Ni₁₂P₅ Confined in Mesoporous\nSiO₂ with Near-Unity CO Selectivity and Enhanced Catalytic\nActivity for CO₂ Hydrogenation

Abstract

CO₂ hydrogenation via the reverse water gas\nshift (RWGS)\nreaction is a promising strategy for CO₂ utilization while\nconstructing Ni-based catalysts with high catalytic activity and perfect\nCO selectivity remains a great challenging. Here, we demonstrate that\nthe product selectivity for CO₂ hydrogenation can be significantly\ntuned from CH₄ to CO by phosphating of SiO₂-supported\nNi catalysts due to the geometric effect. Interestingly, nickel phosphide\ncatalysts with different crystalline phases (Ni₁₂P₅ and Ni₂P) differ sharply in CO₂ conversion,\nand Ni₁₂P₅ is remarkably more active. Furthermore,\nwe developed a facile strategy to confine small Ni₁₂P₅ nanoparticles in mesoporous SiO₂ channels (Ni₁₂P₅@SBA-15). Enhanced activity is exhibited on\nNi₁₂P₅@SBA-15, ascribed to the highly effective\nconfinement effect. The in situ diffuse reflectance infrared Fourier\ntransform spectroscopy and density functional theory calculations\nunveil that catalytic CO₂ hydrogenation follows a direct\nCO₂ dissociation route with adsorbed CO as the key intermediate.\nNotably, strong multibonded CO (threefold and bridge-bonded CO) is\nfeasibly formed on the Ni catalyst accounting for CH₄ as\nthe dominant product whereas only weak linearly bonded CO exists on\nnickel phosphide catalysts resulting in almost 100% CO selectivity.\nThe present results indicate that Ni₁₂P₅@SBA-15\ncombining the geometric effect and the confinement effect can achieve\nnear-unity CO selectivity and enhanced activity for CO₂ hydrogenation.