Effects of the precipitation agents and rare earth additives on the structure and catalytic performance in glycerol hydrogenolysis of Cu/SiO 2 catalysts prepared by precipitation-gel method

Article abstract of DOI:10.1016/j.cattod.2014.02.037

The effects of the precipitation agents (NaOH, Na₂CO ₃, NH₄OH and NH₄HCO₃) and rare earth additives (La, Ce, Y, Pr and Sm) were studied on the structure and catalytic performance in glycerol hydrogenolysis of the Cu/SiO₂ catalysts prepared by precipitation-gel method. The physical-chemical properties of the catalysts were characterized by means of FTIR, H₂-TPR, N₂O chemisorption, XRD, XPS, BET and TEM. The results showed that precipitation agents had obvious effects on the phase structure, reduction property and catalytic performances (activity, selectivity and stability) of the catalysts. The Cu/SiO₂ catalyst precipitated with NaOH presented the highest activity and stability than those with other precipitants, most likely due to its more even dispersion of Cu particles, higher resistant to sintering during glycerol reaction. The incorporation of rare earth additives to Cu/SiO ₂ catalyst could promote the structural stability and inhibit the sintering and leaching of the catalysts, especially noticeable for Y and La, and thus contribute to the long-term stability of the catalysts. Clearly, this study provides directions for the design of more efficient and stable Cu catalysts toward the industrial application of glycerol hydrogenolysis.

Full text of DOI:10.1016/j.cattod.2014.02.037

G Model
CATTOD-8930; No. of Pages10
ARTICLE IN PRESS
Catalysis Today xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Effects of the precipitation agents and rare earth additives on the
structure and catalytic performance in glycerol hydrogenolysis of
Cu/SiO catalysts prepared by precipitation-gel method
2
Zhiwei Huanga,b, Hailong Liua,c, Fang Cui , Jianliang Zuo , Jing Chen
a
a
a,b,∗
, Chungu Xia
a,b,∗
a
State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000,
China
Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, China
b
c
University of Chinese Academy of Sciences, Beijing 100039, China
a r t i c l e i n f o
a b s t r a c t
Article history:
The effects of the precipitation agents (NaOH, Na CO , NH OH and NH HCO ) and rare earth additives
2
3
4
4
3
Received 23 October 2013
Received in revised form 25 February 2014
Accepted 27 February 2014
Available online xxx
(
La, Ce, Y, Pr and Sm) were studied on the structure and catalytic performance in glycerol hydrogenolysis
of the Cu/SiO2 catalysts prepared by precipitation-gel method. The physical–chemical properties of the
catalysts were characterized by means of FTIR, H2-TPR, N2O chemisorption, XRD, XPS, BET and TEM. The
results showed that precipitation agents had obvious effects on the phase structure, reduction property
and catalytic performances (activity, selectivity and stability) of the catalysts. The Cu/SiO2 catalyst pre-
cipitated with NaOH presented the highest activity and stability than those with other precipitants, most
likely due to its more even dispersion of Cu particles, higher resistant to sintering during glycerol reaction.
The incorporation of rare earth additives to Cu/SiO2 catalyst could promote the structural stability and
inhibit the sintering and leaching of the catalysts, especially noticeable for Y and La, and thus contribute
to the long-term stability of the catalysts. Clearly, this study provides directions for the design of more
efficient and stable Cu catalysts toward the industrial application of glycerol hydrogenolysis.
Keywords:
Glycerol hydrogenolysis
1
,2-Propanediol
Cu/SiO2 catalyst
Precipitation agent
Rare earth additive
©
2014 Elsevier B.V. All rights reserved.
1
. Introduction
has attracted many efforts [5–7]. Glycerol is a main byproduct in
the biodiesel production process by transesterification of vegetable
oils and animal fats, and the catalytic hydrogenolysis of glycerol to
value-added 1,2-PDO can contribute to the economy of the whole
process.
The utilization of biomass for the production of renewable
chemicals and fuels, which provides an alternative to petroleum-
based products, is gaining attention over the past decades [1–4].
1
,2-Propanediol (1,2-PDO) is an important commodity chemical
So far, several types of the catalysts reported for glycerol
hydrogenolysis are supported noble metal catalysts (e.g. Ru, Rh
and Pt) [8–12] and transition metal-based catalysts (e.g. Cu, Ni,
Co) [7,13–21]. Although the noble metals exhibit good activity for
glycerol hydrogenolysis, their disadvantages of high cost and poor
selectivity to 1,2-PDO discourage their extensive applications. Due
to its high efficiency for C O bond hydro-dehydrogenation and
poor activity for C C bond cleavage, copper is a known favorable
catalyst for the hydrogenolysis of glycerol to 1,2-PDO, and various
widely used as functional fluids such as antifreezes, coolants, and as
precursors in the synthesis of polyester resins and pharmaceuticals,
etc. Currently, 1,2-PDO is commercially produced by the multi-step
transformation of petroleum-derived propylene via its epoxide
intermediate. This process suffers from a number of disadvantages
such as low energy efficiency, environmental pollution and high
feedstock costs. Therefore, the use of cheap and renewable alter-
native feedstock, such as glycerol,for the production of 1,2-PDO,
supports including SiO2 [14,21], ZnO [16,22], Al O3 [15,23], ZrO2
2
[
[
24], MgO [25], Cr O [13,26] as well as ZnO–Al O [27], MgAlOx
19] and zeolite [15,28] have been explored for the preparation of
2 3 2 3
efficient Cu-based catalysts (Table 1). Glycerol with conversions
from 11 to 100% and 1,2-PDO selectivities from 83.9 to 100% were
generally obtained over these Cu catalysts depending on the cata-
lysts and reaction conditions (Table 1).
∗ Corresponding authors at: State Key Laboratory for Oxo Synthesis and Selec-
tive Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences,
Lanzhou 730000, China. Tel.: +86 931 4968089; fax: +86 931 4968129.
E-mail addresses: chenj@lzb.ac.cn (J. Chen), cgxia@lzb.ac.cn (C. Xia).
http://dx.doi.org/10.1016/j.cattod.2014.02.037
0
920-5861/© 2014 Elsevier B.V. All rights reserved.
Please cite this article in press as: Z. Huang, et al., Effects of the precipitation agents and rare earth additives on the structure and
catalytic performance in glycerol hydrogenolysis of Cu/SiO2 catalysts prepared by precipitation-gel method, Catal. Today (2014),
http://dx.doi.org/10.1016/j.cattod.2014.02.037

G Model
CATTOD-8930; No. of Pages10
ARTICLE IN PRESS
Z. Huang et al. / Catalysis Today xxx (2014) xxx–xxx
2
Table 1
Typical Cu catalysts and their catalytic performances in glycerol hydrogenolysis to 1,2-propanediol since 2007.
Catalyst (mass or volume)
Reactant and reactor
Reaction conditions
Conv. (%)
Sel. (%)
Ref.
