Catalytic oxidation of NO over MnO2 with different crystal structures. Issue 59 (3rd June 2016) - Chen, Hu
Abstract : α-, β-, γ- and δ-MnO2 catalysts were prepared by a hydrothermal method and their catalytic properties for NO oxidation were evaluated. Abstract : α-, β-, γ- and δ-MnO2 catalysts were prepared by a hydrothermal method and their catalytic properties for NO oxidation were evaluated. There were dramatic differences in the activities among the MnO2 catalysts with different crystal structures. The γ-MnO2 catalyst exhibited the best activity among the four catalysts and gave rise to 91% NO conversion at 250 °C. Moreover, 50% of NO conversion was achieved by γ-MnO2 even at 160 °C. To investigate the factors influencing the catalytic activity, the catalysts were then characterized by X-ray diffraction, N2 adsorption, scanning electron microscopy, Fourier transform infrared spectrometry, Raman spectrometry, temperature-programmed reduction by H2 and X-ray photoelectron spectroscopy. On the basis of the characterization results, the tunnel structure and surface chemisorbed oxygen of γ-MnO2 were proposed to be the main factors that contributed to the excellent performance in NO oxidation. In addition, the four catalysts showed stable catalytic activity. Over γ-MnO2, H2 O had a reversible inhibiting effect on catalytic activity, while the conversion of NO could not recover after removing SO2 . In the presence of H2 O and SO2, H2 O was able to slow the progression of catalyst deactivation resulting from SO2 .