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 degrees C, a subsequent and spontaneous "auto-regeneration" of the catalyst is observed above and below this temperature range. Increasing reaction temperature above 700 degrees C or decreasing it below 600 degrees 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. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.