Vanadium oxides anchored on nitrogen-incorporated carbon: An efficient heterogeneous catalyst for the selective oxidation of sulfide to sulfoxide

Article abstract of DOI:10.1016/j.catcom.2020.106101

A highly efficient and durable metal catalyst stabilized by proper support is vital for organic catalytic transformations. In this study, a sequential pyrolysis–acid etching strategy was reported to prepare a nitrogen-rich nanocarbon inlaid with vanadium

Full text of DOI:10.1016/j.catcom.2020.106101

Catalysis Communications 145 (2020) 106101
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Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short communication
Vanadium oxides anchored on nitrogen-incorporated carbon: An efficient
heterogeneous catalyst for the selective oxidation of sulfide to sulfoxide
⁎
⁎
Yanyan Qi, Qionghao Xu, Gaomei Tu, Yanghe Fu, Fumin Zhang , Weidong Zhu
Key Laboratory of the Ministry of Education for Advanced Catalysis Materials, Institute of Physical Chemistry, Zhejiang Normal University, 321004 Jinhua, People's
Republic of China
A R T I C L E I N F O
A B S T R A C T
Keywords:
One-pot pyrolysis
N-incorporated carbon
Heterogeneous catalysis
Selective oxidation
Highly durable catalyst
A highly efficient and durable metal catalyst stabilized by proper support is vital for organic catalytic trans-
formations. In this study, a sequential pyrolysis–acid etching strategy was reported to prepare a nitrogen-rich
nanocarbon inlaid with vanadium oxide catalyst (V@CN-750), which was evolved from the preassembly of a
chitin−V precursor. V@CN-750 exhibited excellent activity and selectivity of 96% and 98%, respectively, for
catalytic oxidation of thioanisole to sulfoxide at 40 °C for 8 h, which is considerably superior to that of V O
2 5
2
nanoparticles and homogeneous VO(acac) . Moreover, V@CN-750 can be recycled at least eight times without
affecting its catalytic performance.
1
. Introduction
a myriad of applications [17,18]. Notably, there are several amino and
hydroxyl groups in its structure that can help trap metal ions owing to
their strong binding affinity. Therefore, chitin has great potential as
both carbon and nitrogen precursors for the derivation of N-in-
corporated carbon inlaid with metal catalysts by taking full advantage
of its high coordination ability with metal ions and carbon metabolism,
and thereby achieving high activity and stability. However, for organic
catalysis, application of chitin as precursors for deriving N-incorporated
carbon implanted with metal active sites as heterogeneous catalysts has
not been sufficiently investigated [19].
2
Vanadyl acetylacetonate, [VO(acac) ], has often been used as a
homogeneous catalyst for several organic oxidation reactions, including
hydroxylation of benzene [1,2], epoxidation of olefins [3], oxidative
dehydrogenation of amines and aldehydes [4], and selective oxidation
of thioanisole and styrene [5]. Although it usually exhibits high activity
and selectivity during these transformations, VO(acac) itself is entirely
2
dissolved in the reaction medium, resulting in a difficult catalyst re-
covery and repeated use [6–8]. To overcome these problems, im-
mobilization of VO(acac)
2
molecules onto porous supports, such as
Selective oxidation of sulfide to sulfoxide is an important organic
reaction that plays an indispensable role in the production of medical
intermediates and fine chemicals [20]. Till date, many metal-based
catalysts have been studied for sulfide selective oxidation, such as Nb,
Mo, W, Fe, Ti, and V, in the presence of a suitable oxidant [21–26].
Despite this considerable progress, sulfoxide synthesis with high se-
lectivity still encounter a major challenge owing to the unavoidable
over oxidation (see Scheme S1 in the Supporting Information) [21].
Herein, a novel method to prepare N-incorporated carbon-supported V
catalyst (V@CN-750) is reported via in situ pyrolysis of chitin and the
activated carbon, clay, and periodic mesoporous organosilica, via the
reaction between the carbonyl group of the acetylacetonate ligand and
amino group pre-grafted onto the material surfaces, has been widely
investigated [9–15]. However, the procedure for preparing most of
these functionalized supports is complicated. Further, in many cases,
the pre-pendant amino groups may block the pore channel of the pre-
pared porous catalyst, which compromises the catalytic activity.
