The selectively regulated vapour phase dehydrogenation of 1,4-butanediol to γ-butyrolactone employing a copper-based ceria catalyst

Article abstract of DOI:10.1039/c9nj03067k

The growing pursuit of the viable application of γ-butyrolactone (GBL) as an industrially important product offers the possibility to use 1,4-butanediol (1,4-BDO) as a potential reactant. In this regard, different proportions of copper-based ceria catalysts (5, 10, 15, and 20CC) were synthesized using a wet impregnation method and their catalytic activities were tested for the vapour phase dehydrogenation of 1,4-BDO to GBL at temperatures from 240-300 °C. The synthesized copper-based ceria catalysts (5CC, 10CC, 15CC, and 20CC) were characterized using various analytical tools and the consequent results revealed that the activities of the CC catalysts were influenced by the physicochemical properties of the materials. In order to determine the influence of various supports on the catalytic activity, the addition of 10 wt% copper (Cu) to TiO₂, Al₂O₃, ZnO, ZSM-5, and SBA-15 supports was carried out, and the respective influence on the catalytic activity was also experimentally established. The most outstanding catalytic activity was seen for the 10 wt% copper-based ceria catalyst, with a high conversion of 93% and selectivity of 98% at 240 °C. Factors like a high surface area, and better dispersion and basicity of active sites had a marked impact on the catalytic activity. Mechanistic analysis suggested that 1,4-BDO undergoes dehydrogenation over the copper surface to give 4-hydroxybutanal, followed by hemiacetylation and subsequent dehydrogenation to give GBL as the selective product. In terms of the stability of the catalysts, the 10 wt% copper-based ceria catalyst maintained a stable GBL selectivity of 98% for up to 7 h on-stream.

Full text of DOI:10.1039/c9nj03067k

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Chechia Hu, Tzu-Jen Lin et al.
Yellowish and blue luminescent graphene oxide quantum dots
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Selectively regulated vapour phase dehydrogenation of 1,4-
butanediol to γ-butyrolactone employing a copper based ceria
catalyst
Received 00th January 20xx,
Accepted 00th January 20xx
Jayesh T. Bhanushalia, Divya Prasada, Komal N. Patila, Gurram Venkata Ramesh Babub, Itika
DOI: 10.1039/x0xx00000x
Kainthlaa, Kamaraju Seetha Rama Raob, Arvind H. Jadhava,⁎, Bhari Mallanna Nagarajaa,⁎
The growing pursuit for the viable application of γ-butyrolactone (GBL) as an industrially important product
offers probabilities to use 1,4-butanediol (1,4-BDO) as a potential reactant. In this regard different
proportions of copper based ceria catalysts (5, 10, 15, 20CC) were synthesized using wet impregnation
method and its catalytic activity was tested for vapour phase dehydrogenation of 1,4-BDO to GBL at
temperatures from 240-300 °C. The synthesized copper based ceria catalysts (5CC, 10CC, 15CC, 20CC) were
characterized by various analytical tools and their consequent results revealed that the activity of CC
catalysts was influenced by the physicochemical properties of materials. In order to determine the influence
of various supports on the catalytic activity, addition of 10 wt.% copper (Cu) on TiO2, Al2O3, ZnO, ZSM-5, SBA-
15 supports was carried out and their respective influence on the catalytic activity was also experimentally
established. The most outstanding catalytic activity was seen for the 10 wt.% copper based ceria catalyst
with a high conversion of 93% and selectivity of 98% at 240 °C. The factors like high surface area, better
dispersion and basicity of the active sites had a marked impact on the catalytic activity. Mechanistic aspects
suggested that 1,4-BDO undergoes dehydrogenation over copper surface to give 4 hydroxybutanal followed
by hemiacetylation and subsequent dehydrogenation to give GBL as the selective product. In terms of
stability of catalysts, the time on stream for 10 wt.% copper based ceria catalyst maintained a stable GBL
selectivity of 98% for upto 7 h.
Keywords: Dehydrogenation, Copper-ceria catalyst, 1,4-butanediol, gamma butyrolactone
Introduction
chlorinated solvents which come across as potential
environmental threats2. Extensive efforts have been put in the
synthesis of GBL via dehydrogenation and lactonization of 1,4-
BDO due to its outstanding nature as a reactant. Conventional
synthesis of GBL can be done employing two methods which
include (i) hydrogenation of maleic anhydride (MA) and (ii)
dehydrogenation of 1,4-BDO. The former method has been
extensively used owing to the less cost of MA but the process
is disadvantageous because synthesis of MA emits CO2 which is
a greenhouse gas produced during oxidation of benzene and n-
butane. The latter process is economical as 1,4-BDO is
commercially manufactured by hydrogenation of acetylene
Oxidation of alcohols is a widely studied area in the field of
research. However, selective oxidation of alcohols not only
needs explicit oxidants and extreme reaction conditions but
also generates a huge amount of waste which is not in
accordance with the laws of green chemistry. Vapour phase
reaction is advantageous considering the fact that these are
solvent free reactions and the resultant products deliver
negligible impurities. Dehydrogenation of 1,4-butanediol (1,4-
BDO) is a prime reaction as it generates γ-butyrolactone (GBL),
which is the main precursor for synthesis of N-methyl-2-
and formaldehyde also popularly known as Reppe process2,3
.
pyrrolidone,
2-pyrrolidone,
N-vinyl-2-pyrrolidone,
polyvinylpyrrolidone, herbicides and rubber additives1. It can
also be considered as a prospective replacement for many
However, acetylene is generated from fossil fuels and is an
expensive raw material. Therefore, researchers have
developed an alternative route for the synthesis of 1,4-BDO
using renewable biomass like glucose, thereby making it an
economical and environmentally benign process2,4
.
Additionally, two molecules of hydrogen which are generated
on dehydrogenative cyclization of 1,4-BDO can be used as a
source of fuel. Various catalysts have been employed in
synthesis of GBL which includes transition metal based
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catalysts such as Cu/ZnO/Al2O3 , Cu-ZnO-ZrO2-Al2O3 ,Cu/MgO5, Copper nitrate trihydrate (Cu(NO3)2.3H2O) (M/s. Sigma Aldrich,
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DOI: 10.1039Z/Cin9cNJ0n3it0r6a7tKe
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Cu-Cr-Mn6, Cu-CaO-Na2O/SiO2 , as well as noble metal based USA), Ammonium ceric nitrate (NH4)2[Ce(NO3)6],
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catalysts such as Au/TiO2 and Au/Fe2O3 . These catalysts are hexahydrate (Zn(NO3)2.6H2O) (M/s. S.D. Fine Chemicals, India), were
however not very cost effective and are not abundantly purchased and used without further purification. γ-Al2O3, TiO2 and
available for usage, thereby paving way for synthesis and HZSM-5 were commercially purchased and used as received. SBA-
implementation of economical catalysts.
15 was synthesized following synthetic procedure published
On the other hand, supports play an active role in the selective elsewhere21, 22. Deionized water was used for the synthesis of all
synthesis of GBL. Acidic supports like Al2O3, Al2O3-SiO2, WO3 the catalysts.
