Studies on continuous selective hydrogenolysis of glycerol over supported Cu-Co bimetallic catalysts

Article abstract of DOI:10.1039/c9nj04945b

Alumina supported copper-cobalt catalysts were made and screened for continuous hydrogenolysis of glycerol to 1,2-propanediol at atmospheric pressure. BET surface area, temperature-programmed reduction, X-ray diffraction, pulse N₂O chemisorption, transmission electron microscopy and X-ray photoelectron spectroscopy techniques were used to derive the characteristics of the catalysts. The presence of Co in Cu/alumina significantly increased the reducibility of CuO species and also the metallic Cu surface area. The catalyst with 10%Cu-7%Co on Al₂O₃ afforded complete glycerol conversion with 77% selectivity to 1,2-propanediol. The catalysts activity was found to be mainly due to the existence of Cu in a highly dispersed state with a high metal surface area and synergistic interactions between the Cu-Co moieties. The influence of the reaction parameters was investigated and the best possible parameters were determined. The most active catalyst showed high stability during the time on stream analysis.

Full text of DOI:10.1039/c9nj04945b

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Studies on continuous selective hydrogenolysis of glycerol over
supported Cu-Co bimetallic catalysts
Narsinga. Raju, Voggu. Rekha, Burri. Abhishek, Peddagolla. Mahesh Kumar, Chenna. Sumana and
Received 00th January 20xx,
Accepted 00th January 20xx
*
Nakka. Lingaiah
DOI: 10.1039/x0xx00000x
Copper-cobalt supported on alumina catalysts were made and screened for continuous hydrogenolysis of glycerol to 1,2-
2
propanediol at atmospheric pressure. BET surface area, temperature-programmed reduction, X-ray diffraction, pulse N O
chemisorption, transmission electron microscopy and X-ray photoelectron spectroscopy techniques were used to derive
catalysts characteristics. The presence of Co in Cu/alumina significantly increased the reducibility of CuO species and also
2 3
metallic Cu surface area. The catalyst with 10%Cu-7%Co on Al O afforded complete glycerol conversion with 77% selectivity
to 1,2-propanediol. The catalysts activity was mainly owing to the existence of Cu in highly dispersed state with high metal
surface area and synergistic interaction between Cu-Co moieties. The reaction parameters influence was screened and best
possible parameters were provided. The most active catalyst showed high stability during time on stream analysis.
to intermediate hydroxyacetone and its hydrogenation over
transition metals. Further, Lewis and Brønsted acid catalysed
hydrogenolysis proceed via different intermediate formation
Introduction
Biodiesel, a potential environmentally friendly diesel fuel to
substitute petro-diesel can be obtained from transesterification
of animal fats or vegetable oils. The global biodiesel production
expected to grow rapidly to 36.9 MMT by 2020 [1-2]. Glycerol,
smallest polyol, available as a main side product in biodiesel
synthesis, which is approximately 10% of total biodiesel
production. Technical challenges and economic factors limited
the consumption of glycerol [3-4]. Glycerol is a well
functionalized chemical and can be renewed into high value
products by diverse catalytic process such as steam reforming,
hydrogenolysis, dehydration, oxidation, carbonylation,
esterification, acetalization and chlorination, etc [5-7]. Among
these catalytic interventions, selective glycerol hydrogenolysis
yielding the same 1,2-PD [12]. The existing literature suggested
that catalysts with noble metals are by and large efficient than
other transition metal catalysts for this reaction. Most of these
catalysts are studied at high pressure in batch mode. The
disadvantages of liquid phase glycerol to 1,2-PD is that the
adsorption of intermediates and by-products on the surface of
the catalyst resulting low catalytic activity and selectivity [13].
