Efficient and sustainable Co3O4 nanocages based nickel catalyst: A suitable platform for the synthesis of quinoxaline derivatives

Article abstract of DOI:10.1016/j.mcat.2021.111454

Engineered nanocages have emerged at the forefront of nanomaterial investigation as they possess tremendous potential to boost key chemical processes owing to their hollow architectures that can help in achieving high reactivity. With an intention to make profitable use of their morphological features guided chemical activity, we developed dispersable Co₃O₄ nanocages decorated with nickel nanoparticles for accessing a broad spectrum of pharmaceutically and biologically active N-heterocyclic quinoxaline nuclei using α-dicarbonyls and 1,2-diamines as precursor reagents. For designing Co₃O₄ nanocages, we employed a simple and scalable method involving Kirkendall effect in which thermal decomposition of Co₃[Co(CN)₆]₂ was carried out thereafter, nanocages were loaded with Ni nanoparticles to obtain the final Ni@Co₃O₄ catalyst. Results revealed that Ni@Co₃O₄ catalyst possesses immense potential to accelerate condensation of diamines and di-carbonyls in absence of any additives under mild reaction conditions. The superior catalytic efficiency has been attributed to the hollow architecture of the nanocatalyst comprising of abundant catalytic sites. This protocol exhibits several remarkable attributes such as mild reaction conditions outstanding functional group tolerance, high yield, immense durability and reusability for six subsequent runs.

Full text of DOI:10.1016/j.mcat.2021.111454

Molecular Catalysis 504 (2021) 111454
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.journals.elsevier.com/molecular-catalysis
Efficient and sustainable Co3O4 nanocages based nickel catalyst: A suitable
platform for the synthesis of quinoxaline derivatives
Aditi Sharmaa, Ranjana Dixitb, Shivani Sharmaa, Sriparna Duttaa, Sneha Yadava,
,
,
Bhavya Aroraa, Manoj B. Gawandec *, Rakesh K. Sharmaa *
a Green Chemistry Network Centre, Department of Chemistry, University of Delhi, Delhi, 110007, India
b Department of Chemistry, Ramjas College, University of Delhi, Delhi, 110007, India
c Department of Industrial and Engineering Chemistry, Institute of Chemical Technology Mumbai, Marathwada, Jalna 431203, India
A R T I C L E I N F O
A B S T R A C T
Keywords:
Engineered nanocages have emerged at the forefront of nanomaterial investigation as they possess tremendous
potential to boost key chemical processes owing to their hollow architectures that can help in achieving high
reactivity. With an intention to make profitable use of their morphological features guided chemical activity, we
developed dispersable Co3O4 nanocages decorated with nickel nanoparticles for accessing a broad spectrum of
Nanocages
Ni@Co3O4composite
Catalyst
Reusability
Quinoxalines
pharmaceutically and biologically active N-heterocyclic quinoxaline nuclei using α-dicarbonyls and 1,2-diamines
as precursor reagents. For designing Co3O4 nanocages, we employed a simple and scalable method involving
Kirkendall effect in which thermal decomposition of Co3[Co(CN)6]2 was carried out thereafter, nanocages were
loaded with Ni nanoparticles to obtain the final Ni@Co3O4 catalyst. Results revealed that Ni@Co3O4 catalyst
possesses immense potential to accelerate condensation of diamines and di-carbonyls in absence of any additives
under mild reaction conditions. The superior catalytic efficiency has been attributed to the hollow architecture of
the nanocatalyst comprising of abundant catalytic sites. This protocol exhibits several remarkable attributes such
as mild reaction conditions outstanding functional group tolerance, high yield, immense durability and reus-
ability for six subsequent runs.
1. Introduction
earth-abundant based catalytic materials such as transition-metal chal-
cogenides, oxides, carbides, nitrides and phosphide [9–12]. Recently,
Currently, nanocatalysis has blossomed as an exciting and integral
area of nanoscience as it allows prospects of alteration in the chemical
composition, dimensions as well as morphology of materials while also
enhancing chemical reactivity. The possibility of engineering the
structure of nanocatalysts via the cooperative integration of discrete
nano objects has particularly provided remarkable opportunities for
designing new catalytic systems with remarkable efficacy [1,2].
