Local structure of Pt and Pd ions in $Ce_{1-x}Ti_xO_2$: X-ray diffraction, x-ray photoelectron spectroscopy, and extended x-ray absorption fine structure

摘要

$Ce_{1-x-y}Ti_xPt_yO_{2-delta}$(x=0.15; y=0.01) and $Ce_{1-x-y}Ti_xPd_yO_{2-delta}$ (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 $CeO_2$ 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 sim 2.47 AA (2.63 AA for Pt–O) which are much higher than average Ce–O bonds of 2.34 AA.