Therefore, finding other supports that tether with abundant anchoring
sites and can be used to stabilize the catalytically active species, such as
vanadium oxide sites derived from VO(acac)
2
, and fabricating high-
2
VO(acac) complex at 750 °C followed with dilute HCl etching. Fur-
performance heterogeneous catalysts with leaching-resistant properties
are still challenging.
Chitin, a long-chain polymer of N-acetylglucosamine, is a derivative
of glucose [16]. Owing to its attractive physiochemical properties, such
as its low cost, eco-friendliness, and abundance, it has vast potential for
thermore, V@CN-750 was used for selective oxidation of sulfide to
sulfoxide to investigate the active phase and stability. Results indicate
that the V@CN-750 catalyst exhibits superior activity, selectivity, and
recyclability for the conversion of sulfide to the corresponding sulfoxide
with tert-butyl hydroperoxide (TBHP) as an oxidant. It is believed that
⁎
Corresponding authors.
E-mail addresses: zhangfumin@zjnu.edu.cn (F. Zhang), weidongzhu@zjnu.cn (W. Zhu).
https://doi.org/10.1016/j.catcom.2020.106101
Received 26 March 2020; Received in revised form 29 May 2020
Available online 03 July 2020
1566-7367/ © 2020 Elsevier B.V. All rights reserved.

Y. Qi, et al.
Catalysis Communications 145 (2020) 106101
Fig. 1. (a) UV Raman spectra of CN and V@CN-750, (b) TEM image and high-resolution XPS spectra of (c) N 1 s and (d) V 2p for V@CN-750.
the strong interaction between the highly dispersed vanadium sites and
nitrogen dopant are responsible for the good catalytic properties of the
prepared V@CN-750.
3
Typically, 1 mmol of sulfide, 3 mL of CH CN (solvent), and 20 mg of
V@CN-750 were added to the tube. The reaction was set to start upon
the addition of 1.5 mmol of TBHP as the oxidant at 40 °C under mag-
netic stirring (1000 rpm). To monitor the reaction kinetics, a set of
parallel experiments were conducted simultaneously, and sampled at
regular intervals. The liquid mixtures were analyzed on a gas chroma-
tograph (Agilent GC-7890B) equipped with a flame ionization detector
and a capillary column (DB-5, 30 m × 0.45 mm × 0.42 μm) at certain
reaction intervals using toluene as the internal standard.
2. Experimental
2
2
.1. Catalyst preparation
.1.1. Synthesis of the V@CN material
General procedure for the recyclability test: After each reaction, the
catalyst was collected from the reaction system via filtration. Then, the
recovered catalyst was rinsed with acetone six times, dried at 120 °C for
2
In a typical experiment, chitosan (2.0 g) and VO(acac) (0.3 g) was
added in sequence to 2-wt% acetic acid solution (120 mL). After the
solids were thoroughly dissolved, the solution was continuously stirred
at 80 °C for 6 h to form a gel-like mixture. Then, it was dried in an oven
at 120 °C for 12 h. Subsequently, pyrolysis process was conducted in a
12 h, and then subjected to the next reaction cycle.
tube furnace under N
2
atmosphere (80 mL/min) at a heating rate of
3. Results and discussion
2.3 °C/min from room temperature to 750 °C and kept at this tem-
perature for 4 h. After the system was naturally cooled down to room
temperature, the obtained solid was transferred to a 1-M HCl solution
and refluxed at 60 °C for 6 h. Finally, the product was collected by
filtration, washed several times with distilled water and absolute
ethanol, and dried overnight in an oven at 120 °C; V@CN-750 was
obtained as the resulting black solid. The products obtained at different
pyrolysis temperatures, i.e., 650 °C and 850 °C, were prepared and
denoted as V@CN-650 and V@CN-850, respectively. The N-in-
corporated carbon (CN) support was synthesized by annealing pure
chitosan at 750 °C using the same method used for the preparation of
V@CN.
