Mesoporous Zr-SBA-16 catalysts for glycerol valorization processes: Towards biorenewable formulations

Article abstract of DOI:10.1039/c4cy00230j

Zr-containing SBA-16 materials were utilized in glycerol valorization for the production of esters (via reaction with levulinic acid) and glycerol formal (GF) via acetalisation with paraformaldehyde. The materials were found to be highly active and selective for the production of valuable compounds from glycerol using benign by design solventless protocols which employ mild reaction conditions. Certain materials were also found to be highly reusable and stable under the investigated conditions.

Full text of DOI:10.1039/c4cy00230j

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Mesoporous Zr–SBA-16 catalysts for glycerol
valorization processes: towards biorenewable
formulations†
Cite this: Catal. Sci. Technol., 2014,
4, 2287
Camino Gonzalez-Arellano, a Leticia Parra-Rodrigueza and Rafael Luqueb
*
Received 20th February 2014,
Accepted 26th March 2014
Zr-containing SBA-16 materials were utilized in glycerol valorization for the production of esters
(via reaction with levulinic acid) and glycerol formal (GF) via acetalisation with paraformaldehyde. The
materials were found to be highly active and selective for the production of valuable compounds from
glycerol using benign by design solventless protocols which employ mild reaction conditions. Certain
materials were also found to be highly reusable and stable under the investigated conditions.
DOI: 10.1039/c4cy00230j
www.rsc.org/catalysis
Generally, esterification processes have been traditionally
promoted by strong mineral acids including HCl and H2SO4
Introduction
Glycerol is an abundant renewable resource considered as a
relevant platform chemical for the production of chemicals,
materials (e.g. polymers) and biofuels/fuel additives.1,2 This
polyol has attracted significant attention in recent years due
to the large volumes of crude glycerol as by-product (ca. 10%)
generated from biodiesel production.2,3 Finding applications
in the pharmaceutical, personal care and food industries, a
number of strategies have been recently developed in order
to convert glycerol into important derivatives including pro-
pylene glycol, acrolein and triacetin among others.4 Catalytic
transformations of glycerol to such valuable compounds have
been extensively reported in the literature in recent years
both under batch and continuous flow conditions.3–9
Glycerol esterification is a relevant transformation based
on the added value of potential derivatives.10,11 As an exam-
ple, triacetin possesses suitable properties as a fuel blender
in gasoline, improving parameters such as cold point
and viscosities. Other esters and related derivatives find
important uses as pharmaceutical intermediates, foodstuffs,
explosives, plasticisers, insecticides, etc.12–14 In some cases,
acid catalysed condensation of glycerol with carboxylic acids
(e.g. levulinic acid) may generate low molecular weight
ketal–ester oligomers, providing a new scenario for renewable
biopolymer formulations.15
as well as other strong acidic systems (e.g. p-toluenesulfonic
acid, PTSA). In recent years, solid acids including zeolites,
acidic mesoporous materials and related catalysts have
replaced homogeneous systems in esterification protocols as
recent research endeavors have been aimed to switch to more
environmentally sound protocols.4,8,9,16
Glycerol acetalisation with aldehydes or ketones for the for-
mation of cyclic oxygenated compounds is another important
process considered in glycerol valorization strategies. The reac-
tion between glycerol and formaldehyde is particularly interest-
ing leading to the so-called glycerol formal (GF). GF comprises
a mixture of 5- and 6-membered oxygenated rings (compounds
5-hydroxy-1,3-dioxane and 4-hydroxymethyl-1,3-dioxolane) and
finds important applications as low-toxic solvent for pharma-
ceutical syntheses (anti-parasite veterinary pharmaceuticals,
sulfomethoxazole, sulfonamide preparations, tetracycline-based
products are injected into GF), binder (cold box), in the syn-
thesis of insecticides, for controlled solvent evaporation in
insecticide delivery systems, as well as in formulations of
water-based inks.17 GF preparation has thus far been mostly
reported under homogeneous catalytic conditions employing
mineral acids such as H2SO4 (with and without solvent)18 or
PTSA.19 Solid acid catalysts have been rarely employed in this
particular reaction due to catalyst stability issues under the
proposed conditions, with few available reports which
employed Amberlyst-3620 and Al-modified zeolites.21
a Departamento de Química Orgánica y Química Inorgánica, Universidad de
Alcalá, Facultad de Farmacia, Autovía A2, 33.600, 28871, Alcalá de Henares,
Madrid, Spain. E-mail: camino.gonzalez@uah.es; Fax: +34 918854683;
Tel: +34 918854677
b Departamento de Química Orgánica, Universidad de Córdoba, Campus de
Rabanales, Edificio Marie Curie (C-3), Ctra Nnal IV-A, km 396, 14014 Córdoba,
Spain. E-mail: q62alsor@uco.es
In continuation of our research endeavors devoted to the
development of simple, efficient and greener heterogeneous
catalytic protocols for biomass-derived molecules, herein
we report preliminary catalytic activity results of previously
reported highly ordered Lewis acidic mesoporous Zr-containing
SBA-16 materials with varying Si/Zr ratios22,23 in the esterifica-
tion of glycerol with levulinic acid (LA). LA is another
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c4cy00230j
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biomass-derived platform chemical which can be concomi-
tantly obtained with formic acid (FA) from hexose dehydration
or cellulose deconstruction from a range of lignocellulosic
materials.8,24,25 Zr–SBA-16 materials were also investigated as
catalysts in the acetalisation of glycerol with formaldehyde for
the production of GF.
