Modulating the electronic interaction between Au and nitrogen-rich porous organic polymers for enhanced CO2 hydrogenation to formic acid

The regulation of the electronic state of catalytic sites is essential to improve the intrinsic activity of catalysts. Herein, we modulated the metal state of Au species by varying their particle size on nitrogen-rich triazine-based porous organic polymer supports. Due to the different interface percentages between Au and nitrogen species in selected supports, the electronic state of the metal can be modulated. The catalyst with the smallest Au particle size presented the most negative metallic state and the highest surface energy, thus exposing more sites for H2 activation and providing sufficient reactive H species to CO2 hydrogenation absorbed on the adjacent N. The designed Au/Trz-TETA (1.23 nm) exhibited high catalytic activity for the CO2 hydrogenation to formic acid and a turnover number (TON) up to 1687 over 10 h, which is higher than that of Au/Trz-DETA (2.24 nm) and Au/Trz-TEPA (1.96 nm) with a bigger metal particle size. This work shows a size-dependent CO2 hydrogenation for various sizes of Au metal catalysts and provides a new way for regulating the metal electronic state.