Role of Amorphous Manganese Oxide in Nitrogen Loss

Studies have been made, by 15N-tracer technique on nitrogen loss resulting from adding amorphous manganese oxide to NH4+-N medium under anaerobic conditions. The fact that the total nitrogen recovery was decreased and that 15NO2, 15N2O, 15N14NO, 15NO, 15N2and 15N14N were emitted has proved that, like amorphous iron oxide, amorphous manganese oxide can also act as an electron acceptor in the oxidation of NH4+-N under anaerobic conditions and give rise to nitrogen loss. This once again illustrates another mechanism by which the loss of ammonium nitrogen in paddy soils is brought about by amorphous iron and manganese oxides. The quantity of nitrogen loss by amorphous manganese oxide increased with an increase in the amount of amorphous manganese oxide added and lessened with time of its aging. The nitrogen loss resulting from amorphous manganese oxide was less than that from amorphous iron oxide. And the nitrogen loss by cooperation of amorphous manganese oxide and microorganisms (soil suspension ) was larger than that by amorphous manganese oxide alone. In the system, nitrogen loss was associated with the specific surface area and oxidation-reduction of amorphous manganese oxide. However, their quantitative relationship and the exact reaction processes of nitrogen loss induced by amorphous manganese oxide remain to be further studied.

Cerium-modified amorphous manganese oxides for efficient catalytic removal of ozone

Manganese-based catalysts were widely developed for catalytic removal of ozone,and the low stability and water inactivation are major challenges.To improve removal performance of ozone,three methods were applied to modify amorphous manganese oxides,including acidification,calcination and Ce modification.The physiochemical properties of prepared samples were characterized,and the catalytic activity for ozone removal was evaluated.All modification methods can promote the removal of ozone by amorphous manganese oxides,and Ce modification showed the most significant enhancement.It was confirmed that the introduction of Ce markedly changed the amount and property of oxygen vacancies in amorphous manganese oxides.Superior catalytic activity of Ce-MnO_(x) can be ascribed to its more content and enhanced formation ability of oxygen vacancies,larger specific surface area and higher oxygen mobility.Furthermore,the durability tests under high relative humidity(80%)determined that Ce-MnO_(x) showed excellent stability and water resistance.These demonstrate the promising potential of amorphously Ce-modified manganese oxides for catalytic removal of ozone.

Highly efficient removal of ozone by amorphous manganese oxides synthesized with a simple hydrothermal method

Amorphous manganese oxides (MnO_(x)) were synthesized by facile hydrothermal reactions between potassium permanganate and manganese acetate.Synthesis parameters,including hydrothermal time and temperature and molar ratio of precursors,significantly affected the ozone removal performance and structure property of MnO_(x).Amorphous MnO_(x)-1.5,which was prepared at the Mn^(2+)/Mn^(7+)molar ratio of 1.5 under hydrothermal conditions of 120℃ and 2 hr,showed the highest ozone removal rate of 93% after 480 min at the room temperature,RH (relative humidity)=80%and WHSV (weight hourly space velocity)=600 L/(g·hr).The morphology,composition and structure of catalysts were investigated with X-ray diffractometer (XRD),Raman spectra,N_(2) physisorption,field emission scanning electron microscope (FESEM),X-ray photoelectron spectroscopy (XPS),H2temperature-programmed reduction (H_(2)-TPR),O_(2) temperature-programmed desorption (O_(2)-TPD) and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS).It was confirmed that high catalytic activity of amorphous MnOxfor ozone removal was mainly ascribed to its abundant oxygen vacancies,high oxygen mobility and large specific surface area.