The selective continuous flow synthesis of lower alcohols from polyols-a mechanistic interpretation of the results

Article abstract of DOI:10.1039/c3cy00649b

In an endeavour to understand the hydrogenolysis pathway of glycerol to lower alcohols over Ni on Al₂O₃ and SiO₂ catalysts, the role of the intermediates (1,2-propanediol (1,2-PDO), 1,3-propanediol (1,3-PDO), ethylene glycol (EG) and ethanol) was investigated. Under the reaction conditions employed in this study, it was clear that the hydrogenolysis of the C-C and C-O bonds of glycerol takes place to a lesser extent as compared to dehydrogenation and dehydration which are seen as the dominating initial steps. Ethanol was produced in high selectivities (~67%) with 1,2-propanediol as feed and 1-propanol (1-PO, ~80%) was the main product obtained when 1,3-propanediol was used as feed. Ethylene glycol gave methanol and methane as products, whereas ethanol gave methane and CO₂ as major products.

Full text of DOI:10.1039/c3cy00649b

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The selective continuous flow synthesis of lower
alcohols from polyols – a mechanistic
interpretation of the results†
Cite this: Catal. Sci. Technol., 2014,
4, 832
Esti van Ryneveld,a Abdul S. Mahomed,a Pieter S. van Heerden,b Mike J. Green,c
d
a
*
Cedric Holzapfel and Holger B. Friedrich
In an endeavour to understand the hydrogenolysis pathway of glycerol to lower alcohols over Ni on Al2O3
and SiO2 catalysts, the role of the intermediates (1,2-propanediol (1,2-PDO), 1,3-propanediol (1,3-PDO),
ethylene glycol (EG) and ethanol) was investigated. Under the reaction conditions employed in this study,
it was clear that the hydrogenolysis of the C–C and C–O bonds of glycerol takes place to a lesser extent
as compared to dehydrogenation and dehydration which are seen as the dominating initial steps. Ethanol
was produced in high selectivities (~67%) with 1,2-propanediol as feed and 1-propanol (1-PO, ~80%) was
the main product obtained when 1,3-propanediol was used as feed. Ethylene glycol gave methanol and
methane as products, whereas ethanol gave methane and CO2 as major products.
Received 29th August 2013,
Accepted 3rd January 2014
DOI: 10.1039/c3cy00649b
www.rsc.org/catalysis
Despite the wealth of information accumulated on glycerol
hydrogenolysis, little attention was given to mechanistic con-
Introduction
Interest in the catalytic conversion of renewable feedstocks to
chemicals has been increasing over the past decade.1 A num-
ber of biomass processes, such as the fermentation of glucose,
the hydrogenolysis of sorbitol and the manufacture of bio-
diesel produce glycerol and consequently glycerol, has gained
considerable importance as a bio-refinery feedstock. With glyc-
erol becoming a cheap, large-volume feedstock, the ability to
use it as a source of organic carbon and as a starting material
for chemical transformations is very appealing. The hydro-
genolysis of glycerol is usually performed in the presence of
hydrogen using various heterogeneous systems including Rh,2
Ru,3–5 Pt,6 Pd, PtRu,7 Cu systems,8,9 Re10 and RANEY® Ni.11,12
Typical products obtained from the hydrogenolysis reaction
are 1,2-propanediol (1,2-PDO), 1,3-propanediol (1,3-PDO),
acetol, ethylene glycol (EG), 1-propanol (1-PO) and 2-propanol
(2-PO). Importantly, 1,2-PDO and EG can also be produced
from cellulosic biomass.13–15 Subsequently, these catalytic
systems can catalyse degradation reactions to yield ethanol,
methanol and methane as secondary products.3
siderations. Tomishige and co-workers3 proposed that 1-PO
and 2-PO can mainly be formed via 1,3-PDO and 1,2-PDO,
respectively, in glycerol hydrogenolysis over a Ru/C catalyst.