50 mL 20 wt%Gly , ABRc
140 ml pure Gly, ABR
177 g, 90 wt%Gly, ABR
65 g 50 wt% Gly, ABR
65 g 50 wt% Gly, ABR
b
473 K, 6 MPa, 6 h
473 K, 5 MPa, 7 h
493 K, 5 MPa, 7 h
493 K, 1.5 MPa, 10 h
473 K, 1.5 MPa, 10 h
463 K, 0.64 MPa
473 K, 4.0 MPa, 8 h
453 K, 3 MPa, 20 h
473 K, 2 MPa, 10 h
453 K, 6.0 MPa
473 K, 5 MPa
513 K, 8 MPa, 5 h
513 K, 6 MPa
493 K, 8 MPa, 12 h
403 K, 2 MPa, 4 h
493 K, 4 MPa
75
46
96
49.6
27
96.2
11
72.0
85.5
80
94
90
82
96.8
96
92.2
90
97.6
98.6
98
98.0
96.2
89.7
83.9
100
>91
[16]
[22]
[29]
[15]
[23]
[27]
[24]
[25]
[19]
[14]
[21]
[28]
[30]
[31]
[26]
[32]
Cu/ZnO (2.2 g)
CuO/ZnO-OGa (3 g)
Cu-Ga2O3/ZnO (2.8 g)
Cu/Al2O3 (2.7 mmol)
Cu-Ag/Al2O3 (∼1 g)
Cu/ZnO/Al2O3
pure Gly, WHSVe = 0.08 h , FBRd
25 g 20 wt%Gly, ABR
8 mL 75 wt%Gly, ABR
−1
Cu/ZrO2 (0.6 g)
Cu/MgO (1.0 g)
Cu0.4/Zn0.6Mg5.0Al2O8.6 (0.4 g)
Cu/SiO2 (4 g)
Cu-B/SiO2 (4 g)
Cu/SBA-15 (0.35 g)
Cu–H4SiW12O40/Al2O3 (5 g)
Cu–Cr (1 g)
Cu–Cr (0.009 mol)
Cu–Cr–Ba (23 g)
8 g 75 wt%Gly, ABR
40 wt% Gly, WHSV = 0.25 h 1, FBR
−
f
−1
10 wt% Gly, LHSV = 0.075 h , FBR
120 mL 40 V%Gly, ABR
100
52.0
90.1
80.3
22.2
65
10 wt% Gly, LHSV = 0.9 h−1, FBR
50 g 90 wt%Gly, ABR
18 g pure Gly, ABR
30 mL/h 20 wt%Gly, FBR
a
OG: prepared by an oxalate gel method.
Gly = glycerol.
ABR: autoclave batch reactor.
FBR: fixed-bed reactor.
WHSH: weight hourly space velocity.
LHSV: liquid hourly space velocity.
b
c
d
e
f
Due to their excellent selectivity, green benefit, and low
cost, Cu/SiO2 catalysts have attracted considerable attention in
glycerol hydrogenolysis to 1,2-PDO [14,21,28,33–35]. Previously,
we reported that the Cu/SiO2 catalyst with high dispersion pre-
pared by precipitation-gel (PG) method exhibited high efficiency
and good stability in the hydrogenolysis of glycerol to 1,2-PDO [14].
2. Experimental
2.1. Catalyst preparation
The CuO/SiO2 catalyst precursor prepared by PG method with
NaOH is as follows: first, an aqueous solution of NaOH (15 wt%) was
dropped into a solution of Cu(NO3)2 (0.5 mol/L) at a constant rate
under vigorous stirring to form precipitate till pH >11. Next, a cal-
Nevertheless, the single-component Cu/SiO catalyst still encoun-
2
ters some technical problems, such as insufficient catalytic activity
and stability for glycerol hydrogenolysis. To address these prob-
lems requires the development of improved catalysts, which could
be achieved by improving the preparation technique and incor-
porating of proper promoters [14,21,28,29,36]. For example, the
incorporation of B [21], Ga [29] and La [36] has been reported to be
effective for stabilizing the active Cu species in glycerol hydrogenol-
ysis.
culated amount of colloidal aqueous silica solution (SiO , 40.0 wt%,
2
Guangzhou Renmin Chemical Plant, China) was added to the solu-
tion of the precipitate to form a gel, and then the gel was allowed
to age at around 353 K for 4 h. Finally, the slurry of the gel was fil-
tered, thoroughly washed with hot distilled water, dried at 393 K
overnight, and calcined at 723 K under air for 3 h. The procedures
for the preparation of Cu/SiO catalysts with Na CO , NH HCO and
2
2
3
4
3
It is well known that the structure and catalytic performances
of the Cu catalysts prepared by precipitation significantly affected
by the precipitation agents. For example, Dong et al. [37] found
NH OH are similar to that for NaOH with the same precipitant con-
4
centration while the pH of the precipitate for NH HCO and NH OH
4
3
4
is around 7. The normal Cu loading of the samples was 25.5 wt%, and
the dried and calcined samples were donated as PGO-base, while
the reduced active catalyst was named as PG-base, e.g. the calcined
sample and reduced catalyst prepared with NaOH are as PGO-NaOH
and PG-NaOH, respectively.
that the activities of CuO–CeO –ZrO2 catalysts in CO oxidation
2
prepared with different precipitants decreased in the order of
Na CO > NH OH > (NH ) CO > NaOH, and ascribed the best per-
2
3
4
4 2
3
formance of the catalyst prepared by Na CO to smaller grains
2
3
with uniform distribution. The composition of the precipitants was
also found to affect the structure and catalytic performances of the
Cu catalysts, e.g. the residual sodium in the Cu/SiO2 catalyst pre-
pared by PG method using NaOH as precipitant profoundly affected
the physicochemical properties and catalytic performance of the
catalyst in glycerol hydrogenolysis [33]. Thus, the detailed com-
parative study regarding the influence of precipitation agent on the
The RE-incorporated CuO/SiO precursors were prepared as fol-
lows: preparation the mother CuO/SiO2 sample by PG method
with NaOH as mentioned above, then impregnation the mother
2
CuO/SiO sample with an aqueous solution of RE(NO )x (RE = La, Ce,
2
3
Y, Pr and Sm) to obtain the required final REOx loading. The sample
was dried under the same conditions as the catalyst prepared by
PG method, and calcined at 723 and 1023 K for 3 h to obtain the
physicochemical properties of the Cu/SiO catalysts prepared by PG
final CuO–REOx–SiO samples. The compositions and codes of the
2
2
method and their catalytic performance in glycerol hydrogenoly-
sis would be helpful for the understanding of the key fundamental
issues including the effect of catalyst structures and functions. In
the present work, four different precipitants, i.e. NaOH, Na CO ,
CuO–REOx–SiO samples are listed in Table 5.
2
2.2. Catalyst characterization
2
3
NH OH and NH HCO , were used to study the effects of the pre-
4
4
3
Fourier transform infrared (FTIR) spectra were recorded at room
cipitation agents on the structures and catalytic performances in
glycerol hydrogenolysis of the Cu/SiO2 catalysts prepared by PG
method. A variety of rare earth (RE) elements including La, Ce, Y,
Pr and Sm were incorporated into the Cu/SiO2 catalyst prepared
by PG method in order to reveal the promotion effect of the rare
earth additives and further improve the reaction stability of the
catalyst.
temperature on powdered samples using the KBr wafer tech-
nique in a Nicolet Nexus 870 FTIR spectrometer. The X-ray powder
diffractions (XRD) of the samples were obtained on a PANalyti-
cal X’pert Pro Diffractometer using nickel filtered Cu K␣ radiation
(
ꢀ = 1.5418 A) operated at 40 kV voltage and 30 mA. The average
crystallite size of CuO was estimated from the average values at
˚
◦
◦
CuO(−1 1 1) (2ꢁ = 35.5 ) and (1 1 1) (2ꢁ = 38.8 ), and the average
Please cite this article in press as: Z. Huang, et al., Effects of the precipitation agents and rare earth additives on the structure and
catalytic performance in glycerol hydrogenolysis of Cu/SiO2 catalysts prepared by precipitation-gel method, Catal. Today (2014),
http://dx.doi.org/10.1016/j.cattod.2014.02.037

G Model
CATTOD-8930; No. of Pages10
ARTICLE IN PRESS
Z. Huang et al. / Catalysis Today xxx (2014) xxx–xxx
3
0
◦
crystallite size of Cu from the value at Cu(1 1 1) (2ꢁ = 43.3 ). X-ray
photoelectron spectra (XPS) were obtained using a VG ESCALAB
2
10 spectrometer equipped with a Mg K␣ X-ray radiation source
(
hꢂ = 1253.6 eV) and a hemispherical electron analyzer. All bind-
ing energies were calibrated using the Si2p peak at 103.4 eV as the
reference.