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based catalysts, metal oxide based Ru catalysts generate Preparation of Cu/CeO2 (CC):
tetrahydrofuran (THF) as the selective product via dehydration Different copper based ceria catalysts with variation in copper
pathway whereas copper based catalysts with basic supports loading (5, 10, 15 and 20 wt.%) were synthesized using the
(MgO, ZnO) have been reported to selectively form GBL10. In traditional wet impregnation method. The required amount of
addition, the degree of dispersion of active components within copper nitrate trihydrate (Cu(NO3)2.3H2O) was added into a pre-
the catalyst system regulates its catalytic performance. Higher mixed solution of ammonium ceric nitrate (NH4)2[Ce(NO3)6] and
dispersion can pilot better catalytic activity which can be water. Further, the solution was heated to 65 °C with constant
achieved by selecting a feasible support satisfying the primary stirring in order to evaporate excess water. The resultant fine
requirement of a non-reactive active part of the catalyst and powder was subjected to drying at 100 °C for 12 h in an oven and
secondary requirement of high surface area. The reaction finally calcined in static air flow at 450 °C for 4 h with a ramping rate
thermodynamics and kinetic factor depends on the metal of 3 °C min-1. Catalysts thus obtained were designated as 5CC, 10CC,
support interaction of the catalyst which indirectly governs its 15CC and 20CC for 5, 10, 15 and 20 wt.% of copper loadings
catalytic activity. Ceria as a support has been used for various respectively and were subsequently characterized using various
reactions such as oxidation of soot11, water gas shift reaction12, analytical tools. Similar procedure was followed for the synthesis of
reduction of NO with NH313, synthesis of cyclic carbonates copper catalysts on TiO2, Al2O3, ZnO, ZSM-5, SBA-15 support
14
using glycol and CO2 and oxy-dehydrogenation of ethane15. matrices.
The selection of ceria as a support is convinced by the
tunability of its textural properties which is optimistic for the Characterization:
reaction and also because of its interaction with different Powder X-ray diffraction patterns of the catalysts were recorded on
metals13. Supportingly, copper has been used in various a Ultima-IV X-ray diffractometer (M/s. Rigaku Corporation, Japan)
reactions as an active metal due to its easily tunable surface using Ni filtered Cu Kα radiation (l = 1.5406 A°) with rate of 2° min-1
area, variation in particle size and dispersive nature16. Copper and a 2θ scan range of 10-80° at 40 kV and 30 mA. Crystalline
based catalysts have also been notably used in varied research phases were identified by comparison with the reference data from
areas like combustion of styrene17, oxidation of benzyl international centre for diffraction data (ICDD) files.
alcohol18, oxidation of butanol19 and hydrogenation of Surface area and pore size distribution analysis were conducted
benzaldehyde20.
with N2 at liquid N2 temperature (-196 °C) on a Belsorp-Max (M/s.
Herein, we report for the first time the utilization of copper Microtrac BEL, Japan.) for getting the multipoint surface area using
based ceria catalysts (5CC, 10CC, 15CC, 20CC) for the Brunauer Emmett and Teller (BET) analysis method and total
dehydrogenation of 1,4-BDO to GBL under vapour phase pore volume by Barrett-Joyner-Halenda (BJH) method. Prior to the
conditions with variation in copper loading. The different measurement, the samples were degassed at 200 °C for 2 h in order
copper based ceria catalyst have been prepared by wet to expel the inter layer moisture under vacuum control. Field
impregnation method and subsequently tested for emission scanning electron microscopy (FE-SEM) measurements
dehydrogenation of 1,4-BDO to GBL by varying the reaction were made using JEOL JSM-7100F, Singapore. Transmission Electron
temperatures and metal loading on ceria support. The stability Microscopy was used to check the interior architecture, SAED
of the catalyst with time on stream has also been analysed. pattern and lattice fringes of the material using TEM microscope
Additionally, a comparison has been done with copper (JEOL JEM-200CX). The accelerating voltage of the electron beam
supported over various supports like SBA-15, ZnO, TiO2, ZSM-5, for the microscope was set for 200 kV.
Al2O3 in order to determine the influence of copper addition The H2-Temperature programmed reduction (TPR) analysis was
on these supports on the catalytic activity. Also, a brief carried out in an indigenous instrument consisting of quartz reactor
summary of already reported catalysts has been shown in attached to a six-port valve attached with a thermal conductivity
order to point out the versatility of the present work. A detector (M/s Mayura Analyticals, India). Approximately 50 mg of
probable mechanism as reported in literature has also been the sample was loaded in the isothermal zone of a quartz reactor
illustrated for the selective dehydrogenation of 1,4-BDO to (i.d. = 6 mm, length = 300 mm) and subjected to pre-treatment at
GBL.
300 °C for 1 h with the heating rate of 10 °C min-1 in He flow to
facilitate the desorption of physisorbed water. After degassing, the
sample was cooled to 100 °C and the He gas was replaced with a
reducing gas (5% H2/Ar) with a flow rate of 30 mL min-1. The
temperature was linearly increased to 700 °C with a ramping rate of
10 °C min-1 and maintained at the same temperature for 0.5 h. The
Experimental
Materials:
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hydrogen consumption was monitored by standard GC software. BDOin is the amount of 1,4 BDO at inlet and BDOout is the amount of
The H2 uptake values were calculated using standard reference 1,4-BDO present in product mixture and YGBL is the yield of GBL.
value obtained by injecting known loop volume of H2 using six-port
View Article Online
DOI: 10.1039/C9NJ03067K
valve.
Results and Discussion
Additionally, measurement of percentage of copper dispersion, Structural and textural properties of catalysts
metal surface area and metal particle size was carried out using N2O BET surface area and pore size distribution: The textural properties
chemisorption in the above mentioned instrument equipped with obtained for 5CC, 10CC, 15CC, 20CC catalysts are summarized in
the Hayasep T column. In a typical analysis procedure, 100 mg of Table 1 along with the respective nitrogen sorption curves as
sample was loaded into quartz reactor and pre-treated at 300 °C for depicted in Fig. 1. The use of pristine ceria support without any
1 h in He flow. Later the sample was reduced at its appropriate copper adherence reveals Type-II isotherm (Fig. 1(a)). The addition
reduction temperature for 3 h in the presence of H2 flow. Then the of 5, 10, 15, 20 wt.% copper on ceria support shows Type-IV
sample was cooled to room temperature and N2O gas (5% N2O/He) isotherm which is characteristic feature of mesoporous materials
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is injected in pulses till the attainment of the saturation point.
(Fig. 1(b-e)). This shows that introduction of copper metal on the
Similarly, measurement of acidity and basicity of the catalysts were ceria support is responsible for the mesoporous nature of the 5CC
carried out using NH3 and CO2 temperature programmed catalyst (Fig. 1(b)). This mesoporosity is retained on further loading
desorption (TPD) analysis in the above mentioned instrument. Prior of copper species in the 10CC, 15CC, 20CC catalysts which can be
to desorption, catalysts were pre-treated in He flow for 1 h at 300 observed in the isotherms obtained (Fig. 1(c-e)). The steep curve
°C and cooled down to 100 °C in the He environment. Subsequently, observed in the adsorption isotherm corresponds to the capillary
catalysts were saturated with 5% NH3/He or 5% CO2 at 100 °C for condensation of pores23. Interestingly, there is decrease in the
0.5 h, followed by stripping with He for 0.5 h to remove the surface area for 5CC catalyst from 34 m2 g-1 to 14 m2 g-1. This shows
physisorbed NH3 and CO2 at the same temperature. Later, the that there is deposition of copper species onto the support matrix24.
temperature was raised from 100 to 700 °C with a ramping rate of Notably, on further increase in copper addition (10CC), the surface
10 °C min-1 and the desorbed gas was monitored with TCD.
area increases to 34 m2 g-1 signifying that copper on ceria support
The type of acidic and basic sites was determined using pyridine (10CC) prevents sintering25. With further addition of copper
adsorbed ATR-IR and isopropanol adsorbed ATR-IR spectra on a particles (15CC and 20CC), the surface area of the catalysts
Perkin Elmer ATR-IR instrument. In
a
typical experimental increases to 58 m2 g-1 and 74 m2 g-1, respectively. Additionally, the
procedure, the catalyst was subjected to degassing under vacuum increment in surface area of 10CC, 15CC and 20CC catalysts can also
at 200 °C for 3 h followed by treatment with dry pyridine and be very well explained based on increase in pore volume and fine
isopropanol respectively. Later, the samples were heated at 120 °C dispersion of copper particles on the ceria support26. Also, the
for 1 h in order to remove excess pyridine and isopropanol. After mesoporous nature of catalysts can be related to increase in
cooling the samples to room temperature, ATR-IR spectra of porosity of catalysts (5CC, 10CC, 15CC and 20CC) which can be
respective-adsorbed samples were recorded. In order to quantify clearly seen to be in accordance with the increase in pore volume26.
