Alexander Sachse

Functionalized Inorganic Monolithic Microreactors for High Productivity in Fine Chemicals Catalytic Synthesis

Highly productive: Grafted monolith silica skeleton microreactors process bulky molecules more efficiently than a batch mode reactor. This efficiency is due to a higher contact area, shorter diffusion path, and lower inhibition by products in the thin monolith skeleton. These materials provide a new approach in the field of heterogeneous catalysis for the synthesis of fine chemicals.

In situ synthesis of Cu–BTC (HKUST-1) in macro-/mesoporous silica monoliths for continuous flow catalysis

The metal-organic framework Cu-BTC has been successfully synthesized as nanoparticles inside the mesopores of silica monoliths featuring a homogeneous macropore network enabling the use of Cu-BTC for continuous flow applications in liquid phase with low pressure drop. High productivity was reached with this catalyst for the Friedländer reaction.

Monolithic flow microreactors improve fine chemicals synthesis

This contribution reviews the preparation, main characteristics and advantages of macroporous monolithic microreactors for the synthesis of fine chemicals by continuous flow catalytic processes. The review focuses on different types of monolith (polymers, polymer/glass, silica, zeolites) exhibiting macropores of typically 2 to 10 μm, a large pore volume (1–2 mL g−1) and a high surface area (>300 m2 g−1) that can be readily functionalized by a variety of active moieties. With respect to traditional batch and packed-bed reactors, monolithic reactors allow easier process implementation, higher productivity and improved selectivity.

Efficient mesoporous silica–titania catalysts from colloidal self-assembly

Mesoporous silica-titania materials of tunable composition and texture, which present a high catalytic activity in the mild oxidation of sulfur compounds, have been obtained by combining the spray-drying process with the colloidal self-assembly of α-chitin nanorods (biopolymer acting as a template) and organometallic oligomers.

Challenges and Strategies in the Synthesis of Mesoporous Alumina Powders and Hierarchical Alumina Monoliths

A new rapid, very simple and one-step sol-gel strategy for the large-scale preparation of highly porous γ-Al2O3 is presented. The resulting mesoporous alumina materials feature high surface areas (400 m2 g−1), large pore volumes (0.8 mL g−1) and the γ-Al2O3 phase is obtained at low temperature (500 °C). The main advantages and drawbacks of different preparations of mesoporous alumina materials exhibiting high specific surface areas and large pore volumes such as surfactant-nanostructured alumina, sol-gel methods and hierarchically macro-/mesoporous alumina monoliths have been analyzed and compared. The most reproducible synthesis of mesoporous alumina are given. Evaporation-Induced Self-Assembly (EISA) is the sole method to lead to nanostructured mesoporous alumina by direct templating, but it is a difficult method to scale-up. Alumina featuring macro- and mesoporosity in monolithic shape is a very promising material for in flow applications; an optimized synthesis is described.

Improved silica–titania catalysts by chitin biotemplating

Silica–titania materials with improved catalytic performance were elaborated as mesoporous microparticles by combining sol–gel and spray-drying processes with the self-assembly properties of α-chitin nanorods acting as biotemplates. Three different synthesis approaches are discussed, leading to materials with varied textural and chemical characteristics studied by SEM, N2 volumetry, TEM, XPS and DR-UV techniques. The use of water or ethanol as initial solvent for chitin nanorod suspensions, as well as the mixing conditions of the precursors, has been shown to have a significant impact on the final properties. Materials of specific surface areas of up to 590 m2 g−1 and porous volumes of up to 0.84 mL g−1, with low surface Si/Ti ratio, could be disclosed. Properties were further investigated by employing the silica–titania materials as heterogeneous catalysts for the sulfoxidation of bulky model compounds. The location of Ti active sites at the pore surface has been maximized and allows for improved productivity.

Selective continuous flow extractive denitrogenation of oil containing S- and N-heteroaromatics using metal-containing ionic liquids supported on monolithic silica with hierarchical porosity

The removal of heteroaromatic nitrogen and sulfur impurities from a model oil through extraction with ionic liquids (ILs) containing metal salts was performed in view of the purification of fuel feeds. Chloride and bis(trifluoromethanesulfonyl)imide salts of Cu+, Cu2+ and Fe3+ were used. The systems based on ILs and metal compounds were applied both in batch-like liquid–liquid and continuous flow liquid–solid conditions. In a first phase, liquid–liquid biphasic extraction was used to choose the most adequate IL classes; the suitable systems were immobilized on a solid support to form metal-containing supported ionic liquid phases (SILPs). In a next phase, these SILPs were applied in breakthrough experiments. A selective extraction of N-compounds was achieved with metal-containing ionic liquids, in both liquid–liquid and liquid–solid conditions. The breakthrough experiments using Cu(NTf2)2− and FeCl4−-containing [BMIM][NTf2] SILPs immobilized on hierarchically structured silica monoliths resulted in an efficient separation of all the nitrogen compounds from the other impurities in the model oil.

Mesoporous alumina from colloidal biotemplating of Al clusters.

A simple and green synthesis route was disclosed for the achievement of mesoporous alumina microparticles employing polysaccharide nanoparticles (α-chitin nanorods) as templates. Pore textures can be tuned by the cationic alumina precursor. Compared to small cations, the use of Al13 and Al30 oxo-hydroxo clusters leads to better defined and elongated mesopores. Electron microscopy and spectroscopic ((13) C, (27) Al NMR, XPS) measurements demonstrated that this is related to the effective coating of α-chitin nanorods by these pre-condensed colloids.