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The selective oxidation of methane, the primary component of natural gas, remains an important challenge in catalysis. We used colloidal gold-palladium nanoparticles, rather than the same nanoparticles supported on titanium oxide, to oxidize methane to methanol with high selectivity (92%) in aqueous solution at mild temperatures. Then, using isotopically labeled oxygen (O₂) as an oxidant in the presence of hydrogen peroxide (H₂O₂), we demonstrated that the resulting methanol incorporated a substantial fraction (70%) of gas-phase O₂. More oxygenated products were formed than the amount of H₂O₂ consumed, suggesting that the controlled breakdown of H₂O₂ activates methane, which subsequently incorporates molecular oxygen through a radical process. If a source of methyl radicals can be established, then the selective oxidation of methane to methanol using molecular oxygen is possible.

Direct solar-driven methane (CH 4 ) reforming is highly desirable but challenging, particularly to achieve a value-added product with high selectivity. Here, we identify a synergistic ensemble effect of atomically dispersed copper (Cu) species and partially reduced tungsten (W δ+ ), stabilised over an oxygen-vacancy-rich WO 3 , which enables exceptional photocatalytic CH 4 conversion to formaldehyde (HCHO) under visible light, leading to nearly 100% selectivity, a very high yield of 4979.0 μmol·g −1 within 2 h, and the normalised mass activity of 8.5 × 10 6  μmol·g -1 Cu ·h −1 of HCHO at ambient temperature. In-situ EPR and XPS analyses indicate that the Cu species serve as the electron acceptor, promoting the photo-induced electron transfer from the conduction band to O 2 , generating reactive •OOH radicals. In parallel, the adjacent W δ+ species act as the hole acceptor and the preferred adsorption and activation site of H 2 O to produce hydroxyl radicals (•OH), and thus activate CH 4 to methyl radicals (•CH 3 ). The synergy of the adjacent dual active sites boosts the overall efficiency and selectivity of the conversion process. Direct solar-driven methane (CH 4 ) reforming is highly desirable but challenging. Here, the synergy of atomic Cu species and partially reduced tungsten (W δ+ ), stabilized over an oxygen-vacancy-rich WO 3 , enables exceptional CH 4 conversion to formaldehyde (HCHO) under visible light.

Photocatalytic coupling of methane to ethane and ethylene (C 2 compounds) offers a promising approach to utilizing the abundant methane resource. However, the state-of-the-art photocatalysts usually suffer from very limited C 2 formation rates. Here, we report our discovery that the anatase TiO 2 nanocrystals mainly exposing {101} facets, which are generally considered less active in photocatalysis, demonstrate surprisingly better performances than those exposing the high-energy {001} facet. The palladium co-catalyst plays a pivotal role and the Pd 2+ site on co-catalyst accounts for the selective C 2 formation. We unveil that the anatase {101} facet favors the formation of hydroxyl radicals in aqueous phase near the surface, where they activate methane molecules into methyl radicals, and the Pd 2+ site participates in facilitating the adsorption and coupling of methyl radicals. This work provides a strategy to design efficient nanocatalysts for selective photocatalytic methane coupling by reaction-space separation to optimize heterogeneous-homogeneous reactions at solid-liquid interfaces. Designing photocatalysts to enhance the efficiency of non-oxidative coupling of methane is a challenging task. Here, the authors report that the anatase TiO 2 with exposed {101} facets and Pd co-catalyst enables efficient and selective methane coupling to ethane via a heterogeneous-homogeneous hybrid reaction pathway.

The delivery of alkyl radicals through photocatalytic deoxygenation of primary alcohols under mild conditions is a so far unmet challenge. In this report, we present a one-pot strategy for deoxygenative Giese reaction of alcohols with electron-deficient alkenes, by using xanthate salts as alcohol-activating groups for radical generation under visible-light photoredox conditions in the presence of triphenylphosphine. The convenient generation of xanthate salts and high reactivity of sequential C–S/C–O bond homolytic cleavage enable efficient deoxygenation of primary, secondary and tertiary alcohols with diverse functionality and structure to generate the corresponding alkyl radicals, including methyl radical. Moreover, chemoselective radical monodeoxygenation of diols is achieved via selective formation of xanthate salts. The generation of alkyl radicals through deoxygenation of abundant alcohols via photoredox catalysis is of interest. In this study, the authors report a one-pot strategy for visible-light-promoted photoredox coupling of alcohols with electron-deficient alkenes, assisted by carbon disulfide and triphenylphosphine.