the deposition of coke on the catalyst surface thermogravimetric
analysis was performed using
instruments, USA).
a TA-Q500 series (M/s TA
Catalytic reaction:
Catalytic activity studies were performed in a fixed bed down flow
quartz reactor at atmospheric pressure. For a typical reaction, 0.5 g
of catalyst was loaded in the reactor and subjected to reduction
with H2 for 3 h at 280 °C. The reaction was performed within the
range of 240-300 °C using N2 (30 mL min-1) as an oxidant at
atmospheric pressure. 1,4-BDO was introduced by a liquid feed
pump (M/s. B. Braun, Germany) with a feed rate of 1 mL h-1. The
products were collected at regular intervals in an ice cold trap and
analyzed on a flame ionization detector (FID) equipped gas
chromatograph, GC-7820 A (M/s. Agilent, USA) using a capillary
column HP-5, 19091J-413 (30 m length, 0.32 mm inner diameter
and 0.25 µm film thickness).
The quantification of each component in the product mixture
was done by injecting a known amount of authentic sample (1,4-
BDO and GBL) and comparing the GC area of authentic sample with
that of the product mixture. The percentage conversion of 1,4-BDO
(CBDO) and percentage selectivity of GBL (SGBL) were calculated as:
CBDO= (BDOin- BDOout)*100/BDOin ; SGBL = YGBL*100/CBDO where,
Fig. 1. N2 sorption isotherms of Cu/CeO2 catalysts.
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The increase in surface area combined with the mesoporosity of the copper based ceria catalysts was performed and the VoiebwtaAirnticelde Odnalitnae
catalysts provide good adsorption sites for reactant molecules to is displayed in Fig. 2. The diffractogram asDsOhIo: 1w0n.10in39t/hCe9NFJi0g3.026(7aK)
gain access to these sites and resultantly leads to easy desorption of and Fig. 2(b) confirms the presence of ceria at 2θ values 28.47°,
32.98°, 47.60°, 56.44°, 59.25°, 69.95° and 77.45° in both calcined as
well as reduced catalysts. It can also be confirmed that ceria
X-ray Diffraction studies: The X-ray diffraction analysis for pristine particles in the
product molecules formed27.
ceria support, calcined copper based ceria catalysts and reduced
Table 1. Textural characteristics of Cu/CeO2 catalysts with different metal loadings.
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Sr. Catalyst Surface
Pore
volume
Pore
diameter
(nm)
Crystallite
size (nm)
H2 uptake
Cu metal
Cu particle
size (nm)
Cu
dispersio
n (%)
No.
area
(mmol g-1) surface area
(m2 g-1)
(m2 g-1) (cm3 g-1)
1
2
3
4
5
C
34
14
34
58
74
0.029
0.004
0.020
0.034
0.044
2.52
2.52
2.52
2.52
2.52
14.70
9.12
-
-
-
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5CC
4.7
7.6
7.3
12.4
30
56
65
32
1.11
1.21
1.55
4.15
90
86
67
25
10CC
15CC
20CC
12.42
6.06
7.20
catalyst exist in cubic system [ICDD: 65-5923] along with hkl values correspond to the highly dispersed copper molecules in the
of (111), (200), (220) and (311) in the crystal plane27. Interestingly,
the peaks corresponding to copper oxide (CuO) and copper are not
observed upto 20 wt.% copper loading signifying that the copper
species is highly dispersed in the catalyst system24.
However, peaks corresponding to CuO at 2θ: 35.42°, 38.61°, 61.50°
and 66.38° along with copper at 2θ: 43.35°, 49.85°, 77.68° are
observed for both 20CC calcined and 20CC reduced catalysts,
respectively. CuO particles in the calcined (20CC) catalyst system
exist in monoclinic phase [ICDD: 2-1040] with hkl values (002),
(111)28 and copper particles present in the reduced (20CC) catalyst
system exhibit cubic phase [ICDD: 3-1005] with hkl values (111)29.
Further, non-existence of CuO particles in the reduced (20CC)
catalyst suggests that on reduction the CuO particles are completely
diminished. Additionally, comparison of crystallite size suggests that
addition of copper particles on the support matrix decreases the
crystallite size. Hence, the decrease in crystallite size suggests that
increase in copper loading increases the crystallinity of the catalyst
system. This is due to the suppression in the growth of crystal which
is attributable to the introduction of copper species into ceria
support matrix27. Surprisingly, 10CC catalyst unveils higher
crystallite size (12.42 nm) when compared to 5CC (9.12 nm), 15CC
(6.06 nm) and 20CC (7.20 nm) catalysts as displayed in Table 1.
H2-temperature programmed reduction studies: The
evaluation of reduction behaviour of copper based ceria
catalysts was analyzed using the H2-TPR technique and the
resultant H2-TPR profiles are illustrated in Fig. 3. It is evident
from the graph that with increase in copper loading, the
reduction peaks for 5CC, 10CC, 15CC and 20CC shifts towards
the lower temperature region. This judgement can be justified
from the comparison of 5CC and 10CC catalysts suggesting that
the metal support interaction decreases with increase in
Fig. 2. XRD spectra of (a) calcined and (b) reduced CC
catalysts.
ceria support matrix as well as the bulk copper molecules 30, 31
.
copper loading and is also suggestive of enhanced dispersion
of copper species in the catalyst system30. The 5CC catalyst
showed two reduction peaks at 189 °C and 225 °C, which
The other catalysts (10CC, 15CC) exhibit single peak at 198 °C
and 209 °C, respectively which convinced us that the Cu2+
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species is finely dispersed within the ceria support matrix. This observation reasons out a clear indication for the absence
Further 20CC catalyst system shows the presence of shoulder of copper peaks in the XRD analysis upto 15wt.% addition of
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DOI: 10.1039/C9NJ03067K
peak at 184 °C along with a prominent peak at 205 °C which copper in the ceria support matrix. Additionally, it can also be
can be correlated with fine dispersion of Cu2+ species inferred that high dispersion is possibly due to weak metal
interacting strongly with ceria support at lower temperature support interaction of copper with ceria support matrix.
and also due to bulkier copper molecules present on the CeO2 Moreover, metal particle size also influences the rate of
support matrix 31. It can also be observed that with the dispersion. Hence, from the tabulated data it can be evidently
increase in copper loading, there is increase in the hydrogen seen that with the increase in addition of copper over ceria
consumption, suggesting that more amount of hydrogen support matrix, the copper particle size increases.
utilisation for reduction delivers more availability of copper The increase in metal particle size decreases the dispersion of
sites which possibly can enhance catalytic activity. The metal onto the support matrix and similar trend is observed
hydrogen consumption observed for 5CC, 10CC, 15CC and for all the aforementioned catalysts. 5CC catalyst exhibits
20CC catalyst systems are 4.7, 7.6, 7.3 and 12.4 mmol g-1, smaller copper particle size with 1.11 nm whereas 10CC
respectively. Thus, it can be concluded that this kind of catalyst shows a moderate particle size with 1.21 nm. With
dispersive behaviour combined with weak metal support further increase in copper loading to 15 wt.% and 20 wt.% in
interaction is responsible in governing the activity of these 15CC and 20CC catalysts, the particle size is seen to be 1.55 nm
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catalysts.
and 4.15 nm. The increase in the metal particle size with
increase in copper loading can be due to the agglomeration of
copper particles taking place on the support matrix which
resultantly decreases the dispersion of copper species on the
support matrix.
