An X-Ray Absorption Spectroscopy Determination of the Morphology of Palladium Particles in K L-Zeolite

Abstract

Particle morphologies for 2 and 3 wt% Pd/K L-zeolite have been determined using X-ray absorption spectroscopy (XAS). X-ray absorption near edge structure–temperature programmed reduction (XANES-TPR) was used to check for the presence of unreduced palladium cations in the locked cages after reduction. A series of calculations were performed to determine coordination numbers for the first three coordination shells for different ideal particle morphologies (spherical, hemispherical, cylindrical, and disc-like). The X-ray absorption fine structure (XAFS) results suggest the formation of ∼10 and 16 atom disc-like particles, for 2 and 3 wt% Pd/K L-zeolite, respectively. The lattice expansion for the 3 wt% Pd/K L-zeolite is consistent with chemisorption and TPD of hydrogen and indicates a bulk hydride formation. The effects of morphology and metal support interaction on neopentane conversion over these catalysts are briefly discussed.