| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2006: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 2005: ¥2,300,000 (Direct Cost: ¥2,300,000)
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| Research Abstract |
Pollution of groundwater with nitrate (NO_3^-) is a widespread problem, since excess intake of nitrate causes blue baby syndrome for infants and diabetes and cancers. The major sources are agricultural practices (fertilizers and excretions of livestock), and the remediation of groundwater is urgent issue. The biological treatment, ion exchange, and reverse osmosis have still much issues. Recently catalytic hydrogenation of NO_3^-to N_2 have attracted much attention. It is necessary to reduce the levels of harmful components to the maximum allowable levels, 50, 0.1-3, and 0.5 ppm for nitrate, nitrite (NO_2^-), and NH_3.
We found that Cu-Pd clusters supported on active carbon are highly selective for the hydrogenation of NO_3^- to NO_2^- at high pH. On the other hand, Pd exchanged beta zeolite catalyzed selectively the hydrogenation of NO_2^- to N_2 and N_2O. From these findings, we were inspired in a two-stage process which allows catalysts optimized for each stage ; NO_3^-hydrogenation
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to NO_2^-in the first stage and NO_2^-hydrogenation in the second stage. Here we wish to report that the two-stage process consisting of Cu-Pd cluster/AC and Pd/beta-zeolite is promising for the purification of water contaminated nitrate. It should be emphasized that the concentration of NH_3 was only 0.7 and 0.6 ppm at 298 and 288 K, respectively which are very close to the allowable value (0.5 ppm) for drinking water.
Then a one-stage process aimed at drinking water using a single catalyst, the catalyst with acceptable activity, selectivity, and stability for the practical use is searched 2wt%Pd-1.2wt%Cu/mordenite (Si/Al=37) was highly selective to N_2 and N_2O, depressing NH_3 (5 ppm from 200 ppm of nitrate) and exhibited robust stability at 278-333 K. Cu-Pd/mordenites that were prepared by ion-exchange method. Recently, Pd-Cu/hydrophobic AC catalysts prepared from Pd-Cu cluster exhibited was found to be high active and selective, that is, be greatly suppressed for the formation of ammonia. Furthermore, this catalyst has worked even in the presence of sulfated ion and chloride ion. Less
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