Reductive Decomposition of Nitrite in a Continuous-Flow Reactor Using Fixed-Bed Structural Pd Catalysts

In order to decompose trace amounts of nitrite in drinking water under mild conditions, a fixed-bed filtering system that used structural catalysts was employed to filter recycled aqueous nitrite. High performance and continuous mass processing are generally accepted as requirements to catalyze the decomposition of aqueous nitrite. However, the use of a fixed-bed operation when recycling aqueous nitrite with palladium catalyst systems could result in either negligible activity when using a carbon monolith impregnated with Pd, or could stop the flow by enhancing the pressure drop when using non-porous alumina spheres coated with Pd/C or structured catalysts consisting of a polyurethane sponge skeleton impregnated with Pd. In the present paper, a Si/SiC ceramic filter was employed as a structured support to prevent pressure drop. When palladium was loaded onto the surface of the filter via electroless plating, continuous flow suitably continued, and the conversion of nitrite was 45% after 60 min. In contrast, when palladium was loaded after the coating of the filter with alumina, complete decomposition was achieved after 60 min under conditions corresponding to those used for the former system. X-ray diffraction, an N2 adsorption-desorption measurement, scanning-electron microscopy and energy-dispersive X-ray spectroscopy analyses revealed that a higher dispersion of palladium on the latter structured catalyst resulted in the greatest level of activity for the reductive decomposition of aqueous nitrite.

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