Implementation of a fast method for the evaluation of the effect of external electric fields on catalysis

Abstract

The concentration of CO2 has over the past century increased exponentially. The core of the issue lies

in the high efficiency of CO2 to absorb and remit IR radiation back to Earth’s surface. Although CO2

is the main responsible, there are other gases sharing the same characteristic and they are known as

Greenhouse Gases. As a consequence of having a higher concentration of them in the atmosphere, the

IR radiation cannot escape and is kept inside leading to a higher mean global temperature.

In the same way plants use photosynthesis to reduce CO2 to obtain glucose, modern chemistry

has developed a process known as artificial photosynthesis, that uses a catalyst to transform CO2 into

other high-interest products, such as methanol. This work studies a disproportionation mechanism of

CO2 into carbon monoxide, our interest product, and carbonate catalysed by a cobalt complex. Due

to CO’s high stability with the metallic centre, a potential well is generated which hinders a second

catalytic turn. On the other hand, the appropriate application of electric fields into chemical systems can induce the catalysis of a reaction, or inhibit it, and even affect the selectivity. With the FDBβ method,

the effect of electric fields can be computationally modelled by only computing the electric properties

(dipole moment, polarisability, ...) of the involved chemical species. Mathematically, it is based on the

Taylor series expansion of the field-dependent electronic energy, where the coefficients are the electric

properties. Then, to define the reaction’s thermochemistry the expansions of products, or transition

states, and reactants are subtracted following its stoichiometry.

In this work, it has been demonstrated that the FDBβ is an excellent tool to study the effect of

electric fields on reactivity. Furthermore, we have developed a FORTRAN95 code capable of finding

the minimum electric field required to impose a preestablished barrier or energy reaction.

By means of the FDBβ the effect on catalysis of an electric field has been studied on the catalytic

reduction CO2-to-CO studied in this work. On one hand, it is found the effect of a positive electric

field on the Z axis favours the CO release. In contrast, although the effect of a negative field on the

Y axis hinders the previous process, it enhances the kinetics of the reaction stabilising the formation

of the transition state that determines the TOF