Investigation of BiVO4 structure variations on the dichlorotoluene ammoxidation performance

Article abstract of DOI:10.1002/jccs.202000438

In this study, BiVO₄ synthesized by hydrothermal and calcination methods were explored as catalysts in the ammoxidation of dichlorotoluenes to shed light on the structure-reactivity correlations. The BiVO₄ samples were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), Brunauer–Emmett–Teller (BET), and UV–Vis spectrophotometry. The results showed that the catalytic activity of BiVO₄ greatly relied on the structure variations. The hydrothermal prepared BiVO₄ exhibited better catalytic activities as a consequence of its greater structure deformation, with maximum yields of 73.1, 72.2, and 70.8% for 3,4-, 2,4- and 2,6- dichlorobenzonitrles, respectively.

Full text of DOI:10.1002/jccs.202000438

Received: 5 October 2020
Revised: 4 December 2020
Accepted: 11 December 2020
DOI: 10.1002/jccs.202000438
A R T I C L E
Investigation of BiVO4 structure variations on the
dichlorotoluene ammoxidation performance
Xiongjian Li1 | Chi Huang2
1Hubei Key Laboratory of Pollutant
Abstract
Analysis & Reuse Technology, College of
Chemistry and Chemical Engineering,
Hubei Normal University, Huangshi, PR
China
2College of Chemistry and Molecular
Sciences, Wuhan University, Wuhan, PR
China
In this study, BiVO4 synthesized by hydrothermal and calcination methods
were explored as catalysts in the ammoxidation of dichlorotoluenes to shed
light on the structure-reactivity correlations. The BiVO4 samples were charac-
terized by X-ray diffraction (XRD), temperature-programmed reduction (TPR),
Brunauer–Emmett–Teller (BET), and UV–Vis spectrophotometry. The results
showed that the catalytic activity of BiVO4 greatly relied on the structure varia-
tions. The hydrothermal prepared BiVO4 exhibited better catalytic activities as
a consequence of its greater structure deformation, with maximum yields of
73.1, 72.2, and 70.8% for 3,4-, 2,4- and 2,6- dichlorobenzonitrles, respectively.
Correspondence
Xiongjian Li, Hubei Key Laboratory of
Pollutant Analysis & Reuse Technology,
College of Chemistry and Chemical
Engineering, Hubei Normal University,
Huangshi, PR China.
K E Y W O R D S
Email: li_xiongjian@163.com
ammoxidation, BiVO4, structure deformation
Funding information
Scientific Research Program of Hubei
Provincial Education Department, Grant/
Award Number: B2020129; National
Natural Science Foundation of China,
Grant/Award Number: 51572201
1 | INTRODUCTION
process compared to the ammoxidation of other alkyl
aromatics and hetero aromatics, because of the steric hin-
Ammoxidations are industrially important reactions due
to that the product nitriles are widely used as organic
intermediates to prepare lots of industrially important
chemicals.1,2 Statistically, approximately 1,500 papers
and more than 1,200 patents have appeared in the
literature on various ammoxidation reactions during the
last 50 years.3 Ammoxidation of 3,4-, 2,4- and 2,6-
dichlorotoluenes (DCTs) are of high significance, since
the target products 3,4-, 2,4- and 2,6-dichlorobenzonitrles
(DCBNs) are valuable intermediates for the industrial
production of a series of pesticides and many agricultural
chemicals such as chlorfluazuron, flufenoxuron, and
flucycloxuron.4–6 In addition, DCBNs are used to prepare
a kind of special engineering plastics with high heat-
resistant properties.5 However, it is noted that the direct
synthesis of DCBN from DCT in the presence of ammo-
nia and oxygen with high yield is somewhat a difficult
drance caused by the two bulky chlorine atoms.4,6 This
contributes to that only a few papers and patents were
dedicated to this route.7
In the past few decades, most of the catalysts for the
ammoxidation of DCT have been focused on vanadium
phosphorus oxides (VPO)-based catalysts.4,8–11 It was
reported that the yields of DCBN obtained over these cat-
alysts were very low; and after they were loaded on sup-
ports such as SiO2, the overall catalytic performance
could be improved to some extent, but remained unsatis-
factory. On the other hand, Al/V, Ti/V, V/Cr etc. oxides
are generally very active, leading to low selective perfor-
mance. Recently, bismuth vanadate oxides (BiVO4) have
been reported to show high catalytic performance among
the mental oxide catalysts for the ammoxidation of
methyl aromatics or heteroaromatics to nitriles.12–14 In
addition, Bi-based catalysts have been widely synthesized
J Chin Chem Soc. 2020;1–5.
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LI AND HUANG
and studied.15–19 However, studies on analyzing the cor-
relations between structure variations of BiVO4 and cata-
lytic activities have not been reported.
In this contribution, BiVO4 were prepared by hydro-
thermal and calcination methods. The ammoxidation
reactions of DCTs to DCBNs were performed on the
BiVO4 catalysts to investigate the structure-reactivity
correlations.
process of monoclinic BiVO4 transforming to the tetrago-
nal phase.21 And above 250ꢀC, the absorption edge no
longer shifts as a consequence of finished phase transi-
tion. Comparatively, it is interesting to note that the total
red-shift of the H-BiVO4 catalyst is larger than that of S-
BiVO4. This clearly reflects that H-BiVO4 has a greater
degree of structure deformation compared to S-BiVO4,
which is well consistent with the XRD analysis.
The BET surface area and pore parameters of BiVO4
catalysts are shown in Table 1. It can be seen that the
2 | RESULTS AND DISCUSSION
The phase structures of as-synthesized BiVO4 catalysts
were characterized by XRD, as shown in Figure 1. Inset
shows the enlargement of 17ꢀ–20ꢀ patterns. It can be seen
that the diffraction peaks of H-BiVO4 catalyst can be per-
fectly indexed to the monoclinic scheelite BiVO4 (JCPDS
No. 75-1867). In contrast, the peaks attributed to tetrago-
nal scheelite BiVO4 (JCPDS No. 01-078-1535) were
detected for sample S-BiVO4, along with the peaks rep-
resenting monoclinic scheelite BiVO4. It is well known
that monoclinic scheelite shows a reversible phase transi-
tion to tetrahedral form at 255ꢀC.20 It indicates that the
high-temperature calcinations modified the structure
deformation of the H-BiVO4 catalyst, that is, S-BiVO4
was in an intermediate state between monoclinic and
tetragonal scheelite, which will be further confirmed
below.
To investigate the structure variations, UV–vis
absorption spectra were performed in the temperature
range of 25–280ꢀC, as shown in Figure 2. As temperature
is increasing, the absorption edges of both as-prepared
BiVO4 catalysts shift continuously to the longer wave-
lengths (i.e., red-shift). This is corresponding to the
FIGURE 2 Temperature-dependent UV–vis diffuse reflectance
spectra of as-obtained catalysts: (a) H-BiVO4, (b) S-BiVO4
TABLE 1 BET surface area and pore parameters of as-prepared
BiVO4 catalysts
Sample
H-BiVO4
S-BiVO4
Surface area (m2/g)
Average pore size (nm)
3.6
1.8
10.56
8.89
FIGURE 1 XRD patterns of as-prepared catalysts: (a) H-BiVO4,
(b) S-BiVO4. Inset shows the enlargement of 17ꢀ–20ꢀ patterns

