Characterization of metallic species on Ni- And Co-containing ZSM-5 catalysts - reduction behavior and catalytic properties

A series of Co- and Ni-containing ZSM-5 zeolites with varying metal loading was prepared by solid-state ion exchange and by wet impregnation. Solid-state ion exchange led to highly dispersed metal ions inside the channels of ZSM-5. For the impregnated samples metal oxide clusters, mainly located on the exterior of the crystallites, were observed. Reduction at 573 K of NiZSM-5 prepared by solid-state ion exchange led to the formation of small metallic clusters inside the pores, whereas reduction at 773 K led to the formation of large Ni clusters outside the channels. CoZSM-5 could be only reduced at 773 K, where larger particles were rapidly formed. After low-temperature reduction, NiHZSM-5 showed in the hydroconversion of n-heptane an enhanced selectivity for isomerization, and after high-temperature reduction, for hydrocracking reactions. On CoHZSM-5 increased metal loading led to an extended hydrogenolysis activity in the hydroconversion of n-heptane.