CYCLOPROPANE REACTIONS OVER BRONSTED, CATION, AND METAL SITES IN NI NAX ZEOLITES/

The reactions of cyclopropane in helium and hydrogen were investigated over two different loadings (10.7 and 6.0 wt%) of ion-exchanged Ni/Na X zeolites. The effects of reduction temperatures and hydrogen treatme nt times on catalytic activity and acidity were studied. Apparent acti vation energies ranged from 35.5 to 95.4 kJ/mol for isomerization reac tions over two loadings of Ni/NaX zeolite reduced under different cond itions. Rates of isomerization, hydrogenation, and hydrogenolysis are also reported. Deactivation and regeneration of catalysts are discusse d. Particle sizes of 8.9 and 17.3 nm were observed in highly reduced N i zeolites. Sintering of Ni was observed on the surfaces of the zeolit e crystallites. Temperature programmed reduction studies show that sto ichiometric amounts of H-2 were used to completely reduce all Ni in th e samples. Infrared analysis of chemisorbed pyridine on these material s show that higher loadings of Ni result in higher initial acidities. Increased amounts of reduced Ni significantly increase the number of B ronsted sites on the surface of the catalyst. Electron paramagnetic re sonance revealed that Ni+ was present in low loaded Ni/NaX samples upo n reduction at low temperatures (350-degrees-C), while higher reductio n temperatures (450-degrees-C) resulted in a broad EPR signal correspo nding to Ni0 only. Na vapor deposition experiments, designed to select ively poison Bronsted sites on the catalyst, reveal that Ni+ ions are active in cyclopropane isomerization reactions at high temperatures. 1 994 Academic Press. Inc.