The catalytic effect of water in basic hydrolysis of CO$_3{}^{2_-}$ in hydrated clusters

TL;DR

This study reveals how water molecules influence the hydrolysis of carbonate ions in nanoscale clusters, showing that increased hydration significantly lowers activation energy and enhances hydrolysis, with implications for CO2 capture technologies.

Contribution

The paper demonstrates that incomplete hydration shells facilitate carbonate hydrolysis, providing new insights into nanoscale ion hydration effects on chemical reactivity.

Findings

Activation free energy decreases from 10.4 to 2.4 kcal/mol as water molecules increase from 1 to 6.

Hydrolysis pathway shifts from stepwise to direct proton transfer with more water molecules.

Incomplete hydration shells promote thermodynamically and kinetically favorable hydrolysis.

Abstract

The hydration of ions in nanoscale hydrated clusters is ubiquitous and essential in many physical and chemical processes. Here we show that the hydrolysis reaction is strongly affected by relative humidity. The hydrolysis of CO32- with n = 1-8 water molecules is investigated by ab initio method. For n = 1-5 water molecules, all the reactants follow a stepwise pathway to the transition state. For n = 6-8 water molecules, all the reactants undergo a direct proton transfer to the transition state with overall lower activation free energy. The activation free energy of the reaction is dramatically reduced from 10.4 to 2.4 kcal/mol as the number of water molecules increases from 1 to 6. Meanwhile, the degree of the hydrolysis of CO32- is significantly increased compared to the bulk water solution scenario. The incomplete hydration shells facilitate the hydrolysis of CO32- with few water molecules (especially for n = 6) to be not only thermodynamically favorable but also kinetically favorable. This discovery provides valuable insights for designing efficient sorbents including that for CO2 air capture.