Ethanol and methane are formed from the degradation reac-
tion of 1,2-PDO and 1,3-PDO; in addition, ethanol can also
be formed during the hydrogenolysis of EG. Methanol is
formed via the degradation reaction of EG. On the other
hand, Montassier et al.16 proposed the dehydrogenation of
glycerol to glyceraldehyde over a metal catalyst, which is
followed by dehydration to 2-hydroxyacrolein and subsequent
hydrogenation to 1,2-propylene glycol.
Previous studies by Lahr and Shanks17 and Auneau et al.18
supported the formation of glyceraldehyde as the first inter-
mediate during the hydrogenolysis of glycerol. Subsequently,
glyceraldehyde can react through four different pathways: (i)
retro-aldol reaction to form glycolaldehyde (EG precursor),
(ii) oxidation and subsequent decarboxylation to also form
glycolaldehyde, (iii) dehydration to the precursor to 1,2-PDO
(2-hydroxypropionaldehyde), or (iv) degradation to unwanted
side products. Finally, the respective glycol precursors are
hydrogenated by the metal function to the products.
a University of KwaZulu-Natal, School of Chemistry & Physics, Private Bag
X54001, Durban, 4000, South Africa. E-mail: friedric@ukzn.ac.za;
Fax: +27 31 260 3091; Tel: +27 31 260 3107
b Sasol Technology, R&D Division, 1 Klasie Havenga Street, Sasolburg, 1947, South Africa
c Newcastle University, School of Chemistry, Bedson Building, Newcastle upon Tyne,
NE1 7RU, UK
Chaminand et al.19 proposed that diols can form via sev-
eral routes. The presence of an acid favours the dehydration
route via protonation of the hydroxyl groups of glycerol and
then the loss of water to form a ketone compound as the
intermediate. This ketone can easily be reduced under the
reaction conditions to form the corresponding diol. The
direct conversion to diols is also possible via chelating
d University of Johannesburg, Department of Chemistry, Auckland Park,
2006, Johannesburg, South Africa
† Electronic supplementary information (ESI) available. See DOI: 10.1039/c3cy00649b
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glycerol in the presence of a metal (e.g. Cu, Pd, or Rh
supported on ZnO, C, or Al2O3) followed by hydrogenolysis.
Recently, we reported the highly selective synthesis of
lower alcohols, i.e. ethanol and 1-PO, via direct hydrogenolysis
of glycerol over supported Ni catalysts.20 These two catalyst
systems were chosen because they are cheap, non-toxic
and readily available. The formation of C1–C3 alcohols in
low levels has previously been reported by Tomishige and
co-workers3 and Gandarias et al.21 Despite the numerous
studies on glycerol hydrogenolysis reported to date,1–12
detailed studies giving insight into the reaction mechanism
of lower alcohol formation have been limited and inconclu-
sive. EG and 1,3-PDO were shown as possible intermediates
to propanol, ethanol and methanol.3,10 It was also sus-
pected that 1,2-PDO leads to short chain alcohol forma-
tion22 and the formation of 1-PO from 1,2-PDO has been
reported.23,24
The objective of the current work is to contribute towards
gaining a more detailed qualitative mechanistic understand-
ing of the formation of lower alcohols from glycerol over Ni
on Al2O3 and SiO2 catalysts. In particular, the work presented
will discuss the role of proposed intermediates (1,2-PDO,
1,3-PDO, and EG) and ethanol, as well as the influence of
the hydrogen partial pressure. As an important result of this
study, we also show the highly selective conversion of 1,2-PDO
and 1,3-PDO to ethanol and 1-propanol, respectively, thus
offering the possibility of producing biodiesel and lower alco-
hols from the same crop.
selectivity was observed over the Ni/Al2O3 catalyst whereas
the Ni/SiO2 gave slightly higher selectivities for CO2. Minor
quantities of acetol and propanol were also observed. The
C1–C3 oxygenated products were formed directly from 1,2-PDO,
while methane and CO2 are secondary products and must be
formed via intermediate species.
