Direct ethanol condensation to diethyl acetal in the vapour phase at atmospheric pressure over CuNP/SBA-15 catalysts

Article abstract of DOI:10.1039/c9nj02287b

Of the biomass valorization technologies, bioethanol production and its selective conversion to diethyl acetal is of utmost importance to meet the increasing demand for bio-fuel additives. Direct synthesis of diethyl acetal in a single step from bioethanol using SBA-15-supported copper nanoparticle (CuNP/SBA-15) catalysts without using hydrogen acceptors and high pressure has been achieved as an alternative to the age-old two-step process via (i) partial oxidation of ethanol to acetaldehyde and (ii) acetaldehyde acetalization with ethanol. The prepared CuNP/SBA-15 catalysts with the SBA-15 support and copper nitrate (Cu (NO₃)₂·H₂O) were characterized by using N₂ adsorption, SEM, TEM, XRD, FT-IR, TPD of NH₃, H₂-TPR and N₂O pulse chemisorption techniques. Analysis of the results showed the physico-chemical characterestics of these catalysts responsible for the acceptorless partial oxidation of ethanol to acetaldehyde and its acetalization with ethanol to yield diethyl acetal with high selectivity.

Full text of DOI:10.1039/c9nj02287b

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The role of atropisomers on the photo-reactivity and fatigue of
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DOI: 10.1039/C9NJ02287B
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Direct ethanol condensation to diethyl acetal in vapour phase at atmospheric
pressure over CuNPs/ SBA-15 catalysts
Gidyonu Paletiab, Nagaiah Peddintia, Naveen Gajulaab, Vasikerappa Kadharabenchiab, Kamaraju Seetha Rama Raoa and David
Raju Burri*ab
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Among the biomass valorization technologies, bioethanol production and its selective conversion to diethyl acetal is
utmost important to meet the augmenting demand of bio-fuel additives. Direct synthesis of diethyl acetal in a single-step
from bioethanol using SBA-15 supported copper nanoparticle (CuNPs/SBA-15) catalysts without using hydrogen acceptors
and high pressure has been achieved as an alternative to the age old-two-step process via (i) partial oxidation of ethanol
to acetaldehyde and (ii) acetaldehyde acetalization with ethanol. The prepared CuNPs/SBA-15 catalysts with SBA-15
support and copper nitrate (Cu (NO3)2.H2O) were characterized by N2 adsorption, SEM, TEM, XRD, FT-IR, TPD of NH3, H2-
TPR and N2O pulse chemisorption techniques and found that the physico-chemical characterestics of these catalysts are
responsible for the acceptorless partial oxidation of ethanol to acetaldehyde and its acetalization with ethanol in yielding
diethyl acetal with high selectivity.
www.rsc.org/
diethyl acetal is a two-step process15 via production of
acetaldehyde in step-1 from ethanol by oxidative
dehydrogenation or hydrolysis of ethylene oxide. The
acetaldehyde produced in step-1 is used for the acetalization
of ethanol to produce diethyl acetal.
1. Introduction
Off late, the research focus is towards the production of
biomass-derived fuels/fuel additives due to progressive
collapse of fossil resources and also to minimize the fossil fuel
environmental issues.1,2 Ethanol, is a major biomass derived
platform chemical, obtains through sugar fermentation,2-4
hence the term bioethanol is more appropriate, which
transforms into various high value chemicals such as
acetaldehyde, acetic acid, ethylene oxide, ethylene, diethyl
ether, ethyl acetate, 1-butene, 1,3-butadiene and diethyl
acetal.5-7 Among these products, diethyl acetal is one of the
important derivatives of bioethanol, which is used as a raw
material in fragrance and pharmaceutical industries8-10and also
an important intermediate in production of industrial
chemicals (alkyl vinyl ethers).11 It is also used as organic
solvents for cellulose and its derivatives,11 and also used for
the production of polyacetal resins that are employed in
electronic components, televisions, cars and printers
equipment.12 Unambiguously, diethyl acetal is a promising
green oxygenate useful for diesel blending, which improves
the cetane number, reduces the particulate matter and NOx
emissions and also facilitates the combustion without
decreasing the ignition quality.1,14 The industrial production of
C2H5OH + 1/2O2 →CH3CHO + H2O ------- (i)
CH3CHO + 2C2H5OH→ CH3CH(OC2H5)2 + H2O ---- (ii)
Production of acetaldehyde (step-1) with high conversions and
selectivities under eco-friendly environment is undoubtedly a
crucial step. In general, acetaldehyde is being produced by
three important methods16 such as (i) partial oxidation of
ethylene, wherein use of an expensive catalyst and high
reaction temperature are notable difficulties, (ii) hydration of
acetylene, wherein, use of mercury as mercuric complex,
which is a toxic material and (iii) dehydrogenation of ethanol
to acetaldehyde. This method is somewhat interesting, but
ceasing of by-products formation is difficult.