LI AND HUANG
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samples appear similar in surface area and average pore
size, which cause no difference in catalytic performance.
In order to investigate the redox properties of as-
prepared BiVO4 catalysts, H2-TPR experiments were per-
formed, as shown in Figure 3. It can be seen that both
BiVO4 catalysts show a maximum reduction peak in the
range 450–650ꢀC attributed to the simultaneous reduc-
tion of Bi3+ and V5+ to Bi0 and V3+. Compared to the
S-BiVO4 catalyst, H-BiVO4 shows a lower reduction tem-
perature, indicating enhanced capabilities of oxygen
anions free from metal cations due to a greater degree of
structure deformation.14,22
H-BiVO4 catalyst are higher than those of S-BiVO4 under
identical conditions. The best yields of 3,4- and
2,4-DCBN obtained over H-BiVO4 are higher than that
over the S-BiVO4 catalyst, reaching up to 73.1 and 72.2%
with corresponding conversions of 89.1 and 85.6%,
respectively.
3 | EXPERIMENTAL
3.1 | Preparation of BiVO4
The catalytic results obtained over as-prepared BiVO4
catalysts in the ammoxidation of 2,6-DCT to 2,6-DCBN
are shown in Figure 4. It can be seen that H-BiVO4
shows higher catalytic activities than S-BiVO4 under
identical conditions. These results reveal that the activity
of BiVO4 catalyst strongly depends on the reduction per-
formance which is greatly related to the structure varia-
tions. Earlier, we have deeply studied the structure
deformation of BiVO4, it has been found that greater
structure distortion leads to better thermochromic perfor-
mance.21 In addition, Yu et al.23 reported the degree of
structure distortion of BiVO4 providing a significant
effect on the photocatalytic performance. Based on these,
the better catalytic performance of H-BiVO4 catalyst is
attributed to the greater structure deformation. Under
optimum conditions, the H-BiVO4 catalyst exhibits a
maximum 2,6-DCBN yield of 70.8% with a conversion of
83.3%, as a result of a larger distortion of structure.
In a typical process, 4.850 g of Bi(NO3)3Á5H2O and a cer-
tain amount of concentrated HNO3 were dissolved in
200 ml of distilled water to obtain Bi-solution; mean-
while, V-solution was prepared by stirring 0.91 g of V2O5
and 12 ml of H2O2 in deionized water for 6 hr. Then, the
Bi-solution was added dropwise into the V-solution, with
PH settled at 11 by adding ammonia solution. The mix-
ture was sealed in a 500 ml stainless steel autoclave and
heated at 180ꢀC for 16 hr. The products were filtered,
washed, and dried at 75ꢀC for 12 hr. The obtained sam-
ples were denoted as H-BiVO4. Additionally, some of the
H-BiVO4 products were calcined at 650ꢀC for 10 hr, den-
oted as S-BiVO4.
3.2 | Characterization
X-ray diffraction (XRD) patterns of samples were
recorded on a D8 X-ray diffractometer with a Cu Kα radi-
ation source, λ = 1.54060 Å. The redox property of the
catalysts were studied by temperature-programmed
reduction (TPR) on a TP-5080 adsorption instrument
(TianJin XianQuan Co., gas composition: H2 (3 ml/min)
and N2 (27 ml/min), heating rate: 10ꢀC/min).
Temperature-dependent UV–vis absorption spectra were
collected by adding a heater at the sample holder on a
Shimadzu UV-3600 spectrophotometer using BaSO4 as
reference. The specific surface area was examined by
Brunauer–Emmett–Teller (BET) N2 gas adsorption
method at 77 K and carried out on JW-BK equipment.
Furthermore, the catalytic performance of the BiVO4
catalysts was also investigated in the ammoxidation of
3,4- and 2,4-DCT, as shown in Figure 5 and Figure 6,
respectively. It can be seen that the catalytic activities of
3.3 | Catalytic activity evaluation
The ammoxidation of DCTs were carried out in a quartz
tube fixed-bed with 30 mm inside diameter at atmo-
spheric pressure.24,25 In a typical experiment, 5 g of
BiVO4 catalyst was loaded. The tests were carried out at
different conditions by varying the temperature, space
velocity (GHSV) of the reactant, and the molar ratios of
air and ammonia to DCT. The flow rates of ammonia and
FIGURE 3 H2-TPR profiles of as-obtained (a) H-BiVO4 and
(b) S-BiVO4 catalysts

