<div>Although changing the size of metal nanoparticle
(NP) is a reasonable way to tune and/or enhance their catalytic
activity, size-selective preparation of NP possessing random-alloy morphology has
been challenging because of the differences in the ionization potential of each
metal ion. This study demonstrates a time-controlled
aggregation–stabilization method for a size-selective preparation of random
alloy NPs composed of Au and Pd, which are stabilized by poly(<i>N</i>-vinyl-2-pyrrolidone) (PVP). By adjusting
the mixing time in the presence of a small amount of PVP, the aggregation was
induced to produce AuPd:PVP with sizes ranging between 1.2 and 8.2 nm at approximately 1 nm
intervals. Transmission electron microscopy (TEM), powder
X-ray diffraction (PXRD), and extended x-ray absorption fine structure (EXAFS) analyses
clearly indicated the formation of various sizes of AuPd nanoalloys with almost
the same morphology, and size-dependent catalytic activity was observed when
hydrodechlorination of 4-choroanisole was performed using 2-propanol as a
reducing agent. AuPd:PVP with a size of 3.1 nm exhibited the highest catalytic
activity. A comparison of the absorption edges on x-ray absorption near edge
structure (XANES) spectra suggested that the electronic state of the Au and Pd species
correlated with their catalytic activity, presumably affecting the rate-determining
step.</div><div>
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Volcano-type correlation between particle size and catalytic activity on hydrodechlorination catalyzed by AuPd nanoalloy