Comparison of electrocataly tic nitrate reduction using 2.5%Pd/ƔAl2O3 pellets and 2.5%Pd/carbon

BELTRAME, T. F.; ZOPPAS, F. M.; MARDER,L.; MARCHESINI, F. A.; MIRÓ, E. E.; BERNARDES, A. M.

Berlin

Conferencia; 3RD Green and Sustainable Chemistry; 2018

Nitrate ion is an underground and surface water contaminant, being present in excess on nature mainly due to the use of fertilizers in agriculture. Reverse osmosis and electrodialysis can be used to treat the water contaminated by nitrate, however, these technologies generates a concentrate nitrate brine, that requires a post-treatment. In this context, the aim of this study was to compare the concentrate nitrate reduction with an electrocatalytic process using copper cathode electrode in presence of 2.5%Pd/ƔAl2O3 pellets or 2.5%Pd/Carbon fiber catalysts. The role of the catalysts is to increase the gaseous compounds selectivity.The experiments were performed in a dual chamber cell separated by a cationic membrane. Sodium nitrate with 600 mg.L-1 of NO3 - was placed in the cathodic compartment, while in the anodic one it was used sodium sulfate (1400 mg.L-1). Nitrate, nitrite and ammonium were analyzed by ion chromatography and the values of gaseous compounds were obtained by mass balance. The catalysts were prepared by wet impregnation method. The tests were accomplished applying 1.5mA.cm-2, with pH solution control (between 6.0-6.5), during 6 hours.The results showed a 50% nitrate reduction using electrocatalytic reduction process. When the 2.5%Pd/ƔAl2O3 pellets catalyst were used, the selectivity to gaseous compounds was 64%, producing 23 mg.L-1 of ammonium and only 0.5 mg.L-1 of nitrite. The use of 2.5%Pd/Carbon fibers increased the selectivity to gaseous compounds (80%), avoiding nitrite generation and producing 14 mg.L-1 of ammonium. The difference on the selectivity between the catalysts probably occurs due to the higher surface area of the carbon fibers (1500 m²/g) than the ƔAl2O3 pellets (160 m²/g). The Pd particles can be more dispersed in the carbon fiber. According to the results, it can be concluded that the 2.5%Pd/Carbon fibers catalyst is a promising material to be used in the electrocatalytic nitrate reduction process.