Hydrogenation and hydration of carbon dioxide: a detailed characterization of the reaction mechanisms based on the reaction force and reaction electronic flux analyses.

Abstract

A computational DFT study of the reaction mechanism of hydrogenation and hydration of carbon dioxide is presented. It has been found that hydrogenation and hydration are endoenergetic reactions that are carried out in two steps, passing by a stable intermediate that is surrounded by energy barriers of 70 kcal/mol and 10 kcal/mol for hydrogenation and 50 kcal/mol and 10 kcal/mol for hydration. Using the reaction force analysis, we were able to characterize the physical nature of the activation barriers and found that activation energies are mostly due to structural rearrangements. An interesting difference in the reaction mechanisms disclosed by the reaction force and electronic flux analyses is that while in the hydrogenation reaction the mechanisms is conditioned by the H2 cleavage with a high energy barrier, in the hydration reaction the formation of a transient four member ring structure favoring an attractive local hydrogen bond interaction pushes the reaction toward the product with a considerably lower energy barrier.