A density functional theory exploration on the Zn catalyst for acetylene hydration.

The acetylene hydration method to produce acetaldehyde has been widely used for over 130 years; however, a detailed molecular-level understanding of the reaction mechanism is still lacking. In the present work, we systematically investigated the mechanisms of such reactions on ZnCl2, Zn(OH) Cl, and Zn(OH)2 catalysts through density functional theory (DFT) methods. The Fukui function, condensed Fukui function, and Hirshfeld charges enabled us to predict the active sites of the catalysts and acquire electron transfer information. From these data, we found that catalysts bearing hydroxyl groups exhibited relatively low adsorption performances compared with catalysts without this functionality. The calculations demonstrated that the three studied catalysts had three distinct reaction paths. For the Zn(OH)Cl and Zn(OH)2 catalysts, the reaction took place through a one-shift H2O molecule transfer route, avoiding higher energy barrier pathways. Interestingly, we found that the energy required for breaking the O-H bond in water determined the activation energy of the studied catalytic reactions. The activation barrier increased in the order Zn(OH)Cl ≈ Zn(OH)2 < ZnCl2. This trend suggests that Zn(OH)Cl and Zn(OH)2 are promising catalysts for the hydration of acetylene. Graphical abstract.