Abstract
Adsorbate interactions of paramagnetic palladium(I) species in Pd(II)-exchanged Na−MCM-22 zeolite are studied by electron spin resonance (ESR) and electron spin-echo modulation (ESEM) spectroscopies. Oxidation and subsequent evacuation at 825 K of Na−MCM-22 zeolite exchanged with Pd(NH3)4Cl2 results in the formation of a Pd(I) species. Monovalent palladium can be produced in PdNa−MCM-22 material by room temperature hydrogen reduction after dehydration and O2 treatment at high temperature. Addition of hydrogen to PdNa−MCM-22 after dehydration, O2 treatment, and evacuation (activation) is found to increase the concentration of Pd(I) at room temperature and at higher temperature is found to reduce Pd(I) to Pd(0)n (palladium clusters). Adsorption of O2 and H2O to an activated sample containing Pd(I) generates a Pd(II)−O2- species with g⊥ > g∥. Adsorption of CO on an activated sample results in a Pd(I)−(CO)2 complex which partially transforms to Pd(I)−CO on evacuation. Adsorption of ethylene on an activated sa...
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