From layer compounds to catalytic materials

This paper intends to review some important directions in which layered compounds have been used as catalysts or converted to catalytic materials. Since several excellent review papers of related topics have already presented in the literatures, duplication of the contents is tried to avoid. Clays an the layered compounds which attracted most of the attention since modified clays and pillared clays have been used and examined as catalysts for more than half a century. Although the use of pillared clays as cracking catalysts was considered to be impractical nowadays, they still demonstrated catalytic activities in many reactions, beneficial from the large porous structures, acidity or other functionality endowed by the pillars. The pillaring technique has also been employed to other layered compounds, especially metal oxides, in which organic-expanded derivatives were often used as the precursor. The applications of the pillared metal oxides in catalysis are also described. Correlatively, some of the organic-expanded layered metal oxides were found to disperse as separated sheets in organic solutions and could serve as a precursor for making monolayer-dispersed supported catalysts. At last, attention is brought to the possibility of transformation of laminar compounds of thin layers into ordered structures of micropores and mesopores under the influence of interlayer template species. That offers a route to make new porous materials, which may not be easily obtained by other methods. (C) 1999 Elsevier Science B.V. All rights reserved.