The reaction products suggest that the formation of etha-
nol and methane occurs via disproportionation of 1,2-PDO.
Disproportionation usually occurs in the absence of hydro-
gen; therefore to understand this pathway better, a set of
experiments was done by changing the H2 partial pressure to
see if ethanol is still formed. The GHSV was kept constant at
1060 h−1 by increasing the N2 partial pressure when decreas-
ing the hydrogen partial pressure.
As observed from Fig. 2, the conversion of 1,2-PDO over
the Ni/SiO2 catalyst did not change significantly as the H2
partial pressure was decreased. However, there was a notable
change in the ethanol selectivity when the hydrogen partial
pressure was reduced to less than 50%. At 0% H2 partial
pressure acetol formed almost exclusively as a result of the
dehydrogenation of 1,2-PDO and the selectivity to ethanol
was significantly reduced to 16%. The hydrogen reduction
run was repeated with the Ni/Al2O3 catalyst and similar
trends were observed (Fig. 3). However, the decrease in etha-
nol selectivity was less profound and the formation of higher
molecular weight condensation products more eminent. The
fact that acetol is the major reaction product shows that the
ability of both nickel catalysts to cleave C–C and C–O bonds
in the absence of hydrogen is significantly reduced. This is of
considerable importance, as it eliminates a disproportion-
ation mechanism in the absence of hydrogen to a large
degree.
Results and discussion
The hydrogenolysis of 1,2-propanediol (1,2-PDO)
Fig. 1 shows the comparative data at iso-conversions (23%)
between Ni/SiO2 and Ni/Al2O3 with 1,2-PDO as feed. From the
data it is clear that the reaction of 1,2-PDO in water at 230 °C
led significantly to ethanol and methane as products for both
systems. The higher selectivity towards ethanol of 62% was
achieved over the Ni/SiO2 catalyst. Slightly higher methane
In the absence of hydrogen it is believed that the reac-
tion starts with the dehydrogenation of 1,2-PDO and sub-
sequent isomerisation of 2-hydroxypropanal yields acetol
Fig. 1 Comparative data between the Ni/SiO2 catalyst and the Ni/Al2O3
catalyst with 1,2-PDO as feed at 23% conversion (230 °C, 60 bar). Others =
acetaldehyde, ethane, propane, methanol, 1,3-PDO, condensation products
and unknowns.
Fig. 2 Influence of the percentage reduction of hydrogen partial
pressure on the conversion of 1,2-PDO and selectivity to products using
Ni/SiO2 (230 °C, 60 bar). Others = acetaldehyde, ethane, propane,
methanol, 1,3-PDO, condensation products and unknowns.
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Table
1
Hydrogenolysis of ethylene glycol in the presence of
hydrogen using Ni/Al2O3 and Ni/SiO2 catalysts (230 °C, 60 bar)a
Product selectivities (C basis)
Ni/Al2O3
Ni/SiO2
Methane
CO2
24.0
2.6
21.5
7.9
Methanol
Ethanol
1,2-PDO
Others
58.4
5.6
3.9
60.2
2.0
8.0
5.5
0.4
Conversion
9.3
11.7
a
Others = ethane, condensation products and unknowns.
Ni/Al2O3 and Ni/SiO2 as catalysts, the product selectivity is
dominated by methanol and methane with very low selectiv-
ity to ethanol. As a result, the combination of dehydration to
acetaldehyde with subsequent hydrogenation to ethanol as
the predominant pathway was discounted. Methanol and
methane formation appears to result primarily from the
dehydrogenation and decarbonylation of EG to yield formal-
dehyde and CO as intermediary products, followed by subse-
quent hydrogenation and disproportionation. However, the
fact that a methanol to methane ratio of >2 was recorded
suggests that direct hydrogenolysis of the C–C bond to yield
methanol directly should also be considered a valid pathway.
