Stabilizer-Free CuIr Alloy Nanoparticle Catalysts

Abstract

We present the direct synthesis of stabilizer-free Cu–Ir alloy nanoparticles (NPs) with tunable compositions. Cu and Ir are classically immiscible in the bulk. Therefore, the physical and catalytic properties of Cu–Ir alloys are largely unknown. A convenient microwave-assisted method utilizes readily available Cu2+ salts and IrCl3 in a modified polyol reaction; NaOH facilitates rapid solvent-assisted coreduction to yield Cu x Ir(100–x)NPs, where x can be varied within the approximate range 10–50. The as-synthesized NPs form stable dispersions of small (∼2 nm) and near-monodisperse cuboctahedra without the requirement of organic stabilizing (capping) agents, resulting in nanostructures that are directly amenable to heterogeneous catalysis. Cu x Ir(100–x)NPs supported on mesoporous Co3O4 show high selectivity toward the selective partial hydrogenation of crotonaldehyde to yield >40% crotyl alcohol in the vapor phase. The selectivity toward CO versus CC bond hydrogenation is largely insensitive to the Cu:Ir ratio but more Ir rich compositions are also more highly active. Density functional theory (DFT) studies explain this behavior in two ways: first the Co3O4 support enhances selective CO bond activation of the crotonaldehyde feedstock via favorable support-reagent adsorption; second, increasingly Ir-rich CuIrNP surfaces provide more Ir- sites, resulting in higher hydrogenation activity.

CuxIr1–x Nanoalloy Catalysts Achieve Near 100% Selectivity for Aqueous Nitrite Reduction to NH3

“…Further, 2D energy-dispersive spectroscopy (EDS) mapping of the NPs showed a homogeneous distribution of Cu and Ir across the NPs. 37 The actual composition of the as-synthesized alloy NPs was found to be close to the nominal ratio, as indicated by inductively coupled plasma optical emission spectroscopy of bulk samples (ICP-OES) (Table S1). Corresponding TEM images showed that the alloy NPs have an average size of around 2 nm, similar to the monometallic IrNPs (Figure S5).…”

“…35,36 Here, bimetallic Cu x Ir (100−x) NPs with various target compositions (x = 10, 25, and 50) were prepared using our previously developed methods. 37 The alloy Cu x Ir (100−x) NPs were deposited on a-SiO 2 , and their catalytic activities for nitrite reduction were measured. Powder X-ray diffraction (PXRD) patterns confirmed the random solid-solution structure of the alloy NPs, as the reflections showed a consistent shift to a higher angle with an increasing Cu content (Figure 3a).…”

“…These results are similar to our previous studies on PtAu and AgIr alloy NPs for hydrogenation: 34,35 although the line between Pt and Au (or Ir and Ag) on the CC hydrogenation volcano plot goes across the volcano peak, alloying Au into Pt (or Ag into Ir) does not lead to an improved performance for CC hydrogenation since their binding energy descriptors at the alloyed ensembles are located far from the volcano peak, which in turn leads to lower activity with the increased ratio of inert metallics. 34,41 Meanwhile, as Cu−Ir was found to be less tunable for H adsorption on Ir-related sites due to the intrinsic properties on the active 5d transition metals (Figure S8), 37 the H-coverage at those Ir sites of the alloys are expected to remain similar to that of Ir(111), leading to the superior NH 3 selectivity similar to pure IrNPs (Figure 2).…”

Solid-State Preparation of Metal and Metal Oxides Nanostructures and Their Application in Environmental Remediation

“…Among the most used photocatalyst are the nanostructured metal oxides [10,11]. However, their current preparation involves mainly in-solution methods [147][148][149][150][151][152][153][154], which present some problems in the isolation of the solid by elimination of the solvent as well as the elimination of the template and of the stabilizer [151].…”

PdAg Alloy Nanocatalysts: Toward Economically Viable Nitrite Reduction in Drinking Water

“…57,78 Ten randomly alloyed Pd 75 Ag 25 (111) surfaces were generated using our Python code based on the Atomic Simulation Environment library. 79 Since our μwI-assisted synthesis process was kinetically controlled, 80,81 the binding site sampling from a sufficient amount of randomly generated surfaces was found to be more representative than the calculations on ordered alloy structures. 82 Each average N or N 2 binding energy was sampled from ten binding sites on these surfaces.…”