Mechanistic Insights into Radical-Induced Selective Oxidation of Methane over Nonmetallic Boron Nitride Catalysts

Broad-spectrum antimicrobial effects of hydrogen boride nanosheets

Hydrogen boride (HB) nanosheets are novel 2D materials that have found application in various fields such as electronics, energy storage, and catalysis. The present study describes the novel antimicrobial effects of HB nanosheets. Transparent thin films of HB coated on a glass substrate inactivate pathogens, such as the omicron variant of SARS-CoV-2, influenza virus, feline calicivirus, and bacteriophages. The infectious titer of these microbes decreases to the detection limit within 10 min in the dark at room temperature. The antiviral function of the HB nanosheets is retained in the absence of moisture, mimicking the environment of dry surfaces. The HB nanosheets also inactivate bacteria and fungi such as Escherichia coli, Staphylococcus aureus, Aspergillus niger, and Penicillium pinophilum. We discussed the mechanism of the broad-spectrum antimicrobial function of HB nanosheets based on the physicochemical properties of HB nanosheets. Denaturation of microbial agents is derived from strong physicochemical interactions between the protein molecules in the pathogens and the surface of the HB films. The present study reports important new properties of HB nanosheets and demonstrates their utility in protecting against the spread of disease on a pandemic scale.

Core-Shell MIL-125-NH2@FeOOH Nanocomposites for Highly Selective Photocatalytic Oxidation of Methane to Formaldehyde in Water Vapor

Formaldehyde (HCHO), a crucial industrial chemical, finds extensive applications across diverse sectors, including household products, commercial materials, aviation, and medical supplies. Methane (CH4), as an abundant C1 resource, presents a promising feedstock for HCHO synthesis. However, the direct conversion of CH4 to HCHO remains challenging due to its inherent chemical inertness, characterized by low polarizability and high C-H bond dissociation energy (439 kJ mol-1), coupled with the high reactivity of intermediate products. The development of efficient strategies for selective CH4 oxidation to high-value HCHO under mild conditions is therefore of significant practical importance. In this study, we developed a series of MIL-125-NH2@FeOOH-x heterostructured photocatalysts (FM-x) through the controlled deposition of FeOOH nanoparticles on MIL-125-NH2 surfaces. Comprehensive characterization and photocatalytic evaluations reveal that the optimized FM-1 catalyst facilitates in situ H2O2 generation and subsequent decomposition into hydroxyl radicals (•OH), enabling efficient CH4 photooxidation. Remarkably, the FM-1 catalyst achieves an exceptional HCHO production rate of 197.79 μmol·gcat-1 with >99.99% selectivity in water vapor, significantly outperforming both pristine FeOOH and MIL-125-NH2 components. This work presents a promising photocatalytic system for selective CH4 conversion, offering new insights into the design of efficient catalysts for C1 chemistry.

Structural evolution and electronic properties of boron sulfides (B2S3)n (n = 1-6): insights from DFT calculations

The low-energy isomers of boron sulfides (B2S3)n (n = 1-6) were constructed by using B2S3 as the building block, and their structure, stability, and reactivity toward small molecules have been explored by density functional theory (DFT) calculations. It is found that the low-energy isomers of (B2S3)n clusters are of rich bonding characteristics for their structural constituents, such as [S-B-S], [B2S3], [B3S3], [S], etc. The planar or non-planar B2S2 rings, as the basic structural units, are bridged together by the S atoms to form the most stable structures of (B2S3)n clusters with n ≥ 2. These low-energy (B2S3)n clusters are predicted to be stable both structurally and electronically, and their boron centers show relatively high activity to the binding of small molecules NH3 and CO, until all boron atoms are ligated by NH3 or CO. The present results provide new insights into the structure and properties of (B2S3)n clusters, which are beneficial to the development of boron chemistry and the application of boron-based materials.

