Tiny Species with Big Impact: High Activity of Cu Single Atoms on CeO2-TiO2 Deciphered by Operando Spectroscopy

Cu single-atom catalysts (SACs) supported on CeO2-TiO2 were prepared by a sol-gel method and tested for CO oxidation between 120 and 350 degrees C. Operando and in situ spectroscopic methods including diffuse reflectance infrared Fourier transform (DRIFT), electron paramagnetic resonance (EPR), and near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) combined with other basic characterizations were applied to identify active sites and to derive reliable structure-reactivity relationships. Rising the Cu content from 0.06 to 0.86 wt % resulted in a significant decrease of the Cu-mass normalized CO2 formation rate from 690 to 310 mu molCO(2)center dot gCu(-1)center dot s(-1) at 250 degrees C, which was attributed to the formation of the less active CuOx species. The catalysts showed high stability during time on stream for more than 1000 min with negligible agglomeration of Cu single sites. Spectroscopic results revealed that active sites are single Cu ions on the surface of highly dispersed ceria particles, shuttling between -Cu2+-O-Ce4+- and -Cu+-square-Ce3+- by supplying active oxygen for oxidation of CO to CO2. The highest concentrations of Cu single sites and O vacancies associated with Ce3+ species correlated with the highest CO oxidation activity.

Automated summary

Cu single-atom catalysts supported on CeO2-TiO2 were prepared using a sol-gel method and showed high efficiency and stability in CO oxidation. Spectroscopic methods such as infrared, electron paramagnetic resonance, and X-ray photoelectron spectroscopy revealed the mechanism of action and structure-reactivity relationships.