Mesoporous molecular sieves as advanced supports for olefin metathesis catalysts

Mesoporous molecular silicas and aluminas based materials are excellent model supports for modification with catalytically active species for various organic reactions. They offer well-ordered structures, although of amorphous type, high BET areas, large mesopore volumes, and particularly the flexibility in the pore size adjustment. For application in metathesis, two principal ways of incorporation of catalytically active sites were investigated. The first one represents the modification with inorganic oxides (W, Mo, Re) while the second one is based on immobilization of organometallic complexes (Mo, Ru, W). This review discusses the preparation and properties of both types of heterogeneous catalysts and relates them to the activities, selectivities, and time-on-stream stabilities in different metathesis reactions. Particular attention is devoted to the role of mesoporous supports (textural properties, pore sizes and pore connectivities) as well as to catalyst recycling, real heterogeneous performance without any leaching of active species, and tolerance toward functional groups in the substrates under study.