Catalytic hydrogenation of CO2 has attracted much attention in recent years. Among the various hydrogenation products of CO2, formic acid presenting as formate is one of the most attractive due to its direct employment as a feedstock chemical or hydrogen source for fuel cells. In addition, the conversion of CO2 to formic acid is believed to be the first and indispensable step in the reduction of CO2 to other chemicals or fuels and a fundamental understanding of this process is essential for C1 chemistry.The activation of CO2 is often challenging, owing to the highly thermodynamic stability of this molecule. In a heterogeneous catalytic system, carbon dioxide chemically reacts with the aqueous base to give bicarbonates, which serves as the real precursor for further hydrogenation to formate. However, such evolution of CO2 to formate through a bicarbonate intermediate actually experiences a thermodynamic sink of the reaction, because the bicarbonate species is considerably more stable than CO2 and final formate. Here, we have delineated a non-bicarbonate route for the direct catalytic hydrogenation of CO2 to formate using a Schiff-base-modified gold nanocatalyst. In this process, the CO2 molecule is activated by formation of a weak carbamate zwitterionic Lewis acid–base intermediate over the Schiff base on the support. The gold nanoparticle serves as a hydrogenation center to generate formate by reaction of this intermediate with the dissociated H atoms. Moreover, the catalytic process benefits from the NEt3 additive in the polar solvent, which allows the formation of a reservoir of CO2 by capturing gaseous CO2 through the same type of weakly carbamate zwitterion intermediate(Figure 1). As a result, the Schiff-base-modified gold nanocatalyst shows excellent activity toward CO2 hydrogenation to formate. This finding opens up a new avenue for the direct activation of CO2, and is likely to have considerable implications in the field of CO2 conversion chemistry.

Design of nano-gold catalysts for carbon dioxide hydrogenation to formic acid

256th National Meeting (2018)

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