In general, synthesis of acetals is carried out in a
homogeneous system in the presence of corrosive liquid
inorganic acids such as sulphuric acid, phosphoric acid, p-
toluenesulfonic acid (PTSA), triflic acid or dry HCl etc.,17 which
produce significant amount of hazardous waste and in addition
involvement of tedious work-up procedure is inevitable.18 In
order to overcome these drawbacks, replacement of
homogeneous catalysts by heterogeneous catalysts is the only
option. However, there is a limited work is focussed on this
issue19-21 particularly, patent literature.22
Address: aCatalysis& Fine chemicals Division, Indian Institute of Chemical
Technology, Hyderabad- 5000607, INDIA, Fax: +91-40-27160921; Tel: +91-40-
27193163; e-mail: david.iict@gov.in
bCSIR-Academy of Scientific and Innovative Research(CSIR-AcSIR), New Delhi, India
Direct synthesis or single-step synthesis of acetals from
alcohols is an attractive alternative to conventional two-step
process and is remain as a challenge to the scientific society,23
because in this method no need for aldehydes or aldehyde
† Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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derivatives. Direct synthesis of symmetric acetals from primary group published several articles. Particularly, SBA-15
View Article Online
alcohols through a tandem aerobic oxidation–acetalization in supported metal/metal nanoparticle DOcIa: t1a0.l1y0s3t9s/C9iNnJc0lu2d28in7Bg
presence of a chloride-free Pd(OAc)2/Cu(OAc)2/p-TsOH bi- Cu/SBA-15 and CuNPs/SBA-15 catalysts for various organic
functional catalyst without using any solvents under mild transformations. 38-42
conditions (50–80°C, 1–10 atm).23 But the study is limited to
methanol to dimethyl acetal.
From the above mentioned literature, design and
development of suitable solid catalysts for direct synthesis of
A few reports are focussed towards the direct synthesis of diethyl acetal from ethanol that are usable under
higher alcohols to corresponding acetals.24-27 In one of the environmentally acceptable and economically viable
reports on direct catalytic conversion of C5 and C6 alcohols to conditions with improved conversion of ethanol and selectivity
corresponding acetals with high conversions and selectivities of diethyl acetal is present requirement. Herein, an attempt is
were claimed in a batch mode reactor using acridine-based made to prepare a hexagonally ordered mesoporous CuNPs
ruthenium pincer complex, i.e., RuHCl(A-iPr-PNP)(CO) catalyst /SBA-15 bifunctional catalyst that can be operated in a gas
at atmospheric pressure, but no reaction of ethanol to diethyl phase continuous mode adoptable to ethanol to diethyl acetal
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acetal was occurred with the same catalyst.28
reaction. The detailed catalyst preparation, characterization
Coming to ethanol to diethyl acetal, Lloyd reported29 that and catalytic application with respect to ethanol to diethyl
the oxidation of ethanol with O2 using PdCl2 either with CuCl2 acetal including optimization of reaction parameters are
or Cu(NO3)2 as a catalyst, the major products are diethyl delineated.
acetal, acetaldehyde and ethyl acetate. The formation of both
diethyl acetal and acetaldehyde from ethanol was reported in
the photocatalytic liquid-phase oxidation over silica-supported
2. Experimental
Nb or Ti oxides, Re, Ru catalysts and also oxidation by H2O2 by
Fe(III) complexes.24-26,30 Through photocatalytic acceptorless
Catalyst preparation
All the chemicals and the P123 structure directing agent (SDA)
were obtained commercially and used without further
purification. The SBA-15 silica support was synthesized under
hydrothermal acidic conditions using triblock co-polymer
(P123) as SDA and tetraethyl orthosilicate (TEOS) for silica
source in accordance with the original report of Zhao et.al.36
and our previous publications.38-42 Prior to prepare
CuNPs/SBA-15 catalysts, the SBA-15 support was dried at 120
°C for 6 h. The requisite amounts of aqueous Cu (NO3)2.3H2O
solution likely to be around 10, 15, 20, 25 and 30 wt% as Cu
metal were impregnated. These catalyst samples were dried at
100 °C for 12 h and calcined at 450 °C for 6 h. A portion of each
catalyst was reduced at 280 °C for 3 h in the flow of H2 gas
using a fixed bed reactor and denoted as XCuNPs/SBA-15,
where X denotes the percentage loading of Cu metal
nanoparticles by weight.
dehydrogenation coupling process the conversion of ethanol
(<30%) to diethyl acetal (˃99% selectivity) over supported
titania noble metal catalysts was reported.31-33
In the gas-phase selective oxidation of ethanol to diethyl
acetal as a main product only 2 papers and 1 patent was
reported.5,15,34 Liu et.al.,15,34 studied the gas-phase selective
oxidative conversion of ethanol on RuO2/SnO2, ZrO2, TiO2,
Al2O3, SiO2 catalysts and claimed the high selectivity (˃99%) on
RuO2/SiO2 and RuO2/TiO2 catalysts. Thavornprasert et.al.,5
reported that the single-step gas-phase selective oxidation of
ethanol to diethyl acetal over rhenium(Re) catalysts supported
on TiO2 and amorphous Mo-based catalysts and claimed that
these catalysts are highly active, which is the best productivity
ever reported so far in the literature.
According to available literature, most of the catalysts
used for acetalization are homogeneous, which require long
reaction time, harsh reaction conditions, stoichiometric
amount of metallic reagents. Most of the heterogeneous
catalysts for acetalization are noble metal based, which are
unambiguously highly expensive compared to base metals like
Ni and Cu. Copper is abundant, cheap and versatile metal. Its
chemistry is extremely rich due to its ease of accessing
different oxidation states such as Cu0, Cu1+, Cu2+ and Cu3+.
