Mechanism of CO selective catalytic reduction denitration on Fe–Mn/AC catalysts at medium and low temperatures under oxygen atmosphere

Abstract

To explore the modification mechanism of Fe and Mn on activated carbon and the denitration mechanism by selective catalytic reduction of carbon monoxide (CO-SCR) on Fe–and Mn-loaded activated carbon (Fe–Mn/AC) catalysts at medium and low temperatures under 8% oxygen, we selected a coconut shell activated carbon as a catalyst carrier and prepared Fe–Mn/AC catalysts. The physical adsorption of CO mainly occurs at low temperatures, and an increase in temperature is beneficial to the CO denitration activity of the metal active components. High Fe2+ content increases the main active sites of the CO + NO reaction, and high Mn3+ content inhibits the conversion of γ-Fe2O3 to α-Fe2O3 and increases the denitration activity. Surface oxygen species (Oα) with high reactivity and mobility are also formed during the denitration process. After denitration, Oα is mainly converted to the lattice oxygen (Oβ), and Mn2+ and Mn3+ are oxidized to Mn4+ in a small amount. The iron oxides and manganese oxides penetrate the internal structure of the catalyst and destroys its oxide crystal structure and the surface functional groups of the activated carbon, resulting in the formation of more oxygen vacancies and lattice defects. Consequently, reduction characteristics and absorption capacities increased and the spectrum peaks of H2-TPR, CO-TPR, and NO-TPR shifted to low temperatures. Moreover, the number of Lewis and Brønsted acid sites increased, resulting in sites that are more reactive. The denitration process involves the following four steps: (1) adsorption of reactant molecules, (2) dissociation of adsorbed molecules, (3) catalytic denitration by metal active components and recombination of active substances for denitration, and (4) product molecule desorption and diffusion.