Charakterisierung und katalytische Aktivität von Ni2+-ausgetauschten X- und Y-Zeolithen. II. Die Reduzierbarkeit des Ni2+ durch niedere Olefine und die Dimerisierungsaktivität der Ni2+-ausgetauschten Zeolithe

Characterization and Catalytic Activity of Ni²⁺ -X and -Y Zeolites. II. Reducibility of Ni²⁺ by Low Olefines and the Dimerization Activity of the Ni²⁺ -Zeolites The reducibility of Ni²⁺ in X and Y zeolites by hydrogen, but-1-ene, propene, and ethene is compared. The degree of reduction was determined after isothermal reduction and reoxidation by the TPR method. At 673 K on X zeolites the reducibility decreases in the order: H₂ > but-1-ene, propene > ethene. On Y zeolites an inversion takes place: but-1-ene, propene > H₂, ethene. The mechanism of reduction by olefins should be determined by an intermediate splitting off of a hydride ion as a reducing species. Such a mechanism explains the higher degree of reduction in the more acid Y zeolites. Assuming low valent nickel as an active center in ethen dimerization the induction period results from the reduction of Ni²⁺ ions.