NiP Confined in Mesoporous SiO with Near-Unity CO Selectivity and Enhanced Catalytic Activity for CO Hydrogenation.

CO hydrogenation via the reverse water gas shift (RWGS) reaction is a promising strategy for CO utilization while constructing Ni-based catalysts with high catalytic activity and perfect CO selectivity remains a great challenging. Here, we demonstrate that the product selectivity for CO hydrogenation can be significantly tuned from CH to CO by phosphating of SiO-supported Ni catalysts due to the geometric effect. Interestingly, nickel phosphide catalysts with different crystalline phases (NiP and NiP) differ sharply in CO conversion, and NiP is remarkably more active. Furthermore, we developed a facile strategy to confine small NiP nanoparticles in mesoporous SiO channels (NiP@SBA-15). Enhanced activity is exhibited on NiP@SBA-15, ascribed to the highly effective confinement effect. The in situ diffuse reflectance infrared Fourier transform spectroscopy and density functional theory calculations unveil that catalytic CO hydrogenation follows a direct CO dissociation route with adsorbed CO as the key intermediate. Notably, strong multibonded CO (threefold and bridge-bonded CO) is feasibly formed on the Ni catalyst accounting for CH as the dominant product whereas only weak linearly bonded CO exists on nickel phosphide catalysts resulting in almost 100% CO selectivity. The present results indicate that NiP@SBA-15 combining the geometric effect and the confinement effect can achieve near-unity CO selectivity and enhanced activity for CO hydrogenation.