PY (total acidity) and DMPY (Brönsted acidity) adsorbed should
correspond to Lewis acidity in the materials.
Catalytic experiments
Esterification of glycerol with levulinic acid. In a typical
esterification, the catalyst (0.1–0.2 g) was suspended in a
mixture of glycerol (1 mmol) and levulinic acid (5 mmol).
The reaction was carried out under continuous stirring inside
an ampoule at 140 °C for 8 h. Upon reaction completion, the
resultant mixture was filtered off, extracted using ethanol and
subsequently analyzed by GC-MS. The products mono- and
di-(1,2-diacetylglycol) and triacetin were identified by GC-MS
Experimental
Materials
Pluronics, sodium metasilicate, zirconyl chloride, glycerol,
levulinic acid, formaldehyde solution (37 wt.% in H2O, formalin)
and formaldehyde employed in this work were purchased
from Aldrich and utilised without further purification.
1
and their ratios were also determined by means of H NMR.
The response factors of the starting material and products
were determined using naphthalene as an external standard.
Glycerol acetalisation with formaldehyde sources. In a
typical acetalisation reaction, the catalyst (0.02–0.1 g) was
Catalyst preparation
Zr–SBA-16 materials were synthesized according to a previous
literature report.22,23 In a typical synthesis, 16 g of 10% aque-
ous solution of Pluronics (EO106PO70EO106, Mav = 12 600),
26 g of distilled water and 4.71 g of sodium metasilicate
(Na2SiO3·9H2O) were stirred together at 40 °C until clear
dissolution. 13.6 g of HCl (35%) with the target amount of
zirconyl chloride (ZrOCl2·8H2O) to achieve the different Si/Zr
ratios were subsequently added under vigorous stirring to
obtain a gel. The molar composition of the gel mixture was
1.0 SiO2 : x Zr : 3.17 × 10−4 pluronics : 6.68 HCl : 137.9 H2O.
The solution was continuously stirred for 120 min (optimum
conditions)22 and subsequently microwave-irradiated in a
microwave digestion system (Milestone Corporation, ETHOS-1)
for 120 min at 100 °C. The solid product was eventually
filtered, dried at 120 °C overnight and calcined at 500 °C.
Three different materials were prepared with Si/Zr ratios of
100, 50 and 25, respectively. These samples have been denoted
as Zr–SBA-16(100), Zr–SBA-16(50) and Zr–SBA-16(25).
The materials possessed similar textural properties to
those included in the previous work (e.g. high surface areas
>600 m2 g−1, pore sizes over 6 nm and pore volumes
>0.6 mL g−1).22,23
Characterisation of surface acidity. Pyridine (PY) and
2,6-dimethylpyridine (DMPY) titration experiments were
conducted at 300 °C via gas phase adsorption of the basic
probe molecules utilising a pulse chromatographic titration
methodology. Briefly, small amounts of probe molecules
(typically 1–2 μL) were injected (to approach conditions of
suspended in
a
mixture of glycerol (1 mmol) and
paraformaldehyde (5 mmol). The reaction was carried out
inside an ampoule under stirring at 100 °C for 8 h. The
resultant mixture was then filtered off, extracted using
ethanol and analyzed by GC-MS. 5-hydroxy-1,3-dioxane and
4-hydroxymethyl-1,3-dioxolane were identified as products by
1
GC-MS and their ratios were also determined using H NMR.
