Volcano-type correlation between particle size and catalytic activity on hydrodechlorination catalyzed by AuPd nanoalloy

Although changing the size of metal nanoparticles (NPs) is a reasonable way to tune and/or enhance their catalytic activity, size-selective preparation of NPs 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 the size-selective preparation of random alloy NPs composed of Au and Pd, which are stabilized by poly(N-vinyl-2-pyrrolidone) (PVP). By adjusting the mixing time in the presence of a small amount of PVP, 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 indicated the formation of various sizes of AuPd nanoalloys, and size-dependent catalytic activity was observed when hydrodechlorination of 4-chloroanisole 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 of 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.