3
.1. Catalyst characterization
Catalyst was prepared based on the utilization of amino and hy-
droxyl group-rich chemistry to trap the vanadium oxides and simulta-
neously derive the N-incorporated carbon amorphous structure. To
achieve this goal, three steps are involved in the current strategy: (i)
forming a chitosan−V precursor, (ii) carbonizing the chitosan–V pre-
cursor at high temperature under an inert atmosphere, and (iii) re-
moving unstable species by diluted HCl etching. The X-ray diffraction
(
XRD) pattern of the prepared V@CN-750 showed only two broad peaks
at 24° and 43° (Fig. S1), corresponding to the (002) and (004) planes of
graphitized carbon, respectively [27]. The carbon support was formed
due to the annealing of chitosan, which was used to chelate with va-
nadium oxides [17]. Moreover, no other crystalline V-based diffraction
peaks were observed, probably due to the formation of noncrystalline
2.2. General procedure for the activity test
Catalytic oxidation of sulfide was conducted in a 10 mL tube.
2

Y. Qi, et al.
Catalysis Communications 145 (2020) 106101
phases. In accordance with the XRD result, the visible Raman spectrum
of V@CN-750 showed only two characteristic bands at approximately
100
−
1
1352 and 1595 cm
(Fig. S2), which were attributed to the dis-
ordered/defected carbon (D band) and graphitic carbon (G band), re-
spectively [28]. These defects can serve as anchor sites to bind and
highly disperse the metal species, which are beneficial for enhancing
the catalytic performance of derived V@CN-750 [26].
8
6
4
0
0
0
Fig. 1a shows the ultraviolet (UV) Raman spectra of CN and V@CN-
7
7
50. The CN support did not show any Raman signals, whereas V@CN-
50 displayed two broad bands at 896 and 1003 cm , which were
−
1
Conversion
Selectivity
attributed to V–O–V and V]O stretching modes of the vanadate spe-
cies, respectively [29]. As shown in Fig. S3, the scanning electron mi-
croscopy (SEM) image of V@CN-750 clearly displayed an irregular
sheet structure and energy-dispersive X-ray (EDX) spectroscopy ele-
mental mapping revealed the uniform distribution of C, N, and V over
the entire carbon skeleton. No apparent nanoparticles were observed
via transmission electron microscopy (TEM) and high-resolution
transmission electron microscopy (HRTEM) analysis (Fig. 1b and Fig.
S4), implying that the vanadium oxide species were highly distributed
on the CN support. The particle size of the catalyst was within 75 to
20
0
0
1
2
3
4
5
6
7
8
Reaction time (h)
Fig. 2. Conversion and selectivity of thioanisole for sulfoxide as a function of
reaction time over V@CN-750.
1
00 μm determined by using a laboratory standard vibrating screen.
Based on the ICP-AES analysis, the actual vanadium content in V@CN-
50 was 7.1 wt% (Table S1), slightly lower than the result obtained by
Table 1
7
Selective oxidation of thioanisole to sulfoxide with TBHP on various catalysts.
TGA (Fig. S5). The specific surface area of V@CN-750 was calculated to
2
be 23.1 m /g (Table S1).
Entry
Catalyst
Time (h)
Conversion (%)
Selectivity (%)
Then, we analyzed the high-resolution N 1 s, V 2p, and O 1 s X-ray
photoelectron spectroscopy (XPS) spectra of V@CN-750 to reveal the N,
V, and O chemical environments. The N 1 s spectra could be decon-
voluted into four peaks assignable to the pyridinic N (398.9 eV), pyr-
rolic N (399.9 eV), graphitic N (401.2 eV), and oxidized N (403.1 eV)
1
2
3
4
5
6
7
Blank
CNs
V@CN-650
V@CN-750
V@CN-850
8
8
8
8
8
4
4
8
1
2
100
100
97
98
97
70
61
100
90
96
92
93
92
1
V
O
2 5
[
30,31], indicating that N was structurally integrated into the carbon
VO(acac)
V@CN-750
2
matrix (Fig. 1c). The XPS percentages showed that the nitrogen content
in V@CN-750 was approximately 6.9 atom% (Table S1). The high N
content provided good wettability, which promoted the full contact
between the catalyst and substrate, thereby boosting the catalytic per-
formance [32–34]. The XPS spectrum of the V 2p region in V@CN-750
showed binding energies of V 2p1/2 and V 2p3/2 at 524.3 and 516.5 eV
a
8
a
In the absence of TBHP.
associated with its relatively higher content of N species (Table S2)
[25,26]. The catalytic performance of V was also tested. It showed
93% conversion after 4 h with 70% conversion to sulfoxide (entry 6).
