Abstract
The effect of the morphology of Ir particles supported on γ-Al2O3, 8 mol%Y2O3-stabilized ZrO2 (YSZ), 10 mol%Gd2O3-doped CeO2 (GDC) and 80 wt%Al2O3–10 wt%CeO2–10 wt%ZrO2 (ACZ) on their stability on oxidative conditions, the associated metal–support interactions and activity for catalytic decomposition of N2O has been studied. Supports with intermediate or high oxygen ion lability (GDC and ACZ) effectively stabilized Ir nanoparticles against sintering, in striking contrast to supports offering negligible or low oxygen ion lability (γ-Al2O3 and YSZ). Turnover frequency studies using size-controlled Ir particles showed strong structure sensitivity, de-N2O catalysis being favoured on large catalyst particles. Although metallic Ir showed some de-N2O activity, IrO2 was more active, possibly present as a superficial overlayer on the iridium particles under reaction conditions. Support-induced turnover rate modifications, resulted from an effective double layer [Oδ−–δ+](Ir) on the surface of iridium nanoparticles, via O2− backspillover from the support, were significant in the case of GDC and ACZ.
Highlights
N2O is a powerful greenhouse gas and the dominant ozonedepleting gas of the twenty-first century [1, 2]
The effect of the morphology of Ir particles supported on γ-Al2O3, 8mol%Y2O3-stabilized ZrO2 (YSZ), 10mol%Gd2O3-doped CeO2 (GDC) and 80wt%Al2O3-10wt%CeO2-10wt%ZrO2 (ACZ) on their stability on oxidative conditions, the associated metal-support interactions and activity for catalytic decomposition of N2O has been studied
This is consistent with the aforementioned sintering behaviour of the catalysts and the known particle size dependence of Ir catalysts in N2O decomposition: large particles are more active than small ones [14] as we find here (Table 4)
Summary
N2O is a powerful greenhouse gas (global warming potential ~300) and the dominant ozonedepleting gas of the twenty-first century [1, 2]. Stationary or mobile combustion sources and certain chemical processes, are the main sources of anthropogenic N2O emissions, whose abatement is of global importance. In this context, the catalytic reduction of N2O to N2 is a most promising approach [3]. Noble metals (NMs) exhibit good activity at intermediate temperatures so despite their high cost they are promising candidates for practical implementation [3,4]. A drawback of both Ir and Ru nanoparticle catalysts is their well known inferior thermal stability compared to Rh and Pt [10]. We report the first observation of a counter-clockwise hysteresis phenomenon in light-off curves of Ir-catalysed N2O decomposition and discuss their origin
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