Oxidative coupling of methane in solid oxide fuel cell tubular membrane reactor with high ethylene yield

Fuel Cell Reactors for the Clean Cogeneration of Electrical Energy and Value-Added Chemicals

Fuel cell reactors can be tailored to simultaneously cogenerate value-added chemicals and electrical energy while releasing negligible CO2 emissions or other pollution; moreover, some of these reactors can even “breathe in” poisonous gas as feedstock. Such clean cogeneration favorably offsets the fast depletion of fossil fuel resources and eases growing environmental concerns. These unique reactors inherit advantages from fuel cells: a high energy conversion efficiency and high selectivity. Compared with similar energy conversion devices with sandwich structures, fuel cell reactors have successfully “hit three birds with one stone” by generating power, producing chemicals, and maintaining eco-friendliness. In this review, we provide a systematic summary on the state of the art regarding fuel cell reactors and key components, as well as the typical cogeneration reactions accomplished in these reactors. Most strategies fall short in reaching a win–win situation that meets production demand while concurrently addressing environmental issues. The use of fuel cells (FCs) as reactors to simultaneously produce value-added chemicals and electrical power without environmental pollution has emerged as a promising direction. The FC reactor has been well recognized due to its “one stone hitting three birds” merit, namely, efficient chemical production, electrical power generation, and environmental friendliness. Fuel cell reactors for cogeneration provide multidisciplinary perspectives on clean chemical production, effective energy utilization, and even pollutant treatment, with far-reaching implications for the wider scientific community and society. The scope of this review focuses on unique reactors that can convert low-value reactants and/or industrial wastes to value-added chemicals while simultaneously cogenerating electrical power in an environmentally friendly manner.

Graphical Abstract

A schematic diagram for the concept of fuel cell reactors for cogeneration of electrical energy and value-added chemicals

Metal-oxide interface enhances methane oxidative coupling reaction in solid oxide electrolyzer

At present, converting methane into fuel and more valuable chemicals is highly desired for industrial application. Here, we demonstrate the in-situ electrochemical conversion of methane (C1) into ethane and ethylene...

Direct Conversion of Methane to C2 Hydrocarbons in Solid-State Membrane Reactors at High Temperatures

Direct conversion of methane to C₂ compounds by oxidative and nonoxidative coupling reactions has been intensively studied in the past four decades; however, because these reactions have intrinsic severe thermodynamic constraints, they have not become viable industrially. Recently, with the increasing availability of inexpensive "green electrons" coming from renewable sources, electrochemical technologies are gaining momentum for reactions that have been challenging for more conventional catalysis. Using solid-state membranes to control the reacting species and separate products in a single step is a crucial advantage. Devices using ionic or mixed ionic-electronic conductors can be explored for methane coupling reactions with great potential to increase selectivity. Although these technologies are still in the early scaling stages, they offer a sustainable path for the utilization of methane and benefit from the advances in both solid oxide fuel cells and electrolyzers. This review identifies promising developments for solid-state methane conversion reactors by assessing multifunctional layers with microstructural control; combining solid electrolytes (proton and oxygen ion conductors) with active and selective electrodes/catalysts; applying more efficient reactor designs; understanding the reaction/degradation mechanisms; defining standards for performance evaluation; and carrying techno-economic analysis.

Selective electrochemical oxidative coupling of methane mediated by Sr2Fe1.5Mo0.5O6-δ and its chemical stability

Efficient conversion of methane to value-added products such as olefins and aromatics has been in pursuit for the past few decades. The demand has increased further due to the recent discoveries of shale gas reserves. Oxidative and non-oxidative coupling of methane (OCM and NOCM) have been actively researched, although catalysts with commercially viable conversion rates are not yet available. Recently, [Formula: see text] (SFMO-075Fe) has been reported to activate methane in an electrochemical OCM (EC-OCM) set up with a C2 selectivity of 82.2%¹. However, alkaline earth metal-based materials are known to suffer chemical instability in carbon-rich environments. Hence, here we evaluated the chemical stability of SFMO in carbon-rich conditions with varying oxygen concentrations at temperatures relevant for EC-OCM. SFMO-075Fe showed good methane activation properties especially at low overpotentials but suffered poor chemical stability as observed via thermogravimetric, powder XRD, and XPS measurements where SrCO₃ was observed to be a major decomposition product along with SrMoO₃ and MoC. Nevertheless, our study demonstrates that electrochemical methods could be used to selectively activate methane towards partial oxidation products such as ethylene at low overpotentials while higher applied biases result in the complete oxidation of methane to carbon dioxide and water.