NH3 & CO2 temperature programmed desorption studies: The
reaction pathway for dehydrogenation reaction can be
governed by both acidic and basic properties of supported
metal catalysts32. NH3 and CO2-TPD analysis was carried out to
find the presence of acidic and basic sites along with the
nature of available adsorption sites on the surface of (5, 10,
15, and 20CC) catalyst systems. The obtained TPD profiles are
illustrated in Fig. 4. In NH3-TPD, the basic NH3 molecule
adsorbs on the acidic centers of catalyst surface, whereas in
CO2-TPD a slightly acidic CO2 adsorbs on the basic regions of
the catalytic system. The variation in the desorption
temperature is directly proportional to variation in acidity and
basicity of the catalyst surface33. Based on previous literature,
the prominence of acidity and basicity can be interpreted
based on the desorption peaks occurring at <300 °C, 300 °C-
500 °C and 500 °C. These peaks are attributed to weak,
intermediate and strong sites respectively24, 34. In continuation,
the NH3-TPD profiles as shown in Fig. 4(a), displays the
presence of NH3 desorption peaks at lower than 300 °C
suggesting that acidic sites in the catalyst system are present
towards lower acidic region. Also, increase in copper loading
displays increase in desorption temperature which explains
that the number of acidic sites increase with the increase in
copper loading (5CC-179 °C, 10CC, 15CC, 20CC-187 °C) on ceria
support. Additionally, the amount of NH3 consumed for 5CC,
10CC, 15CC and 20CC catalysts is 3.66 mmol g-1, 2.49 mmol g-1,
2.53 mmol g-1 and 2.61 mmol g-1, respectively. The obtained
results from NH3-TPD analysis indicate that copper addition
strongly influences the strength of surface acidic sites.
Fig.3. H2-TPR profiles (a) 5CC, (b) 10CC, (c) 15CC, (d)
20CC catalysts.
N2O Chemisorption studies: In order to determine extent of
copper dispersion, copper metal surface area and its particle
size, N2O chemisorption analysis has been carried out and the
respective results are tabulated in Table 1. As can be observed
from the table, with gradual increase in the copper content,
there is notable variation in surface properties of the catalysts.
With increase in copper loading in 5CC, 10CC and 15CC
catalysts, the metal surface area also increases. The metal
surface area for 5CC, 10CC and 15CC catalysts show values as
30 m2 g-1, 56 m2 g-1 and 65 m2 g-1, respectively. With further
increase in copper loading to 20 wt.% in 20CC catalyst, the
surface area decreases to 32 m2 g-1. This decrease shows that
when the amount of copper is greater than 15 wt.%, sintering
takes place on the catalyst surface and hence the metal
surface area in 20CC catalyst decreases. A general trend
suggested that the dispersion of copper kept on decreasing
with increase in copper loading. It can be observed that 5CC
catalyst shows 90% dispersion whereas 10CC, 15CC and 20CC
catalysts exhibit 86%, 67% and 25% dispersion, respectively.
Interestingly, it can be observed that catalysts also contain
surface basic sites as depicted in Fig .4(b). The CO2-TPD profile
for 5CC catalyst system display the existence of all three weak
(192 °C), moderate (427 °C) and strong (635 °C) basic sites.
With further increase in copper loading to 10 wt.%, 15 wt.%
and 20 wt.% in 10CC, 15 CC and 20 CC catalyst, the CO2
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desorption temperature increases which is a clear indication of IR spectra was recorded respectively and theViecwoAnrsticeleqOunelinnet
increase in basicity as seen in the respective graphs. spectrograms are shown in Fig. 5. Pyridine being a basic
DOI: 10.1039/C9NJ03067K
molecule reacts with the acidic sites. The spectra have been
recorded in the range of 1200-1800 cm-1. As shown in Fig. 5(a)
,
6
with the increase in copper content in the as-synthesized
catalyst systems (5, 10, 15 and 20CC), there is not much shift in
the bands observed. The peak around 1437 cm-1 and 1583 cm-1
corresponds to the ring vibrations arising from the co-
ordination of pyridine with Lewis acidic copper sites. Lewis
acid sites combined with Bronsted acid sites can also be
observed at 1484 cm-1 which is due to the co-ordination of
pyridinium ions with these sites. There is not much variation in
the intensities of peaks suggesting that the increase in copper
content does not alter the acidic sites. Also, the spectra is
suggestive of dual type of sites present in copper based ceria
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catalyst system22, 36, 37
.
Fig. 4. (a) NH3 and (b) CO2 TPD profiles of CC catalysts with
different metal loadings.
Interestingly, 10CC catalyst system shows the presence of
weak (194 °C) and strong (583 °C) basic sites. Furthermore,
prominent strong basic sites can be associated with (111)
facets of CuO crystal phase of CC catalysts35. In addition the
amount of CO2 consumed by 5CC, 10CC, 15CC and 20CC
catalysts is 1.24 mmol g-1, 1.53 mmol g-1, 0.49 mmol g-1 and
1.61 mmol g-1, respectively. Hence, based on literature reports
and the results obtained from CO2-TPD, it can be said that
these basic sites play a prime role in selective formation of GBL
whereas the acidic sites favour the formation of THF as
products.5,10 This also gives a probable explanation on the
formation of slight amount of THF during the course of
reaction as a by-product. The presence of strong basic sites
majorly allows the synthesis of GBL as the prime product. As a
concluding remark, the above mentioned NH3 and CO2-TPD
profiles of 5, 10, 15 and 20CC catalysts are indicative of
occurrence of amphoteric character of all the as-synthesized
catalyst systems.
Fig. 5. ATR-IR spectra of CC catalyst (a) Pyridine adsorbed (b)
IPA adsorbed probe molecules.
The nature and type of basic sites were determined using
isopropanol (IPA) probed ATR-IR spectra and the results are
displayed in Fig. 5 (b). The basic sites in the catalyst system
interact co-ordinatively with the acidic protons of C-H groups
in the IPA molecule. The spectrum was recorded in the band
ATR-IR analysis: In an attempt to determine the types of acidic
as well as basic sites, pyridine and isopropanol absorbed ATR-
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region of 2750-3100 cm-1. The relationship between basic sites with copper loading of 10 wt.% is represented inVFieiwg.Ar6ti,clewOhnilcinhe
and IPA can be determined by the change in frequencies exhibits the surface morphology of theDOasI:-1s0y.n10t3h9e/sCi9zNedJ03fr0e6s7hK
related to symmetric stretching of C-H and CH3 groups along 10CC catalyst. As can be inferred from Fig. 6(a-c), the FE-SEM
with asymmetric stretching of CH3 groups after the interaction micrograph of fresh 10CC exhibits dispersed spherical
of IPA with the catalyst surface. There is negligible change in morphology, which is a characteristic feature of copper and
the vibration frequencies of all the four catalysts with variation ceria based materials39. The average particle size is calculated
in addition of copper molecules. However, there is deviation to be between 15 to 17 nm as shown in Fig. 6(d). The
with respect to asymmetric stretching of CH3 groups. The 20CC elemental composition of the 10CC catalyst is determined by
catalyst system showed red shift (2968 cm-1) whereas 5CC, EDX and mapping and the obtained results are displayed in Fig.
10CC and 15CC catalysts exhibit blue shift in the asymmetric 6(e) and Fig. 6(f), respectively. From the figure, it can be
region (2972 cm-1). 5CC and 10CC catalysts also show blue shift clearly observed that only O (9.63%), Ce (80.15%) and Cu
(2930 cm-1) towards the symmetric stretching of CH3 group, (8.41%) elements are detected in 10CC fresh catalyst with no
whereas 15CC and 20CC catalysts exhibit red shift (2931 cm-1) other elements. This proves that copper particles are finely
in this region. This is due to the interaction of CH3 proton with dispersed on the surface of the ceria support matrix.
