Mechanism of NO reduction by CO over single atomic nickel catalyst: DFT and microkinetic study

Abstract

The microscopic reaction mechanism of NO reduction by CO on the graphene-supported single-atom Ni catalyst (Ni/G) was investigated by using density functional theory (DFT) and microkinetic modeling. The results indicate that as the most probably pathway for the NO reduction by CO over the Ni/G catalyst, two NO molecules adsorb onto the Ni atoms via the Langmuir-Hinshelwood mechanism and then transform to N₂O and active oxygen (O*). Subsequently, N₂O is adsorbed on the Ni surface and reduced to N₂ and O*. Finally, CO reduces O* to form CO₂, releasing the active Ni sites. From the energy barrier perspective, the transformation of NO to N₂O and O* has a higher energy barrier, which controls the NO reduction reaction rate. From the microkinetic perspective, the reaction temperature has a significant effect on the rate of O* reduction with CO, which is lower than that of N₂O reduction. As a result, the Ni atoms are gradually occupied by O*, which may inhibit the adsorption and reduction of NO, leading to the deactivation of the Ni/G catalyst.