Published online by Cambridge University Press: 15 February 2011
Cation-substituted hexaaluminate compounds, ABAl11O19-μ (A = La, Pr, Sm, and Nd; B = Cr, Mn, Fe, Co, Ni, and Cu) were investigated for application to high temperature catalytic combustion. Two series of modifications of the compounds was made by cation substitution; substitution of large cations in the mirror plane with lanthanides ions, and of transition metals for Al site in the spinel block. In a series of AMnAlllO19-μ, surface area and catalytic activity increased with an increase in ionic radius of lanthanides. La3+ is superior as the large cation in the mirror plane of the hexaaluminate to other tri-valent cations with small ionic radii. The catalytic activi- ties of LaBAl11O19-μ, were enhanced when Mn and Cu were employed as the B-site substituents. Although Mn and Cu were also effective substituents for enhancing catalytic activity in Ba-based hexaaluminate compounds, their activity was low as compared with the La-based catalysts. These results indicate that the redox cycle of transition metal in hexaaluminate lattice and cata- lytic activity appears to be affected sensitively with the electronic or structural effect of large cation in the mirror plane.