Fine Ru-Ru<sub>2</sub>P Heterostructure Enables Highly\nActive and Selective CO<sub>2</sub> Hydrogenation to CO

The reverse water–gas shift (RWGS) reaction is\na promising\npathway for CO<sub>2</sub> utilization, while discovering optimal\nactive species remains a significant challenge. Here we fabricated\nan ultrasmall Ru-Ru<sub>2</sub>P heterostructure, in which the Ru\nnanoparticle is in close contact with the Ru<sub>2</sub>P nanoparticle\nand modified by Ru<sub>2</sub>P species. Through exploring the catalytic\nperformance of ruthenium phosphides, we found that the product selectivity\nfor CO<sub>2</sub> hydrogenation can be completely tuned from CH<sub>4</sub> to CO through phosphidation of a SiO<sub>2</sub>-supported\nRu catalyst because the distinctive surface structure of ruthenium\nphosphides interdicts the deep hydrogenation of the strongly bonded\nCO intermediate to CH<sub>4</sub>. Enhanced catalytic activity is\nachieved on the Ru-Ru<sub>2</sub>P heterostructure compared to pure\nRu<sub>2</sub>P and RuP owing to its stronger capability to adsorb\nand activate CO<sub>2</sub> and H<sub>2</sub>. Following a 100 h high-temperature\nreaction, the Ru-Ru<sub>2</sub>P heterostructure remained stable with\na nearly constant CO production rate and 100% CO selectivity. Furthermore,\nan in situ diffuse reflectance infrared Fourier transform spectroscopy\nstudy unveils that the RWGS reaction on the ruthenium phosphides proceeds\nthrough the redox mechanism. Our work demonstrates that the Ru-Ru<sub>2</sub>P heterostructure acts as the optimized active species with\nhigh activity and CO selectivity and highlights that the inert catalytic\nactivity for CO intermediate hydrogenation plays a more crucial role\nin determining CO selectivity in catalytic CO<sub>2</sub> hydrogenation\nthan the generally considered weak CO adsorption.