Depending on its oxidation state, the copper metal can
efficiently catalyse the organic reactions through either one-
electron or two-electron mechanisms. Apart from its above
cited advantages, copper is found to be one the prominent
metal for the selective formation of acetaldehyde (crucial
intermediate in acetalization) from ethanol in the non-
oxidative method.35, 36
Catalyst Characterization
The amount of copper present in each catalyst sample was
calculated by ICP-OES (M/s. Thermo Scientific iCAP6500 DU) by
dissolving the CuNPs/SBA-15 catalyst samples in aquaregia
with a few drops of HF (hydrofluoric acid). To investigate the
mesoporous structural ordering of CuNPs/SBA-15 catalysts, X-
ray diffraction (XRD) patterns were recorded at room
temperature using a Rigaku, Multiflex, diffractometer with a
nickel filtered CuK radiation of wave length 0.15418 nm at a
power of 40 kW and a current of 100 mA in the 2θ range of
0.5–5°. To verify the structural characteristics of copper in
CuNPs/SBA-15 catalysts, the samples were recorded in the 2θ
range of 10–80°. The crystallite size estimations were made by
Scherrer equation, considering the most intense metallic
copper reflection (111) that appears at a 2θ = 43.48°. N2
adsorption–desorption isotherms were recorded for calcined
catalysts using a Tristar 3000 V 6.08A instrument (M/S
Santa Barbara Amorphous (SBA-15) is a two-dimensional
(2D) hexagonal silica material having exclusive, imperative and
adaptable properties like large surface area, huge pore
volume, thick pore wall and ordered mesoporocity was
discovered by Zhao et.al.37 Using SBA-15 as a support our
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Micromeritics Instruments Corporation, USA) at -196 °C. The by helium gas (carrier gas for GC) and the temperature was
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CuNPs/SBA-15 samples were outgassed at 300 °C for 4 h prior brought down to room temperature anDdONI:21O0.1g03a9s/C(69N%JN022O287inB
to measurement. BET method was used to calculate the helium) was introduced onto the catalyst in pulses with the
surface areas from N2 quantity adsorbed at -196 °C. BJH help of 6-port valve. It was assumed that the surface Cu metal
method was used to calculate the pore-size distribution sites react with N2O according to the following stoichiometric
considering the desorption branch of the isotherm. The pore equation. 43- 45
volume was taken at a relative pressure P/P0 = 0.989 (single 2Cu+ N2O →Cu2O + N2
point). FT−IR patterns were recorded on a spectrum GX Copper metal surface area (CuSA) = No. Cu moles g-1
x
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spectrometer (M/s. Perkin-Elmer, Germany) in the scan range Avogadro number x cross sectional area of copper metal.
of 4000–400 cm-1. Temperature programmed reduction (TPR) Cu cross sectional area = 6.8 x 10-20 m2 Cu atom-1
-1
studies of all the calcined CuNPs/SBA-15 catalysts were Surface Cu moles
performed on a home-made TPR system that consists of a stoichiometry
quartz reactor, temperature programmer, thermocouple and a
=
2x N2O uptake (mol gcat
)
from
퐍퐨.퐨퐟 퐬퐮퐫퐟퐚퐜퐞 퐂퐮 퐦퐞퐭퐚퐥 퐬퐢퐭퐞퐬
GC (GC-17A with TCD (M/s. Shimadzu, Japan) with a thermal
conductivity detector connected to the outlet of the reactor.
About 50 mg of the catalyst sample was placed at the centre of
the quartz and heated linearly at a rate of 5 °C min-1 from
room temperature to 700 °C and isothermal conditions were
maintained for 30 min at 700 °C, while passing the 11% H2 in
argon gas. In between the out let of the reactor and GC, a
molecular sieve trap was placed to remove the moisture. The
TPR profiles were recorded by the connected GC. The acid site
distributions were obtained from temperature programmed
desorption (TPD) of ammonia. Approximately, 50 mg of
catalyst sample loaded in a sample tube was pre-treated in a
flow of helium at 300 °C for 30 min. Subsequently, the catalyst
sample was saturated with 10% NH3/He gas mixture at 80 °C
for 30 min. After completion of saturation with NH3, helium
was allowed to flow for 30 min at 100 °C for the removal of
physisorbed NH3. Helium gas flow was continued while
increasing the temperature to 800 ᵒC at a ramp of 10 °C min−1
and the desorbed NH3 was monitored with on-line GC
equipped with TCD using standard GC software. FT-IR spectra
of pyridine adsorbed catalysts were recorded by ex-situ
method on a Spectrum GX spectrometer (M/s. Perkin–Elmer,
Germany) at room temperature. 10 mg of the each catalyst
was oven dried at 100 °C for 1 h. To this oven dried sample,
0.1 ml of pyridine was added, followed by vacuum drying at
120 °C for 1 h to remove the physisorbed pyridine. Later, the
samples were finely ground and dispersed in KBr (1:100 ratio)
and made into a pellet. The spectra were collected using
4 cm−1 resolution and averaging five scans in the spectral range
of 400–4000 cm−1. The morphological studies of catalysts were
carried out by scanning electron microscope (M/s. JEOL,
Switzerland). TEM images were obtained on a JEM 2000EXII
apparatus (M/s. JEOL, Switzerland) operating between 160 to
180 kV. Prior to TEM analysis, the catalyst sample was
ultrasonicated in ethanol and a drop of it was placed onto a
carbon coated copper grid and evaporated the solvent in an
oven at 80 °C for 6 h. The N2O pulse chemisorption
% 퐃 =
퐱 ퟏퟎퟎ
Dispersion,
[
]
퐓퐨퐭퐚퐥 퐧퐨. 퐨퐟 퐂퐮 퐦퐞퐭퐚퐥 퐬퐢퐭퐞퐬 퐢퐧 퐜퐚퐭퐚퐥퐲퐬퐭
Catalytic activity test
The catalytic activity tests were performed in fixed-bed glass
down flow reactor (14 mm id and 300 mm length) at
atmospheric pressure. For each catalytic run, the reactor was
loaded with 0.5 g of the catalyst mixed with same amount of
glass beads sandwiched between two quartz wool plugs at the
centre of the reactor. Prior to conduct the reaction, the
catalyst was reduced for 3 h at 280 °C. The reaction was
carried out in the temperature range of 175–275 °C by feeding
ethanol with the flow rate of 1 ml h-1 (feed pump, M/s. B.
