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Evolution of microstructure during the thermal activation of chromium-promoted tin(IV) oxide catalysts: An FT-IR, FT-Raman, XRD, TEM, and XANES/ EXAFS study

Chemistry of Materials, ISSN: 0897-4756, Vol: 11, Issue: 4, Page: 896-909
1999
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  • Citations
    36
    • Citation Indexes
      36
  • Captures
    13

Article Description

The chemical transformations occurring during the thermal activation of chromium-promoted tin(IV) oxide catalysts have been investigated by vibrational spectroscopy (FT-IR and FT-Raman), powder X-ray diffraction, transmission electron microscopy, and extended X-ray absorption fine structure and near-edge structure. Three methods of catalyst preparation have been employed: impregnation of SnO using aqueous CrO solutions, impregnation of SnO using aqueous chromium(III) nitrate solutions, and coprecipitation from aqueous solutions containing both tin(IV) and chromium(III) ions. The freshly prepared gel catalyst materials comprise small (ca. 1-2 nm) particles of hydrous tin(IV) oxide, on the surface of which are sorbed chromate(VI) anions, {Cr(HO)} cations, or polymeric γ-CrOOH depending on the preparative route. In all three cases, however, calcination at 573 K results in the formation of the mixed-valence chromium compound CrO. At higher calcination temperatures CrO is formed, which becomes more crystalline the higher the temperature. Concurrently, the size of the tin(IV) oxide particles increases, only slowly initially (ca. ×2 by 673 K and ca. ×4 by 873 K), but sintering to very large particles occurs at higher temperatures. No incorporation of chromium into the tin(IV) oxide lattice occurs even at high temperature. © 1999 American Chemical Society.

Bibliographic Details

Philip G. Harrison; Nicholas C. Lloyd; Wayne Daniell; Craig Bailey; Wan Azelee

American Chemical Society (ACS)

Chemistry; Chemical Engineering; Materials Science

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