Continuous glycerol hydrogenolysis is the best alternative to
overcome the disadvantages but it is less investigated at
atmospheric pressure. The continuous hydrogenolysis was
reported by few researchers. Zheng et al. reported MOF based
Cu/ZnO catalyst system for continuous glycerol hydrogenolysis
at 20 bar pressure [14]. The Ce promoting effect on Cu-Co-Al
catalyst was reported for continuous hydrogenolysis with 1,2-
PD yield up to 95% at 35 bar pressure [15]. Amadeo group
studied vapor phase GH to 1,2-PD at ambient pressure over Cu
deposited on mesoporous alumina [16]. In these studies, no
indication about the catalyst stability. We also studied
(
GH) to 1,2-propanediol (1,2-PD) represents as a green and low-
cost approach for its utilization. In general, 1, 2-PD is
manufactured mainly by propylene oxide hydration derived
from petroleum. It is a foremost commodity chemical
extensively utilized in antifreeze functional fluids,
pharmaceuticals, paints, food products, polyester resins, etc.
GH is carried over supported metals, namely Pt, Ru, Pd, Cu, Ag,
Ir, Ni and Co are used as effective catalysts for 1,2-PD
preparation [8-10].
The popular reaction in glycerol to 1,2-PD conversion is the
C-O hydrogenolysis where glycerol dehydration followed by
hydrogenation takes place [11]. This reaction needs multi-
functional catalytic system especially acid sites for dehydration
2 3
continuous glycerol hydrogenolysis over Ni-Ag/γ-Al O
catalysts. However, the stability of the catalyst was limited [17].
The main drawback in continuous hydrogenolysis at
atmospheric pressure is catalysts deactivation. The bimetallic
catalysts demonstrated better stability compared to
monometallic catalysts for glycerol hydrogenolysis. The
supported Cu based bi-metallics, such as Cu-Zn, Cu-Ni, Cu-Ag
and Cu-Pd were explored for GH in batch mode at high pressure
[
18-22]. These catalysts showed varied activities at different
reaction conditions. Cu-ZnO/Al catalyst showed high
conversion under pressure conditions with low stability. Ag-Cu/
*
Department of Catalysis & Fine Chemicals, CSIR-Indian Institute of Chemical
Technology, Hyderabad-500 007, Telangana, India.
2 3
O
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gradient reaction temperature with complete glycerol Co contents linked to the growth of surfDacOeI: b10u.1lk03c9o/Cb9aNltJ0o4x9id45eBs
conversion and high selectivity more than 98% with stability up species. The 10Cu-7Co/Al catalyst exhibited more Cu
2 3
O
has been reported to work under ambient pressure with a content beyond 7 wt. %. The lowering of Cu dispeVrieswioAnrticaletOhnilginhe
2 3
O
to 1-5 h. The main drawback in continuous hydrogenolysis at dispersion and metal surface area. This may be owed to the
atmospheric pressure is catalysts deactivation. The catalysts close interactions among Cu and Co species which aid to reduce
activity depends on how efficiently the dehydration flowed by the thermal transmigration and sintering of Cu particles [28].
hydrogenation reaction takes place during hydrogenolysis of
glycerol. The metal surface area, acidity are the important patterns showed mainly the characteristic peaks of CuO, Co
characteristics of the catalysts for this reaction [23]. It is thought and CuCo phases. Additionally, reflections corresponding to
bimetallic catalysts based on Cu may be stable and active for γ-Al were observed at 2θ of 45.9° and 67.0° [29]. The intense
glycerol hydrogenolysis if the catalyst contains high metal peaks corresponding to CuO were observed at 32.5°, 35.5° and
XRD patterns of calcined catalysts are displayed in Fig.1. The
3 4
O ,
0
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O
2 3
O
surface area and acidity.
38.8° [30]. The diffraction peaks at 31.2°, 36.8°, 44.8°, 59.2° and
catalysts 64.9° indicates the presence of Co or CuCo spices in the
In this work, Cu-Co bimetallic supported on γ-Al
2
O
3
3
O
4
2 4
O
were systematically evaluated for continuous GH at catalyst [31]. It is difficult to distinguish the phases between
atmospheric pressure to 1,2-PD. The catalysts were Co and CuCo because of similar cubic framework and
characterized to assess metal surface area, dispersion and other identical unit cell parameters [32]. The intensities of the peaks
structural characteristics. The hydrogenolysis activity majorly related to CuCo or Co were increased with an increase in
discussed up on the catalysts physico-chemical characteristics Co loading beyond 7 wt. %.
derived from various characterization techniques.