Temperature-programmed reduction (TPR) measurements
were carried out in a quartz U-tube reactor with 20 mg of sam-
ple used for each measurement. The samples were first pretreated
at 473 K under He flow for 1 h and then reduced with 5% H /N at
2
2
a flow rate of 40 mL/min and the temperature was increased from
03 to 773 K at a ramping rate of 10 K/min. H2 consumption was
3
continuously monitored by a thermal conductivity detector (TCD).
The dispersions of the catalysts were determined by disso-
ciative N O adsorption-H2 temperature-programmed reduction
2
(
TPR) reverse titration experiments [16,38]. The catalysts were first
reduced at 723 K with 5% H /N2 at a flow rate of 40 mL/min for
2
1
h. After cooling to 323 K in a He flow, the reduced samples were
exposed to a 5% N O/N2 mixture (40 mL/min) for 40 min. Finally,
2
the samples were cooled to room temperature to start another
TPR run with 5% H /N2 at a flow rate of 40 mL/min and a ramp-
2
ing rate of 10 K/min to 573 K. The copper metallic surface area,
average copper particle size and dispersion were calculated by
1
9
2
assuming 1.46 × 10 copper atoms per m and a molar stoichiom-
etry N O/Cus = 0.5, where the symbol Cus means the copper atoms
2
on the surface.
The BET surface area measurements were performed on a
Micromeritics ASAP 2010 instrument at liquid nitrogen temper-
ature. Prior to measurements, the samples were degassed at 573 K
for 4 h. Transmission electron microscopic (TEM) investigations
were carried out using a JEM2010 electron microscope at 200 kV.
2.3. Catalytic activity testing
The discontinuous glycerol reaction was carried out in a 200 mL
stainless steel autoclave at a stirring speed of 400 rpm. Prior to
the reaction, the CuO/SiO2 samples were reduced at 553 K with
a flowing 20%H /N for 3 h. The standard reaction was carried
2
2
out under the following reaction conditions: 6.4 MPa of initial H2
pressure, 80 g of 80 wt% glycerol aqueous solution, 4 g of reduced
catalyst, 12 h. After being purged, the reactor was heated to 453 K,
and the reaction pressure was increased to about 9.0 MPa and
maintained during the reaction. The liquid phase products were
analyzed by using a gas chromatograph with a SE-54 capillary col-
umn (50 m × 0.32 mm) and a flame ionization detector. The gas
products were analyzed by using a gas chromatograph (Porapak
Q column (4 m × 3 mm)) equipped with a TCD. Products were also
identified on a HP 6890/5793 GC-MS with a DB-5MS column.
The detected products were 1,2-PDO, 1,3-PDO (trace), acetol, 1-
propanol, 2-propanol (hydrogenolysis products); ethylene glycol
Fig. 1. FTIR spectra of dried (A) and calcined (B) samples prepared by different
precipitation agents.
−1
per hour) of 0.25 h , glycerol to hydrogen ratio 1:23, 453 K. The
(
EG), ethanol, methanol, CH and CO (the degradation products).
4 2
reaction products were collected in an ice water bath and then
analyzed as indicated above with ignoring the small amount of
methanol generated during the reaction.
The glycerol conversion and selectivity to the reaction products
were calculated on a carbon basis.
The continuous glycerol reaction was preformed in a vertical
fixed-bed reactor at 6.0 MPa total pressure, employing 3–4 g of cat-
alyst (20–40 mesh). The reactor tube was 36 cm long and 1.2 cm in
inner diameter. The reactor was packed with the catalyst between
two plugs of glass wool. Before the reaction, the catalysts were
reduced with a hydrogen flow under atmospheric pressure at 553 K
for 3 h. To increase the fluidity of the reaction media, 40 wt% glyc-
erol in 10 wt% water and 50 wt% methanol were used. The solution
was continuously pumped into the reactor with a high-pressure
pump and preheated to around 373 K before transported into the
reactor. Standard reaction conditions were: weight hourly space
velocity (WHSV, of 0.25 g of glycerol solution per gram of catalyst
3. Results and discussion
3.1. Influence of the precipitation agents on the structure and
catalytic performance of Cu/SiO2 catalysts
FTIR experiments were carried out to study the structure and
composition of the dried and calcined samples prepared with
different precipitation agents. For dried PGO-Na CO3 precursor
2
(Fig. 1A), the apparent absorption bands at approximately 1120,
−
1
800, and 476 cm are assigned to the differentvibration modes of
Please cite this article in press as: Z. Huang, et al., Effects of the precipitation agents and rare earth additives on the structure and
catalytic performance in glycerol hydrogenolysis of Cu/SiO2 catalysts prepared by precipitation-gel method, Catal. Today (2014),
http://dx.doi.org/10.1016/j.cattod.2014.02.037

G Model
CATTOD-8930; No. of Pages10
ARTICLE IN PRESS
Z. Huang et al. / Catalysis Today xxx (2014) xxx–xxx
4
Fig. 2. XRD profiles of dried (A), calcined (B) samples and used catalysts (C) prepared by different precipitation agents.
the Si–O bonds in the amorphous SiO [39,40]. The obvious peak
calcination. The formation of CuO in calcined PGO-NH OH and PGO-
NaOH sample is also confirmed by the XRD pattern given below.
2
4
−1
at around 1033 cm on the low-frequency side of the ␯SiO band
−
1
at 1120 cm together with the presence of the weak ı band at
In contrast, no big difference was seen for both the ␯
around 1035 cm and the ␦OH band at around 672 cm for PGO-
band at
OH
SiO
−1
−1
−1
around 672 cm indicates the presence of copper phyllosilicate
39]. The broad absorption band in the range 3200–3600 cm is
−
1
[
NH HCO and PGO-Na CO samples, referring that the structure of
4
3
2
3
due to the overlapping of the OH stretching vibration of adsorbed
copper phyllosilicate in these samples was largely preserved, which
is in line with the high stability of copper phyllosilicate reported
previously [42].
water and silanols [41]. In comparison with the dried PGO-Na CO
2
3
−
1
precursor, an additional small absorption at 1384 cm
related
to NO3 groups is also observed in the profile of the dried PGO-
NH HCO precursor, suggesting the presence of a small amount
The XRD profiles of the dried and calcined samples prepared
by different precipitation agents are shown in Fig. 2A and B. The
diffraction pattern of the sample precipitated by NaOH reveals the
4
3
of Cu (OH) NO [39], beside copper phyllosilicate. The ␦ band of
2
3
3
OH
−
1
the dried PGO-NaOH precursor appears at 690 cm , revealing the
presence of Cu(OH) [39]. In the case of the dried PGO-NH OH pre-
cursor, the ␦OH band at 682 cm and sharp absorptions at 1349,
formation of a dispersed Cu(OH) phase, while only sharp diffrac-
2
tions of Cu (OH) (NO ) were detected in the sample prepared with
2
4
2
3
3
−
1
NH OH. The apparent feature of dried samples precipitated with
4
−1
1
382 and 1425 cm related to NO groups are characteristic of the
Na CO , NH HCO was the broad and diffused diffraction of amor-
3
2
3
4
3
◦
phous silica at around 2ꢁ = 22 . In addition, the weak and diffuse
presence Cu (OH) NO [39]. The hardly observation of the charac-
2
3
3
−1
◦
◦
teristic ␦ band at around 672 cm and the ␯SiO band at around
diffraction peaks at ca. 31.2 and 35.8 suggest the presence of cop-
per phyllosilicate with poor crystallinity [39,43]. After calcination
at 723 K, copper species in dried precursors of PGO-NaOH and PGO-
OH
−
1
1
035 cm
in the dried PGO-NaOH and PGO-NH OH precursors
4
indicates that the copper phyllosilicate species formed in these two
samples would be quite low.
