Mechanistic insights into the Cu(I) oxide-catalyzed conversion of CO2 to fuels and chemicals: A DFT approach

- Detailed reaction mechanism proposed for CO2 conversion on the most stable surface of Cu2O.
- Very high activation barrier is required to dissociate the physisorbed CO2 molecule.
- Water adsorbs molecularly, while dissociative adsorption for hydrogen is preferred.
- Formate route is more favourable than the formation of carboxyl.
- Formic acid forms rapidly with very low activation barrier but binds strongly to the Cu2O (1 1 1) surface.

Periodic, self-consistent, density functional theory calculations with corrections via a Hubbard U parameter, and inclusion of dispersive forces (DFT-D2), have been employed to study CO2 activation and conversion on the Cu2O (1 1 1) surface. CO2 hydrogenation on the Cu2O (1 1 1) surface was investigated systematically, and the respective microscopic reaction mechanisms were elucidated. We show that, whereas CO2 dissociation is not energetically allowed on the Cu2O (1 1 1) surface, CO2 hydrogenation to a formate intermediate is more favourable than the formation of a carboxyl intermediate. Further hydrogenation from formate to formic acid is energetically allowed, where formate combines with strongly adsorbed surface hydrogen to form bidentate formic acid moieties. Formation of both the formate and the formic acid from adsorbed CO2 and surface hydrogen are exothermic reactions.

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