Reductive Decomposition of Trace Amount of Nitrates and Nitrites in Aqueous Phase

Hiromu HAYASHI*, Masahiro UNO, Satoko KAWASAKI and Shigeru SUGIYAMA

Department of Chemical Science and Technology, Faculty of Engineering, University of Tokushima; Minamijosanjima, Tokushima-shi 770-8506 Japan

Groundwater pollusions by nitrates have received increasing attention in many locations in the world. The Environmental Agency of Japan has announced in Feb.1999 to regulate the maximum contamination of nitrates and nitrites to be less than 10 mg/L, and it is an urgent problem to cope with the situation. The present paper demonstrates that catalytic decomposition of trace amounts of nitrates and nitrites in aqueous phase on a level with drinking water could be carried out under mild conditions of atmospheric pressure of hydrogen at room temperature. Supported bimetallic catalysts, copper-palladium-on-carbon, with high copper-contents revealed excellent activity for nitrates, while single metallic palladium-on-carbon was much more effective than bimetallic catalysts for nitrites. Thus, the intermediate nitrite unfortunately accumulated in solution in the decomposition of nitrate on bimetallic copper-palladium-on-carbon, but the nitrite could be removed in situ with great ease in the presence of isolated palladium free of copper. Powder XRD suggested the active species as Cu3Pd for nitrate decomposition and supported state of metallic components was discussed with portrayals in reference to the catalyst activity.

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