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TEM Analysis: A thorough examination was executed using
TEM and HR-TEM analysis for exploring the microstructural
architecture of the 10CC catalyst as shown in Fig. 7(a-d). It was
seen that the 10CC catalyst possesses spherical morphology
which is a characteristic silhouette exhibited by copper based
ceria materials.40 Additionally, this observation is well-
supported and in accordance with the results obtained from
FE-SEM analysis. Fig. 7(e) displays a typical high resolution
TEM image of the 10CC catalyst. The average particle size
based on HR-TEM analysis was calculated to be in the range of
7 nm. This observation confirms the highly crystalline nature of
the 10CC catalyst. The Lattice fringes with a d-spacing of 0.35
the basic site on the catalyst surface. There is however no
change in the symmetric stretching frequency of C-H groups of
IPA for all catalyst systems observed due to co-ordinative
interaction of acidic C-H proton with the basic site of the
catalyst38. With the increase in the copper loading there is
increase in intensities of asymmetric stretching peaks related
to CH3 group which is suggestive of the influence of copper
group in varying the basicity of catalysts. Hence, the above
explained interpretations convey that the overall synergistic
effect of Lewis basic as well as acidic sites is clearly depicted in
the catalyst systems.
Fig. 6(a-d). FE-SEM micrographs, (e) EDX analysis and (f) mapping of 10CC fresh catalyst.
nm was observed which corresponds to the (111)
crystallographic plane of ceria in the 10CC catalyst. Moreover,
the black patches seen in the TEM images (Fig. 7(a,b))
correspond to the presence of Cu in the 10CC catalyst. The EDS
FE-SEM Analysis: The activity studies carried out with 10 wt.%
copper based ceria catalyst showed better results hence, the
FE-SEM analysis was carried out for 10CC catalyst. The
morphological characteristics of copper based ceria catalysts
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analysis was performed to confirm this observation. As can be
clearly seen from Fig. 7(g) that 10CC catalyst comprises of Cu
element along with Ce and O elements. Fig. 7(f) displays SAED
pattern of the as-synthesized 10CC catalyst which confirms its
polycrystalline nature. This observation also provides
secondary support to the XRD results. The planes
corresponding to (111), (220) and (200) were observed for the
conversion of 1,4-BDO were GBL and tetrahydrofuran (THF).
The effect of temperature on the catalytic activity of copper
based ceria catalysts for their respective conversion and
selectivity and the graphical representation is shown in Fig.
8(a) and Fig. 8(b), respectively.
Fig. 8(a) shows that with gradual increase in temperature
there is a steady decrease in the conversion of all the
synthesized catalysts (5CC, 10CC, 15CC, 20CC). This
observation can be attributed to the carbon deposition or
agglomeration of copper particles in the CC catalysts5.
Consequently, their selectivity towards GBL formation tends to
decrease with increase in temperature (Fig. 8 (b)). This can be
attributed to the increase in the number of acidic sites in due
course of reaction at higher temperatures, which favours
formation of by-product (THF). With further increase in
temperature, less amount of 1,4-BDO gets converted which
can be related to agglomeration of copper particles occurring
View Article Online
DOI: 10.1039/C9NJ03067K
concentric rings in 10CC catalyst 41
.
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Catalytic activity study:
Effect of temperature and Cu loading on the catalytic activity:
After the successful characterization of the as-synthesized
catalysts, they were tested for their respective catalytic
behaviours. To begin with, dehydrogenation of 1,4-BDO was
carried out in vapour phase medium at various temperatures
viz. 240, 260, 280, 300 °C using 5CC, 10CC, 15CC, 20CC copper
based ceria catalysts. The major products obtained on
Fig. 7(a-d) TEM images of 10wt.% Cu/CeO2 catalyst, (e) HR-TEM image of 10wt.% Cu/CeO2 catalyst, (f) SAED
pattern of 10wt.% Cu/CeO2 catalyst and (g) EDS of 10wt.% Cu/CeO2 catalyst.
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at higher temperatures. As a result, surface availability of selectivity of GBL. The TOF values observed for VtiheweAcrtaictleaOlynslintse
DOI: 10.1039/C9NJ03067K
active sites decreases on which the reactant adsorbs which are represented in Table 2. The TOF values observed for 5CC,
indirectly prevents the conversion. Subsequently, deposition of 10CC, 15CC and 20CC catalysts are 3092 μmol sec-1 site-1, 4299
carbon from cracking of the reactant molecule may occur at μmol sec-1 site-1, 3442 μmol sec-1 site-1 and 6838 μmol sec-1
higher temperatures. Considering the above conditions, 240 °C site-1, respectively.
is regarded as the optimum temperature for carrying out This demonstrates that addition of copper metal to the
further studies. The effect of copper loading on the activity of catalyst system plays an effective role in governing the activity
CC catalysts has also been investigated and the obtained of catalysts. Interestingly, 10CC showed prominent results
results are listed in Table 2. Literature studies reported that among all the other catalysts. The increase in the catalytic
merely support materials are inactive towards selective activity of 10CC can be attributed to its high surface area and
dehydrogenation of 1,4-BDO42, 43. Additionally, on carrying out metal support interaction. Additionally, physicochemical
the reaction with bare ceria support, it revealed that bare properties like fine dispersion of the 10CC catalyst as observed
supports show less conversion of 1,4-BDO with around 4% and from XRD, TPR, N2O chemisorption and SEM data, contributes
selectivity towards GBL around 39%. In order to increase the immensely towards its higher activity. Furthermore, the
activity of support, different metals have been used. In this presence of weak and strong basic sites as confirmed from
regard, different amounts of copper loading: 5CC, 10CC, 15CC CO2-TPD, favours the selective formation of GBL when
and 20CC were duly synthesized, characterized and tested for compared to acidic sites which favours THF formation. For
their catalytic activity towards the dehydrogenation of 1,4- higher loadings of copper catalysts (15CC and 20CC), we
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BDO to GBL.
believe that sintering of copper particles lowers down their
From Table 2, it is notable that with the increase in copper respective catalytic activity towards the production of GBL.
loading from 5wt.% (5CC) catalyst to 10wt.% (10CC) catalyst, Secondarily, on comparing the surface area of 5CC, 10CC, 15CC
conversion of 1,4-BDO increases (35% to 93%). With further and 20CC catalysts, it was found that 5, 15 and 20CC catalysts
increase in the copper loading to 15wt.% (15CC) catalyst, the show a steep drop in catalytic activity which might be a result
conversion decreases to 87% which remains same for 20CC of the lesser surface area, which provides less area for
catalyst (Fig. 8). The selectivity of GBL shows similar trend and adsorption of reactant molecules. Thus, considering the data
resemblance in its behaviour with all the four catalyst systems towards catalytic activity, 10CC catalyst at 240 °C shows better
wherein the increase in copper loading invariably increases the catalytic activity and is regarded as the optimum catalyst to
carry out further studies.
Table 2. Activity of catalysts with different Cu loadings, various
supports for dehydrogenation of 1,4-BDO to GBL at 240 °C for 1h of
reaction.
Yiel
GBL
Sel.
(%)
TOF
(μmol/se
c/site)
Sr.
No
Conv.
(%)
THF Sel. d(%
(%)
Catalyst
CeO2
)
61
-
1
4
39
2
2
3
4
5
5CC
35
93
87
86
95
98
97
5
2
3
0
100
33
92
85
86
3092
4299
3442
6838
-
10CC
15CC
20CC
100
6
10CuTi
3
0
0
52
-
7
10CuZn
14
48
7
10CuSBA
-15
10CuAl
10CuZSM
-5
30
-
8
9
30
70
27
9
21
27
9
100
100
73
91
-
-
10
Fig. 8. (a) Effect of temperature with different copper loadings
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J. Name., 2013, 00, 1-3 | 9
on ceria for the conversion of 1,4-BDO for 1 h reaction, (b)
Effect of temperature with different copper loadings of ceria
catalysts towards selectivity of GBL after 1 h. Reaction
conditions: 0.5 g catalyst, 1 mL h- 1 1,4-BDO feed and 30CC min-1.