Polydopamine-Mediated Contact-Electro-Catalysis for Efficient Partial Oxidation of Methane

The direct conversion and efficient utilization of methane pose a critical scientific challenge. Indirect activation via reactive oxygen species (ROS) offers a high probability of contact with methane and conversion efficiency under mild conditions. However, reported product yields are suboptimal due to challenges in activating oxygen and facilitating mass transfer in suspension systems. We propose the use of contact-electro-catalysis (CEC), employing polydopamine (PDA) as a catalyst that undergoes electron transfer with oxygen under ultrasound, generating ROS that drives the partial oxidation of methane (POM). Corresponding experimental results indicate that CH3OH and most HCHO are produced directly from CH4. Furthermore, through in situ characterizations, we have shown that light pretreatment of the catalysts in an oxygenated atmosphere facilitates the forming of more C=O functional groups with strong electron-withdrawing properties, thereby significantly enhancing overall product yields, particularly for CH3OH. Within two hours, product yields reach 1.5 mmol gcat -1 for HCHO and 0.9 mmol gcat -1 for CH3OH. This work introduces a novel approach for efficient POM, while highlighting the distinctive catalytic properties of PDA.

Catalytic partial oxidation of methane over oxide-ion-conductive lanthanum silicate apatites

A lanthanum silicate La9.33Si6O26 (LSO) crystallizes in an apatite-type structure and has been known as a promising oxide-ion conductor. Here, we report the activity of LSO for catalytic partial oxidation of methane (CPOX) to synthesis gas. The LSO catalyst demonstrated relatively high catalytic activity from 500 to 700 °C, with CH4 conversion reaching 22.1% at 700 °C while retaining moderate CO and H2 selectivities of 20-60%. Notably, LSO exhibited higher CPOX activity than non-apatite-type La2SiO5 despite their similar specific surface areas. The higher CPOX activity of LSO is likely attributed to its structural superiority involving mobile oxide ions in the crystal structure. The reaction kinetic study showed that the reaction orders for methane and oxygen in the CPOX reaction over the LSO catalyst were 0.69-0.73 and 0.08-0.21, respectively. Furthermore, the small contribution of adsorbed O species generated from gas-phase O2 molecules indicated that the lattice oxygen may be involved in the reaction mechanism. The kinetic isotope effect (KIE) study using a CD4 suggested that C-H bond breaking is the rate-determining step of CPOX over LSO.

Synthesis and catalytic application of nanostructured metal oxides and phosphates

The design and development of new high-performance catalysts is one of the most important and challenging issues to achieve sustainable chemical and energy production. This Feature Article describes the synthesis of nanostructured metal oxides and phosphates mainly based on earth-abundant metals and their thermocatalytic application to selective oxidation and acid-base reactions. A simple and versatile methodology for the control of nanostructures based on crystalline complex oxides and phosphates with diverse structures and compositions is proposed as another approach to catalyst design. Herein, two unique and verstile methods for the synthesis of metal oxide and phosphate nanostructures are introduced; an amino acid-aided method for metal oxides and phosphates and a precursor crystallization method for porous manganese oxides. Nanomaterials based on perovskite oxides, manganese oxides, and metal phosphates can function as effective heterogeneous catalysts for selective aerobic oxidation, biomass conversion, direct methane conversion, one-pot synthesis, acid-base reactions, and water electrolysis. Furthermore, the structure-activity relationship is clarified based on experimental and computational approaches, and the influence of oxygen vacancy formation, concerted activation of molecules, and the redox/acid-base properties of the outermost surface are discussed. The proposed methodology for nanostructure control would be useful not only for the design and understanding of the complexity of metal oxide catalysts, but also for the development of innovative catalysts.

