Journal of Catalysis
Platinum nanocrystals supported on CoAl mixed metal oxide nanosheets
derived from layered double hydroxides as catalysts for selective
hydrogenation of cinnamaldehyde
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Zhengbin Tian, Qingyang Li, Juying Hou, Lei Pei, Yan Li , Shiyun Ai
College of Chemistry and Material Science, Shandong Agricultural University, Taian, Shandong 271018, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
Pt nanoparticles supported on sheetlike mixed metal oxides (MMO) derived from layered double hydrox-
ides are found to be highly efficient catalysts for the selective hydrogenation of cinnamaldehyde. A series
of characterizations are employed to investigate the structure and composition of the support and cata-
lyst. Divalent species have a significant influence on the activity and selectivity. CoAl MMO-supported
catalysts achieve an increase in both conversion and selectivity to cinnamyl alcohol through the forma-
tion of PtCo alloy on the surfaces of catalysts during preparation. A possible reaction path is proposed. The
effects of Co/Al ratio and calcination temperature on catalytic performance are researched in this work.
Ó 2015 Elsevier Inc. All rights reserved.
Received 25 June 2015
Revised 18 August 2015
Accepted 19 August 2015
Keywords:
Cinnamaldehyde
Selective hydrogenation
Sheetlike MMO
Positively charged center
1
. Introduction
the catalytic process, the undesirable product HCAL would largely
be formed, decreasing the selectivity to the unsaturated alcohol.
Selective hydrogenation of
a
,b-unsaturated aldehydes at the
Over the past few years, common noble metal (Pd, Pt, Ru, and
Au)-based catalysts have been used for the hydrogenation of CAL
[5–7]. Unfortunately, only a few catalysts are suitable for the pur-
pose of C@O hydrogenation; most of these are Pt-based catalysts.
Hence, maintaining high selectivity of Pt-based catalysts while
increasing their activity has become an urgent task for further
development in this field. Many studies have been devoted to
enhancing the selectivity of catalysts toward the unsaturated
alcohol either by fine control of the sizes [8] and/or the exposed
facets of the active metal nanoparticles [9], by exploiting the steric
constraints imposed by the environment of the active site [10], by
decorating the primary metal with a second metal component [11],
or by adding promoters such as an alkali element [12].
It is well known that there is an interaction between the sup-
port and active metal sites that can modify the catalytic properties
of the metal catalyst. This is a feasible way to search for appropri-
ate materials used as catalyst supports for preparing highly active
and selective catalysts for the hydrogenation of CAL. Traditional
carbon materials, such as activated carbon, carbon aerogel [13],
carbonyl (C@O) and olefinic (C@C) groups is highly desirable
in the fine chemical industry, because most of their products
are important intermediates for the synthesis of many chemicals
1]. Cinnamaldehyde (CAL) is a particularly important a,b-
unsaturated aldehyde, since its partial hydrogenation products
[
are important intermediates in the manufacture of chemicals
particularly perfumes, flavors, and pharmaceuticals) [2,3]. Also,
(
it is considered a good model for investigating the catalytic
behavior of the microstructures of heterogeneous catalysts. The
selective hydrogenation of CAL is a rather complex reaction net-
work involving several important intermediates and a number of
series–parallel reactions. Two main competitive products of selec-
tive hydrogenation, hydrocinnamaldehyde (HCAL) and cinnamyl
alcohol (COL), can be produced through the hydrogenation of the
conjugated C@C or C@O bond over the supported metal catalysts
(
Scheme 1). Further hydrogenation of these two intermediates
results in the formation of hydrocinnamyl alcohol (HCOL).
However, the development of catalysts for the selective hydro-
genation of CAL to COL is still challenging. Because the C@O bond
presents a higher binding energy than the C@C bond (715 kJ/mol
and 615 kJ/mol, respectively) [4], the reduction of the C@C bond
is thermodynamically more favorable than that of C@O bond. In
2
and CNTs [14], and SiO [8,15] have been widely used as catalyst
supports. However, there is little metal–support interaction effect
among the catalysts because of the almost electroneutral surface
of the support, resulting in low conversion and poor selectivity.
The efficient supports presenting a strong metal–support interac-
tion effect (SMSI effect), such as TiO2, favor the activation of the
carbonyl group. That is because there is a strong interaction
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021-9517/Ó 2015 Elsevier Inc. All rights reserved.
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