Bifunctional Pt/Au Janus electrocatalysts for simultaneous oxidation/reduction of furfural with bipolar electrochemistry

The sustainable conversion of biomass-derived compounds into high added-value products is a very important contemporary scientific challenge. In this context, we report here the simultaneous electro-oxidation/-reduction of a biomass-derived compound in a one-pot approach using bipolar electrochemistry. Bifunctional Pt/Au Janus electrocatalysts are employed for a selective conversion of furfural into both, furfuryl alcohol and furoic acid, which can't be achieved when using non-Janus particles. The results emphasize the benefits of bipolar electrochemistry in the frame of electrosynthesis processes.

Heterogeneous Enantioselective Catalysis with Chiral Encoded Mesoporous Pt-Ir Films Supported on Ni Foam

The development of heterogeneous catalysts for asymmetric synthesis is one of the most challenging topics in chemistry, as it allows obtaining enantiomerically pure compounds. Recently, metal layers incorporating molecular chiral cavities, obtained by electroreduction of a metal source in the simultaneous presence of a non-ionic surfactant and asymmetric molecules, have been proposed for a wide range of applications, including enantioselective electroanalysis and electrosynthesis, as well as chiral separation. In contrast to this previous work, solely based on electrochemical phenomena, herein we designed and employed nanostructured chiral encoded Pt-Ir alloys, supported on high surface area nickel foams, as heterogeneous catalysts for the asymmetric hydrogenation of aromatic ketones. Fine-tuning the experimental conditions allows achieving very high enantioselectivity (>80%), combined with improved catalyst stability.

Nanoengineered chiral Pt-Ir alloys for high-performance enantioselective electrosynthesis

The design of efficient chiral catalysts is of crucial importance since it allows generating enantiomerically pure compounds. Tremendous efforts have been made over the past decades regarding the development of materials with enantioselective properties for various potential applications ranging from sensing to catalysis and separation. Recently, chiral features have been generated in mesoporous metals. Although these monometallic matrices show interesting enantioselectivity, they suffer from rather low stability, constituting an important roadblock for applications. Here, a straightforward strategy to circumvent this limitation by using nanostructured platinum-iridium alloys is presented. These materials can be successfully encoded with chiral information by co-electrodeposition from Pt and Ir salts in the simultaneous presence of a chiral compound and a lyotropic liquid crystal as asymmetric template and mesoporogen, respectively. The alloys enable a remarkable discrimination between chiral compounds and greatly improved enantioselectivity when used for asymmetric electrosynthesis (>95 %ee), combined with high electrochemical stability.

Chiral Macroporous MOF Surfaces for Electroassisted Enantioselective Adsorption and Separation

The development of surfaces with chiral features is a fascinating challenge for modern materials science, especially when they are used for chiral separation technologies. In this contribution, the design of hierarchically structured chiral macroporous zeolitic imidazolate framework-8 (ZIF-8) electrodes is presented. They are elaborated by an electrochemical deposition-dissolution technique based on the electrodeposition of metal through a colloidal crystal template, followed by controlled electrooxidation. This generates locally metal cations, which can interact with a chiral ligand present in the solution to form metal-organic frameworks (MOFs). The macroporous structure facilitates the access of the chiral recognition sites, located in the mesoporous MOF, and thus helps to overcome mass transport limitations. The efficiency of the designed functional materials for chiral adsorption and separation can be fine-tuned by applying an adjustable electric potential to the electrode surfaces. This hierarchical chiral ZIF-8 structure was deposited at the walls of a microfluidic device and used as a stationary phase for enantioselective separation. The potential-controlled interaction between the stationary phase and the chiral analytes allows baseline separation of two enantiomers. This opens up interesting perspectives for using hierarchically structured chiral MOFs as an efficient material for the selective adsorption and separation of chiral compounds.

Chiral platinum-polypyrrole hybrid films as efficient enantioselective actuators

We report the synthesis of a hybrid bilayer, being composed of a free-standing conducting polymer film and a layer of mesoporous metal, encoded with chiral features. The resulting structure constitutes an enantioselective actuator, which can be electrochemically addressed in a wireless way. The controlled discriminatory deformation of the film allows an easy readout of chiral information.

Potential-Induced Fine-Tuning of the Enantioaffinity of Chiral Metal Phases

Concepts leading to single enantiomers of chiral molecules are of crucial importance for many applications, including pharmacology and biotechnology. Recently, mesoporous metal phases encoded with chiral information have been developed. Fine-tuning of the enantioaffinity of such structures by imposing an electric potential is proposed, which can influence the electrostatic interactions between the chiral metal and the target enantiomer. This allows the binding affinity between the chiral metal and the target enantiomer to be increased, and thus, the discrimination between two enantiomers to be improved. The concept is illustrated by generating chiral encoded metals in a microfluidic channel by reduction of a platinum salt in the presence of a liquid crystal and l-tryptophan as a chiral model template. After removal of the template molecules, the modified microchannel retains a pronounced chiral character. The chiral recognition efficiency of the microchannel can be fine-tuned by applying a suitable potential to the metal phase. This enables the separation of both components of a racemate flowing through the channel. The approach constitutes a promising and complementary strategy in the frame of chiral discrimination technologies.

Catalytic upgrading of carboxylic acids as bio-oil models over hierarchical ZSM-5 obtained via an organosilane approach

Biomass is an interesting renewable energy resource as it is widespread in nature and low cost.