Abstract
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 (111) surface. CO2 hydrogenation on the Cu2O (111) 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 (111) 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.
Highlights
The consistent rise in carbon dioxide (CO2), mainly due to the consumption of carbon-rich fossil fuels [1,2] has already caused the average carbon dioxide concentration of the Earth’s atmosphere to surge past 400 PPM [3,4] and it is expected to reach levels between 700 and 1000 ppm by the end of this century [5]
We found that formate is more stable than the carboxyl intermediate by about $96 kJ/mol and we investigated the formate formation route on the Cu2O (111) surface by determining transition states and activation barriers for both FM1 and FM2
We investigated CO2 hydrogenation and determined the reaction kinetics by exploring the formation of two possible intermediate, viz, carboxyl and formate, towards formic acid formation
Summary
The consistent rise in carbon dioxide (CO2), mainly due to the consumption of carbon-rich fossil fuels [1,2] has already caused the average carbon dioxide concentration of the Earth’s atmosphere to surge past 400 PPM [3,4] and it is expected to reach levels between 700 and 1000 ppm by the end of this century [5]. Among the large number of products that could be derived from CO2, an important feedstock chemical and fuel is formic acid [7,16,17,18]. Efforts have been made to directly synthesize formic acid from carbon dioxide via catalytic hydrogenation, due to its sustainability over other existing routes [18]. Another reason to study the hydrogenation of CO2 to formic acid (HCO2H) is the opportunity of direct access to chemicals based on waste products from the use of fossil fuels for energy [12]
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