Furthermore, VO(acac) also showed a relative lower catalytic activity
2 5
O
(
Fig. 1d), respectively, which indicated the presence of V(IV) in the
derived carbon networks [30,31]. This was essentially similar to the V
p band profile of [VO(acac) ] [13]. Furthermore, O 1 s XPS spectra in
2
2
2
and selectivity (entry 7). Herein, V@CN-750 could achieve this trans-
formation with a high activity and selectivity under mild conditions,
thereby promoting the development of selective oxidation of sulfides to
sulfoxides. The excellent catalytic properties of V@CN-750 are likely
owing to the combination of abundant nitrogen dopant and well-dis-
persed vanadium sites encapsulated in the carbon skeletons [13].
Based on the above results and previous work [15], a possible re-
action mechanism for the selective oxidation of sulfide is briefly de-
scribed as follows: initially, in V@CN-750, the vanadium sites that
coordinated with the adjacent nitrogen functionalities interacts with
the active oxygen atom of TBHP to obtain oxygenated intermediate.
Subsequently, the intermediate species experience nucleophilic attack
by sulfur molecules, followed by concerted oxygen intermolecular
transfer. Finally, it results in the formation of sulfoxide simultaneously
with the regeneration of V@CN-750.
The durability of V@CN-750 was also tested. As shown in Fig. S16,
the catalytic activity and selectivity remained almost unchanged for at
least up to eight reaction cycles, confirming the excellent recyclability
of the developed catalyst. A hot filtration experiment was also con-
ducted and distinctly excluded the potential leaching problem of the
active V-species from the V@CN-750 catalyst (Fig. S17). Moreover,
XRD, SEM, TEM, and XPS measurements of the catalyst after the re-
action were also performed (Figs. S18–S21). No obvious changes were
observed compared with the fresh one, thereby confirming that V@CN-
750 exhibited excellent stability under the investigated catalytic con-
ditions.
Fig. S6c can be fitted into three main peaks centered at 531.1, 532.4,
and 533.2 eV, which are corresponding to V-O-N, O-C=O, and CeO
bonds, respectively [30–32]. The peaks at 531.1 eV for V–O–N bond
shows the formation of vanadium oxide on CN surface (Fig. S6 and
Tables S3 and S4), which agrees with the analysis of V 2p3/2 XPS
spectra.
Then, catalytic oxidation of thioanisole to sulfoxide was exploited as
a model reaction to investigate the catalytic performance of V@CN-750.
The kinetic profile was recorded and is shown in Fig. 2. The conversion
of thioanisole increased rapidly during the first 4 h, whereas the se-
lectivity was kept as 99% to that of sulfoxide. For V@CN-750, a high
thioanisole conversion of 96% with a sulfoxide selectivity of 98% was
achieved at 40 °C for 8 h. Notably, a limited amount of the deep oxi-
dation product, methyl phenyl sulfone, was detected as the only by-
product during the oxidation process.
The catalytic oxidation performances of various catalysts are com-
pared in Table 1. Almost no reaction occurred in a blank experiment
(
without catalyst), in the presence of the pure CN support, and in the
absence of TBHP (entries 1, 2, and 8), showing that a suitable catalyst
and oxidant are essential for sulfoxidation. For comparison, V@CN-650
and V@CN-850 were also prepared and characterized. The corre-
sponding results are shown in Figs. S7–S15 and Tables S1–S4. These
results suggest that the control catalysts have similar V contents and
morphological features to those of V@CN-750. When applied to this
reaction, these two catalysts exhibited slightly lower performances than
V@CN-750 (entries 3 and 5). The higher activity of V@CN-750 is likely
We subsequently explored the generality of V@CN-750 in the
3

Y. Qi, et al.
Catalysis Communications 145 (2020) 106101
Table 2
Scope of substrates in the catalytic oxidation of sulfides in the presence of TBHP catalyzed by V@CN-750.