3
O
4
2 4
O
2
O
4
3 4
O
Results and discussion
Catalysts Physico-chemical properties
Table 1 presents the physical characteristics of the catalysts.
In comparison to mono Cu/Al O , bimetallic Cu-Co/Al O
2 3 2 3
catalysts exhibited high surface area. The Co addition to Cu led
to enhancement in surface area. This is distinct when Co
content increased from 3 to 7 wt. %. Further, raise in Co content
to 13 wt. %, a trivial drop was detected in surface area. This
could be owed to the formation of bulk cobalt oxide species and
these large particles could block the micro pores of Al O . A
2 3
similar trend was also noticed in Ce-Cu/MgO and Ni-Cu/Al
bimetallic catalysts [26, 27].
2 3
O
Table 1: Physico-chemical properties of Cu-Co/Al
2 3
O catalysts.
Avg.
S.
No
.
BET
Cu S.
A.
(m /g)
Pore
Dia.
(nm)
8.2
Disp.
(%)
H
2
Catalyst
S. A.
Uptake
(µmol)
2
2
(m /g)
1
2
Al
2
O
3
167
115
-
-
Fig. 1. X-ray diffraction patterns of calcined catalysts (a) 10Cu/Al
2 3 2 3,
O ,(b) 10Cu-3Co/Al O
10Cu/
Al
10Cu-3Co/
Al
10Cu-5Co/
Al
10Cu-7Co/
Al
10Cu-10Co/
Al
10Cu-13Co/
Al
8.0
7.6
6.5
5.1
4.7
4.0
34.5
233.7
286
512
(c) 10Cu-5Co/Al 3, (d) 10Cu-7Co/Al , (e)10Cu-10Co/Al 3, (f) 10Cu-13Co/Al O3, (g)
2
O
2
O
3
2
O
2
2
O
3
1
2 3.
0Co/Al O
3
4
5
6
7
125
132
142
130
123
27.7
25.9
49.9
37.1
21.1
175.9
187.7
337.9
251.5
143.1
2
O
3
The reduced catalysts diffraction patterns are shown in Fig.
. The main diffraction peaks of Al remain unaltered. All the
peaks correspond to CuO have been compromised after
reduction. The intense peaks were noticed at 43.9°, 50.66° and
1079
1434
1065
1032
2
2 3
O
2
O
3
2
O
3
7
4.1° and these were evidently related to metallic copper
moieties [33]. The reduced XRD patterns of bimetallic catalysts
majorly exhibited metallic copper species and no diffraction
peaks observed for metallic cobalt species. As it is observed in
2
O
3
2
O
3
Fig.2, that peaks corresponding to Co
The dispersion of Cu metal and metal surface area measured Fig. 1 are not dominantly scene. This suggests that the Co
from N
O dissociative approach improved with increase in Co partly reduced or the surface is mostly covered with CuO
O
3 4
that are observed in
3 4
O
is
2
loading up to 7 wt. % in the catalyst. A small decrease in Cu species. Interestingly, a new peak evolved right next to the main
dispersion and metal surface area was noticed with raise in Co Cu (43.9 ) peak, which can be related to reduced cobalt oxide.
o
2
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The catalysts reduction tendency was studied by pattern with three reduction peak maxima, attriVbieuwteArdticlteoOntlhinee
temperature-programmed reduction and the profiles are made reduction of Cu and Co species. When DcOomI: 1p0a.1r0e3d9/Cth9eNJT0P49R45oBf
known in the insert of Fig. 3. The TPR results of mono metallic monometallic 10Co, no broad reduction peak at high
Cu, Co along with bimetallic 10Cu-7Co on Al
figure 3 for sake of clarity.
2
O
3
are shown in the temperature was noticed in case of 10Cu-10Co catalyst, which
may be because of the Co-Cu interactions as observed from XRD
results.
