Selective oxidative esterification of alcohols over Au-Pd/graphene

A COF template-derived mesoporous CeO2-supported Au nanoparticles catalyst for the oxidative esterification of benzaldehydes and benzyl alcohols

The direct oxidative esterification of benzaldehydes and benzyl alcohols to high value-added aromatic esters under mild and green reaction conditions is significant in the fine chemical industry. The accurate design of catalysts with high catalytic performance is crucial for this process. Herein, 2,4,6-trimethylpyridine, benzoic anhydride, and terephthalaldehyde were used to prepare a covalent organic framework (COF) material, which was then used as a template to construct a mesoporous CeO2-supported Au nanoparticles catalyst. The obtained Au@CeO2 catalyst was thoroughly characterized, and it possessed a mesoporous structure with a high surface area. Meanwhile, the as-prepared Au@CeO2 exhibited excellent catalytic performance in the oxidative esterification of benzaldehydes and benzyl alcohols with methanol, affording the corresponding aromatic esters under mild and green reaction conditions. Furthermore, the Au@CeO2 catalyst could also be recycled. Therefore, this study provides a green and sustainable pathway for the synthesis of high-value-added esters through a direct oxidative esterification strategy.

Enlightening the bimetallic effect of Au@Pd nanoparticles on Ni oxide nanostructures with enhanced catalytic activity

Bimetallic decoration of semiconductor electrodes typically improves catalytic and sensing performances because of a well-claimed synergistic effect. A microscopic and quantitative investigation of such an effect on energy bands of semiconductor can be really useful for further exploitation. Au, Pd and Au@Pd (core@shell) nanoparticles (10-20 nm in size) were synthesized through chemical reduction method and characterized with scanning and transmission microscopy, Rutherford backscattering spectrometry, cyclic voltammetry electrochemical impedance spectroscopy and Mott-Schottky analysis. The nanoparticles have been used to decorate Ni-based nanostructured electrodes with the aim to quantitatively investigate the effect of decoration with mono or bimetallic nanoparticles. Decorated electrodes show higher redox currents than bare ones and a shift in redox peaks (up to 0.3 V), which can be ascribed to a more efficient electron transport and improved catalytic properties. These effects were satisfactorily modeled (COMSOL) employing a nano Schottky junction at the nanoparticle-semiconductor interface, pointing out large energy band bending (up to 0.4 eV), space charge region and local electric field (up to [Formula: see text]) in bimetallic decoration. Sensing test of glucose and H₂O₂ by decorated Ni oxide electrodes were performed to consolidate our model. The presence of bimetallic nanoparticles enhances enormously the electrochemical performances of the material in terms of sensitivity, catalytic activity, and electrical transport. The modification of energy band diagram in semiconductor is analyzed and discussed also in terms of electron transfer during redox reactions.

Harnessing a Continuous-Flow Persulfuric Acid Generator for Direct Oxidative Aldehyde Esterifications

Persulfuric acid is a well-known oxidant in various industrial-scale purification procedures. However, due to its tendency toward explosive decomposition, its usefulness in organic synthesis remained largely underexplored. Herein, a continuous in situ persulfuric acid generator was developed and applied for oxidative esterification of aldehydes under flow conditions. Sulfuric acid served as a readily available and benign precursor to form persulfuric acid in situ. By taking advantage of the continuous-flow generator concept, safety hazards were significantly reduced, whilst a robust and effective approach was ensured for direct transformations of aldehydes to valuable esters. The process proved useful for the transformation of diverse aliphatic as well as aromatic aldehydes, while its preparative capability was verified by the multigram-scale synthesis of a pharmaceutically relevant key intermediate. The present flow protocol demonstrates the safe, sustainable, and scalable application of persulfuric acid in a manner that would not be amenable to conventional batch processing.

Graphenylene-supported single-atom (Ru and Mo) catalysts for CO and NO oxidations

Based on density functional theory (DFT) calculations, the adsorption geometries, stability and catalytic properties of single-atom Ru and Mo anchored on graphenylene sheets (gra-Ru and gra-Mo) are comparatively investigated.