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(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 resistdealloying upon heating up to 300 degrees 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 alpha,beta-unsaturated aldehyde crotonaldehyde, yielding the industrially desirable crotyl alcohol. Furthermore, deposition of Ag-IrNPs inside Co3O4 mesopores results in an additional similar to 56% selectivity enhancement.