Table 2: Catalytic activity of glycerol hydrogenolysis over Cu-Co/Al
2
O
3
catalysts.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
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7
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1
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0
1
2
3
4
5
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7
8
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0
Selectivity %
Glycerol
Conv. (%)
Catalysts
1,2-
PDO
Other
s
EG
Acetol
10Cu/Al
0Cu-3Co/Al
10Cu-5Co/Al
0Cu-7Co/Al
2
O
3
92.4
86.7
88.3
98.5
95.4
86.4
84.2
52.4
53.5
62.5
77.2
68.4
58.3
30.8
1.8
1.9
2.1
3.2
3.6
6.7
26.2
41.5
41.1
33.2
18.1
23.9
28.2
20.7
4.3
3.5
2.2
1.5
4.1
6.8
22.3
1
2
2
2
O
3
3
3
O
O
1
1
1
0Cu-10Co/Al
0Cu-13Co/Al
2
O
O
3
3
2
1
2 3
0Co/Al O
Reaction Conditions: Glycerol conc: 20 wt.%, Reaction Temp.: 200 °C, Cat. Wt: 1g,
Fig.2. X-ray diffraction patterns of reduced catalysts (a) 10Cu/Al
2 3 2 3,
O , (b) 10Cu-3Co/Al O
-1
LHSV: 2.5 h
(
c) 10Cu-5Co/Al 3, (d) 10Cu-7Co/Al , (e) 10Cu-10Co/Al 3, (f) 10Cu-13Co/Al O
2
O
2
O
3
2
O
2 3.
An interesting observation has been made from the TPR
profiles that the H consumption is increasing with the addition
of Co to Cu up to a Co content of 7% as shown in Table 1. The
consumption for the 10Cu-7Co catalyst is 1434 µmol. Pure
Cu/Al catalyst showed the lowest amount of H consumption
which indicates the presence of low amount of reducible CuO
particles on the surface of the catalyst. The Co/Al catalyst
also showed high H consumption of 1260 µmol. The variation
in Co amount there is change in the Cu surface area and CuO
reducibility. The main factors responsible for H consumption
The monometallic CuO/Al
in between 210 to 230 °C. The peak at low temperature was
2 3
O showed a two-stage reduction
2
+
2
+1
linked to the reduction of Cu to Cu and further reduction of
H
2
+1
0
Cu to Cu is noticed at high temperature. The monometallic Co
O
2 3
2
o
catalyst showed a reduction peak at 355 C which is the easy
+
3
+2
reduction step of Co to Co and a broad peak ranging from
2 3
O
o
+2
0
4
80 to 650 C due to the reduction of Co to Co . The catalyst
2
with 10%Cu-3%Co showed distinct reduction peaks where, it
showed a reduction pattern at low temperature, related to the
reduction of CuO to Cu and the high temperature peak related
to the reduction of Co
than the monometallic CuO/Al
high Co content showed indistinguishable two low
temperatures reduction peaks at < 350 °C. These reduction
peaks might be associated with the reduction of Cu-Co oxides.
The existence of Cu effectively decreases cobalt oxide reduction
temperature. This might be related to the hydrogen activation
on Cu metal sites which helps in easy reduction of Cu-Co mixed
oxides. Similar observations were reported by Wang et.al [34].
They discussed about addition of small amount of Cu to
2
0
are the availability and reducibility of CuO. As it is seen in all the
catalysts the amount of CuO is the same with varying Co
amount. The variation in TPR profiles can be attributed to the
influence of Cu on cobalt oxide. The catalyst with optimal
3
O
4
to CoO as this peak intensity is higher
catalyst. The catalysts with
2 3
O
amount of Co (10Cu-7Co) showed the highest amount of H
2
consumption along with high Cu surface area that attributed to
the synergetic effect between Co and Cu.
The surface chemical states of Cu-Co bimetallic samples
were systematically probed by XPS technique. The binding
energy (B.E) values of calcined, reduced and spent 10%Cu-
7
%Co/γ-Al
Co catalysts B.E values of Cu2p3/2 and Cu2p1/2 were noticed at
33.8 and 953.8eV, respectively. The B.E of Cu2p1/2 was
2 3
O samples are displayed in Fig. 4. The calcined Cu-
Co/Al
2 3
O ,
the reduction peak temperature lowered
dramatically. As it is observed, in case of the Cu-Co catalysts
with 5Co and 7Co content showed two peak maxima which can
be attributed to the reduction of both CuO and Co O . In case
3 4
9
noticeably high (more than 20eV) as a result of a spin-orbit
coupling. Indeed, there were no satellite peaks at 934 and 954
eV in calcined Cu-Co bimetallic catalysts [35, 36]. This suggests
of 7Co catalyst the peak is broader compared to 5Co catalyst
indicating the presence of more reducible oxides on the surface.
