A new type of highly basic catalysts is obtained by promoting Mg–Al layered double hydroxides with sodium aluminate. The Mg–Al mixed oxides obtained by the calcination of pristine hydrotalcites are poorly active in the synthesis of glycerol carbonate from glycerol and dimethyl carbonate (DCM). Pure sodium aluminate on the other hand is highly active in this reaction, but it is also highly corrosive, making its handling problematic. Remarkably, promoting hydrotalcites with low amounts of sodium aluminate is sufficient to reach high yields. At 90 °C, with 3 wt % catalyst and with a DMC/glycerol ratio of 2:1, a glycerol conversion of 92 % was achieved after 30 min over the 10 wt % NaAlO2/hydrotalcite catalyst with almost 100 % selectivity towards glycerol carbonate. The texture and the crystallinity of the catalysts were strongly affected by the addition of NaAlO2. The high activity was clearly correlated with the boost in basicity brought about by sodium aluminate promotion. Whereas pristine hydrotalcites possess only weak basic sites, the basicity of the catalysts increased drastically upon promotion with NaAlO2, both in amount and strength. Diffuse reflectance infrared spectroscopy coupled with CO2 adsorption measurements revealed the presence of surface carbonates arising from strongly basic sites. Importantly, our study demonstrates that these basic catalysts are truly heterogeneous, stable, and reusable.

ω-Transaminases have been immobilized on macrocellular silica monoliths and used as heterogeneous biocatalysts in a continuous flow mode enantioselective transamination reaction. The support was prepared by a sol-gel method based on emulsion templating. The enzyme was immobilized on the structured silica monoliths both by adsorption, and by covalent grafting using amino-functionalized silica monoliths and glutaraldehyde as a coupling agent. A simple reactor set-up based on the use of a heat-shrinkable Teflon tube is presented and successfully used for the continuous flow kinetic resolution of a chiral amine, 4-bromo-α-methylbenzylamine. The porous structure of the supports ensures effective mass transfer and the reactor works in the plug flow regime without preferential flow paths. When immobilized in the monolith and used in the flow reactor, transaminases retain their activity and their enantioselectivity. The solid biocatalyst is also shown to be stable both on stream and during storage. These essential features pave the way to the successful development of an environmentally friendly process for chiral amines production.

Higher performance can be obtained in flow biocatalytic transamination reactions if the key parameters of support functionalization and of enzyme grafting are controlled.

Self-standing macrocellular titanosilicate monolith foams are obtained using a one-pot sol-gel route and show excellent performance in the epoxidation of cyclohexene. Thanks to the High Internal Phase Emulsion (HIPE) templating method, the materials feature a high void fraction, a hierarchically porous texture and good mechanical strength. Highly dispersed Ti species can be incorporated in tetrahedral coordination in the silica matrix. These characteristics allow the obtained 'SiTi(HIPE)' materials to reach high catalytic turnover in the epoxidation of cyclohexene. The monoliths can advantageously be used to run the reaction in continuous flow mode.Titanosilicates are an important class of materials that catalyze selective oxidation reactions. [1] For example, the combination of TS-1 zeolite -in which Ti atoms substitute Si atoms in the crystalline framework -with H 2 O 2 is omnipresent in industrial applications, notably for hydroxylation and epoxidation reactions. [2,3] The crystallinity and the intrinsic hydrophobicity of TS-1 make this material particularly efficient to catalyze the oxidation of small substrates with high selectivities. [4] However, the microporosity of TS-1 makes it less efficient for the conversion of bulky olefins, as the restricted diffusion of the reactants and products in and out the porosity can severely lower the catalytic activity which is consequently mainly restrained to the external surface. [5,6] An additional limitation is linked to the fact that the Ti loading incorporated into the zeolitic framework can hardly be tuned -with a typical maximal Ti loading of 2.5 % (here and after the loading is expressed as mol Ti/(mol Ti + mol Si) × 100 %). [7] These issues triggered intensive research on the incorporation of titanium in silicabased materials with larger pores in order to broaden the range of applications for titanosilicates. [8][9][10] New strategies in this field are flourishing, taking benefits of bottom-up sol-gel routes [11] involving templating methods -possibly combined to supercritical [12,13] or aerosol [14,15] drying strategies -or realized under non-aqueous conditions. [16][17][18] Despite those successes, the resulting materials are often obtained in the form of fine powders which require further steps to shape the catalysts as extrudates, pellets or monoliths, before they could be used in industrial flow processes. [19] This shaping step represents an additional challenge as it necessitates a fine control of the mechanical properties and the diffusion regimes without sacrificing the intrinsic performance of the catalyst. Alternatively, the catalyst can be dispersed onto a pre-shaped solid support [20][21][22] that should meet several specifications (texture, surface composition, mechanical stability, etc.). With such strategy, a challenge is to maximize the loading and the dispersion of the catalyst while avoiding leaching and/or deactivation. [23] Thus, the one-step preparation of Ti-containing materials that do not require further shaping steps is highly sought f...

