The Catalyst Review (July 2016) - 15

EXPERIMENTAL
Pd Nanocubes@ZIF-8: Integration of Plasmon-Driven Photothermal Conversion
with a Metal-Organic Framework for Efficient and Selective Catalysis...
Traditional hydrogenation reactions are typically carried out using hydride
reagents such as sodium borohydride. However, these materials are
expensive and their decomposition products are often difficult to remove.
Herein, the authors make use of a novel approach to develop a catalytic
hydrogenation reaction that does not depend on the use of heat and highpressure hydrogen gas. This transformation is achieved by making use of
a Pd nanocubes@ZIF-8 composite material fabricated by encapsulation of
the Pd nanocubes in ZIF-8, a common metal-organic framework (MOF).
Of particular interest is the fact that 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 photothermal
conversion. Furthermore, owing to the MOF shell, the nanocomposite
catalyst shows excellent recyclability and selectivity because large olefins
cannot reach the Pd active sites (Scheme 1).

Scheme 1. Self-assembly of Pd NCs@ZIF-8 and plasmondriven selective catalysis of the hydrogenation of olefins.

Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM)
studies suggest that the Pd NCs have a well-defined structure with sizes of 17
+ or -3 nm and are enclosed by {100} facets (Figure 1a, b). A scanning electron
microscopy (SEM) image shows the size of an individual Pd NCs@ZIF-8 particle to
be 250-350 nm (Figure 1c). TEM images confirm the core-shell nanostructure of
the composite material, with the Pd NCs well encapsulated by the ZIF-8 shell and
retention of the shape and size of the Pd NCs (Figure 1d).

Figure 1. a) TEM and b) HRTEM images of Pd NCs.
c) SEM and d) TEM images of Pd NCs@ZIF-8. Inset
in (d): Pd nanocubes inside ZIF-8.

Full-spectrum light irradiation was then employed to investigate the surfaceplasmon-driven photothermal conversion in the room temperature catalytic
hydrogenation of olefins (Figure 2). To assess the importance of photothermal
effects for the overall reaction, the catalytic hydrogenation over Pd NCs@ZIF-8
was conducted with all parameters unaltered except for changing light irradiation
to heating. The results clearly show that the reaction efficiency is much better
under 100 mWcm-2 full spectrum irradiation than upon heating at 50ºC. The
authors believe that the observed superior catalytic performance can be ascribed
to the broad absorption band of the Pd NCs and many accessible active Pd sites
on corner and edge positions. Source: Yang Q, Xu Q, Yu SH, and Jiang HL. (2016).
Angew. Chem. Int. Ed., 55: 3685-3689.
Figure 2. a) The yields of the hydrogenation of 1-hexene with 1 atm H2 over Pd NCs@ZIF-8 under full-spectrum irradiation with
different light intensities at room temperature or upon heating at different temperatures. b) Dependence of the hydrogenation
yield of 1-hexene on the reaction time over Pd NCs or Pd NCs@ZIF-8. c) Recyclability of Pd NCs@ZIF-8 and Pd NCs for the
hydrogenation of 1-hexene. d) Conversions of the hydrogenation of various alkenes over Pd NCs@ZIF-8 and Pd NCs. Reaction
conditions in (b)-(d): 100 mWcm-2 full-spectrum irradiation, room temperature.

The Catalyst Review

July 2016

The Catalyst Review (July 2016)

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