Single–atom Ir1 supported on rutile TiO2 for excellent selective catalytic oxidation of ammonia

Abstract

Gaseous ammonia (NH3) in the atmosphere is potentially harmful to both human health and the environment. The selective catalytic oxidation of NH3 (termed as NH3–SCO) into N2 and H2O is a promising method for decreasing NH3 emissions. A highly efficient catalyst is required for controlling NH3 emissions by this method in practice. In this study, we prepared Ir/TiO2 catalysts using different crystal structures of TiO2 (rutile, P25 or anatase) as supports by a simple impregnation method and evaluated their performance in the NH3–SCO. We found that the Ir/TiO2–R (rutile) catalyst performed better than the Ir/TiO2–P25 (mixed–phase) and Ir/TiO2–A (anatase) catalyst. High–angle annular dark–field images of the aberration–corrected scanning transmission electron microscopy revealed that the Ir species were mainly atomically dispersed on the TiO2 support in Ir/TiO2–R with 1 wt% Ir loading, whereas the Ir species agglomerated to form clusters or nanoparticles in Ir/TiO2–P25 and Ir/TiO2–A. The combined results of X–ray absorption fine structure, H2–temperature–programmed reduction, and in situ diffuse reflectance for infrared Fourier Transform spectroscopy studies suggested that atomically dispersed Ir species had stronger electronic metal–support interaction with rutile TiO2, which resulted in easier to adsorb and activate O2 at the interface and thus, better low–temperature activity of the Ir/TiO2–R catalyst.