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

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.