A remarkable enhancement of catalytic activity for KBH4 treating the carbothermal reduced Ni/AC catalyst in glycerol hydrogenolysis

Article abstract of DOI:10.1016/j.catcom.2009.12.009

It reported a novel procedure for preparing Ni/AC catalyst for the glycerol hydrogenolysis, which involved carbothermal reduction of supported nickel nitrate and further treatment with KBH₄. The activity of the as-prepared catalyst was remarkably enhanced compared with KBH₄, H₂ or carbothermal reduced Ni/AC catalyst. The Ni particles and the variation of oxygen-containing surface groups (OSGs) were studied by XRD, TEM, FT-IR, He-TPD and NH₃-TPD techniques. The high dispersed Ni and the acidity generated by the OSGs have the synergy effect on the activity of glycerol hydrogenolysis.

Full text of DOI:10.1016/j.catcom.2009.12.009

Catalysis Communications 11 (2010) 493–497
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
A remarkable enhancement of catalytic activity for KBH4 treating
the carbothermal reduced Ni/AC catalyst in glycerol hydrogenolysis
a
a
Weiqiang Yu a,b, Jie Xu a, , Hong Ma , Chen Chen , Jing Zhao a,b, Hong Miao a, Qi Song a,b
*
a State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, PR China
b Graduate University of Chinese Academy of Sciences, Beijing 100049, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
It reported a novel procedure for preparing Ni/AC catalyst for the glycerol hydrogenolysis, which involved
carbothermal reduction of supported nickel nitrate and further treatment with KBH4. The activity of the
as-prepared catalyst was remarkably enhanced compared with KBH4, H2 or carbothermal reduced Ni/AC
catalyst. The Ni particles and the variation of oxygen-containing surface groups (OSGs) were studied by
XRD, TEM, FT–IR, He-TPD and NH3-TPD techniques. The high dispersed Ni and the acidity generated by
the OSGs have the synergy effect on the activity of glycerol hydrogenolysis.
Received 16 September 2009
Received in revised form 5 November 2009
Accepted 4 December 2009
Available online 11 December 2009
Keywords:
Ó 2009 Elsevier B.V. All rights reserved.
Carbothermal reduction
Glycerol hydrogenolysis
Potassium borohydride
Propylene glycol
1. Introduction
Carbon supported nickel catalyst was an excellent non-noble
hydrogenation catalyst used in various hydrogenation reactions
Catalytic conversion of renewable biomass resources into valu-
able chemicals is a challenging and promising process. Glycerol,
which is the by-product of biodiesel manufactures [1] and also de-
rived from sugars or sugar alcohols [2], is an important biomass-
derived compound. The low price and rich availability make it a
potential feedstock for the manufacture of high value-added chem-
icals, especially 1,2-propylene glycol (1,2-PG). 1,2-PG is of great de-
mand for producing polymers and resins, as well as
pharmaceuticals, foods, cosmetics or functional fluids. The current
industrial production of 1,2-PG is from petroleum derivatives by
chemical catalytic routes via hydration of propylene oxide [3].
Comparably, as an alternative route, the catalytic converting of
glycerol to 1,2-PG seems to be more advantageous. A number of re-
ports were published for the catalytic hydrogenolysis of glycerol.
Noble metal catalysts of Ru, Rh, Pd and Pt [4–9] were explored in
this reaction; however, the majority of noble metal catalysts were
not so efficient. Over Ru/C plus Amberlyst, the conversion is only
12.9% [4,5]; Rh/SiO2 only gave 19.6% conversion with 34.6% selec-
tivity of 1,2-PG [6]. In recent years, non-noble metals had attracted
increasing attention and Raney Ni, Cu–Cr, Cu–ZnO, and Cu/SiO2
[10–14] were reported for glycerol hydrogenolysis. The research
of supported non-noble Ni catalyst was slightly reported in this
kind of reaction.
[15–17]. The rich oxygen-containing surface groups (OSGs) in the
carbon supports, i.e. carboxylic, phenolic, quinone, lactonic and
etheric groups, strongly influenced the hydrogenation performance
[18–21]. It demonstrated that the OSGs have positive effect includ-
ing: (1) enhancing the metal dispersion due to the metal particles
anchored by selective groups [18,20]; (2) change the surface polar-
ity to facilitate the adsorption of organic reactant [19]; (3) adjust-
ing the surface acidity or basicity to promote the hydrogenation
activity [21]. The composition and amount of OSGs played impor-
tant roles on hydrogenation reaction. In this work, it reported a no-
vel procedure for preparing Ni/AC (activated carbon) catalyst by
the treatment of KBH4 on carbothermal reduced catalyst, and
investigated the effect of OSGs on catalytic activity in glycerol
hydrogenolysis.
2. Experimental
Ni(NO3)2/AC was prepared by incipient wetness impregnation
method as follows: AC (coconut shell, 80–100 mesh, 1318 m2/g
BET surface area) was immersed in desired amount of 1.2 M
Ni(NO3)2 aqueous solution for 24 h at room temperature and then
dried overnight at 393 K. The loading amount of nickel in the
catalyst was all 10 wt.%. The carbothermal reduction and H2 reduc-
tion of Ni(NO3)2/AC were carried out in tubular furnace with
90 min ramp and a 180 min hold at 723 K under flow N2 and H2
(99.999% purity). The samples were denoted as Ni/AC-C and
* Corresponding author. Tel./fax: +86 411 84379245.
E-mail address: xujie@dicp.ac.cn (J. Xu).
1566-7367/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2009.12.009

