Ir-Catalysed Nitrous Oxide (N2O) Decomposition:Effect of Ir Particle Size and Metal–Support Interactions

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

Unique Role of Anchoring Penta-Coordinated Al3+ Sites in the Sintering of gamma-Al2O3-Supported Pt Catalysts

gamma-Al2O3-supported Pt group catalysts are widely used in many industrially important catalytic processes. However, gamma-Al2O3-supported Pt catalysts are prone to deactivation via metal sintering at high temperatures, in oxidative reaction environments, or both. Using a combination of experimental HRTEM and EXAFS measurements and theoretical DFT calculations, we find that pentacoordinated Al3+ sites (Al-p) on the gamma-Al2O3(100) surface can inhibit Pt sintering both thermodynamically and kinetically because of their strong interactions with atomic Pt or Pt oxide species. The present work suggests a promising approach for stabilizing the size and morphology of supported catalytically active phasesclose191