Towards sustainable kinetic resolution, a combination of bio-catalysis, flow chemistry and bio-based solvents

The esterification of 2-phenylpropionic acid was investigated as a model system for enzyme catalysed (CALB, Novozyme 435) reactions in bio-based solvents. A multi-parameter correlation taking into account solvent parameters was developed to explain experimental observations. A continuous flow process using p-cymene as the solvent was operated over several weeks, thus combining a sustainable solvent and flow chemistry for kinetic resolution

On the stability of isolated iridium sites in N-rich frameworks against agglomeration under reducing conditions

Stabilization of single metal atoms is a persistent challenge in heterogeneous catalysis. Especially supported late transitions metals are prone to undergo agglomeration to nanoparticles under reducing conditions. In this study, nitrogen-rich covalent triazine frameworks (CTFs) are used to immobilize iridium complexes. Upon reduction at 400°C, immobilized Ir(acac)(COD) on CTF does not form nanoparticles but transforms into a highly active Ir single atom catalyst. The resulting catalyst systems outperforms both the immobilized complex and supported nanoparticles in the dehydrogenation of formic acid as probe reaction. This superior performance could be traced back to decisive changes of the coordination geometry positively influencing activity, selectivity and stability. Spectroscopic analysis reveals an increase of electron density on the cationic iridium site by donation from the CTF macroligand after removal of the organic ligand sphere from the Ir(acac)(COD) precursor complex upon reductive treatment. This work demonstrates the ability of nitrogen moieties to stabilize molecular metal species against agglomeration and opens avenues for catalysts design using isolated sites in high-temperature applications under reducing atmosphere

Understanding the structure of isolated iridium sites anchored on a covalent triazine framework

As a showcase for experimentally accessible single-site catalysts, well-defined and characterized isolated Ir sites anchored on a covalent triazine framework (CTF) were investigated with computational methods

Dynamics of palladium single-atoms on graphitic carbon nitride during ethylene hydrogenation

Single-atoms on carbon–nitrogen supports are considered catalysts for a multitude of reactions. However, doubts remain whether really these species or subnanometer clusters formed under reaction conditions are the active species. In this work, we investigate the dynamics of palladium single-atoms on graphitic carbon nitride during ethylene hydrogenation and H2-D2 exchange. By employing aberration-corrected scanning transmission electron microscopy, x-ray photoelectron spectroscopy and x-ray absorption spectroscopy, we will show that palladium, originally present as single-atoms, agglomerates to clusters at 100 °C in a gas atmosphere that contains both ethylene and hydrogen. This agglomeration goes in hand with the emergence of catalytic activity in both ethylene hydrogenation and H2-D2 exchange, suggesting that clusters, rather than single-atoms, are the active species. The results presented herein highlight the potential of analytics over the course of reaction to identify the active species and provide new insights into the influence of gas atmosphere on metal speciation

Africa and China: a strategic partnership?

Relations between Africa and China have increased over the years and become more dominated by China's economic interests. With an annual growth rate of 8-9 per cent, and a booming economy, China's dependency on accessing natural resources is a top priority and has accordingly expanded its horizons. Africa, with all its seemingly unlimited natural resources, is an ideal partner. In addition, the African continent as a whole offers a potential market for China's low-value manufactured commodities. This paper is an attempt to present an overview of contemporary Sino-African relations and the state of trade relations, with special emphasis on natural resources and the export market for Chinese products and investments in Afric