494
W. Yu et al. / Catalysis Communications 11 (2010) 493–497
Table 1
The characteristics of the as-prepared Ni/AC catalysts.
COb
mol/g)
a
Catalysts
SBET
Vtotal
dXRD
dTEM
(nm)
(m2/g)
(cm3/g)
(nm)
(l
Ni/AC-C
Ni/AC-CB
Ni/AC-H
Ni/AC-HB
NiB/AC
1095
1056
1295
1317
1135
0.44
0.43
0.58
0.53
0.46
16.5
16.9
20.4
28.9
–
20.8
23.3
26.4
29.6
24.7
368.2
385.8
160.5
257.7
299.2
a
Average crystallite size calculated by Scherrer equation according to the Ni
(111).
b
Amount of CO evolved in He-TPD test.
of the catalysts were examined by transmission electron micros-
copy (TEM) on a JEOL JEM-2000EX electron microscope. The
surface area of catalysts was measured with the BET method by
using N2 adsorption–desorption measurements at 77 K in
a
Fig. 1. XRD patterns of (a) Ni/AC-C, (b) Ni/AC-CB, (c) Ni/AC-H, (d) Ni/AC-HB and (e)
NiB/AC.
Quantachrome Autosorb-1. Fourier transform infrared spectra
(FT–IR) were collected on a Bruker Tensor 27 FT–IR spectrometer.
He-temperature-programmed desorption (He-TPD) and NH3-tem-
perature-programmed desorption (NH3-TPD) were used to study
the surface groups and catalyst acidity on a Micromeritics Auto-
Chem II 2920 instrument.
Hydrogenolysis of glycerol was carried out in a 600 mL batch
autoclave reactor (Parr Instrument Co.). The reactor was initially
loaded with glycerol aqueous solution (25 wt.%) and the catalyst.
After air had been flushed out, the reactor was heated to 473 K
and pressurized with 5 MPa of H2, and then the reaction was
started. The pressure was kept constant by supplying H2 during
the reaction. The products were identified by Agilent 6890N GC/
Ni/AC-H, respectively. Then, the reduced samples of Ni/AC-C and
Ni/AC-H were treated by 2.0 M KBH4 containing 0.2 M NaOH with
continuous stirring. The catalysts were named as Ni/AC-CB and Ni/
AC-HB, respectively. The NiB/AC amorphous alloy catalyst was pre-
pared by the reduction of the dried Ni (NO3)2/AC with the 2.0 M
KBH4 solution containing 0.2 M NaOH.
The identification of crystal phases was performed by X-ray
powder diffraction (XRD) using Rigaku D/Max 3400 powder dif-
fraction system with Cu K
a radiation (k = 0.1542 nm) at 40 kV
and 200 mA with a scanning rate of 5°/min. The microstructures
50
a
25
f
0
10
20
20
30
30
40
40
50
50
50
25
b
0
10 c
50
25
0
20
30
40
50
10 d
50
25
0
20
20
30
30
40
40
50
50
10 e
50
25
0
10
Particle diameter (nm)
Fig. 2. TEM micrographs of Ni based catalysts (a) Ni/AC-C, (b) Ni/AC-CB, (c) NiB/AC, (d) Ni/AC-H, (e) Ni/AC-HB and (f) their particle size distribution.

