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AbstractShulants for the Hanford Waste Vitrification Plant feed containing the major nonradioactive components Al, Cd, Fe, Mn, Nd, Ni, Si, Zr, Na, C032-, NOg-, and NO2-were used to study reactions of formic acid at 90°C catalyzed by the noble metals Ru, Rh, and/or Pd found in significant quantities in uranium fission products. Such reactions were monitored using gas chromatography to analyze the C02, H2, NO, and N20 in the gas phase and a sdcroammonia eIectrode to analyze the NH4+/NH3 in the liquid phase as a function of time. The following reactions have been studied in these systems since they are undesirable side reactions in nuclear waste processing: (1) Decomposition of formic acid' to CO2 + H2 is undesirable because of the potential fire and explosion hazard of H2.Rhodium, which was introduced as soluble RhC13.3&0, was found to be the most active catalyst for H2 generation from formic acid above 4O0C in the presence of nitrite, ion. The Hz production rate has an approximate pseudo first-order dependence on the Rh concentration, (2) Generation of NH3 from the formic acid reduction of nitrate and/or nitrite is undesirable because of a possible explosion hazard from NH4NO3 accumulation in a waste processing plant off-gas system. The Rh-catalyzed reduction of nitrogen-oxygen compounds to ammonia by formic acid was found to exhibit the following features:(a) Nitrate rather than nitrite is the principal source of NH3. (b) Ammonia production occurs at the expense of hydrogen production. (c) Supported rhodium metal catalysts are mormctive than rhodium in any other form, suggesting that ammonia production involves I hetecogeneous rather than homogeneous catalysis.
