–B-0.5, Ni–P–B-1
This results from the strong interactions between the metallic Ni and Ni–P–B-6. The Ni–B image presented small particles with
and elemental B. Consequently, the more electrons transferred from serious agglomeration. After adding P, the particle size was
0
0
B to Ni , the lower the amorphous degree. In addition, amorphous increased greatly. Ni–P–B-1 displayed regular spherical particles
B and P oxides acting as dispersants, could also account for the high with an average size of about 170 nm, which might be attri-
2
4
amorphous degree for Ni–P–B.
buted to the weaker reducibility of NaH
2 2 4
PO to that of NaBH .
2
+
In comparison with NaBH , the reduction of Ni by NaH PO
4
2
2
proceeded more smoothly, which ensured nucleation and
growth of the regularly spherical particles. The Ni–P–B-6 image
shows that besides some spherical particles with an average
size of about 200 nm, there also appeared some small shapeless
particles. According to the differences among the SEM images
of Ni–B, Ni–P–B-1 and Ni–P–B-6 and the XPS results, these small
particles in Ni–P–B-6 image could be attributed to B oxide. The
surface area results were consistent with these SEM results. The
surface area of Ni–B, Ni–P–B-0.5, Ni–P–B-1 and Ni–P–B-6 were
2
À1
2
À1
2
À1
2
À1
2
2.9 m g , 9.1 m g , 9.1 m g , and 7.6 m g , respectively.
The potential HDO activity of Ni–B and Ni–P–B were tested
using p-cresol as a model compound. As shown in Table 2,
the conversion using Ni–B, Ni–P–B-0.5 and Ni–P–B-1 were
higher than 98% at 498 K for 1 h. The products were toluene,
3-methylcyclohexene, methylcyclohexane, 4-methylcyclohexanol
Fig. 1 XRD spectra of Ni–B, Ni–P–B-0.5, Ni–P–B-1 and Ni–P–B-6.
and 4-methylcyclohexanone. 4-Methylcyclohexanol selectivity
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Table 2 Comparison of the HDO reaction of p-cresol using Ni–P–B at observed in the SEM images, and the corresponding conversion
a
4
98 K for 1 h
was reduced from 98.9% to 59.8%. These results suggest that
the relatively large particle size and regular particle shape of
Ni–P–B might facilitate the adsorption of p-cresol on the catalyst
surface and thus increase its conversion. Li et al. have also
reported a similar conclusion.
When comparing Ni–P–B-0.5 with Ni–P–B-1, their surface
area and particle size were almost the same, but Ni–P–B-1
exhibits a higher deoxygenation degree (96.8%) than Ni–P–B-0.5
Catalysts
Ni–B
98.8
Ni–P–B-0.5
98.8
Ni–P–B-1
98.9
Ni–P–B-6
59.8
Conversion, mol%
Products distribution, mol%
2
4
4
4
3
-Methylcyclohexanol
-Methylcyclohexanone
-Methylcyclohexene
60.1
10.6
2.7
23.7
2.9
7.6
3.2
2.0
81.6
5.5
87.0
0.7
1.1
1.8
89.9
6.5
96.8
0
0
12.7
49.0
38.3
56.8
Methylcyclohexane
Toluene
b
DD, wt%
29.5
(
87.0%). This was mainly attributed to the different surface
a
n+
Reaction conditions: 0.20 g of catalyst, 13.51 g of p-cresol, 86.49 g of composition of the catalyst. P on the catalyst surface acts as a
b
dodecane and 4.0 MPa hydrogen pressure. Deoxygenation degree
Br o¨ nsted acid site, which determines the deoxygenation activity.
(
DD, wt%) is defined as [1 À oxygen content in the final organic
0
n+
Both the Ni content and P content on the Ni–P–B-0.5 catalyst
compounds/total oxygen content in the initial material].
surface were higher than that on Ni–P–B-1, but Ni–P–B-1 has more
n+
P
sites than Ni–P–B-0.5 on the catalyst surface, leading to a
decreased while toluene selectivity increased with an increase
in the molar ratio of P/B in the Ni–P–B catalyst. Toluene is
produced from the direct deoxygenation (DDO) of p-cresol, its
selectivity using Ni–B, Ni–P–B-0.5 or Ni–P–B-1 was low (o7%),
indicating that the HYD route was the dominant reaction pathway
in the HDO of p-cresol using these catalysts. The surface area of
Ni–P–B-0.5 was much lower than that of Ni–B, which would
decrease its HDO activity because of the lower number of available
active sites per unit weight of catalyst. However, the conversion
using Ni–B and Ni–P–B-0.5 were the same (98.8%), which suggests
that these catalysts have very high hydrogenation activity and their
surface area has a minor effect on their activity.