Braun, Germany) along with N2 carrier gas. The product
mixture was collected in an ice cooled trap and analysed the
product mixture for every 1 h by GC-17A (M/s. Shimadzu
Instruments, Japan) equipped with FID and EB–5 capillary
column (30 m x 0.53 mm x 5.0 µm). The products were
confirmed by GC-MS, (QP-2010, M/s. Shimadzu Instruments,
Japan) with MS column (30 m x 0.25 mm x 0.25 µm).
3. Results and discussion
Textural properties of catalysts
measurements were done on
a
home-made pulse
chemisorption setup. An automatic gas sampling valve and a
GC (GC-17A, M/s. Shimadzu Instruments Corporation, Japan)
equipped with TCD and Porapak-T column in separating N2O
and N2 connected at the inlet and outlet respectively. Prior to
each experiment the catalyst was reduced in H2 flow at 280 °C
for 3 h. After completion of the reduction, H2 gas was replaced
Fig. 1 N2 adsorption desorption isotherms of CuNPs/SBA-15 catalysts and pore
size distribution graph is as inset
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The textural properties like BET surface area (SBET), pore CuNPs/SBA-15 catalysts (Fig. 2), exhibiting a strong diffraction
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DOI: 10.1039/C9NJ02287B
volume and pore diameter are presented in Table 1, peak at 2θ = 43.48° followed by two more intense diffraction
accordingly, the surface area of the SBA-15 support is 807 m2g- peaks at 50.5° and 74.1° characteristic of Cu0 (JCPDS 04-0836),
1
which is having the highest surface area compared to all which indicates that the presence of metallic Cu in all the
6
other catalysts prepared from the SBA-15 support. Gradual catalysts.
decrease in surface area with increase in CuNPs loading on
SBA-15, revealing the occupancy of some surface area of the
support by CuNPs according to loaded CuNPs amount. Since
the catalysts were prepared by impregnation technique, the
homogeneous Cu(NO3)2.3H2O can reach to either pore
surfaces or external surface of the support. The average pore
volume of SBA-15 support is 1.35, cm3 g-1 which is the highest
pore volume compared to the pore volume of catalysts
prepared from it and further more the pore volumes of
catalysts are deceasing with increase in CuNPs loading and are
the usual trend. The pore diameters of support and catalysts
are more or less constant.
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To verify the textural strength of catalysts, N2 adsorption–
desorption isotherms for SBA-15 and CuNPs/SBA-15 catalysts
were generated and displayed Fig. 1, which are of type IV and
Fig. 2 XRD patterns of reduced CuNPs/SBA-15 catalysts and low angle XRD graph
is shown as inset
exhibited H1 hysteresis loops, as per IUPAC classification the
pore channels are hexagonally ordered similar to that of SBA-
Additionally, a broad hump is observed in all the patterns of
15 support, revealing the retention of porous texture of SBA-
catalysts at around 22°, which corresponds to amorphous silica
15 support in all the Cu/SBA-15 catalysts.38-42 The data
of SBA-15 support. The crystallite sizes are marginally
presented in Fig. 1 explicitly confirming the robustness of the
increased with increase in CuNPs loading on SBA-15 support
CuNPs/SBA-15 catalysts. The pore size distribution graph has
(Table 2).
shown as inset in Fig. 1, wherein the pore sizes of all the
Table 2 Catalyst composition and crystallite size from XRD
catalysts are more or less uniform and are narrowly
distributed, symbolizing the pore texture of SBA-15 support.38-
Catalyst
CuNPs loading, wt%
bCrystallite
size nm
13.1
42
Taken
10
a obtained
Table 1 Textural property of CuNPs/SBA-15 catalysts
10CuNPs/SBA-15
15CuNPs/SBA-15
20CuNPs/SBA-15
25CuNPs/SBA-15
30CuNPs/SBA-15
8.7
15
14.6
19.4
24.6
29.3
14.1
Catalyst
SBET
Pore
volume
cm3g-1
1.35
Pore
diameter
nm
6.33
7.18
6.27
7.21
6.34
7.17
20
15.3
m2g-1
25
16.0
30
17.7
SBA-15
807
460
329
305
296
242
10CuNPs/SBA-15
15CuNPs/SBA-15
20CuNPs/SBA-15
25CuNPs/SBA-15
30CuNPs/SBA-15
0.81
0.63
0.55
0.53
a obtained from ICP-OES, b obtained from Scherrer equation
FT-IR analysis
0.43
Structural characteristics by low and wide angle XRD
To assess the structural features of the catalysts including SBA-
15 support, low and wide angle XRD patterns were obtained.
The wide angle XRD patterns are shown in Fig. 2, wherein low
angle XRD patterns are presented as inset. The SBA-15 support
exhibited well-resolved diffraction peaks with a sharp peak at
about 0.89 and two more weak peaks are observed at about
1.56 and 1.80° on the 2θ scale. Similar kind of XRD patterns
were obtained for all the CuNPs/SBA-15 catalysts, but with
gradual diminishing in peak intensity with increasing CuNPs
loading on the SBA-15 support. On the whole, appearance of
diffraction peaks of (100), (110) and (200) planes even in the
XRD pattern of 30CuNPs/SBA-15 catalyst, elucidating the
Fig.
3 FT-IR spectra of CuNPs/SBA-15 catalysts (a) SBA-15 support, (b)
10CuNPs/SBA-15, (c) 15CuNPs/SBA-15, (d) 20CuNPs/SBA-15, (e) 25CuNPs/SBA-
15 and (f) 30CuNPs/SBA-15
presence hexagonally ordered mesoporous structure in all the
38-42
catalysts.
