Bimetallic nanoparticles containing Au and Pd were synthesized using poly(vinylpyrrolidone) (PVP) as the polymer stabilizer using both co-reduction and sequential reduction strategies. The nanoparticle structures and catalytic activities for the aerobic oxidation of crotyl alcohol to crotonaldehyde at room temperature in the absence of base were investigated. The chemical, structural, and electronic properties of these nanoparticles were investigated using Pd-K-edge and Au-LIII-edge extended X-ray absorption fine structure (EXAFS) spectroscopy and Pd-LIII and Au-LIII edge X-ray absorption near edge structure (XANES) spectroscopy. EXAFS analysis for the sequentially reduced bimetallic systems indicates the presence of significantly Pd-enriched surfaces and Au cores. XANES spectra of the Pd-LIII edges indicated that the sequentially reduced particles showed significant d-charge depletion compared to pure monometallic Pd and co-reduced AuPd nanoparticles. The sequentially reduced nanoparticles with Pd rich surfaces were extremely active for crotyl alcohol oxidation at room temperature in the absence of base, and were quite selective for the formation of crotonaldehyde. A proposed mechanism for the reaction involving the oxidation and re-reduction of Pd on the surface of the particles is postulated based on catalytic activity measurements using sequentially reduced particles and control reactions with Pd2+ salts in the absence and presence of Au, Pd, and Pt nanoparticles.

A series of poly(vinylpyrrolidone) (PVP)-stabilized metallic and bimetallic PdAu nanoparticles (coreduced and core-shell) with narrow size distributions were encapsulated into alumina matrixes by sol-gel chemistry, and their chemical, structural, electronic, and catalytic behaviors were investigated. Monodisperse nanoparticles were uniformly distributed in the alumina frameworks as observed by TEM images, and single-particle energydispersive spectroscopy (EDS) analyses confirmed the high compositional uniformity of the bimetallic nanoparticles. A combination of TEM, EDS mapping, TGA, XANES and EXAFS studies were used to fully characterize the alumina-supported nanoparticles before and after thermal treatments. It was observed that the size distribution of the final PdAu nanoparticles was highly dependent on calcination conditions, and careful high-temperature calcinations at 300 °C could be used to remove organic PVP stabilizers with minimal particle aggregation and/or structural transformations. The resulting supported nanoparticle catalysts were found to be active as hydrogenation catalysts. EXAFS analysis of coreduced PdAu nanoparticles indicated they had near-alloy structures with slightly Au-rich cores and Pd-rich shells before and after calcination, while intentionally designed Pd-core Au-shell nanoparticles retained their structures after calcination. XANES spectra of both coreduced and core-shell PdAu nanoparticles were also examined and showed that the PdAu coreduced nanoparticles had fewer Au valence d-band vacancies in comparison to monometallic nanoparticles while the PdAu core-shell nanoparticles had relatively higher Au valence d-band vacancies than the coreduced PdAu nanoparticles.

Low levels of 1-methylimidazole additives have been found to have dramatic effects on the resulting stability of gold and bimetallic nanoparticles in ionic liquids (ILs).

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