Recent advances in engineering montmorillonite into catalysts and related catalysis

Montmorillonite, a ubiquitous clay mineral, has been engineered into a variety of porous and nanostructured catalysts, owing to its peculiar layered structure with characteristic surface and intercalation chemistry. Such a class of catalysts have continuously received considerable attention in both science and industry. This review examines recent advance in engineering montmorillonite into metal ion-exchanged montmorillonite catalysts, acid-activated montmorillonite catalysts, organo-montmorillonite catalysts, pillared interlayered montmorillonite catalysts and montmorillonite-supported catalysts. The former two types of montmorillonite-based catalysts have been used in the catalytic cracking, dehydration, hydrolysis, esterification, polymerization, alkylation, and Fischer-Tropic synthesis. The introduction of oxide pillars in the interlayer space of montmorillonite and the immobilization of metal oxides or zero-valent metals on the surface of montmorillonite allow montmorillonite to be used in the catalytic oxidation, reduction, isomerization and coupling reactions. Currently, the role of montmorillonite in acid catalysis, redox catalysis, and free radical catalysis have been partly revealed. The effect of the structures and the active sites of modified montmorillonite on its catalytic performance need to be investigated in more detail. Future work is suggested to focus on solving engineering problems and exploring novel catalytic applications of montmorillonite, in particular exfoliated montmorillonite nanolayers.