This study proposes an integrated oxidative coupling of methane (OCM) process for the co-production of ethylene and hydrogen, aiming to overcome the limitations of conventional single-reactor OCM and improve system-level performance while addressing resource sustainability in ethylene production. The proposed processes employ a two-stage isothermal reaction system to improve methane conversion and C 2 selectivity, combined with an alternative separation strategy and on-site energy recovery via combined heat and power integration. Rigorous process simulations were conducted to establish mass and energy balances, followed by comprehensive techno-economic and environmental analysis. The optimal configuration achieved an ethylene unit production cost of 0.97 USD/kg, representing a 55.9% reduction relative to a conventional single-reactor OCM benchmark (2.2 USD/kg), driven by staged conversion, elimination of methane recycles, and hydrogen coproduction. Net CO 2 -equivalent emissions were reduced by 66.2% to 4.50 kg CO 2 per kg C 2 H 4 . Sensitivity analysis identified hydrogen value, methane price, and the methane/oxygen ratio as key determinants of economic feasibility. A multi-metric assessment incorporating energy use, carbon efficiency, feedstock availability, and price elasticity shows that methane-based direct conversion pathways exhibit favorable structural characteristics, particularly in terms of feedstock robustness. These results provide practical solutions to cost-competitively diversify resources for ethylene production, while leveraging emerging hydrogen markets. • Two-stage OCM reactors improve methane conversion and ethylene selectivity. • A developed process enables co-production of ethylene and hydrogen. • Ethylene unit production cost reaches 0.97 $/kg, 55.9% lower than benchmark. • Net CO 2-eq emissions reduced to 4.50 kg CO 2 per kg of ethylene, 66.2% improvement. • Multi-metric assessment supports methane-based routes for sustainable ethylene production.

ConspectusThe direct oxidation of methane, which is the main component of natural gas, shale gas, methane clathrates, and biogas, to value-added products is an economically attractive and environmentally friendly alternative to strongly endothermic methane steam reforming to synthesis gas (CO/H2). Among the different routes, the oxidative coupling of methane (OCM) to ethylene/ethane (C2-hydrocarbons) is the most promising one. A key limiting factor is insufficiently high selectivity to C2-hydrocarbons due to their overoxidation to carbon oxides (COx) at industrially relevant degrees of methane conversion. Although it is generally agreed that both selective and unselective reactions are initiated by oxygen species on the surface of catalysts, the kind, role, and origin of these species remain elusive, which hampers the tailored design of catalysts.In this Account, we summarize our recent progress in understanding how product selectivity in the OCM reaction can be tuned by controlling the type of oxygen species through catalyst composition or reaction conditions. The combination of in situ time- and temperature-resolved catalyst characterization with transient kinetic methods, i.e., temporal analysis of products (TAP) and steady-state isotopic transient kinetic analysis (SSITKA), has been proven to be effective for understanding the origin and role of oxygen species involved in selective and unselective pathways. We also present strategies for regulating the concentrations of selective and unselective oxygen species. For the Mn-M(M = Na, K, Rb, or Cs)2WO4 system, the electronegativity of the alkali metal was found to influence the ability of the catalysts to form selective oxygen species from gas-phase oxygen. The binding strength of atomic oxygen species is a key parameter for hindering the oxidation of methane to COx over Gd2O3-based catalysts. This property can be adjusted by using a metal oxide promoter. The nature and concentration of different oxygen species can also be controlled through the use of steam or an alternative oxidizing agent, N2O, and by performing the OCM reaction in a chemical looping mode, i.e., by alternating between CH4- and air-containing feeds. Using steam in the latter option enabled us to largely enhance the productivity of C2-hydrocarbons, thus making this technology more attractive for large-scale applications. The knowledge summarized in this Account is expected to present insights for further studies in the development of selective catalysts for various alkane oxidation reactions and in the optimization of reactor operation.

