Physico-chemical and catalytic properties of ytterbium introduced into Y-zeolite

Abstract

Ytterbium was introduced into K⁺-exchanged Y-zeolite (Yb/K-Y) by impregnation from a liquid ammonia solution of the metal, and the change in the chemical state of the metal with evacuation temperature was investigated by infrared (IR), X-ray absorption fine structure (XAFS) and X-ray photoelectron (XPS) spectroscopies.

When ammonia was removed by brief evacuation at room temperature followed by evacuation at 333 K, the IR spectrum showed the presence of Yb amides. The amide species were observed up to 423 K. The Yb L₂-edge X-ray absorption near-edge structure (XANES) spectrum showed that the Yb species exist as 16.4% Yb(II) and 83.6% Yb(III) after evacuation at 333 K. The fraction of Yb²⁺ increased with increasing evacuation temperature and reached 44.2% at 573 K by the decomposition of Yb(II, III) amides to Yb(II, III) imides. The fraction of Yb(III) species increased at an evacuation temperature >600 K, owing to the decomposition of Yb imides to Yb nitride with concomitant formation of hydrogen. The Yb(II) imide species catalyses the isomerization of but-1-ene and the Michael reaction of cyclopent-2-enone with dimethylmalonate, while the Yb(III) nitride species catalyses the hydrogenation of ethene.