Oxidative Coupling Of Methane Research Articles

Autothermal Oxidative Coupling of Methane over Pt/Al2O3 Catalysts Doped with Rare Earth Oxides

AbstractThe effect of rare earth oxides as dopants on the Pt‐governed oxidative coupling of methane (Pt‐OCM) is investigated. The addition of 20 wt.‐% of La‐, Nd‐, Sm‐, and Pr‐oxides to the support benefits the C2 product selectivity and offers the potential to enhance the catalyst stability. Compared to the reference catalyst Pt/Al2O3, the addition of Sm2O3 increased the total selectivity by up to 23 %. Furthermore, La2O3 addition was found beneficial with respect to the (thermal) stability of the catalyst. Dopant content variations uncovered that the catalyst formulation with 20 wt.‐% La2O3 represents an optimum regarding performance and stability.

Direct Oxidative Coupling of Methane into Ethylene in a Catalyst-Enhanced Planar Solid Oxide Fuel Cell Stack Reactor

This study presents an efficient method to convert methane into valuable olefins using a Solid Oxide Fuel Cell (SOFC) membrane reactor. Methane, abundant in natural and shale gas, serves as a sustainable feedstock due to its favorable carbon-hydrogen ratio. The SOFC membrane reactor eliminates costly air separation units and safety risks associated with explosive methane-oxygen mixtures. A planar SOFC stack achieves over 30% methane conversion, 40% ethylene selectivity, and power generation capabilities. Optimization with mixed-conducting ceramics enhances electrical performance without compromising catalytic activity. The stack's scalability is demonstrated, with the 5-cell configuration surpassing the 2-cell setup. This innovative approach offers a sustainable solution to methane waste, producing high-value chemicals while reducing environmental impact.

Microkinetic Modeling to Decode Catalytic Reactions and Empower Catalytic Design

AbstractKinetic model development is integral for designing, redesigning, monitoring, and optimizing chemical processes. Of the various approaches used within this field, microkinetic modeling is a crucial tool that focuses on surface events to analyze overall and preferential reaction pathways. This work covers noticeable features of microkinetic modeling for three critical case studies: (i) ammonia to hydrogen, (ii) oxidative coupling of methane to chemicals, and (iii) carbon dioxide hydrogenation for methanol synthesis. We analyze how microkinetic modeling enables predicting and optimizing complex reaction networks, allowing the design of efficient and tailored catalysts with enhanced activity and selectivity.

Riser Reactor with a Multistage Oxygen Feeding Strategy for the Oxidative Coupling of Methane

Riser Reactor with a Multistage Oxygen Feeding Strategy for the Oxidative Coupling of Methane

K2SO4-promoted TiO2 for the efficient oxidative coupling of methane

The oxidative coupling of methane (OCM) into C2−3 hydrocarbons is still limited to a few types of catalysts with low product yield. Herein, we reported our discovery that a K2SO4-promoted TiO2 catalyst can effectively catalyze the OCM reactions with a C2−3 yield of up to 26 %, which is comparable to the classical Mn-NaWOx/SiO2 catalyst. Besides, this catalyst not only exhibits promising stability for at least 200 h without signs of deactivation under typical OCM conditions but also demonstrates high sulfur-resistance performance, outperforming most reported catalysts. We have evidenced that K+ ions are responsible for increasing the surface basicity of rutile TiO2, thus benefiting C2−3 selectivity. The presence of SO42− can prevent the formation of potassium titanates, which catalyze the over-oxidation of CH4. The surface lattice oxygen species are confirmed to be the active sites for selective CH4 activation, while the chemisorbed oxygen species catalyze the combustion of CH4 to CO2.

The investigation of oxygen species in silicalite-1 supported MnOx-Na2WO4 catalyst towards efficient oxidative coupling of methane

The oxidative coupling of methane (OCM) as a promising single-step method towards olefins has attracted significant attention in efficient methane conversion and utilization. Here, we report a promising porous MnOx-Na2WO4/S-1 catalyst. The microporous silicalite-1 support ensures a uniform distribution of the elements Na, W and Mn on the catalyst surface, resulting in more active sites. In addition, the catalyst with weakly bonded and easily reduced lattice oxygen favors the generation of oxygen defect sites on the MnOx, further promoting the formation of electrophilic species (peroxide and superoxide). Hence, a high ratio of (O2- + O-)/O2- was achieved to boost the OCM performance. Furthermore, the MnOx-Na2WO4 catalyst supported by S-1 exhibited the ability to inhibit the loss of active components. As a result, an excellent C2 yield of 24.2% was achieved at 760 ℃ for OCM, accompanied by 43.1% CH4 conversion and 56.2% C2 selectivity. Moreover, the catalyst exhibited excellent stability without any deactivation in 50 hours.

