Abstract
Catalytic transformation of CO2 to formate is generally realized through bicarbonate hydrogenation in an alkaline environment, while it suffers from a thermodynamic sink due to the considerable thermodynamic stability of the bicarbonate intermediate. Here, we devise a route for the direct catalytic conversion of CO2 over a Schiff-base-modified gold nanocatalyst that is comparable to the fastest known nanocatalysts, with a turnover number (TON) of up to 14,470 over 12 h at 90 °C. Theoretical calculations and spectral analysis results demonstrate that the activation of CO2 can be achieved through a weakly bonded carbamate zwitterion intermediate derived from a simple Lewis base adduct of CO2. However, this can only occur with a hydrogen lacking Lewis base center in a polar solvent. This finding offers a promising avenue for the direct activation of CO2 and is likely to have considerable implications in the fields of CO2 conversion and gold catalytic chemistry.
Highlights
Catalytic transformation of CO2 to formate is generally realized through bicarbonate hydrogenation in an alkaline environment, while it suffers from a thermodynamic sink due to the considerable thermodynamic stability of the bicarbonate intermediate
The catalytic activity in homogeneous catalysis is very sensitive to the ligand used and the ligands are expensive and leachable, which limits their wide-spread application
The production of formate over supported Pd nanoparticles will be boosted when bicarbonate is used instead of gaseous CO2 as the C1 source[16]. Such evolution of CO2 to formate through bicarbonate intermediates experiences a thermodynamic sink in the reaction, because the bicarbonate species are considerably more stable than the parent CO2 and final formate
Summary
Catalytic transformation of CO2 to formate is generally realized through bicarbonate hydrogenation in an alkaline environment, while it suffers from a thermodynamic sink due to the considerable thermodynamic stability of the bicarbonate intermediate. Without ligand promotion in a heterogeneous catalytic system, CO2 is always activated in a bent conformation by the interaction between the dissolved base with CO213 In such a process, CO2 chemically reacts with an aqueous base, such as KOH or NaOH, to give bicarbonates (HCO3−), which serve as the real precursors for further hydrogenation to formate[5,14,15]. We propose an unusual CO2 activation pathway that, through a weakly bonded carbamate zwitterion complex on the Schiff-base-mediated gold catalyst, can effectively avoid the thermodynamic sink of the conventional bicarbonate reactant, and lead to the direct hydrogenation of CO2 to formate
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