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.