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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.

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The action of nanosized Pt-containing Al 2 O 3 catalysts to avoid coking and sintering was studied in steam reforming of glycerol. The solids exhibited almost 100% conversion toward syngas produced at a suitable water to glycerol ratio. Depending on the promoter, a drastic drop in hydrogen yield was observed due to coking and sintering effects. Spent catalyst characterizations by Raman, HRTEM, XRD, TG and SEM-EDS as well as textural property techniques showed that coking, rather than sintering, was the main cause that determined the low hydrogen selectivity of nanosized Pt-containing Al 2 O 3 with La 2 O 3 or ZrO 2 . In contrast, coking did not cover the active sites of Pt-containing Al 2 O 3 with MgO or CeO 2 . Thus, steam suppressed carbon deposition and improved the nanosized Pt/MgO-Al 2 O 3 catalyst stability in the steam reforming of glycerol.

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