B, N-co-doped graphene-supported Ir and Pt clusters for methane activation and C─C coupling: A density functional theory study

Methane conversion by using transition metal catalysts plays in an important role in various usages of the industrial process. The mechanism of methane conversion on B, N-co-doped graphene supported Ir and Pt clusters, BNG-Ir4 and BNG-Pt4, have been investigated using density functional theory calculations. Methane was found to adsorb on BNG-Ir4 and BNG-Pt4 clusters via strong agostic interactions. The first step of methane dehydrogenation on BNG-Ir4 has a lower energy barrier, indicating a facile methane dissociation on BNG-Ir4. In addition, it shows that hydrogen molecule can form on the BNG-Ir4 and hydrogen can desorb from the surface. Besides, the C-C coupling reaction of CH₃ to form ethane is a more thermodynamically favorable process than CH₃ dehydrogenation on BNG-Ir4. Further, ethane is easier to desorb from the surface due to its low desorption energy. Therefore, the BNG-Ir4 cluster is a potential catalyst for activating methane to form ethane and to produce hydrogen. © 2019 Wiley Periodicals, Inc.

Electric Field and Mobile Oxygen Promote Low-Temperature Oxidative Coupling of Methane over La1-x Ca x AlO3-δ Perovskite Catalysts

Oxidative coupling of methane (OCM) over La_1-x M _x AlO_3-δ (M = Ca, Sr, Ba; x = 0, 0.1, 0.2, 0.3) in an electric field at low temperature (423 K) was investigated. Among the tested catalysts, the La_0.7Ca_0.3AlO_3-δ catalyst showed the highest performance in terms of C₂H₆ + C₂H₄ yield (11.1%). Surface mobile oxygen species (O₂ ^2- or O^-), which were considered as active oxygen species for the OCM reaction, increased with increasing Ca doping amount, and thereby the La_0.7Ca_0.3AlO_3-δ catalyst showed the best catalytic activity.

Synthesis of new composite materials for processing of methane into important petrochemical products

The aim of this research was to develop the technology of new composite material synthesis for the processing of natural gas methane into olefins. The effects of technological parameters (temperature, volumetric rate, reaction mixture composition) on methane’s oxidative conversion into important petrochemical products has been studied. The paper presents data on methods developed for synthesis and physicochemical characteristics of catalysts. The technological parameters of the process conducted by means of integrated automated laboratory setup were optimized. It has been established that 10% K-30% Mn-10% Nb/50% glycine catalyst prepared by the solution combustion synthesis (SHS) method in solution was active for olefin formation at oxidative transformation of mixture 41.8% CH4+16.2% O2+42% Ar at a volumetric velocity of 3500 h-1. It was determined that at T=800°С, yields of C2H6 and C2H4 were 3.3 and 14.3%, respectively.

Catalytic Layer Optimization for Hydrogen Permeation Membranes Based on La5.5WO11.25-δ/La0.87Sr0.13CrO3-δ Composites

(LWO/LSC) composite is one of the most promising mixed ionic-electronic conducting materials for hydrogen separation at high temperature. However, these materials present limited catalytic surface activity toward H₂ activation and water splitting, which determines the overall H₂ separation rate. For the implementation of these materials as catalytic membrane reactors, effective catalytic layers have to be developed that are compatible and stable under the reaction conditions. This contribution presents the development of catalytic layers based on sputtered metals (Cu and Pd), electrochemical characterization by impendace spectroscopy, and the study of the H₂ flow obtained by coating them on 60/40-LWO/LSC membranes. Stability of the catalytic layers is also evaluated under H₂ permeation conditions and CH₄-containing atmospheres.