Catalyst testing, recyclability tests and product analysis
Upon reaction completion, the catalyst was washed with
ethanol and then filtered off through a silica plug. Product
mixtures were analyzed using GC-MS. Chromatograms were
recorded on a GS-MS turbo system (5975-7820A) model
equipped with a HP-5MS capillary column (30 m × 0.25 mm ×
0.25 μm), under the following conditions:
Esterification: 50 °C ramp 5 °C min−1 until 100 °C,
another ramp 10 °C min−1 until 175 °C and the last ramp
10 °C min−1 until 230 °C held 20 min. Retention times: peak
at 9.66 min levulinic acid, at 15.99 min monoacetylglycerol, at
23.07 min diacetylglycerol and at 36.17 min triacetylglycerol.
Acetalization: injector temperature 250 °C, detector
150 °C, oven temperature program: 40 °C (10 min) ramp
5 °C min−1 until 100 °C and another ramp 9 °C min−1 until
200 °C. Retention times: peak at 1.54 min aldehyde, at
10.54 min 4-hydroxymethyl-1,3-dioxolane, at 11.40 min
5-hydroxy-1,3-dioxane and at 22.90 min glycerol (broad peak).
In recycle studies, the catalyst was reused upon reaction
completion by simple centrifugation and separation followed
by subsequent washing three times with ethanol and drying
prior to reutilization in the target process.
gas-chromatography linearity) into
a gas chromatograph
through a microreactor in which the solid acid catalyst was
previously placed. Basic compounds are adsorbed until com-
plete saturation from where the peaks of the probe molecules
in the gas phase are detected in the GC. The quantity of
probe molecules adsorbed by the solid acid catalyst can
subsequently be easily quantified. In order to distinguish
between Lewis and Brönsted acidity, the assumption that all
DMPY selectively titrates Brönsted sites (methyl groups
hinder coordination of nitrogen atoms with Lewis acid sites)
while PY titrates both Brönsted and Lewis acidity in the mate-
rials was made. Thus, the difference between the amounts of
Results and discussion
Zr incorporation has an important effect on developing
acidity in silicate materials, as in the case of SBA-16. The
acidity of the materials was found to significantly increase
with increasing Zr content in the materials, in particular
Lewis acidity (Table 1),22,23 while all textural and surface
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properties remained very similar for the three acidic meso-
porous materials to previously reported literature data.
achieved for all materials at 100 °C even after 15 h reaction.
Selectivities obtained at this temperature (70–83%) favored a
significant production of monoacetylglycerides. Performed reac-
tions employed different quantities of catalysts to study the
normalised activity per active Zr site. A temperature increase to
140 °C was subsequently attempted in order to push the
reaction to quantitative yields as activities were only slightly
increased at temperatures between 100 and 140 °C. Normalised
results (per active Zr site) included in Table 3 proved that reac-
tion completion could be achieved after 8 h, with interesting
selectivities towards the production of the diester (ca. 65–70%).
Longer times of reaction (15 h) only possessed a minor
influence on the selectivity of the systems, with slightly improved
values towards the production of tri-ester (37–50 mol%), at the
expense of mono-esters (Table 3, entries 2 to 4).
Esterification of glycerol
Three samples of SBA-16 with Si/Zr ratios of 25, 50 and 100
were studied. Blank runs (in the absence of a catalyst)
provided almost negligible or very low activities to products
even at high temperatures (>140 °C, Tables 2 and 3). The
screening and optimization of reaction conditions pointed
out that Zr–SBA-16 materials gave very low activities at
temperatures under 140 °C and for reactions conducted with
lower quantities of catalyst to those included in Table 2.
Reaction runs under solventless conditions (as compared to
the addition of solvents including acetonitrile, toluene, etc.)
also led to a cleaner and improved separation work-up even at
low temperatures of reaction (<100 °C). The results from Table 2
clearly demonstrate that only moderate conversion could be
Taking into account optimization results obtained for the
reaction (Tables 2 and 3), Zr–SBA-16(25) seemed to provide
the optimum activity in the reaction for which this catalyst
Table 1 Acidic properties of Zr–SBA-16 materials as measured by PY and DMPY titration experiments
Materials
Total acidity (μmol PY g−1
)
Brönsted acidity (μmol DMPY g−1
)
Lewis acidity (μmol g−1
)
Zr–SBA-16(100)
Zr–SBA-16(50)
Zr–SBA-16(25)
40
116
233
28
36
33
12
80
200
Table 2 Comparison of catalyst conversion and selectivity for the esterification of glycerol with levulinic acid using Zr–SBA-16 materials
Entry
Catalyst
Catal./gly
Selectivity (mono/di/tri, mol%)
Conversiona (mol%)
1
2
3
Zr–SBA-16(100)
Zr–SBA-16(50)
Zr–SBA-16(25)
200 mg/1 mmol
100 mg/1 mmol
25 mg/1 mmol
71/29/0
83/16/0
77/23/0
40
65
70
a
Reaction conditions: 1 mmol of glycerol, 5 mmol of levulinic acid, catalyst, solventless, 100 °C, 15 h reaction.