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DOI: 10.1039/C9NJ03067K
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Effect of supports on the catalytic activity of 10 wt.% copper
catalysts: The effect of various supports on the catalytic activity of
10wt.% copper catalysts is illustrated graphically in Fig. 9. It can be
clearly observed that supports like Al2O3 and ZSM-5 show 100%
conversion at all temperature whereas, supports like TiO2, ZnO
show much lower conversions due to their physicochemical
properties. Interestingly, the selectivity towards GBL shown by
these supports is comparatively low, owing to high acidic nature of
these materials. In order to determine and confirm the acidic
nature of the catalysts with various supports, NH3 and CO2-TPD
analysis was carried out and the results are graphically represented
in Fig. 10. Fig. 10(a) represents the NH3-TPD data and Fig. 10(b)
represents CO2-TPD data of the catalysts with 10 wt.% Cu supported
on Al2O3 (10CuAl), SBA15 (10CuSBA15), HZSM5 (10CuHZSM5), TiO2
(10CuTi) and ZnO (10CuZn), respectively. From the NH3-TPD profile
it can be clearly observed that 10CuAl, 10CuSBA15, 10CuHZSM5,
10CuTi and 10CuZn catalysts exhibit all three types of acidic sites
including weak, moderate and strong sites. The respective CO2-TPD
profiles of the above mentioned catalyst as shown in Fig. 10(b),
confirms that there are basic sites. However, the comparison of
both NH3 and CO2-TPD denotes that the amount of acidic sites are
more compared to the basic sites and as a result the catalysts
appear acidic in nature. This observation is accountable for the low
selectivity of GBL from the dehydrogenation of 1,4-BDO using
various supports.
Fig. 9. Effect of temperature with different supports on 10wt.%
of Cu for dehydrogenation reaction. (a) Conversion of 1,4-BDO
and (b) Selectivity of GBL.Reaction conditions: 0.5 g catalyst, 1
mL h-1 1,4-BDO feed and 30CC min-1 N2 gas flow.
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govern the catalytic activity 10 wt.% copper catalystsVwieiwthArstiuclpe pOonlrintes
like SBA-15, Al2O3,TiO2 and ZnO may have strong metal support
DOI: 10.1039/C9NJ03067K
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Fig. 11. The stability test for 10CC catalyst for the
dehydrogenation of 1,4-BDO to GBL. Reaction conditions: 0.5
g catalyst, 1mL h-1 1,4-BDO feed, 240 °C reaction temperature
and 30CC min-1 N2 gas flow.
interaction, high acidity, lower surface area, less dispersion of
copper particles which may result in decrease in catalytic activity of
Fig. 10. (a) NH3-TPD, (b) CO2 TPD and (c) H2-TPR profiles of
10wt.% Cu catalysts with different supports.
Secondly, extent of metal-support interaction, dispersion of copper
on the support matrix was determined by H2-TPR and the results
are displayed in Fig. 10(c). It can be clearly observed that the
reduction temperature observed for all the catalysts is higher than
the reduction temperature of Cu in CC catalysts. Thus confirming
that 10 wt.% Cu catalysts with different support have low dispersion
of Cu on the supports. With various factors mentioned above which
Fig. 12. (a) XRD Spectra of 10CC spent catalyst. (b) N2-
physisorption analysis of 10CC spent catalyst.
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10 wt.% Cu catalysts with different supports. Aforementioned,
considering all the facts 10CC is considered the best catalyst for
dehydrogenative cyclisation of 1,4-BDO.
attributed to the coke deposition on its surface which can be
View Article Online
confirmed from the EDX mapping of spent 1D0OCCI:U10c.1a0t3a9ly/Cst9.NTJh0i3s0a6ls7oK
concludes that during the course of the reaction the agglomeration
of the particles influence its catalytic activity. In case of 10CCU
spent catalyst, O (3.77%), Ce (69.15%), Cu (7.95%) and C (3.77%)
particles are present as can be observed from EDX analysis and
mapping of spent catalyst in Fig. 13(e-f). Also, carbon is the only
element detected in the sample along with Ce, Cu and O in the
10CCU spent catalyst. The mapping analysis depicts that vapour
phase reaction leads to the coke deposition on the surface of the
catalyst which accounts for the presence of carbon in the 10CCU
spent catalyst.
Time on stream studies: The elucidation of potential role of
catalysts is studied using time on stream analysis for 10CC catalyst
at 240 °C and the result is displayed in Fig. 11. Notably, with the
passing time, conversion decreases from 93% to 70%. About 25%
decrease in conversion is observed however, the selectivity (98%)
remains same throughout the run. Consequently, the conversion
observed after second hour decreases from 93% to 87% and similar
trend is observed for consecutive hours. The decrease in conversion
with time can be attributed to coke deposition on the catalyst
surface and also sintering of copper particles which can be observed
and confirmed from FE-SEM and EDX data. Additionally, XRD plot of
the used catalyst shows the presence of carbon deposition in the
rhombohedral phase (ICDD: 50-927) along with ceria (ICDD: 65-
5923) at 2θ values 43.47°, 50.50°, 74.35° over the catalyst surface
which is evident from Fig. 12(a). N2-physisorption analysis of spent
catalyst is suggestive of decrease in surface (24m2/g) area and the
presence of a type II isotherm (Fig. 12(b)) which demonstrates that
deposition of coke particles leads to decrease in porosity44.
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In order to explicate the formation of coke on the surface of 10CC
catalyst system thermogravimetric analysis was carried out for
spent 10CCU catalyst and the resultant thermogram is displayed in
Fig. 14(a). The thermogram clearly depicts deposition of coke on
the surface of 10CCU catalyst at around 500 °C24. The amount of
coke deposited can be accounted to 4% which is similar to the
results obtained in EDX analysis of spent catalyst. Initial drop in
weight percentage at 50 °C in the thermogram may be due to
expulsion of moisture present in the catalyst. The sole reason for
the drop in catalytic activity can be related to coke deposition and
we believe this may also be the reason why the catalysts shows
agglomeration after the catalytic run.
Secondly, in order to determine the surface morphology of 10CCU
spent catalyst FE-SEM analysis was carried out and the resulting
images are represented in Fig. 13(a-d). In case of spent 10CCU
catalyst, the spherical parental morphology is retained even after
being used. It can be observed that the particles on the surface of
the catalyst show agglomeration and there is simultaneous increase
in the average particle size (15 to 20nm) (Fig. 13(d)). This can be
Furthermore, TEM and HR-TEM analysis was performed to confirm
the deposition of carbon on the 10CCU spent catalyst surface as
displayed in Fig. 14(b). It can be clearly observed that the
characteristic spherical parent morphology of 10CC catalyst is well-
Fig. 13(a-d). FE-SEM micrographs, (e,f) EDX analysis and mapping of 10CCU spent catalyst.
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dehydrogenation over the copper surface to give 4-hydroxybutanal,
DOI: 10.1039/C9NJ03067K
along with interaction of reactant molecule (1,4-BDO) with the
preserved in the 10CCU spent catalyst. Notably, the images depict
the clear visible agglomeration of the Cu particles in the 10CCU
spent catalyst. Additionally, based on the HRTEM image carbon
deposition could be clearly observed in the lattice fringes of the
10CCU spent catalyst. Further, the EDS analysis also shows the
presence of carbon along with Cu, Ce and O. This observation
further provides secondary support to the TGA analysis of the
10CCU spent catalyst which also conveys that there was deposition
of carbon species on the 10CCU catalyst. The SAED pattern also
shows that the polycrystalline nature of the 10CC catalyst is
retained in the 10CCU spent catalyst.
