Maximized Ir atom utilization via downsizing active sites to single-atom scale for highly stable dry reforming of methane

Abstract

Noble metals such as iridium with high Tammann temperature are inclined to sintering resistance and may be promising in the high-temperature dry reforming of methane (DRM) process, yet the low atom utilization remains intractable. Herein, we synthesized Ir/TiO2 catalysts via the conventional incipient wetness impregnation method and further downsized the Ir species from a nanoparticulate to a single-atom scale by gradually decreasing Ir loadings from 1.0 wt.% to 0.01 wt.%. With the advantage of single atoms for maximized atom utilization, Ir single atoms were employed to enhance atom utilization in the DRM process. Various characterizations, such as aberration-corrected high-angle annular dark-field scanning transmission electron microscopy, CO adsorbed in situ diffuse reflectance infrared Fourier transform spectra and X-ray absorption spectra demonstrated the existence of Ir single atoms in 0.01% and 0.05% Ir/TiO2. During the DRM process, Ir single-atom catalysts exhibited a better specific reaction rate of as high as 697.71 molCH4·gIr-1·h-1 at 750 °C compared with that over Ir nanoparticles of mere 447.12 molCH4·gIr-1·h-1, which unambiguously showed the remarkable Ir atom utilization over Ir single atoms. Besides, the Ir single-atom catalysts also exhibited excellent stability during the DRM process for 50 h and revealed outstanding anti-coking and good sintering-resistance properties examined by the thermal gravimetric analysis-mass spectrometer and Raman spectroscopy. The strategy of employing Ir single atoms for the maximum atom utilization in the high-temperature reaction process can pave the way for better exploitation of noble metals in other industrial reaction processes.