Loading mechanism and double-site reaction mechanism of Cu on activated carbon for enhanced oxidation of CO from flue gas

Abstract

To strengthen the CO oxidation activity of activated carbon for flue gas purification, AC was modified through acid treatment and metal loading. AC-supported Cu shows excellent catalytic oxidation activity compared with other metal-modified AC samples. To investigate the action modes of Cu loaded on activated carbon and the mechanism of CO oxidation, various samples were characterized by XRD, N2O titration, SEM, N2 physisorption, TPD, H2-TPR, XPS, in situ DRIFTS and EPR. The results show that oxygen-containing functional groups increase the loading amount and dispersion of Cu. Moreover, Cu species strongly bound to oxygen-containing functional groups are the main contributors to CO oxidation. The roles of oxygen-containing functional groups are further revealed: carboxyl groups are the anchoring sites of Cu, and hydroxyl groups supply oxygen to restore the active structure. Similarly, Ce indirectly promote the oxidation activity of CO by re-oxidizing Cu+ to Cu2+, which accelerates the catalytic cycle. The reaction mechanism on AC-supported Cu samples has been proposed to follow the double-site Langmuir–Hinshelwood mechanism, with Cu2+ as oxidation sites, Cu+ as adsorption sites and the formation of oxygen vacancies on Cu+ during the reaction. AC-Cu performs the highest oxidation activity at a proportion of Cu+ of 0.5–0.6. SO2 causes irreversible chemical poisoning to CO oxidation, while NO leads to reversible poisoning due to competitive adsorption with CO. The novel AC-supported Cu catalyst with Ce improves the resistance against SO2 and NO, and the reason is explained. These findings provide theoretical guidance for the preparation and application of metal-modified activated carbon.