Entry
1
Sulfide
Time (h)
8
Conversion (%)
Selectivity (%)
97
96
95
99
S
S
2
3
8
8
96
96
S
F
4
8
97
96
S
S
Cl
5
6
8
9
97
98
96
99
Br
S
Cl
7
8
10
15
92
96
97
96
S
S
O
9
24
24
24
89
68
73
98
94
92
S
HO
1
1
0
1
S
H N
2
S
Reaction conditions: sulfide (1 mmol), TBHP (1.5 mmol), catalyst (20 mg), MeCN (3 mL), and temperature (40 °C).
selective oxidation of diverse aromatic sulfides at the same tempera-
ture. As listed in Table 2, in general, various aromatic sulfides bearing
electron-donating and withdrawing groups, regardless of the ortho- or
para-positions, could be efficiently converted to their corresponding
sulfoxide with high yields. Halogen-substituted sulfide, such as those
with eF, eCl, and eBr were tolerated under the present conditions,
yielding the desired sulfoxide with a 96% selectivity. Notably, even for
benzyl phenyl sulfide (a bulky substitution), a high 73% conversion
with 92% sulfoxide still could be achieved by prolonging the reaction
time to 24 h.
4. Conclusions
We developed a reusable heterogeneous non-noble metal catalyst
comprising vanadium oxides entrapped within N-incorporated carbon
via a facile and cost-effective strategy. The resulting V@CN-750
4

Y. Qi, et al.
Catalysis Communications 145 (2020) 106101
demonstrated excellent catalytic activity, chemoselectivity, and stabi-
lity for catalytic oxidation of sulfides to sulfoxides, which was sig-
nificantly better than those of V
[14] C. Pereira, J.F. Silva, A.M. Pereira, J.P. Araújo, G. Blanco, J.M. Pintado, C. Freire,
[
VO(acac)
to catalytic application in the epoxidation of geraniol, Catal. Sci. Technol. 1 (2011)
84–793.
2
] hybrid catalyst: from complex immobilization onto silica nanoparticles
2 5
O nanoparticles and homogeneous VO
7
(
acac) , likely originating from the abundant nitrogen dopant and
2
[15] H. Vardhan, G. Verma, S. Ramani, A. Nafady, A.M. Al-Enizi, Y. Pan, Z. Yang,
H. Yang, S. Ma, Covalent organic framework decorated with vanadium as a new
platform for prins reaction and sulfide oxidation, ACS Appl. Mater. Interfaces 11
highly dispersed vanadium oxide species within the carbon networks.
(
2019) 3070–3079.
Declaration of Competing Interest
[16] V. Zargar, M. Asghari, A. Dashti, A review on chitin and chitosan polymers:
structure, chemistry, solubility, derivatives, and applications, Chem. Bio. Eng. Rev.
2
(2015) 204–226.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
[17] X.H. Wang, Y.M. Du, L.H. Fan, H. Liu, Y. Hu, Chitosan-metal complexes as anti-
microbial agent: synthesis, characterization and structure-activity study, Polym.
Bull. 55 (2005) 105–113.
18] G. Saikia, K. Ahmed, S.R. Gogoi, M. Sharma, H. Talukdar, N.S. Islam, A chitosan
supported peroxidovanadium (V) complex: synthesis, characterization and appli-
cation as an eco-compatible heterogeneous catalyst for selective sulfoxidation in
water, Polyhedron 159 (2019) 192–205.
[
Acknowledgments
[
[
19] Y. Cao, M. Tang, M. Li, J. Deng, F. Xu, L. Xie, Y. Wang, In situ synthesis of chitin-
derived Rh/N–C cataylsts: efficient hydrogenation of benzoic acid and derivatives,
ACS Sustain. Chem. Eng. 5 (2017) 9894–9902.
20] Z. Guo, B. Liu, Q. Zhang, W. Deng, Y. Wang, Y. Yang, Recent advances in hetero-
geneous selective oxidation catalysis for sustainable chemistry, Chem. Soc. Rev. 43
This work was supported by the National Natural Science
Foundation of China (21576243) and the Natural Science Foundation of
Zhejiang Province (Nos. LY18B060006 and LY18B030006).
(
2014) 3480–3524.
