NO Reduction on Carbon-Supported Chromium Catalysts

Carbon-supported chromium catalysts were obtained from activated carbons prepared by chemical activation of orange skin with phosphoric acid. These catalysts present a high development of the porous structure, with a relatively large contribution of micro- and mesopores. The presence of chromium produces a considerable improvement of the NO reduction compared to that obtained for the corresponding support. The removal of the carbon-oxygen complexes by thermal treatment is unfavorable for the NO reduction in both activated carbons and chromium catalysts. Oxygen surface groups improve the chromium dispersion and seem to play an important role in the NO reduction mechanism. A linear relationship between the apparent reaction rate of NO reduction and the amount of acidic surface groups was found. The presence of C3H6 and CO considerably increases the NO reduction on the chromium catalyst. This catalyst exhibited a high resistance toward SO2 poisoning at different experimental conditions. The presence of oxygen increases the oxygen surface groups of the catalyst that seem to be responsible for the enhancement of the NO reduction at low temperatures.