Unidentical Twins: Geometrically Similar but Chemically Distinct Metal-Free Sites in Boron Oxide for Methane Oxidation to HCHO, CO and CO2

Metal-free boron-based catalysts such as boron oxide (B2O3) and boron nitride (h-BN) are promising catalysts for methane oxidation to HCHO and CO. The B2O3 catalyst contains various probable boron sites (B1 to B6), which may be responsible for methane oxidation. In this work, we utilized density functional theory to compare two relevant geometrically identical boron sites (B2 and B4) for their reactivities. The two sites are explored in-detail for the conversion of methane to formaldehyde (M2F), carbon monoxide and carbon dioxide. The B4 site activates the methane C-H bond easily as compared to the B2 site. In M2F conversion, the rate-determining step for the B2 site is the co-activation of dioxygen and methane, whereas over the B4 site, formaldehyde formation is the rate-determining step. The computationally-determined RDS for the B4 site coincides well with the reported experiments. It is further revealed that this site also prefers the formation of CO over CO2, which is in-line with the experiments in literature. It is also shown through orbital analysis that methanol formation does not occur during methane oxidation. We employed descriptors such as condensed Fukui functions and global electrophilicity index to chemically distinct these twin sites.

Boosting Reactive Oxygen Species Formation Over Pd and VOδ Co-Modified TiO2 for Methane Oxidation into Valuable Oxygenates

Direct photocatalytic methane oxidation into value-added products provides a promising strategy for methane utilization. However, the inefficient generation of reactive oxygen species (ROS) partly limits the activation of CH4. Herein, it is reported that Pd and VOδ co-modified TiO2 enables direct and selective methane oxidation into liquid oxygenates in the presence of O2 and H2. Due to the extra ROS production from the in situ formed H2O2, a highly improved yield rate of 5014 µmol g-1 h-1 for liquid oxygenates with a selectivity of 89.3% is achieved over the optimized Pd0.5V0.2-TiO2 catalyst at ambient temperature, which is much better than those (2682 µmol g-1 h-1, 77.8%) without H2. Detailed investigations also demonstrate the synergistic effect between Pd and VOδ species for enhancing the charge carrier separation and transfer, as well as improving the catalytic activity for O2 reduction and H2O2 production.

Methane-H2S Reforming Catalyzed by Carbon and Metal Sulfide Stabilized Sulfur Dimers

H2S reforming of methane (HRM) provides a potential strategy to directly utilize sour natural gas for the production of COx-free H2 and sulfur chemicals. Several carbon allotropes were found to be active and selective for HRM, while the additional presence of transition metals led to further rate enhancements and outstanding stability (e.g., Ru supported on carbon black). Most metals are transformed to sulfides, but the carbon supports prevent sintering under the harsh reaction conditions. Supported by theoretical calculations, kinetic and isotopic investigations with representative catalysts showed that H2S decomposition and the recombination of surface H atoms are quasi-equilibrated, while the first C-H bond scission is the kinetically relevant step. Theory and experiments jointly establish that dynamically formed surface sulfur dimers are responsible for methane activation and catalytic turnovers on sulfide and carbon surfaces that are otherwise inert without reaction-derived active sites.

Mapping the Catalytic-Space for the Reactivity of Metal-free Boron Nitride with O2 for H2O-Mediated Conversion of Methane to HCHO and CO

Transition-metal based catalysts have been widely employed to catalyze partial oxidation of light alkanes. Recently, metal-free hexagonal-boron nitride (h-BN) has emerged as a promising catalyst for the oxidation of CH4 to HCHO and CO; however, the intricate catalytic surface of h-BN at molecular and electronic levels remains inadequately understood. Key questions include how electron-deficient boron atoms in h-BN reduce O2, and whether the partial oxidation of methane over h-BN exhibits similarities to traditional transition-metal catalysts. In our study, we computationally-mapped in-detail the surface catalytic-space of h-BN for methane oxidation. We considered different structures of h-BN and show that these structures contain numerous sites for O2 binding and therefore various routes for methane oxidation are possible. The activation barriers for methane oxidation via various paths varies from ~83 to ~123 kcal mol-1. To comprehend the differences in activation barriers, we employed geometrical, orbital and distortion/interaction analysis (DIA). Orbital analysis reveals that methane activation over h-BN in presence of dioxygen follows a standard hydrogen atom transfer mechanism. It is also shown that water plays an intriguing role in reducing the barrier for HCHO and CO formation by acting as a bridge.