In situ DRIFTS study of the NO + CO reaction on Fe–Co binary metal oxides over activated semi-coke supports

Abstract

Activated semi-coke loaded with Fe and Co species by a hydrothermal method exhibited excellent CO-deNO_x performance. In this study, the reaction mechanism and the evolution of surface-adsorbed species were investigated by CO-TPR, NO-TPO, and in situ DRIFTS. The results demonstrated that in the temperature range of 100–350 °C, the adsorbed CO coordinated to Fe species, inducing an electron migration that influenced the valence state of Fe. Furthermore, the Fe³⁺ species were found to be the active sites for the transformation of adsorbed CO, whereas the Co³⁺ species provided the sites for NO evolution. In the catalytic reaction, the Fe–Co interaction could also promote the transformation of adsorbed NO and CO. The DRIFTS spectra revealed that at relatively low temperatures, the transformation of NO species occurred in the following order: NO → NO₂⁻ → NO–NO₃⁻ → N₂O; at higher temperatures, the NO species evolved in the order: NO → NO₂⁻ → bidentate NO₃⁻ → chelate NO₃⁻ + N₂. However, the CO transformation process was the same at both low and high temperatures: CO → COO⁻ → CO₃²⁻ → CO₂. NO₂⁻ proved to be an important intermediate in the NO + CO reaction.