NOBLE METAL-CATALYZED AMMONIA GENERATION BY FORMIC-ACID REDUCTION OF NITRATE IN SIMULATED NUCLEAR WASTE MEDIA

Simulants for the Hanford Waste Vitrification Plant(HWVP) feed contain ing the major non-radioactive components Al, Cd, Fe, Mn, Nd, Mi, Si, Z r, Na, CO32-, NO3-, and NO2- were used to study the formic acid reduct ion of nitrate and/or nitrite to ammonia at 90 degrees C catalyzed by the noble metals Ru, Rh, and/or Pd found as fission products in waste from the reprocessing of irradiated uranium. Reactions of this type we re monitored using gas chromatography to analyze the CO2, H-2, NO, and N2O in the gas phase and a microammonia electrode to analyze the NH4/NH3 in the liquid phase as a function of time. The rhodium-catalyzed reduction of nitrogen-oxygen compounds to ammonia by formic acid was f ound to exhibit the following features: (1) Nitrate rather than nitrit e is the principal source of ammonia. (2) Ammonia production occurs at the expense of hydrogen production. (3) Supported rhodium metal catal ysts are more active than rhodium in any other form, suggesting that a mmonia production involves heterogeneous rather than homogeneous catal ysis.