VALENCE VARIATION OF YB ENCAPSULATED IN THE SUPERCAGE OF Y-TYPE ZEOLITE

Yb/K-Y exhibits various catalytic reactivities by evacuation at various temperatures. By evacuation with elevating temperature, successive desorption of hydrogen, ammmonia, and hydrogen was observed. Yb L2 edge XANES spectra showed that Yb is present as a mixture of Yb2+ and Yb3+. The sample as prepared consists of Yb3+ species mainly. With elevating the evacuation temperature, the fraction of Yb2+ increases and reaches a maximum in the vicinity of 500 K. Then, the fraction of Yb2+ decreases and reaches a minimum at 873 K. The valence variation is in a good accordance with a catalytic variation. Desorption of hydrgen and ammonia corresponds to the chemical change of Yb species: amine --> imine --> nitride.