Thus, at present, the detailed mechanism for the dispropor-
tionation of EG cannot be differentiated.
Fig.
3 Influence of the percentage reduction of hydrogen partial
pressure on the conversion of 1,2-PDO and selectivity to products using
Ni/Al2O3 (230 °C, 60 bar). Others = acetaldehyde, ethane, propane,
methanol, 1,3-PDO, condensation products and unknowns.
as the major product. The formation of ethanol as a minor
product over both nickel catalysts suggests that once
2-hydroxypropanal is formed, bimolecular surface reactions
(Tishchenko/Cannizzaro25 type conversions) lead to surface-
bound 1,2-PDO and 2-hydroxypropanoic acid, which decar-
boxylates to ethanol and CO2.
The introduction of gaseous hydrogen, even at 50% hydro-
gen partial pressure, gives high selectivity to ethanol. Indeed,
the selectivity to ethanol was essentially quantitative, in
terms of the carbon number, at 13% conversion. The meth-
ane selectivity decreased as the hydrogen partial pressure was
reduced, whereas the CO2 selectivity increased slightly, up to
50% H2 partial pressure reduction. Supported by the work of
Chen et al.26 on the decomposition of ethylene glycol, the
overall level of decomposition in the presence of hydrogen
suggests that the reaction starts with the dehydrogenation
and decarbonylation of 1,2-PDO to form acetaldehyde, CO
and H2. Subsequent hydrogenation of acetaldehyde yielded
ethanol as the major product. The adsorption of CO on Ni at
>200 °C is dissociative, resulting in disproportionation to
CO2 and a Ni–C species. The surface carbon species formed
from CO is readily hydrogenated to methane.27–29 Although
CO2 formation can also be explained via rapid water gas
shift,30 the high methane to CO2 ratio points to CO dissocia-
tion as the faster overall reaction pathway.
Interestingly, 1,2-PDO was observed during the hydrogenolysis
of EG over both catalyst systems. The formation of 1,2-PDO
from EG can be explained by an aldol reaction to form glycer-
aldehyde, followed by the loss of water and subsequent hydro-
genation to yield 1,2-PDO.
The effect of hydrogen partial pressure using the Ni/SiO2
catalyst was also studied. As the H2 partial pressure was
reduced from 100% to 0% the methanol and methane con-
centration decreased and an increase in acetol, 1,2-PDO and
glycerol dimer31 concentration was seen (Fig. 4).
The hydrogenolysis of 1,3-propanediol
During the hydrogenolysis of glycerol, 1-propanol was the
alcohol produced in highest selectivity (25–40%) at higher
temperatures (>275 °C) over these supported Ni catalysts.20
Consequently, the low selectivity of 1-propanol observed
when using 1,2-PDO as feed suggested that the formation of
propanol is likely occurring via 1,3-PDO. The results of the
hydrogenolysis of 1,3-PDO over the Ni/Al2O3 and Ni/SiO2 cata-
lysts at 230 °C are presented in Fig. 5. At similar conversions,
both catalysts gave very high selectivities to 1-propanol
(>80%) with the co-production of some ethanol. Other prod-
ucts obtained from these reactions are methane and carbon
dioxide, as well as heavier products, the result of cracking
and condensation reactions, respectively. 1-Propanol forms
via the dehydration reaction of 1,3-PDO with subsequent
hydrogenation. The small concentrations of EtOH observed
The hydrogenolysis of ethylene glycol (EG)
EG was also reported as one of the liquid products during
the hydrogenolysis of glycerol, albeit in significantly lower
yields than 1,2-PDO. In order to understand the catalytic
chemistry of this simple diol, the conversion of EG was next
studied over the Ni catalysts in the presence of hydrogen
(Table 1). The results in Table 1 show that, using both
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Fig. 6 Influence of the percentage reduction of hydrogen partial
pressure on the conversion of 1,3-PDO and selectivity to products
using Ni/SiO2 (230 °C, 60 bar). Others = methanol, acetol, 1,2-PDO,
glycerol, glycerol dimers, methane, ethane and propane.