higher 4-methylcyclohexanol selectivity in the HDO reaction of
p-cresol using Ni–P–B-0.5 than that found using Ni–P–B-1. When
0
the molar ratio of P/B in the Ni–P–B increased to 6, the Ni content
declined, leading to its lower hydrogenation activity. Moreover,
the P and B content on the catalyst surface were enhanced, which
0
covered some of the Ni sites and further decreased its hydro-
n+
genation activity. However, Ni–P–B-6 has much more P sites on
its surface, suggesting its high deoxygenation activity. Hence, the
conversion of p-cresol using Ni–P–B-6 decreased to 59.8% and its
4-methylcyclohexanol selectivity was very low. Among the catalysts
prepared, Ni–P–B-1 showed the highest HDO activity. The conver-
sion was high, up to 98.9% with a deoxygenation degree of 96.8%.
Therefore, an appropriate molar ratio of P/B in the Ni–P–B was
beneficial to enhance its HDO activity.
In conclusion, a Ni–P–B amorphous catalyst with a uniform
particle size and high HDO activity was successfully prepared
It has been reported that the HYD and DDO route result
from a co-planar position adsorption and vertical orientation
3
3,34
adsorption on the catalyst’s surface,
respectively. The forma-
tion of toluene concerning the vertical orientation adsorption
requires a high activation energy, leading to a high HDO reaction
temperature. The activity test results show that two parallel
reaction routes (HYD and DDO, Fig. 3) exist in the HDO reaction
of p-cresol using Ni–P–B and the dominant route was HYD.
Moreover, dodecane is non-polar, which also favors the co-planar
using a chemical reduction of NiSO
4
with NaH
2
À
PO
2
and NaBH
than that found
and Na
4
.
2
+
The more smooth reduction of Ni by H
using NaBH and the buffer action of (NH
2
PO
SO
2
4
)
4 2
4
3 6 5 7
C H O
ensured the nucleation and growth of the regularly spherical
particles. By adjusting the molar ratio of P/B in Ni–P–B changed
35
0
0
adsorption. This means that the majority of p-cresol was adsorbed
on the catalyst surface via the co-planar position. Hence, the
catalyst particle size and shape would have significant influence
on the product distribution. Table 2 shows that the conversion of
p-cresol using Ni–B with a smaller particle size and higher surface
area was 98.8%. But, the conversion was also very high (98.9%) on
Ni–P–B-1 with a larger particle size and lower surface area.
In addition, when the molar ratio of P/B in Ni–P–B increased
from 1 to 6, some of the small and irregular particles were
the transferred electrons between Ni and B and the content of
P oxide on the catalyst surface, and influenced the hydrogena-
tion activity and deoxygenation activity. This method appears to
be a promising approach for adjusting the hydrogenation and
deoxygenation activity to obtain a high HDO activity catalyst.
Experimental section
Ni–P–B amorphous catalysts were designed and prepared as
follows: NiSO
10 mmol) and NaH
and then placed in a 250 mL three-necked flask. 20 mL of an
aqueous solution of NaBH was added dropwise to the three-
4
(5 mmol), (NH
4 2 4 3 6 5 7
) SO (10 mmol), Na C H O
(
2
PO were dissolved in 20 mL of water,
2
4
necked flask at room temperature. The Ni/(P + B) molar ratio
was controlled to 1 : 6 in each case. The black precipitate was
collected, washed with ultra-pure water and absolute ethanol,
and finally dried under vacuum at 323 K for 4 h. The resulting
sample was donated as Ni–P–B-X, where X represents the molar
Fig. 3 Reaction network for the HDO reaction of p-cresol using Ni–P–B. ratio of P/B in the initial solution.
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The HDO activity measurements were carried out in a 300 mL 12 M. S. Zanuttini, B. O. Dalla Costa, C. A. Querini and M. A. Peralta,
sealed autoclave. Fresh catalyst (0.2 g), p-cresol (13.51 g) and
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À1
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