Preparation of supported LaMnO₃ catalysts by selective deposition on alumina and their catalytic activity for propane oxidation

Alumina-supported LaMnO₃ (LaMnO₃/Al₂O₃) catalysts with various dispersion and locations were prepared by utilizing the alumina pore structures. LaMnO₃ perovskite oxides were selectively deposited in and/or outside the pore of γ-Al₂O₃ support by controlling the deposition methods. The LaMnO₃/Al₂O₃ catalysts were characterized and their catalytic activities for propane oxidation were investigated. X-ray diffraction, electron diffraction, and catalytic studies confirmed the formation of a perovskite structure on the alumina support. The catalytic activity for propane oxidation strongly depended on the preparation method, and the perovskite catalysts deposited in the inside pore of alumina exhibited higher activity than those deposited on the outside pore of alumina. The surface area of perovskite oxides on support was quantitatively evaluated by temperature-programmed desorption of CO₂. The trend for the surface areas of LaMnO₃ on γ-Al₂O₃ estimated by the method was consistent with the trend of the rate for complete propane oxidation normalized by catalyst weight, whereas the rate normalized by the surface area of perovskite oxide was almost independent of the dispersion, crystallite sizes, and deposition methods. The activity of LaMnO₃/Al₂O₃ with the intrapore deposition was almost independent of calcination temperatures ranging from 650 to 1000 °C, in marked contrast with the extrapore deposition catalysts, whose activities greatly decreased with increasing calcination temperatures. For the intrapore deposition catalysts, the highest activities were obtained when the loading level was 20 wt % and decreased with a further increase in the loading level. At high loading levels (40 wt %), extrapore deposition of LaMnO₃ on the intrapore deposition catalysts improved their activities for propane oxidation.