Effect of Reduction Treatment on Copper Modified Activated Carbons on NOx Adsorption at Room Temperature

Activated carbon was impregnated with copper salt and then exposed to reductive environment using hydrazine hydrate or heat treatment under nitrogen at 925 degrees C. On the obtained samples, adsorption of NO2 was carried out at dynamic conditions at ambient: temperature. The adsorbents before and after exposure to nitrogen dioxide were characterized by X-ray diffraction (XRD), thermal analysis, scanning electron microcopy/energy dispersive X-ray spectroscopy (SEM-EDX), X-ray photoelectron spectroscopy (GS), N-2-sorption at -196 degrees C, and potentiometric titration. Copper loading improved the adsorption capacity of NO2 as well as the retention of NO formed in the process of NO2 reduction on the carbon surface. That improvement is linked to the presence of copper metal and its high dispersion on the surface. Even though both reduction methods lead to the reduction of copper, different reactions with the carbon surface take place. Heat treatment results in a significant percentage of metallic copper and a reduction of oxygen functional groups of the carbon matrix, whereas hydrazine, besides reduction of copper, leads to an incorporation of nitrogen. The results suggest that NO2 mainly is converted to copper nitrates although the possibility to its reduction to N-2 is not ruled out. A high capacity on hydrazine treated samples is linked to the high dispersion of metallic copper on the surface of this carbon.