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LI AND HUANG
FIGURE 4 Conversion
(a) and yield (b) performance of
the BiVO4 catalysts in the
ammoxidation of 2,6-DCT;
molar ratio of 2,6-DCT: air:
NH3 = 1:25:7, GHSV = 126 h−1
FIGURE 5 Conversion (a) and yield (b) performance of the BiVO4 catalysts in the ammoxidation of 3,4-DCT; molar ratio of 3,4-DCT:
air: NH3 = 1:25:9, GHSV = 220 h−1
FIGURE 6 Conversion (a) and yield (b) performance of the BiVO4 catalysts in the ammoxidation of 2,4-DCT; molar ratio of 2,4-DCT:
air: NH3 = 1:20:7, GHSV = 176 h−1
air were adjusted by gas flowmeters, and the liquid DCTs
were introduced by a micropump, vaporized, and mixed
in a preheated vessel with ammonia and air. The reaction
was performed at 430–450ꢀC, depending on the BiVO4

LI AND HUANG
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catalysts. The outlet stream was cooled and collected
every 1 hr after attaining steady-state conditions and
then analyzed off-line by
a
gas chromatograph
(Lunanruihong, China; column: SE-30) equipped with
FID module. The reaction equations of the synthesis of
DCBNs by the ammoxidation of DCTs could be expressed
in Scheme 1.
4 | CONCLUSIONS
In conclusion, the catalytic properties of BiVO4 catalysts
prepared by hydrothermal and calcination methods were
investigated in the ammoxidation of dichlorotoluenes. It
was found that the activity of BiVO4 catalyst is greatly
related to the structure variations. Hydrothermal synthe-
sized BiVO4 catalyst displayed better ammoxidation activ-
ities, attributed to the greater structure deformation
leading to better redox properties. The maximum yields
of 3,4-, 2,4- and 2,6-DCBN obtained over hydrothermal
prepared BiVO4 reached up to 73.1, 72.2 and 70.8%,
respectively.
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How to cite this article: Li X, Huang C.
Investigation of BiVO4 structure variations on the
dichlorotoluene ammoxidation performance.
J Chin Chem Soc. 2020;1–5. https://doi.org/10.
1002/jccs.202000438
ACKNOWLEDGMENTS
This work was partially supported by the National Natu-
ral Science Foundation of China (Grant 51572201) and
Scientific Research Program of Hubei Provincial Educa-
tion Department (B2020129).