Amongst the several accomplishments, the introduction of solid sup-
ported heterogeneous nanoscaled catalysts wherein homogeneous metal
complexes are anchored onto the surface of suitable support matrices
has proven to be highly promising especially in view of environmental
cognizance and economic viability [3–8]. Until now most of the het-
erogenized catalysts documented in literature comprise of noble metals
that are not only toxic but also expensive, which restrict their applica-
tions. This has necessitated the exploration of sustainable alternatives
and sincere efforts in this regard have led to the emergence of
metallic cobalt oxide Co3O4 based three-dimensional (3D) hollow
porous nanocages have emerged as a competent catalyst support for
developing heterogeneous catalytic systems owing to their unique fea-
tures such as low density, high surface area-to-volume ratio, nontoxicity,
good accessibility, cost-effectiveness and recyclability which are also
desirable properties of a green catalyst [13–15]. In addition, for
designing versatile catalyst, Co3O4 nanocages permit the integration of
multiple catalytic active sites owing to their hollow assembly, intensi-
fying their role in various important organic reactions. However, the
efficacy of cobalt oxide hybrid catalyst remains unexplored for obtaining
quinoxalines that constitute an essential class of aromatic N-heterocy-
cles. These important moieties have enticed significant enthusiasm of
the scientists/material chemists by bestowing a broad range of anti-
bacterial, antiviral, antituberculotic, anti-inflammatory agents, kinase
inhibiting and other properties comprising more than 50% of all drug
constituents in therapeutic use. [16–19] Moreover, these compounds
* Corresponding authors.
E-mail addresses: mb.gawande@marj.ictmumbai.edu.in, manoj.gawande@upol.cz (M.B. Gawande), mb.gawande@marj.ictmumbai.edu.in (R.K. Sharma).
https://doi.org/10.1016/j.mcat.2021.111454
Received 31 July 2020; Received in revised form 23 November 2020; Accepted 29 January 2021
Available online 26 February 2021
2468-8231/© 2021 Published by Elsevier B.V.

A. Sharma et al.
Molecular Catalysis 504 (2021) 111454
have also carved out a unique niche in material science due to their
widespread applicability in fabricating luminescent compounds, organic
dyes and building blocks for obtaining organic semiconductors rigid
subunits of macrocyclic receptors for molecular recognition and chem-
ically controllable switches [20–26]. Owing to the exceptional profile of
quinoxaline motifs, various research groups have paid huge attention
towards developing a multitude of catalytic systems for their construc-
tion through oxidative cyclization of N-arylenamines heteroannulation
of nitroketene N,S-arylaminoacetals and 1,2-diketones, reductive cycli-
zation of 2-nitroanilines and 1,2-diketones, dehydrogenative coupling of
1,2-diaminobenzene, oxidation–condensation of reaction of vicinal diols
or keto alcohols with diamines and 1,2-diols and coupling reactions of
o-phenylenediamine with terminal alkynes [27–36]. Nevertheless,
several inevitable drawbacks have been encountered in these conven-
tional methodologies such as intricate reaction procedures, use of
expensive and toxic reactants, high catalyst loading, long reaction time,
unsatisfactory yields, use of precious metals and poor catalyst recycla-
bility which pose detrimental environmental as well as economic issues
[37–39]. Therefore, in search of improved synthetic methodologies,
recyclability up to six cycles without significantly affecting the structure
or the texture of the catalyst. The recyclability and leaching tests helped
in ascertaining the durability of the Ni@Co3O4 nanocages signifying
stable active sites that offered better steric control over reaction in-
termediates. It is envisioned that the obtained results from the present
study would infuriate a spark of interest amongst the researchers for
translation of small scale synthesis to industrial scale processes.
2. Results and discussion
Scheme 1 depicts the preparation of Ni@Co3O4 catalyst. Firstly,
Co3[Co(CN)6]2 was fabricated following the protocol already reported
in literature by Chen and co-workers [55]. Thereafter, calcination of
precursor nanocubes was carried out at 400 ◦C for 1 h. Further, nickel
nanoparticles were prepared by the methodology reported by Bour-
emana [56] which were then loaded on Co3O4 nanocages via ultra-
sonication to get the final nanocatalyst.
