Preparation and NO reduction property of apatite-type ALa₉Si₆O₂₆ (A = Li, Na, K) supported Pt catalyst

抄録

Apatite-type ALa₉Si₆O₂₆ (A = Li, Na, K) were prepared by solid state reaction method. The hexagonal unit cell volumes of ALa₉Si₆O₂₆ increased with increasing ionic radii of alkali metal ions, indicating that the alkali metal ions were incorporated into the apatite-type lattice. The specific surface areas of ALa₉Si₆O₂₆ were less than 1 m²/g. X-ray photoelectron spectroscopy measurement showed that Pt species on as-prepared catalysts were highly oxidized. Reduction temperature of Pt oxides on the catalyst for temperature-programmed reduction by H₂ was decreased by substitution of alkali metal ion at La site in the apatite-type silicate. For C₃H₆–NO–O₂ reaction, Pt/NaLa₉Si₆O₂₆ catalyst exhibited a maximum NO conversion of 42%, the highest among Pt/ALa₉Si₆O₂₆ catalysts. The temperature for maximum NO conversion over Pt/NaLa₉Si₆O₂₆ catalyst was lower than that over Pt/γ-Al₂O₃ catalyst under the same reaction condition. The temperature of 50% C₃H₆ conversion for C₃H₆–O₂ reaction over Pt/ALa₉Si₆O₂₆ catalysts increased in the sequence of A = K < A = Na < A = Li. In addition, C₃H₆ oxidation activity was suppressed by presence of CO₂ and NO on the catalyst. These results suggest that the basic sites on the apatite-type support affect the catalytic activities of Pt/ALa₉Si₆O₂₆ catalysts for C₃H₆–NO–O₂ and C₃H₆–O₂ reaction.