NH OH were both converted to CuO (Fig. 2B). The diffraction peaks
4
After calcination at 723 K, the absorption bands associated
with NO3 groups in the dried PGO-NH OH and PGO-NH HCO
of CuO for the calcined PGO-NaOH sample are much broader and
less intense than those of the PGO-NH OH sample, suggesting the
4
4
3
4
precursors and the characteric ␦OH band of Cu(OH)2 in the
dried PGO-NaOH disappeared (Fig. 1B), suggesting the complete
former sample shows much smaller crystallite size (5.7 vs. 29.3 nm)
and higher metal dispersion than those of the latter sample.
Differently, no obvious difference was seen for the samples
decomposition of Cu (OH) NO and Cu(OH)2 species to CuO after
2
3
3
Please cite this article in press as: Z. Huang, et al., Effects of the precipitation agents and rare earth additives on the structure and
catalytic performance in glycerol hydrogenolysis of Cu/SiO2 catalysts prepared by precipitation-gel method, Catal. Today (2014),
http://dx.doi.org/10.1016/j.cattod.2014.02.037

G Model
CATTOD-8930; No. of Pages10
ARTICLE IN PRESS
Z. Huang et al. / Catalysis Today xxx (2014) xxx–xxx
5
precipitated with Na CO and NH HCO after calcination, suggest-
2
3
4
3
ing the high stability of the copper species in these two samples,
which is in line with the FTIR results.
Fig. 2C shows the XRD profiles of the catalysts after 12 h glyc-
erol reaction at 453 K. Sharp and intensified diffraction peaks of
metallic copper were seen in all used catalysts, with those for the
used PG-NH OH and PG-NH HCO much sharper. These findings
4
4
3
suggest that copper species in PG-NH OH and PG-NH HCO cata-
4
4
3
lysts were seriously aggregated to much larger particles (40.2 nm
and 26.4 nm, respectively) during glycerol reaction as compared to
PG-Na CO and PG-NaOH catalysts, which are 9.7 nm and 10.2 nm,
2
3
respectively (Table 2), showing the much higher stability of the
+
catalysts prepared by Na containing bases, probably due to that
the residual Na+ in the catalyst could help retard the leaching of
the active copper and reduce the aggregation of copper particles
[
33]. In addition, Cu O with different diffraction intensity is also
2
observed in all used catalysts, which may be formed by the aggre-
gation of the highly dispersed Cu O in the inadequately prereduced
2
catalysts during glycerol reaction [14,35].
Table 2 shows the textural properties of the calcined CuO/SiO2
samples prepared with different precipitation agents. The cata-
lysts prepared with Na CO and NH HCO presented high surface
2
3
4
3
2
areas of 345.1 and 382.6 m /g, respectively, which are much higher
than those of the catalysts prepared with NaOH (186.1 m /g) and
NH OH (112.5 m /g). The larger surface areas of the catalysts pre-
2
2
4
pared with NH HCO and Na CO would be ascribed to their higher
4
3
2
3
dispersions, as which decreased in the order PG-NH HCO > PG-
4
3
Fig. 3. XP spectra of the calcined CuO/SiO2 samples prepared by different pre-
cipitation agents: (a) PGO-Na2CO3, (b) PGO-NH4HCO3, (c) PGO-NH4OH and (d)
PGO-NaOH.
Na CO > PG-NaOH > PG-NH OH (Table 2), which is good consistent
2
3
4
with the dispersion of the samples revealed by XRD. Additionally,
the presence of larger amounts of copper phyllosilicate in the cal-
cined PGO-NH HCO and PGO-Na CO , as evidenced by FTIR, may
4
3
2
3
also contribute to the higher surface areas of these samples [44]. The
average pore diameters for these samples varied in a narrow range
of 6.7–13.0 nm. As a result of Cu dispersion, the PG-NH HCO and
is seen for calcined PGO-NH OH sample as compared to its bulk
4
ratio (0.334), indicating serious aggregation of the sample [14,48],
which supported the finding by XRD characterization. It is note-
worthy that there was almost no detection of Na on the surface of
4
3
PG-Na CO catalysts possessed relatively small Cu particle sizes of
2
3
3
.3 and 3.8 nm, respectively, in comparison to 5.1 and 6.8 nm for
PGO-NH HCO and PGO-NH OH samples, which is in line with the
4 3 4
PG-NaOH and PG-NH OH, respectively.
AAS results compiled in Table 2.
4
XPS experiments were carried out to determine the oxida-
tion state of copper as well as the chemical compositions of the
samples. The XP spectra of the calcined PGO-Na CO and PGO-
Fig. 4 shows the TPR profiles of the CuO/SiO samples prepared
by different precipitation agents along with the reference of unsup-
2
ported bulk CuO (from Alfa Aesar). As can be seen, PGO-NH OH
2
3
4
NH HCO samples each showed a sharp photoelectron peak at
around 936.2 eV (Cu2p3/2), while the calcined PGO-NaOH and
sample showed a main reduction peak centered at 543 K and a
small shoulder peak centered at a low temperature of 510 K. PGO-
NH HCO sample is reduced with a main reduction peak centered
4
3
PGO-NH OH samples showed broad photoelectron peaks at about
4
4
3
9
35.5 eV with PGO-NH OH a bit lower, which is 935.3 eV (Fig. 3 and
at 517 K and a weak shoulder peak centered around 533 K. Similar
to PGO-NH HCO , PGO-Na CO also showed two reduction peaks
4
Table 3). These high binding energy (BE) values along with the pres-
ence of the characteristic shakeup satellite peaks suggest that the
copper oxidation state is +2 in all samples [45]. In comparison with
the Cu2p3/2 BE of pure CuO, which was determined at 934.1 eV,
such large positive BE shift of the Cu2p core level for these sam-
ples indicates the presence of copper phyllosilicate, according to
our previous studies [35,46] and also references [43,44]. The pres-
ence of copper phyllosilicate in PGO-Na CO3 and PGO-NH HCO3
has been confirmed by FTIR analysis, as reported above (Fig. 1). The
FWHM of the Cu2p3/2 spectra for PGO-NaOH and PGO-NH OH sam-
ples is above 4.1 eV, while that for PGO-Na CO and PGO-NH HCO
samples is below 3.2 eV (Table 3). Such high FWHM of the Cu2p3/2
4
3
2
3
with the main peak present at 517 K and the obvious shoulder peak
at 538 K. Differently, PGO-NaOH samples showed an unsymmet-
ric hydrogen consumption peak centered around 534 K, while the
unsupported pure CuO showed a good symmetric reduction peak
centered around 549 K, which is around 6–16 K higher than that of
the higher temperature peak of the CuO/SiO samples.
2
Since dispersed CuO with small particle sizes can be more
2
4
readily reduced to Cu0 than did the bulk CuO with larger sizes
2
+
[45,49], while dispersed and surface interacted Cu species are
4
0
reported to be more difficult to be reduced to Cu than bulk CuO
2
3
4
3
+
0
[50,51], because the further reduction of Cu –Cu requires a much
higher temperature (i.e. >873 K) [43]. Therefore, the reduction peak
spectra for PGO-NaOH and PGO-NH OH infers the presence of two
4
kinds of Cu(II) species, i.e. copper phyllosilicate and CuO (from XRD
characterizations) in these samples. The Cu/Si ratio on the calcined
PGO sample obtained by XPS analysis is 0.405, which is close to
the bulk ratio (0.349) of the sample, suggesting a uniform disper-
sion of Cu species in the sample. The XPS surface Cu/Si atom ratios
for PGO-Na CO and PGO-NH HCO samples are 4.0 and 3.5 times
higher than their corresponding bulk ratios, respectively, revealing
that copper species in both samples are largely enriched on the
surface [47]. Differently, a much lower surface Cu/Si ratio (0.133)
at 517 K or below for the CuO/SiO2 samples prepared by NH OH,
4
NH HCO and Na CO might be associated with the partial reduc-
4
3
2
3
2+
tion of the highly dispersed surface interacted Cu species, that
is copper phyllosilicate, to Cu . The presence of copper phyllosil-
+
icate in these samples has been verified by XPS characterization.
