Unveiling the source of activity of carbon integral honeycomb monoliths in the catalytic methane decomposition reaction

•Coal-based carbon integral honeycomb monoliths for thermocatalytic CH4 decomposition.•Combination of Rietveld-XRD, HAADF, XPS and EELS provide fine pieces of information.•Structure of graphite layers has influence on the catalytic activity.•Interaction between carbon and inorganic additives modulate carbon reactivity.

Carbon integral honeycomb monoliths with good performance in the thermocatalytic decomposition of methane were deeply characterized to understand the differences of behaviour resulting from their different pre-treatment. In particular three types of carbon monoliths were investigated, just carbonized, and activated with and without pre-oxidation. Advanced techniques such as X-ray Diffraction with Rietveld analysis, X-ray Photoelectron Spectroscopy and Scanning-Transmission Electron Microscopy with HAADF and EELS analysis were applied to unveil the origin of their differences which could not be correlated with the textural properties nor with the surface groups functionality. Particular attention was paid to the initial defects concentration and the nature of the carbon produced during the reaction, not finding either clear differences between the three types of monoliths studied. On the contrary the simply activated monoliths, with the highest activity, seemed to have higher content of a relatively amorphous graphite in which more actives sites for the reaction must be present. They also exhibited higher initial percentage of carbon atoms on the surface and a relative increase of C–C bonds after reaction. In addition the interaction between the carbonaceous phase and some of the phases of the clay used to extrude the starting coal could influence the carbon reactivity.

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