Low-temperature Denitration Mechanism of NH₃-SCR over Fe/AC Catalyst

Abstract

To study the modification mechanism of activated carbon (AC) by Fe and the low-temperature NH₃-selective catalytic reduction (SCR) denitration mechanism of Fe/AC catalysts, Fe/AC catalysts were prepared using coconut shell AC activated by nitric acid as the support and iron oxide as the active component. The crystal structure, surface morphology, pore structure, functional groups and valence states of the active components of Fe/AC catalysts were characterised by X-ray diffraction, scanning electron microscopy, nitrogen adsorption and desorption, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, respectively. The effect of Fe loading and calcination temperature on the low-temperature denitration of NH₃-SCR over Fe/AC catalysts was studied using NH₃ as the reducing gas at low temperature (150 °C). The results show that the iron oxide on the Fe/AC catalyst is spherical and uniformly dispersed on the surface of AC, thereby improving the crystallisation performance and increasing the number of active sites and specific surface area on AC in contact with the reaction gas. Hence, a rapid NH₃-SCR reaction was realised. When the roasting temperature remains constant, the iron oxide crystals formed by increasing the amount of loading can enter the AC pore structure and accumulate to form more micropores. When the roasting temperature is raised from 400 to 500 °C, the iron oxide is mainly transformed from α-Fe₂O₃ to γ-Fe₂O₃, which improves the iron oxide dispersion and increases its denitration active site, allowing gas adsorption. When the Fe loading amount is 10%, and the roasting temperature is 500 °C, the NO removal rate of the Fe/AC catalyst can reach 95%. According to the study, the low-temperature NH₃-SCR mechanism of Fe/AC catalyst is proposed, in which the redox reaction between Fe²⁺ and Fe³⁺ will facilitate the formation of reactive oxygen vacancies, which increases the amount of oxygen adsorption on the surface, especially the increase in surface acid sites, and promotes and adsorbs more reaction gases (NH₃, O₂, NO). The transformation from the standard SCR reaction to the fast SCR reaction is accelerated.

Keywords

nitric acid activation method / coconut shell activated carbon / Fe/AC catalyst / NH₃-SCR / low-temperature denitrification mechanism

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