The role of Ni2+ diffusion on the reducibility of NiO/MgO system: A combined TRP-XPS study

The progressive dissolution of nickel ions in the lattice of MgO matrix, promoted by the calcination temperature, has been monitored using XPS. The reducibility of Ni/MgO catalysts is affected by the modification of the surface chemical composition. TPR peaks have been correlated with several NiO forms. Both XPS and TPR results indicate a different behaviour pattern for the supported and physically mixed NiO/MgO systems, and this has been attributed to the different available contact area between NiO and MgO. The formation of both NiO rich and MgO rich NiO-MgO solid solutions, with the tendency to evolve towards the bulk solid solution, has been invoked to explain the substantial changes in the TPR pattern of the different air calcined systems.