Fig. 4 Influence of the percentage reduction of hydrogen partial
pressure on the conversion of EG and selectivity to products using
Ni/SiO2 (230 °C, 60 bar). Others = 2-propanol, 1-propanol, 1,3-PDO, glyc-
erol, ethane, propane, and acetaldehyde.
ethanol was selected as the model substrate and studied
under the reactions conditions favouring lower alcohol for-
mation from glycerol. Previous studies have demonstrated
that disproportionation of ethanol can occur via three reac-
tion pathways, dehydrogenation, decarbonylation, and total
decomposition, producing CO, H2, CH4, C and O.32
Table 2 shows the hydrogenolysis of ethanol using a
Ni/SiO2 catalyst at 230 °C and 60 bar hydrogen pressure. As
expected the major products were methane and CO2, with
small amounts of methanol formed. This result clearly
shows that high concentrations of ethanol will dispropor-
tionate rapidly under these conditions and provides evidence
for another pathway for the formation of methane and CO2.
Since these results gave the expected product range it was
deemed unnecessary to repeat this experiment using the
Ni/Al2O3 catalyst.
Although hydrogen partial pressure reduction runs were
not performed on ethanol for this study, it was assumed that
acetaldehyde would be formed. Rass-Hansen et al.33 proposed
that the steam reforming of ethanol proceeded through two
different routes, either by dehydrogenation to acetaldehyde
or by dehydration forming ethylene. These intermediate
products can then be steam reformed to a mixture of meth-
ane, carbon dioxide, carbon monoxide, hydrogen and water.
Fig. 5 Comparative data between Ni/Al2O3 and Ni/SiO2 with 1,3-PDO
as feed (230 °C, 60 bar). Others = ethane, propane, acrolein, methanol,
propenol, condensation products and unknowns.
are the result of direct decarbonylation of 1,3-PDO. As
discussed previously, CO undergoes disproportionation over
Ni to form methane and CO2.
The conversion of 1,3-PDO over the Ni/SiO2 catalyst did not
change significantly as the H2 partial pressure was decreased
from 100% to 50% (Fig. 6). The major product formed was
1-propanol with small amounts of ethanol also observed.
However, there was a notable change in the 1-propanol selec-
tivity when the hydrogen partial pressure was reduced to 0%
and acrolein started to form. At 0% hydrogen partial pressure
an increase in conversion was observed. The hydrogen reduc-
tion experiment was repeated with the Ni/Al2O3 catalyst and
similar trends were observed (ESI, Fig. S1†).
Table 2 Hydrogenolysis of ethanol in the presence of hydrogen using
Ni/SiO2 catalysts (230 °C, 60 bar)a
Products
Product selectivities (C basis)
Methane
CO2
Methanol
Others
59.4
32.1
6.9
1.6
Ethanol as feed
Conversion
28.7
a
In order to explore to what extent the C1–C3 alcohols can
undergo consecutive C–C and C–O bond cleavage reactions
Others
=
acetaldehyde, ethane, condensation products and
unknowns.
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Proposed mechanism
disproportionated to CO and ethane. The CO is converted to
CO2 via the water–gas shift (WGS) reaction or hydrogenated
to CH4. Wawrzetz et al.25 showed that the conversion of
1-propanol leads to the formation of propanal as the primary
product over Pt supported on alumina. Ethane and CO2, as
well as propanoic acid, were formed as secondary products.
They excluded direct hydrogenolysis as a pathway to form
ethane, but rather suggested that once the propanal is
formed, bimolecular surface reactions (Tishchenko/Cannizzaro)
lead to surface-bound propanol which decarboxylates to
ethane and CO2. Both pathways are conceivable under the
reaction conditions because the Tishchenko reaction is
catalysed by acidic sites, whereas the Cannizzaro reaction
needs more basic sites.