Keeping in mind the importance of sustainable methods, ease of
recoverability and reusability, we herein describe cobalt oxide nanoc-
ages supported nickel nanoparticles for accomplishing the successful
synthesis of quinoxaline and its derivatives. The superb catalytic per-
formance of the developed catalyst can be attributed to hollow assembly
that offers nanoreactor confinement that resulted in good to excellent
yield of the target products. The structure of resulting nanocatalyst is
confirmed by various microscopic and spectroscopic techniques such as
FT-IR, TEM, SEM, XPS, XRD, ED-XRF, AAS and EDS.
catalytic condensation of α-diketones and 1,2-diamines has appeared as
an attractive strategy for already reported ones which often employ
several transition metal catalysts including ZrCl4, MnCl2, TiO2,
Zn2+-K10-clay, MIL-101-Cr–NH–RSO3H, H14[NaP5W30O110]/SiO2,
InCl3, ZrO2-Al2O3 etc. [28,36,40–44]. Although, these aforementioned
protocols unfold several remarkable features, but the intrinsic diffi-
culties arising due to the separation of catalyst from reaction system and
reusability of homogeneous catalysts, inescapably add to cost and even
render its bleak commercial utility due to presence of these metal resi-
dues in product stream. Therefore, there is a need to design sustainable
and cost-effective catalytic systems which can readily overcome the
challenges associated with homogeneous catalysis and can be efficiently
employed for the construction of quinoxaline moieties.
2.1. Catalyst characterizations
2.1.1. FT-IR spectroscopy
The FT-IR spectrum of Co3[Co(CN)6]2 illustrates significant absorp-
tion peak at 2172 cmꢀ 1 due to stretching vibrations of C N bond, while
–
–
–
Our quest for designing sustainable nanocatalytic protocols [45–54]
has led to the development of 3D Co3O4 nanocages which have been
designed using kirkendall effect involving the thermal decomposition of
precursor Co3[Co(CN)6]2 nanocubes followed by its decoration with Ni
nanoparticles. The developed 3D nanocatalyst prove beneficial for
expediting the synthesis of quinoxalines which are potentially useful
precursors for pharmaceutical and synthetic materials within a lesser
time period with additional prospects of ready recovery and excellent
emergence of absorption bands at 1608 and 459 cmꢀ 1 can be attributed
– –
to O H O scissor bending of water molecules and Co–C stretching
vibration mode respectively (Fig. 1) [57–59]. Thereafter, calcination of
nanocubes can be validated by the presence of peak at 1389 cm-1 which
corresponds to the NO3- and bands at 663 and 559 cmꢀ 1 associated with
the Co-O vibrations [60]. Further, anchoring of nickel nanoparticles
onto the surface of nanocages is verified by the decrease in intensities of
the absorption peaks [61].
Scheme 1. Synthetic procedure for the formation of Ni@Co3O4 nanocatalyst.
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A. Sharma et al.
Molecular Catalysis 504 (2021) 111454
2.1.3. SEM and TEM
The results obtained from SEM analysis clearly exhibit that Co3[Co
(CN)6]2 has well defined cubic shape with smooth facets which indicate
single crystal like feature of synthesized nanocubes. Further, negligible
changes were observed in Co3O4 as compared to Co3[Co(CN)6]2 after
calcination suggesting that shape of these cages does not change and
consistent with nanocubes, but surface conditions of Co3O4 became
rougher than those of Co3[Co(CN)6]2 (Fig. 3). Moreover, Ni@Co3O4
possesses hollow structures with loaded Ni nanoparticles (Fig. S1)
providing catalytically active sites for concerned condensation reaction
of α-diketones and o-phenylenediamines. A representative TEM micro-
graph of precursor Co3[Co(CN)6]2 complex further verifies polyhedral
morphology with an average size of about 65 nm. It is also noticed that
the morphology is preserved even after post annealing treatment and
surface modification via decoration of nickel nanoparticles onto cubes
(Fig. 4) [68]. In addition, SAED (Selected area electron diffraction)
pattern of nanocatalyst shows sharp white spotty diffraction rings
indicating polycrystalline nature of particles (Fig. 4d).
2.1.4. XPS
Fig. 1. FT-IR spectra of (a) Co3[Co(CN)6]2 (b) Co3O4 and (c) Ni@Co3O4
XPS measurements further revealed the elemental compositions and
valence states of Ni@Co3O4 nanocatalyst displayed in the Ni and Co 2p
core-level XPS spectra (Fig. 5). Ni@Co3O4 nanocatalyst showed two
typical primary peaks from Co with two spin-orbit doublets of Co 2p3/2
and 2p1/2 (Fig. 5b). The two peaks of Co 2p3/2 spectrum of Ni@Co3O4
appeared at 778.79 and 780.52 eV, which fitted to Co3+ (778.79 eV)
and Co2+ (780.52 eV) [69–71]. Additionally, the two peaks of Co 2p1/2
spectrum of Ni@Co3O4 appeared at 794.08 and 795.81 eV, represented
to Co3+ (794.08) and Co2+ (795.81) with a clear split spin-orbit
component (Δ metal =15.29 eV). The Co 2p peaks of the Ni@Co3O4
exhibit two weak satellite peaks centred at about 785.36 and 802.39 eV,
which indicated that the Co atoms were mostly in the 3+ state (Fig. 5b).
