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.