Effect of operating conditions on the performance of riser reactor for oxidative coupling of methane

Oxidative coupling of methane (OCM) is characterized by high temperature and strong heat released. A riser reactor is designed for the OCM process to improve gas-solid contacting and heat transfer. This work illustrates the effect of hydrodynamic conditions and feed gas composition on the performance of an OCM riser reactor. The findings suggest that oxidative reactions predominantly occur within the acceleration zone and developed flow zone. Furthermore, at the low superficial gas velocity accompanied by a high solid circulating rate, the C2 yield initially increases in the acceleration zone, followed by a decrease in the developed flow zone and deceleration zone. The optimal operating conditions are a specific region corresponding to the solids holdup ranges from 0.015 to 0.02. Moreover, the C2 yield can be elevated using an appropriate feed mixture.

Progress through Temporal Analysis of Products and Steady‐state Isotopic Transient Kinetic Analysis to Elucidate Oxidation, CO2 Hydrogenation and Lower Olefins Production Reactions

A prerequisite for the development or optimization of heterogenous catalysts is a comprehensive understanding of the reaction mechanism and kinetics at the level as elementary as possible. In comparison with steady‐state catalytic tests typically used for this purpose, non‐steady‐state (transient) studies provide deeper insights due to higher time resolution. For several decades, temporal analysis of products (TAP) and steady‐state isotopic transient kinetic analysis (SSITKA) have been successfully applied to the analysis of various heterogenous reactions. In this review, we highlight the contributions made by TAP and SSITKA studies between 2017 and 2023 to the understanding of reaction mechanisms and to the derivation of microkinetics. The versatility of these methods is illustrated by the examples of oxidative coupling of methane, CO/CO2 hydrogenation to hydrocarbons or methanol, metathesis of ethylene with 2‐butenes to propene, acrolein oxidation to acrylic acid, methanol conversion to olefins and non‐oxidative propane dehydrogenation to propene. We also provide our personal views on possible developments in this area.

Alkaline Earth Metal Aluminate Support for Selective Oxidative Coupling of Methane

AbstractThe oxidative coupling of methane (OCM) provides a direct route to transform methane into higher value products. The alkali metal tungstate catalysts have demonstrated high selectivity towards C2 products, ethane (C2H6) and ethylene (C2H4). However, the severe sintering of the SiO2 support limits the reaction rate requiring active site densification to compete with unselective gas phase combustion reaction especially at high pressure operations. This work studies alkaline earth metal oxides as supports for K2WO4 catalysts to maintain comparatively high surface area under OCM conditions. Among Mg, Ca, and Sr aluminates, the K2WO4/MgAl2O4 catalyst exhibited the highest C2 yields. To achieve high C2 product selectivity, a relatively large loading of K2WO4 (20 wt %) was required likely to cover the unselective surface sites of MgAl2O4 support. The catalyst further showed high levels of stability when utilized at high pressures (0.9 MPa) for over 60 h, without any change in product selectivity. The Mn/K2WO4/MgAl2O4 showed multifold higher CH4 conversion rate, compared with the SiO2 counterpart. The findings showcase the potential of the MgAl2O4 support as a viable candidate for alkali metal tungstate catalysts for OCM, which introduces high density of active components in given volume in the reactor, which induces high contribution of the catalyst relative to the pure gas phase oxidation.

Controllably Modulating Oxygen Vacancies on Nonstoichiometric Nd−Ce−O Binary Oxides for Low‐temperature Oxidative Coupling of Methane

AbstractHerein, we synthesised a series of nonstoichiometric Nd−Ce−O composite oxides with a fluorite or rare‐earth C‐type phase structure using the glycine combustion method for the oxidative coupling of methane (OCM) reaction. As the amount of Nd3+ increases, the oxygen vacancies in this series of composite oxides gradually increase, leading to an amount increasing in the C2‐selective oxygen species O2− generated by the oxygen vacancies. In addition, with the increase in Nd3+, the number of moderate basic sites on the catalyst surface also improves, another significant factor affecting the OCM reaction performance of the composite oxides. Nd0.9Ce0.1O1.55 possesses optimal low‐temperature OCM reaction performance, achieving 8.0 % C2 yield at 450 °C and 14.1 % C2 yield at 700 °C. This can be attributed to the nonstoichiometric rare‐earth C‐type crystalline phase structure of Nd0.9Ce0.1O1.55, which exhibits the highest abundance of oxygen vacancies, selective oxygen species O2−, and moderate basic sites.