Table 3 Optimised results for the esterification of glycerol with levulinic acid using Zr–SBA-16 materials
Entry
Catalyst
Catal./gly
Selectivity (mono/di/tri, mol%)
Conversiona (mol%)
1
2
3
4
No catalyst
—
4/66/30
20
Zr–SBA-16(100)
Zr–SBA-16(50)
Zr–SBA-16(25)
200 mg/1 mmol
100 mg/1 mmol
25 mg/1 mmol
11/64/25 (0/50/50)b
12/64/24 (0/61/38)b
4/68/28 (0/62/37)b
>99
>99
>99
a
b
Reaction conditions: 1 mmol of glycerol, 5 mmol of levulinic acid, catalyst, solventless, 140 °C, 8 h reaction. Values in brackets correspond
to selectivities to products after 15 h reaction under identical conditions.
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was selected for reusability tests. The catalyst was proven to
be highly reusable under the investigated conditions (Table 4),
with fully preserved initial activity even after 4 uses under
identical reaction conditions. Interestingly, the di/tri ratio in
the reused materials was also identical in all cases, with
almost identical selectivities to those of the fresh catalyst.
Similarly, reaction runs in the presence of paraformaldehyde
and polar solvents (e.g. water) gave negligible conversion in
the systems even after 15 h reaction. Interestingly, quantita-
tive yields to products could be obtained in the solventless
acetalisation of glycerol with paraformaldehyde as formalde-
hyde source (Table 5, entry 3).
The proposed reaction was recently attempted by Ruiz et al.21
using hydrophobic zeolites and gold-based systems in which
the authors did not find a direct correlation between acidity
and activity in the systems (i.e. materials with large number
of/stronger acid sites were not necessarily most active).
Results summarized in Table 6 compare the catalytic per-
formance of different Zr–SBA-16 materials in the selected
reaction after 8 h reaction. Interestingly, Zr–SBA-16(100) pro-
vided an unexpectedly optimum activity among all three
materials under the investigated reaction conditions, with a
conversion of 60% (Table 6, entry 1 vs. 2 and 3). Selectivities
to the two main C5 and C6 cyclic products in the reaction
(4-hydroxymethyl 1,3-dioxolane and 5-hydroxy 1,3-dioxane)
followed the expected thermodynamically favored trend towards
cyclic C6 product formation in the approximate order of
ca. 75/25.21 Results pointed to an increase in catalytic activity
with an increase in the quantity of catalyst, which however
does not seem to correlate with the acidity in the materials,
in good agreement with results from Ruiz et al.21
Glycerol acetalization
Zr–SBA-16 materials were also tested in the acetalisation of
glycerol with formaldehyde for the preparation of GF. Several
parameters were investigated in the proposed reaction, starting
with the formaldehyde source and solventless/solvent containing
systems. Results have been summarised in Tables 5 and 6.
Blank runs (in the absence of a catalyst) gave no conversion
after long times of reactions and high temperatures. Reactions
using formalin as formaldehyde source provided very low
conversion in the systems under the investigated conditions.
Table
4 Reusability study in the esterification of glycerol with
levulinic acid using Zr–SBA-16(25) as catalysta
Run
Selectivity (mono/di/tri, mol%)
Conversion (mol%)
1
2
3
4
0/62/37
0/54/46
0/52/48
0/53/47
>99
>99
>99
>99
Optimised activities for the best performing system in this
work were subsequently compared to different literature
reported acid catalysts. Gratifyingly, Zr–SBA-16(100) exhibited
improved catalytic activities at shorter times of reaction with
a
Reactions conditions: 50 mg catalyst, 1 mmol glycerol, 5 mmol
levulinic acid, 140 °C, 15 h reaction.
