ELECTRON-PARAMAGNETIC-RESONANCE AND ELECTRON-SPIN ECHO MODULATION SPECTROSCOPIC STUDIES ON THE LOCATION AND ADSORBATE INTERACTIONS OF PARAMAGNETIC PD ION SPECIES IN PDII-EXCHANGED K-L ZEOLITE

Dehydration and adsorbate (O2, H2O, CD3OH, CH3OD, CH3CH2OD, C2D4, CO) interactions of paramagnetic palladium ion species in Pd(II)-exchanged K-L channel type zeolite are studied by electron paramagnetic resonance (EPR) and electron spin echo modulation (ESEM) spectroscopies. The EPR spectrum of an activated sample at ca. 400-500-degrees-C shows the formation of one Pd(I) species which has g(parallel-to) = 2.821 and g(perpendicular-to) = 2.125 and which is suggested to be located at the centre of double eight rings of the L zeolite framework. Adsorption of oxygen on an activated sample oxidizes the reduced Pd(I) to Pd(II) interacting with a superoxide ion. Equilibration with methanol or ethanol results in a broad isotropic EPR signal which is attributed to the formation of small charged palladium clusters. ESEM shows that the Pd clusters coordinate to one molecule of methanol or ethanol. EPR and ESEM results indicate that equilibration with C2D forms a new Pd(I) species with g(parallel-to) = 2.661 and g(perpendicular-to) = 2.125 coordinating to one molecule of ethene. Adsorption of carbon monoxide results in a complex containing two molecules of carbon monoxide based upon resolved C-13 superhyperfine and analysis of C-13 modulation.