Rational Design of Supported PdAu Nanoparticle Catalysts from Structured Nanoparticle Precursors

Abstract

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.

Chemical Preparation of Supported Bimetallic Catalysts. Gold-Based Bimetallic, a Case Study

“…No increase in the bimetallic particle size, initially of 3 nm, was observed after the mesoporous silica has been formed and even after thermal treatments under O 2 and then under H 2 at 450˝C, carried out to eliminate the organics. PVP-stabilized Au-Pd colloids with several Au/Pd ratios, and synthesized either by co-reduction of the precursors in methanol by NaBH 4 or by sequential reduction of K 2 PdCl 4 in methanol by NaBH 4 then of HAuCl 4 by ascorbic acid, were added to a alumina-precursor sol-gel mixture [119]. After calcination and reduction at 300˝C to form alumina and remove PVP, the metal particles arising from co-reduction had a slightly Au-rich core and Pd-rich shell, and were slightly larger (5.5 nm) than in colloids (4.1 nm).…”

Structural evolution of bimetallic Pd-Ru catalysts in oxidative and reductive applications

“…More details about obtaining EXAFS function can be found in previous publications [23,24]. The EXAFS fitting was performed in R-space using theoretical phase shifts and amplitudes generated by FEFF.…”

Catalysing Sustainable Fuel and Chemical Synthesis

“…In contrast, the combustion of propene, the undesired secondary product of crotonaldehyde decarbonylation, is enhanced by co-adsorbed oxygen [160]. Scott et al prepared the inverse Au core-Pd shell nanoparticles and explored the catalytic cycle for alcohol selox to assess their associated stability [205,[209][210][211][212]. In situ Pd-K and Pd-L III edge XAS of a Au nanoparticle/ Pd(II) salt solution were undertaken to discriminate two possible reaction mechanisms.…”