Twin boundary defect engineering in Au cocatalyst to promote alcohol splitting for coproduction of H2 and fine chemicals

The microstructure of Au metal cocatalyst has been shown to significantly influence its optical and electronic properties. However, the impact of Au defect engineering on photocatalytic activity remains underexplored. In this study, we synthesize different Au-TiO2 composites by in-situ hybridizing face-centered cubic (F-Au) and twin boundary defect Au (T-Au) nanoparticles (NPs) onto the surface of TiO2. We find that T-Au NPs with twin defects serve as highly efficient cocatalysts for converting alcohols into their corresponding aldehydes while also generating H2. The optimized T-Au/TiO2 composite yields an H2 evolution rate of 6850 µmol h-1 g-1 and a BAD formation rate of 6830 µmol h-1 g-1, about 38 times higher than that of blank TiO2. Compared to F-Au/TiO2, the T-Au/TiO2 composite enhances charge separation, extends the lifetime of electrons, and provides more active sites for H2 reduction. The twin defect also improves alcohol reactant adsorption, boosting overall photocatalytic performance. This research paves the way for more studies on defect engineering in metal cocatalysts for enhanced catalytic activities in organic synthesis and H2 evolution.

Nitronium salts as mild and inexpensive oxidizing reagents toward designing efficient strategies in organic syntheses; A mechanistic investigation based on the DFT insights

Today, introducing and evaluating the performance of novel reagents are an undeniable part of designing a successful synthetic strategy. Herein, we study the efficiency and mechanism of recently synthesized nitronium salts (e.g., NO₂FSO₃, NO₂CF₃SO₃, NO₂HS₂O₇, NO₂BF₄, NO₂PF₆, and NO₂HSO₄) in the oxidation reaction of ethanol to acetic acid, as a model of the primary alcohol transformations to linear carboxylic acid. An aldehyde molecule is the first produced species in this reaction which is converted to the acetic acid molecule in the presence of in situ-produced nitric acid. Concerning the proposed mechanism, among the studied nitronium salts, two different behaviors can be observed in the transition state of the step in which the aldehyde molecule is formed. The calculated barrier energies of this step have been scrutinized by powerful descriptors such as Quantum Theory of Atoms in Molecules (QTAIM), Natural Bond Orbital (NBO), Electrostatic Potential (ESP) surfaces, and Activation Strain Model (ASM). The outcomes of the studied descriptors illustrate that nitronium salts have different performances in progressing the formation of the aldehyde molecule. Indeed, the likeness of the transition state of this step to the products for NO₂FSO₃, NO₂CF₃SO₃, and NO₂HS₂O₇ species is more significant than the others. Accordingly, these reagents have more potential to apply as oxidizing agents in the primary alcohol transformations to linear carboxylic acid.

Compatibility between Activity and Selectivity in Catalytic Oxidation of Benzyl Alcohol with Au-Pd Nanoparticles through Redox Switching of SnOx

A balance between catalytic activity and product selectivity remains a dilemma for the partial oxidation processes because the products are prone to be overoxidized. In this work, we report on the partial oxidation of benzyl alcohol using a modified catalyst consisting of nanosized Au-Pd particles (NPs) with tin oxide (SnO_x) deposited on a mesoporous silica support. We found that the SnO_x promotes the autogenous reduction of PdO to active Pd⁰ species on the Au-Pd NP catalyst (SnO_x@AP-ox) before H₂ reduction, which is due to the high oxophilicity of Sn. The presence of active Pd⁰ species and the enhancement of oxygen transfer by SnO_x led to high catalytic activity. The benzaldehyde selectivity was enhanced with the increase of SnO_x content on catalyst SnO_x@AP-ox, which is ascribed to the modulated affinity of reactants and products on the catalyst surface through the redox switching of Sn species. After H₂ reduction, SnO_x was partially reduced and Au-Pd-Sn alloy was formed. The formation of Au-Pd-Sn alloy weakened both the catalytic synergy of Au-Pd alloy NPs and the adsorption of benzyl alcohol on the reduced catalyst, thus leading to low catalytic activity.