W. Yu et al. / Catalysis Communications 11 (2010) 493–497
495
5973 MS detector and quantified by Agilent 4890D GC equipped
m) capillary
column with the internal standard method. Conversion is defined
as the molar ratio of the consumed glycerol in the reaction to the
initial added glycerol. Selectivity is defined as the molar ratio of
the product to the consumed glycerol in the reaction [11].
Temperature(K)
800 1000
with FID detector and a HP-5 (30 m  0.53 mm  0.6
l
600
CO
1200
6
5
7
6
5
4
3
2
1
0
a
4
Ni/AC-CB
3. Results and discussion
3
Fig. 1 showed the XRD patterns of these catalysts. The Ni/AC-C
displayed three typical peaks of metallic Ni around 44o, 52o, and
76o of 2h [22]. For Ni/AC-CB, the typical peaks of metallic Ni still ex-
isted and the Ni crystallite size slightly changed from 16.5 to
16.9 nm according to Scherrer calculation. It was indicated that
KBH4 treatment did not change the metallic Ni. The XRD curve of
Ni/AC-H (-HB) still showed the peak of metallic Ni, however, the
Ni crystallite size of Ni/AC-HB was much larger (Table 1). Differ-
ently, NiB/AC had the typical amorphous alloy characteristics
[23] with a weak and broad peak at 44o of 2h.
Fig. 2 exhibited the morphology of the fresh prepared catalysts.
It could be observed that the particles in Ni/AC-C and Ni/AC-CB
were highly and evenly dispersed on AC support. The size
distribution of particles was much narrower, and the average size
of the metal particles was appropriately close. However, for Ni/AC-
H (-HB) and NiB/AC, the dispersion of particles was unsatisfactory
and the size turned bigger.
The specific surface areas of the catalysts were shown in Table 1.
For Ni/AC-C (-CB) and NiB/AC, the BET surface area was decreased
obviously in comparison with AC, suggesting surface was probably
changed or partial pores were blocked. However, the catalysts still
maintain a rather high surface area. The surface area of Ni/AC-H (-
HB) slightly changed compared to AC, which indicated that this
treatment had no effect on the catalysts.
Fig. 3 showed the He-TPD spectra results of all the samples trea-
ted by different methods. The amount of CO2 releasing in all the
catalyst was much less than the CO releasing. Compared with AC,
the OSGs of Ni/AC-C catalyst was increased evidently. There were
two obviously CO peaks in the 920 K and 1080 K, which could be
attributed to the phenolic and carbonyl group, respectively [24].
It was probably because the released HNO3 and NOx from nickel ni-
trate decomposition [25] would oxygenate partial surface of AC.
For the Ni/AC-CB, the CO peak in the 1070 K was weakened and
the peak of 920 K was strengthened, which indicated that the car-
bonyl group was reduced to phenolic group during the KBH4 treat-
ing. The total amount of evolved CO was almost approaching (Seen
in Table 1). For Ni/AC-H and Ni/AC-HB, same phenomenon could be
seen; however, the amount of OSGs was low. For NiB/AC, the He-
TPD was similar to that of Ni/AC-CB, and the releasing amount of
CO was between that of Ni/AC-CB and Ni/AC-HB. The results indi-
cated that KBH4 could reduce the carbonyl group to phenolic group
which leaded to the redistribution of OSGs.
FTIR spectra were another proof for the OSGs change (seen in
Fig. 4). The peak in 1560 cmÀ1 was attributed to quinone structure
[26]. It was strengthened for Ni/AC-C in comparison with AC and
then weakened for Ni/AC-CB. The phenomenon was in accordance
with the results of He-TPD analysis.
Catalysts were in further tested by NH3-TPD analysis to esti-
mate the acidity, and the results were shown in Fig. 5. For Ni/AC-
CB, the strength and the amount of acidity were enhanced remark-
ably and it owned the highest acidity in all the catalysts. The obvi-
ous increasing of acidity probably resulted from KBH4 reducing the
carbonyl structure to phenolic hydroxyls, which was considered as
one kind of the acid groups in AC [27].
2
Ni/AC-C
1
AC
AC
0
Ni/AC-CB
Ni/AC-C
CO2
1200
-1
0
2000
Time(s)
4000
Temperature (K)
800 1000
600
CO
4
5
b
3
2
4
3
2
1
0
Ni/AC-H
Ni/AC-HB
1
AC
0
AC
Ni/AC-HB
Ni/AC-H
CO2
-1
0
2000
Time (s)
4000
Temperature (K)
800 1000
600
1200
4
3
5
c
CO
4
3
2
1
0
NiB/AC
2
1
AC
AC
0
NiB/AC
CO2
-1
0
2000
Time (s)
4000
Fig. 3. He-TPD profiles for (a) Ni/AC-C and Ni/AC-CB, (b) Ni/AC-H and Ni/AC-HB and
(c) NiB/AC.
Catalytic performances were tested in the hydrogenolysis of
glycerol (Table 2). Ni/AC-H and Ni/AC-C only gave 7.4% and 6.3%
of glycerol conversion, respectively. The further KBH4 treating re-
sulted in their activity obviously increased. The glycerol conversion

