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

Abstract

Apatite-type ALa 9 Si 6 O 26 (A = Li, Na, K) were prepared by solid state reaction method. The hexagonal unit cell volumes of ALa 9 Si 6 O 26 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 ALa 9 Si 6 O 26 were less than 1 m 2 /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 H 2 was decreased by substitution of alkali metal ion at La site in the apatitetype silicate. For C 3 H 6 NOO 2 reaction, Pt/NaLa 9 Si 6 O 26 catalyst exhibited a maximum NO conversion of 42%, the highest among Pt/ALa 9 Si 6 O 26 catalysts. The temperature for maximum NO conversion over Pt/NaLa 9 Si 6 O 26 catalyst was lower than that over Pt/£-Al 2 O 3 catalyst under the same reaction condition. The temperature of 50% C 3 H 6 conversion for C 3 H 6 O 2 reaction over Pt/ALa 9 Si 6 O 26 catalysts increased in the sequence of A = K < A = Na < A = Li. In addition, C 3 H 6 oxidation activity was suppressed by presence of CO 2 and NO on the catalyst. These results suggest that the basic sites on the apatite-type support affect the catalytic activities of Pt/ALa 9 Si 6 O 26 catalysts for C 3 H 6 NOO 2 and C 3 H 6 O 2 reaction.

The structure and texture genesis of apatite-type lanthanum silicates during their synthesis by co-precipitation

“…Over the recent years apatite-type lanthanum silicates also attracted a lot of interest as catalysts of redox reactions [28][29][30][31][32][33]. For instance, papers by Nakata group demonstrate that the use of apatite-type lanthanum silicates as a support instead of Ȗ-Al 2 O 3 ensures higher catalytic activity of platinum catalysts in NO x selective reduction by propylene as well as in C 3 H 6 oxidation in mixtures containing C 3 H 6 , NO and O 2 [28][29][30][31].…”

“…For instance, papers by Nakata group demonstrate that the use of apatite-type lanthanum silicates as a support instead of Ȗ-Al 2 O 3 ensures higher catalytic activity of platinum catalysts in NO x selective reduction by propylene as well as in C 3 H 6 oxidation in mixtures containing C 3 H 6 , NO and O 2 [28][29][30][31]. Lanthanum substitution by alkaline and alkaliearth elements was shown to increase activity of such catalysts.…”