Ionic Liquid-Stabilized Single-Atom Rh Catalyst against Leaching

Abstract

Single-atom catalysts (SACs) are promising in some reactions typically promoted by homogeneous catalysts. However, the leaching of active species from the support in liquid-phase reactions hinders their potential applications. Herein, taking the hydroformylation reaction as an example, we report ionic liquid (IL)-induced stabilization of single Rh atoms against leaching. Among the ILs examined, 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([OHEmim][Tf2N])-stabilized single-atom Rh1/TiO2 showed a turnover frequency (TOF) of around 800 h−1 in styrene hydroformylation and was able to be recycled for five runs without significant deactivation. At the same time, the activity for unprotected Rh1/TiO2 decreased over two orders of magnitude under similar conditions. Density-functional theory (DFT) simulations revealed that the IL acts as a linker to connect both Rh and TiO2, thereby enhancing the binding energy of Rh species on TiO2 from 0.69 to 1.19 eV. This work offers a new approach to enhance the stability of atomically dispersed metal catalysts against leaching.