The Direct Synthesis of Hydrogen Peroxide Over Supported Pd-Based Catalysts: An Investigation into the Role of the Support and Secondary Metal Modifiers

Exploring the Mechanisms of Charge Transfer and Identifying Active Sites in the Hydrogen Evolution Reaction Using Hollow C@MoS2-Au@CdS Nanostructures as Photocatalysts

Plasmonic metal-semiconductor nanocomposites are promising candidates for considerably enhancing the solar-to-hydrogen conversion efficiency of semiconductor-based photocatalysts across the entire solar spectrum. However, the underlying enhancement mechanism remains unclear, and the overall efficiency is still low. Herein, a hollow C@MoS2-Au@CdS nanocomposite photocatalyst is developed to achieve improved photocatalytic hydrogen evolution reaction (HER) across a broad spectral range. Transient absorption spectroscopy experiments and electromagnetic field simulations demonstrate that compared to the treated sample, the untreated sample exhibits a high density of sulfur vacancies. Consequently, under near-field enhancement, photogenerated electrons from CdS and hot electrons generated by intra-band or inter-band transitions of Au nanoparticles are efficiently transferred to the CdS surface, thus significantly improving the HER activity of CdS. Additionally, in situ, Raman spectroscopy provided spectral evidence of S─H intermediate species on the CdS surface during the HER process, which is verified through isotope experiments. Density functional theory simulations identify sulfur atoms in CdS as the catalytic active sites for HER. These findings enhance the understanding of charge transfer mechanisms and HER pathways, offering valuable insights for the design of plasmonic photocatalysts with enhanced efficiency.

Sustainable catalysts in a short time: harnessing bacteria for swift palladium nanoparticle production

Adapting biological systems for nanoparticle synthesis opens an orthogonal Green direction in nanoscience by reducing the reliance on harsh chemicals and energy-intensive procedures. This study addresses the challenge of efficient catalyst preparation for organic synthesis, focusing on the rapid formation of palladium (Pd) nanoparticles using bacterial cells as a renewable and eco-friendly support. The preparation of catalytically active nanoparticles on the bacterium Paracoccus yeei VKM B-3302 represents a more suitable approach to increase the reaction efficiency due to its resistance to metal salts. We introduce an efficient method that significantly reduces the preparation time of Pd nanoparticles on Paracoccus yeei bacteria to only 7 min, greatly accelerating the process compared with traditional methods. Our findings reveal the major role of live bacterial cells in the formation and stabilization of Pd nanoparticles, which exhibit high catalytic activity in the Mizoroki-Heck reaction. This method not only ensures high yields of the desired product but also offers a greener and more sustainable alternative to conventional catalytic processes. The rapid preparation and high efficiency of this biohybrid catalyst opens new perspectives for the application of biosupported nanoparticles in organic synthesis and a transformative sustainable pathway for chemical production processes.

Recent advances in tailoring the microenvironment of Pd-based catalysts for enhancing the performance in the direct synthesis of hydrogen peroxide

Hydrogen peroxide (H2O2) is a valuable clean chemical, which is widely applied in modern industrial production. In the past few decades, H2O2 has been mainly produced industrially by the anthraquinone method, but the process is complicated and energy consuming, which is only economical for large-scale production and is harmful to the environment. The direct synthesis of H2O2 is considered a promising process to replace the anthraquinone method with high atomic economy, no hazardous by-products, and convenient operation, which has attracted much attention. In this review, we systematically present the recent advances in tuning the microenvironment of Pd-based catalysts for enhancing the performance of the direct synthesis of H2O2, including the modulation of active sites and support, from the viewpoint of the reaction mechanism. Finally, a summary and perspective on the most pressing issues and associated untapped research prospects with the direct synthesis of H2O2 are discussed. The purpose of this review is to provide in-depth insights and guidelines to promote the development of novel catalysts for the direct synthesis of H2O2.

Surfactant- and Ligand-Free Synthesis of Platinum Nanoparticles in Aqueous Solution for Catalytic Applications

The synthesis of surfactant-free and organic ligand-free metallic nanoparticles in solution remains challenging due to the nanoparticles’ tendency to aggregate. Surfactant- and ligand-free nanoparticles are particularly desirable in catalytic applications as surfactants, and ligands can block access to the nanoparticles’ surfaces. In this contribution, platinum nanoparticles are synthesized in aqueous solution without surfactants or bound organic ligands. Pt is reduced by sodium borohydride, and the borohydride has a dual role of reducing agent and weakly interacting stabilizer. The 5.3 nm Pt nanoparticles are characterized using UV-visible spectroscopy and transmission electron microscopy. The Pt nanoparticles are then applied as catalysts in two different reactions: the redox reaction of hexacyanoferrate(III) and thiosulfate ions, and H2O2 decomposition. Catalytic activity is observed for both reactions, and the Pt nanoparticles show up to an order of magnitude greater activity over the most active catalysts reported in the literature for hexacyanoferrate(III)/thiosulfate redox reactions. It is hypothesized that this enhanced catalytic activity is due to the increased electron density that the surrounding borohydride ions give to the Pt nanoparticle surface, as well as the absence of surfactants or organic ligands blocking surface sites.

Improving Catalytic Activity towards the Direct Synthesis of H2O2 through Cu Incorporation into AuPd Catalysts

With a focus on catalysts prepared by an excess-chloride wet impregnation procedure and supported on the zeolite ZSM-5(30), the introduction of low concentrations of tertiary base metals, in particular Cu, into supported AuPd nanoparticles can be observed to enhance catalytic activity towards the direct synthesis of H2O2. Indeed the optimal catalyst formulation (1%AuPd(0.975)Cu(0.025)/ZSM-5) is able to achieve rates of H2O2 synthesis (115 molH2O2kgcat−1h−1) approximately 1.7 times that of the bi-metallic analogue (69 molH2O2kgcat−1h−1) and rival that previously reported over comparable materials which use Pt as a dopant. Notably, the introduction of Cu at higher loadings results in an inhibition of performance. Detailed analysis by CO-DRFITS and XPS reveals that the improved performance observed over the optimal catalyst can be attributed to the electronic modification of the Pd species and the formation of domains of a mixed Pd2+/Pd0 oxidation state as well as structural changed within the nanoalloy.