Design of meso-TiO2@MnOx–CeOx/CNTs with a core–shell structure as DeNOxcatalysts: promotion of activity, stability and SO2-tolerance

Abstract

Developing low-temperature deNO_x catalysts with high catalytic activity, SO₂-tolerance and stability is highly desirable but remains challenging. Herein, by coating the mesoporous TiO₂ layers on carbon nanotubes (CNTs)-supported MnO_x and CeO_x nanoparticles (NPs), we obtained a core–shell structural deNO_x catalyst with high catalytic activity, good SO₂-tolerance and enhanced stability. Transmission electron microscopy, X-ray diffraction, N₂ sorption, X-ray photoelectron spectroscopy, H₂ temperature-programmed reduction and NH₃ temperature-programmed desorption have been used to elucidate the structure and surface properties of the obtained catalysts. Both the specific surface area and chemisorbed oxygen species are enhanced by the coating of meso-TiO₂ sheaths. The meso-TiO₂ sheaths not only enhance the acid strength but also raise acid amounts. Moreover, there is a strong interaction among the manganese oxide, cerium oxide and meso-TiO₂ sheaths. Based on these favorable properties, the meso-TiO₂ coated catalyst exhibits a higher activity and more extensive operating-temperature window, compared to the uncoated catalyst. In addition, the meso-TiO₂ sheaths can serve as an effective barrier to prevent the aggregation of metal oxide NPs during stability testing. As a result, the meso-TiO₂ overcoated catalyst exhibits a much better stability than the uncoated one. More importantly, the meso-TiO₂ sheaths can not only prevent the generation of ammonium sulfate species from blocking the active sites but also inhibit the formation of manganese sulfate, resulting in a higher SO₂-tolerance. These results indicate that the design of a core–shell structure is effective to promote the performance of deNO_x catalysts.