Catalysis Communications
Short Communication
Promotion of Sn on the Pd/AC catalyst for the selective hydrogenation
of cinnamaldehyde
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Jia Zhao, Xiaoliang Xu, Xiaonian Li , Jianguo Wang
Industrial Catalysis Institute of Zhejiang University of Technology, State Key Laboratory Breeding Base of Green Chemistry-Synthesis Technology, Hangzhou, 310014, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 July 2013
Received in revised form 11 September 2013
Accepted 19 September 2013
Available online 26 September 2013
The effect of Sn on the Pd/AC catalysts for the selective hydrogenation of cinnamaldehyde (CALD) was investigated.
TEM, EDX, XRD and XPS have been employed to characterize Pd–Sn/AC. 80% cinnamyl alcohol (COL) selectivity can
be obtained at 96% CALD conversion, even 100% selectivity can be achieved at 3% conversion. The PdSn type alloy
is responsible for the enhancement of unsaturated alcohol (UA) selectivity, as confirmed by XRD and EDX. XPS
technique confirmed that the promoting effect of Sn was related to Pd–Sn interaction. The favorable adsorption
of C = O bond on the PdSn has been supported by means of density functional theory.
Keywords:
Sn-modified
© 2013 Elsevier B.V. All rights reserved.
Pd–Sn alloy
Cinnamaldehyde
Selective hydrogenation
1. Introduction
of additives such as Ir, Cu, and Sn on Pd/SiO2 catalysts for CALD hydroge-
nation. They did not observe a decrease in HCAL selectivity upon Ir or Cu
Cinnamyl alcohol (COL) as a representative unsaturated alcohol
(UA) is widely used in perfumery and as a deodorant [1]. In addition,
the hydrogenation of cinnamaldehyde (CALD) is a suitable model reac-
tion to investigate the effect of catalyst structure on selectivity. The hy-
drogenation of CALD can occur at either olefinic or carbonyl groups. The
former leads to the formation of hydrocinnamaldehyde (HCAL), and the
latter results in COL. Further hydrogenation can obtain hydrocinnamyl
alcohol (HCOL). Forming HCAL is also thermodynamically preferred
and can be achieved easily compared to forming COL.
The UA is the desired product, but over most nonpromoted
monometallic catalyst the saturated aldehyde is selectively formed [2].
Great efforts have been made to improve the UA selectivity, such as
alloying with a second metal. Recently, the tin alloying of Ru has been
extensively applied in the selective hydrogenation of carbonyl group.
For instance, Galvagno [3] reported that Ru–Sn/AC catalyst exhibited
80% selectivity to UA not above 30% conversion. Moreover, when Ru–
Sn catalysts are supported on reducible oxides such as TiO2, even
87.8% UA selectivity can be obtained at 21% citral conversion [4].
However, it was observed that UA selectivity would be decreased with
the increase of conversion. Therefore, to find a stable catalyst with
high selectivity and good conversion has become an increasingly
urgent issue. Based on that, more and more attention has been attracted
on Pd–Sn alloy catalysts as potential catalysts in selective unsaturated
aldehydes hydrogenation reactions. Mahmoud [5] studied the influence
addition onto Pd. However, a decrease in the HCAL selectivity was
observed after Sn addition onto Pd, which can be attributed to the
formation of a Pd2Sn structural phase. Better catalytic performance of
Pd–Sn bimetallic catalysts was obtained by Vicente [6] who reported
that higher than 75% UA selectivity could be reached at 30% citral con-
version when Pd3Sn was formed in Pd–Sn/SiO2 catalysts. The influence
of tin on the catalytic selectivity of Pd/AC, for one thing, can be attribut-
ed to the interaction between oxidized tin species and the oxygen atom
of the carbonyl bond, thus weakening the C = O bond and favoring its
hydrogenation. For another, the dilution effect of Pd caused by Sn can
significantly enhance the selectivity of UA intermediates through the
conversion of the on-top adsorption mode of the carbonyl group.
Despite the effectiveness of Pd–Sn alloy phases such as Pd3Sn and
Pd2Sn being employed to catalyze selective hydrogenation of unsaturat-
ed aldehydes, the problem of lack of stability of UA selectivity particular-
ly at high conversion was still not resolved. With the aim of improving
the yield toward the hydrogenation of the carbonyl bond, an unreported
Pd–Sn/AC catalyst bearing PdSn structure alloy was prepared and ana-
lyzed. The excellent performances of Pd–Sn/AC in the hydrogenation
of CALD into COL were obtained.
2. Experimental section
2.1. Catalyst preparation and characterization
A commercially starting activated carbon with particle size less than
61 μm, specific surface area of 1703 m2/g was made from coconut shells
(Fujian Xinsen Carbon Co., Ltd. China). The Sn-modified Pd/AC catalysts
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