[21] J. Zhang, T. Jiang, Y. Mai, X. Wang, J. Chen, B. Liao, Selective catalytic oxidation of
sulfides to sulfoxides or sulfones over amorphous Nb /AC catalysts in aqueous
Appendix A. Supplementary data
2 5
O
phase at room temperature, Catal. Commun. 127 (2019) 10–14.
22] R. Fazaeli, H. Aliyan, M.A. Ahmadi, S. Hashemian, Host (aluminum incorporated
mesocellulous silica foam (Al-MCF))-guest (tungsten polyoxometalate) nano-
composite material: an efficient and reusable catalyst for selective oxidation of
sulfides to sulfoxides and sulfones, Catal. Commun. 29 (2012) 48–52.
23] A. Bayat, M. Shakourian-Fard, M.M. Hashemi, Selective oxidation of sulfides to
sulfoxides by a molybdate-based catalyst using 30% hydrogen peroxide, Catal.
Commun. 52 (2014) 16–21.
[24] F. Rajabi, S. Naserian, A. Primo, R. Luque, Efficient and highly selective aqueous
oxidation of sulfides to sulfoxides at room temperature catalysed by supported iron
oxide nanoparticles on SBA-15, Adv. Synth. Catal. 353 (2011) 2060–2066.
[25] Q. Wang, W. Ma, Q. Tong, G. Du, J. Wang, M. Zhang, H. Jiang, H. Yang, Y. Liu,
M. Cheng, Graphene oxide foam supported titanium (IV): recoverable hetero-
geneous catalyst for efficient, selective oxidation of arylalkyl sulfides to sulfoxides
under mild conditions, Sci. Rep. 7 (2017) 7209.
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.catcom.2020.106101.
[
References
[
[
1] J. Xu, Y. Hong, M.J. Cheng, B. Xue, Y.X. Li, Vanadyl acetylacetonate grafted on
ordered mesoporous silica KIT-6 and its enhanced catalytic performance for direct
hydroxylation of benzene to phenol, Microporous Mesoporous Mater. 285 (2019)
2
23–230.
[
[
[
2] L. Carneiro, A.R. Silva, Selective direct hydroxylation of benzene to phenol with
hydrogen peroxide by iron and vanadyl based homogeneous and heterogeneous
catalysts, Catal. Sci. Technol. 6 (2016) 8166–8176.
3] M. Vandichel, K. Leus, P. Van Der Voort, M. Waroquier, V. Van Speybroeck,
Mechanistic insight into the cyclohexene epoxidation with VO(acac)
2
and tert-butyl
3
[26] L. Fang, Q. Xu, Y. Qi, X. Wu, Y. Fu, Q. Xiao, F. Zhang, W. Zhu, Fe/Fe C@N-doped
hydroperoxide, J. Catal. 294 (2012) 1–18.
porous carbon microspindles templated from a metal–organic framework as highly
selective and stable catalysts for the catalytic oxidation of sulfides to sulfoxides,
Mol. Catal. 486 (2020) 110863.
4] Z. Bie, G. Li, L. Wang, Y. Lv, J. Niu, S. Gao, A facile vanadium-catalyzed aerobic
oxidative synthesis of quinazolinones from 2-aminobenzamides with aldehydes or
alcohols, Tetrahedron Lett. 57 (2016) 4935–4938.
[27] W. Liu, L. Zhang, X. Liu, X. Liu, X. Yang, S. Miao, W. Wang, A. Wang, T. Zhang,
Discriminating catalytically active FeNx species of atomically dispersed Fe–N–C
catalyst for selective oxidation of the C–H bond, J. Am. Chem. Soc. 139 (2017)
10790–10798.
[
[
[
5] A.G.J. Ligtenbarg, R. Hage, B.L. Feringa, Catalytic oxidations by vanadium com-
plexes, Coord. Chem. Rev. 237 (2003) 89–101.
6] V. Conte, A. Coletti, B. Floris, G. Licini, C. Zonta, Mechanistic aspects of vanadium
catalysed oxidations with peroxides, Coord. Chem. Rev. 255 (2011) 2165–2177.