Photoredox catalysis has provided many approaches to C(sp 3 )–H functionalization that enable selective oxidation and C(sp 3 )–C bond formation via the intermediacy of a carbon-centered radical. While highly enabling, functionalization of the carbon-centered radical is largely mediated by electrophilic reagents. Notably, nucleophilic reagents represent an abundant and practical reagent class, motivating the interest in developing a general C(sp 3 )–H functionalization strategy with nucleophiles. Here we describe a strategy that transforms C(sp 3 )–H bonds into carbocations via sequential hydrogen atom transfer (HAT) and oxidative radical-polar crossover. The resulting carbocation is functionalized by a variety of nucleophiles—including halides, water, alcohols, thiols, an electron-rich arene, and an azide—to effect diverse bond formations. Mechanistic studies indicate that HAT is mediated by methyl radical—a previously unexplored HAT agent with differing polarity to many of those used in photoredox catalysis—enabling new site-selectivity for late-stage C(sp 3 )–H functionalization. When carbon-based units are functionalized in photoredox catalysis, electrophilic coupling partners are often used, such that the polarities of the two fragments are appropriately matched. Here the authors show a generalized methodology to instead use nucleophilic coupling partners, which are cheaper and often simpler, via successive hydrogen atom transfer and oxidative radical-polar crossover.

With their unusual electronic structures, organic radical molecules display luminescence properties potentially relevant to lighting applications; yet, their luminescence quantum yield and stability lag behind those of other organic emitters. Here, we designed donor–acceptor neutral radicals based on an electron-poor perchlorotriphenylmethyl or tris(2,4,6-trichlorophenyl)methyl radical moiety combined with different electron-rich groups. Experimental and quantum-chemical studies demonstrate that the molecules do not follow the Aufbau principle: the singly occupied molecular orbital is found to lie below the highest (doubly) occupied molecular orbital. These donor–acceptor radicals have a strong emission yield (up to 54%) and high photostability, with estimated half-lives reaching up to several months under pulsed ultraviolet laser irradiation. Organic light-emitting diodes based on such a radical emitter show deep-red/near-infrared emission with a maximal external quantum efficiency of 5.3%. Our results provide a simple molecular-design strategy for stable, highly luminescent radicals with non-Aufbau electronic structures.

Neutral π-radicals have potential for use as light emitters in optoelectronic devices due to the absence of energetically low-lying non-emissive states. Here, we report a defect-free synthetic methodology via mesityl substitution at the para -positions of tris(2,4,6-trichlorophenyl)methyl radical. These materials reveal a number of novel optoelectronic properties. Firstly, mesityl substituted radicals show strongly enhanced photoluminescence arising from symmetry breaking in the excited state. Secondly, photoexcitation of thin films of 8 wt% radical in 4,4’-bis(carbazol-9-yl)-1,1’-biphenyl host matrix produces long lived (in the order of microseconds) intermolecular charge transfer states, following hole transfer to the host, that can show unexpectedly efficient red-shifted emission. Thirdly, covalent attachment of carbazole into the mesitylated radical gives very high photoluminescence yield of 93% in 4,4’-bis(carbazol-9-yl)-1,1’-biphenyl films and light-emitting diodes with maximum external quantum efficiency of 28% at a wavelength of 689 nm. Fourthly, a main-chain copolymer of the mesitylated radical and 9,9-dioctyl-9 H -fluorene shows red-shifted emission beyond 800 nm. Neutral π-radicals are potential emitters for optoelectronic devices due to the absence of energetically low-lying non-emissive states. Here, the authors report mesityl-substituted tris(2,4,6-trichlorophenyl)methyl radicals and achieve maximum device efficiency of 28% at a wavelength of 689 nm.