Oxygen Defect Engineering of SrTiO ₃ Catalysts for Oxidative Coupling of Methane

ABSTRACT The photocatalytic oxidative coupling of methane (OCM) offers a sustainable pathway for converting methane into valuable C2 compounds under ambient conditions. We explore the movement of oxygen species in photocatalytic OCM, particularly the cooperative effects between inert supports loaded with Au and semiconductor compounds (ZnO/TiO 2 , ZTO). The experimental results demonstrate that the coexistence of Au and ZTO is essential for C 2 H 6 production, even without any direct interfacing between the two components. EPR characterization indicates that superoxide radicals (·O 2 − ) may migrate from ZTO to Au sites, forming active Au─O species which activate methane into methyl radicals (·CH 3 ) for subsequent coupling into C 2 H 6 . Interestingly, in the photocatalytic OCM system, the C 2 H 6 yield remained stable upon progressive reduction of the semiconductor content before eventually declining. This trend suggests saturation of ·O 2 − intermediates likely arising from the kinetic balance between generation and quenching of ·O 2 − , where the semiconductor mediates the conversion of O 2 and lattice oxygen to ·O 2 − . We interpret this self‐regulating phenomenon as an Oxygen‐Mediated Self‐Buffering (O‐MSB) mechanism.

Abstract Direct and selective upgrading of methane to multicarbon hydrocarbons under mild conditions remains one of the most compelling yet elusive goals spanning chemistry, energy, and environmental science. Solar-driven photocatalysis now offers an avenue to activate the inert C–H bonds of methane at ambient temperature and pressure; however, a clear, comparative mechanistic understanding of oxidative coupling versus non-oxidative coupling remains lacking, hindering rational catalyst design and pathway optimization. This review systematically dissects the photocatalytic reaction mechanisms of oxidative versus non-oxidative coupling, outlines key challenges associated with catalyst efficiency, selectivity, and stability, and highlights promising research directions for both pathways. The primary objective of this review is to further advance photocatalytic methane conversion technologies and to provide strategic guidance for the rational design of high-performance photocatalysts.

Photocatalytic nonoxidative coupling of methane (CH4, NOCM) to ethane (C2H6) is a promising route for CH4 valorization, yet its efficient implementation requires the seamless coordination of CH4 adsorption, C-H bond activation, and C-C coupling. This intrinsic complexity makes it fundamentally challenging for a single type of active site to drive the entire NOCM process efficiently. Herein, we induce the formation of Ce3+ sites on the surface of CeO2 by loading Ag nanoparticles (NPs) for NOCM, and achieve highly efficient and selective conversion of CH4 to C2H6. Mechanistic studies indicate that the Ce3+ sites enhance CH4 adsorption and facilitate C-H bond activation to generate methyl radicals (˙CH3). Subsequently, Ag NPs promote the coupling of ˙CH3, ultimately producing C2H6. This study presents a synergistic catalysis strategy for designing efficient photocatalysts to achieve the selective coupling of CH4 into higher-value chemicals.

Solid oxide electrochemical reactors (SOERs) offer a compelling pathway for upgrading feedstocks into value-added chemicals using renewable electricity, in which electrode reaction kinetics can be precisely regulated by external electricity to surpass reaction thermodynamic limitations. However, the practical deployment of SOERs remains constrained by low product yields and instability. Existing studies have largely focused on isolated material innovations and have reported scattered performance data under seemingly similar conditions, lacking an integrated perspective that bridges material design, device engineering, and electrochemical coupling. Here, we present a comprehensive review of both protonic and oxygen-ion-conducting SOERs for chemical synthesis. We first outline reaction mechanisms and cell configurations across key reactions, including cathodic CO2 upgrading, anodic methane coupling, alkane-to-olefin conversion, and their hybrid pathways, establishing a foundation for next-generation material development. We then summarize the critical factors governing conversion efficiency, product selectivity, and operation stability from both electrochemical and catalytic perspectives. Subsequently, recent advances in electrode development for enhancing electrochemical performance and product yields are summarized and compared. Finally, future opportunities and research directions are outlined to accelerate the commercial translation of SOER technologies. This review provides a framework for understanding complex SOER-driven chemical upgrading and offers guidance for its development.

The rational development of molecular catalysts, supported on an inorganic material, requires advanced analytic methodologies to probe the structure, dynamics, and electronic properties of the catalytic center(s). While spectroscopic tools, in particular solid-state MAS NMR, have greatly advanced our understanding of metal sites in molecules and materials, it remains challenging to address the detailed structure and dynamics of paramagnetic centers. Fe(II) sites are ubiquitous across catalytic systems from enzymes to molecular and heterogeneous catalysts. Across supported systems, silica-supported Fe(II) species have recently been shown to enable the nonoxidative coupling of methane, and the surface sites have been investigated via Surface Organometallic Chemistry. Here, we show how state-of-the-art MAS NMR experiments combined with quantum computations enable us to resolve the structure and the dynamics of a dimeric Fe(II) complex, used for the production of isolated iron sites on the surface of amorphous silica. We also show through analysis of the 1H and 13C NMR signatures of the silica-supported species that a large structural difference exists between molecular and supported species; the latter displaying a remarkably homogeneous, monomeric, and highly dynamic single-atom sites.

