Tuning the CO 2 Hydrogenation Selectivity of Rhodium Single-Atom Catalysts on Zirconium Dioxide with Alkali Ions.

Tuning the coordination environments of metal single atoms (M 1 ) in single-atom catalysts has shown large impacts on catalytic activity and stability but often barely on selectivity in thermocatalysis. Here, we report that simultaneously regulating both Rh 1 atoms and ZrO 2 support with alkali ions (e.g., Na) enables efficient switching of the reaction products from nearly 100 % CH 4 to above 99 % CO in CO 2 hydrogenation in a wide temperature range (240-440 °C) along with a record high activity of 9.4 mol CO  g Rh -1  h -1 at 300 °C and long-term stability. In situ spectroscopic characterization and theoretical calculations unveil that alkali ions on ZrO 2 change the surface intermediate from formate to carboxy species during CO 2 activation, thus leading to exclusive CO formation. Meanwhile, alkali ions also reinforce the electronic Rh 1 -support interactions, endowing the Rh 1 atoms more electron deficient, which improves the stability against sintering and inhibits deep hydrogenation of CO to CH 4 .