New ceria-based catalysts for pollution abatement

In the present work, we describe the use of fluorite-structured solid solutions, based on mixtures of CeO2/La2O3/Pr2O3, and similar systems, i.e. CeO2/Ln(2)O(3)/Pr2O3 where Ln=Tb, Sm, and Gd as effective catalysts for methane combustion. Mixed lanthanide oxide doped ceria solid solutions were prepared using an evaporation method from nitrate precursors and were subsequently calcined to 1073 K. Sample charactcrisation was achieved using powder X-ray diffraction (PXRD) and temperature programmed reduction (TPR). PXRDs obtained subsequent to a 12 h calcination at 1073 K for 12 h all show peaks corresponding to a fluorite-based structure. There are no additional features suggestive of large-scale segregation or ordered superstructure formation. This was confirmed by Rietveld analysis which showed that the lattice possesses cubic nature with a=b=c=5.50 Angstrom. Methane combustion tests show that the most effective catalysts are those lanthanide oxide doped ceria catalysts prepared with 5% Pi. molar metal ratios. TPR experiments suggest PrO2 is an essential component and both surface and bulk chemistries have important roles in catalytic activity. (C) 2000 Elsevier Science B.V. All rights reserved.