Evolution of the Ni-active centres into ex hydrotalcite oxide catalysts during the COx-free hydrogen production by methane decomposition

The catalytic study of the Ni-catalysts based on Ni/Mg/Al mixed oxides from hydrotalcite-like compounds (ex-LDH) shows a particular behaviour in the methane decomposition reaction. While deactivation of the catalyst occurs in the presence of methane within the range of temperature 600–700 °C, a subsequent and spontaneous “auto-regeneration” of the catalyst is observed above and below this temperature range. Increasing reaction temperature above 700 °C or decreasing it below 600 °C allows recover completely catalytic activity of the deactivated catalyst. This catalyst “auto-regeneration” process is an absolutely reversible process. XPS results of the spent catalysts suggest that the origin of this behaviour is a reversible change in the nature of the carbon deposit as a function of temperature. Consequently, the kinetic control of the carbon formation avoids the catalyst deactivation, and allows to reach the thermodynamic limit of the hydrogen produced.

Graphical abstractMethane conversion or H2 production (H2 is the only gas product) obtained with DeCH4 catalytic results of ex-LDH-I (15 %Ni) catalyst during the three consecutives TP-cycles carried out: (a), without any treatment between each TP-cycle, and (b), with a O2-regeneration treatment between each TP-cycle.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Particular behaviour is shown by Ni/Mg/Al ex-LDH catalyst during the CH4 decomposition. ► Deactivation of ex-LDH at 600–700 °C is followed by a spontaneous auto-regeneration. ► This catalyst auto-regeneration process is absolutely reversible with the temperature. ► XPS suggests that the origin of auto-regeneration is a reversible change of deposited carbon nature with Ta. ► Kinetics control avoids the catalyst deactivation, allowing reach the thermodynamic limit of the H2 produced.