Pd expectedly showed high reduction activity (289 L/g-surface-metal/min) and high N2 selectivity (>99% at 20% conversion) at low pH, and near inactivity at high pH. Surprisingly, the Rh catalyst, while inactive at low pH, showed moderate activity (22 L/g-surfacemetal/min) and high NH4+ selectivity (>90% at 20% conversion) at high pH.