Methane (CH 4 ), the most abundant hydrocarbon in the atmosphere, originates largely from biogenic sources 1 linked to an increasing number of organisms occurring in oxic and anoxic environments. Traditionally, biogenic CH 4 has been regarded as the final product of anoxic decomposition of organic matter by methanogenic archaea. However, plants 2 , 3 , fungi 4 , algae 5 and cyanobacteria 6 can produce CH 4 in the presence of oxygen. Although methanogens are known to produce CH 4 enzymatically during anaerobic energy metabolism 7 , the requirements and pathways for CH 4 production by non-methanogenic cells are poorly understood. Here, we demonstrate that CH 4 formation by Bacillus subtilis and Escherichia coli is triggered by free iron and reactive oxygen species (ROS), which are generated by metabolic activity and enhanced by oxidative stress. ROS-induced methyl radicals, which are derived from organic compounds containing sulfur- or nitrogen-bonded methyl groups, are key intermediates that ultimately lead to CH 4 production. We further show CH 4 production by many other model organisms from the Bacteria, Archaea and Eukarya domains, including in several human cell lines. All these organisms respond to inducers of oxidative stress by enhanced CH 4 formation. Our results imply that all living cells probably possess a common mechanism of CH 4 formation that is based on interactions among ROS, iron and methyl donors, opening new perspectives for understanding biochemical CH 4 formation and cycling. Methane formation by a ROS-mediated process is linked to metabolic activity and is identified as a conserved feature across living systems.

Molybdenum supported on zeolites has been extensively studied as a catalyst for methane dehydroaromatization. Despite significant progress, the actual intermediates and particularly the first C-C bond formation have not yet been elucidated. Herein we report evolution of methyl radicals during non-oxidative methane activation over molybdenum single sites, which leads selectively to value-added chemicals. Operando X-ray absorption spectroscopy and online synchrotron vacuum ultraviolet photoionization mass spectroscopy in combination with electron microscopy and density functional theory calculations reveal the essential role of molybdenum single sites in the generation of methyl radicals and that the formation rate of methyl radicals is linearly correlated with the number of molybdenum single sites. Methyl radicals transform to ethane in the gas phase, which readily dehydrogenates to ethylene in the absence of zeolites. This is essentially similar to the reaction pathway over the previously reported SiO 2 lattice-confined single site iron catalyst. However, the availability of a zeolite, either in a physical mixture or as a support, directs the subsequent reaction pathway towards aromatization within the zeolite confined pores, resulting in benzene as the dominant hydrocarbon product. The findings reveal that methyl radical chemistry could be a general feature for metal single site catalysis regardless of the support (either zeolites MCM-22 and ZSM-5 or SiO 2 ) whereas the reaction over aggregated molybdenum carbide nanoparticles likely facilitates carbon deposition through surface C-C coupling. These findings allow furthering the fundamental insights into non-oxidative methane conversion to value-added chemicals. Understanding of the direct methane conversion mechanism is essential for further development of efficient catalysts. Here, authors demonstrate a general methyl radical chemistry for metal single site catalysis regardless of the support (either zeolite or SiO 2 ) in non-oxidative methane activation.

Partial oxidation of methane into primary oxidation products with high value remains a challenge. In this work, photocatalytic oxidation of methane (CH 4 ) with high methyl hydroperoxide (CH 3 OOH) selectivity is achieved using pure titanium oxide (TiO 2 ) without any cocatalyst at room temperature and atmospheric pressure. The CH 3 OOH production rate can reach up to 2050 ± 88 µmol·g −1 ·h −1 at pH ≈ 7.0 with 100% selectivity in the liquid product. The stable reaction cycle can reach more than 30 times. This low-cost system achieves superior CH 4 conversion activity and selectivity compared with similar work. The energy of hydrogen peroxide (H 2 O 2 ) to adsorbed hydroperoxyl radical (⋆OOH) has a significantly lower reaction energy than conversion to adsorbed hydroxyl radical (⋆OH) on the (210) surface of the TiO 2 . The ⋆OOH preferentially combines with methyl radical (·CH 3 ) to form the most energetically favorable CH 3 OOH. The mild oxidative environment of this system prevents the reduction of CH 3 OOH to CH 3 OH or over-oxidation of CH 4 , which ensures the final CH 3 OOH with high selectivity and stability. This work provided a low-cost but highly efficient method to achieve partial oxidation with superior selectivity, i.e., to convert CH 4 into high-value chemicals.