Studies of the oxidation state and location of palladium species in Al13-pillared montmorillonite

Abstract

Electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) have been used to establish the oxidation state of palladium in Pd(NH₃)²⁺₄-doped Al₁₃-pillared Texas montmorillonite clay (Pd/Al₁₃ STx) after various sample treatments. Heating of Pd/Al₁₃ STx in flowing oxygen at 350 and 500 °C produces Pd³⁺which appears to migrate into the montmorillonite lattice. Both Pd²⁺ and Pd³⁺ are strongly bound to the internal and external surfaces of the montmorillonite layers. Some of the Pd²⁺ species present after heating can be reduced to Pd⁺ by subjecting the sample to flowing hydrogen at ambient temperature. Pd³⁺ cations generated during heating are essentially unaffected by this reductive treatment.