ZEOLITE-SUPPORTED TRANSITION-METAL CATALYSTS

This chapter discusses zeolite-supported transit ion metal catalysts. In catalytic applications, zeolites are predominantly used in their acidic form. The most important process in this category is fluidized catalytic cracking, based on rare-earth-exchanged zeolites, mainly X and Y of the faujasite structure with small admixtures of ZSM-5. Another industrial process in this group is catalytic dewaxing using mordenite and ZSM-5. Within the vast group of zeolite catalysts, the focus in the chapter is on one subgroup: materials that contain reduced particles of a transition metal or several transition metals dispersed inside zeolite cavities. A majority of transition metal/zeolite catalysts are bifunctional, i.e., strong acid sites are present in the same zeolite. A process based on a zeolite-encaged metal in the absence of acid sites is the dehydrocyclization of small linear alkanes (such as n-hexane) to aromatics. NOx abatement by zeolite-supported Cu is mentioned briefly in the chapter that illustrates the potential for environmental catalysis; it also opens prospectives for stabilizing elements in unusual valence states, in addition to unusual states of aggregation and complexation. © 1993, Academic Press Inc.