The shoulder peaks in the high temperature range in these sam-
ples, which are close to that of the reduction of bulk CuO, could be
ascribed to the reduction of separate CuO particles in these sam-
ples. For calcined PGO-NaOH sample, the unsymmetric reduction
2
3
4
3
Please cite this article in press as: Z. Huang, et al., Effects of the precipitation agents and rare earth additives on the structure and
catalytic performance in glycerol hydrogenolysis of Cu/SiO2 catalysts prepared by precipitation-gel method, Catal. Today (2014),
http://dx.doi.org/10.1016/j.cattod.2014.02.037

G Model
CATTOD-8930; No. of Pages10
ARTICLE IN PRESS
Z. Huang et al. / Catalysis Today xxx (2014) xxx–xxx
6
Table 2
Textural properties of CuO/SiO2 samples prepared by different precipitation agents.
Content (wt%)a
Crystallite size (nm)b
BET (m /g)c
2
Dpore (nm)c
Cu dispersion (%)d
SCu e (m /g Cu)
2
dCu f (nm)
Sample
Cu
Na
CuO
Cu0 used
PGO-NaOH
26.7
26.1
24.4
25.0
0.07
0.07
B.D.
B.D.
5.4
B.D.
B.D.
29.3
10.2
9.7
26.4
40.2
186.1
345.1
382.6
112.5
13.0
6.7
8.0
19.6
26.5
29.9
14.7
138.3
187.0
210.9
103.7
5.1
3.8
3.3
6.8
PGO-Na2CO3
PGO-NH4HCO3
PGO-NH4OH
9.4
a
Obtained from atomic absorption spectrometry (AAS) analysis. B.D. = below detection.
Calculated from the Scherrer equation.
BET method.
Cu dispersion obtained from dissociative N2O adsorption.
Cu surface area measured by dissociative N2O adsorption.
Mean Cu particle size calculated from dissociative N2O adsorption.
b
c
d
e
f
Table 3
XPS analysis of CuO/SiO2 samples prepared by different precipitation agents.
Sample
Cu2p3/2 (eV)
FWHM of Cu2p3/2 (eV)
Cu/Si at
Assignment
Bulk
Surface
PGO-NaOH
935.6
935.3
936.2
936.3
4.1
4.5
3.2
2.7
0.349
0.334
0.304
0.314
0.405
0.133
1.213
1.096
CuO, Cu2Si2O5(OH)2
CuO, Cu2Si2O5(OH)2
Cu2Si2O5(OH)2
PGO-NH4OH
PGO-Na2CO3
PGO-NH4HCO3
Cu2Si2O5(OH)2
peak centered around 534 K is most likely contributed by the one-
step reduction of low interacted copper oxide (CuO–Cu ) and the
the lowest conversion of 9.7%. The serious aggregation of Cu would
be account for the inferior activities of the PG-NH HCO and
0
4
3
0
partial reduction of highly dispersed and surface interacted copper
PG-NH OH catalysts, as their Cu crystallite sizes after reaction sig-
4
2
+
+
species (Cu –Cu ).
nificantly sintered to 26.4 and 40.2 nm (Table 2), respectively. In
Fig. 5 shows the TEM images of the calcined CuO/SiO samples
addition, the serious leaching of active Cu species for PG-NH HCO3
2
4
prepared with different precipitation agents. Both CuO nanowires
and dispersed CuO particles were observed in PGO-NaOH (Fig. 5a),
which is in line with our previous findings [46]. In calcined PGO-
and PG-NH OH catalysts (>10 ␮g/g, Table 4), probably due to the
presence of residual NH4 in these catalysts, might be another rea-
son for the low activities of these two catalysts [33,37]. On the
4
+
NH OH sample (Fig. 5b), randomly oriented filandrous species,
contrary, the residual Na in the PG-NaOH and PG-Na CO3 may
4
2
which can be assigned to copper phyllosilicate according to the
literature [43] and the above characterizations, along with a few
large sheet like particles assignable to CuO were observed. The
inhibit the sintering and leaching of Cu and thus contribute to the
high reactivity of the catalysts [33,52]. Note that although the used
PG-Na CO3 presented essentially the same Cu crystallite size as
2
observation of large CuO particles in calcined PGO-NH OH sample
the used PG-NaOH (9.7 vs. 10.2 nm), the former catalyst exhib-
ited a lower activity than the latter. Previous studies reveal that
glycerol hydrogenolysis reaction is likely a structure-sensitive reac-
tion [28,33]. The rather small Cu particle size in the prereduced
4
is in line with XRD characterization. For calcined PGO-Na CO and
2
3
PGO-NH HCO mainly randomly oriented filandrous copper phyl-
4
3
losilicate were seen (Fig. 5c,d). The highly diffusive ring pattern in
the select area electron diffraction (SAED) of these two samples
reveals an amorphous structure.
Table 4 shows the catalytic activities and selectivities of the
Cu/SiO2 catalysts prepared by PG method using different pre-
cipitants. As can be seen, PG-NaOH presented the highest initial
activity. After 12 h reaction at 453 K and 9.0 MPa reaction pres-
sure, a high conversion of 45.7% was obtained. Unexpectedly, the
PG-Na CO3 catalyst (< 4 nm, Table 2) might not facilitate for the
2
conversion of glycerol, thus resulted in an inferior activity than PG-
NaOH catalyst, whose initial Cu particle size is a bit larger (5.1 nm).
The product selectivities of the Cu/SiO2 catalysts were also
affected by the precipitation agent. The selectivities to 1,2-PDO
for PG-NH HCO3 and PG-NH OH were as high as 98.4 and 98.1%,
4
4
respectively, which were around 3% higher than those for PG-NaOH
and PG-Na CO (both 95.3%). Inversely, the selectivities to EG were
PG-NH HCO catalyst with the highest Cu surface area (Table 2)
4
3
2
3
showed a much lower conversion of 33.8%. The PG-Na CO exhib-
2–2.5% higher for PG-NaOH and PG-Na CO than for PG-NH HCO
2
3
2 3 4 3
ited a moderate conversion of 36.8% and the PG-NH OH showed
and PG-NH OH. Such differences in product selectivities for the
4
4
Table 4
a
Effect of precipitants on the catalytic performances of Cu/SiO2 catalysts prepared by PG method.
Catalyst
Conversion (%)
Selectivity (%)
,2-PDO
Leaching of Cu2+ (␮g/g)
1
EG
Othersb
PG-NaOH
PG-NaOH
PG-Na2CO3
PG-Na2CO3
PG-NH4HCO3
PG-NH4HCO3
PG-NH4OH
45.7
38.4
36.8
25.8
33.8
9.7
95.3
96.0
95.3
96.2
98.4
99.0
98.1
3.0
2.6
3.1
2.3
0.7
0.3
0.6
1.7
1.4
1.6
1.5
0.9
0.7
1.3
2.6
2.2
3.9
c
c
2.5
11.2
10.9
14.3
c
5.3
a
Reaction conditions: 4 g reduced catalyst, 80 g 80 wt% glycerol aqueous solution, 453 K, total pressure 9.0 MPa, 12 h.
Others: mainly methanol, ethanol and propanols.
The catalyst reused for the second time.
b
c
Please cite this article in press as: Z. Huang, et al., Effects of the precipitation agents and rare earth additives on the structure and
catalytic performance in glycerol hydrogenolysis of Cu/SiO2 catalysts prepared by precipitation-gel method, Catal. Today (2014),
http://dx.doi.org/10.1016/j.cattod.2014.02.037

G Model
CATTOD-8930; No. of Pages10
ARTICLE IN PRESS
Z. Huang et al. / Catalysis Today xxx (2014) xxx–xxx
7
Table 5
Composition, BET surface areas and crystallite sizes of the CuO-REOx/SiO2 samples calcined at 723 and 1023 K.