ω-Transaminases have been immobilized on macrocellular silica monoliths and used as heterogeneous biocatalysts in a continuous flow mode enantioselective transamination reaction. The support was prepared by a sol-gel method based on emulsion templating. The enzyme was immobilized on the structured silica monoliths both by adsorption, and by covalent grafting using amino-functionalized silica monoliths and glutaraldehyde as a coupling agent. A simple reactor set-up based on the use of a heat-shrinkable Teflon tube is presented and successfully used for the continuous flow kinetic resolution of a chiral amine, 4-bromo-α-methylbenzylamine. The porous structure of the supports ensures effective mass transfer and the reactor works in the plug flow regime without preferential flow paths. When immobilized in the monolith and used in the flow reactor, transaminases retain their activity and their enantioselectivity. The solid biocatalyst is also shown to be stable both on stream and during storage. These essential features pave the way to the successful development of an environmentally friendly process for chiral amines production.

ω-Transaminases have been immobilized on macrocellular silica monoliths and used as heterogeneous biocatalysts in a continuous flow mode enantioselective transamination reaction. The support was prepared by a sol-gel method based on emulsion-templating. The enzyme was immobilized on the structured silica monoliths both by adsorption, and by covalent grafting using amino-functionalized silica monoliths and glutaraldehyde as a coupling agent. A simple reactor set-up based on the use of a heat-shrinkable Teflon tube is presented and successfully used for the continuous flow kinetic resolution of a chiral amine, 4-bromo-α-methylbenzylamine. The porous structure of the supports ensures effective mass transfer and the reactor works in the plug flow regime without preferential flow paths. When immobilized in the monolith and used in the flow reactor, transaminases retain their activity and their enantioselectivity. The solid biocatalyst is also shown to be stable both on stream and during storage. These essential features pave the way to the successful development of an environmentally friendly process for chiral amines production.

Chiral amines are essential building blocks to manufacture a plethora of valuable compounds, including active pharmaceutical ingredients (API). It is estimated that about half of the current API contain chiral...

<div>Transaminases are immobilized onto macrocellular silica monoliths and used for carrying a continuous flow mode transamination reaction. Monoliths were prepared via an emulsion-templated sol-gel method and functionalized by amino-moieties (APTES) in order to covalently immobilize the enzymes, using glutaraldehyde as a cross-linking agent. In order to obtain higher performance and improved reproducibility, we investigate the key parameters of APTES functionalization and of enzyme grafting. Four functionalization protocols were studied. It is shown that controlling the moisture levels in monolith and in the functionalisation solution led to a 3-fold increase in activity as compared to the previously reported data, and greatly improved the reproducibility. Additionally, we report a strong beneficial effect of running the enzyme immobilization at room temperature instead of 4°C, further enhancing the obtained activity. Finally, the popular method which consists in stabilizing the covalent attachment of the enzyme by reducing the imine bonds formed between the enzyme and the functionalized surface was investigated. We highlight a strong enzyme deactivation caused by cyanoborohydride, making this strategy irrelevant in this case. All in all, the improvements presented here for enzyme immobilization in macrocellular silica monoliths, lead to the preparation of more active materials for continuous flow mode biocatalysis.<br></div>