Computationally guided dopant discovery for boosting TiO2 catalysts in plasma-assisted non-oxidative coupling of methane

Oxidative coupling of methane (OCM) over Ce-loaded CaO catalysts: Investigating the active sites

A two-phase engineering model for non-oxidative methane coupling in fluidized bed reactors: A framework for reactor design and electrification assessment

Au/TiO2 photocatalysts with controlled Au sizes show a rise-to-plateau dependence in photocatalytic methane coupling, reaching 14.9 mmol g-1 h-1 C2+ at 89.1% selectivity near 7.8 nm. The face-rich Au on larger particles, reinforced by stronger Au-TiO2 interaction, as the dominant active motif for C-C coupling.

Abstract Photocatalytic oxidative coupling of methane (POCM) is a promising strategy for the production of sustainable C 2+ hydrocarbons; however, it typically relies on large quantities of noble metals, such as gold, to serve as active sites for methyl coupling. In this study, we demonstrate that ZnO-supported gold nanoclusters with an average diameter of 1.1 nm provide a robust alternative to conventional gold nanoparticles, enabling efficient POCM even at ultralow gold loadings of 0.1 wt%. The optimized photocatalyst affords a C 2 –C 4 hydrocarbon production rate of 3.89 mmol/(g h) with 94.8% selectivity under 365 nm irradiation in a batch reactor. Results reveal that the abundant interfaces between highly dispersed gold nanoclusters and ZnO substrates facilitate charge carrier separation and promote a light-induced Mars–van Krevelen reaction pathway. Methyl adsorption causes gold nanoclusters to exhibit a more intense d- σ hybridization state compared to gold nanoparticles, enhancing electron transfer interactions and substantially reducing the transition-state energy barrier for methyl coupling.

Nonoxidative coupling of methane represents a long-standing challenge in heterogeneous catalysis, as it requires activation of the carbon-hydrogen (C-H) bond, controlled carbon-carbon (C-C) bond formation, and effective hydrogen management without relying on oxidants. Here, we report a low-temperature C-H activation and nonoxidative C-C coupling of methane over atomically dispersed titanium-aluminum-boron nanopowder (Ti-Al-B NP) utilizing a catalytic microreactor coupled to synchrotron single-photon photoionization reflectron time-of-flight mass spectrometry. The soft-ionization, in situ probing method detects the nascent reaction products and radical intermediates under operando conditions, including methyl radical, C2 hydrocarbons, and molecular hydrogen. Methane activation is initiated at 800 K, approximately 700 K below the gas-phase decomposition threshold, leading predominantly to ethylene formation with selectivity reaching up to 78% among the C-C coupled products. Electronic structure calculations on model Ti-Al-B clusters elucidate a cooperative catalytic mechanism in which titanium enables methane adsorption and C-H activation, boron acts as a reversible hydrogen reservoir, and aluminum stabilizes methylene intermediates, thereby facilitating selective C-C coupling and dehydrogenation. These findings establish a distinct catalyst architecture for nonoxidative methane coupling based on earth abundant elements alternative to expensive platinum and other noble metal-containing conventional catalysts and provide molecular-level design principles for controlling dehydrogenation and subsequent C-C bond formation in challenging light alkane conversions.

Effect of in-situ plasma surface treatments on the activity and regeneration of Pd/TiO2 for the photocatalytic non-oxidative coupling of methane

Unraveling the evolution of oxygen species and its role in adjusting catalytic performance over LaAlO3-based catalysts in oxidative coupling of methane

• Introduced a new optimization framework for staged adiabatic reactors using OCM. • Distributed O 2 feeding with interstage cooling improves reactor safety and control. • C 2 yield enhanced 8 times higher with staged reactor zoning and cooling. • Framework can be extended for other highly exothermic catalytic systems. Managing heat is a major challenge for oxidative coupling of methane (OCM) because of its high exothermicity. While recent innovations have mainly focused on reactor design, most studies assume isothermal operation, which is often impractical for scale-up. Adiabatic operation better reflects industrial conditions but remains underexplored. Additionally, little attention has been given to distributing O 2 along the reactor or using interstage cooling to smooth temperature variations inside the OCM reactor and improve performance. In this work, we address those gaps by optimizing a multi-zone reactor design with distribution feeding of O 2 . Using Simulated Annealing, we model up to 30 reactor zones, each treated as a fixed-bed, one-dimensional and pseudo-homogeneous system. Our results show that distributing oxygen across multiple zones with interstage cooling increases the C 2 yield by almost 8 times, from 5.7% in a single zone to 46.5 % across 30 zones, achieving smoother temperature profiles without changing the catalyst.

