Formic acid stability in different solvents by DFT calculations.

ABSTRACT

CONTEXT New technologies have been developed toward the use of green energies. The production of formic acid (FA) from carbon dioxide (CO[Formula see text]) hydrogenation with H[Formula see text] is a sustainable process for H[Formula see text] storage. However, the FA adduct stabilization is thermodynamically dependent on the type of solvent and thermodynamic conditions. The results suggest a wide range of dielectric permittivity values between the dimethyl sulfoxide (DMSO) and water solvents to stabilize the FA in the absence of base. The thermodynamics analysis and the infrared and charge density difference results show that the formation of the FA complex with H[Formula see text]O is temperature dependent and has a major influence on aqueous solvents compared to the FA adduct with amine, in good agreement with the experiment. In these conditions, the stability thermodynamic of the FA molecule may be favorable at non-organic solvents and dielectric permittivity values closer to water. Therefore, a mixture of aqueous solvents with possible ionic composition could be used to increase the thermodynamic stability of H[Formula see text] storage in CO[Formula see text] conversion processes. METHODS: Using the Quantum ESPRESSO package, density functional theory (DFT) calculations were performed with periodic boundary conditions, and the electronic wave functions were expanded in plane waves. For the exchange-correlation functional, we use the vdW-DF functional with the inclusion of van der Waals (vdW) forces. Electron-ion interactions are treated by the projector augmented wave (PAW) method with pseudopotentials available in the PSlibrary repository. The wave functions and the electronic densities were expanded employing accurate cut-off energies of 6.80[Formula see text]10[Formula see text] and 5.44[Formula see text]10[Formula see text] eV, respectively. The electronic density was computed from the wave functions calculated at the [Formula see text]-point in the first Brillouin-zone. Each structural optimization was minimized according to the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm, with force and energy convergence criteria of 25 meV[Formula see text]Å[Formula see text] and 1.36 meV, respectively. The electrostatic solvation effects were performed by the [Formula see text] package with the Self-Consistent Continuum Solvation (SCCS) approach.