Breaking the Trade-Off between CO Tolerance and Intrinsic Activity in Hydrogenation on Metal Oxide-Supported Noble Metal Single Atoms through Coordination Environment Engineering

Downsizing the metal center to a single atom could enhance the CO tolerance of metal oxide-supported noble metals in catalytic hydrogenation. However, the dissociation of H2 on such single-atom catalysts is weakened; meanwhile, it tends to produce heterolytic active H species, i.e., M–Hδ+ and O–Hδ−, and breaking O–Hδ−, a key or even rate-determining step, requires a high energy barrier. The situation mentioned above can inevitably compromise the intrinsic activity. Herein, coordination environment engineering is proven to be able to break such a “seesaw effect” between CO tolerance and intrinsic activity in catalytic hydrogenation. Specifically, we construct N-doped metal oxide-supported noble metal single atoms (e.g., Pt1/N-MoO2), which exhibit high CO tolerance compared to Pt nanoparticles supported on MoO2 (Pt NPs/MoO2) and commercial Pt/C. More importantly, the turnover frequency (TOF) of Pt1/N-MoO2 for nitrobenzene hydrogenation is 2.8 times that of Pt1/MoO2, despite both possessing high CO tolerance. Experimental and theoretical studies show that N-doped MoO2 support tune the electron-deficiency feature of Pt single atoms, leading to weaker CO adsorption than nanoparticles. Meanwhile, the dissociation of H2 and breaking of O–Hδ− occur more readily on Pt1/N-MoO2 than Pt1/MoO2, affording Pt1/N-MoO2 better intrinsic activity. Lastly, this coordination environment engineering can be extended to other metal oxide-supported noble metals, affording high CO tolerance and improved intrinsic activity.