The wide angle XRD patterns of all the
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FT-IR spectral analysis was made for all the CuNPs/SBA-15
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catalysts including SBA-15 support and the obtained spectra
are presented in Fig. 3, accordingly the absorption bands at
around 1087, 807 and 464 cm−1 are due to the Si- O- Si
stretching vibration. The absorption band at around 960 cm−1
can be assigned to either Si- OH or Si- O -Si stretching
vibrations. The broad absorption band at around 3400 cm-1 is
due to the presence of surface OH groups with strong
hydrogen bonding interactions. The absorption bands at
around 660 and 570 cm-1 ascribed to Cu- O vibrations in
copper oxide lattice.46
The nature of acidic sites present in the CuNPs/SBA-15
catalysts were evaluated by performing pyridine adsorbed FT-
IR and the corresponding patterns were presented in Fig. 4.
Pristine SBA-15 and all CuNPs/SBA-15 catalyst samples show
two bands at 1445 and 1597 cm-1 which is ascribed to the
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Fig. 5 SEM images of (A) SBA-15, (B) 25CuNPs/SBA-15 catalyst and TEM images of
(C) SBA-15, (D) 25CuNPs/SBA-15 catalyst
Reduction behaviour of CuNPs/SBA-15 catalysts
Assessing the reduction behaviour of Cu2+ species that
supported on SBA-15 has been investigated by a well known
and a valid TPR technique. The H2-TPR profiles of calcined
CuNPs/SBA-15 catalysts are displayed in Fig. 6. From the
reduction profile of 10Cu/SBA-15 catalyst, only a single peak is
observed at 250 °C, which corresponds to the reduction of Cu2+
species into metallic Cu. In the case of remaining catalyst
15CuNPs/SBA-15 catalyst two reduction peaks can be
observed, where a main reduction peak appeared at 295 °C
due to reduction of CuO to Cu0 or metallic Cu species (CuO +
H2 → Cu + H2O) in a single stage and a shoulder peak that
appears at 250 °C may be due to reduction of Cu1+ species into
metallic Cu (Cu2O + H2 → 2Cu + H2O). Similar reduction
behaviour is observed the higher CuNPs loading catalysts. It is
clearly seen in the case of 30CuNPs/SBA-15 catalyst, wherein
the main reduction peak appearing at 335 °C and a minor peak
at 295 °C.
Fig.4 Pyridine adsorbed FT-IR spectra of CuNPs/SBA-15 catalysts (a) SBA-15
support, (b) 10CuNPs/SBA-15, (c) 15CuNPs/SBA-15, (d) 20CuNPs/SBA-15, (e)
25CuNPs/SBA-15 and (f) 30CuNPs/SBA-15
presence of surface Lewis acidic sites coordinated to pyridine.
The additional band at 1488 cm-1 is a result of combination of
Lewis and Bronsted acidic sites.47-49 It can be observed that the
intensities of these bands are increasing with the copper
loadings. In the present case all the CuNPs/SBA-15 catalyst
samples contain majority of surface Lewis acidic sites
compared to Bronsted acidic sites.
Morphological aspects of SBA-15 and 25CuNPs/SBA-15 catalyst
The morphological features of SBA-15 support and
25CuNPs/SBA-15 catalyst were analysed by scanning electron
microscope and the acquired SEM images are presented in Fig.
5 (A & B), which are matching with the reported images.50 TEM
images are shown in Fig. 5 (C & D), wherein, existences of
array of uniform pore channels are clearly appearing in Figure
5 (D), but not the presence of CuNPs.
Fig. 6 TPR profiles of calcined CuNPs/SBA-15 catalysts
The results reveal that the interaction between CuO and SBA-
15 support increases with CuNPs loading and the CuO species
seems to be getting aggregated both in pores and on the
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external surface of SBA-15 support and tends towards bulk catalysts from 10CuNPs/SBA-15 to 25CuNPs/SBA-15 catalyst
nature CuO species. The H2 consumption values of the increased and dropped down on 30CuNPs/SBA-15 catalyst and
CuNPs/SBA-15 catalysts are 111.60, 129.28, 209.91, 265.03, also sudden drop in dispersion and significant increase in
and 282.33 µmol g-1 for 10, 15, 20, 25 and 30 CuNPs/SBA-15 particle size is observed for 30CuNPs/SBA-15 catalyst,
View Article Online
DOI: 10.1039/C9NJ02287B
catalysts, respectively.
considering above changes occurred in 30CuNPs/SBA-15
catalyst, it seems that the 25CuNPs/SBA-15 catalyst will be the
best catalyst. Deposition of 25 weight% CuNPs on the support
with the average particle size of 13nm without adding any
surfactant/stabilizers by adopting a facile wet impregnation is
unambiguously a significant research improvement in catalyst
synthesis
Strength of acidic sites by TPD of NH3 for CuNPs/SBA-15 catalysts
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Direct conversion of ethanol to diethyl acetal
The direct conversion of ethanol to diethyl acetal over
CuNPs/SBA-15 catalyst in gas phase at atmospheric pressure,
wherein one ethanol molecule reduced to acetaldehyde which
condensed with other two ethanol molecules forms as diethyl
acetal by losing one water molecule as shown in scheme 1.
OH
CuNPs/SBA-15
3
- H2O
Fig. 7 TPD of NH3 profiles of CuNPs/SBA-15 catalysts (a) SBA-15 support, (b)
10CuNPs/SBA-15, (c) 15CuNPs/SBA-15, (d) 20CuNPs/SBA-15, (e) 25CuNPs/SBA-
15 and (f) 30CuNPs/SBA-15
O
O
Ethanol
Diethylacetal
The NH3 desorption profiles of SBA-15, Cu/SBA-15 catalysts
are depicted in Fig. 7. The acidic sites population can be
classified depending upon desorption temperature of
ammonia as weak acidic sites (<250 °C), medium (250-400 °C)
and strong acidic sites (>400 °C). The desorption signals
observed in the TPD profile of pure SBA-15 can be ascribed to
the surface hydroxyl groups. All the catalysts except SBA-15,
showed a desorption peak in the temperature range of 130-
250 °C indicating the weakly chemisorbed NH3 molecules
corresponding to the presence of high amount of weak acidic
sites arising from the dispersed copper. Another small peak at
around 380 °C could be observed due to the presence of
medium acidic sites. From the total acidity values the acidity of
the catalysts increases linearly with the copper loadings.
