Plasma-Assisted Reforming of Methane

Insight into ventilation air methane combustion of ultralow sub-nanometer palladium catalyst within the MFI zeolite

Methane's complete catalytic oxidation process has been widely studied, but efficient catalytic oxidation of low-concentration methane (≤0.75 %) remains a crucial problem in the coal chemical industry. How to prevent the sintering deactivation of the active component in Pd-based catalysts and achieve efficient and stable operation of sub-nanometer catalysts remains challenging. Here, we utilize the interaction between amine ligands and Pd nanoparticles to stabilize and encapsulate the Pd particles within the pores of a molecular sieve carrier, effectively promoting the high dispersion of Pd particles. By leveraging the low acidity, high hydrophobicity, and high hydrothermal stability of the zeolite carrier, the Pd@S-1 catalyst exhibits excellent activity and stability in the catalytic oxidation of methane at low concentrations. Finally, density functional theory is employed to investigate the reaction mechanism of low-concentration methane during the catalytic process. Encapsulating the active metal component in zeolite to improve catalytic activity and stability provides a theoretical basis and direction for preparing complete oxidation catalysts for low-concentration methane.

Mitigation of environmental impacts and challenges during hydrogen production

This paper presents hydrogen production methodologies, their impacts on the environment, and mitigation. Three different types of production procedures, namely fossil fuel-based, renewable energy-based, and biological, are presented along with their key technological characteristics and environmental feasibility. The effects of greenhouse gas emissions from its production on different natural cycles are carried out to show the environmental impact. Different production methods, problem identification, and mitigation of environmental impacts are separately pointed out. Analyses are shown for available methods in terms of their production cost, efficiency, maturity level, advantages, problems, and solutions. A comparative analysis is carried out along with different existing methods to find a suitable H2 production method. Finally, the transition pathway from fossil fuel to biohydrogen production is intended to promote biohydrogen for transportation and industrial applications. It demonstrates the possibility and potentiality of biohydrogen production for a sustainable future.

Photofragmentation laser-induced fluorescence imaging of CH3 by structured illumination in a plasma discharge

Methyl is crucial in plasma-assisted hydrocarbon chemistry, making precise in situ imaging essential for understanding various plasma applications. Its importance in methane chemistry arises from its role as a primary byproduct during the initial phase of methane dehydrogenation. Detecting the CH3 radical is challenging due to its high reactivity and the prevalence of strongly pre-dissociative electronically excited states. To address this, photofragmentation planar laser-induced fluorescence (PF-LIF) techniques have been developed. These involve laser-induced photodissociation of the CH3 radical into CH fragments, which are then probed using another laser. This method allows for both temporally and spatially resolved measurements. However, quantifying the signal from photofragmented species is complicated by the overlap with naturally occurring CH fragments. We employ PF-LIF with structured illumination to distinguish photofragmented species from naturally occurring ones using a frequency-sensitive lock-in technique. This methodology is demonstrated in an atmospheric pressure dielectric barrier discharge (DBD) containing argon and methane, enabling spatially and temporally resolved data acquisition of the CH3 radical. This approach facilitates interference-free PF-LIF measurements of methyl in various applications.

Direct HCN synthesis via plasma-assisted conversion of methane and nitrogen

Hydrogen cyanide (HCN) is synthesized from ammonia (NH3) and methane (CH4) at ~1200°C over a Pt catalyst. Ammonia synthesis entails several complex, highly emitting processes. Plasma-assisted HCN synthesis directly from CH4 and nitrogen (N2) could be pivotal for on-demand HCN production. Here, we evaluate the potential of dielectric barrier discharge (DBD) N2/CH4 plasma for decentralized catalyst-free selective HCN production. We demonstrate a single-step conversion of methane and nitrogen to HCN with a 72% yield at <300°C. HCN is favored at low CH4 concentrations with ethane (C2H6) as the secondary product. We propose a first-principles microkinetic model with few electron impact reactions. The model accurately predicts primary product yields and elucidates that methyl radical (·CH3) is a common intermediate in HCN and C2H6 synthesis. Compared to current industrial processes, N2/CH4 DBD plasma can achieve minimal CO2 emissions.

Mild Methane Electrochemical Oxidation Boosted via Plasma Pre-Activation

Obtaining partial methane oxidation reaction (MOR) with various oxygenates via a mild electrochemical method is practically difficult because of activation of stable C─H bond and consequent reaction pathway regulation. Here, a real-time tandem MOR with cascaded plasma and electrocatalysis to activate and convert the methane (CH4 ) synergistically is reported for the first time. Boosted CH4 conversion is demonstrated toward value-added products including, alcohols, carboxylates, and ketone via use of commercial Pd-based electrocatalysts. Compared with hash industrial processes, a mild condition, that is, anode potential < 1.0 V versus RHE (reversible hydrogen electrode) is used that mitigates overoxidation of oxygenates and obviates competing reaction(s). One evidence that Pd(II) sites and surface adsorbed hydroxyls are important in facilitating activated-CH4 species conversion, and establish a reaction mechanism for conversion(s) that involves coupling reactions between adsorbed hydroxyls, carbon monoxide and C1 /C2 alkyls. One conclude that pre-activation is important in boosting electrochemical partial MOR under mild conditions and will be of benefit in the development of sustainable CH4 conversion technology.