Fine Ru-Ru2P Heterostructure Enables Highly Active and Selective CO2 Hydrogenation to CO

The reverse water–gas shift (RWGS) reaction is a promising pathway for CO₂ utilization, while discovering optimal active species remains a significant challenge. Here we fabricated an ultrasmall Ru-Ru₂P heterostructure, in which the Ru nanoparticle is in close contact with the Ru₂P nanoparticle and modified by Ru₂P species. Through exploring the catalytic performance of ruthenium phosphides, we found that the product selectivity for CO₂ hydrogenation can be completely tuned from CH₄ to CO through phosphidation of a SiO₂-supported Ru catalyst because the distinctive surface structure of ruthenium phosphides interdicts the deep hydrogenation of the strongly bonded CO intermediate to CH₄. Enhanced catalytic activity is achieved on the Ru-Ru₂P heterostructure compared to pure Ru₂P and RuP owing to its stronger capability to adsorb and activate CO₂ and H₂. Following a 100 h high-temperature reaction, the Ru-Ru₂P heterostructure remained stable with a nearly constant CO production rate and 100% CO selectivity. Furthermore, an in situ diffuse reflectance infrared Fourier transform spectroscopy study unveils that the RWGS reaction on the ruthenium phosphides proceeds through the redox mechanism. Our work demonstrates that the Ru-Ru₂P heterostructure acts as the optimized active species with high activity and CO selectivity and highlights that the inert catalytic activity for CO intermediate hydrogenation plays a more crucial role in determining CO selectivity in catalytic CO₂ hydrogenation than the generally considered weak CO adsorption.