Nanoscale solid catalyst for glycerol

The first chemical industrial application of glycerol was developed by Alfred Nobel, who reported in 1860 the transformation of glycerol to nitroglycerin, which gave access later to dynamite. Then, during the 20th century, chemists started to progressively find new applications of glycerol especially in the pharmaceutical and cosmetic industries, where it was used for its emollient, demulcent, and humectant properties. Later, glycerol was also used as a plasticizer in the polymer industry and as a moistening agent or solvent in the food industry. Then, rapidly nearly every industry used glycerol, making this natural polyol one of the most valuable alcohols

Glycerol is the main co-product of the vegetable oils industry (especially biodiesel). With the rapid development of oleochemistry, the production of glycerol is rapidly increasing and chemists are trying to find new applications of glycerol to encourage a better industrial development of vegetable oils. In this Review, attention is focused on the selective use of glycerol as a safe organic building block for organic chemistry. An overview is given of the different heterogeneous catalytic routes developed by chemists for the successful and environmentally friendly use of glycerol in sustainable organic chemistry. In particular, the effects of different catalyst structural parameters are discussed to clearly highlight how catalysis can help organic chemists to overcome the drawbacks stemming from the use of glycerol as a safe organic building block. It is shown that heterogeneous catalysis offers efficient routes for bypassing the traditional use of highly toxic and expensive epichlorohydrin, 3-chloro-1,2-propanediol, or glycidol, which are usually used as a glyceryl donor in organic chemistry.

To maintain the environmental benefit of using glycerol as a sustainable organic building block, heterogeneous catalysis was often preferred to homogeneous catalysis. Indeed, heterogeneous catalysis offers many advantages such as easy removal of solid catalysts from the reaction media and, in some cases, their possible recycling. However, from a scientific point of view, it is well established that the activities of solid catalysts are usually lower than those of homogeneous catalysts mainly because of the poorer accessibility of the grafted catalytic sites. This aspect is even more complex when catalytic processes are carried out in glycerol, as, with organic substrates, the reaction media becomes biphasic raising some problems of substrate diffusion. The rapid development of materials chemistry recently has given access to a wide range of different elaborate solid catalyst structures, usually well-defined at a nanoscale, and now offers to chemists a means to improve the performance, activity and selectivity of solid catalysts. On the basis of these fascinating studies, researchers started to design new solid catalysts, which were found particularly efficient for the successful use of glycerol as organic building block.

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