Microwave-Assisted Synthesis of Classically Immiscible Ag–Ir Alloy Nanoparticle Catalysts

We present the synthesis of Ag–Ir alloys in the form of solid-solution nanoparticles (NPs). Ag and Ir are classically immiscible in the bulk and therefore the physical properties of Ag–Ir alloys are unknown. A convenient microwave-assisted, solution-phase method that employs readily available Ag­(NO...

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Bibliographic Details
Published in:ACS catalysis 2018-12, Vol.8 (12), p.11386-11397
Main Authors: Guo, Hongyu, Li, Hao, Jarvis, Karalee, Wan, Haiqin, Kunal, Pranaw, Dunning, Samuel G, Liu, Yulu, Henkelman, Graeme, Humphrey, Simon M
Format: Article
Language:English
Subjects:
alloy nanoparticles
chemistry
crotonaldehyde hydrogenation
heterogeneous catalysis
INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
iridium
metallic nanoparticles
microwave synthesis
silver
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Summary:We present the synthesis of Ag–Ir alloys in the form of solid-solution nanoparticles (NPs). Ag and Ir are classically immiscible in the bulk and therefore the physical properties of Ag–Ir alloys are unknown. A convenient microwave-assisted, solution-phase method that employs readily available Ag­(NO3) and IrCl3 precursors enables the preparation of small (2.5–5.5 nm) Ag–IrNPs with alloyed structures. Ag x Ir(100–x)NPs can be obtained by this method between x = 6–31. The Ag–IrNPs resist dealloying upon heating up to 300 °C. Ir-rich Ag–IrNPs dispersed on amorphous silica are significantly more active gas-phase alkene hydrogenation catalysts than pure IrNPs. Density functional theory (DFT) and theoretical modeling studies reveal that the Ag–IrNPswhich are consistently larger than monometallic IrNPs prepared under the same conditionshave comparatively fewer strong H-binding edge sites. This promotes faster H atom transfer to coadsorbed alkenes. Ag–IrNPs supported on amorphous Co3O4 show a linear composition dependence in the selective hydrogenation of CO versus CC bonds: more Ag-rich Ag–IrNPs are more selective toward CO hydrogenation of the α,β-unsaturated aldehyde crotonaldehyde, yielding the industrially desirable crotyl alcohol. Furthermore, deposition of Ag–IrNPs inside Co3O4 mesopores results in an additional ∼56% selectivity enhancement.
ISSN:2155-5435
2155-5435
DOI:10.1021/acscatal.8b02103