A first-principles microkinetic study on the hydrogenation of carbon dioxide over Cu(211) in the presence of water

The hydrogenation of carbon dioxide (CO₂) is one of important processes to effectively convert and utilize CO₂, which is also regarded as the key step at the industrial methanol synthesis. Water is likely to play an important role in this process, but it still remains elusive. To systematically understand its influence, here we computationally compare the reaction mechanisms of CO₂ hydrogenation over the stepped Cu(211) surface between in the absence and presence of water based on microkinetic simulations upon density functional theory (DFT) calculations. The effects of water on each hydrogenation step and the whole activity and selectivity are checked and its physical origin is discussed. It is found that the water could kinetically accelerate the hydrogenation on CO₂ to COOH, promoting the reverse water gas shift reaction to produce carbon monoxide (CO). It hardly influences the CO₂ hydrogenation to methanol kinetically. In addition, the too high initial partial pressure of water will thermodynamically inhibit the CO₂ conversion.