The peak at lower temperature considered due to reduction of
2
+
+1
Cu to Cu reduction peak is not observed, which may be due
to the formation of more CuCo species and less availability
of CuO. The peak is mostly related to reduction of Co
2 4
O
3 4
O
species. The catalysts with 10Co and 13Co showed different
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metallic copper particles, which was in fulfilment with the
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DOI: 10.1039/C9NJ04945B
2
results of dissociative N O adsorption results.
Transmission electron microscopy (TEM) images of 10Cu-
Co/Al catalysts are shown in Fig.5. The particles of Cu-Co
catalysts were distributed uniformly with different phases on
the support Al . A few overlapped springs specie showed in
circles were observed in the catalyst. The d spacing of 0.47 nm
illustrated the formation of CuCo , and Co phase in the
7
2 3
O
2 3
O
O
2 4
3 4
O
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calcined sample. Besides, d (111) spacing 0.23 nm and 0.28 nm
mostly ascribed to higher number of finely dispersed CuO
species, which is in better correlation with reported ones [34].
Fig.3. TPR patterns of calcined catalysts (a) CuO/Al
2
O
3, (b) 10Cu-Co/Al
2
O3, (c) 10Cu-
5
Co/Al
2
O
3, (d) 10Cu-7Co/Al
2
O
3
, (e) 10Cu-10Co/Al
2
O
3, (f) 10Cu-13Co/Al
2
O
3
. (g) 10Co/Al O
2 3.
that Cu is in the form of CuO. B.E values of Co2p3/2 and Co2p1/2
were observed at 781.8 and 797 eV respectively. The BE
separation for the catalyst between the spin-orbit doublets of
Co2p levels was consistent at 15eV, that distinguish the
presence of Co O spinal. The reduced Cu-Co samples exhibited
3 4
B.E values at 932.5 and 952.5 eV respectively for Cu2p3/2 and
Cu2p1/2. These values are ascribed to the presence of Cu
metallic species. It was obvious that facile reduction of surface
CuO particles into Cu particles takes place during reduction. In
case of Co species, no change in the binding energy values was
0
2 3
Fig. 5. TEM image of 10Cu-7Co/Al O catalysts
0
Glycerol hydrogenolysis activity
2 3
The hydrogenolysis of glycerol activity of Cu/Al O and Cu-
3 4
observed. This indicates that Co O is not reduced during
Co/ Al O
2 3
catalysts are shown in Table 2. Based on initial
was selected as
optimal Cu content for glycerol hydrogenolysis. This catalyst
showed about 99% glycerol conversion with 56% selectivity
towards 1,2-PD at steady sate condition (after 3h of reaction
time).
reduction step. The presence of cobalt oxide moieties in
reduced Cu-Co catalyst, clearly indicates that cobalt oxide
particles may possibly had efficient interaction with tetrahedral
voids of γ-Al
reduction of cobalt oxide.
screening of the catalysts 10% Cu on Al
2 3
O
2 3
O support, thus obviously retard the easy
2 3
Fig. 4. XPS patterns of 10Cu-7Co/Al O catalysts.
The binding energies of CoO species slightly moved to higher
values for Co2p3/2 at 782.5 eV and Co2p1/2 at 798.4 eV with
absence of satellite peaks at 786 and 803 eV. This considerably
shows that the Co species were reduced partially to Co in Cu-
Co bimetallic catalysts [37, 38]. Even after, the prolonged time-
on-stream activity the spent Cu-Co catalysts displays a similar
peak as that of virgin catalyst. The results suggest that more
number of Cu species are available over the surface of the better catalytic activity in terms of high glycerol conversion and
catalyst rather than Co particles. XPS result also confirms that selectivity to 1,2-PD compared to Cu/Al O catalyst. In case of
addition of Co to Cu appreciably enhanced the dispersion of the monometallic catalysts both Cu and Co both showed
3
+
2+
Fig. 6. Influence of reaction temperature on glycerol hydrogenolysis.
