Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Preparation, catalytic performance and theoretical study of porous
2
−
sulfated binary metal oxides shell (SO /M1 O -M2 O ) using pollen
4
x
y
x y
grain templates
Peng cheng Wang, Kai Yao, Jie Zhu, Xiang Liu, Ting ting Lu, Ming Lu ⁎
School of Chemical Engineering, Nanjing University of science and technology, Xiaolingwei 200, Nanjing, Jiangsu Province, China
a r t i c l e i n f o
a b s t r a c t
Porous micro-sized particles of binary metal oxide (SO2 /M1 O -M2 O ) shell were prepared by template-
−
Article history:
Received 1 April 2013
Received in revised form 8 May 2013
Accepted 14 May 2013
Available online 19 May 2013
4
x
y
x y
2
directed synthesis method employing HCl-treated pollen grains. With 150 m /g high surface area, these
solid acids could provide more acid sites and thus obtain better catalytic activity. Using aromatic nitration
as the typical reaction, their catalytic performances were evaluated and showed a significant improvement
in both conversion and regioselectivity. Then, with chlorobenzene as substrate, theoretical studies were
performed to investigate the interaction between transition metals and chlorobenzene. The results showed
that the excellent para-selectivity was closely relative to the metal ion in these solid acids.
© 2013 Elsevier B.V. All rights reserved.
Keywords:
Aromatic nitration
Pollen temple
Regioselectivity
Metal oxides
Interaction mechanism
1
. Introduction
There was a growing interest in searching effective and recyclable
The materials reproduced the morphology of bio-templates might
show some fantastic properties such as low density, high surface area,
nano-sized pore and recoverability [29,30]. Because of these advan-
tages, great attention had been paid to them for a variety of potential
applications.
catalytic materials for some industrial reactions with great importance
but serious pollution. For example, replacing strong liquid acid with
solid acid, like zeolites, heteropoly acid and metal oxides [1–4], was
an excellent improvement in some acid catalyzed reactions such as es-
terification, alkylation, hydrolyzation isomerization and isopropylation
In the present work, we described a facile method for replicating the
complex surface morphology of HCl-treated pollen grains, in which case
the metal oxide could produce complex colloidal materials with surface
2
[5–8]. Applying metal oxides, especially sulfur-promoted solid acids
area increasing to 150 m /g. With higher surface area, the catalysts
2
−
2−
2−
like SO
4
/ZrO
2
, SO
4
/ZrO
2
-WO
3
and SO
4
/TiO
2
-MoO
2
in nitration
could provide more acid site: more Brönsted site helped to generate
+
had also been reported by several researchers [9–14]. From their
results, we found that the binary mixed oxides usually showed better
performance.
more NO
2
and more Lewis acid sites (metal atom), which meant
more opportunity to interact with aromatic. Then with the nitration of
chlorobenzene as example, we elucidated the reason of high selectivity
by calculating the electron clouds, electron spin density (ESD) and espe-
cially second-order perturbation (SOP) with Gaussian 03[31]. Unlike
the former literature that mainly focused on charge-transfer mecha-
nism [32,33], this work would elaborate the selectivity and catalytic ac-
tivity by the interaction between transition metals and chlorobenzene.
x y
Recently, to improve the utilization rate of M O and catalyst effi-
ciency, many researchers attempted to control the size of metal oxide
into submicron or nano-particle [15–17]. However, different from
easy separation of traditional large block catalyst (usually by simple
filtration), the recovery of this nano-particle would be more complex
and difficult. So several methods were developed, such as polymer
supporting [18–20], magnetic technology [21–23] and temperature-
dependent phase transition [24,25]. Preparation of porous particle
was another effective way to realize the aim. Many inexpensive natu-
ral materials owing unique biological structures were ideal templates
for this structure. These templates with stable bio-substrate included
bacterial, fungal colonies, insect wings, plant leaves and so on [26–28].
2. Results and discussion
2.1. Preparation and characterization of the catalysts
Fig. 1 showed the SEM images of HCl-treated pollen and the pre-
pared metal oxides. HCl removed the contents but the outer layer of a
porous hollow structure was mostly preserved (1a and 1b). This outer
layer kept its functional groups especially −COOH and −OH. As can
⁎
be seen in IR spectrum in Fig. S1, there was a peak at 3419.42 cm−
1
,