SBET a (m /g)
2
Crystallite size b (nm)
Sample
SBET a (m /g)
2
Crystallite size b (nm)
Sample
Composition
RE/Cu/Si
Cu-0-723
Cu-Y-723
Cu-La-723
Cu-Ce-723
Cu-Pr-723
Cu-Sm-723
0/1.0/3.0
180
151
144
162
150
144
5.6
5.6
5.8
6.0
5.7
6.0
Cu-0-1023
Cu-Y-1023
Cu-La-1023
Cu-Ce-1023
Cu-Pr-1023
Cu-Sm-1023
26
95
87
38
48
50
24.9
7.7
7.9
20.7
15.5
13.7
0.083/1.0/3.0
0.095/1.0/3.0
0.088/1.0/3.0
0.089/1.0/3.0
0.095/1.0/3.0
a
BET method.
b
CuO crystallite size calculated from the Scherrer equation.
catalysts [28]. In comparison with PG-Na CO , the higher recycle
2
3
stability for PG-NaOH would be ascribed to its more even dispersion
of Cu species, as revealed by XPS analysis (Table 3), which increased
the reaction stability of the catalyst.
3.2. Effect of rare earth additives on the structure and catalytic
performance of Cu/SiO2 catalysts
From the above studying one knows that the reaction stability
of the single-component Cu/SiO catalysts, even for the most stable
2
PG-NaOH catalyst, is still unsatisfactory. To improve the stability of
the Cu/SiO2 catalyst, a variety of rare earth (RE) elements includ-
ing La, Ce, Y, Pr and Sm were incorporated into the Cu/SiO catalyst
2
prepared by PG method using NaOH as precipitant. Fig. 6 shows the
XRD patterns of CuO–REOx/SiO samples calcined at 723 K (A) and
2
1
023 K (B). In comparison with Cu-0-723, no big diffrences were
seen after the incorporation of Y, La, Pr and Sm, while additional
diffractions assignable to CeO were seen for Cu-Ce-723. After calci-
2
nation at a relatively high temperature of 1023 K, the diffractions of
CuO for all samples intensified, especially noticeable for Cu-0-1023
(Fig. 6B). Compared with Cu-0-1023, the lower and broader diffrac-
tions of CuO for the RE-incorporated samples refer a lower sintering
of CuO particles, especially for Cu-Y-1023 and Cu-La-1023. Except
for Cu-Ce-1023, no diffractions related to REOx were seen for the Y,
La, Pr and Sm incorporated samples, even after calcined at 1023 K,
probably due to the low contents and the much high dispersion of
these REOx in the samples.
Table 5 shows the textural properties of the CuO/SiO2 sam-
ples prepared by PG method with and without incorporation of RE
calcined at two different temperatures of 723 and 1023 K. No big
differences in crystallite sizes were observed between the samples
without and with the incorporation of RE after calcination at 723 K.
While a slight decrease in surface area of all the RE-incorporated
samples was seen as compared to the mother CuO/SiO2 sample,
probably due to the coverage of the sample surface with REOx parti-
cles and blocking of some pores by REOx particles. After calcination
at a much high temperature of 1023 K, the CuO crystallite size
Fig. 4. TPR profiles of the calcined CuO/SiO2 samples prepared by different pre-
cipitation agents: PGO-NH4OH, PGO-NH4HCO3, PGO-Na2CO3, PGO-NaOH and the
reference of bulk CuO.
Na-free PG-NH HCO and PG-NH OH catalysts and the Na-
4
3
4
containing PG-NaOH and PG-Na CO catalysts indicate that it was
2
3
the residual Na in Cu/SiO catalyst mainly resulted in the formation
2
of EG, which is in good agreement with previous detailed study on
the effect of Na on the catalytic performance of Cu/SiO2 catalyst
[
33].
To study the recycle ability as well as the deactivation behav-
for the non-RE incorporated Cu/SiO sample remarkably increased
2
ior of the catalysts, we also carried out the recycle experiments of
PG-NaOH, PG-Na CO and PG-NH HCO After reaction, the freshly
to 24.9 nm, while the sizes for all RE-doped samples were below
21 nm, especially noticeable for Y and La incorporated samples,
which are 7.7 and 7.9 nm, respectively (Table 5). These results indi-
cate that the incorporated REOx particles, which insert between
CuO particles and/or cover on CuO particles (partial or full), could
prevent the sintering of Cu particles. The BET surface areas of all the
2
3
4
3.
used catalysts were filtrated and recharged into the autoclave
together with the fresh reactant to perform the next run. As can
be seen from Table 4, the reactivity of all the three catalysts in
terms of conversion decreased to some extent after recycle, while
their selectivity to 1,2-PDO slightly increased. Serious loss of activ-
ity, decreased by ∼71%, was observed on the reused PG-NH HCO ,
RE-doped samples were larger than that of the none-RE incorpo-
2
rated CuO/SiO sample (decreased to just 26 m /g) with the surface
4
3
2
while only moderate decrease of activity, decreased by 16 and 30%
was seen for the PG-NaOH and PG-Na CO catalysts after recy-
areas of Y and La incorporated samples much larger, which are
around 3.5 times that of the mother sample, showing that the incor-
poration of RE could remarkably enhance the thermal resistance of
the samples, probably by inhibiting the loss of the support surface
area. The above findings suggest that the incorporation of RE to
2
3
cle, respectively. The profound sintering of Cu particles and serious
leaching of active Cu would be account for the significant deactiva-
tion of PG-NH HCO . Besides the sintering and leaching of Cu, the
4
3
presence of strongly adsorbed species (reactant and/or products)
on the catalysts surface may also resulted the deactivation of the
CuO/SiO sample, especially Y and La, could inhibit the sintering of
the sample and thus maintain high thermal stability of the samples.
2
Please cite this article in press as: Z. Huang, et al., Effects of the precipitation agents and rare earth additives on the structure and
catalytic performance in glycerol hydrogenolysis of Cu/SiO2 catalysts prepared by precipitation-gel method, Catal. Today (2014),
http://dx.doi.org/10.1016/j.cattod.2014.02.037

G Model
CATTOD-8930; No. of Pages10
ARTICLE IN PRESS
Z. Huang et al. / Catalysis Today xxx (2014) xxx–xxx
8
Fig. 5. TEM images of samples prepared by different precipitation agents: (a) PGO-NaOH, (b) PGO-NH4OH, (c) PGO-Na2CO3 and (d) PGO-NH4HCO3.
Table 6 shows the catalytic activity test of the Cu/SiO2 cata-
lysts with and without the incorporation of REOx calcined at 723
and 1023 K in glycerol hydrogenolysis in non-continuous autoclave.
As can be seen, for the catalysts calcined at 723 K, the undoped
incorporated catalysts. The conversion of Pr-incorporated catalyst
even increased from 44.3 to 52.1% after calcined at 1023 K. The
conversions of all the RE-incorporated catalysts calcined at 1023 K
were around 2 times higher than that of undoped Cu/SiO , show-
2
Cu/SiO showed a high conversion of 73.3% after reaction at 473 K
ing that the incorporation of RE to Cu/SiO2 catalyst could greatly
promote the reaction stability of the catalysts, even after treat-
ing under serious conditions. The promotional effects of RE may
be originated from the following aspects: first the incorporation
of RE prevented the sintering of Cu and thus maintained the high
dispersion of the active Cu, second the electronic transfer from
RE would decrease the electron density of active Cu and stabilize
the active sites in their appropriate valence state [53], third the
2
for 10 h, while all the RE-incorporated catalysts presented lower
conversions, lowered by 10–29%. The decrease of activity for the
RE-incorporated catalysts would be resulted by partially covering
of the active sites by REOx particles. However, after calcination at
1
023 K, the conversion of the undoped Cu/SiO2 catalyst sharply
decreased to 24.7% (decreased by 66%), while only slight decrease
of conversions (17–19%) were seen for the Y, La, Ce, and Sm
Table 6
a
Catalytic activity and selectivity of glycerol hydrogenolysis over Cu-REOx/SiO2 catalysts calcined at 723 and 1023 K.