Cu-Co bimetallic supported on Al O catalysts exhibited
2 3
2
3
different selectivities. Cu/Al catalyst is more selective
2 3
O
4
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towards acetol and 1,2-PD whereas Co/Al
selectivity to EG and other by-products. The 10Cu-3Co/Al
catalyst displayed about 86% glycerol conversion with limited
selectivity to 1,2-PD. Further increase in Co, the 10Cu-5Co/Al
catalyst achieved higher catalytic activity with about 62%
2 3
selectivity towards 1,2-PD. The catalyst with 10Cu-7Co on Al O
showed exceptional glycerol hydrogenolysis activity among all
the Cu-Co catalysts. This catalyst showed about 100%
conversion of glycerol with 77% of 1,2-PD selectivity. Further
increase in Co content in the catalysts, there was no
improvement in activity and a decrease in selectivity towards
2 3
O showed high
View Article Online
DOI: 10.1039/C9NJ04945B
2 3
O
2 3
O
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,2-PD was observed. The activity results of these catalysts can
be justified based on their characteristics. The high activity of
0Cu-7Co/ Al is mainly related to the presence of high Cu
1
2 3
O
metal surface area and its dispersion. The existence of Cu is its
metallic form and having strong interaction with Co species as
evidence from TPR analysis might led to exceptional
hydrogenolysis activity for this catalyst. The presence of Co in
Fig. 7. The role of glycerol concentration on hydrogenolysis activity.
3 4
its lower oxidation state (CoO) rather than Co O in the catalysts
Effect of glycerol concentration
also favours the hydrogenolysis as Co is well known for its
hydrogenation activity. The main text of the article should
appear here with headings as appropriate.
Glycerol hydrogenolysis was evaluated in the concentration
range of 10 to 40wt% and the outcomes are displayed in Fig.7.
The conversion of glycerol increased with enhancement in
glycerol concentration up to 20wt% and then a gradual fall in
conversion was noticed. About 20wt% glycerol concentration
could afford full conversion with 77% 1,2-PD selectivity. Further
increase in the glycerol concentration more than 20%, the
conversion of glycerol and selectivity of 1,2-PD was
considerably decreased. At high glycerol concentration
decrease in conversion of glycerol was because of unavailability
of more number of active sites of catalyst for the largely present
glycerol as the amount of catalyst is constant. Based on
different reactant concentrations, 20% glycerol was the
optimum concentration to get highest activity.
Effect of reaction temperature
Glycerol hydrogenolysis was carried out at different
temperature ranging from 180 to 240 °C over most preferable
1
2 3
0Cu-7Co/Al O catalyst and the results are presented in Fig. 6.
Glycerol conversion was about 90% at 180 °C with 48% 1,2-PD
selectivity. At a moderate reaction temperature of 180 °C,
probably dehydration of glycerol to acetol takes place and its
further hydrogenation is limited. These results are in well
agreement with reported ones [39]. With rise in reaction
temperature to 200 °C, a complete glycerol conversion was
observed with 77% selectivity. Further rise in reaction
temperature beyond 200 °C, 1,2-PD selectivity was drastically
declined. In general, at high reaction temperature over
hydrogenated products (methanol, 1-propanol, 2-propanol, and
ethanol) formation was favorable and accordingly desired
product selectivity is decreased. The preferred reaction
temperature is 200 °C for selective formation of 1,2-PD in
hydrogenolysis of glycerol over the present catalytic system.
Fig.8. The effect of LHSV on hydrogenolysis of glycerol.