Scheme 1 The reaction scheme for Diethyl acetal formation from ethanol
Influence of CuNPs on direct ethanol conversion to diethyl acetal
N2O pulse Chemisorption studies
Table 3 Characteristics of CuNPs/SBA-15 catalysts (N2O chemisorption)
Fig. 8 Effect of CuNPs loading on catalytic activity. Reaction conditions: Temperature:
225 ᵒC, Catalyst weight: 0.5 g, N2 flow: 30 ml min-1, Feed flow: 1 ml h-1.
Catalyst
N2O
aCuSA
bCuD
%
cCuPS
nm
uptake µ m2g-1
mol g-1
To investigate the optimum loading of CuNPs on the SBA-15
support, the direct conversion of ethanol to diethyl acetal was
conducted on all the six catalysts (10CuNPs/SBA-15 to
30CuNPs/SBA-15) in the gas-phase at 225 °C in the inert
atmosphere using nitrogen gas and the data are displayed
in Fig 8, which demonstrate that the increase in conversion of
ethanol with increase in CuNPs loading from 10 to 25% is due
to increase in the number of active sites available for
participating in the reaction. However, the increase in
conversion with increase in CuNPs loading from 25 to 30% is
marginal, implying that high metal content may lead to
agglomeration of CuNPs metal particles and furthermore,
10CuNPs/SBA-15 98
15CuNPs/SBA-15 110
20CuNPs/SBA-15 130
25CuNPs/SBA-15 156
30CuNPs/SBA-15 139
8.1
9.1
10.7
12.9
11.5
12.5
9.4
8.3
8.0
5.8
8.3
11.1
12.5
13.0
17.6
Copper metal (a surface area, b dispersion and c particle size)
To estimate the copper metal surface area, dispersion and
particle size N2O pulse chemisorptions were conducted and
acquired data is presented in Table 3. According to Table 3,
both N2O uptake and copper metal surface area of the
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selectivity to diethyl acetal decreased significantly due to The TOS study was conducted on 25CuNPs/SBA-15 catalyst at
simultaneous increase in the selectivity to other product 225 °C for a period 10 h, the conversion of ethanol and
View Article Online
DOI: 10.1039/C9NJ02287B
(acetaldehyde, butanol and ethyl acetate).
selectivity of diethyl acetal are constant at 48% and 93%
It can be ascertained that the active sites responsible for respectively, revealing the activity of catalyst is stable under
the dehydrogenation followed by dehydration of ethanol and the employed reaction conditions (Fig. 10).
formation of other product are different. Among the
CuNPs/SBA-15 catalyst series, the 25CuNPs/SBA-15 catalyst
exhibited highest activity with 48% conversion of ethanol and
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93% selectivity of diethyl acetal. The remaining 7% are
acetaldehyde, ethylacetate and butanol, where as Lu et al,
reported that the major product is acetaldehyde with
selectivity of 68.1% on 10Cu/SBA-15 catalyst. The discrepancy
in the catalytic activity may be due to variation in the catalyst
preparation, activation and operating conditions.51 The
present results demonstrate that there is
a significant
influence of the CuNPs loading on the SBA-15 support. It
seems that there is a striking balance between the conversion
of ethanol and selectivity to diethyl acetal over the
25CuNPs/SBA-15 catalyst. Hence, the best catalyst is
25CuNPs/SBA-15 catalyst with in this catalyst series.
Fig. 10 Time-on-stream activity of 25CuNPs/SBA-15 catalyst. Reaction conditions:
Temperature: 225 ᵒC, Catalyst weight: 0.5 g, N2 flow: 30 ml min-1, Feed flow: 1
ml h-1.
Effect of reaction temperature on activity over 25CuNPs/SBA-15
The maximum yield of diethyl acetal is about 45% over
25CuNPs/SBA-15 catalyst at 225 °C in the fixed bed gas phase
reactor at atmospheric pressure, which is the highest yield of
diethyl acetal so far in the open literature.
In general, acetalization occurs between an aldehyde and
alcohol, if any of these two reactants absent, it is hard to
expect acetalization product. But, it is possible with alcohols
alone by direct coupling over
a suitable catalyst and
conditions. In-situ formation of an aldehyde via acceptor less
dehydrogenation of an alcohol molecule is an essential initial
step. According to earlier reports52 copper metal is capable of
dehydrogenating the alcohol to aldehyde even in the absence
of acceptors, which is the basis for choosing the copper metal
as active component, particularly in the form of nanoparticles,
because nanoparticles perform the reaction well compared to
bulk copper metal particles. The high activity of 25CuNPs/SBA-
15 catalyst is mainly two reasons, (i) unique porous network of
SBA-15 (ii) 13 nm sized copper nanoparticles with high copper
amount (25wt%). The texture of SBA-15 support is hexagonally
ordered pores with uniformly sized mesopores. Each bundle of
hexagonally ordered pores of SBA-15 support is expected to
act like small copper nanoparticles loaded multi-tubular
reactor in the case of smaller CuNPs particles (˂ 6.34 nm) that
are located inner pore walls of SBA-15 support. As reported in
the literature the appropriate catalyst for this reaction likely to
be bifunctional, which should posses both acidic and redox
sites, wherein redox sites enable the partially oxidised redox
products like acetaldehyde from ethanol and the acidic sites
facilitate condensation.5 To sum up, 25CuNPs/SBA-15 catalyst
with large amount of copper nanoparticles with small particle
size (13 nm), uniform dispersion, acidic and redox bi-functional
characteristics, ordered mesoporosity, ease of active sites
accessibility, confined environment etc., cooperatively
facilitated in getting the higher conversion of ethanol (48%)
and higher selectivity of diethyl acetal (93%) via single-step
Fig. 9 Effect of reaction temperature on activity over 25CuNPs/SBA-15 Reaction
conditions: Catalyst weight: 0.5 g, N2 flow: 30 ml min-1, Feed flow: 1 ml h-1.
