Modified Tin(IV) Oxide (M/SnO₂ M=Cr, La, Pr, Nd, Sm, Gd) Catalysts for the Oxidation of Carbon Monoxide and Propane

Author： Harrison P.G. Bailey C. Azelee W.

ISSN： 0021-9517

Source： Journal of Catalysis, Vol.186, Iss.1, 1999-08, pp. : 147-159

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Abstract

Materials formed by the incorporation of rare earth cations (M=La, Pr, Nd, Sm, Gd) into tin(IV) oxide using coprecipitation methods show no significant enhancement of catalytic activity toward the oxidation of carbon monoxide or propane over that of tin(IV) oxide itself. For chromium-promoted tin(IV) oxide catalysts, the temperature by which complete conversion of carbon monoxide and propane occurs is dependent on both the Cr:Sn atom ratio in the catalyst and the preparative route by which the chromium is incorporated into the catalyst. As prepared all the materials are hydrous gels comprising very small (<10 nm) particles of tin(IV) oxide over which the modifying metal component appears to be dispersed uniformly. Chromium(VI) oxyanions of the types CrO₄^2-, Cr₂O₇^2-, and Cr₃O₁₀^2- are sorbed on to the surface of the tin(IV) oxide particles in the freshly prepared material derived from aqueous CrO₃ and tin(IV) oxide gel. Prior to calcination the materials are microporous, but significant changes in specific surface area, pore volume, and pore size occur at temperature >673 K. Powder X-ray diffraction and electron microscopy confirm the formation of Cr₂O₃ on calcination at 1273 K.