View Article Online
10CC catalyst surface. The proton gets abstracted from one of the
hydroxyl groups by the basic sites of the 10CC catalyst. Secondly,
the hydride ion transfer results in the formation of highly unstable
4-hydroxybutanal intermediate. The latter step involves
hemiacetylation of 4-hydroxybutanal and finally undergoes
dehydrogenation to give GBL as the product. The initial part of this
step involves hemiacetylation of 4-hydroxybutanal to 2-
hydroxytetrahydrofuran (2HTHF). Later, the basic sites of the 10CC
catalyst as observed from CO2-TPD analysis and ATR-IR
spectroscopy abstracts the proton from the hydroxyl group to give
an intermediate. However, the charge transfer between oxide ion
of the intermediate and hydride ion transfer from the C-H group
generates the final product GBL. Resultantly, the formed product
(GBL) desorbs from the 10CC catalyst surface and closes the catalyst
cycle.
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Various researchers have elucidated the mechanistic pathway of
dehydrogenation of 1.4-BDO. The mechanism over catalytic
dehydrogenation of 1,4-BDO can be attributed as suggested by
Zhang et al.2, Ichikawa et al.3 and Huang et al.8. The plausible
mechanistic pathway for oxidative catalytic dehydrogenation of 1,4-
BDO is picturised in Scheme 1. As per the mechanism, the reaction
follows two steps. In the first step 1,4-BDO undergoes
Fig. 14(a). Thermogravimetric analysis of 10CC spent catalyst
used for dehydrogenation of 1,4-BDO to GBL.
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Fig. 14(b) TEM, HR-TEM, SAED pattern and EDS images of 10CCU spent catalyst.
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Scheme 1. Plausible mechanism of dehydrogenation of 1,4-BDO to GBL over CC catalysts.
The comparison of various reported catalytic systems along with
the present catalyst system towards dehydrogenation of 1,4-BDO Conclusions
has been summarised in Table 3. Reddy et al. reported the use of
Cu-Co/MgO, Cu/MgO for dehydrogenation of 1,4-BDO along with
Copper based ceria catalytic systems were synthesized
successfully by simple wet impregnation method. Selective
vapour phase dehydrogenation of 1,4-BDO to GBL was carried
out at various temperatures (240-300 °C) and different copper
loadings (5, 10, 15 and 20 wt.%) using 5CC, 10CC, 15CC, 20CC
catalysts and their influence on the catalytic activity was
studied. Catalytic activity tests confirmed that 10CC catalyst
was highly active at 240 °C for the selective dehydrogenation
reaction with 93% conversion and 98% selectivity. The
characterization studies confirmed that the cause for the
better activity of the catalyst systems was attributed to their
respective physicochemical properties. Namely, fine dispersion
of copper metal onto the ceria support, greater surface area
and basic nature of catalyst particles was responsible for
better catalytic activity. Additionally, the effect of supports like
TiO2, ZnO, Al2O3, SBA-15, ZSM-5 on the catalytic activity of
copper supported catalysts was also carried out and the results
have been elucidated in detail. Further screening of all the
synthesized catalysts along with a summarized comparison
table of reported catalysts showed that the copper based ceria
catalytic system exhibited the highest conversion and
selectivity for the aforementioned reaction due to its highly
basic nature. The stability test using time on stream analysis
suggested that the catalyst activity was stable for 7 h with
about 23% decrease in conversion, however, the selectivity
remained same. The decrease in the activity of copper based
ceria (10CC) catalyst was attributed to the coke deposition,
the coupling reaction of 1,4-BDO with hydrogenation of various
reactants at 250 °C and atmospheric pressure (Table 3, Entries 1-5).
The reactions gave conversion ranging from 87% to 99% and
selectivity ranging from 98-100%. Ichikawa et al. reported the use
of Cu-ZnO-ZrO2-Al2O3 for dehydrogenation of 1,4-BDO (Table 3,
Entry 6). The reaction was carried out at 240 °C and atmospheric
pressure in order to obtain a conversion of 84% and selectivity of
98%. Various authors tried dehydrogenation of 1,4-BDO with
different catalysts in liquid phase medium. Huang et al. carried out
liquid phase reaction of 1,4-BDO using Au/TiO2 and Au/Fe2O3 at 140
°C. 1.25 MPa pressure (Table 3, Entries 10-11). The conversion
obtained was 95-99% with 99-100% selectivity. Ichiki et al. reported
the use of Cu-Cr-Mn in liquid phase dehydrogenation of 1,4-BDO at
230 °C and 0.4 MPa pressure (Table 3, Entry 7). The conversion
obtained was 99% and selectivity was 97%. Various other catalysts
were reported for dehydrogenation of 1,4-BDO at different
temperature and pressures which showed good to low selectivity
towards GBL formation (Table 3, Entries 8-9, 12-14). These already
reported reactions either used promoters or were carried out at
high temperatures. The present work was performed using Cu/CeO2
catalysts at 240 °C at atmospheric pressure giving a conversion of
93% and selectivity of 98%. The key to obtain better selectivity
towards the GBL is the presence of basic sites in the catalysts. The
performance of the present work without the use of promoter and sintering of copper particles and decrease in surface area.
under low temperature condition proves the efficiency of the
present catalyst system with the reported literature.
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The authors thank Prof. Geetha R. Balakrishna, Director,
DOI: 10.1039/C9NJ03067K
CNMS, Jain University, Bangalore, India and Head of
department, I & PC division, IICT, Hyderabad, India for their
constant support. The authors thank Nano Mission, DST,
Government of India, for financial support SR/NM/NS-
20/2014.
View Article Online
.
Table 3. Comparison of different catalyst systems for
Sr.
No.
Catalyst
Temp. Press.
Conv.
(%)
Sel.
(%)
Ref.
(°C)
(atm)
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1
Cu-
Co/MgO
250
1
95
87
95
96
99
84
99
100
100
99
95
94
86
99
93
98
100
96
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99
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98
100
99
0
10
5
References
1. Y. L. Zhu, J. Yang, G. Q. Dong, H. Y. Zheng, H. H. Zhang, H. W.
Xiang and Y. W. Li, Applied Catalysis B: Environmental, 2005, 57,
183-190.
2. B. Zhang, Y. Zhu, G. Ding, H. Zheng and Y. Li, Applied Catalysis A:
General, 2012, 443-444, 191-201.
3. N. Ichikawa, S. Sato, R. Takahashi, T. Sodesawa and K. Inui,
Journal of Molecular Catalysis A: Chemical, 2004, 212, 197-203.
4. D. W. Hwang, P. Kashinathan, J. M. Lee, J. H. Lee, U. H. Lee, J. S.
Hwang, Y. K. Hwang and J. S. Chang, Green Chemistry, 2011, 13,
1672-1675.
5. K. Hariprasadreddy, R. Rahul, S. Sreevardhanreddy, B. Davidraju
and K. Ramarao, Catalysis Communications, 2009, 10, 879-883.
6. K. M. T. Ichiki, S. Suzuki, H. Ueno and K. Kobayashi, US Patent
No. 5210229, 1993.
7. H.J. Mercker, F. F. Pape, J. Simon, A. Henne, M. Hesse, U.
Kohler, R. Dostalek, C. F. Erdbrugger and D. Kratz, US patent No.
6093677, 2000.
8. J. Huang, W. Dai, H. Li and K. Fan, Journal of Catalysis, 2007,
252, 69-76.
9. J. Huang, W. L. Dai and K.Fan, Journal of Physical Chemistry C,
2008, 112, 16110-16117.
10. K. H. P. Reddy, N. Anand, P. S. S. Prasad, K. S. R. Rao and B. D.
Raju, Catalysis Communications, 2011, 12, 866-869.
