Fabio Lorenzini

The Co‐Entrapment of a Homogeneous Catalyst and an Ionic Liquid by a Sol–gel Method: Recyclable Ionogel Hydrogenation Catalysts

Molecular hydrogenation catalysts have been co-entrapped with the ionic liquid [Bmim]NTf(2) inside a silica matrix by a sol-gel method. These catalytic ionogels have been compared to simple catalyst-doped glasses, the parent homogeneous catalysts, commercial heterogeneous catalysts, and Rh-doped mesoporous silica. The most active ionogel has been characterised by transmission electron microscopy, X-ray photoelectron spectroscopy, and solid state NMR before and after catalysis. The ionogel catalysts were found to be remarkably active, recyclable and resistant to chemical change.

Combining bio- and chemo-catalysis for the conversion of bio-renewable alcohols: homogeneous iridium catalysed hydrogen transfer initiated dehydration of 1,3-propanediol to aldehydes

Combining whole cell biocatalysis and chemocatalysis in a single reaction sequence avoids unnecessary separations, and the associated waste and energy consumption. Bacterial fermentation has been employed to convert waste glycerol from biodiesel production into 1,3-propanediol. This 1,3-propanediol can be extracted selectively from the aqueous fermentation broth using ionic liquids. 1,3-Propanediol in ionic liquid solution was converted to propionaldehyde by hydrogen transfer initiated dehydration (HTID) catalysed by a Cp*IrCl2(NHC) (Cp* = pentamethylcyclopentadienyl; NHC = carbene ligand) complex. The use of an ionic liquid solvent enabled the reaction to be performed under reduced pressure, facilitating the isolation of the product, and improving the reaction selectivity. The Ir(III) catalyst in ionic liquid was found to be highly recyclable.

Conversion of Biomass Using Simultaneous Chemo- and Bio-catalysis

As many countries move towards fossil fuel divestment, greater emphasis is being placed on the use of sustainable sources for the production of fuels and chemicals. Due to the current scale of production of petroleum, a mixed portfolio of alternative sources is needed to supply these demands. Biomass is a potential renewable and sustainable source for the production of biofuels and valuable chemicals. The conversion of biomass into biofuels and bio-derived platform chemicals to be directly placed into chemical production streams has been intensely explored over the last decade. One interesting avenue highlighted in this chapter is the development of systems that combine bio- and chemo-catalysis to convert biomass into value-added chemicals: in this endeavour, the targeted transformations are enabled by the concerted action of both chemical and biological catalysts. The combination of racemization catalysts and bio-catalytic enzymes for the production of optically pure products such as alcohols, amines and acyloins, in dynamic kinetic resolution, is hereby discussed along with several recent examples of biomass valorisation using actual, or potential, protocols involving the simultaneous use of both bio- and chemo-catalytic steps.

Combining Bio- and Chemo-catalysis for the Sustainable Production of Chemicals

The combination of bio- and chemo-catalysis to form a single synthetic route is a powerful methodology for the improvement of chemical synthesis. The extreme methods of biocatalysis (whole cell and isolated enzyme) fulfill very different roles. Biocatalysis by isolated enzymes enables highly efficient chemical transformations of extremely high selectivity and low contamination; however, conditions and substrates are limited to a narrow range. Whole cell biocatalysis enables the conversion of crude substrates, such as those derived from biomass; however, the products tend to be impure and delivered in dilute aqueous solution. Chemocatalysis is a well-established technique, and the addition of chemical catalysis and chemocatalytic methods to biocatalysis enables synthetic chemists to avoid the shortcomings of a biocatalytic step. For example, in enzymatic catalysis the addition of a chemical catalyst can allow the conversion of a racemic alcohol to an enantiopure, instead of racemic, product. In whole cell biocatalysis chemical reagents can assist the separation, transformation, and further isolation of the functionality of interest. The cooperation of bio- and chemo-catalysts enables sustainable production of chemicals that would be impossible using biocatalysis alone, while achieving selectivities and using substrates not currently possible with chemocatalysis alone.