Thermal Non-Oxidative Aromatization of Light Alkanes Catalyzed by Gallium Nitride

In aqua dual selective photocatalytic conversion of methane to formic acid and methanol with oxygen and water as oxidants without overoxidation

The direct and selective transformation of naturally abundant methane (CH₄) into high-value-added oxygenates, e.g., methanol, ethanol, and formic acid, is one of the "Holy Grails" in chemistry and chemical productions. However, complex mixtures of products, often due to over-oxidations, make such transformations highly challenging. Herein, gallium nitride (GaN), a methane-active semiconductor, catalyzes the photooxidation of methane and empowers the fine-controlling of chemoselectivity toward methanol and formic acids, simply by regulating the O₂ content in water. In contrast to previous methods, no overoxidation products (CO₂ and CO) were observed in this process. Mechanistic investigations and the corresponding quantitative experiments indicated that the controllable generation of moderately reactive oxygen radicals (•OOH and •OH) in combination with the direct methane activation triggered by GaN is responsible for the highly selective reactivity and tunability through a photo-generated radical process.

Selective conversion of methane to cyclohexane and hydrogen via efficient hydrogen transfer catalyzed by GaN supported platinum clusters

Non-oxidative liquefaction of methane at room temperature and ambient pressure has long been a scientific "holy grail" of chemical research. Herein, we exploit an unprecedented catalytic transformation of methane exclusively to cyclohexane and hydrogen evolution through effective surface-hydrogen-transfer (SHT) at the heterojunctions boundary consisting of electron-rich platinum cluster (Pt) loaded on methane-activating gallium nitride (GaN) host. The experimental analysis demonstrates that the interface-induced overall reaction starts with methane aromatization to benzene and surface-bound hydrogen initiated by the Ga-N pairs, followed by the hydrogenation of benzene to cyclohexane with surface-bound hydrogen. The in-situ activated hydrogen at electron-rich metal Pt cluster is crucial for the hydrogenation and enables an outstanding selectivity (up to 92%) and productivity (41 μmol g-1) towards cyclohexane and hydrogen evolution concurrently at 300 °C, which is well-delivered after 5 recycling runs.

Green Carbon Science: Efficient Carbon Resource Processing, Utilization, and Recycling Towards Carbon Neutrality

Green carbon science is defined as "Study and optimization of the transformation of carbon containing compounds and the relevant processes involved in the entire carbon cycle from carbon resource processing, carbon energy utilization, and carbon recycling to use carbon resources efficiently and minimize the net CO2 emission." [1] Green carbon science is related closely to carbon neutrality, and the relevant fields have developed quickly in the last decade. In this Minireview, we proposed the concept of carbon energy index, and the recent progresses in petroleum refining, production of liquid fuels, chemicals, and materials using coal, methane, CO2, biomass, and waste plastics are highlighted in combination with green carbon science, and an outlook for these important fields is provided in the final section.

Light-Induced Nonoxidative Coupling of Methane Using Stable Solid Solutions

Achieving efficient and direct conversion of methane under mild conditions is of great significance for innovations in the chemical industry. However, the efficiency and lifetime of most catalysts remain too far from practical requirements, since it is difficult to break the first C-H bond of methane as well as to suppress the following complete dehydrogenation (or overoxidation) and the resulting carbonaceous deposition (or CO₂ ). Here, we report that wurtzite GaN:ZnO solid solutions exhibit unique and unprecedented photocatalytic performances for the nonoxidative coupling of methane at room temperature, exclusively generating ethane with nearly stoichiometric H₂ . High conversion rate (>330 μmol g^-1  h^-1 ), long-term stability (>70 h), and superior coke-resistance were achieved. At 293 K, the methane conversion exceeds 7 %, comparable to the equilibrium conversion of thermal catalysis at 910 K. Mechanistic studies revealed that the N-Zn_Ga -O_N units and the absence of acid sites on the surface played crucial roles in reactivity and coke resistance, respectively.

Selective Coke Combustion by Oxygen Pulsing During Mo/ZSM-5-Catalyzed Methane Dehydroaromatization

Non‐oxidative methane dehydroaromatization is a promising reaction to directly convert natural gas into aromatic hydrocarbons and hydrogen. Commercialization of this technology is hampered by rapid catalyst deactivation because of coking. A novel approach is presented involving selective oxidation of coke during methane dehydroaromatization at 700 °C. Periodic pulsing of oxygen into the methane feed results in substantially higher cumulative product yield with synthesis gas; a H₂/CO ratio close to two is the main side‐product of coke combustion. Using ¹³C isotope labeling of methane it is demonstrated that oxygen predominantly reacts with molybdenum carbide species. The resulting molybdenum oxides catalyze coke oxidation. Less than one‐fifth of the available oxygen reacts with gaseous methane. Combined with periodic regeneration at 550 °C, this strategy is a significant step forward, towards a process for converting methane into liquid hydrocarbons.