Reaction Mechanism and Kinetics for the Selective Hydrogenation of Carbon Dioxide to Formic Acid and Methanol over the [Cu 2 ] 0,±1 Dimer.

With the rapid growth of industrialization, deforestation, and burning of fossil fuels, undeniably there has been an incredible escalation of the CO 2 concentration in the atmosphere. In order to mitigate the problem, the capture and utilization of CO 2 in different value-added chemicals have thus remained topics of concerned research for more than a decade. Accordingly, we have performed molecular -level catalytic hydrogenation of CO 2 to formic acid using bare [Cu 2 ] 0,±1 dimers as catalysts. The entire investigation has been performed using a density functional theory (DFT) method employing the Perdew-Burke-Ernzerhof (PBE) functional with the def2TZVPP basis set to explore the different possible routes and efficiency of the catalysts. Results reveal the feasibility of H 2 dissociation on all three Cu 2 , Cu 2 + , and Cu 2 - dimers. The negatively charged hydride formed during H 2 dissociation on Cu 2 and Cu 2 + dimers facilitates the formation of the HCOO* intermediate over COOH*, thereby providing product selectivity for HCOOH above CO. However, the reaction on the Cu 2 - dimer forms both HCOO* and COOH* intermediates, but HCOO*, being kinetically more favorable, results in HCOOH production. The free-energy change suggests that the complete reaction on Cu 2 and Cu 2 + dimers forms a stable product compared to the Cu 2 - dimer. Furthermore, H 3 COH production is studied using the title catalysts via the obtained HCOOH* intermediate from the reaction channel. Transition state theory (TST) has been considered to evaluate the rate constants for each step of the reaction. Overall results suggest Cu 2 to be better compared to Cu 2 + and Cu 2 - dimers for HCOOH formation and Cu 2 + over Cu 2 and Cu 2 - dimers to be more efficient for H 3 COH formation. This work opens the way for further investigation of the reaction mechanism and development of an efficient catalyst for CO 2 hydrogenation.