Application of Si/SiC ceramic filters as support for structural palladium catalysts for the reductive decomposition of aqueous nitrite

A Si/SiC ceramic filter was used to support a structural palladium catalyst in a continuous fixed-bed flow reactor during a reductive decomposition of nitrite. A previous report described the use of non-porous alumina spheres coated with Pd/C, a carbon monolith impregnated with Pd or a structural catalyst consisting of a polyurethane sponge skeleton impregnated with Pd resulted either in negligible activity or a complete stoppage of the flow by increasing the pressure drop in the flow system. The use of a Si/SiC filter impregnated with palladium, however, overcame the demerits and resulted in an 11% conversion of nitrite in 60 min. The use of a Si/SiC filter coated with a char intermediate followed by impregnation with Pd (Pd/C/Si/SiC) resulted in a structural catalyst that enhanced the activity to yield a 33% conversion of nitrite in 60 min. When five Pd/C/Si/SiC structural catalysts were used, however, the complete decomposition was achieved in the same amount of time. Although improvement was previously observed by using an alumina intermediate, use of the char intermediate resulted in a new factor for activity improvement. The characterization results show that it was the affinity between aqueous nitrite and the intermediate rather than palladium dispersion that contributed the most to the improvement of activity.

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