Abstract
To reveal the origin of the CO oxidation activity of Ruthenium nanoparticles (Ru NPs), we structurally characterized Ru NPs through Rietveld refinement analysis of high-energy X-ray diffraction data. For hexagonal close-packed (hcp) Ru NPs, the CO oxidation activity decreased with decreasing domain surface area. However, for face-centered cubic (fcc) Ru NPs, the CO oxidation activity became stronger with decreasing domain surface area. In comparing fcc Ru NPs with hcp Ru NPs, we found that the hcp Ru NPs of approximately 2 nm, which had a smaller domain surface area and smaller atomic displacement, showed a higher catalytic activity than that of fcc Ru NPs of the same size. In contrast, fcc Ru NPs larger than 3.5 nm, which had a larger domain surface area, lattice distortion, and larger atomic displacement, exhibited higher catalytic activity than that of hcp Ru NPs of the same size. In addition, the fcc Ru NPs had larger atomic displacements than hcp Ru NPs for diameters ranging from 2.2 to 5.4 nm. Enhancement of the CO oxidation activity in fcc Ru NPs may be caused by an increase in imperfections due to lattice distortions of close-packed planes and static atomic displacements.
Highlights
To reveal the origin of the CO oxidation activity of Ruthenium nanoparticles (Ru NPs), we structurally characterized Ru NPs through Rietveld refinement analysis of high-energy X-ray diffraction data
For fcc Ru NPs, the full width at half maximum (FWHM) of the diffraction peaks became sharper from Sample 1 to Sample 2
We determined the crystallographic information such as average crystalline domain size, domain surface area, lattice distortion, and B factor to reveal the origin of the CO oxidation activity of Ru NPs
Summary
To reveal the origin of the CO oxidation activity of Ruthenium nanoparticles (Ru NPs), we structurally characterized Ru NPs through Rietveld refinement analysis of high-energy X-ray diffraction data. Fcc Ru NPs larger than 3.5 nm, which had a larger domain surface area, lattice distortion, and larger atomic displacement, exhibited higher catalytic activity than that of hcp Ru NPs of the same size. Ruthenium (Ru) has recently attracted much attention as a catalyst for the oxidation of CO because of its high catalytic activity[1,2,3,4,5] This phenomenon was reported in 2013 for face-centered-cubic (fcc) type Ru nanoparticles (NPs) obtained by chemical reduction[6]. To help reveal the origin of the CO oxidation activity of Ru NPs, we used the results of the Rietveld analysis to evaluate the dependence of lattice distortion, domain surface area, and static atomic displacement on particle size
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