Active Palladium Structures on Ceria Obtained by Tuning\nPd–Pd Distance for Efficient Methane Combustion

Efficiently\nremoving/converting methane via methane combustion\nimposes challenges on catalyst design: <i>how to design local\nstructures of a catalytic site so that it has both high intrinsic\nactivity and atomic efficiency</i>? By manipulating the atomic\ndistance of isolated Pd atoms, herein we show that the intrinsic activity\nof Pd catalysts can be significantly improved for methane combustion\nvia a stable Pd<sub>2</sub> structure on a ceria nanorod support.\nGuided by theory and confirmed by experiment, we find that the turnover\nfrequency (TOF) of the Pd<sub>2</sub> structure with the Pd–Pd\ndistance of 2.99 Å is higher than that of the Pd<sub>2</sub> structure\nwith the Pd–Pd distance of 2.75 Å; at least 26 times that\nof ceria supported Pd single atoms and 4 times that of ceria supported\nPdO nanoparticles. The high intrinsic activity of the 2.99 Å\nPd–Pd structure is attributed to the conductive local redox\nenvironment from the two O atoms bridging the two Pd<sup>2+</sup> ions,\nwhich facilitates both methane adsorption and activation as well as\nthe production of water and carbon dioxide during the methane oxidation\nprocess. This work highlights the sensitivity of catalytic behavior\non the local structure of active sites and the fine-tuning of the\nmetal–metal distance enabled by a support local environment\nfor guiding the design of efficient catalysts for reactions that highly\nrely on Pt-group metals.