11. M. Piumetti, S. Bensaid, N. Russo and D. Fino, Applied Catalysis
B: Environmental, 2015, 165, 742-751.
12. Qi Fu, H. Saltsburg and M. F. Stephanopoulos, Science, 2003,
301, 935-938.
13. C. Tang, H. Zhang and L. Dong, Catalysis Science & Technology,
2016, 6, 1248-1264.
14. K. Tomishige, H. Yasuda, Y. Yoshida, M. Nurunnabi, B. Li and K.
Kunimori, Green Chemistry, 2004, 6, 206-214.
15. R.X. Valenzuela, G. Bueno, A. Solbes, F.Sapiña, E.Martínez and
V. C. Corberán, Topics in Catalysis, 2001, 15, 481-488.
16. N. Haddad, A. Saadi, A. Löfberg, R. N. Vannier, E. Bordes-Richard
and C. Rabia, Journal of Molecular Catalysis A: Chemical, 2015,
396, 207-215.
17. H. Pan, M. Xu, Z. Li, S. Huang and C. He, Chemosphere, 2009, 76,
721-726.
18. C. D. Pina, E. Falletta and M. Rossi, Journal of catalysis, 2008,
260, 384-386.
19. J. N. Keuler, L. Lorenzen and S. Miachon, Applied Catalysis A:
General, 2001, 218, 171-180.
20. T. B. Jayesh, K. Itika, G. V. Ramesh Babu, K. S. Rama Rao, R. S.
Keri, A. H. Jadhav and B. M. Nagaraja, Catalysis
Communications, 2018, 106, 73-77.
2
Cu/MgO
250
250
250
250
240
1
3
Cu-
Co/MgO
1
45
46
47
3
4
Cu/MgO
1
5
Co-
Cu/MgO
1
6
Cu-ZnO-
ZrO2-Al2O3
Cu-Cr-Mn* 230
1
7
0.4
0.3
1
6
8
Cu/ZnO/Al 240
2O3
1
9
Cu-CaO-
Na2O/SiO2
210
140
140
225
350
240
240
7
*
10
11
12
13
14
15
Au/TiO2
1.25
1.25
1.5
1
8
*
Au/Fe2O3
9
ZSM-5*
ZrO2
42
43
2
0
Cu-
Ba/SiO2
1
100
98
Cu/CeO2
1
Pres
ent
wor
k
*:pressure in MPa
dehydrogenation of 1,4-BDO.
Conflicts of interest
The authors state that there are no conflicts to declare.
21. D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F.
Chmelka and G. D. Stucky, Science, 1998, 279, 548-552.
22. S. S. Enumula, K. S. Koppadi, V. R. Babu Gurram, D. R. Burri and
S. R. Rao Kamaraju, Sustainable Energy & Fuels, 2017, 1, 644-
651.
Acknowledgements
16 | J. Name., 2012, 00, 1-3
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Page 17 of 18
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Please do not adjust margins
Journal Name
23. I. Kainthla, G. V. Ramesh Babu, J. T. Bhanushali, R. S. Keri, K. S.
Rama Rao and B. M. Nagaraja, New Journal of Chemistry, 2017,
41, 4173-4181.
24. I. Kainthla, G. V. R. Babu, J. T. Bhanushali, K. S. R. Rao and B. M.
Nagaraja, Journal of CO2 Utilization, 2017, 18, 309-317.
25. B. M. Nagaraja, C. H. Shin and K. D. Jung, Applied Catalysis A:
General, 2013, 467, 211-223.
ARTICLE
1
2
3
4
5
6
7
8
View Article Online
DOI: 10.1039/C9NJ03067K
9
26. Y. Liu, K. Fang, J. Chen and Y. Sun, Green Chem., 2007, 9, 611-
615.
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
27. H. Zhu, Y. Chen, Z. Wang, W. Liu and L. Wang, RSC Advances,
2018, 8, 14888-14897.
28. T. B. Siregar and N. A. S. Amin, Jurnal Teknologi, 2006, 44(F), 69-
82.
29. E. Shaaban, H. Hassan, S. Aly, H. A. Elshaikh and M. Mahmoud,
Applied Physica A, 2016, 122, 722-730.
30. Z. Jiang, Z. Hao, J. Yu, H. Hou, C. Hu and J. Su, Catalysis Letters,
2005, 99, 157-163.
31. M. Lykaki, E. Pachatouridou, S. A. C. Carabineiro, E. Iliopoulou,
C. Andriopoulou, N. Kallithrakas-Kontos, S. Boghosian and M.
Konsolakis, Applied Catalysis B: Environmental, 2018, 230, 18-
28.
32. H. P. R. Kannapu, Y.-W. Suh, A. Narani, V. Vaddeboina, D. R.
Burri and R. R. Kamaraju Seetha, RSC Advances, 2017, 7, 35346-
35356.
33. M. Lewandowski and Z. Sarbak, Fuel, 2000, 79, 487-495.
34. Z. Y. Zakaria, J. Linnekoski and N. A. S. Amin, Chemical
Engineering Journal, 2012, 207-208, 803-813.
35. A. H. Jadhav, D. Prasad, H. S. Jadhav, B. M. Nagaraja and J. G.
Seo, Energy, 2018, 160, 635-647.
36. S. S. Enumula, V. R. B. Gurram, R. R. Chada, D. R. Burri and S. R.
R. Kamaraju, Journal of Molecular Catalysis A: Chemical, 2017,
426, 30-38.
37. Y. L. Yang and Y. Kou, Chemical Communications, 2004, 226-227.
38. T. Komanoya, K. Nakajima, M. Kitano and M. Hara, The Journal
of Physical Chemistry C, 2015, 119, 26540-26546.
39. W. Liu, X. Liu, L. Feng, J. Guo, A. Xie, S. Wang, J. Zhang and Y.
Yang, Nanoscale, 2014, 6, 10693-10700.
40. S. W. X. Zheng, X. Wang, S. Wang, X. Wang and S. Wu, Materials
Letters 2005, 59, 2769-2773.
41. H. M. O. Amadine, K. Abdelouhadi, A. Fihri, S. El Kazzouli, C. Len,
A. El Bouari and A. Solhy, Journal of Molecular Catalysis A:
Chemical, 2014, 395, 409-419.
42. M. Aghaziarati, M. Kazemeini, M. Soltanieh and S. Sahebdelfar,
Industrial & Engineering Chemistry Research, 2007, 46, 726-733.
43. A. Igarashi, S. Sato, R. Takahashi, T. Sodesawa and M. Kobune,
Catalysis Communications, 2007, 8, 807-810.
44. I. Kainthla, V. R. B. Gurram, J. T. Bhanushali, S. R. R. Kamaraju, R.
S. Keri, S. W. Gosavi, A. H. Jadhav and B. M. Nagaraja, Catalysis
Letters, 2018, 148, 2891-2900.
45. H. P. R. Kannapu, Y.-W. Suh, A. Narani, D. R. Burri and R. R.
Kamaraju Seetha, Catalysis Letters, 2016, 147, 90-101.
46. K. H. P. Reddy, Y.-W. Suh, N. Anand, B. D. Raju and K. S. R. Rao,
Catalysis Communications, 2017, 95, 21-25.
47. H. P. R. Kannapu, C. K. P. Neeli, K. S. R. Rao, V. N. Kalevaru, A.
Martin and D. R.Burri, Catalysis Science & Technology, 2016, 6,
5494-5503.
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Graphical Abstract
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Highlights
1. Copper based ceria catalysts were synthesized for dehydrogenation of 1,4-BDO to
GBL.
2. Effect of supports on the catalytic activity of cu supported catalysts was also
determined.
3. Copper based ceria catalysts exhibited conversion of 93% and 98% selectivity.
4. The catalysts showed stable activity upto 7 h with time.