Abstract
Hybrid organic-inorganic catalysts have been extensively investigated by several research groups in the last decades, as they allow combining the structural robust-ness of inorganic solids with the versatility of organic chemistry. Within the field of hybrid catalysts, synthetic strategies based on silica are among the most exploitable, due to the convenience of sol-gel chemistry, to the array of silyl-derivative precursors that can be synthesized and to the number of post-synthetic functionalization strategies available, amongst others. This review proposes to highlight these advantages, firstly describing the most common synthetic tools and the chemistry behind sol-gel syntheses of hybrid catalysts, then presenting exemplificative studies involving mono- and multi-functional silica-based hybrid catalysts featuring different types of active sites (acid, base, redox). Materials obtained through different approaches are described and their properties, as well as their catalytic performances, are compared. The general scope of this review is to gather useful information for those approaching the synthesis of organic-inorganic hybrid materials, while providing an overview on the state-of-the art in the synthesis of such materials and highlighting their capacities.
Highlights
Introduction to Hybrid OrganicInorganic MaterialsCatalysis plays a crucial role in the chemical industry since many decades
They are indispensable in the production of transportation fuels, with about 440 oil refineries heavily relying on them and in the production of bulk and fine chemicals in all branches of the chemical industry
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Summary
Catalysis plays a crucial role in the chemical industry since many decades. Approximately, 85–90% of the products of chemical industry are made in catalytic processes. Silica-based hybrids can be achieved by (i) post-synthetic modification of the pore surface of a purely inorganic silica material (grafting), (ii) co-condensation of a silica precursor and a silyl derivative bearing the functional group of interest (“one-pot” approach), (iii) condensation of bisilylated precursors featuring the functional group of interest in the linker between the two alkoxysilyl groups Not long after their discovery, researchers began attempting to incorporate organic components within an inorganic silica framework to achieve symbiosis of the properties of both components. Upon varying the size of the R bridged unit, materials featuring layers of different width were obtained (5.6–11.9 Å) [27] Building upon these early studies, a variety of organic groups, ranging from hydrocarbons and heteroaromatics to metal complexes, have been successfully incorporated into PMO hybrids (Figure 7B) [22,25,28]
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