Local structure of Pt and Pd ions in Ce_1-xTi_xO₂: X-ray diffraction, X-ray photoelectron spectroscopy, and extended X-ray absorption fine structure

Abstract

Ce_1-x-yTi_xPt_yO_2-δ (x = 0.15; y = 0.01) and Ce1_-x-yTi_xPd_yO_2-δ (x = 0.25; y = 0.02 and 0.05) are found to be good CO oxidation catalysts [ T. Baidya et al., J. Phys. Chem. B 110, 5262 (2006); T. Baidya et al., J. Phys. Chem. C 111, 830 (2007) ]. A detailed structural study of these compounds has been carried out by extended x-ray absorption fine structure along with x-ray diffraction and x-ray photoelectron spectroscopy. The gross cubic fluorite structure of CeO₂ is retained in the mixed oxides. Oxide ion sublattice around Ti as well as Pt and Pd ions is destabilized in the solid solution. Instead of ideal eight coordinations, Ti, Pd, and Pt ions have 4+3, 4+3, and 3+4 coordinations creating long and short bonds. The long Ti-O, Pd-O, and Pt-O bonds are ~2.47 Å (2.63 Å for Pt-O) which are much higher than average Ce-O bonds of 2.34 Å.