Role of sulfur vacancies in MoS2 monolayers in stabilizing Co atoms for efficient CO oxidation

By performing first-principles calculations, a MoS₂ monolayer with a Co atom doped at the sulfur defect (Co-^SMoS₂) was investigated as a single-atom catalyst (SAC) for CO oxidation. The Co atom is strongly constrained at the S-vacancy site of MoS₂ without forming clusters by showing a high diffusion energy barrier, ensuring good stability to catalyze CO oxidation. The CO and O₂ adsorption behavior on Co-^SMoS₂ surface and four reaction pathways, namely, the Eley–Rideal (ER), Langmuir–Hinshelwood (LH), trimolecular Eley–Rideal (TER) as well as the New Eley–Rideal (NER) mechanisms are studied to understand the catalytic activity of Co-^SMoS₂ for CO oxidation. The CO oxidation is more likely to proceed through the LH mechanism, and the energy barrier for the rate-limiting step is only 0.19 eV, smaller than that of noble metal-based SACs. Additionally, the NER mechanism is also favorable with a low energy barrier of 0.26 eV, indicating that the Co-^SMoS₂ catalyst can effectively promote CO oxidation at low temperatures. Our investigation demonstrates that the S-vacancy of MoS₂ plays an important role in enhancing the stability and catalytic activity of Co atoms and Co-^SMoS₂ is predicted to be a promising catalyst for CO oxidation.

Molybdenum disulfide monolayers with Co atoms embedded in the sulfur vacancies are promising two dimensional non-noble metal-based single-atom catalysts to promote carbon monoxide oxidation.

Metal-Support Interactions of Single-Atom Catalysts for Biomedical Applications

The development of single-atom catalysts (SACs) has become a rapidly growing research field. It is a critical challenge to understand the interactions between the single-atom metal active sites and the support materials. Recently, original research reports of SACs in biomedical applications have emerged in the literature, yet this topic has seldom been reviewed. Here, this review focuses on the latest advances in single-atom catalysis for biomedical applications and highlights the keys for the design of SACs, such as understanding the interactions between metals and supports and classifying various enzyme-like activities. This review helps bridge the knowledge of multiple disciplines and provides prospects regarding the development of SACs for biomedicine.

Single-Atom (Iron-Based) Catalysts: Synthesis and Applications

Supported single-metal atom catalysts (SACs) are constituted of isolated active metal centers, which are heterogenized on inert supports such as graphene, porous carbon, and metal oxides. Their thermal stability, electronic properties, and catalytic activities can be controlled via interactions between the single-metal atom center and neighboring heteroatoms such as nitrogen, oxygen, and sulfur. Due to the atomic dispersion of the active catalytic centers, the amount of metal required for catalysis can be decreased, thus offering new possibilities to control the selectivity of a given transformation as well as to improve catalyst turnover frequencies and turnover numbers. This review aims to comprehensively summarize the synthesis of Fe-SACs with a focus on anchoring single atoms (SA) on carbon/graphene supports. The characterization of these advanced materials using various spectroscopic techniques and their applications in diverse research areas are described. When applicable, mechanistic investigations conducted to understand the specific behavior of Fe-SACs-based catalysts are highlighted, including the use of theoretical models.

Catalytic CO oxidation reaction over N-substituted graphene nanoribbon with edge defects

Density functional theory calculations, including dispersion effects, are used to demonstrate how substitutional nitrogen atoms can improve the catalytic reactivity of graphene nanoribbons (GNR) with edge defects in the CO oxidation process. It is demonstrated that the addition of nitrogen impurities significantly enhances O₂ adsorption on GNR. Carbon atoms near the edges of defects are the most active sites for capturing O₂ molecules. The lower adsorption energy of CO relative to O₂ implies that the N-modified GNR is resistant to CO poisoning. The Eley-Rideal (E-R) mechanism has activation energies as low as 0.38 eV, making it the most energetically relevant pathway for the CO + O₂ reaction. The findings of this study might help in the design of catalysts for metal-free catalysis of CO oxidation.

Low-Temperature Synthesis of Single Palladium Atoms Supported on Defective Hexagonal Boron Nitride Nanosheet for Chemoselective Hydrogenation of Cinnamaldehyde

Metal-support interactions are of great importance in determining the support-activity in heterogeneous catalysis. Here we report a low-temperature synthetic strategy to create atomically dispersed palladium atoms anchored on defective hexagonal boron nitride (h-BN) nanosheet. Density functional theory (DFT) calculations suggest that the nitrogen-containing B vacancy can provide stable anchoring sites for palladium atoms. The presence of single palladium atoms was confirmed by spherical aberration correction electron microscopy and extended X-ray absorption fine structure measurement. This catalyst showed exceptional efficiency in chemoselective hydrogenation of cinnamaldehyde, along with excellent recyclability, sintering-resistant ability, and scalability. We anticipate this synthetic approach for the synthesis of high-quality SACs based on h-BN support is amenable to large-scale production of bench-stable catalysts with maximum atom efficiency for industrial applications.

Atomically dispersed palladium catalyses Suzuki-Miyaura reactions under phosphine-free conditions

Single-atom catalysts have emerged as a new frontier in catalysis science. However, their applications are still limited to small molecule activations in the gas phase, the classic organic transformations catalyzed by single-atom catalysts are still rare. Here, we report the use of a single-atom Pd catalyst for the classic Suzuki-Miyaura carbon-carbon coupling reaction under phosphine-free and open-air conditions at room temperature. The single-atom Pd catalyst is prepared through anchoring Pd on bimetal oxides (Pd-ZnO-ZrO₂). The significant synergetic effect of ZnO and ZrO₂ is observed. The catalyst exhibits high activity and tolerance of a wide scope of substrates. Characterization demonstrates that Pd single atoms are coordinated with two oxygen atoms in Pd-ZnO-ZrO₂ catalyst. The catalyst can be fabricated on a multi-gram scale using a simple in situ co-precipitation method, which endows this catalytic system with great potential in practical applications.

An effective approach for tuning catalytic activity of C3N nanosheets: Chemical-doping with the Si atom

It is well-known that the catalytic oxidation of CO molecule into CO₂ is one of the most important strategies for the removing of this toxic gas from the atmosphere. In the present study, we investigate the reaction pathways and energy barriers for the oxidation of CO by O₂ molecule over the Si-doped C₃N nanosheet. According to our results, doping of C₃N nanosheet with a Si atom could greatly modify its surface reactivity and electronic structure. Due to the large positive charge on the Si, this atom acts as the most active site to adsorb CO and O₂ molecules. Three possible reaction mechanisms are studied for the CO oxidation, namely the Eley-Rideal (ER), Langmuir-Hinshelwood (LH) and new Eley-Rideal (NER). Comparing the activation energies indicates that the CO oxidation reaction proceeds via the LH mechanism over the title surface. The energy barrier needed to remove the activated oxygen atom (O*) from the Si atom is only 0.22 eV, which is most likely to overcome at room temperature. The results of this study may be useful to fabricate noble-metal free catalysts to remove toxic CO molecules from the atmosphere.