Ni<sub>12</sub>P<sub>5</sub> Confined in Mesoporous SiO<sub>2</sub> with Near-Unity CO Selectivity and Enhanced Catalytic Activity for CO<sub>2</sub> Hydrogenation
Shidong Bao, Tao Liu, Heyun Fu, Zhaoyi Xu, Xiaolei Qu, Shourong Zheng, Dongqiang Zhu
Abstract
CO 2 hydrogenation via the reverse water gas shift (RWGS) reaction is a promising strategy for CO 2 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 2 hydrogenation can be significantly tuned from CH 4 to CO by phosphating of SiO 2 -supported Ni catalysts due to the geometric effect. Interestingly, nickel phosphide catalysts with different crystalline phases (Ni 12 P 5 and Ni 2 P) differ sharply in CO 2 conversion, and Ni 12 P 5 is remarkably more active. Furthermore, we developed a facile strategy to confine small Ni 12 P 5 nanoparticles in mesoporous SiO 2 channels (Ni 12 P 5 @SBA-15). Enhanced activity is exhibited on Ni 12 P 5 @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 2 hydrogenation follows a direct CO 2 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 4 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 Ni 12 P 5 @SBA-15 combining the geometric effect and the confinement effect can achieve near-unity CO selectivity and enhanced activity for CO 2 hydrogenation.