Angewandte
Communications
Chemie
MOF Composites
Pd Nanocubes@ZIF-8: Integration of Plasmon-Driven Photothermal
Conversion with a Metal–Organic Framework for Efficient and
Selective Catalysis
Qihao Yang, Qiang Xu, Shu-Hong Yu, and Hai-Long Jiang*
Abstract: Composite nanomaterials usually possess synergetic
properties resulting from the respective components and can be
used for a wide range of applications. In this work, a Pd
nanocubes@ZIF-8 composite material has been rationally
fabricated by encapsulation of the Pd nanocubes in ZIF-8,
a common metal–organic framework (MOF). This composite
was used for the efficient and selective catalytic hydrogenation
of olefins at room temperature under 1 atm H2 and light
irradiation, and benefits from plasmonic photothermal effects
of the Pd nanocube cores while the ZIF-8 shell plays multiple
roles; it accelerates the reaction by H2 enrichment, acts as
a “molecular sieve” for olefins with specific sizes, and stabilizes
the Pd cores. Remarkably, the catalytic efficiency of a reaction
under 60 mWcmÀ2 full-spectrum or 100 mWcmÀ2 visible-light
irradiation at room temperature turned out to be comparable to
that of a process driven by heating at 508C. Furthermore, the
catalyst remained stable and could be easily recycled. To the
best of our knowledge, this work represents the first combina-
tion of the photothermal effects of metal nanocrystals with the
favorable properties of MOFs for efficient and selective
catalysis.
environment, cost, and safety, the development of catalytic
hydrogenation reactions that do not depend on the use of heat
and high-pressure hydrogen gas is highly desirable.
To this end, solar energy can be utilized instead of heat to
drive a reaction by making use of the surface plasmonic
properties of metal nanocrystals.[4] To efficiently convert
sunlight into the heat required for the hydrogenation
reaction, the metal nanocrystals (e.g., Pd, one of the most
active species owing to its strong interaction with H2
molecules[3,5]) should possess sufficient plasmonic absorption
cross-sections to harvest light over a broad spectral range. Pd
nanocrystals with a variety of shapes have been reported, with
Pd nanocubes (NCs) being one of the most active and widely
studied systems.[6] It is expected that Pd NCs not only display
high activity in such hydrogenation reactions but also enable
the utilization of solar energy to drive the reaction by making
use of their well-known surface plasmon effects.
On the other hand, the small Pd NCs are usually not
uniformly dispersed and readily aggregate to some extent
during the reaction, especially upon heating, which greatly
impedes their catalytic performance. To address this issue, the
encapsulation of Pd NCs inside porous materials as shells with
small pore openings should be a judicious solution, which
would offer the following advantages: 1) The Pd NCs will
maintain their high dispersion inside the host materials during
catalytic recycling; 2) the pore structure of the shell is
beneficial to the transportation of substrates/products and
guarantees the accessibility of the Pd active sites; 3) the
porous shell leads to enhanced catalytic efficiency by H2
enrichment;[7] and 4) the use of shells with different pore
sizes would enable the size-selective hydrogenation of differ-
ent substrates. To sieve various molecules with different sizes,
the shell should display a well-defined porous structure and
uniform pore sizes. In this context, metal–organic frameworks
(MOFs, also called porous coordination polymers), which not
only possess diversified and tailorable structures with uniform
pores but can also be used for various functional applica-
tions,[8,9] especially for gas sorption, could be ideal candidates.
Bearing these facts in mind, we rationally grew a repre-
sentative MOF, Zn(2-methylimidazole)2 (ZIF-8),[10] on Pd
NCs to obtain Pd NCs@ZIF-8 with a core–shell structure.
This composite structure displays a plasmonic band covering
the UV-to-visible spectral range and thus induces high
temperatures to drive the hydrogenation reaction by photo-
thermal conversion. Compared to Pd NCs with similar sizes,
the catalytic activity of Pd NCs@ZIF-8 in the hydrogenation
of 1-hexene under 100 mWcmÀ2 full-spectrum light irradia-
tion at room temperature is significantly enhanced, and the
reaction efficiency is even higher than that of a reaction
T
he hydrogenation of compounds with unsaturated bonds is
a very common transformation involved in many chemical
processes.[1] Traditionally, hydrogenation reactions are carried
out with hydride reagents, for example, sodium borohydride,
lithium aluminum hydride, or ammonia borane.[2] Although
these reductants are effective, they are of high cost, and their
decomposition leads to byproducts that are difficult to
separate from the reaction system. Catalytic reduction with
molecular hydrogen (H2) obviously represents an attractive,
more atom-economic alternative. Hydrogenation in the
presence of H2 typically requires high temperatures and/or
H2 pressures.[3] However, from the viewpoints of energy,
[*] Q. Yang, Prof. Dr. S.-H. Yu, Prof. Dr. H.-L. Jiang
Hefei National Laboratory for Physical Sciences at the Microscale
CAS Key Laboratory of Soft Matter Chemistry
Collaborative Innovation Center of Suzhou Nano Science and
Technology, Department of Chemistry
University of Science and Technology of China
Hefei, Anhui 230026 (P.R. China)
E-mail: jianglab@ustc.edu.cn
Prof. Dr. Q. Xu
National Institute of Advanced Industrial Science and Technology
Ikeda, Osaka 563–8577 (Japan)
Supporting information and ORCID(s) from the author(s) for this
Angew. Chem. Int. Ed. 2016, 55, 3685 –3689
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3685