Ni₁₂P₅ Confined in Mesoporous SiO₂ with Near-Unity CO Selectivity and Enhanced Catalytic Activity for CO₂ Hydrogenation

Abstract

CO₂ hydrogenation via the reverse water gas shift (RWGS) reaction is a promising strategy for CO₂ 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 CO₂ hydrogenation can be significantly tuned from CH₄ to CO by phosphating of SiO₂-supported Ni catalysts due to the geometric effect. Interestingly, nickel phosphide catalysts with different crystalline phases (Ni₁₂P₅ and Ni₂P) differ sharply in CO₂ conversion, and Ni₁₂P₅ is remarkably more active. Furthermore, we developed a facile strategy to confine small Ni₁₂P₅ nanoparticles in mesoporous SiO₂ channels (Ni₁₂P₅@SBA-15). Enhanced activity is exhibited on Ni₁₂P₅@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 CO₂ hydrogenation follows a direct CO₂ 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 CH₄ 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 Ni₁₂P₅@SBA-15 combining the geometric effect and the confinement effect can achieve near-unity CO selectivity and enhanced activity for CO₂ hydrogenation.