The Ni 2p core-level spectrum shows two intense peaks at around
~854.93 and 872.63 eV binding energies, attributed to Ni 2p3/2 and Ni
2p1/2, respectively, accompanied by those of their corresponding satel-
lites at around ~ 860.15 and 879.88 eV (Fig. 5c). These peaks are
attributed to Ni (2+) in the form of oxide and hydroxide phases. Addi-
tionally, a peak located at 852.32 eV in Ni 2p3/2 and 869.53 Ni 2p1/2
indicates that the metallic nickel (0) phase is present with split spin-orbit
component (Δmetal =17.7 eV) [72–74] (Fig. 5c). In Fig. 3d, the peak at
528.75 eV belonged to (typical metal-oxygen bonds) the lattice O2ꢀ in
Ni doped Co3O4, whereas the peak at 530.73 eV demonstrates the ex-
istence of hydroxyl groups.
nanocatalyst.
2.1.2. X-ray diffraction studies
XRD pattern of Co3[Co(CN)6]2 exhibits intense and sharp charac-
teristic peaks at 17.35◦, 24.65◦, 35.05◦, 39.35◦, 43.3◦, 50.45◦, 53.78◦
56.7◦, 65.7◦ and 68.3◦ which correspond to (200), (220), (400), (420),
(422), (440), (600), (620), (640) and (642) planes respectively (Fig. 1a).
All perceived XRD peaks are in good agreement with pure face-centered
cubic (fcc) phase of Co3[Co(CN)6]2.nH2O (JCPDS: 77–1161) with an
Fm3m system (Fig. 2a). [62,63] Further, thermal decomposition of
precursor of nanocubes results in the formation of Co3O4 nanocages
which is well confirmed with the appearance of diffraction values at
18.57◦, 31.34◦, 36.87◦, 38.31◦, 44.84◦, 55.82◦, 59.36◦ and 65.28◦
assigned to the (111), (220), (311), (222), (400), (422), (511) and (440)
planes of face-centred cubic (fcc) Co3O4; respectively [planes of spinel
Co3O4 JCPDS Card no. 42-1467] (Fig. 2b) [64,65] whereas Ni doped
Co3O4 showed additional peaks at 2θ values of 44.6◦, 51.7◦ and 76.5◦
that can be indexed to (111), (200) and (220) planes Ni@Co3O4 nano-
composite. New peaks confirm successful anchoring of nickel nano-
particles over Co3O4 nanocages (Fig. 2c). [66,67]
2.1.5. Elemental and compositional analysis
Chemical composition of Ni@Co3O4 nanocomposite was studied
through EDS and ED-XRF spectroscopy. Ni@Co3O4 clearly shows pres-
ence of elements Co, O and Ni in elemental mapping images which
provides evidence for successful decoration of nickel particles onto
surface of cobalt oxide nanocages (Fig. S2). In addition, EDS survey
spectra displays elements Co, Ni and O confirming high purity of
Ni@Co3O4 catalyst (Fig. S3). Further, appearance of nickel peak in ED-
XRF spectrum of Ni@Co3O4 also authenticates successful metalation of
Co3O4 nanocages (Fig. S4). Consequently, amount of nickel present in
nanocatalyst was estimated through AAS and it was found that
0.427 mmol/g of nickel is present in the catalyst.
2.2. Catalytic activity tests
2.2.1. Optimization of reaction parameters
To examine efficiency of newly fabricated Ni@Co3O4, investigative
experiments with various catalytic conditions (catalyst loading, solvent
and time period) were scrutinized for condensation of o-phenylenedi-
amine with hexane-3,4-dione as test substrates to acquire optimized
reaction parameters (Table S1). Initially, model reaction was carried out
in absence of catalyst and it was noted that no desired product was
Fig. 2. Powder XRD of (a) Co3[Co(CN)6]2 (b) Co3O4 (c) Ni@Co3O4
nanocatalyst.
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A. Sharma et al.
Molecular Catalysis 504 (2021) 111454
Fig. 3. SEM micrographs of (a) Co3[Co(CN)6]2, (b) Co3O4 and (c) Ni@Co3O4 nanocatalyst.
