A density functional theory study of the water–gas shift reaction catalyzed by a Cr(CO)6 complex†

The mechanism of the water–gas shift reaction (WGSR) catalyzed by Cr(CO)₆ in both gaseous and aqueous phases was analyzed using density functional theory (DFT). The Gibbs free energy of activation for the entire reaction was calculated to be 36.46 kcal mol⁻¹ for the gaseous phase and 37.10 kcal mol⁻¹ for the aqueous phase. The study showed that the energy barriers along the reaction pathway were slightly higher in the aqueous phase compared to the gaseous phase. The turnover frequency (TOF) of the reaction was calculated using the energy span model (ESM), and it was found to be slightly lower in the aqueous phase (3.83 × 10⁻¹⁵ s⁻¹) compared to the gaseous phase (1.13 × 10⁻¹⁴ s⁻¹) at a temperature of 298 K. The study also investigated the energy changes along the reaction pathway at different temperatures (300–900 K), showing that the WGSR rate increases with temperature. The changes in the reaction environment and temperature can alter the TOF-determined intermediates (TDIs). This research aims to address the mechanistic gaps of the WGSR in the aqueous phase, providing thorough theoretical guidance for the development of chromium-based catalysts.