Electron spin resonance (ESR), electron spin echo modulation (ESEM) and X-ray photoelectron spectroscopy (XPS) studies have been carried out on [Pd(NH3)4]2+-doped, Al13-pillared Laponite (Pd-Al13-Lap) clay activated in flowing oxygen at 250 to 500-degrees-C for 14 to 16 h. ESR and XPS studies indicate that some of the Pd2+ cations are converted into Pd3+. Activation at 250-degrees-C results in a broad ESR resonance from Pd3+ in an axial environment (species A). ESEM indicates that species A is Pd3+ bound to an Al13-pillar. At activation temperatures greater than 300-degrees-C an ostensibly isotropic signal develops (species B). ESEM data recorded for species B shows no Al-27 or Li-7 modulation and therefore species B is assigned to Pd3+ bound to the Laponite layers at sites remote from Li substitution sites in the octahedral sheet. At activation temperatures from 360 to 500-degrees-C, two ESR signals form (species A1 and A2) that are also indicative of Pd3+ in an axially symmetric environment. These signals appear near the resonant field of species A. ESEM indicates that species A1 is due to Pd3+ cations bound to the Laponite layers in the vicinity of a Li substitution site which could be either within the pseudohexagonal cavities in the basal oxygen surface or at crystallite edges. ESEM analysis of species A2 gives no Al-27 or Li-7 modulation as with species B, although the ESR suggests that species A2 occupies a site of lower symmetry than species B. Reduction of Pd-Al13-Lap with hydrogen gives ESR signals C, D, and E characteristic of a paramagnetic Pd species with orthorhombic symmetry. XPS analysis of this reduced sample indicates that these species are Pd+ cations.
