An Experimental and Density Functional Theory Simulation Study of NO Reduction Mechanisms over Fe⁰ Supported on...

NO reduction over highly dispersed zerovalent iron (Fe⁰) supported on graphene (G), with and without the presence of CO in the reacting stream, was systematically studied using a fixed-bed reactor, and the reaction mechanism was examined with the aid of in situ Fourier transform infrared (FTIR) spectroscopy and density functional theory (DFT) calculations. The in situ FTIR results showed that NO adsorbed on the Fe⁰ site is reduced to form active surface oxygen species (O*), which is then reduced by carbon in graphene to form CO₂. The presence of CO in the reacting stream helps to reduce the oxidized Fe(O) sites to regenerate Fe⁰ sites, making NO reduction easier. It was revealed that NO and CO₂ are easily adsorbed on the active surface oxygen species (O*) to form nitrate and carbonate, inhibiting their reduction by CO and deactivating the catalyst. The DFT calculations results suggest that the role of Fe is to reduce the energy barrier of the NO adsorption and decomposition, which controls the formation of active surface oxygen species and N₂. The combined FTIR and DFT results offer new insights into the possible mechanism of catalytic NO reduction over graphene loaded with Fe, with and without CO.