Chemical looping (CL) technologies have emerged as transformative approaches for energy conversion, carbon capture, and sustainable chemical production. Based on cyclic redox reactions of solid oxygen or nitrogen carriers, CL processes enable inherent separation of CO2, high thermal efficiency, and reduced pollutant formation compared with conventional combustion and reforming methods. This review provides a comprehensive assessment of the current status and recent advances across multiple CL applications, including combustion of gaseous, liquid, and solid fuels, hydrogen generation via reforming, gasification, and water splitting, and novel extensions for ammonia synthesis, air separation, oxidative coupling of methane, and oxidative dehydrogenation of light hydrocarbons. Key developments in oxygen carrier (OC) materials, ranging from Ni-, Cu-, Fe-, Mn-, and Co-based oxides to natural ores, mixed oxides, perovskites, and composites, are critically evaluated in terms of redox activity, stability, cost, and environmental impact. Various reactor configurations and pilot-scale demonstrations worldwide are reviewed, highlighting progress in scaling CL from laboratories to MWth pilot units. Techno-economic and life cycle assessments consistently point to CL’s potential for achieving low-carbon power and chemical production, although challenges remain in oxygen carrier durability, reactor scale-up, and system integration under industrial conditions. Collectively, these advances position chemical looping as a versatile pathway for decarbonized energy generation, negative-emissions bioenergy systems, hydrogen production, and sustainable chemical manufacturing.

Photocatalytic methane coupling represents a promising strategy for the production of valuable C2+ chemicals. Herein, the rational design of an Au24Zn1 nanocluster-embedded ZnO catalyst was demonstrated to enhance photocatalytic performance, and the resultant Au24Zn1/ZnO catalyst exhibited a C2+ selectivity of 93.5% and a yield of 663.1 μmol·gcat-1·h-1 (510.1 mmol·gAu-1·h-1) in a batch reactor. X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared Fourier transform spectroscopy-CO adsorption (CO-DRIFTS) revealed that the clusters functioned as hole acceptors, thereby accelerating the separation of photogenerated carriers. Radical experiments and isotope-labeling studies confirmed that the •OH radical derived from water serves as the primary reactive oxygen species responsible for activating methane to •CH3 radicals under the coexistence of H2O and O2, which demonstrates a significant discrepancy compared to the reported photogenerated hole activation pathway. Additionally, the •OOH radical generated via oxygen reduction played a supporting role both in modulating the concentration of •OH radicals and promoting the catalytic cycle. The cooperation contributed to the high yield and excellent selectivity of the C2+ products. This work provides valuable insights into the mechanistic pathway of methane conversion and highlights the potential of metal nanocluster-based materials in photocatalysis.

ABSTRACT The catalytic transformation of natural gas (primarily C 1 –C 3 light alkanes) into value‐added chemicals represents a fundamental research frontier in the energy and chemical industry, yet conventional approaches typically demand elevated temperatures to achieve considerable C–H bond activation and conversion. The utilization of molecular oxygen as an oxidant presents significant thermodynamic benefits, enabling the potential for low‐temperature aerobic conversion of light alkanes. However, oxidants also introduce challenges in inhibiting overoxidation and enhancing product selectivity. Photocatalysis, leveraging the distinctive capacity of photogenerated high‐energy charge carriers to selectively cleave strong C–H bonds, further circumvents reaction kinetics and selectivity limitations for converting inert light alkanes under mild conditions. In this Perspective, we focus particularly on the selective C–H bond activation in oxygen‐containing environment for the photocatalytic oxidation coupling of methane, while also reviewing recent advances in photocatalytic dehydrogenation of ethane and propane. We conclude by critically analyzing the current challenges and future opportunities in low‐temperature aerobic photocatalytic conversion of light alkanes.