Catalyst
Conversion (%)
Selectivity (%)
,2-PDO
Leaching of Cu2+ (␮g/g)
1
EG
Othersb
Cu-0-723
Cu-Y-723
73.3
62.0
63.2
62.7
44.3
57.4
24.7
51.2
51.6
50.6
52.1
47.2
92.2
93.9
92.6
93.4
93.6
92.4
94.5
94.6
93.9
93.5
93.5
93.9
7.1
4.7
5.7
5.5
4.8
5.5
4.6
4.6
5.1
5.6
5.5
5.0
0.7
1.4
1.7
1.1
1.6
2.1
0.9
0.8
1.0
0.9
1.0
1.1
6.9
0.4
0.9
0.8
0.3
0.4
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
Cu-La-723
Cu-Ce-723
Cu-Pr-723
Cu-Sm-723
Cu-0-1023
Cu-Y-1023
Cu-La-1023
Cu-Ce-1023
Cu-Pr-1023
Cu-Sm-1023
a
Reaction condition: 1.0 g reduced catalyst, 20 g 80% glycerol aqueous solution, 473 K, 8 MPa H2, 10 h. (N.D. = not determined).
Others: mainly methanol, ethanol and propanols.
b
Please cite this article in press as: Z. Huang, et al., Effects of the precipitation agents and rare earth additives on the structure and
catalytic performance in glycerol hydrogenolysis of Cu/SiO2 catalysts prepared by precipitation-gel method, Catal. Today (2014),
http://dx.doi.org/10.1016/j.cattod.2014.02.037

G Model
CATTOD-8930; No. of Pages10
ARTICLE IN PRESS
Z. Huang et al. / Catalysis Today xxx (2014) xxx–xxx
9
Fig. 7. Time on-stream behavior of Cu-0-723 and Cu-La-723 catalysts. Reaction con-
−
1
ditions: WHSV of 0.25 h , glycerol to hydrogen mole ratio 1:23, pressure 6.0 MPa,
53 K.
4
reaction. Although the Cu-0-723 catalyst exhibited a higher ini-
tial conversion of 87%, it rapidly deactivated after around 220 h
reaction. Both catalysts maintained high 1,2-PDO selectivities of
around 97–98% in the continuous flow reaction conditions. The
remarkable increase of long-term stability of the Cu-La-723 clearly
confirmed the promotion effect of RE on the reaction stability of
the Cu/SiO2 catalyst. The decrease of initial activity over Cu-La-
7
23 catalyst in continuous fixed-bed flow reactor is in agreement
with the results obtained in non-continuous autoclave reaction.
Although the conversion of the La-doped Cu/SiO2 catalyst needs
further improvement, which can be achieved by increasing reac-
tion temperature or decreasing the WHSV as reported previously
[
21,27], its long-term stability and high selectivity toward 1,2-PDO
are very attractive, especially from the practical aspects for indus-
trial applications.
4. Conclusions
The effects of the precipitation agents (NaOH, Na CO , NH OH
2
3
4
and NH HCO ) and rare earth additives (La, Ce, Y, Pr and Sm) on
4
3
the structure and catalytic performance in glycerol hydrogenoly-
sis of the Cu/SiO2 catalysts prepared by precipitation-gel method
have been studied. Characterization results showed that the surface
Fig. 6. XRD patterns of Cu–REOx/SiO2 samples calcined at 723 K (A) and 1023 K (B).
structure and composition of the Cu/SiO catalysts differ greatly by
synergistic effect between RE-involved sites could increase the
reaction activity [36,54]. In addition, the incorporation of RE could
retard the leaching of active Cu, as which sharply declined from
2
the precipitation agents applied. Due to a more even dispersion of
Cu particles, a higher resistant to sintering and leaching of active
Cu, the catalyst prepared by NaOH exhibited the highest activity
and stability in glycerol hydrogenolysis than those by other precipi-
tants, however, a slight decrease of selectivity to 1,2-PDO due to the
6
.9 ␮g/g for Cu/SiO catalyst to below 0.9 ␮g/g for the RE-doped cat-
2
alysts (Table 6), which would also benefit for the reaction stability
of the RE-doped catalysts. It should be noted that the selectivity to
+
presence of residual Na was seen. The incorporation of rare earth
1
,2-PDO maintained at around 92.2–94.6%, seems not to be affected
additives, especially Y and La, to Cu/SiO2 catalyst could obviously
inhibit the sintering and leaching of Cu, and thus maintain high
thermal stability and long-term reaction stability of the catalysts.
These findings shed light on the design of more efficient and stable
catalysts for the industrial application of glycerol hydrogenolysis
to 1,2-PDO.
much by the incorporation of RE as well as the pretreatment tem-
peratures.
To date, the high deactivation and inadequate lifetime of
Cu-based catalysts remain significant problems that hinder the
practical industrialization of glycerol hydrogenolysis to 1,2-PDO.
Since the incorporation of La could greatly improve the structure
stability of the Cu/SiO catalyst, and also exhibited a higher glycerol
2
Acknowledgements
reactivity than other Re-doped catalysts, the long-term catalytic
performances of the La-doped Cu/SiO2 catalyst and unmodified
Cu/SiO2 catalysts were compared in the liquid phase hydrogenol-
ysis of glycerol at 453 K and 6 MPa reaction pressure (Fig. 7). The
Cu-La-723 catalyst showed a lower initial conversion of 78%, but
retained a steady conversion of ∼70% after a 600 h time-on stream
The authors gratefully acknowledge the financial support from
the National Natural Science Foundation of China (Grant Nos.
2
1133011, 21203221) and Science and Technology Support Pro-
gram of Gansu Province, China (Grant No. 1304FKCA113).
Please cite this article in press as: Z. Huang, et al., Effects of the precipitation agents and rare earth additives on the structure and
catalytic performance in glycerol hydrogenolysis of Cu/SiO2 catalysts prepared by precipitation-gel method, Catal. Today (2014),
http://dx.doi.org/10.1016/j.cattod.2014.02.037

G Model
CATTOD-8930; No. of Pages10
ARTICLE IN PRESS
1
0
Z. Huang et al. / Catalysis Today xxx (2014) xxx–xxx
References
[28] E.S. Vasiliadou, T.M. Eggenhuisen, P. Munnik, P.E. de Jongh, K.P. de Jong, A.A.
Lemonidou, Appl. Catal. B 145 (2014) 108–119.
[
29] A. Bienholz, R. Blume, A. Knop-Gericke, F. Girgsdies, M. Behrens, P. Claus, J. Phys.
Chem. C 115 (2010) 999–1005.
30] S.L. Hao, W.C. Peng, N. Zhao, F.K. Xiao, W. Wei, Y.H. Sun, J. Chem. Technol.
Biotechnol. 85 (2010) 1499–1503.
[
1] A.J. Ragauskas, C.K. Williams, B.H. Davison, G. Britovsek, J. Cairney, C.A. Eckert,
W.J. Frederick Jr., J.P. Hallett, D.J. Leak, C.L. Liotta, J.R. Mielenz, R. Murphy, R.
Templer, T. Tschaplinski, Science 311 (2006) 484–489.
[
[
[
[
2] A. Corma, S. Iborra, A. Velty, Chem. Rev. 107 (2007) 2411–2502.
3] D.M. Alonso, J.Q. Bond, J.A. Dumesic, Green Chem. 12 (2010) 1493–1513.
4] J.C. Serrano-Ruiz, R. Luque, A. Sepúlveda-Escribano, Chem. Soc. Rev. 40 (2011)
[
[
31] N.D. Kim, S. Oh, J.B. Joo, K.S. Jung, J. Yi, Top. Catal. 53 (2010) 517–522.
