Catalytic Combustion of Methane Over Metal Oxide Catalysts

<jats:title>Abstract</jats:title><jats:p>Cation-substituted hexaaluminate compounds, ABAl<jats:sub>11</jats:sub>O<jats:sub>19-μ</jats:sub> (A = La, Pr, Sm, and Nd; <jats:italic>B</jats:italic> = 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 AMnAl<jats:sub>ll</jats:sub>O<jats:sub>19-μ</jats:sub>, surface area and catalytic activity increased with an increase in ionic radius of lanthanides. La<jats:sup>3+</jats:sup> 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 LaBAl<jats:sub>11</jats:sub>O<jats:sub>19-μ</jats:sub>, 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.</jats:p>