7] R.R. Langeslay, D.M. Kaphan, C.L. Marshall, P.C. Stair, A.P. Sattelberger,
M. Delferro, Catalytic applications of vanadium: a mechanistic perspective, Chem.
Rev. 119 (2019) 2128–2191.
[28] J. Pan, Q. Xu, L. Fang, G. Tu, Y. Fu, G. Chen, F. Zhang, W. Zhu, Ru nanoclusters
2 2
supported on HfO @CN derived from NH -UiO-66(Hf) as stable catalysts for the
hydrogenation of levulinic acid to γ-valerolactone, Catal. Commun. 128 (2019)
105710.
[
8] D. Talukdar, K. Sharma, S.K. Bharadwaj, A.J. Thakur, VO(acac)
alyst for the oxidation of aldehydes to the corresponding acids in the presence of
aqueous H , Synlett 24 (2013) 963–966.
9] B. Jarrais, A.R. Silva, C. Freire, Anchoring of vanadyl acetylacetonate onto amine-
functionalised activated carbons: catalytic activity in the epoxidation of an allylic
alcohol, Eur. J. Inorg. Chem. (2005) 4582–4589.
2
: an efficient cat-
[29] W. Zhang, T. Meng, J. Tang, W. Zhuang, Y. Zhou, J. Wang, Direct synthesis of 2,5-
diformylfuran from carbohydrates using high-silica MOR zeolite-supported isolated
vanadium species, ACS Sustain. Chem. Eng. 5 (2017) 10029–10037.
[30] H.h. Liu, H.l. Zhang, H.b. Xu, T.p. Lou, Z.t. Sui, Y. Zhang, In situ self-sacrificed
template synthesis of vanadium nitride/nitrogen-doped graphene nanocomposites
for electrochemical capacitors, Nanoscale 10 (2018) 5246–5253.
2 2
O
[
[
[
[
[
10] F. Xu, Z. Zhang, Polyaniline-grafted VO(acac)
2
: an effective catalyst for the synth-
[31] Z.Y. Wu, S.L. Xu, Q.Q. Yan, Z.Q. Chen, Y.W. Ding, C. Li, H.W. Liang, S.H. Yu,
Transition metal-assisted carbonization of small organic molecules toward func-
tional carbon materials, Sci. Adv. 4 (2018) eaat0788.
[32] S. Mao, C. Wang, Y. Wang, The chemical nature of N doping on N doped carbon
supported noble metal catalysts, J. Catal. 375 (2019) 456–465.
[33] J. Li, M. Chen, D.A. Cullen, S. Hwang, M. Wang, B. Li, K. Liu, S. Karakalos,
M. Lucero, H. Zhang, C. Lei, H. Xu, G.E. Sterbinsky, Z. Feng, D. Su, K.L. More,
G. Wang, Z. Wang, G. Wu, Atomically dispersed manganese catalysts for oxygen
reduction in proton-exchange membrane fuel cells, Nat. Catal. 1 (2018) 935–945.
[34] W. Zhang, P. Oulego, T.K. Slot, G. Rothenberg, N.R. Shiju, Selective aerobic oxi-
dation of lactate to pyruvate catalyzed by vanadium-nitrogen-doped carbon na-
nosheets, ChemCatChem 11 (2019) 3381–3387.
esis of 2,5-diformylfuran from 5-hydroxymethylfurfural and fructose,
ChemCatChem 7 (2015) 1470–1477.
11] C. Pereira, A.R. Silva, A.P. Carvalho, J. Pires, C. Freire, Vanadyl acetylacetonate
anchored onto amine-functionalised clays and catalytic activity in the epoxidation
of geraniol, J. Mol. Catal. A Chem. 283 (2008) 5–14.
12] M. Baltes, P. Van Der Voort, O. Collart, E.F. Vansant, The adsorption of VO(acac)2
on a mesoporous silica support by liquid phase and gas phase modification to
prepare supported vanadium oxide catalysts, J. Porous. Mater. 5 (1998) 317–324.
13] P. Borah, X. Ma, K.T. Nguyen, Y. Zhao, A vanadyl complex grafted to periodic
mesoporous organosilica: a green catalyst for selective hydroxylation of benzene to
phenol, Angew. Chem. Int. Ed. 51 (2012) 7756–7761.
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