Table 5 Glycerol acetalization catalysed by Zr–SBA-16(25) using different formaldehyde source systemsa
Aldehyde source
Conversion (%)
Formalin (solventless)
8
Paraformaldehyde (water)
Paraformaldehyde (solventless)
—
>99
a
Reaction conditions: 1 mmol of glycerol, 1 mmol of aldehyde, Zr–SBA-15(25) (20 mg), 100 °C, 15 h reaction.
Table 6 Catalytic activity of Zr–SBA-16 materials in the acetalisation of glycerol with paraformaldehyde
Entry
Catalyst
Catal./gly
Selectivity (dioxolane/dioxane)
Conversiona (%)
1
2
3
4
5
6
Zr–SBA-16(100)
Zr–SBA-16(50)
Zr–SBA-16(25)
Zr–SBA-16(100)
Zr–SBA-16(50)
Zr–SBA-16(25)
50 mg/1 mmol
50 mg/1 mmol
50 mg/1 mmol
100 mg/1 mmol
100 mg/1 mmol
100 mg/1 mmol
29/71
24/76
23/77
24/76
27/73
26/74
60
29
30
77
48
44
a
Reaction conditions: 1 mmol glycerol, 1 mmol paraformaldehyde, 100 °C, 8 h reaction.
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Table 7 A comparison of catalytic activities of different protocols and catalysts in the acetalisation of glycerol with paraformaldehydea
Paper
Entry [ref.]
Reaction conditions [mmol gly : mg catal.]
Solvent
T (°C)
Time (h)
Conversion (%)
1 [21]
2 [21]
3 [21]
4 [21]
5 [21]
This work
AuCl3, 5 mol%
AuCl3, 5 mol%
PTSA, [13 : 25]
Beta(F)-50, [13 : 25]
Amberlyst-36, [13 : 25]
Zr–SBA-16(100), [1 : 100]
Dioxane
80
80
100
100
100
100
4
4
10
10
10
8
93
83
80
60
60
77
—
—
—
—
—
a
Reaction conditions: 1 mmol glycerol, 1 mmol paraformaldehyde.
Fig. 1 Experiments of catalyst recycling in the acetalization of glycerol with paraformaldehyde. 1 mmol glycerol, 1 mmol paraformaldehyde,
100 mg catalyst, solventless, 100 °C, 8 h.
respect to most literature reported solid acid heterogeneous
catalysts as well as almost comparable activities to those of
homogeneous catalysts (Table 7).
Comparatively, Fig. 1C illustrates a rather steady decrease
in activity and deactivation through subsequent reuses of
Zr–SBA-16(25), which in any case lost almost 50% of its initial
glycerol acetalisation activity after 5 uses (Fig. 1C). Gratify-
ingly, Zr–SBA-16(50) could be successfully reused up to five
times under identical reaction conditions, without any
noticeable decrease in activity. These results clearly improved
those previously reported in the literature,21 constituting an
unprecedented example of an active, stable and highly
reusable solid acid in glycerol acetalisation with formaldehyde.
A gold complex was reported to provide better yields to
In view of these premises, the recyclability studies were
conducted for all materials in order to establish an activity/
deactivation comparison between the different Zr-containing
SBA-16 materials. Results are depicted in Fig. 1. Fig. 1A
clearly shows that Zr–SBA-16(100) exhibited a rather poor
reusability, losing over 60% of its initial activity after 3 uses.
Rapid deactivation of acid sites in this material seemed to be
coincidental to results reported by Reddy et al.26
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products in a solvent-mediated protocol, being reusable under
the investigated conditions. However, such gold-based cata-
lyst is comparably more expensive and required a significant
reaction work-up (i.e. precipitation + filtration) as compared
to reusable and easily separable Zr-containing mesoporous
materials under solventless conditions.
6 M. V. Sivaiah, S. Robles-Manuel, S. Valange and J. Barrault,
Catal. Today, 2012, 198, 305–313.
7 F. Jérôme, Y. Pouilloux and J. Barrault, ChemSusChem,
2008, 1, 586–613.
8 J. C. Serrano-Ruiz, R. Luque and A. Sepúlveda-Escribano,
Chem. Soc. Rev., 2011, 40, 5266–5281.
9 C. Len and R. Luque, Sustainable Chem. Processes, 2014, 2, 1.
10 C. H. Zhou, H. Zhao, D. S. Tong, L. M. Wu and W. H. Yu,
Catal. Rev.: Sci. Eng., 2013, 55, 369–453.
11 A. Patel and S. Singh, Fuel, 2014, 118, 358–364.
12 M. Rezayat and H. S. Ghaziaskar, Green Chem., 2009, 11,
710–715.
