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Browsing Chemistry by Subject "Bimetallic"
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Item Following the Reactivity of Au25(SC8H9)18 - Clusters With Pd2+ and Ag+ Ions Using in Situ X-ray Absorption Spectroscopy: A Tale of Two Metals(American Chemical Society, 2015) Shivhare, Atal; Lee, Kee Eun; Hu, Yongfeng; Scott, Robert WJThis work examines the reaction between Au25(SC8H9)18– clusters with palladium acetate (Pd2+) and silver nitrate (Ag+) using UV–vis, transmission electron microscopy (TEM), extended X-ray absorption spectroscopy (EXAFS), and in situ liquid cell X-ray absorption spectroscopy (XAS). UV–vis results show that upon the addition of Pd2+ and Ag+ salts to Au25(SC8H9)18– clusters significant changes are seen in the optical properties of the clusters. In the case of Pd, there is little to no change in the size of the clusters evidenced by TEM, while for Ag systems, significant particle growth is seen. In situ XAS results show that Pd2+ reacts with the staple motifs of Au25(SC8H9)18– clusters and forms Pd(II) thiolate species, as shown by the Pd L3- and Au L3-edge data as well as Pd K-edge EXAFS results. However, Ag L3-edge data suggest that Ag+ reduces to Ag on the cluster core and does not form Ag(I) thiolate species. This work highlights the power of using in situ XANES to follow Au cluster transformations in liquid environments.Item in situ X-ray Absorption Spectroscopic Analysis of Gold-Palladium Bimetallic Nanoparticle Catalysts(American Chemical Society, 2013) MacLennan, Aimee; Banerjee, Abhinandan; Hu, Yongfeng; Miller, Jeffrey T; Scott, Robert WJGold–palladium core–shell nanoparticles have been previously shown to be extremely effective catalysts for a number of oxidation reactions including the aerobic oxidation of alcohols. However, the novel activity and durability of such catalysts are still poorly understood, and there are several putative mechanisms by which oxidation reactions can proceed. Previously we showed that Pd(II) salts in the presence of Au nanoparticles were also effective catalysts for the room temperature oxidation of crotyl alcohol. Herein we show an in situ X-ray absorption spectroscopy (XAS) study at both the Pd–K and Pd-LIII edges of Au nanoparticle/Pd(II) salt solutions in the presence of crotyl alcohol. Liquid cells with X-ray permeable windows were used to obtain quick-scan XAS data during the oxidation of crotyl alcohol, allowing for time-resolved Pd speciation information and information about the reaction mechanism and kinetics. XAS measurements definitively show that the first step of this reaction involves Pd reduction onto the Au nanoparticles; in addition, further studies of the stability of the resulting Au–Pd core–shell nanoparticles toward oxygen gas suggests that the role of Au in such catalysts is to prevent the reoxidation of the catalytically active surface Pd atoms. Catalytic crotyl alcohol oxidation measurements were done which validated that the in situ reduction of Pd(II) in the presence of Au nanoparticles did indeed result in catalytically active AuPd bimetallic catalysts.Item Rational Design and Characterization of Bimetallic Gold-Palladium Nanoparticle Catalysts(Wiley, 2015) Scott, Robert WJThis feature article covers a long‐term project in our laboratory at the University of Saskatchewan towards the rational synthesis of controlled‐architectures of gold‐palladium bimetallic nanoparticle catalysts for use as low‐temperature alcohol oxidation catalysts. Syntheses involve controlled growth of nanoparticle architectures via solution‐based nanoparticle synthetic strategies, followed by deposition of the designed particles onto solid supports. In addition, characterization methods used to elucidate structures of the synthesized particles before and after activation for catalysis will be discussed. This includes traditional characterization methods such as transmission electron microscopy and X‐ray absorption fine structure spectroscopy (EXAFS), but also includes, more recently, the use of in situ X‐ray absorption spectroscopy studies of gold‐palladium nanoparticle catalysts. Strategies and challenges towards the rational synthesis of heterogeneous supported‐nanoparticle catalysts based on bimetallic nanoparticle precursors will be detailed and contrasted with more traditional routes to synthesize such catalytic materials.Item Supported Bimetallic AuPd Clusters Using Activated Au25 Clusters(Elsevier, 2017) Lee, Kee Eun; Shivhare, Atal; Hu, Yongfeng; Scott, Robert WJBimetallic AuPd nanoparticles on alumina supports were prepared using Au25(SR)18 precursors activated by mild calcination or LiBH4 treatment, followed by selective deposition of Pd via ascorbic acid reduction. Comparison of their catalytic activity for the oxidation of crotyl alcohol showed that bimetallic structure had significantly improved catalysis compared to Pd/Al2O3. In particular, AuPd samples grown from LiBH4-activated Au25 clusters exhibit the highest catalytic activity as well as high selectivity towards crotonaldehyde formation, likely due to their smaller particle sizes as compared to AuPd samples grown from calcined Au25 clusters. X-ray absorption spectroscopy (XAS) at the Au L3-edge, Pd L3-edge and Pd K-edges showed that the resulting bimetallic AuPd nanoparticles had Au-Pd core-shell structures with a 4d-electron poor Pd surface.