Titelbild: Fundamentals of Unanticipated Efficiency of Gd2O3‐based Catalysts in Oxidative Coupling of Methane (Angew. Chem. 14/2024)

Titelbild: Fundamentals of Unanticipated Efficiency of Gd₂O₃‐based Catalysts in Oxidative Coupling of Methane (Angew. Chem. 14/2024)

Cover Picture: Fundamentals of Unanticipated Efficiency of Gd2O3‐based Catalysts in Oxidative Coupling of Methane (Angew. Chem. Int. Ed. 14/2024)

Cover Picture: Fundamentals of Unanticipated Efficiency of Gd₂O₃‐based Catalysts in Oxidative Coupling of Methane (Angew. Chem. Int. Ed. 14/2024)

MonteCat: A Basin-Hopping-Inspired Catalyst Descriptor Search Algorithm for Machine Learning Models.

Proposing relevant catalyst descriptors that can relate the information on a catalyst's composition to its actual performance is an ongoing area in catalyst informatics, as it is a necessary step to improve our understanding on the target reactions. Herein, a small descriptor-engineered data set containing 3289 descriptor variables and the performance of 200 catalysts for the oxidative coupling of methane (OCM) is analyzed, and a descriptor search algorithm based on the workflow of the Basin-hopping optimization methodology is proposed to select the descriptors that better fit a predictive model. The algorithm, which can be considered wrapper in nature, consists of the successive generation of random-based modifications to the descriptor subset used in a regression model and adopting them depending on their effect on the model's score. The results are presented after being tested on linear and Support Vector Regression models with average cross-validation r2 scores of 0.8268 and 0.6875, respectively.

Directional Activation of Oxygen by the Au-Loaded ZnAl-LDH with Defect Structure for Highly Efficient Photocatalytic Oxidative Coupling of Methane.

Photocatalytic oxidative coupling of CH4 (OCM) is a promising CH4 conversion process that can achieve efficient methane conversion with the assistance of O2 . It remains to be highly challenging to improve the photocatalytic OCM activity from catalyst design and to deepen the understanding of the reactant activation in the OCM process. In this work, the Au-loaded ZnAl-layered double hydroxides (LDHs) with and without oxygen vacancy are constructed (denoted as Au/ZnAl and Au/ZnAl-v), respectively. When applied for photocatalytic OCM, the Au/ZnAl-v shows a CH4 conversion rate of 8.5 mmol g-1 h-1 with 92% selectivity of C2 H6 at 40°C, outperforming most reported photocatalytic OCM systems at low temperature reported in the literature. Furthermore, the catalytic performance of Au/ZnAl-v can be stable for 100h. In contrast, the An/ZnAl exhibits a CH4 conversion rate of 0.8 mmol g-1 h-1 with 46% selectivity of C2 H6 . Detailed characterizations and DFT calculation studies reveal that the introduced Ov sites on Au/ZnAl-v are able to activate O2 , and the resulting superoxide radical O2 ·- greatly promotes the activation of CH4 . The coupling of CH3 · groups with the assistance of Au cocatalyst leads to the formation of C2 H6 with high photocatalytic activity.

Fundamentals of Unanticipated Efficiency of Gd2O3-based Catalysts in Oxidative Coupling of Methane.

Improving the selectivity in the oxidative coupling of methane to ethane/ethylene poses a significant challenge for commercialization. The required improvements are hampered by the uncertainties associated with the reaction mechanism due to its complexity. Herein, we report about 90 % selectivity to the target products at 11 % methane conversion over Gd2O3-based catalysts at 700 °C using N2O as the oxidant. Sophisticated kinetic studies have suggested the nature of adsorbed oxygen species and their binding strength as key parameters for undesired methane oxidation to carbon oxides. These descriptors can be controlled by a metal oxide promoter for Gd2O3.

Fundamentals of Unanticipated Efficiency of Gd2O3‐based Catalysts in Oxidative Coupling of Methane

AbstractImproving the selectivity in the oxidative coupling of methane to ethane/ethylene poses a significant challenge for commercialization. The required improvements are hampered by the uncertainties associated with the reaction mechanism due to its complexity. Herein, we report about 90 % selectivity to the target products at 11 % methane conversion over Gd2O3‐based catalysts at 700 °C using N2O as the oxidant. Sophisticated kinetic studies have suggested the nature of adsorbed oxygen species and their binding strength as key parameters for undesired methane oxidation to carbon oxides. These descriptors can be controlled by a metal oxide promoter for Gd2O3.

