Synergic catalytic effects in confined spaces

Abstract

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.

Design and fabrication of mesoporous heterogeneous basic catalysts

“…By spatial isolation in mesoporous supports, the coexistence of incompatible active sites becomes possible. [387][388][389][390][391]. The acidic sites include silanols, 365,366 ureas, 367 sulfonic acids, 368-370 carboxylic acids, 371 phosphotungstic acids, 372 and Lewis acids originating from Al-doped silica frameworks; [373][374][375] whereas the basic sites vary from amines (primary, [376][377][378] secondary, 379-381 tertiary amine, 382 and chiral amines 383,384 ) to alkaline earth metal oxides 385 and layered double oxides.…”

Effects of Mesopore Internal Surfaces on the Structure of Immobilized Pd-Bisphosphine Complexes Analyzed by Variable-Temperature XAFS and Their Catalytic Performances

“…Mesoporous silica is an ideal support material for the preparation of highly active catalysts because of its high surface area, inert nature of silica, and functionalization ability [1][2][3][4][5][6][7][8][9][10]. Among various approaches to functionalizing mesoporous silica, silane-coupling reaction, a reaction between surface silanol and functional molecules containing a trialkoxy group, is one of the most common procedures for the preparation of a supported catalyst.…”

Tuning the aspect ratio of arrays of silica nanochannels

“…Ordered mesoporous silica materials provide a versatile platform for the development of a variety of applications, including diverse fields such as sensor technology, [1][2][3][4] drug delivery, 5-8 catalysis, [9][10][11] imaging, 12,13 and light-harvesting. 14,15 As the different applications require specific particle sizes and shapes, methods to control the growth of the mesoporous silica particles have become increasingly important.…”