In order to know the effect of reaction temperature on the
activity of 25CuNPs/SBA-15, the direct conversion of ethanol
was conducted at five different temperatures from 175 to 275
°C (Fig.9). With the increase in reaction temperature from 175
to 225 °C, conversion of ethanol increased from 26% to 48%
and selectivity of diethyl acetal increased from 79% to 93%. In
other words the yield of diethyl acetal increased from 21% to
45%. i.e., the yield of diethyl acetal at 225 °C is 45%. Beyond
the reaction temperature of 225 °C, decrease in ethanol
conversion as well as selectivity of diethyl acetal are observed
and at the same time selectivity of by-products increased
significantly. Since ethanol conversion to acetaldehyde is a
primary step, its further conversion to diethyl acetal is an
equilibrium reaction, favouring of backward reaction with
increased temperatures is a common phenomenon and
increment in the selectivity of by-products at higher
temperatures is expected.
Time-on-stream (TOS) study on 25CuNPs/SBA-15 catalyst
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synthesis or direct synthesis of diethyl acetal from ethanol in
the environmentally acceptable vapour phase conditions using
a fixed bed reactor.
which are the best results so far, based on the
employed reaction conditions.
4. Superior and robust activity of this 25%CuNPs/SBA-15
catalyst can be ascertained from its compatible
porous network, confined environment, smaller
copper particle size and their ample amount.
View Article Online
DOI: 10.1039/C9NJ02287B
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There are no conflicts of interest to declare
- H2
- H2O
O
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Acknowledgements
H
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GP, NP and VK are acknowledging the DST, New Delhi, India for
granting the research fellowships.
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References
1
J. C. Serrano-Ruiz and J. A. Dumesic, Energy Environ. Sci.
2011, 4, 83.
Scheme 2 Single-step synthesis of Diethyl acetal from ethanol over mesoporous
SBA-15 supported copper nanoparticle catalysts
2
3
T. Wheeler and J. von Braun, Science, 2013, 341, 508.
M. Neureiter, H. Danner, C. Thomasser, B. Aidi and R. Braun,
Appl. Biochem. Biotech., 2002, 98, 49.
The mechanistic aspects of ethanol to Diethyl acetal (Scheme
2) are shown in steps as follows
1. Ethanol adsorbed by the catalyst that leads to oxidative
addition of ethanol with Cu0 to Cu2+.
2. Absorption of α-hydrogen from ethanol and eliminate the H2
in reductive elimination to form the acetaldehyde.
3. The acetaldehyde which is formed in the second step has
highly electronic deficient, the nucleophilic O in the ethanol
attacks the electrophilic C in the C=O, breaking the π bond and
giving the electrons to the positive O and forms the hemi-
acetal.
4
5
O. J. Sanchez and C. A. Cardona, Bioresour. Technol. 2008,
99, 5270.
K.-A. Thavornprasert, B. de la G. de Menorva, M. Capron, J.
Gornay, L. Jalowiecki-Duhamel, X. Secordel, S. Cristol, J.-L.
Dubois and F. Dumeignil, Biofuels, 2012, 3(1), 25.
S. Hanspal, Z. D .Young, J. T. Prillaman and R. J. Davis, J.
Catal., 2017, 352, 182.
C. Angelici, B. M. Weckhuysen and P. C. A. Bruijnincx,
ChemSusChem, 2013, 6, 1595.
F. A. J. Meskens, Synthesis 1981, 7, 501.
6
7
8
9
B. D. Mookherjee, R. W. Trenkle, S. M. Patel and S. M.
Brown, US5321006 (1994).
10 M. Kaufhold and M. Del-Chabawi, US5527969 (1996).
11 V. M. T. M. Silva and A. E. Rodrigues, Chem. Eng. Sci.,2001,
56, 1255.
12 V. M. T. M. Silva and A. E. Rodrigues, AIChE. J., 2005, 51,
2752.
13 K. Bonhoff, F. Obenaus, Pat DE 2911411 (1980) to Daimler,
Benz Germany
14 N. Marshall, Petrochemical Processes, Gulf publishing, Texas,
1989.
15 Liu and E. Iglesia, J. Phys. Chem. B 2005, 109, 2155.
16 J. McKetta, Encyclopedia of Chemical Processing and Design.
Marcel Dekker, Inc. New York, 188, 1, 114.
17 M. Kaufhold, M. El-Chahawi. Pat. DE 44 04 515 A1 (1995).
18 H. Yang, B. Li and Y. Cui, Synth. Commun., 1993, 28, 1233.
19 K. Shimizu, E. Hayashi, T. Hatamachi, T. Kodama and Y.
Kitatama, Trahedron Lett. 2004, 45, 5135.
20 Y. J. Kim and R. S. Varma, Tetrahedron Lett. 2005, 46, 7447.
21 B. C. Ranu, R. Jana and S. Samanta, Adv. Synth. Catal. 2004,
346, 446.
