Catalysis Communications
Short communication
Aluminum metal–organic framework as a new host for preparation of
encapsulated metal complex catalysts
a
a,
a
b,
Yanfeng Chen , Binbin Fan ⁎, Ningyue Lu , Ruifeng Li ⁎
a
Institute of Special Chemicals, Taiyuan University of Technology, Taiyuan 030024, PR China
Key Laboratory of Coal Science and Technology MOE, Taiyuan University of Technology, Taiyuan 030024, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
A facile strategy for encapsulation of metal complex guests into MOFs was proposed. This strategy involves pre-
adsorbing metal salt on MOF, and then coordinating the metal ions with the organic ligand, as exemplified by en-
capsulation of tris(1,10-phenanthroline) Cu(II) complexes (CuPhen) in MIL-100(Al) (denoted as CuPhen/MIL).
CuPhen encapsulated in MIL-100(Al) showed higher catalytic activity than the neat CuPhen and CuPhen encap-
sulated in zeolite-Y. The prepared CuPhen/MIL catalyst was stable and could be reused at least three times with-
out significant loss in activity. This work is beneficial for the host–guest chemistry study and the development of
new heterogeneous catalysts.
Received 27 December 2014
Received in revised form 6 February 2015
Accepted 7 February 2015
Available online 10 February 2015
Keywords:
Metal–organic frameworks
Cyclohexane oxidation
MIL-100(Al)
© 2015 Elsevier B.V. All rights reserved.
Encapsulation
Metal complexes
1
. Introduction
Metal complexes as homogeneous catalysts have widespread applica-
promising functional hybrid materials [17–20]. Compared with the tradi-
tional porous materials, such as zeolite and mesoporous materials, MOFs
have more topologies and tunable and functionalizable nanospaces
[20–23], which provide an excellent platform to accommodate guest
species and to prepare new host–guest materials. MIL-100(Al)
tions in many catalytic reactions. However, the difficulties in recovery and
recycling of the catalysts limit their reuse [1–4]. Therefore, many efforts
have been devoted to solve these problems, in which immobilization of
metal complexes on solid matrices is a promising approach [5–7]. In the
various immobilized catalysts, it has been established that zeolite encap-
sulated organometallic compounds and transition metal complexes
(Al
3 2 2 2 2
O(OH)(H O) [BTC] ·nH O, BTC = benzene-1,3,5-tricarboxylate) is
one of the mesoporous metal(III) trimesate MIL-100. The porosity of
MIL-100(Al) originates from both 25 Å and 29 Å mesopores, which are
accessible via 5.5 Å and 8.7 Å windows, respectively [24,25]. The struc-
tural properties of MIL-100(Al) make it a potential and promising host
for preparation of “ship-in-a-bottle” catalysts since its two distinctly dif-
ferent polyhedral cages can accommodate large metal complexes and
the small pore size can effectively limit the escape of the encapsulated
guests. At present, the application of MIL-100(Al) as the host matrix for
encapsulation of metal complexes has been rarely reported.
In this work, tris(1,10-phenanthroline) Cu(II) complexes (CuPhen),
being able to efficiently catalyze cyclohexane oxidation, were encapsulat-
ed into MIL-100(Al) by pre-adsorption of Cu(II) salt into the MIL-100(Al)
followed by coordination of Cu(II) ions with 1,10-phenanthroline ligand.
The prepared hybrids showed much higher catalytic activity than the
neat CuPhen and CuPhen encapsulated in zeolite-Y in cycloalkane oxida-
(“ship-in-a-bottle” hybrids) can be highly selective and efficient catalysts
[7–10]. The steric constrain imposed by the walls of the zeolite plays a
vital role in modifying the properties, namely, magnetic, electronic, and
redox behaviors of the encapsulated complexes [7,11–13]. These changes
in the properties of the transition metal complexes upon encapsulation
have led various researchers to develop newer heterogeneous catalysts
and apply them in various organic transformations [9,11,14–16]. Never-
theless, for zeolite encapsulated metal complex hybrids, the commonly
used zeolite host is zeolite-Y due to its unique structural properties, that
is, large supercages (for accommodating metal complexes) and small
pore size (for preventing the leaching of the encapsulated guests).
While other zeolites, due to their structural limitation, cannot be used
as the hosts for “ship-in-a-bottle” hybrids. The small selected range for
hosts, to some extent, limits the development of the new encapsulated
hybrids.
2 2
tion with H O .
2. Experimental
Metal–organic frameworks (MOFs), owing to their high porosity,
large surface area and chemical tenability, have become highly
2.1. Catalyst preparation
MIL-100(Al) was hydrothermally synthesized and purified accord-
⁎
ing to a previously published procedure [26]. MIL-100(Al) encapsulated
566-7367/© 2015 Elsevier B.V. All rights reserved.
1