32] C.V. Rode, A.A. Ghalwadkar, R.B. Mane, A.M. Hengne, S.T. Jadkar, N.S. Biradar,
Org. Process Res. Dev. 14 (2010) 1385–1392.
33] Z. Huang, F. Cui, H. Kang, J. Chen, C. Xia, Appl. Catal. A 366 (2009) 288–298.
34] E.S. Vasiliadou, A.A. Lemonidou, Appl. Catal. A 396 (2011) 177–185.
35] Z. Huang, F. Cui, J. Xue, J. Zuo, J. Chen, C. Xia, Catal. Today 183 (2012) 42–51.
36] J. Zuo, Z. Huang, F. Cui, J. Chen, C. Xia, Chin. J. Mol. Catal. 24 (2010) 195–201.
37] X.F. Dong, H.B. Zou, W.M. Lin, Int. J. Hydrogen Energy 31 (2006) 2337–2344.
38] C.J.G. Van Der Grift, A.F.H. Wielers, B.P.J. Joghi, J. Van Beijnum, M. De Boer, M.
Versluijs-Helder, J.W. Geus, J. Catal. 131 (1991) 178–189.
5
266–5281.
5] A.M. Ruppert, K. Weinberg, R. Palkovits, Angew. Chem. Int. Ed. 51 (2012)
564–2601.
[
[
[
[
[
[
[
2
[
[
6] J. ten Dam, U. Hanefeld, ChemSusChem 4 (2011) 1017–1034.
7] C.H. Zhou, H. Zhao, D.S. Tong, L.M. Wu, W.H. Yu, Catal. Rev. Sci. Eng. 55 (2013)
3
69–453.
8] T. Miyazawa, Y. Kusunoki, K. Kunimori, K. Tomishige, J. Catal. 240 (2006)
13–221.
9] E.P. Maris, R.J. Davis, J. Catal. 249 (2007) 328–337.
[
[
2
[
39] T. Toupance, M. Kermarec, J.-F. Lambert, C. Louis, J. Phys. Chem. B 106 (2002)
2277–2286.
[
[
10] I. Furikado, T. Miyazawa, S. Koso, A. Shimao, K. Kunimori, K. Tomishige, Green
Chem. 9 (2007) 582–588.
11] I. Gandarias, P.L. Arias, J. Requies, M.B. Güemez, J.L.G. Fierro, Appl. Catal. B 97
[
40] G. Díaz, R. Pérez-Hernández, A. Gómez-Cortés, M. Benaissa, R. Mariscal, J.L.G.
Fierro, J. Catal. 187 (1999) 1–14.
41] Z. Wang, Q. Liu, J. Yu, T. Wu, G. Wang, Appl. Catal. A 239 (2003) 87–94.
42] T.M. Yurieva, G.N. Kustova, T.P. Minyukova, E.K. Poels, A. Bliek, M.P. Demeshk-
ina, L.M. Plyasova, T.A. Krieger, V.I. Zaikovskii, Mater. Res. Innovat. 5 (2001)
[
[
(
2010) 248–256.
[
[
12] S. Wang, K. Yin, Y. Zhang, H. Liu, ACS Catal. 3 (2013) 2112–2121.
13] M.A. Dasari, P.-P. Kiatsimkul, W.R. Sutterlin, G.J. Suppes, Appl. Catal. A 281
2005) 225–231.
14] Z. Huang, F. Cui, H. Kang, J. Chen, X. Zhang, C. Xia, Chem. Mater. 20 (2008)
090–5099.
15] L. Guo, J. Zhou, J. Mao, X. Guo, S. Zhang, Appl. Catal. A 367 (2009) 93–98.
16] S. Wang, Y. Zhang, H. Liu, Chem. Asian J. 5 (2010) 1100–1111.
17] W. Yu, J. Zhao, H. Ma, H. Miao, Q. Song, J. Xu, Appl. Catal. A 383 (2010) 73–78.
18] Q. Liu, X. Guo, Y. Li, W. Shen, J. Phys. Chem. C 113 (2009) 3436–3441.
19] S. Xia, R. Nie, X. Lu, L. Wang, P. Chen, Z. Hou, J. Catal. 296 (2012) 1–11.
20] F. Vila, M. López Granados, M. Ojeda, J.L.G. Fierro, R. Mariscal, Catal. Today 187
3
–11.
43] L.F. Chen, P.J. Guo, M.H. Qiao, S.R. Yan, H.X. Li, W. Shen, H.L. Xu, K.N. Fan, J. Catal.
57 (2008) 172–180.
44] C.J.G. Van Der Grift, P.A. Elberse, A. Mulder, J.W. Geus, Appl. Catal. 59 (1990)
75–289.
45] K.V.R. Chary, K.K. Seela, G.V. Sagar, B. Sreedhar, J. Phys. Chem. B 108 (2004)
58–663.
46] Z. Huang, F. Cui, J. Xue, J. Zuo, J. Chen, C. Xia, J. Phys. Chem. C 114 (2010)
6104–16113.
(
[
[
[
[
[
[
[
[
2
5
[
[
[
[
[
[
2
6
1
47] X.C. Zheng, S.P. Wang, S.R. Wang, S.M. Zhang, W.P. Huang, S.H. Wu, Mater. Sci.
Eng. C 25 (2005) 516–520.
48] M.A. Kohler, H.E. Curry-Hyde, A.E. Hughes, B.A. Sexton, N.W. Cant, J. Catal. 108
(
2012) 122–128.
[
[
[
[
21] S. Zhu, X. Gao, Y. Zhu, Y. Zhu, H. Zheng, Y. Li, J. Catal. 303 (2013) 70–79.
22] A. Bienholz, F. Schwab, P. Claus, Green Chem. 12 (2010) 290–295.
23] J. Zhou, L. Guo, X. Guo, J. Mao, S. Zhang, Green Chem. 12 (2010) 1835–1843.
24] D. Durán-Martín, M. Ojeda, M.L. Granados, J.L.G. Fierro, R. Mariscal, Catal. Today
10 (2013) 98–105.
25] Z. Yuan, J. Wang, L. Wang, W. Xie, P. Chen, Z. Hou, X. Zheng, Bioresour. Technol.
01 (2010) 7088–7092.
26] Z. Xiao, J. Xiu, X. Wang, B. Zhang, C.T. Williams, D. Su, C. Liang, Catal. Sci. Technol.
(2013) 1108–1115.
27] L. Huang, Y.L. Zhu, H.Y. Zheng, Y.W. Li, Z.Y. Zeng, J. Chem. Technol. Biotechnol.
3 (2008) 1670–1675.
(
1987) 323–333.
49] A.J. Marchi, J.L.G. Fierro, J. Santamaría, A. Monzón, Appl. Catal. A 142 (1996)
75–386.
3
2
[
[
[
50] E.D. Guerreiro, O.F. Gorriz, G. Larsen, L.A. Arrúa, Appl. Catal. A 204 (2000) 33–48.
51] F.W. Chang, W.Y. Kuo, K.C. Lee, Appl. Catal. A 246 (2003) 253–264.
52] J. Llorca, N.s. Homs, J. Sales, J.-L.G. Fierro, P. Ramírez de la Piscina, J. Catal. 222
[
[
[
1
(
2004) 470–480.
3
[
[
53] R. Kam, C. Selomulya, R. Amal, J. Scott, J. Catal. 273 (2010) 73–81.
54] X. Zheng, X. Zhang, X. Wang, S. Wang, S. Wu, Appl. Catal. A 295 (2005) 142–149.
8
Please cite this article in press as: Z. Huang, et al., Effects of the precipitation agents and rare earth additives on the structure and
catalytic performance in glycerol hydrogenolysis of Cu/SiO2 catalysts prepared by precipitation-gel method, Catal. Today (2014),
http://dx.doi.org/10.1016/j.cattod.2014.02.037