Acetol, formed by the dehydration of glycerol, was
observed in the liquid phase with rather high selectivities at
higher temperatures. Acetol is hydrogenated to give 1,2-PDO,
which then dehydrogenates to 2-hydroxypropanal (2-HPA).
Subsequently, 2-HPA is decarbonylated to ethanol and CO
(yields CO2 via WGS). Ethanol can be further dehydrogenated
to give acetaldehyde and under these conditions the acetalde-
hyde will disproportionate rapidly to give ultimately CO and
methane.
In combination with our previously reported results which
showed the hydrogenolysis of glycerol over these supported
nickel catalysts,20 the following qualitative mechanism to
explain the formation of the lower alcohols, such as
1-propanol, ethanol and methanol, is proposed (Scheme 1).
The three primary intermediate products that are formed
over the supported Ni catalysts from glycerol are glyceralde-
hyde, 3-hydroxypropionaldehyde (3-HPA) and acetol. Glyceral-
dehyde is formed via dehydrogenation, whereas 3-HPA and
acetol are formed via the dehydration of the hydroxyl group
at the secondary and primary carbon atoms, respectively.
Glycerol can be dehydrogenated to glyceraldehyde over a
metal catalyst. The formation of EG can then occur via direct
decarbonylation of glyceraldehyde in the presence of hydro-
gen yielding CO as a by-product. The rate of this reaction
appeared to be so fast that glyceraldehyde was not observed
in the liquid phase. Alternatively, glyceraldehyde can also
undergo retro-aldol condensation to yield glycolaldehyde and
formaldehyde, which are subsequently hydrogenated to yield
EG and methanol, respectively. This reaction is in equilib-
rium and can be reversed by the aldol condensation of glycol-
aldehyde and formaldehyde. The CH4 and CO2 observed from
secondary reactions result from direct CO hydrogenation and
the water–gas shift reaction, respectively.
From the mechanism proposed, we conclude that the
main route for the formation of 1-propanol is via the hydro-
genation of 3-HPA. The formation of ethanol takes place via
acetol, whereas methanol is formed via glycolaldehyde.
The formation of 1,3-PDO can occur via two routes.
Glycerol is dehydrated to form 3-HPA on acid sites, which is
then hydrogenated to 1,3-PDO over a metal. 1-Propanol is
then formed via dehydration reaction of 1,3-PDO with subse- Conclusions
quent hydrogenation. On the other hand, glyceraldehyde can
In an endeavour to obtain a better understanding of the
be directly dehydrated and then subsequently hydrogenated
to yield 1,3-PDO. Since 3-HPA is more reactive compared to
acetol,3,25 it was not observed as an intermediate in the liquid
phase. Potentially, 3-HPA can also undergo decarbonylation
to give CO and ethanol. Small amounts of ethane were also
detected during the hydrogenolysis of 1,3-PDO. 1-Propanol
can be dehydrogenated to propanal which is then
hydrogenolysis of diols and triols, the role of the intermedi-
ates in the hydrogenolysis reaction was investigated in the
presence and absence of hydrogen.
Under the reaction conditions employed in this study, it
was clear that in the case of glycerol the hydrogenolysis of
C–C and C–O bonds takes place to a lesser extent, particu-
larly in the earlier stages of the reaction. Dehydrogenation
and dehydration are seen as the dominating initial steps.
From our proposed mechanism, ethanol was the domi-
nant product formed from 1,2-PDO and it is proposed that
1,2-PDO is the intermediate in the formation of ethanol
from glycerol over the supported Ni catalysts. In the
absence of hydrogen, acetol was the main product formed
and this suggested
disproportionation.
a slow route via hydrogen-assisted
1-Propanol formed via the dehydration of glycerol to yield
3-HPA, and then subsequent hydrogenation gave 1,3-PDO.
