Characterization of Co-ZSM-5 catalysts prepared by solid-state exchange:influence of Co/Al ratio on cobalt speciation and catalytic properties

摘要

Physicochemical and catalytic properties of cobalt-containing ZSM-5 zeolites prepared from cobalt acetate by solid-state ion-exchange are compared as a function of the Co/Al atomic ratio.When Co/Al=1/2,cobalt is present both as ions in cationic sites and oxide particles on the zeolite;for Co/Al=1 or 3/2,TEM and EXAFS show that a cobalt phyllosilicate phase is present on the outer surface of the zeolite,but Lewis acid sites (Co~(2+) ions) are still accessible as revealed by pyridine adsorption.Catalyst prepared with Co/Al=1 exhibits high activity and selectivity toward acetonitrile in the ammoxidation of ethane and ethylene.Co~(2+) ions inside the zeolite and on the phyllosilicate surface seem to be the active species.