Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

PP-III-29continuous and pressurized reactors, using hydrogen as a reducing agent. The NO 3 – , NO 2 – andNH 4 + concentration in the aqueous-phase samples was determined by UV/VIS spectroscopy.Results and discussionFrom our previous studies it was observed that in order to obtain a good activity andselectivity it is necessary an adequate contact of the three phases present (the optimized solidcatalyst, the liquid media containing the nitrates and the gaseous hydrogen) [9]. This can beeasily obtained in a batch reactor, where the nitrates present in one liter of a natural watercontaining 90 ppm of NO 3 – are completely removed in 30 minutes, producing 15 ppm ofammonia.Nevertheless when the reaction is made in a continuous reactor, the results obtained arenot so good, indicating some mass transfer limitations and some deactivation of the catalyst.Comparing the different continuous reactors, it was observed that in the flow piston reactor, afast decrease on the nitrates concentration is observed during the first 5-10 minutes,stabilizing the conversions at 60% after 1 hour reaction. This conversion is stable during 5hours reaction, when the catalyst starts to deactivate. In the stirred flow tank reactor, betterresults were obtained, obtaining 100% conversion during 5 hours. Afterwards, just as in thepiston flow reactor, the catalyst starts to deactivate. The deactivation is due to the depositionof calcium salts and to the oxidation of the reduced active sites It is also interesting to indicatethat with both reactors the formation of ammonia and nitrite is lower than with the batchreactor, presenting a maximum during the first minutes of the reaction but stabilizing around5 ppm of ammonia after 1 hour reaction.The use of a pressurized reactor at different pressure conditions do no improve the resultsobtained with these catalysts in the nitrate conversion, neither in its selectivity.References1. S. Hörold, K.D. Vorlop, T. Tracke and M. Sell, Catal. Today, 17 (1993) 21.2. A. Pintar, J. Batista, Catal. Today 53 (1999) 35.3. A.E. Palomares, J.G. Prato, F. Márquez, A. Corma, Appl. Catal. B, 41 (2003) 3.4. M.J. Chollier-Brym, R. Gavagnin, G. Strukul, M. Marella, M. Tomaselli, P. Ruiz, Cat. Today, 75 (2002) 49.5. F. Epron, F. Gauthard, C. Pineda, J. Barbier, Appl. Catal. A., 237 (2002) 253.6. R. Gavagnin, L. Biasetto, F. Pinna, G. Strukul, Appl. Catal. B, 38 (2002) 91.7. U. Prüsse, K.D. Vorlop, J. Mol. Catalyst A, 173 (2001) 313.8. O.M. Ilnitch, L.V. Nosova, V.V. Gorodetskii, V.P. Ivanov, S.N: Trukhan, E.N. Gribov, S.V. Bogdanov,F.P. Cuperus, J. Mol. Chem. 158 (2000) 237.9. A.E. Palomares, J.G. Prato, F. Márquez, A. Corma, J. Catal. 221 (2004) 62.358