Reactive adsorption of NO2 at dry conditions on sewage sludge-derived materials

Composite inorganic-carbonaceous adsorbents were obtained by pyrolysis of sewage sludge at 500, 650, and 950 degrees C for various periods of time. They were used as media for reactive adsorption of NO2. The surface structure and chemistry of the initial and exhausted materials were analyzed using adsorption of nitrogen, XRD, FTIR, and thermal analysis. The results indicate the high level of conversion of NO2 to NO with the retention of both species on the surface depending on its chemistry. At 650 degrees C as the pyrolysis temperature, the most efficient adsorbents were obtained owing to a high reactivity of their oxides toward the formation of nitrites and nitrates. When the pyrolysis temperature is low, NO2 is reduced to NO on surface sulfides and reacts with surface oxides, forming nitrites and nitrates. When adsorbents are obtained at 950 degrees C, the chemically stable surface prevents the formation of nitrites and nitrates, and the majority of NO2 is reduced to NO in the highly carbonized carbonaceous phase.