Stabilization mechanism and crystallographic sites of Ru in Fe-promoted barium hexaaluminate under high-temperature condition for N2O decomposition

The stabilization of volatile ruthenium from catalysts at high temperatures is an important issue in both academia and industry. In this paper, Ru-substituted barium hexaalumimates (BaRu0.2FeAl10.8O19) with beta(1)-Al2O3 structure were prepared using the carbonates route and investigated for high-concentration of N2O decomposition. It was for the first time found that the evaporation of ruthenium species under high-temperature condition (1100-1200 degrees C) could be effectively suppressed by the addition of Fe in the hexaaluminate precursor. Fe promoted the formation of intermediate stable BaRuO3 phase, which greatly alleviated the evaporation of Ru species during calcination, and thus allowed more Ru species enter into the final sintering-resistant hexaaluminate lattice after high-temperature treatment. Ru ions in the hexaaluminate structure only occupied the distorted tetrahedral interstitial Al(5) sites in the loosely packed mirror plane, which originated from Ru species in oxidic entities dispersed on the Ba-modified gamma-Al2O3 and the intermediate BaRuO3 in the precursors. Ru ions in the Al(5) sites were key factors responsible for the high activity of N2O decomposition. (C) 2012 Elsevier B.V. All rights reserved.