1,3-PDO is then dehydrated to yield 1-propanol. Methanol is
formed via the dehydrogenation of glycerol to yield glyceral-
dehyde and via retro-aldol condensation glycolaldehyde and
formaldehyde, which is subsequently hydrogenated to yield
methanol, are obtained.
From the hydrogenolysis of EG, methanol and methane
were observed as major products, whereas the hydrogenolysis
of ethanol gave methane and CO2 as major products.
Scheme 1 Proposed mechanism for the formation of lower alcohols.
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5 J. Feng, H. Fu, J. Wang, R. Li, H. Chen and X. Li, Catal.
Commun., 2008, 9, 1458–1464.
6 Z. Yuan, P. Wu, J. Gao, X. Lu, Z. Hou and X. Zheng, Catal.
Lett., 2009, 130, 261–265.
7 E. P. Maris, W. C. Ketchie, M. Murayama and R. J. Davis,
J. Catal., 2007, 251, 281–294.
8 B. Zhao, C. Li and C. Xu, Catal. Sci. Technol., 2012, 2,
1985–1994.
Experimental section
Samples
The Ni/Al2O3 and Ni/SiO2 bulk systems were obtained as
pre-reduced commercial samples (Sued-Chemie). The Ni
content was between 45–55 wt% for Ni/Al2O3 and Ni/SiO2.
The glycerol, 1,2-PDO and 1,3-PDO, acetol and EG were pur-
chased from Sigma Aldrich and used without further purifi-
cation. The ethanol was obtained from Merck. The polyol
feeds (1,2-PDO, 1,3-PDO and EG) as well as the EtOH were
prepared as 60 wt% mixtures in water.
9 C. Liang, Z. Ma, L. Ding and J. Qiu, Catal. Lett., 2009, 130,
169–176.
10 Y. Amada, Y. Shinmi, S. Koso, T. Kubota, Y. Nakagawa and
K. Tomishige, Appl. Catal., B, 2011, 105, 117–127.
11 M. A. Dasari, P. P. Kiatsimkul, W. R. Sutterlin and
G. J. Suppes, Appl. Catal., A, 2005, 281, 225–231.
12 A. Perosa and P. Tundo, Ind. Eng. Chem. Res., 2005, 44,
8535–8537.
13 H. Kobayashi, T. Komanoya, S. K. Guha, K. Hara and
A. Fukuoka, Appl. Catal., A, 2011, 409–410, 13–20.
14 G. Baek, S. J. Yu and E. D. Park, Bioresour. Technol.,
2012, 114, 684–690.
15 M. Liu, H. Wang, J. Han and Y. Niu, Carbohydr. Polym.,
2012, 89, 607–612.
16 C. Montassier, J. C. Menezo, L. C. Hoang, C. Renaud and
J. Barbier, J. Mol. Catal., 1991, 70, 99–110.
17 D. G. Lahr and B. H. Shanks, J. Catal., 2005, 232, 386–394.
18 F. Auneau, C. Michel, F. Delbecq, C. Pinel and P. Sautet,
Chem.–Eur. J., 2011, 17, 14288–14299.
19 J. Chaminand, L. Djakovitch, P. Gallezot, P. Marion, C. Pinel
and C. Rosier, Green Chem., 2004, 6, 359–361.
20 E. van Ryneveld, A. S. Mahomed, P. S. van Heerden,
M. J. Green and H. B. Friedrich, Green Chem., 2011, 13,
1819–1827.
Catalytic reactions
The catalytic reaction of diols (1,2-PDO, 1,3-PDO and EG) and
EtOH was performed in a stainless steel (20 mm internal
diameter × 250 mm length) continuous flow fixed bed reactor
in down flow mode. The catalyst volume was 5 ml (ca. 8.5 g)
and it was mixed with an equal amount of carborundum.
