Synergic catalytic effects in confined spaces
Combining the merits of confined effects and synergic effects is a promising way to build efficient and versatile heterogeneous catalytic systems. Recently, heterogeneous bifunctional and even trifunctional catalysts have attracted more and more attention because the synergic catalysis between the multifunctional groups could be developed within confined spaces. Significantly, many incompatible functional groups have been successfully incorporated into one confined space and show superior catalytic performance. Understanding the synergic catalytic effects in confined spaces is of great significance for constructing sophisticated and efficient catalytic systems. This feature article summarizes the recent advances in synergic catalysis in confined spaces as well as the methods to build synergic catalysts. The confined spaces provided by the one- or three-dimensional rigid pores of mesoporous silicas or the two-dimensional flexible interlayer regions of layered double hydroxides (LDHs) are mainly involved. An important reason for choosing mesoporous silica and LDH solids is that they additionally participate in synergic effects through their intrinsic active sites, the acidic hydroxyl groups on mesoporous silicas and acid-base bifunctional sites on layered double hydroxides, for example. Visible enhancement of catalytic activity or enantioselectivity or both was observed in aldol, Michael, Friedel-Crafts and Henry reactions, cyanosilylation, hydrolytic kinetic resolution of epoxides, etc.