Role of liquid hourly space velocity (LHSV) on catalytic activity
The significant influence of LHSV on catalytic activity during
continuous hydrogenolysis of glycerol is shown in Fig. 8. These
results intimate that the conversion of was constant up to LHSV
This journal is © The Royal Society of Chemistry 20xx
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of 2.5 h and then decreased with further increase in LHSV value (NO
3
)
2
.3H
2
O and Co (NO
3
)
2
.6H
2
O were mixed in de-ionized
View Article Online
-
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DOI: 10.1039/C9NJ04945B
to 3.3 h . This was expected as the numbers of active sites water and added to γ-Al
2 3
O . With continuous stirring the excess
available were constant and at higher LHSV the selectivity water was evaporated slowly on hot plate. After removal of
towards 1,2-PD decreased and the selectivity towards acetol is water the semi-dried catalyst samples were further dried at 120
increased. This indicates that the acidic sites of the catalyst °C for overnight and calcined at 400 °C for 3 h to obtain finished
were sufficient for dehydration of glycerol and the active Cu catalyst. The Cu content was fixed at 10 wt. % and the Co weight
metal sites are not sufficient to hydrogenate acetol to 1,2-PD. ratio was varied from 3 wt. % to 13wt. %. The catalysts are
The elevated activity of the catalyst relatively at higher LHSV named as 10Cu3Co/Al
values reiterates the efficiency of the Cu-Co/Al
towards glycerol hydrogenolysis.
2
O
3
where the indicate the catalyst
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2 3
O catalysts contains 10 wt. % Cu and 3wt % Co.
Catalysts characterizations
Time on stream analysis
Powder X-ray diffraction (XRD) patterns of the samples were
recorded on Rigaku X-ray diffract meter using Ni-filtered CuKα
radiation (λ = 1.5406 Å) under continuous scan with a speed of
The main disadvantage in case of vapor phase
hydrogenolysis is the longevity of the catalyst. The Cu based
catalysts prone to deactivation during glycerol hydrogenolysis
because of the significant growth in Cu particle size and
sintering under reaction conditions [41]. Therefore, stability of
the catalyst is the main concern for continuous hydrogenolysis
of glycerol. In order to check the stability, the reaction was
-1
2
°min at 30 kV and 15mA.
BET surface areas were measured by N
2
adsorption isotherm at
196 °C using BELSORP II (BEL Japan. Inc.) adsorption unit.
−
Approximately 0.2 g of catalyst is used for measurement. The
o
catalysts were pre-treated by degassing at 300 C for 3 h to
carried for 24 h over 10Cu-7Co/Al
results are shown in Fig.9. The monometallic Cu/Al
O
2 3
catalyst at 200 °C and
catalyst
remove adsorbed gases and moisture.
2 3
O
Temperature-programmed reduction (TPR) was carried using
BELCAT II (BEL Japan, Inc.) equipment. Before the TPR run,
samples were pre-treated with Ar (60 ml/min) gas for 2 h at 300
C. After pretreatment, Ar gas was replaced by 5% H /Ar mixed
2
gas and the sample was subjected to temperature programmed
also studied for time on stream analysis to know its stability and
the results are shown in the same figure. The conversion and
selectivity were decreased continuously with time for
monometallic Cu catalyst. The decrease in activity of Cu/Al
catalyst might be due to sintering and agglomeration of Cu
species [42]. The Cu-Co/Al bimetallic catalyst exhibited
stable activity for the entire period of 24 h with constant
glycerol conversion and selectivity to 1,2-PD. This result
suggested that the Cu-Co bimetallic catalyst is stable with
consistent activity even at atmospheric pressure. It is a potential
catalyst for practical application for hydrogenolysis of glycerol.
°
2 3
O
−1
heating with ramping of 10°C min up to 800 °C. Thermal
2 3
O
conductivity detector (TCD) was used to monitor H
consumption.
2
The morphological features of the catalysts were captured by
transmission electron microscopy (TEM). The TEM images were
captured using a Philips Tecnai FEI F20, operating at 120 kV. The
sample was prepared by dispersing the catalyst in ethanol by
ultrasonic dispersion for 30 min. The suspension drops of were
layered on a copper grid prior to the measurements.
XPS analysis was carried out using a KRATOS AXIS 165 with a
DUAL anode (Mg and Al) apparatus using the Mg K
XPS experimental details are reported elsewhere [17].
The dissociative N O adsorption method was carried out on
α
anode. The
2
same BELCAT II instrument used for TPR analysis. The details of
the experimental procedure to determine copper metal surface
area, dispersion and particle size are reported in our earlier
publication [24].
