Abstract
The emission of carbon dioxide in large amounts is commonly believed to
be the main cause of global climate changes. Development of
CO2 capture processes is still a big current challenge.
Some anions have been studied for the gas sequestration process due
their great affinity to CO2. In this work, electronic
structure calculations were performed at the MP2/aug-cc-pvtz level to
compute the interaction between 20 anions and CO2. A CBS
scheme, using extrapolated energies, was also employed for both gas
phase and solvent calculations. The reactions between the anions and
CO2 were therefore studied in four different conditions
(gas phase, toluene, tetrahydrofuran and water). The trends observed for
the reaction thermodynamics with the MP2 method is similar to that
observed previously with the B3LYP-D3 and M06-2X functionals. The
reactions in the gas phase are highly exothermic and do not involve any
activation energy. The solvent effect reduces the exothermicity and
induces an intrinsic activation barrier. The negative charge is
dispersed in the adduct, leading to a weaker interaction in a polar
solvent. Then, increasing the medium polarity, the energy difference
between the adduct and the reactants decreases. We also observed a limit
for solvent stabilization in the low dielectric constant range. For
example, the results obtained with tetrahydrofuran are closer to those
obtained with water than to those obtained with toluene. Considering
both the thermodynamics of the reaction and the differential solvent
effects, we were able to indicate anions derived from alkyl sulfides as
the most convenient for CO2 sequestration among the set
here considered.