The catalyst had a particle size distribution of 300–500 μm.
The molar ratio of hydrogen to diol solution was 2 : 1 with a
GHSV of 1060 h−1 and a LHSV of 3.0 h−1. The catalytic reac-
tions were done at 230 °C and 60 bar. Partial pressure reduc-
tion runs were performed by reducing the H2 partial pressure
but increasing the N2 partial pressure to maintain the same
GHSV and total pressure. Prior to the reaction, the catalyst
was reduced at 180 °C for 12 h after which the reactor was
commissioned under operating conditions. The liquid prod-
ucts and the unreacted feed were collected in sequential
catch pots cooled to 3 °C and −20 °C, respectively, and the
volume of the gaseous components was measured using a
Ritter drum-type gas flow meter. The liquid and gaseous
products were collected at regular intervals and were ana-
lyzed using a GC (HP 6890) equipped with a FID and a DB-1701
column. Further, the gas sample was injected on a GC equipped
with a TCD (Agilent 6850) using a ShinCarbon packed column
for CH4 & COx evaluation. Data was obtained at steady state
and carbon balances were 100% 5.
21 I. Gandarias, P. L. Arias, J. Requies, M. B. Guemez and
J. L. G. Fierro, Appl. Catal., B, 2010, 97, 248–256.
22 E. S. Vasilidou, E. Heracleous, I. A. Vasalos and
A. A. Lemonidou, Appl. Catal., B, 2009, 92, 90–99.
23 Z. Xiao, C. Li, J. Xiu, X. Wang, C. T. Williams and C. Liang,
J. Mol. Catal. A: Chem., 2012, 365, 24–31.
24 S. Koso, H. Watanabe, K. Okumura, Y. Nakagawa and
K. Tomishige, Appl. Catal., B, 2012, 111–112, 27–37.
25 A. Wawrzetz, B. Peng, A. Hrabar, A. Jentys, A. A. Lemonidou
and J. A. Lercher, J. Catal., 2010, 269, 411–420.
26 O. Skoplyak, M. A. Bartreau and J. G. Chen, Surf. Sci.,
2008, 602, 3578–3587.
Acknowledgements
We gratefully acknowledge funding from Sasol Technology.
All catalytic work was performed at Sasol Technology
Research and Development and catalyst characterisation was
done at the University of KwaZulu-Natal. We would also like
to thank the Electron Microscope Unit at the University of
KwaZulu-Natal for the help with the characterisation data.
27 J. A. Rabo, A. P. Risch and M. L. Poutsma, J. Catal., 1978, 53,
295–311.
28 M. Araki and V. Ponec, J. Catal., 1976, 44, 439–448.
29 G. A. Mills and F. W. Steffgen, Catal. Rev., 1974, 8, 159–210.
30 D. Roy, B. Subramaniam and R. V. Chaudhari, Catal. Today,
2010, 156, 31–37.
31 E. van Ryneveld, A. S. Mahomed, P. S. van Heerden and
H. B. Friedrich, Catal. Lett., 2011, 141, 958–967.
32 A. Birot, F. Epron, C. Descorme and D. Duprez, Appl. Catal.,
B, 2008, 79, 17–25.
Notes and references
1 Y. Zheng, X. Chen and Y. Shen, Chem. Rev., 2008, 108,
5253–5277.
2 I Furikado, T. Miyazawa, S. Koso, A. Shimao, K. Kunimori
and K. Tomishige, Green Chem., 2007, 9, 582–588.
3 T. Miyazawa, Y. Kusunoki, K. Kunimori and K. Tomishige,
J. Catal., 2006, 240, 213–221.
33 J. Rass-Hansen, R. Johansson, M. Moller and C. H. Christensen,
Int. J. Hydrogen Energy, 2008, 33, 4547–4554.
4 E. P. Maris and R. J. Davis, J. Catal., 2007, 249, 328–337.
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