Evaluation of glycerol hydrogenolysis reaction
In a typical reaction, about 1g of catalyst is loaded which is
sandwiched in a quartz reactor of 10 mm ID between two quartz
wool plugs. This reactor was placed in a tubular furnace
equipped with programmable temperature controller and
monitored by thermocouple placed middle of the catalyst bed.
2 3
Fig. 9. Time on stream analysis during glycerol hydrogenolysis over Cu and Cu-Co/γ-Al O
catalysts.
The reactions are done by changing temperature in the range of
80-240 C at ambient pressure. The catalyst was reduced prior
o
1
o
to the reaction at 400 C with hydrogen flow of 70 ml/min for 2
h. Then the catalyst bed cooled to the required temperature
Experimental
Catalysts preparation
-1
and the feed were introduced at a flow rate LHSV of 2.5 h into
the preheater before passing into the reactor by a
Alumina supported copper-cobalt bimetallic catalysts were microprocessor-based feed pump (Braun Corp. Germany). The
synthesized by impregnation method. Calculated amount of Cu outlet of the reactor is connected to the condenser to collect
6
| J. Name., 2012, 00, 1-3
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4 L. Zheng, X. Li, W. Du, D. Shi, W. Ning, X. Lu andVZie.wHAortiucl,eAOpnlpinle.
Catal. B: Environ., 2017, 203, 146-153.DOI: 10.1039/C9NJ04945B
5 Fufeng Cai and Guomin Xia, Catal. Sci. Technol., 2016, 6, 5656-
the products. The products are analyzed using gas
chromatography fitted with flame ionization detector by
separating the products using an Inno-wax capillary column.
The products and the details of the calculations are reported
elsewhere [25].
5
667.
16 M.L. Dieuzeidea, R. de Urtiagaa, M. Jobbagyb and N. Amadeo,
Catal.Today., 2017, 296, 19–25.
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7 V. Rekha. N. Raju. C. Sumana and N. Lingaiah, Catal. Lett.,
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8 M. Balaraju, V. Rekha, P. S. S. Prasad, R. B. N. Prasad and N.
Conclusions
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0
Lingaiah, Catal. Lett., 2008, 126, 119-124.
Co-Cu/Al
2
O
3
catalysts were prepared with high Cu 19 I. Gandarias, J. Requies, P. L. Arias, U. Armbruster and A.
Martin, J. Catal., 2012, 290, 79–89.
dispersion and metal surface area. These are highly active for
hydrogenolysis of glycerol at ambient pressure to produce 1,2-
PD selectively. The presence of Cu significantly improved the
reduction of cobalt oxide species. The facile reducibility and
high dispersion of Cu particles are accountable for high activity
2
0 I. Furikado, T. Miyazawa, S. Koso, A. Shimao, K. Kunimori and
K. Tomishige, Green Chem., 2007, 9, 582–588.
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3 A. Bienholz, H. Hofmann and P. Claus, Appl. Catal. A:Gen.,
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011, 391, 153–157.
exhibited complete glycerol conversion with 77% yield towards
1,2-PD. Different reaction parameters like reaction
temperature, influence of reactant flow rates, and glycerol
concentration were optimized. The catalyst is highly stable with
constant activity for long period of operation.
4 M. Balaraju, K. Jagadeeswaraiah, P. S. S. Prasad and N.
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9 S. L. Hao, W. C. Peng, N. Zhao, F. K. Xiao, W. Wei and Y. H. Sun,
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0 S. Zhu, X. Gao, Y. Zhu, Y. Zhu, H. Zheng and Y. Li, J. Catal., 2013,
“There are no conflicts to declare”.
Acknowledgements
One of the authors NR thanks Council of Scientific and Industrial
Research, New Delhi for the financial support in the form of
research fellowship.
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DOI: 10.1039/C9NJ04945B
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Studies on continuous selective hydrogenolysis of glycerol over supported Cu-Co bimetallic
catalysts
Narsinga Raju, Voggu Rekha, Burri Abhishek, Peddagolla Mahesh Kumar, Chenna Sumana and
0
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*
Nakka Lingaiah
OH
OH
OH +
H2
HO
OH
Cu
CuCo O
CoO
2
4
γ - Al O
2
3