Biphasic Pd−Au Alloy Catalyst for Low-Temperature CO Oxidation

Abstract

Low-temperature CO oxidation over a compositional series of Pd-Au nanoalloy catalysts supported on silica fume was studied. Except for the pure metals, these materials invariably showed biphasic separation into palladium- and gold-rich components. Performance was optimal for a catalyst of bulk composition Pd(4)Au(1), a mixture of Pd(90)Au(10) (72.5 at. %) and Pd(31)Au(69) (27.5 at. %), that was remarkably active at 300 K and more stable than a pure Au catalyst. For bulk materials dominated by Pd (Pd:Au = 16:1; 8:1; 4:1), the palladium-rich alloy fraction frequently adopted hollow sphere or annular morphology, while the gold-rich crystals were often multiply twinned. Quantitative powder X-ray diffraction (XRD) showed that under the synthesis conditions used, the Au solubility limit in Pd crystals was approximately 12 at. %, while Pd was more soluble in Au (approximately 31 at. %). This was consistent with X-ray photoelectron spectroscopy (XPS), which revealed that the surfaces of Pd-rich alloys were enriched in gold relative to the bulk composition. In situ Fourier transform infrared spectra collected during CO oxidation contained a new band at 2114 cm(-1) (attributed to linear CO-Au/Au-Pd bonds) and reduced intensity of a band at 2090 cm(-1) (arising from a linear CO-Pd bond) with escalating Au content, indicating that the Pd sites became increasingly obscured by Au. High-resolution electron micrographs (HRTEM) of the Pd-rich alloys revealed atomic scale surface defects consistent with this interpretation. These results demonstrate that gold-containing biphasic Pd nanoalloys may be highly durable alternatives for a range of catalytic reactions.

Surface Composition and Catalytic Evolution of Au x Pd1−x (x = 0.25, 0.50 and 0.75) Nanoparticles Under CO/O2 Reaction in Torr Pressure Regime and at 200 °C

“…Here we selected Au x Pd 1-x bimetallic nanoparticle system as model catalysts [4,[17][18][19][20][21][22][23][24]. CO/O 2 reaction was chosen to avoid different products of parallel reaction channels so that we could have a better understanding of relationship of surface composition and catalytic activity.…”

Ambient-stable tetragonal phase in silver nanostructures

“…M etal nanoparticles with tailored crystalline phases and internal microstructures (for example, twins and stacking faults) represent a class of promising building blocks in achieving ultrahigh-strength materials [1][2][3][4][5][6][7][8] and efficient catalysts 9 . Controlled synthesis of metal nanoparticles with well-defined compositions, sizes and morphologies has been extensively studied in the last decade [10][11][12][13][14] .…”

Gold, an alternative to platinum group metals in automobile catalytic converters

“…A mixture of Pd (90%)/Au (10%) (72.5%) and Pd (31%)/Au (69%) (27.5%) was found to be remarkably active at 27°C while at the same time this catalyst was more stable than a pure Au catalyst [71].…”