Fig. 4. TEM micrographs of (a) Co3[Co(CN)6]2, (b) Co3O4 (c) Ni@Co3O4 nanocatalyst and (d) SAED image of Ni@Co3O4 catalyst.
formed, confirming that the role of catalyst is imperative for concerned
reaction. Moreover, support used in the current work is cobalt oxide
nanocages and its interaction with nickel nanoparticles creates an
environment that favors the condensation of test substrates. We
observed that the nanoparticles supported on nanocages tend to produce
desired product with high conversion percentage and isolated yield.
Next, effect of amount of catalyst was tested by keeping other parame-
ters constant for synthesis of quinoxaline. The amount of Ni@Co3O4 was
increased from 2 mg to 6 mg. Results revealed that conversion per-
centage of desired quinoxaline increased exponentially. However, an
increase in amount of Ni@Co3O4 nanocatalyst to 8 mg had no significant
influence on conversion percentage of desired product. Afterwards, to
study effect of solvent on reaction kinetics, test substrates were allowed
to react in polar as well as non-polar solvents. The obtained results
unveiled that poor conversion percentage of the desired product was
attained in non-polar solvents (toluene, hexane), while in presence of
polar solvents such as ethanol, methanol, H2O improved conversion of
desired product was achieved. Best results were noted in ethanol with
highest conversion percentage. Subsequently, to scrutinize time inter-
val, test substrates were stirred vigorously for different intervals of time.
The best optimized time was noted to be 15 min.
2.2.2. Synthesis of quinoxalines using Ni@Co3O4 nanocatalyst
After optimizing the reaction conditions, numerous 1,2-diketones
were allowed to react with 1,2-diamines to evaluate generality and
versatility of this approach. As shown in Table 1, electronically diverse
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A. Sharma et al.
Molecular Catalysis 504 (2021) 111454
Fig. 5. Full-range XPS spectra of (a) Ni@Co3O4 nanocatalyst and core-level spectra of (b) Co 2p, (c) Ni 2p, and (d) O 1s.
nucleophiles, including electron neutral, electron-deficient and
electron-rich diketones as well as diamines underwent reaction
smoothly as they delivered desired quinoxaline moieties with excellent
conversion percentage. Nevertheless, substrates containing deactivating
groups such as Cl, Br etc. required longer reaction time (entry 5–9).
Moreover, aromatic and aliphatic 1,2-diketones also resulted in good
conversion percentage and exhibited high turnover number (TON).
Broad substrate scope and reaction devoid of unwanted products are
some of the important features of the protocol.
[75].
2.2.5. Catalyst reuse studies
Another key consideration in addition to high activity, for the
practical application of high-performance catalysts is innate stability of
catalyst. To validate if nanocages supported nickel catalyst can be
reused and maintained its catalytic activity even after multiple runs,
reusability experiments were conducted by using hexane-3,4-dione and
o-phenylenediamine as representative substrates for the concerned re-
action. Thereafter, catalyst was separated out from reaction mixture via
centrifugation and supernatant was then analyzed by GC–MS. After-
wards, fresh mixture of test substrates was allowed to react in the
presence of recovered catalyst for 15 min time duration. It was noted
that newly synthesized nanocomposite Ni@Co3O4 could be reprocessed/
recycled up to 6 times without any appreciable loss in its catalytic ac-
tivity (Fig. 6b). Furthermore, FT-IR and SEM images of spent catalyst
after 6th run exhibited that overall hierarchically structured cubic
morphology and structure was preserved (Figs. S5 and S6).
2.2.3. Hot filtration test
Sometimes, during the course of reaction, there is a possibility of
leaching of active catalytic species of a heterogeneous catalyst. Thus, in
order to verify that the obtained catalytic performance is truly caused by
newly designed Ni@Co3O4 nanocatalyst, following experiment was
performed. Condensation of hexane-3,4-dione and o-phenylenediamine
was carried out using nanocages supported nickel nanoparticles using
ethanol as solvent at 30 ◦C. Once the reaction was allowed to proceed for
7.5 min, Ni@Co3O4 was recovered from the reaction system. The clear
supernatant was then again stirred for subsequent 15 min; but no in-
crease in conversion percentage was observed which demonstrated that
reaction mixture did not contain any catalytically active homogeneous
species.