496
W. Yu et al. / Catalysis Communications 11 (2010) 493–497
Table 2
Catalytic performance of the as-prepared Ni/AC catalysts.
Catalysts
Conversion (%)
Selectivity (%)a
1,2-PG
EG
a
b
Ni/AC-C
Ni/AC-CB
Ni/AC-CBc
Ni/AC-H
Ni/AC-HB
NiB/AC
7.4
18.3
76.1
77.4
38.2
63.5
38.3
n.d.b
8.0
7.9
29.1
n.d.
n.d.
43.3
63.2
6.3
10.8
16.6
Reaction conditions: 150 g 25 wt.% glycerol aqueous solution, 0.695 g Ni in the
catalyst, 5 MPa H2, 473 K, 6 h.
a
Other byproducts mainly including methanol, ethanol and propane.
Not detected.
24 h of reaction time.
c
b
c
The high activity of the as-prepared Ni/AC-CB could attribute to
synergy effect of hydrogenation center and acidity generated from
the variation of OSGs. The carbothermal reduction process formed
the metallic Ni as the hydrogenation center, and simultaneously
generated large amount of OSGs, which could anchor the new
formed metallic Ni [20] and lead to high dispersion. However,
the activity of such catalyst (Ni/AC-C) was unsatisfactory. It indi-
cated only metallic Ni was not efficient for glycerol hydrogenolysis.
When it was further treated with KBH4 to reduce the carbonyl
group, the glycerol conversion was enhanced immediately. NH3-
TPD verified that the acidity was greatly increased by the transfor-
mation of OSGs. The high acidity combined with the metallic Ni
corporately enhanced the activity. The mechanism of glycerol
hydrogenolysis was consistent with the recent reports [3,9,14].
Over Ni/AC-CB, glycerol was first dehydrated to the intermediate
of acetol over the acid sites generated by the variation of OSGs,
and this process was a rate-determining step. After the step was
finished, the hydrogenation of acetol was quickly realized on the
high dispersed Ni metal formed by carbothermal reduction.
However, for Ni/AC-C, Ni/AC-H, Ni/AC-HB and NiB/AC, they had
low amount of acid, which make the rate-determining step could
not effectively progress and absolutely resulted in the lower
activity.
2000
1600
1200
800
Wavenumber (cm-1)
Fig. 4. FT–IR spectra of the catalysts of (a) AC, (b) Ni/AC-C and (c) Ni/AC-CB.
f
e
d
4. Conclusions
c
The efficient catalyst was successfully prepared by KBH4 treat-
ing the carbothermal reduced Ni/AC. The XRD, TEM, FT–IR, He-
TPD and NH3-TPD characterization indicated that carbothermal
reduction provided the Ni active sites and simultaneously gener-
ated large amount of OSGs in AC support, and further KBH4 treating
reduced the carbonyl group to phenolic group which greatly in-
creased the catalyst acidity. The as-prepared catalyt gave 43.3%
conversion of glycerol and 76.1% selectivity for 1,2-PG over Ni/
AC-CB catalyst at 200 °C under 5 MPa H2 after 6 h, and 63.2% con-
version with 77.4% selectivity for 1,2-PG after 24 h. The result was
much better than that of catalysts prepared by KBH4 reduction,
carbothermal reduction, and H2 reduction. It suggested that the
highly dispersed Ni and the acidity generated from OSGs have
the synergy effect on the activity of glycerol hydrogenolysis.
b
a
450
500
550
600
650
700
750
Temperature (K)
Fig. 5. NH3-TPD curves of (a) AC, (b) NiB/AC, (c) Ni/AC-H, (d) Ni/AC-HB, (e) Ni/AC-C
and (f) Ni/AC-CB.
increased to 10.8% over Ni/AC-HB and 43.3% over Ni/AC-CB cata-
lyst. NiB/AC amorphous alloy was in further investigated and the
glycerol conversion was 16.6%, which was between the Ni/AC-CB
and Ni/AC-HB. The activity of Ni/AC-CB was the highest among
these catalysts. The conversion was increased by about 6 times
in comparison with Ni/AC-C, and the selectivity of 1,2-PG was obvi-
ously improved to 76.1%. The result was better than that of some
already reported catalysts in similar condition [4–6]. When
extending the reaction time to 24 h, the conversion reached
63.2% with 77.4% selectivity of 1,2-PG. The activity sequence was
that Ni/AC-CB > NiB/AC > Ni/AC-HB > Ni/AC-C ꢀ Ni/AC-H.
Acknowledgements
This work was financially supported by the Key Program of CAS
Action Plan of Science and Technology for Revitalization of North-
east China and Forefront Program of Knowledge Innovation Project
of CAS (K2006D1).

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