Hollow Mesoporous Organosilica Spheres Encapsulating PdAg Nanoparticles and Poly(Ethyleneimine) as Reusable Catalysts for CO2 Hydrogenation to Formate

CO2 hydrogenation to formic acid, a renewable hydrogen storage compound, has been regarded as a key reaction to realize hydrogen energy cycles. However, the development of robust heterogeneous catalysts with high activity and stability has been a challenge. We herein report a synthesis of hollow nanostructured composite consisting of PdAg nanoparticles (NPs) and aminopolymers, poly(ethyleneimine) (PEI), confined in hollow mesoporous organosilica spheres (HMOSs), which act as an efficient and stable heterogeneous catalyst for hydrogenation of CO2 to formate. The catalyst exhibits high formate yield with a turnover number (TON) of over 2700 and 13 700 for 22 and 110 h, respectively, under mild reaction conditions (total 2.0 MPa, 100 degrees C), which outperforms the conventional supported Pd catalysts because of the cooperative action of PEI and PdAg NPs confined in a nanospace to directly capture, activate, and hydrogenate the CO2 molecule. The catalyst is reusable over multiple cycles with high activity because of the protective effect and alkali-tolerant property of HMOSs. This study offers a strategy for the design and development of an efficient and stable heterogeneous catalyst for CO2 conversion.