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Formation and characterization of nanosize α -Rh2O3

Rhodium and Rh-oxide based catalysts have found important applications, for example, in methanol or methane oxidations, decomposition of NOx gases to N2 and O2 etc. The catalytic chemistry of rhodium involves various redox reactions in which rhodium participate in different Rh-oxide forms. Reference literature demonstrates a high discrepancy between the number of publications about the catalytic activity of Rh-catalyst, on one hand, and, on the other, the redox chemistry of rhodium. For that reason, we have investigated the formation of α -Rh2O3 at the laboratory level. We focused on the formation of α -Rh2O3 from amorphous rhodium (hydrous)oxide obtained by precipitation from Rh(NO3)3 aqueous solution. The isolated precipitate was dried, then heated in air atmosphere up to 650°C. Samples were characterized by XRD, FT-IR, Raman and FE-SEM. The XRD of sample obtained at 400°C showed a broad and intensive peak which can be assigned to the amorphous nature of the sample. This peak is positioned at the Bragg angles corresponding to prominent peaks of α -Rh2O3. For the same sample, FT-IR spectrum showed one very broad and intensive peak centered at 544 cm-1, while the corresponding Raman spectrum showed broad peaks at 268, 411 and 556 cm-1. The Raman spectrum of the sample obtained at 650 cm-1 showed peaks at 276, 422, 568 and 610 cm-1, which can be attributed to α -Rh2O3 in line with XRD. FE-SEM showed a gradual increase in size (in the nanometer range) of rhodium oxide particles with an increase of temperature reaching 650°C.

α -Rh2O3; XRPD; FT-IR; Raman; FE-SEM

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