DFT study reveals an unusual non-bifunctional mechanism for CO2 hydrogenation using a kind of PNP-Fe catalyst

Abstract

Mechanistic study on CO2 hydrogenation catalyzed by a kind of PNP-Fe catalyst is presented here by density functional theory calculations. The reported HPNP-Fe bifunctional catalyst was found to hydrogenate CO2 through a non-bifunctional mechanism, which can be ascribed to the ring-strain of the four-member-ring transition state for the hydrogen cleavage step over the FeN bond. However, the NH group was found to assist the external base to cleavage hydrogen molecule through hydrogen-bonding. But the HPNP-Fe is not advantageous for the catalytic reactivity compared with the MePNP-Fe, which is due to the too stable formate complex stabilized by the hydrogen-bonding with NH group. This computational study reminds us to pay attention to both the merit and the demerit of bifuinctional catalyst.