The development of a sustainable catalytic system for
optimizing
the use of noble metals (NMs) plays a crucial role in expanding the
application of NMs. In this paper, we synthesized a series of core–shell
nanoparticles (NPs) with metal Cu as a core and ultrathin NM M (M
= Pt, Pd, Rh, Ru, Ir, and Au) as a shell. Cu–M NPs were fabricated
via a one-pot method, which involved a two-step process of Cu nucleating
first at a low temperature and then NMs nucleating and growing on
the Cu core at a high temperature later. For Pd precursor salt with
a lower decomposition temperature, introducing trioctylphosphine (TOP)
to enable the in situ formation of Pd-TOP complex
was pivotal to obtaining Cu–Pd. X-ray diffraction, high-angle
annular dark-field scanning transmission electron microscopy, and
energy-dispersive X-ray spectroscopy-mapping characterizations highlight
the core–shell NPs with an ultrathin shell. The catalytic performance
of the Cu–M NPs was investigated by using selective hydrogenation
of nitrobenzene as a probe reaction. Among them, Cu–Rh demonstrated
enhanced activity toward nitrobenzene hydrogenation to aniline with
a TOF value as high as 2847 h–1. While a part of
aniline would undergo excessive hydrogenation to cyclohexylamine over
a pure Rh NP catalyst. Valence band spectra measurement and density
functional theory calculations both prove that the activity modulation
is principally governed by the charge transfer. The introduction of
Cu core downshifts the d-band center of the Rh shell, weakens the
adsorption of aniline, and thereby terminates the further reduction
of aniline. The synthesis of Cu–M NPs can not only reduce the
dosage of NMs but also present the potential for activity control
by adjusting the properties of the shell metals. These core–shell
NPs provide considerable promise for terminating the reaction to the
intermediate product in consecutive hydrogenation reactions.