2.2.6. Comparison with literature reports
The comparative studies of catalytic activity of the synthesized
nickel decorated cobalt oxide nanocages was carried out with existing
catalytic approaches for the condensation of α-diketones with diamines
to afford biologically significant quinoxalines and comparative results
are compiled (Table S2) [37,40,41,43,76]. To date, a number of cata-
lytic systems have been employed for successful formation of quinoxa-
lines which suffer from recyclability issues and have serious limitations.
However, as-synthesized Ni@Co3O4 recyclable nanocatalyst revealed
excellent activity under optimized reaction parameters as it could be
reused for multiple runs without affecting its catalytic efficacy. More-
over, it is also noteworthy that present protocol with comparable reac-
tion conditions proves its supremacy in comparison to those reported in
2.2.4. Plausible mechanism
A plausible mechanism based on previous literature reports has been
proposed and is outlined in Fig. 6a. Firstly, interaction of 1,2-diketone
with nickel nanoparticles of Ni@Co3O4 (A) generates complex B.
Thereafter, nucleophilic attack of one of amine group of 1,2-diamine
resulted in formation of complex C. Afterwards, another amine group
attacked on carbonyl group resulting in formation of amino-1,2-diol (E)
with subsequent dehydration to afford desirable quinoxaline moiety
5

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Molecular Catalysis 504 (2021) 111454
Table 1
Synthesis of quinoxaline derivatives using Ni@Co3O4 as a catalyst.
Entry
1.
Reactant 1
Reactant 2
Product
Time (min)
15
bConversion (%)
100
cTON
390
2.
3.
4.
5.
15
15
15
20
100
85
390
332
332
371
85
95
6.
7.
8.
20
20
20
100
97
390
379
390
100
9.
20
100
390
10.
11.
20
15
100
100
390
390
12.
13.
15
15
99.5
100
388
390
(continued on next page)
6

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Molecular Catalysis 504 (2021) 111454
Table 1 (continued)
Entry
14.
Reactant 1
Reactant 2
Product
Time (min)
bConversion (%)
cTON
388
20
99.5
aReaction Conditions:
α
-dicarbonyls (1 mmol), 1,2-diamines (1 mmol), ethanol (2 mL), catalyst (6 mg), 30 ◦C.
b
Conversion percentage was determined by NMR.
c
TON is the number of moles of product per mole of catalyst.
literature, thus making it greener protocol for furnishing quinoxaline
moieties.
3. Conclusion
We have successfully designed a new heterogeneous catalyst which is
composed of cobalt oxide nanocages supported Ni nanoparticles for
synthesis of pharmaceutically important quinoxalines. Fine nickel
nanoparticles with narrow size distribution were utilized to decorate
Co3O4 nanocages via a simple method. The remarkable efficiency of
Ni@Co3O4 for condensation reaction of α-dicarbonyls with 1,2-diamines
could be attributed to nanometer size and unique architecture of
nanocages. Moreover, no leaching of nickel metal or detrimental
agglomeration of nanoparticles was noted in the recovered catalyst and
also catalytic activity could be completely redeemed after recovery of
the catalyst signifying excellent stability, durability, recoverability and
recyclability of synthesized catalytic system. Adding to the interest,
these nanocages can be engineered utilizing modern tools of nanotech-
nology to meet many of the future challenges.
CRediT authorship contribution statement
Aditi Sharma: Writing - original draft, Data curation, Methodology,
Investigation. Ranjana Dixit: Conceptualization, Methodology, Formal
analysis. Shivani Sharma: Visualization, Writing - review & editing.
Sriparna Dutta: Formal analysis, Validation. Sneha Yadav: Software,
Investigation. Bhavya Arora: Resources. Manoj B. Gawande: Super-
vision. Rakesh K. Sharma: Conceptualization, Supervision.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Fig. 6. (a) Plausible mechanism for the condensation of α-dicarbonyls with 1,2-
Acknowledgements
diamines and (b) Recycle runs for the synthesis of quinoxalines [reaction con-
ditions: hexane-3,4-dione (1 mmol), 1,2-diamines (1 mmol), ethanol (2 mL),
catalyst (6 mg/ 0.061 mol%), 15 min, 30 ◦C].
One of author, Aditi Sharma expresses her gratitude towards CSIR,
New Delhi, India, for the award of Senior Research fellowship and also
thanks to USICꢀ CIL, University of Delhi, JNU and TERI Gurugram for
FT-IR, SEM, EDS, XRD, TEM and XPS analysis.
7

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Molecular Catalysis 504 (2021) 111454
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Appendix A. Supplementary data
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.mcat.2021.111454.
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