Oxidative coupling of methane using oxidant mixtures of CO2 and O2 over Sr/La2O3

Oxidative coupling of methane with CO2 (CO2-OCM) is beneficial because it avoids complete oxidation, an undesired reaction that occurs during O2-oxidative coupling of methane. Previous literature has sparsely considered the respective roles of CO2 and O2 as reactants at CO2-OCM reaction conditions. This work explores the roles of CO2 and O2 in OCM over Sr/La2O3 with different reactant oxidant mixtures. While CO2 alone did not significantly activate methane at 875 °C, a tenfold increase in C2 yield resulted from adding 2 % O2. The role of CO2 in heterogeneous reactions was supported by XPS and XRD, which showed presence of carbonate species on the catalyst surface while the bulk phase remained La2O3. The work shows that a small amount of gaseous oxygen in the reactants can greatly improve methane conversion, and while oxygen is crucial in converting methane, CO2 plays an important role during ethane dehydrogenation.

Continuous Flow System for Highly Efficient and Durable Photocatalytic Oxidative Coupling of Methane.

Photocatalytic oxidative coupling of methane (OCM) into value-added industrial chemicals offers an appealing green technique for achieving sustainable development, whereas it encounters double bottlenecks in relatively low methane conversion rate and severe overoxidation. Herein, we engineer a continuous gas flow system to achieve efficient photocatalytic OCM while suppressing overoxidation by synergizing the moderate active oxygen species, surface plasmon-mediated polarization, and multipoint gas intake flow reactor. Particularly, a remarkable CH4 conversion rate of 218.2 μmol h-1 with an excellent selectivity of ∼90% toward C2+ hydrocarbons and a remarkable stability over 240 h is achieved over a designed Au/TiO2 photocatalyst in our continuous gas flow system with a homemade three-dimensional (3D) printed flow reactor. This work provides an informative concept to engineer a high-performance flow system for photocatalytic OCM by synergizing the design of the reactor and photocatalyst to synchronously regulate the mass transfer, activation of reactants, and inhibition of overoxidation.

Detailed kinetic modeling of catalytic oxidative coupling of methane

The oxidative coupling of methane (OCM) at high temperature over monolithic Pt-based catalysts operated at short contact times is investigated as an attractive method for methane upgrading to higher value products like ethylene and acetylene. An experimental measurement campaign aiming at elucidating the effect of operation parameters on the catalyst performance revealed that lower N2 dilution, lower CH4/O2 ratio, and higher space velocities promote high C2 yields. A maximum C2 yield of 10 % with 94 % CH4 conversion was obtained at a CH4/O2 ratio of 1.1, 50 % N2 dilution, and a space velocity of 4.5 × 105 h−1. Since both heterogenous and homogenous gas-phase chemistry together are required for determining C2 formation pathways, a detailed OCM surface reaction mechanism over Pt is presented consisting of 26 species and 86 reactions that are consistent from the view of thermodynamics and micro-kinetic reversibility. The combination of this OCM surface mechanism with a detailed gas-phase mechanism allows a numerical micro-kinetic description of the experimental measurements. The simulations presented in this study suggest that C2 formation takes place in the gas-phase at temperature above 1200 K with both oxidative and pyrolytic pathways for methane dehydrogenation to form CH3 radicals, whose coupling results in C2H6, C2H4 and C2H2 formation. Furthermore, the simultaneous presence of sufficient oxygen content and heat are vital for high C2 species yields.

Automatic feature engineering for catalyst design using small data without prior knowledge of target catalysis

The empirical aspect of descriptor design in catalyst informatics, particularly when confronted with limited data, necessitates adequate prior knowledge for delving into unknown territories, thus presenting a logical contradiction. This study introduces a technique for automatic feature engineering (AFE) that works on small catalyst datasets, without reliance on specific assumptions or pre-existing knowledge about the target catalysis when designing descriptors and building machine-learning models. This technique generates numerous features through mathematical operations on general physicochemical features of catalytic components and extracts relevant features for the desired catalysis, essentially screening numerous hypotheses on a machine. AFE yields reasonable regression results for three types of heterogeneous catalysis: oxidative coupling of methane (OCM), conversion of ethanol to butadiene, and three-way catalysis, where only the training set is swapped. Moreover, through the application of active learning that combines AFE and high-throughput experimentation for OCM, we successfully visualize the machine’s process of acquiring precise recognition of the catalyst design. Thus, AFE is a versatile technique for data-driven catalysis research and a key step towards fully automated catalyst discoveries.