Pd-Cu and Pt-Cu Catalysts Supported on Carbon Nanotubes for Nitrate Reduction in Water

The influence of the preparation conditions on the performance of Pd-Cu and Pt-Cu supported on multiwalled carbon nanotubes for the reduction of nitrates was studied and compared with that obtained using a commercial activated carbon as support. Different preparation conditions lead to different catalytic activities and selectivities. Generally, the activity decreases by increasing the calcination and reduction temperatures for the catalysts supported on the original carbon nanotubes, where the nitrate conversion varies from 67% (noncalcined and nonreduced) to 15% (calcined and reduced at 200 degrees C) for the pair Pd-Cu after 5 h of reaction; the inverse performance was observed for the catalysts supported on carbon nanotubes previously oxidized with HNO3 and on this same sample heat treated at 400 degrees C. The functional groups created during the oxidation treatment have a negative effect on the catalyst performance. For all the preparation conditions tested, the Pd-Cu pair is more selective to nitrogen than the pair Pt-Cu; 82% and 37% are the highest values obtained for each pair, respectively. Carbon nanotubes are demonstrated to be a good support for this reaction.