22 J. Andrade, D. Arntz, M. Kraft and G. Prescher. Pat. DE 34 03
426 A1 (1985), to Degussa AG, Germany.
23 A. C. Bueno, J. A. Goncalves and E. V. Gusevskaya, Appl.
Catal. A: Gen., 2007, 329, 1.
4. Absorption of hydrogen from α-position of hemi acetal
forms the ethyl acetate.
5. The carbonyl carbon in ethyl acetate is somewhat electron
deficient, the nucleophilic O in the alcohol attacks the
electrophilic C in the C=O, breaking the π bond and giving the
electrons to the positive O and forms the oxonium ion
intermediate.
6. Finally the oxonium ion rearranged to loss the water
molecule and forms the diethyl acetal.
Conclusions
1. SBA-15 supported copper nanoparticle catalysts
(CuNPs/SBA-15) up to 30wt% copper nanoparticle
loading, <20 nm particle size and hexagonally ordered
porous network are prepared.
2. Novel synthesis of diethyl acetal from ethanol over
CuNPs/SBA-15 catalysts in a single-step without using
aldehyde or aldehyde derivatives, solvents and
harmful acids or expensive reagents was achieved.
3. Facile gas-phase operation (25%CuNPs/SBA-15
catalyst) with high conversion of ethanol (48%) and
high selectivity of diethyl acetal (93%) was achieved,
24 T. Tanaka, S. Takenaka, T. Funabiki and S. Yoshida, Chem.
Lett. 1994, 809.
25 C. Heitler, D. B. Scaife and B. W. Thompson, J. Chem. Soc. A,
1967, 1409.
26 A. L. Suing, C. R. Dewan, P. S. White and H. H. Thorp, Inorg.
Chem. 2000, 39, 6080.
27 H. Mimoun, DE Patent 1979, 2920678.
8 | J. Name., 2012, 00, 1-3
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Page 9 of 9
New Journal of Chemistry
Please do not adjust margins
Journal Name
ARTICLE
1
2
3
4
5
6
7
8
9
28 Gunanathan, L. J. W. Shimon and D. Milstein, J. Am. Chem.
View Article Online
DOI: 10.1039/C9NJ02287B
Soc. 2009, 131, 3146.
29 C W. G. Lloyd, J. Org. Chem. 1967, 32, 2817.
30 T. Tanaka, S. Takenaka, T. Funabiki and S. Yoshida, Stud. Surf.
Sci. Catal. 1994, 90, 485.
31 H. Zhang, W. Zhang, M. Zhao, P. Yang and Z. Zhu, Chem.
Commun., 2017,53, 1518.
32 H. Zhang, Z. Zhu, Y. Wu, T. Zhao and L. Li, Green Chem.,
2014, 16, 4076.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
33 H. Zhang, Y. Wu, L. Li and Z. Zhu, ChemSusChem, 2015, 8,
1226.
34 H. Liu, E. Iglesia, 2005, US0059839A1
35 F.-W. Chang, H.-C. Yang, R. L. Selva and W.-Y. Kuo, Appl Catal
A Gen, 2006, 304, 30.
36 R. Prasad, Mater Lett., 2005, 59, 3945.
37 D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F.
Chmelka and G. D. Stucky, Science 1998, 179, 548.
38 N. Anand, K. H. P. Reddy, V. Swapna, K. S. R. Rao and D. R.
Burri, Micropor. Mesopor. Mater. 2011, 143, 132.
39 S. Ganji, S. Mutyala, C. K. P Neeli, K. S. R. Rao and D. R. Burri,
RSC Adv., 2013, 3, 11533.
40 40. C. K. P. Neeli, M. R. Kumar, G Saidulu, K. S. R. Rao and D.
R. Burri, J. Chem. Technol. Biotech. 2015, 90,1657.
41 C. K. P Neeli, V. S. P. Ganjala, V. Vakati, K. S. R. Rao, D. R.
Burri, New J. Chem., 2016, 40, 679.
42 S. Ganji, P. Bukya, V. Vakati, K. S. R. Rao and D. R. Burri, Catal.
Sci. Technol. 2013, 3, 409.
43 P. Nagaiah, M. Venkat Rao, K. Thirupathaiah, V.
Venkateshwarlu, D. R. Burri and K. S. Rama Rao, Res. Chem.
Intermed. 2018, 44, 5817.
44 G. Krishna Reddy, K. S. Rama Rao and P. Kanta Rao, Catal.
Lett.1999, 59, 157.
45 J. W. Evans, M. S. Wainwright, A. J. Bridgewater and D. J.
Yang, Appl. Catal. 1983, 7, 75.
46 V. Subbaramaiah, V. C. Srivastava, and Indra Deo Mall, AIChE
Journal, 2013, 59(7), 2577.
47 S. S. Enumula, K S Koppadi, V R B Gurram, D. R. Burri and S.
R. R. Kamaraju, Sustainable Energy Fuels, 2017, 1, 644.
48 X. L. Yang, W. L. Dai, R. Gao and K. Fan, J. Catal., 2007,
249,278.
49 K. Barbera, P. Lanzafame, A. Pistone, S. Millesi, G.
Malandrino, A. Gulino, S. Perathoner and G. Centi, J. Catal.,
2015, 323, 19.
50 M. Kondeboina, S. S. Enumula, V. R. B. Gurram, R. R. Chada,
D. R. Burri and S. R. R. Kamaraju, J. Ind. Eng. Chem.,2018, 61,
227.
51 Q.-N. Wang, L. Shi, and A.-H. Lu, ChemCatChem, 2015,7,
2846.
52 R. K. Marella, C. K. P. Neeli, S. R. R. Kamaraju and D. R. Burri,
Catal. Sci. Technol., 2012, 2, 1833.
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