The CO oxidation catalytic activity of catalysts is strongly influenced by the oxygen vacancy defects (OVDs) concentration and the valence state of active metal. Herein, a defect engineering approach was implemented to enhance the oxygen vacancy defects and to modify the valence of metal ions in manganese oxide octahedral molecular sieves (OMS-2) by the introduction of copper (Cu). The characterization and theoretical calculation results reveal that the incorporation of Cu2+ ion into the OMS-2 structure led to a rise in specific surface area and pore volume, weakening of Mn-O bonds, higher proportion of the low-coordinated oxygen species adsorbed in oxygen vacancies (Oads) and an increase in the average oxidation state of manganese. These structural modifications were discovered to considerably reduce the apparent activation energy (Ea), thus ultimately significantly enhancing the CO oxidation activity (T99 at 148 ℃at GHSV = 13,200 h-1) than the original OMS-2 (T99 = 215 ℃ at GHSV = 13,200 h-1). Furthermore, In-situ diffuse reflectance infrared Fourier transform (DRIFT) and In-situ near-ambient pressure X-ray photoelectron spectroscopy (in situ NAP-XPS) results indicate that the bimetallic synergy enhanced by doping strategy accelerates the conversion of oxygen to chemisorbed oxygen species and the reaction rate of CO oxidation through Mn3++Cu2+↔Mn4++Cu+ redox cycle. The findings of this study offer novel perspectives on the design of catalysts with exceptional performance in CO oxidation.
Keywords: Bimetallic synergy; CO oxidation; Cu-doping; In situ DRIFT; Manganese oxide octahedral molecular sieves (OMS-2); NAP-XPS; Surface Defects.
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