Protonic ceramic fuel cells, like their higher-temperature solid-oxide fuel cell counterparts, can directly use both hydrogen and hydrocarbon fuels to produce electricity at potentially more than 50 per cent efficiency. Most previous direct-hydrocarbon fuel cell research has focused on solid-oxide fuel cells based on oxygen-ion-conducting electrolytes, but carbon deposition (coking) and sulfur poisoning typically occur when such fuel cells are directly operated on hydrocarbon- and/or sulfur-containing fuels, resulting in severe performance degradation over time. Despite studies suggesting good performance and anti-coking resistance in hydrocarbon-fuelled protonic ceramic fuel cells, there have been no systematic studies of long-term durability. Here we present results from long-term testing of protonic ceramic fuel cells using a total of 11 different fuels (hydrogen, methane, domestic natural gas (with and without hydrogen sulfide), propane, n-butane, i-butane, iso-octane, methanol, ethanol and ammonia) at temperatures between 500 and 600 degrees Celsius. Several cells have been tested for over 6,000 hours, and we demonstrate excellent performance and exceptional durability (less than 1.5 per cent degradation per 1,000 hours in most cases) across all fuels without any modifications in the cell composition or architecture. Large fluctuations in temperature are tolerated, and coking is not observed even after thousands of hours of continuous operation. Finally, sulfur, a notorious poison for both low-temperature and high-temperature fuel cells, does not seem to affect the performance of protonic ceramic fuel cells when supplied at levels consistent with commercial fuels. The fuel flexibility and long-term durability demonstrated by the protonic ceramic fuel cell devices highlight the promise of this technology and its potential for commercial application.

This paper reviews the state-of-the-art in catalytic processes to convert methane (a major component of natural gas) to more valuable hydrocarbons as fuels or chemicals. The scope is restricted to "direct" conversion, meaning that processes involving synthesis gas as an intermediate are not considered. Oxygenated products (e.g., alcohols) are also not considered. In all cases, the processes are concerned with catalytic dehydrogenation. The two most widely studied processes are Oxidative Coupling of Methane (OCM) and Methane Dehydroaromatization (MDA). After reviewing the relevant catalysis literature, the paper goes on to review reactor implementations. Hydrogen-and/or oxygenpermeable membranes can potentially play valuable roles in improving methane conversion and product yields. Despite over 30 years of research, there are still no direct-conversion processes that can compete commercially with methane reforming followed by processes such as Fischer-Tropsch synthesis. Thus, the future practical development and deployment of OCM and MDA will rely on the research and development of advanced catalysts and innovative processes. The present review helps to document the foundation on which the needed development can build.

We develop and validate detailed reaction mechanisms to represent the oxidative coupling of methane (OCM) over a La2O3/CeO2 nanofabric catalyst. The reaction mechanism includes 39 reversible gas‐phase reactions and 52 irreversible surface reactions between 22 gas‐phase species and 11 surface species. We use a model‐based interpretation of spatially resolved concentration and temperature profiles measured by using a laboratory‐scale packed‐bed reactor. The reaction mechanisms are validated for inlet feed compositions in the range of 7≤CH4/O2≤11. The results are supported by a reaction pathway analysis that provides insight into the relative contributions of the gas‐phase and surface reactions to form the desired C2+ and the undesired COx products. The results provide new quantitative insights into the complex nature of the OCM chemistry, which can assist practical process and reactor development.

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