13 J. A. Melero, R. Grieken, G. Morales and M. Paniagua, Energy
Fuels, 2007, 21, 1782–1791.
14 X. Liao, Y. Zhu, S. G. Wang, H. Chen and Y. Li, Appl. Catal.,
B, 2010, 94, 64–69.
15 A. S. Amarasekara and S. A. Hawkins, Eur. Polym. J.,
2011, 47, 2451–2457.
16 R. Luque, V. Budarin, J. H. Clark and D. J. Macquarrie,
Appl. Catal., B, 2008, 82, 157–162.
17 (a) G. A. Rodriguez, D. R. Delgado, F. Martines,
M. A. A. Fakhee and A. Jovyban, J. Solution Chem., 2012, 41,
1477–1494; (b) Q. Guo, Tianjin Shengji Group Co. Ltd., CN
101590013 A S24056, 2009.
18 J. Wang, X. Shen and R. Chi, Faming Zhuanli Shenging
Gongkai Shuomingshu, CN 1015255329 A 20090909, 2009.
19 S. Radi and H. B. Lazrek, Bull. Korean Chem. Soc., 2002, 23,
437–440.
Conclusions
Preliminary results for Zr–SBA-16 materials with varying Si/Zr
ratios indicated that these mesoporous solid acids can have
excellent activities in acid catalysed reactions with biomass-
derived platform molecules, namely glycerol and levulinic
acid. Quantitative conversion was achieved in the esterifica-
tion of glycerol with levulinic acid with moderate selectivities
to diacetylglycerides, Zr–SBA-16(25) being most active in the
reaction as expected from its large concentration of acid
sites. Comparably, Zr–SBA-16(100) exhibited optimum activi-
ties under optimized conditions in the acetalisation of
glycerol with paraformaldehyde as formaldehyde source.
Investigated catalysts were generally highly stable and reusable
under the investigated conditions, with a particularly outstand-
ing recyclability of Zr–SBA-16(50) in glycerol acetalisation.
Acknowledgements
Rafael Luque and Camino González-Arellano gratefully
acknowledge support from the Spanish MICINN via the
concession of a Ramón y Cajal contract (ref. RYC 2009-04199
and RYC 2010-06268). Rafael Luque gratefully acknowledges
funding from MICINN under project CTQ2011-28954-C02-02.
20 J. Deustch, A. Martin and H. Lieske, J. Catal., 2007, 245,
428–435.
21 V. R. Ruiz, A. Velty, L. L. Santos, A. Leyva-Pérez,
M. J. Sabater, S. Iborra and A. Corma, J. Catal., 2010, 271,
351–357.
Notes and references
1 T. Werpy and G. Petersen, in Top Value Added Chemicals
From Biomass, the Pacific Northwest National Laboratory
(PNNL) and the National Renewable Energy Laboratory
(NREL), U.S. Department of Energy, 2004.
2 J. J. Bozell and G. R. Petersen, Green Chem., 2010, 12,
539–554.
3 M. Pagliaro, R. Ciriminna, H. Kimura, M. Rossi and C. Della
Pina, Angew. Chem., Int. Ed., 2007, 46, 4434–4440.
4 C. H. Zhou, J. N. Beltramini, Y. X. Fan and G. Q. Lu, Chem.
Soc. Rev., 2008, 37, 527–549.
5 L. Li, T. I. Korányi, B. F. Sels and P. P. Pescarmona, Green
Chem., 2012, 14, 1611–1619.
22 http://dspace.inha.ac.kr/pdfupload/16412.pdf.
23 N. Jiang, J. B. Koo, S. C. Han and S. E. Park, Res. Chem.
Intermed., 2008, 34, 507–517.
24 (a) R. S. Assary, P. C. Redfern, J. R. Hammond and
L. A. Curtiss, J. Phys. Chem. B, 2010, 114, 9002–9009;
(b) J. J. Bozell, L. Moens, D. C. Elliot, Y. Wang,
G. G. Neuenscwander, S. W. Fitzpatrick, R. J. Bilski and
J. L. Jarnefeld, Resour., Conserv. Recycl., 2000, 28, 227–239.
25 R. O. M. A. de Souza, L. S. M. Miranda and R. Luque,
Green Chem., 2014, DOI: 10.1039/c3gc41885e.
26 B. Mallesham, P. Sudarsaman, G. Raju and B. M. Reddy,
Green Chem., 2013, 15, 478–489.
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