ELECTRON-SPIN-RESONANCE AND ELECTRON-SPIN ECHO MODULATION STUDY OF PARAMAGNETIC RU SPECIES GENERATED IN LI-X, NA-X, K-X, AND CA-X ZEOLITES - ADSORPTION OF CARBON-MONOXIDE, OXYGEN, AND WATER

Paramagnetic ruthenium species are formed in X zeolites with different cocations after evacuation at 300°C and subsequent adsorption of various molecules. The various species formed after activation were characterized by electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopies. No major difference was observed in the ESR spectra after activation for the zeolites exchanged with [Ru(NH3)6]Cl3 or [Ru(NH3)5Cl]Cl2. Activation of these zeolites did not generate any substantial amount of paramagnetic species. However, exposure of the activated zeolite, except for RuLi-X, to CO, O2, and H2O resulted in a significant increase in the spin concentration which was assigned mainly to Ru(III) species. The increase in the spin concentration is suggested to be due to dissociation of Ru(III) dimers in the β-cage of the zeolite structure when an adsorbate is added. Adsorption of CO and O2 generated one or more Ru(III) adducts depending on the nature of the cocation. The number of coordinated CO molecules was assessed by infrared spectroscopy. Adsorption of D2O generated Ru(III) coordinated to three water molecules based on ESEM data; this adduct has the same coordination geometry regardless of the cocation type, but the cocation does affect the rhombic g-factor magnitudes. ESEM results also show that Ru(III) species are situated less than 0.36 nm from an aluminum nucleus. © 1990 American Chemical Society.