Superior performance of Ir-substituted hexaaluminate catalysts for N2O decomposition

Novel Ir-substituted hexaaluminate catalysts were developed for the first time and used for catalytic decomposition of high concentration of N2O. The catalysts were prepared by one-pot precipitation and characterized by X-ray diffraction (XRD), N2-adsorption, scanning electronic microscopy (SEM) and temperature-programmed reduction (H2-TPR). The XRD results showed that only a limited amount of iridium was incorporated into the hexaaluminate lattice by substituting Al3+ to form BaIrxFe1−xAl11O19 after being calcined at 1200 °C, while the other part of iridium existed as IrO2 phase. The activity tests for high concentration (30%, v/v) of N2O decomposition demonstrated that the BaIrxFe1−xAl11O19 hexaaluminates exhibited much higher activities and stabilities than the Ir/Al2O3-1200, and the pre-reduction with H2 was essential for activating the catalysts. By comparing BaIrxFe1−xAl11O19 with BaIrxAl12−xO19 (x = 0–0.8), it was found that iridium was the active component in the N2O decomposition and the framework iridium was more active than the large IrO2 particles. On the other hand, Fe facilitated the formation of hexaaluminate as well as the incorporation of iridium into the framework.