MgAl2O4 supported Ir single atoms and nanoparticles were synthesized with traditional impregnation methods. Tricarbonyl structure was observed on Ir single atoms for the first time using DRIFTS of adsorbed CO, compared with linear and bridge CO species on Ir nanoparticles. Unique O2 and H2 chemisorption stoichiometries were also observed on Ir single atoms with the ratio of 2 O and 4 H, respectively. The stability of these multi-atomic configurations were confirmed by ab-initio density functional theory (DFT) calculations. On the other hand, Ir nanoparticles showed adsorption of 1 H, 1 CO and 1 O per surface Ir atom. These significant different gas metal ratios during O2/CO/H2 chemisorption provided a powerful tool to differentiate Ir single atoms from nanoparticles. This method could also be potentially applied to many other noble metals. CO oxidation kinetics on Ir single atoms and nanoparticles showed totally different mechanisms. Positive CO order (∼ 0.6 - 0.8) and low O2 order (∼ 0.1 - 0.2) were measured on Ir single atoms, and negative CO order (~ −1) and high O2 order (∼ 1) were measured on Ir nanoparticles. The Ir single atoms are shown to be active and stable at low temperature and the origin of the activity will be explained using DFT calculations and in-situ DRIFTS measurements.

Origin of low temperature CO oxidation activity on Ir single atoms – Experimental and computational study

253rd National Meeting (2017)

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